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3.14: Experiments and Hypotheses

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Now we’ll focus on the methods of scientific inquiry. Science often involves making observations and developing hypotheses. Experiments and further observations are often used to test the hypotheses.

A scientific experiment is a carefully organized procedure in which the scientist intervenes in a system to change something, then observes the result of the change. Scientific inquiry often involves doing experiments, though not always. For example, a scientist studying the mating behaviors of ladybugs might begin with detailed observations of ladybugs mating in their natural habitats. While this research may not be experimental, it is scientific: it involves careful and verifiable observation of the natural world. The same scientist might then treat some of the ladybugs with a hormone hypothesized to trigger mating and observe whether these ladybugs mated sooner or more often than untreated ones. This would qualify as an experiment because the scientist is now making a change in the system and observing the effects.

Forming a Hypothesis

When conducting scientific experiments, researchers develop hypotheses to guide experimental design. A hypothesis is a suggested explanation that is both testable and falsifiable. You must be able to test your hypothesis, and it must be possible to prove your hypothesis true or false.

For example, Michael observes that maple trees lose their leaves in the fall. He might then propose a possible explanation for this observation: “cold weather causes maple trees to lose their leaves in the fall.” This statement is testable. He could grow maple trees in a warm enclosed environment such as a greenhouse and see if their leaves still dropped in the fall. The hypothesis is also falsifiable. If the leaves still dropped in the warm environment, then clearly temperature was not the main factor in causing maple leaves to drop in autumn.

In the Try It below, you can practice recognizing scientific hypotheses. As you consider each statement, try to think as a scientist would: can I test this hypothesis with observations or experiments? Is the statement falsifiable? If the answer to either of these questions is “no,” the statement is not a valid scientific hypothesis.

Practice Questions

Determine whether each following statement is a scientific hypothesis.

Air pollution from automobile exhaust can trigger symptoms in people with asthma.

• No. This statement is not testable or falsifiable.
• No. This statement is not testable.
• No. This statement is not falsifiable.
• Yes. This statement is testable and falsifiable.

[reveal-answer q=”429550″] Show Answer [/reveal-answer] [hidden-answer a=”429550″]d: Yes. This statement is testable and falsifiable. This could be tested with a number of different kinds of observations and experiments, and it is possible to gather evidence that indicates that air pollution is not linked with asthma.

[/hidden-answer]

Natural disasters, such as tornadoes, are punishments for bad thoughts and behaviors.

[reveal-answer q=”74245″]Show Answer[/reveal-answer] [hidden-answer a=”74245″]

a: No. This statement is not testable or falsifiable. “Bad thoughts and behaviors” are excessively vague and subjective variables that would be impossible to measure or agree upon in a reliable way. The statement might be “falsifiable” if you came up with a counterexample: a “wicked” place that was not punished by a natural disaster. But some would question whether the people in that place were really wicked, and others would continue to predict that a natural disaster was bound to strike that place at some point. There is no reason to suspect that people’s immoral behavior affects the weather unless you bring up the intervention of a supernatural being, making this idea even harder to test.

Testing a Vaccine

Let’s examine the scientific process by discussing an actual scientific experiment conducted by researchers at the University of Washington. These researchers investigated whether a vaccine may reduce the incidence of the human papillomavirus (HPV). The experimental process and results were published in an article titled, “ A controlled trial of a human papillomavirus type 16 vaccine .”

Preliminary observations made by the researchers who conducted the HPV experiment are listed below:

• Human papillomavirus (HPV) is the most common sexually transmitted virus in the United States.
• There are about 40 different types of HPV. A significant number of people that have HPV are unaware of it because many of these viruses cause no symptoms.
• Some types of HPV can cause cervical cancer.
• About 4,000 women a year die of cervical cancer in the United States.

Practice Question

Researchers have developed a potential vaccine against HPV and want to test it. What is the first testable hypothesis that the researchers should study?

• HPV causes cervical cancer.
• People should not have unprotected sex with many partners.
• People who get the vaccine will not get HPV.
• The HPV vaccine will protect people against cancer.

[reveal-answer q=”20917″] Show Answer [/reveal-answer] [hidden-answer a=”20917″]Hypothesis A is not the best choice because this information is already known from previous studies. Hypothesis B is not testable because scientific hypotheses are not value statements; they do not include judgments like “should,” “better than,” etc. Scientific evidence certainly might support this value judgment, but a hypothesis would take a different form: “Having unprotected sex with many partners increases a person’s risk for cervical cancer.” Before the researchers can test if the vaccine protects against cancer (hypothesis D), they want to test if it protects against the virus. This statement will make an excellent hypothesis for the next study. The researchers should first test hypothesis C—whether or not the new vaccine can prevent HPV.[/hidden-answer]

Experimental Design

You’ve successfully identified a hypothesis for the University of Washington’s study on HPV: People who get the HPV vaccine will not get HPV.

The next step is to design an experiment that will test this hypothesis. There are several important factors to consider when designing a scientific experiment. First, scientific experiments must have an experimental group. This is the group that receives the experimental treatment necessary to address the hypothesis.

The experimental group receives the vaccine, but how can we know if the vaccine made a difference? Many things may change HPV infection rates in a group of people over time. To clearly show that the vaccine was effective in helping the experimental group, we need to include in our study an otherwise similar control group that does not get the treatment. We can then compare the two groups and determine if the vaccine made a difference. The control group shows us what happens in the absence of the factor under study.

However, the control group cannot get “nothing.” Instead, the control group often receives a placebo. A placebo is a procedure that has no expected therapeutic effect—such as giving a person a sugar pill or a shot containing only plain saline solution with no drug. Scientific studies have shown that the “placebo effect” can alter experimental results because when individuals are told that they are or are not being treated, this knowledge can alter their actions or their emotions, which can then alter the results of the experiment.

Moreover, if the doctor knows which group a patient is in, this can also influence the results of the experiment. Without saying so directly, the doctor may show—through body language or other subtle cues—his or her views about whether the patient is likely to get well. These errors can then alter the patient’s experience and change the results of the experiment. Therefore, many clinical studies are “double blind.” In these studies, neither the doctor nor the patient knows which group the patient is in until all experimental results have been collected.

Both placebo treatments and double-blind procedures are designed to prevent bias. Bias is any systematic error that makes a particular experimental outcome more or less likely. Errors can happen in any experiment: people make mistakes in measurement, instruments fail, computer glitches can alter data. But most such errors are random and don’t favor one outcome over another. Patients’ belief in a treatment can make it more likely to appear to “work.” Placebos and double-blind procedures are used to level the playing field so that both groups of study subjects are treated equally and share similar beliefs about their treatment.

The scientists who are researching the effectiveness of the HPV vaccine will test their hypothesis by separating 2,392 young women into two groups: the control group and the experimental group. Answer the following questions about these two groups.

• This group is given a placebo.
• This group is deliberately infected with HPV.
• This group is given nothing.
• This group is given the HPV vaccine.

[reveal-answer q=”918962″] Show Answers [/reveal-answer] [hidden-answer a=”918962″]

• a: This group is given a placebo. A placebo will be a shot, just like the HPV vaccine, but it will have no active ingredient. It may change peoples’ thinking or behavior to have such a shot given to them, but it will not stimulate the immune systems of the subjects in the same way as predicted for the vaccine itself.
• d: This group is given the HPV vaccine. The experimental group will receive the HPV vaccine and researchers will then be able to see if it works, when compared to the control group.

Experimental Variables

A variable is a characteristic of a subject (in this case, of a person in the study) that can vary over time or among individuals. Sometimes a variable takes the form of a category, such as male or female; often a variable can be measured precisely, such as body height. Ideally, only one variable is different between the control group and the experimental group in a scientific experiment. Otherwise, the researchers will not be able to determine which variable caused any differences seen in the results. For example, imagine that the people in the control group were, on average, much more sexually active than the people in the experimental group. If, at the end of the experiment, the control group had a higher rate of HPV infection, could you confidently determine why? Maybe the experimental subjects were protected by the vaccine, but maybe they were protected by their low level of sexual contact.

To avoid this situation, experimenters make sure that their subject groups are as similar as possible in all variables except for the variable that is being tested in the experiment. This variable, or factor, will be deliberately changed in the experimental group. The one variable that is different between the two groups is called the independent variable. An independent variable is known or hypothesized to cause some outcome. Imagine an educational researcher investigating the effectiveness of a new teaching strategy in a classroom. The experimental group receives the new teaching strategy, while the control group receives the traditional strategy. It is the teaching strategy that is the independent variable in this scenario. In an experiment, the independent variable is the variable that the scientist deliberately changes or imposes on the subjects.

Dependent variables are known or hypothesized consequences; they are the effects that result from changes or differences in an independent variable. In an experiment, the dependent variables are those that the scientist measures before, during, and particularly at the end of the experiment to see if they have changed as expected. The dependent variable must be stated so that it is clear how it will be observed or measured. Rather than comparing “learning” among students (which is a vague and difficult to measure concept), an educational researcher might choose to compare test scores, which are very specific and easy to measure.

In any real-world example, many, many variables MIGHT affect the outcome of an experiment, yet only one or a few independent variables can be tested. Other variables must be kept as similar as possible between the study groups and are called control variables . For our educational research example, if the control group consisted only of people between the ages of 18 and 20 and the experimental group contained people between the ages of 30 and 35, we would not know if it was the teaching strategy or the students’ ages that played a larger role in the results. To avoid this problem, a good study will be set up so that each group contains students with a similar age profile. In a well-designed educational research study, student age will be a controlled variable, along with other possibly important factors like gender, past educational achievement, and pre-existing knowledge of the subject area.

What is the independent variable in this experiment?

• Sex (all of the subjects will be female)
• Presence or absence of the HPV vaccine
• Presence or absence of HPV (the virus)

[reveal-answer q=”68680″]Show Answer[/reveal-answer] [hidden-answer a=”68680″]Answer b. Presence or absence of the HPV vaccine. This is the variable that is different between the control and the experimental groups. All the subjects in this study are female, so this variable is the same in all groups. In a well-designed study, the two groups will be of similar age. The presence or absence of the virus is what the researchers will measure at the end of the experiment. Ideally the two groups will both be HPV-free at the start of the experiment.

List three control variables other than age.

[practice-area rows=”3″][/practice-area] [reveal-answer q=”903121″]Show Answer[/reveal-answer] [hidden-answer a=”903121″]Some possible control variables would be: general health of the women, sexual activity, lifestyle, diet, socioeconomic status, etc.

What is the dependent variable in this experiment?

• Sex (male or female)
• Rates of HPV infection
• Age (years)

[reveal-answer q=”907103″]Show Answer[/reveal-answer] [hidden-answer a=”907103″]Answer b. Rates of HPV infection. The researchers will measure how many individuals got infected with HPV after a given period of time.[/hidden-answer]

Contributors and Attributions

• Revision and adaptation. Authored by : Shelli Carter and Lumen Learning. Provided by : Lumen Learning. License : CC BY-NC-SA: Attribution-NonCommercial-ShareAlike
• Scientific Inquiry. Provided by : Open Learning Initiative. Located at : https://oli.cmu.edu/jcourse/workbook/activity/page?context=434a5c2680020ca6017c03488572e0f8 . Project : Introduction to Biology (Open + Free). License : CC BY-NC-SA: Attribution-NonCommercial-ShareAlike

Teaching AP® Science

Resources By Kristi Schertz

Air Pollution Lab- Airborne Particulates for Distance Learning

One of the best and easy-to-implement labs in my class is an air pollution lab. Traditionally, my students are in person as we use petri dishes, but this year, I came up with an at-home lab for distance learning. This lab can be used in many different courses and I use it in unit 7 for AP® Environmental Science. Click for a student version of the at-home lab . The original in-person lab can be found on this post.

At this point in my curriculum, my students have performed a controlled a experiment about soil salinization and have designed a noise pollution lab in Unit 5 so they do not need much scaffolding. This lab gives them further practice with experimental design.

Experimental design lab is essential for students to do a few times in the year, because the AP® Exam WILL have experimental design questions in the multiple choice section and on FRQ #1. It is AP Science Practice # 4: Scientific Experiments .

Materials for the Airborne Particulates At-Home Lab

• 3 index cards OR pieces of paper
• Vaseline, Chapstick, lip gloss or something else that clear and sticky
• Ruler or PDF of ruler
• Ziploc bag with toothpicks, or a sealed food container
• Magnifier on a Smartphone (Best option is a free app with magnifying glass with light, but you can also use the built-in magnifier on a phone along with a separate light source)

Day one of the air pollution lab takes about 45-60 minutes. Student lab groups brainstorm and come up with a question to test, a hypothesis, and design. They must get approval from me before making their cards.  My students have already done an experimental design lab so this process is fairly quick at this point. If this is the first experimental design lab of the year, expect this to take longer and for students to need more revision.

This lab is challenging with the constants. They can never really isolate all the variables and because of this, they will get flawed data. This is really important!!   Analyzing the weaknesses in their lab help them identify flawed experiments later on in life and on the AP® Exam. I aim to develop scientifically literature citizens.

I give students some ideas such as comparing indoor vs. outdoor particulates, front yard vs. back yard or the number of pets. Some students come up with very creative ideas outside of these suggestions.

If rain is in the forecast, make sure they don’t set out the cards in the rain (or sprinklers). Also, they need to make sure they all set out the cards on the same day for the same amount of time, because weather can influence.

After approvals, students make their cards. Students need to put one card in a sealed bag or food container as the control.

Here is a YouTube video I made showing students how to make their cards.

Day 2 of the Airborne Particulates Lab

Day 2 of the air pollution lab is several days later . With this lab, it can take a week to get enough particulates that students can see with their phone magnifiers instead of a stereoscope.

Students can download a free app “magnifying glass+ light” or they can use the built-in magnifier on their phones. If they use the built-in ones, they will need another source of bright light. Below is a screenshot of a the particulates using the app.

I provide a spreadsheet template for students to use if they wish, but they will not turn it in as I am grading their graphs. I also provide sample data and graphs as reference and a YouTube Link for how to make graphs using this google sheets template. (Click on links in this paragraph for these resources)

My students make and present posters for this air pollution lab and in distance learning, they make a google slide. Click for a template of the google slide presentation that my students fill in per group . It really helps them discuss and analyze the results. Why their hypothesis was correct or not AND more importantly, why this lab was flawed. They can never fully control all the variables and I want them to see that other factors may have influenced their results. This is the best part of the lab–learning to identify flawed experiments.

My poster template is inspired by Argument-Based Inquiry, but I have added more sections and clearer instructions.

You can also have students write a formal lab report individual or as a group as assessment as well.

Click for a poster rubric.

* AP ®  is a trademark registered and/or owned by the College Board which was not involved in the production of, and does not endorse this site.

Kristi Schertz

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APES Lab Supplies Part 1: Essential Labs

Cutting and filling ecocolumns, ecocolumns: taking aquatic chamber data, 2 thoughts on “ air pollution lab- airborne particulates for distance learning ”.

