Wildfires dominated the news as Southern California experienced an unseasonably dry winter in early 2025. And with wildfires, of course, comes smoke and poor air quality. Being aware of not only the quality and safety of the air we breathe but also how our actions may contribute to air pollution has never been more crucial. We often think about the environmental effects of human behavior on the ozone layer and greenhouse gases, but because they are invisible, they may be harder for kids to perceive and understand. (For more on the greenhouse effect, try this experiment from our August 2024 post.) In honor of Earth Day next month, we offer an air pollution catcher experiment to help kids see what might otherwise be invisible to them, making a huge, abstract problem more understandable. But first, a little background on how we track air pollution in the US today.
What Is the Air Quality Index?
Many Californians as well as Americans across the US may be paying more attention to the local Air Quality Index, or AQI, in their areas, before spending time outdoors. The Clean Air Act, first passed by Congress in 1970 and signed into law by President Richard Nixon on New Year’s Eve that year, regulates pollutants in the air we breathe.1 The EPA’s Air Quality Index tracks five major pollutants in the atmosphere: nitrogen dioxide, sulfur dioxide, carbon monoxide, ground-level ozone, and particle pollution, or particulate matter. Of all these pollutants, levels of ozone and particle pollution, which is measured by the size of the particles, such as PM2.5 and PM10, are tracked and reported by the EPA on its Air Quality Index website with the NowCast AQI in real time and color-coded for relative safety. Levels 50 or less, green, are “good,” and increase to over 300, maroon, “hazardous,” a health emergency. (The EPA’s AQI resource for students has a rhyme to help kids remember: “When the AQI is green, the air is clean!”)2 But what do all these numbers mean?
Particle Pollution
Particulate matter (PM) refers to bits of solid or liquid matter of varying sizes suspended in our air.3 They range from common materials such as pollen, dust, mold spores, and soot, to organic chemicals and acids. The EPA tracks the particles of most concern, which are 10 micrometers or smaller (hence PM10 and PM2.5). These particles are easiest to inhale and may lodge in the lungs, causing asthma, heart disease, and other illnesses over time.4
Our experiment will investigate particles large enough to be seen by the naked eye or under a microscope or magnifying glass. The AQI numbers for particle pollution track the concentration of these particles in the atmosphere. For our experiment, we’ll count the number of particles in a small area of our sample.
Air Pollution Catcher Experiment
This air pollution experiment can be done outdoors or indoors to catch pollution particles. With just some common household materials and a few days’ time, this experiment will help kids better understand what’s in a cloud of smoke, a puff of exhaust from a truck’s tailpipe, or a haze of smog. Try the variation to make the experiment more collaborative and provide more opportunities for engagement. (Safety note: Adult supervision will be needed for making holes in the catchers and hanging them high enough to be out of the way.)
What You’ll Need:
- Thick white paper (paperboard, a paper plate, or cardstock are ideal)
- String or yarn
- Scissors
- Petroleum jelly or a plant-based alternative (Alba Botanica’s Un-Petroleum Jelly works well to avoid fossil fuel by-products, but use what you have!)
- Hole punch, large sewing needle, or knitting needle
- Permanent marker
- Magnifying glass or microscope
- Notebook
- Pen
How to Do It
- Identify at least one location to hang your pollution catcher(s). Kids can test indoor air quality with one inside your home and outdoor air quality with one in your yard or another outside area. Busier places, such as near a street, are great.
- Make the catcher(s):
- With a hole punch or needle, make a hole at the top of your paper plate or cardstock. Thread your yarn or string through the hole, making sure there’s enough to hang your catcher.
- If you are making more than one catcher, use permanent marker to write the location and date at the top of each catcher. This will help kids keep track of particle pollution in different locations. If your catchers are different sizes, use marker to outline a square of the same size on each catcher for consistency.
- Apply a thin layer of petroleum jelly or a plant-based alternative to one side of each catcher or inside each square, making sure to keep the string out of the way as you work.
- With a hole punch or needle, make a hole at the top of your paper plate or cardstock. Thread your yarn or string through the hole, making sure there’s enough to hang your catcher.
- Hang the catcher(s).
- Wait a few days, or up to a week, before helping kids retrieve the catcher(s).
- Record findings:
- Place the catcher(s) on a flat surface.
- Record the date and location of each catcher in your notebook.
- Invite kids to view each catcher’s sticky surface and describe what they see. Count the particles visible with the naked eye, and write down the number.
- Next, use a magnifying glass or microscope to view the same area. How many particles are visible now? Write down the number.
Variations