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4 Lab 4: Environmental Hazards – Air Pollution

Introduction

Air pollution is defined as the emission or release of pollutants into the atmosphere, where the pollutants are visible or invisible particles/gases that are not a part of the normal composition of air. Perhaps the most obvious pollutants are the airborne wastes associated with fuel combustion, which are seen emitted from factories, power plants, and vehicles. Particulate matter is often the most visible source of air pollution, and is arguably the largest source of anthropogenic air pollution. However, there are also natural (non-anthropogenic) sources, such as the particulate matter and gases emitted by volcanoes, the smoke from lightning-causes fires, dust storms, and pollen. Regardless of source, particulate matter can be harmful to plant, animal, and human life and well-being.

The primary objectives for today are to:

• Develop a working definition of particulate matter and comprehend the indices used to track/monitor it
• Assess and compare air quality across the United States, in Omaha, and in other locations worldwide
• Measure air quality in different locations and make comparisons across space

Sources of Air Pollution

There are three categories of anthropogenic air pollution: Point, Area, and Mobile. A point source is perhaps most simply thought of as a feature that is fixed in space that emits a large amount of pollutants, such as a factory smokestack. In contrast, area sources are a combination of multiple, less impactful, sources that when combined, emit a large amount of pollutants. An example of area sources would be a park with multiple campsites, where each site had a campfire. A single campfire itself produces small amounts of pollutants, but the combined impact of 20-30 campfires together create a substantial emission. Mobile sources are ones that move, such as those from sources of transportation (i.e. cars, trucks, trains, plains, etc.).

The Environmental Protection Agency (EPA) defines five Criteria Pollutants, pollutants for which there are established laws and standards for air quality. They are: ozone (ground level), particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Definitions of these criteria pollutants is available below, and further information can be found at: https://www.epa.gov/criteria-air-pollutants . With higher concentrations of these pollutants, there are higher health risks including: aggravated cardiovascular and respiratory illness, added stress to the heart and lungs, respiratory system cell damage, fatigue, asthma, irritation of eyes, nose, and throat, and shortness of breath.

Ozone (ground-level): Tri-atomic oxygen (O3) which forms by chemical reaction between nitrogen oxides (NOx) and volatile organic compounds (VOC) when exposed to sunlight. NOx and VOC are byproducts of various combustion reactions.

Particulate Matter (PM): Small particles in the air, such as dust, dirt, soot, or smoke. There are two varieties: PM2.5 and PM10. The number corresponds to the size of the particulates, in micrometers. PM2.5 are about 2.5 micrometers and smaller (about the 30 times larger than the thickness of a human hair. PM10 are 10 micrometers or smaller.

Carbon Monoxide (CO): A odorless and colorless gas released when something is burned, such as natural gas, gasoline, and organic matter.

Sulfur Dioxide (SO2): Compound primarily resulting from fossil-fuel-based combustion at power plants, however vehicles, mining and volcanic eruptions also emit SO2.

Nitrogen Dioxide (NO2): A highly reactive gas which is emitted to the atmosphere due to the burning of fuel such as gasoline and diesel.

Air Quality Index

To assist in determining how clean (or polluted) the air is, and inform the associated health risks, the Air Quality Index (AQI) was created. It focuses on the health impacts you may experience after a few hours or days breathing the polluted air, and is based on levels of five (of six; excludes lead) criteria pollutants. The AQI works as a running scale from 0-500, where the lower the number, the cleaner and safer the air, and the higher the number, the more polluted the air. While lower is better, values below 100 are generally considered satisfactory. The following tables outlines the AQI’s values.

Measuring Air Quality

Hand-held instruments will be provided in class. They sample the air directly in contact with the device, and report the value onto the screen. Similar to lab 2, these are “point and click” type instruments. Please treat these with care and do not touch the sensor. Do not breathe into the sensor.

Further Information and Data used in Lab

In reaching the learning goals for today’s lab, we will be utilizing data from a variety of air quality monitoring groups within the US and worldwide. AirNow, a part of the EPA ( https://www.airnow.gov/ ), provides near real-time observations of air quality and allows for comparisons between cities, based on the last 10 years of data ( https://www3.epa.gov/aircompare/ ). Additionally, data are available globally from World Air Quality Index project ( https://waqi.info/ ). We will be providing you case-study data for analysis in lab, however you are welcome to explore these data on your own.

Part 1 – Real-Time Air Pollution Conditions

You will be provided with (a) AQI map of the United States, (b) AQI map of the Omaha area, (c) table of AQI criteria pollutants for Omaha area, (d) AQI map for the world, and (e) AQI data for two specific locations outside the United States.

1. Using (a), describe the AQI across the U.S. Be sure to note the general areas where AQI is not Good (i.e. where is it Moderate, USG, Unhealthy, Very Unhealthy, and/or Hazardous).

2. Where is the location with the highest AQI? What’s the AQI, approximately?

3. What sort of health impacts could be expected at an ‘unhealthy’ or high category?

4. Using (b) and (c), answer the following:

The current AQI in Omaha is _________________.

The current Ozone AQI is __________________.

The current PM10 AQI is ___________________.

The current PM2.5 AQI is ___________________.

5. Examining the forecast for today and tomorrow (using (c)), do we need to be concerned about air quality? Why or why not?

6. Keeping these values in mind, let’s put them into context of values across the world. Using (d), where is AQI data generally available, based on the map? Where is it not available?

7. Hypothesize why AQI data is available (or not available) where it is (or isn’t).

8. Two locations, not in the United States, are provided to examine in further detail (e). Use them to answer the following questions. If you’d prefer to choose your own locations, please confirm this with your instructor prior to working.

Location 1 _____________________             AQI ____________

8a. What is the primary pollutant contributing to the AQI?

8b. The color of the clouds in the Air Quality Forecast area (slightly down the page) match the colors of the AQI. How is AQI forecasted to change over the next few days, in comparison to its current value?

8c. What about this specific location may contribute to its AQI? (hint: think about population, sources of pollution, general climate, etc.)

Location 2 _____________________          AQI ____________

8d. What is the primary pollutant contributing to the AQI?

8e. The color of the clouds in the Air Quality Forecast area (slightly down the page) match the colors of the AQI. How is AQI forecasted to change over the next few days, in comparison to its current value?

8f. What about this specific location may contribute to its AQI? (hint: think about population, sources of pollution, general climate, etc.)

Part 2 – Sampling Air Quality

Using the provided instruments, you will work as a team to measure levels of Particulate Matter (PM) at three near-by locations: in the classroom, in the atrium of DSC, outside in an open area. Fill out the tables below and answer the analysis questions.

9. Of the three locations (classroom, atrium, outside), which do you hypothesize to have the highest levels of PM? Why?

10. How could you test your hypothesis?

11. Fill out the tables below, based on your observations. Take 3 samples at each site and calculate an average for both PM 2.5 and PM 10.

12. Which site had the highest PM average? Was your hypothesis correct?

13. Which site had the most variation between the three PM samples?

14. Consider the outside observation. How does that compare to the PM value of the Omaha AQI values, (b) and (c)?

15. Why do you suspect our observed value in lab was (different/similar) to the value reported by AirNow?

Introduction to Human-Environment Geography: A Laboratory Manual Copyright © 2021 by Zachary J. Suriano is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Air Pollution

Introduction: (initial observation).

Air pollution is the contamination of the air by noxious gases and minute particles of solid and liquid matter (particulates) in concentrations that endanger health. In addition to many economical and agricultural losses, air pollution is the main cause of many diseases and deaths every year. Excessive growth rate of air pollution is a major concern for many countries and scientists from all over the world are studying on causes, prevention methods and cleanup of the air pollution.

This project is an opportunity to follow the foot steps of other scientists and learn about the air pollution causes and cleanups.

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “ Ask Question ” button on the top of this page to send me a message.

If you are new in doing science project, click on “ How to Start ” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.  

Project advisor

Information Gathering:

Find out about air pollution. Read books, magazines or ask professionals who might know in order to learn about the causes of air pollution and methods of prevention and cleanup. Keep track of where you got your information from.

For basic general information,  encyclopedia  is a good start.

Air Pollution Control

To show how air pollution is controlled.

Grade level

6th, 7th & 8th grades

Essential Elements

(Science) 1 (A) Properly demonstrate the use of laboratory equipment; 2 (A) Observe physical and chemical properties of matter; 5 (A) Measure physical and chemical properties of matter.

At the end of the lesson the student will be able to distinguish between an electrostatic precipitator and a wet scrubber and the principles behind the operation of these control techniques.

When any product is made by industry, waste may be produced that can pollute the air. Wet scrubbers and electrostatic precipitators are two devices used to clean up the air waste stream before it enters the atmosphere.

Air contaminants are emitted into the atmosphere as particulates, aerosols, vapors, or gases. The most common methods of eliminating or reducing pollutants to an acceptable level are destroying the pollutant by thermal or catalytic combustion, changing the pollutant to a less toxic form, or collecting the pollution by use of equipment to prevent its escape into the atmosphere. Pollutant recovery may be accomplished by the use of one or more of the following:

Baghouses  – Dry particulates are trapped on filters made of cloth, paper or similar materials. Particles are shaken or blown from the filters down into a collection hopper. Baghouses are used to control air pollutants from steel mills, foundries, and other industrial furnaces and can collect more than 98 percent of the particulates. Cyclones  – Dust-laden gas is whirled very rapidly inside a collector shaped like a cylinder. The swirling motion creates centrifugal forces causing the particles to be thrown against the walls of the cylinder and to drop into a hopper. Cyclones are used for controlling pollutants from cotton gins, rock crushers, and many other industrial processes and can remove up to 95 percent of solid pollutants. Electrostatic precipitators  – By use of static electricity, they attract particles in much the same way that static electricity in clothing picks up small bits of dust and lint. Electrostatic precipitators, 98 to 99 percent effective, are used instead of baghouses when the particles are suspended in very hot gases, such as in emissions from power plants, steel and paper mills, smelters, and cement plants. Wet scrubbers  – Particulates, vapors, and gases are controlled by passing the gas stream through a liquid solution. Scrubbers are used on coal burning power plants, asphalt/concrete plants, and a variety of other facilities that emit sulfur dioxides, hydrogen sulfides, and other gases with a high water solubility. Wet scrubbers are often used for corrosive, acidic, or basic gas streams. ( Note that recovery control devices include adsorption and condenser techniques as well.)

• Which type of air cleaner would be the best for removing particles?
• Which type of air cleaner would be the best for removing waste gases?
• Does a wet scrubber clean up all of the pollutants?
• What problems are produced by having too many pollutants in the air we breathe?
• If industry is just part of the problem, what can we do to control the amount of air pollution that we cause?

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to demonstrate at least one of the air filtration methods. Construct a filter and show that it actually does collect or filter some pollutants.

Possible questions are:

Which filtration method is best for particle pollution? Which area has the highest amount of invisible pollutants? What are the causes of air pollution and how can it be prevented? (After identifying the cause of pollution, we can simply stop it by switching to other methods that do not cause pollution. For example if we identify fossil fuels such as coal and oil as a source of pollution, we can try using solar energy, hydroelectric energy or wind energy.) How effective is any system of air filtration?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other. For question 1, variables are:

The independent variable (also known as manipulated variable) is the filtration method.

The dependent variable (also known as responding variable) is the amount of pollutants they filter.

Constants are the type of pollutants and filtration time.

For question 2, variables are:

The independent variable (also known as manipulated variable) is the location.

The dependent variable (also known as responding variable) is the pollution rank.

Constants are the experiment method, time and supplies.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

Sample Hypothesis:

My hypothesis is that by passing polluted air through water we can filter pollutants and produce clean air. This hypothesis is based on my observation of air freshness after a heavy rain.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

(Visible and Invisible pollutants)

Which area has the highest amount of invisible pollutants?

The atmosphere is almost completely made up of invisible gaseous substances. Most major air pollutants are also invisible, although large amounts of them concentrated in areas such as cities can be see as smog. One often visible air pollutant is particulate matter, especially when the surfaces of buildings and other structures have been exposed to it for long periods of time or when it is present in large amounts. Particulate matter is made up of tiny particles of solid matter and/or droplets of liquid. Natural sources include volcanic ash, pollen, and dust blown by the wind. Coal and oil burned by power plants and industries and diesel fuel burned by many vehicles are the chief sources of man-made particulate pollutants, but not all important sources are large scale. The use of wood in fireplaces and wood-burning stoves also produces significant amounts of particulate matter in localized areas, although the total amounts are much smaller than those from vehicles, power plants, and industries.

In this experiment we will test for visible and invisible pollutants in the air and try to tell the difference between visible and invisible air pollution.

chart paper measuring cups small glass jars large glass jars petroleum jelly 3 bean plants approximately the same size tap water vinegar vinegar-water mixture in 1 to 3 ratio pH paper or indicator

Visible Pollutants test

Smear petroleum jelly on each small jar. Carefully place each small jar inside a large jar. Decide on several places around the school or home where you think visible pollutants will occur. Make predictions about which area will have more visible pollutants and why. Record predictions in journal. Place jars in test areas for several days. Check the jars daily. Record observations in journal. Collect jars for comparison. Observe and rank the jars from the one with the most visible pollutants to the one with the least. Assign each jar a number. Discuss why certain areas have more visible pollutants than others. Mark a map showing the ranking of areas from the lowest dust to the highest dust.

Invisible Pollutants test

Sets up a bean plant garden with three containers, each container having one bean plant. Determine and compare the pH of the three solutions and predict how the plants will be affected by each solution. Record pH and predictions in journal. Plants will be watered every day with 1/8 to 1/4 cup of a solution: one plant with tap water, one plant with straight vinegar, and one plant with the vinegar-water mixture. Procedure is recorded in journal. Observe plants daily. Record in journal what happens to each plant. Sketches may be part of the observations. Compare plants and discuss observations at the end of a day, week, two weeks, or until plants die. Using the observations, write a conclusion for this experiment. Record in journal. Invisible pollutants are like acid rain. Use the result of your experiment to conclude how does acid rain affect the plants.

Research the history of acid rain. Include information on the causes of acid rain, when we first became aware of the problem, what problems have been caused by acid rain, what measures have been taken to

combat acid rain. Has the situation improved? Post a chart for the causes of visible pollutants and what can be done to prevent them.

Experiment 2: Make a electrostatic precipitator Particles (called particulate matter) can be captured before they enter the atmosphere by an electrostatic precipitator. In this experiment we use a plastic tube and black pepper to see how particles are attracted to the sides of the tube much like the pollutants are attracted in large industrial electrostatic precipitators.

Materials, Equipment, and Preparation plastic tube (fluorescent light tube) wire coat hanger plastic grocery bag electric blow dryer punch holes, black pepper or rice crispies Picture on the right shows an industrial model of electrostatic precipitator.

The electrostatic precipitator works on the principle of a static electric charge attracting particles where they are removed.

A 2-foot plastic tube in which fluorescent lights are stored can be used to simulate an electrostatic precipitator. The plastic tube can be charged by running a coat hanger with a plastic grocery bag attached to it.

(The plastic bag as it moves through the tube strips the negatively charged electrons from the inside of the tube making the overall net charge positive. Anything that has a negative charge will be attracted to the tube because opposites attract.)

Hold the tube over some punch holes, black pepper, or rice crispies. Hold an electric hair dryer so the air stream blows across the top of the tube. The air mass creates a low pressure area at the top and the greater air pressure at the bottom pushes the punch holes up the tube. (This is called Bernoulli’s Principal)

***The Results*** If the tube is charged, the punch holes will stick to the sides. This activity can be used to study static electricity. If the tube is not charged, the holes will shoot out in a spray. This activity can be used to study Bernoulli’s principle.

Experiment 3: How to Make a Wet Scrubber

Warning: This experiment requires proper equipment and expert adult supervision. Please skip this experiment without proper equipment and supervision.

The wet scrubber is one of the most common pollution control devices used by industry. It operates on a very simple principle: a polluted gas stream is brought into contact with a liquid so that the pollutants can be absorbed. In this experiment we will try to build a wet scrubber. (See diagram A)

Materials Paper towels 12-cm piece of glass Three 2.5-cm pieces of glass tubing Three 55-ml flasks Two glass impingers (glass tubing drawn at one end to give it a smaller diameter so as to let out smaller bubbles) Heat source (burner or hot plate) Three 2-hole rubber stoppers (of a size to fit the mouths of the flasks) Two 30-cm pieces of rubber tubing Ring stand apparatus Vacuum source Procedure Write your answers on a separate sheet. Set up the apparatus as shown in attached figure . Put a paper towel in a 55-ml flask and place this above the burner. Using a 2-hole stopper that makes an air-tight seal with the flask, insert a 12-cm section of glass tubing through one of the holes. The tubing should reach to approximately 1.2-cm from the bottom of the flask. Insert a 2.5-cm piece of glass tubing into the other hole of the stopper. Connect a 30-cm piece of rubber tubing to the 2.5-cm piece of glass tubing, making sure an air-tight seal exists. Fill a second 500-ml flask approximately 3/4 full of water. Using a second double-hole stopper, put a 2.5-cm piece of glass tubing into one of the holes, and insert the glass impinger into the other. Construct a third flask like the second. Connect the rubber tubing and heat the first flask (combustion chamber) until smoke appears. Put a vacuum on the third flask to draw a stream of smoke through the second flask (the wet scrubber). If smoke collects in the second flask above the water, a second scrubber can be added. Ask the students if particles are the only pollutants produced by industry. Discuss how a wet scrubber collects not only particulate matter but also captures waste gases. Demonstrate how the water scrubber works. Discuss that the white plume you see coming from a smokestack may really be steam coming from a water scrubber. After observing the wet scrubber, answer the following questions: Why does the water in the wet-scrubber change color? Why does the wet-scrubber have an impinger (in other words, why is it important for small bubbles to be formed)? What does the scrubber filter out of the air? Not filter out? Suggest ways to dispose of the pollutants that are now trapped in the water.

Materials and Equipment:

List of material can be extracted from the experiment section.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

Description

Summery of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

List of References

It is always important for students, parents and teachers to know a good source for science related equipment and supplies they need for their science activities. Please note that many online stores for science supplies are managed by MiniScience.

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Measuring Air Pollution – A Simple Fieldwork Experiment

In this guest blog post Dr Paul Ganderton provides guidance on completing fieldwork involving measuring air pollution. You can follow Paul on Twitter via @ecogeog .  

Fieldwork should be frequent and compulsory! There, said it! Against the mounting paperwork and issues in my system, I stand for practical work for all students as often as possible. However, we do need to be aware of the real constraints in this endeavour. As much as we’d like to spend every lesson out in the field (and imagine how much they’d learn!), we need to allow other subjects their time. Cash is a real issue as well. I’m guessing no-one’s funding has expanded to keep pace with the cost of fieldwork equipment. This is why I’ve developed a series of field experiments that are simple, cheap and effective.

Let’s get started. These are the key factors to I bear in mind at the planning stage:

• Validity – will the fieldwork give me decent data that can be seen (albeit in more sophisticated forms) in real geographical science?;
• Complexity – if the work is done remotely by students, can the instructions be unambiguous so the whole class can be confident everyone’s data are comparable?;
• Timescale – can the work be set up reasonably quickly and get decent results so students keep their enthusiasm? I like the idea of thinking fast and slow and cooking fast and slow, so why not Geography fast and slow! This one’s fast; a week’s trip gives me slow! (Both are valid but I love the quick experiment. It motivates students, gets them to realize that Geography is mostly a practical science);
• Cost – yes, I’d love the latest monitoring equipment (please) but in the real world, you don’t get the luxury and it’s crucial all students take part.

Putting this piece of fieldwork in context of these three ideas:

• This follows accurately the methods used in air pollution research. Today, remote sensors are used but the basic idea of gathering point data is very much alive;
• This experiment has been road tested loads of times. I’ve never had a student fail. I even demonstrate in class first and get them to trial setting up a unit;
• I plan this to last for about 7 days. So, students go home on holiday/half-term, set this up, forget it and bring the materials in at the start of the new term. Total student time – about 1 hour tops. About 3 lessons in class – 1 before to outline the experiment; 2 for analysis and discussion afterwards;
• Cost – borrowing from your science department and a couple of household items means your main cost is just 1 stake per student (woodwork department scrap or hardware store). Depending on your jurisdiction, about 1GBP/$2 all up.

Moving on to the fieldwork stuff:

• Equipment – for each student: 1 stake 1.5m high, ideally 20x20mm square; 4 microscope slides; enough sticky tape to bind top and bottom of the slide to the post; petroleum jelly to smear on each slide. For the analysis, an identification guide and microscope.
• Take the stake and tape one slide to one of the faces. Make sure that only about 1cm is covered top and bottom of the slide so there’s enough space for the jelly;
• Repeat for the other 3 faces. It’s important that the slides are all at the top of the stake. I’ve had students tape all four on at once. It’s not hard. If slides are glass, a quick warning about wearing gloves or taking care might be useful. Label each slide as N, S, E or W;
• On the exposed glass (not tape), smear petroleum jelly on the slide. How much? More than a smear, less than a big splodge – I suppose 0.25mm – it needs to be able to withstand a week’s weather;
• Find a spot to locate the stake. The obvious choice is in the garden, away from objects that impede air flow. Some students might live in apartments so they may have only a balcony or even just a window. No problems, just adjust as needed and use this as a case study in discussing sampling arrangements! Make sure the stake is oriented so the North-facing slide faces North etc.
• Leave alone for about 7 days if possible;
• At the end, take the slides carefully off the stake avoiding smudging the jelly. Transport the slides to school so that they are not smeared. I find taping them to a piece of cardboard is good. A lunch box where the slides are stuck to the bottom is excellent. Discuss with students how to transport their data without ruining it!
• If the work has gone well, you should have 4 slides with a variety of particles embedded in them. From this point, there are two main questions – what are the particles and how many are there?;
• For the former, there are usually only 5 common particles: pollen, dust, fibres, fly ash, diesel carbon and grit. Give students an identification guide and a microscope and get them to see how many different categories of particle they can recognize (1) . Put this in a table/spreadsheet;
• For the latter, there needs to be some common system. It’s possible to count but would take far too long and be likely erroneous (bored students!). A simpler scale is the Likert-type Scale: Absent, Rare, Uncommon, Common, Abundant. Add these labels to the table/spreadsheet;
• Take each slide in turn. Analyse the types of particles and their abundance. Put the data in the table and repeat until slides have been recorded;
• Record the location of each stake on a map (paper or electronic).
• Discussion:

At this stage, you should have 4 readings for each stake and a map detailing locations. This is the pattern – the what and where . Now we get students to find out why . At this point, you can go in any number of directions which is what makes this such a good piece of fieldwork! Here are just a few of the questions I’ve posed over the years (with suggestions for answers/discussions):

• Which direction has the most particles? (prevailing winds?)
• Which particles are most common? (pollen, suggesting countryside or diesel carbon, suggesting roads?)
• Are particles equally common on all sides or just some? (group of trees on one side?)
• Do particle counts vary in one direction (distance from roads or quarries/forests etc.?)
• Which of these particles causes most impact to (a) the environment (e.g. dust covering plants affecting photosynthesis); and (b) people (poor air quality links to asthma etc.). Get students to research this as a part of their study.
• Taking it further:

The advantage of this work is that you can take it in a number of equally valid directions:

• Critique of method – is it realistic and likely to give decent results?;
• What factors might make the results less valid?;
• What is the sampling method and how might it be improved?;
• What pollutant factors are most important in our towns and cities? Is this research equally useful in other towns/nations? Why/why not?;
• What can be done to reduce air pollution in our town?
• What are the 3 key takeaway points that you have learned? Why did you choose those 3?
• Carry out simple statistical/graphical techniques to allow comparison between sites. What pattern is shown and how can we account for it?
• Air pollution and public health is a huge study area. Students can study the impact of exhaust fumes on health and mental development , explore the issues surrounding Lead in petrol, look at exposure to pollutants on child development etc.

There we have it. A simple yet effective fieldwork item that could be used for different years/topics. It yields itself to so much analysis and interpretation. It develops citizenship and personal health ideas through appreciating the pollution level around us. Given that a bit of promotion never hurt any subject, it can be said that this approach to a topic allows you to develop an appreciation of Geography and its potential in the real world.

Dr Paul Ganderton @ecogeog

• Particle Identification. It’s easy to make a chart from Google images as was done for this blogpost. Here are some images to help you differentiate:

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Diesel/engine particles:

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The scientific method and climate change: How scientists know

By Holly Shaftel, NASA's Jet Propulsion Laboratory

The scientific method is the gold standard for exploring our natural world. You might have learned about it in grade school, but here’s a quick reminder: It’s the process that scientists use to understand everything from animal behavior to the forces that shape our planet—including climate change.

“The way science works is that I go out and study something, and maybe I collect data or write equations, or I run a big computer program,” said Josh Willis, principal investigator of NASA’s Oceans Melting Greenland (OMG) mission and oceanographer at NASA’s Jet Propulsion Laboratory. “And I use it to learn something about how the world works.”

Using the scientific method, scientists have shown that humans are extremely likely the dominant cause of today’s climate change. The story goes back to the late 1800s, but in 1958, for example, Charles Keeling of the Mauna Loa Observatory in Waimea, Hawaii, started taking meticulous measurements of carbon dioxide (CO 2 ) in the atmosphere, showing the first significant evidence of rapidly rising CO 2 levels and producing the Keeling Curve climate scientists know today.

“The way science works is that I go out and study something, and maybe I collect data or write equations, or I run a big computer program, and I use it to learn something about how the world works.”- Josh Willis, NASA oceanographer and Oceans Melting Greenland principal investigator

Since then, thousands of peer-reviewed scientific papers have come to the same conclusion about climate change, telling us that human activities emit greenhouse gases into the atmosphere, raising Earth’s average temperature and bringing a range of consequences to our ecosystems.

“The weight of all of this information taken together points to the single consistent fact that humans and our activity are warming the planet,” Willis said.

The scientific method’s steps

The exact steps of the scientific method can vary by discipline, but since we have only one Earth (and no “test” Earth), climate scientists follow a few general guidelines to better understand carbon dioxide levels, sea level rise, global temperature and more.

• Form a hypothesis (a statement that an experiment can test)
• Make observations (conduct experiments and gather data)
• Analyze and interpret the data
• Draw conclusions
• Publish results that can be validated with further experiments (rinse and repeat)

As you can see, the scientific method is iterative (repetitive), meaning that climate scientists are constantly making new discoveries about the world based on the building blocks of scientific knowledge.

“The weight of all of this information taken together points to the single consistent fact that humans and our activity are warming the planet." - Josh Willis, NASA oceanographer and Oceans Melting Greenland principal investigator

The scientific method at work.

How does the scientific method work in the real world of climate science? Let’s take NASA’s Oceans Melting Greenland (OMG) campaign, a multi-year survey of Greenland’s ice melt that’s paving the way for improved sea level rise estimates, as an example.

• Form a hypothesis OMG hypothesizes that the oceans are playing a major role in Greenland ice loss.
• Make observations Over a five-year period, OMG will survey Greenland by air and ship to collect ocean temperature and salinity (saltiness) data and take ice thinning measurements to help climate scientists better understand how the ice and warming ocean interact with each other. OMG will also collect data on the sea floor’s shape and depth, which determines how much warm water can reach any given glacier.
• Analyze and interpret data As the OMG crew and scientists collect data around 27,000 miles (over 43,000 kilometers) of Greenland coastline over that five-year period, each year scientists will analyze the data to see how much the oceans warmed or cooled and how the ice changed in response.
• Draw conclusions In one OMG study , scientists discovered that many Greenland glaciers extend deeper (some around 1,000 feet, or about 300 meters) beneath the ocean’s surface than once thought, making them quite vulnerable to the warming ocean. They also discovered that Greenland’s west coast is generally more vulnerable than its east coast.
• Publish results Scientists like Willis write up the results, send in the paper for peer review (a process in which other experts in the field anonymously critique the submission), and then those peers determine whether the information is correct and valuable enough to be published in an academic journal, such as Nature or Earth and Planetary Science Letters . Then it becomes another contribution to the well-substantiated body of climate change knowledge, which evolves and grows stronger as scientists gather and confirm more evidence. Other scientists can take that information further by conducting their own studies to better understand sea level rise.

All in all, the scientific method is “a way of going from observations to answers,” NASA terrestrial ecosystem scientist Erika Podest, based at JPL, said. It adds clarity to our way of thinking and shows that scientific knowledge is always evolving.

Related Terms

• Climate Change
• Climate Science
• Earth Science

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NASA is now publicly distributing science-quality data from its newest Earth-observing satellite, providing first-of-their-kind measurements of ocean health, air quality, and the effects of a changing climate. The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite was launched on Feb. 8, and has been put through several weeks of in-orbit testing of the spacecraft and instruments to ensure […]

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• v.47(1); Jan-Feb 2021

Language: English | Portuguese

Environmental air pollution: respiratory effects

Poluição do ar ambiental: efeitos respiratórios, ubiratan de paula santos.

1 . Divisão de Pneumologia, Instituto do Coração - InCor - Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo, São Paulo (SP) Brasil.

Marcos Abdo Arbex

2 . Faculdade de Medicina, Universidade de Araraquara - UNIARA - Araraquara (SP) Brasil.

3 . Núcleo de Estudos em Epidemiologia Ambiental, Laboratório de Poluição Atmosférica Experimental - NEEA-LPAE - Departamento de Patologia, Faculdade de Medicina, Universidade de São Paulo, São Paulo (SP) Brasil.

Alfésio Luis Ferreira Braga

4 . Grupo de Avaliação de Exposição e Risco Ambiental, Programa de Pós-Graduação em Saúde Coletiva, Universidade Católica de Santos - UNISANTOS - Santos (SP) Brasil.

Rafael Futoshi Mizutani

5 . Grupo de Doenças Respiratórias Ambientais, Ocupacionais e de Cessação de Tabagismo, Divisão de Pneumologia, Instituto do Coração - InCor - Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo, São Paulo (SP) Brasil.

José Eduardo Delfini Cançado

6 . Faculdade de Ciências Médicas, Santa Casa de Misericórdia de São Paulo, São Paulo (SP) Brasil.

Mário Terra-Filho

7 . Departamento de Cardiopneumologia, Divisão de Pneumologia, Instituto do Coração - InCor - Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo, São Paulo (SP) Brasil.

José Miguel Chatkin

8 . Disciplina de Medicina Interna/Pneumologia, Escola de Medicina, Pontifícia Universidade Católica do Rio Grande do Sul - PUCRS - Porto Alegre (RS), Brasil.

9 . Hospital São Lucas, Pontifícia Universidade Católica do Rio Grande do Sul - PUCRS - Porto Alegre (RS), Brasil.

Environmental air pollution is a major risk factor for morbidity and mortality worldwide. Environmental air pollution has a direct impact on human health, being responsible for an increase in the incidence of and number of deaths due to cardiopulmonary, neoplastic, and metabolic diseases; it also contributes to global warming and the consequent climate change associated with extreme events and environmental imbalances. In this review, we present articles that show the impact that exposure to different sources and types of air pollutants has on the respiratory system; we present the acute effects—such as increases in symptoms and in the number of emergency room visits, hospitalizations, and deaths—and the chronic effects—such as increases in the incidence of asthma, COPD, and lung cancer, as well as a rapid decline in lung function. The effects of air pollution in more susceptible populations and the effects associated with physical exercise in polluted environments are also presented and discussed. Finally, we present the major studies on the subject conducted in Brazil. Health care and disease prevention services should be aware of this important risk factor in order to counsel more susceptible individuals about protective measures that can facilitate their treatment, as well as promoting the adoption of environmental measures that contribute to the reduction of such emissions.

A poluição do ar ambiental é um dos principais fatores de risco de morbidade e mortalidade global. Ela tem impacto direto na saúde humana, sendo responsável pelo aumento de incidência e de óbitos por doenças cardiorrespiratórias, neoplásicas e metabólicas; também contribui para o aquecimento global e para as consequentes alterações do clima associadas a eventos extremos e aos desequilíbrios ambientais. Nesta revisão, apresentamos artigos que evidenciam o impacto da exposição a diferentes fontes e tipos de poluentes do ar no sistema respiratório; apresentamos os efeitos agudos — como aumento de sintomas e no número de atendimentos em serviços de emergência, internações e óbitos — e crônicos — como o aumento da incidência de asma, DPOC e câncer de pulmão, assim como o declínio acelerado da função pulmonar. Também são apresentados e discutidos os efeitos da poluição atmosférica em populações mais suscetíveis e dos efeitos associados à realização de exercícios físicos em ambientes poluídos. Por fim, apresentamos os principais estudos brasileiros sobre o assunto. Os serviços de atenção à saúde e de prevenção de doenças devem ficar atentos a esse importante fator de risco para orientar indivíduos mais suscetíveis sobre medidas de proteção que possam facilitar seu tratamento, além de estimular a adoção de medidas ambientais que contribuam para a redução dessas emissões.

INTRODUCTION

A major problem in the world today is air pollution, not only because of its impact on climate change but also because of its impact on public and individual health, being an important risk factor for increased morbidity and mortality.

Although exposure to air pollution has records that date back more than 20 centuries ago, until the well-known episodes of a sudden increase in pollutants that occurred in the Meuse Valley (Belgium, 1930), in Donora (Pennsylvania, USA, 1948), and above all in London (United Kingdom, 1952), studies on the effects of exposure to air pollutants were restricted to work environments and to exposure to toxic agents used in wars. 1 It was only from the mid-20th century onward that the subject began to be studied more and more, 2 with the first document on the effects of air pollution on health, prepared by the WHO and published in 1958, recommending that pollutant levels be reduced for health protection. 3 , 4

Air pollution is estimated to have been responsible for approximately 5 million deaths worldwide in 2017, 70% of which being caused by outdoor environmental air pollution. Environmental and household air pollution jointly rank fifth among the five leading risk factors for death worldwide ( Table 1 ). 5

PM 2.5 : fine particulate matter < 2.5 µm in aerodynamic diameter; DALYs: disability-adjusted life years (the sum of the number of years of life lost due to premature death and the number of years lived with limitation/disability). In air pollution-related deaths and air pollution-related DALYs, the sum of the separate impacts of the pollutants is slightly higher than the sum of their combined impact.

AIR POLLUTION AND ITS MAJOR SOURCES

The majority of emissions of pollutants are a result of human activity. Currently, the main sources of pollution in urban areas are motor vehicles and industries. 6 In some countries, including Brazil, the main source of environmental pollution originating from non-urban areas is the burning of biomass (sugarcane fields, pastures, savanna, and forests). Natural emissions, such as those from dust storms in large desert areas, those from accidental fires, and nitrogen oxides (NO x ) emissions from lightning, may contribute secondarily to the generation of air pollutants. 6 , 7

Pollutants are classified as either primary or secondary. Primary pollutants are those emitted directly into the atmosphere by industries, thermoelectric power plants, and motor vehicles powered by fuels. Primary pollutants include sulfur dioxide (SO 2 ); nitrogen oxides (NO x : NO and NO 2 ); particulate matter (PM)—total suspended particles less than 10 µm in aerodynamic diameter (PM 10 ) and less than 2.5 µm in aerodynamic diameter (PM 2.5 )—; and carbon monoxide (CO). In some countries, volatile organic compounds (VOCs) and metals are also monitored. Fine and ultrafine particles, since they have a higher surface/mass ratio and can be transferred to the systemic circulation, have a more marked effect. 8 Secondary pollutants are those formed from chemical reactions induced by NO x -catalyzed photochemical oxidation of VOCs, which, in the presence of ultraviolet rays from sunlight, give rise to ozone. 9 Other secondary pollutants are formed through a process of nucleation and condensation of gaseous pollutants (NO 2 and SO 2 ) and acid mists, such as NO x and secondary PM, formed by sulfates and nitrates. 1 , 7 , 10 )

Exposure to air pollution varies widely across countries, regions, cities, and households. A study based on 2017 data estimates that 42% of people were exposed to fine PM (PM 2.5 ) above concentrations considered to be of minimal risk and 43% of those people were exposed to ozone worldwide. 5

IMPACT ON HEALTH

Globally, most deaths and years of life lost due to premature death or lived with disability (disability-adjusted life years) that are secondary to air pollution exposure are a result of cardiopulmonary disease, lung cancer, or type 2 diabetes ( Table 2 ). 5 A study using a novel approach 11 reported values that were higher than those calculated by the Global Burden of Disease (GBD) models 12 : an estimated 8.8 million deaths globally in 2015 11 versus 4.24 million. 12 In addition, the loss of life expectancy was reported to be 2.9 years worldwide in 2015. 13 In two of the aformentioned studies, the number of environmental air pollution-related deaths in 2015 in Brazil was estimated to be 52,300 12 and 102,000, 11 environmental air pollution being the ninth leading risk factor for mortality. 12

PM 2.5 : fine particulate matter < 2.5 µm in aerodynamic diameter; DALYs: disability-adjusted life years (the sum of the number of years of life lost due to premature death and the number of years lived with limitation/disability). a Ozone was responsible for 472,000 (95% CI: 177,000 to 768,000) deaths and 7.37 million (95% CI: 2.74 to 12.00 million) DALYs.

Why and how air pollution has an impact on health: mechanisms involved in respiratory effects

The damage caused by particulate and gaseous pollutants depends on the inhaled concentration of such pollutants, the defenses of the respiratory system, and the solubility of gaseous pollutants. The possible mechanisms involved in cardiorespiratory effects include inflammation and oxidative stress induced by reactive oxygen and nitrogen species (RONS) generated by inhaled pollutants. 14 , 15 Recent studies suggest a relevant role for inhaled environmentally persistent free radicals (EPFR) produced by combustion of catechols, phenols, and hydroquinones, which can remain in the air for up to 21 days. 16

Chronic or acute inhalation of PM, O 3 , and EPFR generates RONS, which trigger an inflammatory process and amplify it through the endogenous production of more RONS. If RONS production overcomes antioxidant defenses, there is activation of the mitogen-activated protein kinase (MAPK) complex, involved in the activation of nuclear transcription factors, such as NF-κB and AP-1, which stimulate the synthesis of RNA and the production of pro-inflammatory cytokines IL-8 and TNF-α, possibly inducing the formation of DNA adducts. 14 , 17 Air pollution has also been associated with epigenetic effects that, although potentially reversible without the occurrence of mutations, can produce changes in DNA expression, potentiating the inflammatory effects of pollutants. 8

Air pollution has also been associated with reduced function of regulatory T lymphocytes, increased IgE levels, and increased production of CD4+ and CD8+ T lymphocytes, along with a greater Th2 response to stimuli by antigens in polluted environments, which would be associated with diseases such as rhinitis and asthma. 6 , 8

Air pollution: respiratory effects

Air pollution is associated with various health effects, in addition to respiratory effects ( Figure 1 ). Acute respiratory effects are those associated with recent exposure (hours or days), whereas chronic ones are a result of prolonged exposure, usually longer than 6 months.

With regard to acute effects, there is a consistent association between increased pollutant levels and increased numbers of emergency room visits, hospitalizations, and deaths, especially among individuals with chronic respiratory diseases, children, and elderly individuals. 18 A study involving 112 cities in the USA found a 1.68% increase in mortality due to respiratory disease for every 10 μg/m 3 increase in PM 2.5 concentration. 19 A systematic review and meta-analysis of 110 time-series studies conducted in several regions of the world revealed a 1.51% increase in mortality from respiratory diseases for every 10 μg/m 3 increase in PM 2.5 concentration. 20 In addition, a study conducted in Latin America 21 revealed a 2% increase in the risk of mortality from respiratory and cardiovascular diseases for every 10 µg/m 3 increase in PM 2.5 concentration, which is in line with the findings of studies conducted in Europe and North America.

The effects of chronic exposure have been associated with increased overall mortality from respiratory diseases, increased incidence of asthma and COPD, increased incidence of and mortality from lung cancer, reduced lung function, and a deficit in lung development during childhood. 22 , 23 One of the first studies on the subject, conducted in six major cities in the USA, revealed that the risk of death from cardiopulmonary diseases was 26% higher among individuals living in more polluted cities than among those living in less polluted cities. 24 These findings have been confirmed in other studies, including a prospective study involving 500,000 adults from all 50 U.S. states that revealed 9% and 18% increases in the risk of mortality from cardiopulmonary diseases and lung cancer, respectively, that were associated with a 10-µg/m 3 increase in PM 2.5 concentration. 25

Pollution and rhinitis

A growing number of studies show an association between environmental air pollution and increased incidence and exacerbation of rhinitis. Authors suggest that genetic factors alone do not appear to be sufficient to justify the increase observed in the prevalence and exacerbation of allergic diseases, in particular, eczema, rhinitis and asthma. Exposure to PM 10 and PM 2.5 appears as a factor that has a major impact in increasing the prevalence of these diseases, especially in children and adolescents. 6 , 27

Pollution and asthma

Exposure to pollutants such as PM, NO 2 , ozone, and carbon, as well as to motor vehicle traffic-related air pollution, is associated with a higher number of exacerbations, hospitalizations, and deaths in patients with asthma. 6 , 28 , 29

One of the first studies evaluating the acute effects of air pollution, which involved 3,676 children from 12 locations in the state of California, USA, 30 showed that children with asthma who were exposed to NO 2 , PM 10 , and PM 2.5 had a higher prevalence of respiratory symptoms and a greater need for medication than did children without asthma. The most significant association was with exposure to NO 2 , with a 2.7 times higher prevalence of symptoms for every 24 ppb increase in NO 2 concentration. A study conducted in Hubei province, China, with 4,454 individuals who died from asthma between 2013 and 2018 found increases of 7%, 9%, and 11% in mortality that were associated with PM 2.5 , O 3 , and NO 2 , respectively. 31

In recent years, studies have revealed that air pollution is also associated with an increased incidence of asthma, especially in children and adolescents, 6 , 23 , 32 - 34 with less robust data on adults. 35 , 36 One of the first prospective studies on the subject, also conducted in California, showed an association between chronic exposure to ozone and an increased incidence of asthma. 37 Another study evaluated the global incidence of air pollution-related asthma. For 2015, 4 milllion new cases of asthma (13% of global incidence) were estimated to be associated with exposure to NO 2 in children and young people under 18 years of age, 150,000 of which were in Brazil and Paraguay (aggregate data). 38 In adults, a study conducted in Australia showed that individuals exposed to NO 2 for at least 5 years and those living less than 200 m from a major road were at an increased risk of developing asthma and experiencing a marked decline in lung function. 39

Pollution and COPD

Since the 1990s, epidemiological studies have shown an association between air pollution and acute respiratory events in individuals with COPD, with an increased number of exacerbations, emergency room visits, hospitalizations, and deaths. 40 One of the first studies on the subject, which evaluated hospitalizations secondary to COPD exacerbation that were associated with exposure to pollutants, found that, for every 10 μm/m 3 increase in PM 10 concentration, there was a 2.5% increase in hospitalizations. A recent study 41 involving 303,887 individuals in the United Kingdom revealed that a 5 μg/m 3 increase in PM 2.5 concentration was associated with 83 mL and 62 mL reductions in FEV 1 and FVC, respectively, as well as with a 52% increase in COPD prevalence.

More recent studies suggest that exposure to pollutants is associated with an increased incidence of COPD. 23 , 41 A cohort study conducted in Norway involving 57,000 individuals found an 8% increase in COPD incidence that was associated with a 5.8 µg/m 3 increase in NO 2 concentration. 42 Another recently published cohort study, 43 involving 7,071 individuals in six U.S. metropolitan regions between 2000 and 2018, found an increased percentage of areas of pulmonary emphysema, as assessed by HRCT, that were associated with exposure to O 3 , PM 2.5 , NO x , and carbon particles. A study analyzing 2017 data estimated that 1.1 million COPD deaths were attributable to air pollution worldwide, 5 representing 34.6% of all COPD deaths in that year. 44

Pollution and lung function

In recent years, evidence has been accumulating on the effects of air pollution on lung function, confirming the findings of earlier studies. 45 , 46 The effects of air pollution appear to be more marked during the first years of life, including during the intrauterine period. Jedrychowski et al. 47 evaluated maternal exposure to PM 2.5 during the second trimester of pregnancy and found lower FEV 1 and FVC values (differences of 87 mL and 91 mL, respectively) at 5 years of age in children whose mothers had higher exposure to PM 2.5 . In the city of Guangzhou, China, a study of highly polluted areas (an annual average PM 10 concentration between 80 and 96 µg/m 3 ) showed that higher levels of pollution are associated with a reduction in the growth rate of FEF 25-75% and FEV 1 in boys. 48

A prospective study 49 that followed children from age 10 to age 18 years in 12 cities in California found a reduction in the total growth of FEV 1 that was associated with PM 2.5 , NO 2 , acid vapor, and carbon particles. The proportion of young individuals who, at age 18 years, had an FEV 1 of less than 80% of the predicted value was 4.9 times higher (a prevalence of 7.9%) in the communities with the highest levels of PM 2.5 than in the communities with the lowest levels.

A study conducted in the city of São Paulo, Brazil, involving taxi drivers and traffic controllers revealed that exposure to high levels of PM 2.5 was associated with a nonsignificant reduction in FEV 1 and FVC, but there was a significant increase in FEF 25-75% , suggesting possible interstitial changes due to exposure to polllutants. 50

Pollution and respiratory infections

Exposure to air pollutants increases the risk of upper and lower airway infections. Exposure to PM was responsible for 433,000 deaths from respiratory infections globally in 2017, especially affecting children and elderly individuals. 5 A systematic review estimated a 12% increase in the risk of pneumonia in children for every annual average increase of 10 μg/m 3 in PM 2.5 concentration. 51 In line with this, a systematic review and meta-analysis using six European cohorts and involving 16,000 children showed an up to 30% increase in NO 2 exposure-related risk of pneumonia. 35

Current studies suggest a possible contributing effect of air pollution on the spread of SARS-CoV-2 (COVID-19). A study conducted in Italy revealed that, in cities where the concentrations of air pollutants were higher before the epidemic, there was an accelerated spread of the virus, as well as a higher number of infected individuals, when compared with less polluted cities. 52 , 53 A recently published study that characterized, with the use of satellites, the global concentration of PM 2.5 and its anthropogenic fraction, estimated that exposure to PM would have contributed 15% (95% CI: 7-33%) to global COVID-19 mortality, being an important cofactor for increasing the risk of COVID-19 morbidity and mortality. 54 , 55

Pollution and lung cancer

The International Agency for Research on Cancer considers environmental air pollution carcinogenic to humans, because it increases the risk of lung cancer. 56 Although a positive association has also been found between exposure to this type of pollution and bladder cancer, a causal relationship has yet to be established. According to global data, 5 an estimated 2.16 million new cases of lung cancer and 1.88 million lung cancer deaths occurred in 2017, lung cancer being the leading cause of cancer death among men and the third leading cause of cancer death among women. It is estimated that 14% (n = 265,000) of lung cancer deaths are attributable to environmental air pollution, 5 a proportion that ranges from 1% to 25% across countries. The mean risk for developing lung cancer ranges across studies from 20% to 30% for a 10 µg/m 3 increase in PM 10 concentration and a 5 µg/m 3 increase in PM 2.5 concentration. 56 , 57

Air pollution can induce genotoxic effects that include formation of DNA adducts, breaks in DNA strands, and damage to DNA bases due to oxidation, genetic mutations, chromosomal damage to somatic cells, gametic mutations, and oncogenic transformation. Molecular epidemiological studies in humans reveal associations between the frequencies of DNA damage (such as adducts in lymphocytes) and cytogenetic damage (such as chromosomal translocations and micronuclei) and exposures to PM and/or carcinogenic polycyclic aromatic hydrocarbons. Multiple proven effects lend plausibility to the association between air pollution and lung cancer development through a direct effect, as well as to tumor development via oxidative stress and persistent inflammation. 56

Pollution and physical exercise

Low physical activity is an important risk factor for mortality and was associated with 1.26 million deaths in 2017. Regular mild- to moderate-intensity exercise contributes to reducing or delaying the onset of chronic diseases by up to 10 years. 58

Exercising in air-polluted environments can have health consequences in susceptible populations, such as children, the elderly, and individuals with chronic diseases, as well as resulting in poorer physical performance in athletes. 59 , 60 A study conducted in communities with high ozone concentrations in California 61 found that the risk of developing asthma was 3.3 times higher in children playing three or more sports per week than in children playing no sports. Sports had no effect in cities with low ozone concentrations.

In healthy individuals, the respiratory effects of air pollution do not appear to be significant. 62 A study conducted in London, United Kingdom, 63 compared changes over time in lung function and sputum inflammatory markers in adults with asthma who walked for 2 h in a park and, on a separate occasion, along a busy traffic street. Participants with asthma showed a significant decline in lung function and an increase in inflammatory markers after walking along a busy traffic street. 63 A study with a similar design that compared healthy individuals, individuals with COPD, and individuals with stable coronary disease revealed that, in all participants, walking for 2 h in a park led to an increase in lung function, an increase that was absent or reduced after walking along a busy traffic street. 59 Studies in humans 59 and studies using mathematical models 64 , 65 have shown that, for healthy individuals and even for individuals with chronic diseases, mild-to-moderate exercise in polluted environments, even where pollution levels are above the reference values recommended by the WHO, 7 has beneficial effects that override the effects of inhalation of an increased load of pollutants. Therefore, the balance of studies suggests that mild-to-moderate exercise is beneficial even in polluted places. 8 , 60 , 64 , 65

Other pulmonary conditions

Recent studies have shown an association of exposure to air pollution with sleep apnea, 8 increased risk of bronchiolitis obliterans, increased risk of death in lung transplant recipients, 66 and increased risk of progression to interstitial lung disease. 67

SUSCEPTIBLE/VULNERABLE POPULATIONS

Intrinsic and extrinsic factors increase the vulnerability and/or susceptibility of individuals to the adverse effects of air pollutants. In addition to age, having a preexisting chronic disease, such as asthma, COPD, pulmonary fibrosis, arrhythmias, hypertension, ischemic heart disease, diabetes, autoimmune diseases, and obesity, makes individuals more vulnerable. 8 , 68

Individuals with poor socioeconomic status are most vulnerable, since they are likely to be exposed for longer periods on their way to work and tend to live closer to industrial areas. In addition, they live in overcrowded households, in areas without appropriate green spaces, and have diets poor in fruits and vegetables, which are rich in antioxidants. 8 , 68

Pregnant women

Exposure to air pollutants during pregnancy can compromise fetal development and cause intrauterine growth restriction, prematurity, low birth weight, congenital anomalies, and intrauterine and perinatal death. 8 , 69

Intense cell proliferation, physiological immaturity, accelerated organ development, and changes in metabolism increase the fetus’ susceptibility to inhalation of air pollutants by the mother, and the mother in turn can have her respiratory system compromised by the action of pollutants, which can thereby affect the transport of oxygen and nutrients across the placenta. Exposure to high concentrations of PM is associated with placental inflammation, abnormal trophoblastic invasion, and decreased placental angiogenesis, impacting fetal development. 69

Worldwide, 93% of children live in environments in which air pollutant concentrations are above those recommended by the WHO. 70 The WHO estimates that one in every four deaths of children under 5 years of age is directly or indirectly related to environmental risks. 70 Global analyses for 2015 estimated the number of deaths from respiratory infections resulting from exposure to environmental air pollution among children aged 5 years or younger to be 727,000. 71 Children have higher minute ventilation and higher basal metabolic rates and engage in more physical activity than do adults, as well as spending more time outdoors.

The fact that children’s immune system is not fully developed increases their susceptibility to respiratory infections. 8 , 70 Inside the womb, fetuses can be affected by pollutants inhaled by the mother, with can have health consequences in adulthood, such as an increased risk of asthma. 8 , 70 , 72

Elderly individuals

The elderly population is growing because of increased life expectancy and steadily declining birth rates. In 2013, elderly individuals aged 80 years or older represented 14% of the world population.

Elderly individuals are susceptible to the adverse effects of exposure to air pollutants because they have a less efficient immune system (immunosenescence) and a progressive decline in lung function, which can lead to decreased exercise tolerance. Wu et al., 73 in a study conducted in Beijing, China, observed a greater increase in hospitalizations for air pollution-related pneumonia in the elderly compared with younger age groups. A cohort study conducted in the USA 74 that used Medicare data showed that, between 2000 and 2012, acute exposures to fine PM and ozone during the warmest seasons of the year (spring and summer) were associated with an increased risk of all-cause mortality among elderly individuals. The same effect was observed even on days with concentrations below the air quality limits set by the U.S. Environmental Protection Agency.

Genetic susceptibility

The production of free radicals and the induction of inflammatory response by pollutants in the respiratory system can be neutralized by the antioxidant agents present in the aqueous layer lining the respiratory epithelium—glutathione S-transferase (GST), superoxide dismutase, catalase, tocopherol, ascorbic acid, and uric acid—which can prevent oxidative stress and represent the first line of defense against the adverse effects of pollutants. Polymorphisms in genes responsible for controlling oxidative stress ( NQO1 , GSTM1 , and GSTP1 ) and in inflammatory genes ( TNF ) alter the presence and intensity of respiratory symptoms and change lung function and the risk of developing asthma in response to pollutants. 75

Of the antioxidant agents present in the respiratory epithelium, the GST family is considered one of the most important, being represented by three major classes of enzymes: GSTM1; GSTP1; and GSTT1. 76 Polymorphisms in genes encoding the enzymes of the GST family can change the expression or function of these enzymes in the lung tissue, resulting in different responses to inflammation and oxidative stress and, consequently, in increased susceptibility to the adverse effects of air pollutants. 76 A study conducted by Prado et al. 77 found a marked loss of lung function in sugarcane workers exposed to air pollution who had deletions in the GSTM1 and GSTT1 genes.

Studies have also revealed the epigenetic effect of exposure to PM, an effect that can override genetic susceptibility. Altered epigenetic regulation of white blood cells and various other tissue cells, especially PM-induced changes in DNA methylation, appears to contribute to the health effects associated with air pollution. 23

BRAZIL: RELEVANT STUDIES ON THE EFFECTS OF AIR POLLUTION

Since the late 1970s, the effects of air pollutants, from both vehicular and industrial sources and from biomass burning, have been systematically studied in Brazil.

Air pollution from fossil fuel burning

Over the past 30 years, 170 studies on the subject conducted in Brazil have been published. From 1975 onward, the Air Pollution Experimental Laboratory of the University of São Paulo School of Medicine Department of Pathology, in the city of São Paulo, located in the state of São Paulo, Brazil, carried out experimental and epidemiological studies to assess the adverse effects of exposure to air pollutants. The first study exposed rats to the environmental air in the city of São Paulo and to the environmental air in the city of Atibaia, also located in the state of São Paulo and where the air, at the time, was considered cleaner. After 6 months of exposure, there were changes in mucus rheological properties, destruction of cilia, and, consequently, increased bacterial colonization of the respiratory epithelium, all of which led to the death of 50% of the rats exposed to the air in the city of São Paulo. 78 In parallel, using models from ecological time series studies, another study showed that daily increases in NO x concentration were associated with increased mortality from respiratory diseases in children aged 5 years or younger in the city of São Paulo. 79 Another study by the group showed that lung autopsy samples from residents of the city of Guarulhos, located in the state of São Paulo and where pollution levels were high at the time of the study, presented more evidence of histopathologic damage than did those from residents of the cities of Ourinhos and Ribeirão Preto, also located in the state of São Paulo but where pollution levels were lower, even after controlling for smoking. 80

In another study, mice were exposed to different concentrations of inhaled fine PM, and even those exposed to low concentrations showed oxidative stress, inflammation, and lung tissue damage. 81

Ecological time series studies have shown associations between increased emergency room visits in children with respiratory diseases and increased air pollution 82 ; between increased hospitalizations for respiratory diseases in children and adolescents and increased concentrations of PM 10 and SO 2 83 ; and between increased emergency room visits due to pneumonia and influenza, 84 as well as due to asthma and COPD 85 , 86 in adults and increased air pollution.

A study conducted on workers exposed to environmental air pollution in the city of São Paulo, located in the state of São Paulo, Brazil, revealed that, those with the highest level of exposure had a reduction in FVC compared with those with the lowest level of exposure. 50 Chart 1 summarizes the major studies on the respiratory impact of urban air pollution conducted in Brazil.

PM 10 : particulate matter with an aerodynamic diameter less than 10 µm; PM 2.5 : particulate matter with an aerodynamic diameter less than 2.5 µm; and NO x : nitrogen oxides.

Air pollution from biomass burning

Over the past 20 years, studies conducted in Brazil have assessed the impacts that forest fires (especially in the Brazilian Amazon) and pre-harvest sugarcane burning (especially in the state of São Paulo) have on the health of the exposed population ( Chart 2 ).

TSP: total suspended particles; PM 10 : particulate matter with an aerodynamic diameter less than 10 µm; and PM 2.5 : particulate matter with an aerodynamic diameter less than 2.5 µm.

Studies conducted in urban areas located in sugarcane producing regions in the state of São Paulo have shown that, during the sugarcane burning season, there were increases in emergency room visits for inhalation therapy 87 and for pneumonia, 88 as well as an increase in hospitalizations of children and elderly individuals for all respiratory diseases, 89 specifically for asthma. 90 In Monte Aprazível, a town in the state of São Paulo, rhinitis prevalence increased and lung function decreased in children during the sugarcane burning season. 91 Another study revealed that, during manual harvesting of burnt cane, workers had exacerbated respiratory symptoms, reduced lung function, reduced antioxidant enzyme activity, and increased oxidative stress markers. 77 In another group of sugarcane workers, it was found that, during the sugarcane burning season, there were changes in mucus properties and impairment of nasal mucociliary clearance. 92

Emissions from fires in the Amazon region can be transported long distances and, in addition to affecting the global climate, 93 can impact the health of children and the elderly. 94 , 95 Studies conducted in the state of Mato Grosso have shown that increased exposure to PM contributed to increased hospitalizations of children less than 5 years of age due to respiratory diseases 96 and to acute decreases in PEF. 97

In an experimental study in mice, animals received repeated intranasal instillation of PM from different sources, and PM from biomass burning were found to be more toxic than PM from vehicular traffic. 98

FINAL CONSIDERATIONS

Environmental air pollution affects billions of people every day worldwide, having a major impact on morbidity and mortality, as well as contributing to global warming.

The presence of chronic systemic diseases increases the susceptibility of individuals to the adverse effects of air pollutants, manifesting from mild forms of illness to death, which occurs in patients with increased susceptibility. Recent studies show that exposure to air pollutants can cause asthma, COPD, and lung cancer. Exposure of pregnant women to air pollutants has serious adverse effects on the fetus that, if not lethal, can result in compromised health in childhood, adolescence, adulthood, and old age. Regular physical exercise can contribute to minimizing the effects of air pollution.

The most effective measures for reducing the impact of air pollution on human health are those related to reducing emissions. Expansion of public transportation, the use of cleaner fuels in vehicles, industries, and households, as well as a change in building construction standards, which require a lot of energy, are feasible and necessary measures to reduce global warming and its direct effects on human health. 99 It is estimated that reducing emission levels to those recommended by the WHO and the Paris Agreement can lead to up to 60% decrease in pollution-related deaths annually. 11 In this context, physicians should be able to inform and advise the population about healthy eating habits, regular physical exercise, and chronic disease control. Physicians should also contribute to strengthening the necessary measures to reduce emissions in favor of environmental recovery. The current SARS-CoV-2 virus pandemic, which follows the SARS and MERS outbreaks in 2000 and 2012, respectively, shows that we cannot adopt a passive behavior regarding environmental imbalances caused by the way the planet is developed and occupied.

Financial support: None.

Explore the natural world through science and sustainability

How to Conduct a Simple Air Quality Experiment + FREE Printables

Looking for a simple way to visualize air quality with your kids? Try this science experiment with free printables written in English and Spanish that can be done at home or in a classroom to engage your learners in STEM and bring attention to local air pollution issues.

What is Air Quality and How is it Measured?

Air quality refers to the level of pollutants present in the air. These pollutants can be gases, particulate matter, and biological molecules that can have harmful effects on human health and the environment.

Air quality is typically measured using a network of monitoring stations that collect data on a range of pollutants, such as nitrogen oxides, sulfur dioxide, ozone, particulate matter, and carbon monoxide. These monitoring stations use a variety of instruments and techniques to measure the concentration of these pollutants in the air.

Examining Air Quality with Kids: A Science Experiment

A few years ago, when wildfires were ravaging the West Coast of the United States, I decided to conduct a simple at-home air quality experiment in an effort to explain to my kids what the term “air quality” meant. I also wanted to show them the amount of particulate matter in the air, and how the amount of “dirt” varies from one location to the next.

I asked a group of parents, educators, and friends from across the U.S. to join me in this experiment, in order to compare our results to those from other parts of the country.

Free Ways to Find the Materials Needed for the Air Quality Experiment

In a continued effort to conduct science experiments as sustainably as possible, I recommend you try the following steps to collect the materials you need, prior to purchasing them new.

Ask Your Friends, Family, and Neighbors

Did your grandmother ever tell you a story about how she went to the neighbor’s house to borrow a cup of sugar? As the pace of our modern lives has increased, we have forgotten or have never known what it’s like to walk across the street to ask to borrow something. Capitalize on the kindness of your neighbors, family members, and friends, and revitalize the simple act of borrowing!

Shop Your Local Buy Nothing Group or Facebook Marketplace

If you’re missing some materials to conduct the air quality experiment, consider putting a request on your local Buy Nothing Group or Facebook Marketplace. You’ll be amazed at how quickly your request is met by others looking to declutter their homes! Another option is to stop into your local secondhand or consignment shop and see what items they have available. I have successfully shopped secondhand for science experiment materials more times than I can count. 

Check With Your Local Library

Libraries are for borrowing much more than just books! My local library continually hosts children’s activities and crafting sessions. Put a request into your librarian for extra supplies they may have left over from a workshop. My good friend Jen, editor of Honestly Modern, has written an entire series based on ways you can capitalize on your local libraries’ resources . 

Materials Needed for the Air Quality Experiment

Here is a list of supplies you’ll need to do this simple disappearing paper science experiment:

• White card-stock, poster board, paper plate or index card
• Petroleum jelly, solid coconut oil, lip balm or clear packing tape
• Magnifying glass
• Air Quality Experiment printable in English or Spanish

Instructions to Conduct the Air Quality Science Experiment

Follow these simple instructions to set-up and monitor the indoor and outdoor air quality of your learning space.

• Cut 2 three inch (7.6 cm) squares from the white card stock.
• Punch a hole in the top of each square.
• Run a string through each hole.
• Cover one side of each paper square with petroleum jelly/coconut oil.
• Take a “before” picture of each paper square.
• Hang one square inside, and the other square outside, for 5 days.
• After 5 days, take an “after” picture of each square.
• Compare both squares using a magnifying glass to estimate the total number of particles present.
• Record findings on the Air Quality Experiment printable.

Video Tutorial of the Air Quality Science Experiment

Here is a quick video tutorial to walk you and your learners through the simple steps to set up the air quality science experiment.

Explaining the Data We Collected: A Teachable Example

When my family and I conducted this experiment, we had seven other families participate with us. Eight locations were sampled for 5 days, during the week of September 14th, 2020, and the air quality index (A.Q.I.) range for each location was recorded, based on the data reported by AirNow.gov . 

Samples taken inside are labeled with an “I” and samples taken outside are labeled with an “O”. 

Understanding How Air Quality is Measured in the U.S.

In the U.S., air quality is measured on a scale known as A.Q.I., which stands for Air Quality Index.

Basically, it measures the levels of 5 major air pollutants:

• Ground level ozone (O3)
• Carbon monoxide (CO)
• Sulfur Dioxide (SO2)
• Nitrogen Dioxide (NO2)
• Airborne particles (also called Particulate Matter or PM), like soot, smoke, etc.

The Environmental Protection Agency (E.P.A.) determines which air pollutants get monitored (and which are completely ignored) and set the standards for “acceptable” levels of each. Notice that the A.Q.I. doesn’t monitor daily lead levels in the air, even though the heavy metal is categorized as a criteria air pollutant. Instead, the EPA collects and distributes data on lead in the air on a rolling 3-month average.

The A.Q.I. does not take into account 9 other major air pollutants, such as benzene, asbestos and creosote, many of which are known human carcinogens.

What is the Air Quality Index (A.Q.I.) Used For?

The Air Quality Index is used by states to forecast the air quality for the next day. 

The scale has a range of 0-500, with a level of 50 or below registering as “good” air (posing little to no threat to human health), while anywhere from 301-500 is considered hazardous to human health.

“air-quality-index” by California Air Resources Board is licensed under CC BY 2.0

The stark contrast between the outdoor samples taken from Asheville, NC and Los Angeles, CA visually display the depletion of air quality due to the addition of smoke and soot in the air during the week of September 14th, 2020.

Free, Bilingual Air Quality Experiment Printable

For a free, downloadable lesson for this activity,  written in both English and Spanish, click on the buttons below! Spanish translation courtesy of @gogreenfortheocean .

Thank You to Our Science Volunteers!

A huge thank you goes to all of the volunteers for this project:

@asmalllife , @honestlymodern , @from_scratch_nutrition , @justtemple , @alysia.ehle , @happytohealthyou and @vyolivan .

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8 Student Experiments to Measure Air Quality

by Carisa A.

As pollution is becoming more rampant worldwide, educators are deeply encouraged to teach students about the science of pollution and what they can do to care for the environment. From the release of greenhouse gases, worsening climate change, and burning of fossil fuels, the rate at which pollutants are produced is unprecedented. Hence, we have suggested 8 experimental ideas that teachers can use to actively involve their students to measure air quality. These ideas range from qualitative to quantitative methods and promote active discussion on which type of method would prove the most effective in producing reliable data. By measuring air quality, students can make sense of the different standards of air quality and recognize when it becomes appropriate to mitigate their effects. Without further ado, let’s jump into it!

PM 2.5 Meter

Particulate Matter (PM) 2.5 refers to particles or compounds which spans less than 2.5 micrometers in diameter. They are fine particles that are commonly produced from factories, vehicle exhaust, burning of crops or volcanic eruptions. Long-term exposure to high concentrations of these particles can put people at risk of developing respiratory illnesses, inflammation, trigger asthma and can even lead to lung cancer.

There are many types of PM 2.5 meters in the market, with some of them capable of measuring other types of pollutants as well. PM 2.5 is most commonly measured in units of µg/m3 (micrograms per meter cubed), or through AQI measurements (meter below ).

Depending on the meter you purchase, it may display either one of the units of measurement. However, keep in mind that the two measurements are not directly proportional to each other as measurements in µg/m3 are representative of the actual amount of PM in the area whereas AQI measurements are subjective to the air quality standards that have been internationally agreed upon for your particular region. This difference in proportionality is represented in the following graph :

Having a corresponding AQI level alongside PM2.5 measurements can help students measure the precise amount of PM2.5 in a certain area and use them to determine the quality of the air. Students could measure air quality in different areas, comparing the results obtained and discuss the probable causes and sources of PM from the location. It is also a great way to measure quantitative values that are useful for writing scientific reports while reinforcing the numbers with a qualitative interpretation of the air quality.

You could perform these measurements with your students for a variety of experiments. For example, by comparing the PM measurements from outdoor areas to indoors, students would become aware of the differences in air quality and discuss the possible outdoor/indoor pollutants that may cause one to have higher PM levels than the other. Another great experiment would be to compare the PM levels of rooms that use purifiers and those that do not. This would demonstrate the effectiveness of air purifiers to students and how they are beneficial to maintaining their general wellbeing.

The following graph compares the different levels of PM 2.5 and US AQI PM 2.5 measurements provided by sarta.innovations2019.org :

Blue Sky Test

The color of the sky is a reliable qualitative method to measure air quality. The color can change due to airborne particles that reflect and refract light. For example, a blue sky would indicate little to no air pollution whereas bright red ones are a result of heavy pollution.

The University of Southern California developed an algorithm through its mobile sensing project to measure the air quality by analyzing pictures of the sky taken from the Android app that they created. The pictures that would be taken would take into account the user’s location, orientation, time taken and transfer the data collected into their server. It would calibrate the image and compare it with their own model of the sky.

Although their app isn’t officially listed in the Play Store, all you have to do is click this link from your Android mobile device and click ‘Download Android App’ on from their website. If your phone is preventing the download, click here to find out more about installing APK files on your phone.

Mountain Visibility Test

Similar to the blue sky test, checking the visibility of mountains, or a large construction that can be seen from a long distance is also a qualitative indicator for air pollution. When we see places that are more polluted, we easily recognize the thick haze and dust that clearly obscures the view. But if we live in a polluted area, a clear view of mountains or other constructions may seem foreign in comparison as demonstrated from the following pictures provided by the US National Park Service :

This method measures visibility as an indicator of air pollution. A great idea is to get in touch with schools from different areas to see if they would like to collaborate to gather picture samples of their view. This way, teachers could show their students what mountains or distant constructions from various places look like. This can prompt a discussion about why some areas are more visible than others while explaining how air pollution impacts the view.

Students could also compare the images with public available AQI data from the region and see if there is a direct correlation between the AQI and visibility. Using the previous AQI Index table, students would be able to understand the different standards of air quality and associate it to qualitative observations on their surrounding environment. Furthermore, you could perform this experiment using AQI websites such as AirVisual or aqicn.org to identify the AQI values of different locations worldwide and compare it with images of landmarks in a particular country from which students could effectively assess the visibility.

This is a simple and easy qualitative analysis that can be performed anywhere in the world. However, it is advisable to make observations in the morning when there is the least fog and other factors impacting visibility .

Sticky Tape Method

Although the most dangerous particles are smaller in size, it is still a good indicator of air pollution to also measure the amount of larger particles such as dust, soot, dirt, smoke that can be potentially seen.

The sticky tape method is very simple, all you have to do is cut a small piece of transparent sticky tape and attach it to the bark of a tree or the surface of a building. Leave it for 10 seconds to let any PM on the surface stick onto the tape, peel the tape off and stick it onto a piece of paper. Students should be advised to label the time and location at which they took the sample.

Students could perform experiments by either collecting tape samples in the same location over different periods of time or taking samples in different locations at a certain period of time depending on their chosen independent and dependent variables. They can make qualitative observations of how PM levels change in different times and locations. This can be expanded by discussing the possible reasons as to why some areas or times have more PM in the air than others.

Lichen Observation & App

Sulfur dioxide (SO2) is a gas with a pungent scent which is known to be harmful towards our health. It is mostly generated from the burning of fossil fuels from industrial processes such as the generation of electricity from burning coal. It reacts to evaporated moisture in the air to produce several acidic compounds such as sulfuric acid, which can cause acid rain when dissolved in rainwater, leading to the acidification of forests.

Nitrogen can also be an overlooked pollutant as it is a common constituent in fertilizers and organic waste from households and sewage. When they have washed away into water bodies, it increases the acidity of the water, causing numerous wildlife deaths and disrupting the ecosystem. Like sulfur dioxide, it also causes acid rain when neutral nitrogen particles react with lightning in the air and mix with rainwater.

Lichen is an effective bio-indicator of sulfur and nitrogen pollutants. If lichen is a naturally occurring substance in your area, it will not be present if they are in the air and there would be green algae in its place. Many more species can act as a bioindicator for particular pollutants depending on vegetation that are sensitive or tolerant to them. A massive study was conducted using lichens to measure the air quality throughout the UK by the OPAL Air Survey .

The study conducted modeled the relationship between lichens as a bioindicator, nitrogenous pollutants, and their climate. Furthermore, the data was easily collected by everyday citizens throughout the UK and can be performed as school experiments as well. The map of the UK on the left demonstrated the amount of nitrogen dioxide (NO2) around the country while the one on the right referred to NHx radicals such as ammonia (NH3) and ammonium (NH4), which can cause ammonia pollution. The following image is their result:

The UK Centre for Ecology & Hydrology developed the Lichen Web-App , which provides guidelines on how to identify what type of lichen is suitable for testing, how to perform chemical tests on them and a comprehensive list of different species that are sensitive or tolerant towards nitrogen. It also enables you to track and record any trunks and branches that have lichens on them. They also created a measurement system called Nitrogen Air Quality Index (NAQI) to accurately associate the different levels of nitrogen to indicate their corresponding level of air quality.

Students could emulate this study on a much smaller scale and explore their environment for lichen or other similar species. This would also make them aware of how vegetation is often sensitive towards pollution.

Palmes Passive Diffusion Tubes

Nitrogen can exist in many forms, one of them being nitrogen dioxide (NO2). Nitrogen dioxide is a gaseous pollutant produced from the burning of fossil fuels such as those in power plants and vehicle exhausts. It undergoes a process in which neutral nitrogen (N2) and oxygen (O2) particles react in high temperatures to produce nitrous oxides (NOx) including NO2, all of which can inflict respiratory conditions such as inflammation, coughing, irritations, etc. This is clearly demonstrated from the image on the right which was performed in an experiment from the University of Edinburgh.

Passive diffusion tubes are an effective long-term method to measure nitrogen dioxide. These small plastic tubes contain a mesh disc made of steel covered with a chemical called triethanolamine (TEA). If nitrogen dioxide is present and passes through the mesh, it would react with TEA and change the color and chemical composition. Diffusion tubes can measure the change in nitrogen dioxide levels over many months inside classrooms or outside your school based on how much TEA is left in the tube.

Ozone Testing Experiments

Ozone (O3) is a gas that is popularly known as a gaseous layer in the stratosphere which protects the earth from harmful UV radiation from the sun. However, ones at the troposphere are mainly the result of the chemical reactions between nitrous oxides (NOx), volatile organic compounds (VOCs) and the sunlight. At high concentrations, they can cause chest pains, coughs, throat irritations and are especially harmful to those suffering from respiratory conditions such as asthma.

We can test for the presence of ozone in two different ways:

Ozone badges are very simple and can be made into different forms. All of them rely on a change in color when high concentrations of ozone are present. The badges as seen from the image are commercially produced indicators that are commonly used by workers who are required to operate in areas with elevated ozone concentrations.

For a more advanced chemical experiment, you could also perform the Schoenbein experiment. Students would require cornstarch and potassium iodide to make indicator strips that would react with ozone if present in the air, evidently turning blue or purple. According to the resulting Schoenbein number from the color scale below, we can determine the amount of ozone present in parts per billion (ppb) as seen from the following from the graph.

It is important to perform this experiment in days with low humidity (the lines from the graph represent how the Schoenbein numbers vary based on the different percentages of humidity in the air). Under these circumstances, ozone would be more likely to break apart into atmospheric oxygen. This experiment also yields the best results in the ozone season, which occurs during heated temperatures throughout the summer and in areas with high vehicle activity.

While this method is relatively safe, it is advised to perform this under the supervision of Chemistry teachers who can provide them with the chemicals and laboratory equipment needed.

Surface Wipes

Surface wipes are similar to the sticky tape method, which simply involves wiping a cotton bud on a surface to observe how much PM was released in a particular time or area. Students can compare the cotton buds that were wiped on the surfaces that are more exposed to the ones less exposed to pollutants, such as on the opposite sides of a handrail or bench. The following video is a lighthearted and entertaining experiment performed by a YouTuber from Sydney to observe the city’s air quality, which has dramatically worsened as of late due to the Australian bushfires:

Teachers and students are encouraged to be creative, improvise and innovate experiments similar to this. That way, educators could create a stimulating and critical learning environment for students to teach them about scientific research methods.

As a teacher or parent, you can choose from a myriad of creative options to teach your child how to measure air quality. Depending on their style of learning and personal preference, you can weigh the benefits of performing qualitative or quantitative methods to help them understand the state of the environment. By performing diverse experiments, they would be able to understand how different collection methods result in corresponding data types. After experimenting with multiple methods, they can then determine which type would be the most suitable to fulfill the research’s purpose. We hope that these experiments would be able to pique their curiosity and encourage them to make meaningful discussions about the health effects and environmental impacts of air pollution!

AirGradient DIY Air Quality Kits

Build your own open source air quality sensor measuring PM2.5, CO2, TVOC, Temperature and Humidity. Easy to build, accurate and affordable!

Valley to Mountain

Graphic of a person walking with an air sensor through a door and graphical text that reads Indoor v. Outdoor.

Free Resources > Indoor-v-Outdoor

Air Quality Experiment: Indoor V. Outdoor

You can design a simple experiment to compare indoor and outdoor air quality by using your Kids Making Sense PM sensor. Begin by measuring air pollution inside of your house, then walk outside, and then back inside. What did you find? Is the air quality better or worse indoors? Can you explain your results?

We tried the experiment in two different locations exposed to wildfire smoke, with surprising results.

We turned on the sensor and measured the particulate matter while standing inside by the front door. Then we opened the front door and walked outside (A) where it was quite smoky. We then came back inside (B) and closed the door.

Experiment 1 showed much higher pollution levels outdoors.

In Experiment 2, the PM concentrations inside were slightly elevated, but not very high. However, when we walked outside (C), PM concentrations decreased. That was not what we expected! We then walked back inside (D) and confirmed that the air outside was actually slightly cleaner than the air inside the home.

As with any scientific experiment, the value is in understanding why we got these results. Some indoor activities that may have caused higher PM levels indoors include cooking and dusting. Another possibility is that polluted air was trapped inside, while winds outside shifted and blew the smoke away.

Experiment 2 showed slightly lower pollution levels outdoors.

In both cases, we could improve our indoor air quality by using an air filter. These two examples highlight that the same experiment can often result in different outcomes - the value is in understanding why!

What will your students discover when they conduct their own experiments?

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Air Quality Information: Making Sense of Air Pollution Data to Inform Decisions in Underserved Communities Overburdened by Air Pollution Exposures Funding Opportunity

Overview information, u.s. environmental protection agency office of science advisor, policy and engagement office of research and development science to achieve results (star) program, air quality information: making sense of air pollution data to inform decisions in underserved communities overburdened by air pollution exposures.

This is the initial announcement of this funding opportunity

Funding Opportunity Number:  EPA-G2024-STAR-D1

Assistance Listing Number  66.509

Solicitation Opening Date:   April 8, 2024 Solicitation Closing Date:  June 26, 2024: 11:59:59 pm Eastern Time

Informational Webinar:  April 22, 2024, at 2:00 p.m. - 3:00 p.m. ET

Register Here

The U.S. Environmental Protection Agency (EPA) Office of Research and Development (ORD), as part of the Science to Achieve Results (STAR) program and in collaboration with the Air, Climate, and Energy (ACE) research program, is seeking applications proposing community-engaged research in underserved communities to advance the use of air pollution data and communication of air quality information for empowering local decisions and actions that address community-identified air pollution concerns. Specifically, this funding opportunity is soliciting research projects that involve substantial engagement with communities, community-based organizations, and/or Tribes to address both of the following priorities:

• methods and tools for data integration and analysis to characterize community exposures to air pollution in underserved communities
• effective communication of air quality information to communities and decision makers to support actions to address air pollution concerns in underserved communities

This research solicitation supports the Administration’s priorities to address environmental justice (EJ).

Air Quality Information: Making Sense of Air Pollution Data to Inform Decisions in Underserved Communities Overburdened by Air Pollution Exposures Funding Opportunity (pdf) (684.7 KB)

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April 4, 2024

Geoengineering Test Quietly Launches Salt Crystals into Atmosphere

A solar geoengineering experiment in San Francisco could lead to brighter clouds that reflect sunlight. The risks are numerous

By Corbin Hiar & E&E News

An aerial view of a layer of stratocumulus clouds.

SubstanceP/Getty Images

CLIMATEWIRE | The nation's first outdoor test to limit global warming by increasing cloud cover launched Tuesday from the deck of a decommissioned aircraft carrier in the San Francisco Bay.

The experiment, which organizers didn't widely announce to avoid public backlash, marks the acceleration of a contentious field of research known as solar radiation modification. The concept involves shooting substances such as aerosols into the sky to reflect sunlight away from the Earth.

The move led by researchers at the University of Washington has renewed questions about how to effectively and ethically study promising climate technologies that could also harm communities and ecosystems in unexpected ways. The experiment is spraying microscopic salt particles into the air, and the secrecy surrounding its timing caught even some experts off guard.

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"Since this experiment was kept under wraps until the test started, we are eager to see how public engagement is being planned and who will be involved," said Shuchi Talati, the executive director of the Alliance for Just Deliberation on Solar Geoengineering, a nonprofit that seeks to include developing countries in decisions about solar modification, also known as geoengineering. She is not involved in the experiment and only learned about it after being contacted by a reporter.

"While it complies with all current regulatory requirements, there is a clear need to reexamine what a strong regulatory framework must look like in a world where [solar radiation modification] experimentation is happening," Talati added.

The Coastal Atmospheric Aerosol Research and Engagement, or CAARE, project is using specially built sprayers to shoot trillions of sea salt particles into the sky in an effort to increase the density — and reflective capacity — of marine clouds. The experiment is taking place, when conditions permit, atop the USS Hornet Sea, Air & Space Museum in Alameda, California, and will run through the end of May, according to a weather modification form the team filed with federal regulators.

The project comes as global heat continues to obliterate monthly and yearly temperature records and amid growing interest in solar radiation modification from Silicon Valley funders and some environmental groups . It also follows the termination of a Harvard University experiment last month that planned to inject reflective aerosols into the stratosphere near Sweden before it was canceled after encountering opposition from Indigenous groups.

Solar radiation modification is controversial because widespread use of technologies like marine cloud brightening could alter weather patterns in unclear ways and potentially limit the productivity of fisheries and farms. It also wouldn't address the main cause of climate change — the use of fossil fuels — and could lead to a catastrophic spike in global temperatures if major geoengineering activities were discontinued before greenhouse gases decrease to manageable levels.

The University of Washington and SilverLining, a geoengineering research advocacy group involved in the CAARE project, declined interview requests. The mayor of Alameda, where the experiment is being conducted, didn't respond to emailed questions about the project.

The secrecy surrounding the landmark experiment seems to have been by design, according to The New York Times , which, along with a local newspaper, was granted exclusive access to cover the initial firing of the spray cannons.

"The idea of interfering with nature is so contentious, organizers of Tuesday's test kept the details tightly held, concerned that critics would try to stop them," the Times reported. The White House also distanced itself from the experiment, which is being conducted with the cooperation of a Smithsonian-affiliated museum.

The project team has touted its transparency, noting that visitors to the USS Hornet, which now serves as a floating museum, will be able to view the experiment.

"The world needs to rapidly advance its understanding of the effects of aerosol particles on climate,” Kelly Wanser, the executive director of SilverLining, said in a press release. "With a deep commitment to open science and a culture of humility, the University of Washington has developed an approach that integrates science with societal engagement, and can help society in essential steps toward advancing science, developing regulations, promoting equitable and effective decision-making, and building shared understanding in these areas."

The CAARE project is part of a larger coastal study that the University of Washington consortium is planning to pursue. The second phase of that effort would take place on a pier around a mile offshore in a coastal environment, according to a study description the school released Monday.

While a peer review of that proposal was generally positive, the scientists also flagged some transparency shortcomings.

"One reviewer noted that it would help to have more information on the site location," said a Washington-University- commissioned report . "Is there local resistance or concerns (whether founded or unfounded) around issues like local air quality, etc.? How many options exist, and how do different options affect the field study plan?"

The study plan also made no mention of its potential ecological impacts, a key consideration recommended by a 2022 Biden administration marine cloud brightening workshop . That's a significant oversight, according to Greg Goldsmith, the associate dean for research and development at Chapman University.

"History has shown us that when we insert ourselves into modification of nature, there are always very serious unintended consequences," said Goldsmith, who studies the implications of climate change for plant structure and function. "And therefore, it would be prudent to listen to what history has shown and look for consequences."

Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2024. E&E News provides essential news for energy and environment professionals.

Editor’s Note (4/8/24): Our partners at Climatewire have edited this article after posting to clarify that neither Shuchi Talati nor the Alliance for Just Deliberation on Solar Geoengineering is involved in the described solar geoengineering project.

Module 1: Introduction to Biology

Experiments and hypotheses, learning outcomes.

• Form a hypothesis and use it to design a scientific experiment

Now we’ll focus on the methods of scientific inquiry. Science often involves making observations and developing hypotheses. Experiments and further observations are often used to test the hypotheses.

A scientific experiment is a carefully organized procedure in which the scientist intervenes in a system to change something, then observes the result of the change. Scientific inquiry often involves doing experiments, though not always. For example, a scientist studying the mating behaviors of ladybugs might begin with detailed observations of ladybugs mating in their natural habitats. While this research may not be experimental, it is scientific: it involves careful and verifiable observation of the natural world. The same scientist might then treat some of the ladybugs with a hormone hypothesized to trigger mating and observe whether these ladybugs mated sooner or more often than untreated ones. This would qualify as an experiment because the scientist is now making a change in the system and observing the effects.

Forming a Hypothesis

When conducting scientific experiments, researchers develop hypotheses to guide experimental design. A hypothesis is a suggested explanation that is both testable and falsifiable. You must be able to test your hypothesis, and it must be possible to prove your hypothesis true or false.

For example, Michael observes that maple trees lose their leaves in the fall. He might then propose a possible explanation for this observation: “cold weather causes maple trees to lose their leaves in the fall.” This statement is testable. He could grow maple trees in a warm enclosed environment such as a greenhouse and see if their leaves still dropped in the fall. The hypothesis is also falsifiable. If the leaves still dropped in the warm environment, then clearly temperature was not the main factor in causing maple leaves to drop in autumn.

In the Try It below, you can practice recognizing scientific hypotheses. As you consider each statement, try to think as a scientist would: can I test this hypothesis with observations or experiments? Is the statement falsifiable? If the answer to either of these questions is “no,” the statement is not a valid scientific hypothesis.

Practice Questions

Determine whether each following statement is a scientific hypothesis.

Air pollution from automobile exhaust can trigger symptoms in people with asthma.

• No. This statement is not testable or falsifiable.
• No. This statement is not testable.
• No. This statement is not falsifiable.
• Yes. This statement is testable and falsifiable.

Natural disasters, such as tornadoes, are punishments for bad thoughts and behaviors.

a: No. This statement is not testable or falsifiable. “Bad thoughts and behaviors” are excessively vague and subjective variables that would be impossible to measure or agree upon in a reliable way. The statement might be “falsifiable” if you came up with a counterexample: a “wicked” place that was not punished by a natural disaster. But some would question whether the people in that place were really wicked, and others would continue to predict that a natural disaster was bound to strike that place at some point. There is no reason to suspect that people’s immoral behavior affects the weather unless you bring up the intervention of a supernatural being, making this idea even harder to test.

Testing a Vaccine

Let’s examine the scientific process by discussing an actual scientific experiment conducted by researchers at the University of Washington. These researchers investigated whether a vaccine may reduce the incidence of the human papillomavirus (HPV). The experimental process and results were published in an article titled, “ A controlled trial of a human papillomavirus type 16 vaccine .”

Preliminary observations made by the researchers who conducted the HPV experiment are listed below:

• Human papillomavirus (HPV) is the most common sexually transmitted virus in the United States.
• There are about 40 different types of HPV. A significant number of people that have HPV are unaware of it because many of these viruses cause no symptoms.
• Some types of HPV can cause cervical cancer.
• About 4,000 women a year die of cervical cancer in the United States.

Practice Question

Researchers have developed a potential vaccine against HPV and want to test it. What is the first testable hypothesis that the researchers should study?

• HPV causes cervical cancer.
• People should not have unprotected sex with many partners.
• People who get the vaccine will not get HPV.
• The HPV vaccine will protect people against cancer.

Experimental Design

You’ve successfully identified a hypothesis for the University of Washington’s study on HPV: People who get the HPV vaccine will not get HPV.

The next step is to design an experiment that will test this hypothesis. There are several important factors to consider when designing a scientific experiment. First, scientific experiments must have an experimental group. This is the group that receives the experimental treatment necessary to address the hypothesis.

The experimental group receives the vaccine, but how can we know if the vaccine made a difference? Many things may change HPV infection rates in a group of people over time. To clearly show that the vaccine was effective in helping the experimental group, we need to include in our study an otherwise similar control group that does not get the treatment. We can then compare the two groups and determine if the vaccine made a difference. The control group shows us what happens in the absence of the factor under study.

However, the control group cannot get “nothing.” Instead, the control group often receives a placebo. A placebo is a procedure that has no expected therapeutic effect—such as giving a person a sugar pill or a shot containing only plain saline solution with no drug. Scientific studies have shown that the “placebo effect” can alter experimental results because when individuals are told that they are or are not being treated, this knowledge can alter their actions or their emotions, which can then alter the results of the experiment.

Moreover, if the doctor knows which group a patient is in, this can also influence the results of the experiment. Without saying so directly, the doctor may show—through body language or other subtle cues—their views about whether the patient is likely to get well. These errors can then alter the patient’s experience and change the results of the experiment. Therefore, many clinical studies are “double blind.” In these studies, neither the doctor nor the patient knows which group the patient is in until all experimental results have been collected.

Both placebo treatments and double-blind procedures are designed to prevent bias. Bias is any systematic error that makes a particular experimental outcome more or less likely. Errors can happen in any experiment: people make mistakes in measurement, instruments fail, computer glitches can alter data. But most such errors are random and don’t favor one outcome over another. Patients’ belief in a treatment can make it more likely to appear to “work.” Placebos and double-blind procedures are used to level the playing field so that both groups of study subjects are treated equally and share similar beliefs about their treatment.

The scientists who are researching the effectiveness of the HPV vaccine will test their hypothesis by separating 2,392 young women into two groups: the control group and the experimental group. Answer the following questions about these two groups.

• This group is given a placebo.
• This group is deliberately infected with HPV.
• This group is given nothing.
• This group is given the HPV vaccine.
• a: This group is given a placebo. A placebo will be a shot, just like the HPV vaccine, but it will have no active ingredient. It may change peoples’ thinking or behavior to have such a shot given to them, but it will not stimulate the immune systems of the subjects in the same way as predicted for the vaccine itself.
• d: This group is given the HPV vaccine. The experimental group will receive the HPV vaccine and researchers will then be able to see if it works, when compared to the control group.

Experimental Variables

A variable is a characteristic of a subject (in this case, of a person in the study) that can vary over time or among individuals. Sometimes a variable takes the form of a category, such as male or female; often a variable can be measured precisely, such as body height. Ideally, only one variable is different between the control group and the experimental group in a scientific experiment. Otherwise, the researchers will not be able to determine which variable caused any differences seen in the results. For example, imagine that the people in the control group were, on average, much more sexually active than the people in the experimental group. If, at the end of the experiment, the control group had a higher rate of HPV infection, could you confidently determine why? Maybe the experimental subjects were protected by the vaccine, but maybe they were protected by their low level of sexual contact.

To avoid this situation, experimenters make sure that their subject groups are as similar as possible in all variables except for the variable that is being tested in the experiment. This variable, or factor, will be deliberately changed in the experimental group. The one variable that is different between the two groups is called the independent variable. An independent variable is known or hypothesized to cause some outcome. Imagine an educational researcher investigating the effectiveness of a new teaching strategy in a classroom. The experimental group receives the new teaching strategy, while the control group receives the traditional strategy. It is the teaching strategy that is the independent variable in this scenario. In an experiment, the independent variable is the variable that the scientist deliberately changes or imposes on the subjects.

Dependent variables are known or hypothesized consequences; they are the effects that result from changes or differences in an independent variable. In an experiment, the dependent variables are those that the scientist measures before, during, and particularly at the end of the experiment to see if they have changed as expected. The dependent variable must be stated so that it is clear how it will be observed or measured. Rather than comparing “learning” among students (which is a vague and difficult to measure concept), an educational researcher might choose to compare test scores, which are very specific and easy to measure.

In any real-world example, many, many variables MIGHT affect the outcome of an experiment, yet only one or a few independent variables can be tested. Other variables must be kept as similar as possible between the study groups and are called control variables . For our educational research example, if the control group consisted only of people between the ages of 18 and 20 and the experimental group contained people between the ages of 30 and 35, we would not know if it was the teaching strategy or the students’ ages that played a larger role in the results. To avoid this problem, a good study will be set up so that each group contains students with a similar age profile. In a well-designed educational research study, student age will be a controlled variable, along with other possibly important factors like gender, past educational achievement, and pre-existing knowledge of the subject area.

What is the independent variable in this experiment?

• Sex (all of the subjects will be female)
• Presence or absence of the HPV vaccine
• Presence or absence of HPV (the virus)

List three control variables other than age.

What is the dependent variable in this experiment?

• Sex (male or female)
• Rates of HPV infection
• Age (years)

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• Revision and adaptation. Authored by : Shelli Carter and Lumen Learning. Provided by : Lumen Learning. License : CC BY-NC-SA: Attribution-NonCommercial-ShareAlike
• Scientific Inquiry. Provided by : Open Learning Initiative. Located at : https://oli.cmu.edu/jcourse/workbook/activity/page?context=434a5c2680020ca6017c03488572e0f8 . Project : Introduction to Biology (Open + Free). License : CC BY-NC-SA: Attribution-NonCommercial-ShareAlike

Mapping America’s access to nature, neighborhood by neighborhood

A city is a science experiment. What happens when we separate human beings from the environment in which they evolved? Can people be healthy without nature? The results have been bleak. Countless studies have shown that people who spend less time in nature die younger and suffer higher rates of mental and physical ailments.

“There’s a really, really strong case for proximity to nature influencing health in a really big way,” said Jared Hanley, the co-founder and CEO of NatureQuant, an Oregon start-up whose mission is to discover what kind of nature best supports human health, map where it is and persuade people to spend more time in it.

Using satellite imagery and data on dozens of factors — including air and noise pollution, park space, open water and tree canopy — NatureQuant has distilled the elements of health-supporting nature into a single variable called NatureScore. Aggregated to the level of Census tracts — roughly the size of a neighborhood — the data provide a high-resolution image of where nature is abundant and where it is lacking across the United States.

Quantifying nature reveals unsettling truths — about how the densest neighborhoods are often bereft of nature, and about how the poorest city dwellers have the least access to the nature’s health benefits. But it could also help pinpoint which parts of our urban landscapes would benefit most from an infusion of nature.

What’s at stake

The scientific basis for nature’s health benefits is now overwhelming. Study after peer-reviewed study has shown that nature exposure is linked to living longer , sleeping better , displaying improved cognitive function , and enjoying lower rates of heart disease , obesity , depression and stress .

In rural areas, both rich and poor can easily spend time in nature. But in cities, NatureScores are higher where people have more education, are more likely to be White and earn more money.

Why does nature make us healthy? One answer is the “old friends hypothesis” that our immune systems grow stronger when regularly exposed to the natural pathogens with which we evolved. Or maybe it’s that being in nature nudges us to exercise and socialize. A third theory is that cities are just unhealthy, exposing us to lead, asbestos and vehicle exhaust, not to mention the stress of traffic and noisy construction.

Yet like space dust accreting to form planets, humans seem compelled to gather in cities. Two hundred years ago, just 7 percent of people in the United States lived in an urbanized area. By 1970, when Joni Mitchell was lamenting that we’d “paved paradise,” that figure was up to 75 percent. Today, 86 percent of us live in cities, and the share continues to rise.

The denser the city, the less health-supporting nature you are likely to find. Among the 500 most populous cities in the United States, Suffolk, Va., with just 147 people per square mile, has the highest NatureScore. Union City, N.J., is by far the densest — almost 30,000 people per square mile — and has one of the lowest NatureScores.

But density is not destiny. New York, for instance, has a better NatureScore than Los Angeles and Chicago, even though its population density is higher. And the best way to boost a city’s NatureScore is to plant trees.

The Arbor Day Foundation, which directs millions of dollars to tree planting projects around the world, started using NatureQuant’s data in 2021. If a donor comes to the Arbor Day Foundation with a plan to plant trees in a posh part of town, the data can help make the argument that the trees would do more good elsewhere.

“Everybody wants to plant in their neighborhood,” said Jeff Salem, director of communications for the Arbor Day Foundation. “But this helps that conversation of, ‘Hey, you might live in North Chicago in a really great neighborhood, but really, as you can see here, there’s some neighborhoods on the South Side that really could use your support with trees.’”

In rural America, it doesn’t matter if you are rich or poor, Black or White, dropped out of high school or have a PhD: you are still likely to have access to health-supporting nature. But in cities, differences in access to nature are as stark as other forms of inequality.

For example, among the fifth of Census tracts with the lowest levels of education, the average NatureScore is just 37, compared with an average score of 68 in the most educated Census tracts. The Census tracts with the lowest share of White people have an average NatureScore of 45, compared with 73 in the tracts with highest share of Whites.

NatureScores can identify neighborhoods that need trees. Planting them is another matter. “We use [the data] as a starting point. But, you know, the devil is in the details,” said Christina Smith, the executive director of Groundwork Bridgeport, an environmental nonprofit in Bridgeport, Conn., where she grew up.

Suppose you want to boost a neighborhood’s NatureScore by lining the sidewalk with trees. Before you buy the first sapling, you need to make sure the sidewalk is wide enough to fit a tree and still comply with the Americans With Disabilities Act. And you’ll need money to hire workers or face the dangerous prospect of twenty high school volunteers packed into a narrow sidewalk with cars whizzing by.

What about just giving free trees to neighborhood residents? If most people rent, they won’t have the authority to plant on their property. If you manage to track down property owners, they might not want the burden of planting and caring for trees.

Yet Groundwork Bridgeport has figured out how to host successful tree giveaways (door knocking works better than direct mail, and it helps to have friends at community gardens). Last year, they distributed 100 trees to residents on the east side of the city. If all those trees are still around in 30 years, it will boost the area’s NatureScore by 15 points, amounting to an increase of a year of life expectancy for people in the neighborhood, NatureQuant told me.

Thirty years is a long time to wait, which is one of the reasons cash-strapped city governments often view tree planting as a frivolous expense compared to more pressing matters like crime and homelessness. “Trees are not a silver bullet. Trees are not going to solve poverty,” said Dan Lambe, the Arbor Day Foundation’s CEO.

But quantifying nature can make sure trees are going where they’re needed most, Lambe said: “We know we can make a difference in people’s lives by emphasizing neighborhoods that have been disadvantaged, who have been ignored, that just simply don’t have the tree benefits.”

Check my work

The NatureScores by Census tract were provided by NatureQuant, Inc., which described its methodology in this paper . Those data are as of July 31, 2023. You can find my analysis of those data along with 2020 socioeconomic data from the U.S. Census Bureau in this computational notebook . The top 500 U.S. cities were also provided by NatureQuant and are based on 2020 NatureScore data. You can find my analysis of the city data in this notebook .

You can use the code and data to produce your own analyses and charts — and to make sure mine are accurate. If you do, email me at [email protected] .

Parkinson's Disease: New theory on the disease's origins and spread

The nose or the gut? For the past two decades, the scientific community has debated the wellspring of the toxic proteins at the source of Parkinson's disease. In 2003, a German pathologist, Heiko Braak, MD, first proposed that the disease begins outside the brain. More recently, Per Borghammer, MD, with Aarhus University Hospital in Denmark, and his colleagues argue that the disease is the result of processes that start in either the brain's smell center (brain-first) or the body's intestinal tract (body-first).

A new hypothesis paper appearing in the Journal of Parkinson's Disease on World Parkinson's Day unites the brain- and body-first models with some of the likely causes of the disease-environmental toxicants that are either inhaled or ingested. The authors of the new study, who include Borghammer, argue that inhalation of certain pesticides, common dry cleaning chemicals, and air pollution predispose to a brain-first model of the disease. Other ingested toxicants, such as tainted food and contaminated drinking water, lead to body-first model of the disease.

"In both the brain-first and body-first scenarios the pathology arises in structures in the body closely connected to the outside world," said Ray Dorsey, MD, a professor of Neurology at the University of Rochester Medical Center and co-author of the piece. "Here we propose that Parkinson's is a systemic disease and that its initial roots likely begin in the nose and in the gut and are tied to environmental factors increasingly recognized as major contributors, if not causes, of the disease. This further reinforces the idea that Parkinson's, the world's fastest growing brain disease, may be fueled by toxicants and is therefore largely preventable."

Different pathways to the brain, different forms of disease

A misfolded protein called alpha-synuclein has been in scientists' sights for the last 25 years as one of the driving forces behind Parkinson's. Over time, the protein accumulates in the brain in clumps, called Lewy bodies, and causes progressive dysfunction and death of many types of nerve cells, including those in the dopamine-producing regions of the brain that control motor function. When first proposed, Braak thought that an unidentified pathogen, such as a virus, may be responsible for the disease.

The new piece argues that toxins encountered in the environment, specifically the dry cleaning and degreasing chemicals trichloroethylene (TCE) and perchloroethylene (PCE), the weed killer paraquat, and air pollution, could be common causes for the formation of toxic alpha-synuclein. TCE and PCE contaminates thousands of former industrial, commercial, and military sites, most notably the Marine Corps base Camp Lejeune, and paraquat is one of the most widely used herbicides in the US, despite being banned for safety concerns in more than 30 countries, including the European Union and China. Air pollution was at toxic levels in nineteenth century London when James Parkinson, whose 269th birthday is celebrated today, first described the condition.

The nose and the gut are lined with a soft permeable tissue, and both have well established connections to the brain. In the brain-first model, the chemicals are inhaled and may enter the brain via the nerve responsible for smell. From the brain's smell center, alpha-synuclein spreads to other parts of the brain principally on one side, including regions with concentrations of dopamine-producing neurons. The death of these cells is a hallmark of Parkinson's disease. The disease may cause asymmetric tremor and slowness in movement and, a slower rate of progression after diagnosis, and only much later, significant cognitive impairment or dementia.

When ingested, the chemicals pass through the lining of the gastrointestinal tract. Initial alpha-synuclein pathology may begin in the gut's own nervous system from where it can spread to both sides of the brain and spinal cord. This body-first pathway is often associated with Lewy body dementia, a disease in the same family as Parkinson's, which is characterized by early constipation and sleep disturbance, followed by more symmetric slowing in movements and earlier dementia, as the disease spreads through both brain hemispheres.

New models to understand and study brain diseases

"These environmental toxicants are widespread and not everyone has Parkinson's disease," said Dorsey. "The timing, dose, and duration of exposure and interactions with genetic and other environmental factors are probably key to determining who ultimately develops Parkinson's. In most instances, these exposures likely occurred years or decades before symptoms develop."

Pointing to a growing body of research linking environmental exposure to Parkinson's disease, the authors believe the new models may enable the scientific community to connect specific exposures to specific forms of the disease. This effort will be aided by increasing public awareness of the adverse health effects of many chemicals in our environment. The authors conclude that their hypothesis "may explain many of the mysteries of Parkinson's disease and open the door toward the ultimate goal-prevention."

In addition to Parkinson's, these models of environmental exposure may advance understanding of how toxicants contribute to other brain disorders, including autism in children, ALS in adults, and Alzheimer's in seniors. Dorsey and his colleagues at the University of Rochester have organized a symposium on the Brain and the Environment in Washington, DC, on May 20 that will examine the role toxicants in our food, water, and air are playing in all these brain diseases.

Additional authors of the hypothesis paper include Briana De Miranda, PhD, with the University of Alabama at Birmingham, and Jacob Horsager, MD, PhD, with Aarhus University Hospital in Denmark.

• Parkinson's Research
• Chronic Illness
• Brain Tumor
• Diseases and Conditions
• Parkinson's
• Disorders and Syndromes
• Brain-Computer Interfaces
• Parkinson's disease
• Deep brain stimulation
• Homosexuality
• Dopamine hypothesis of schizophrenia
• Excitotoxicity and cell damage

Story Source:

Materials provided by University of Rochester Medical Center . Original written by Mark Michaud. Note: Content may be edited for style and length.

Journal Reference :

• E. Ray Dorsey, Briana R. De Miranda, Jacob Horsager, Per Borghammer. The Body, the Brain, the Environment, and Parkinson’s Disease . Journal of Parkinson's Disease , 2024; 1 DOI: 10.3233/JPD-240019

Cite This Page :

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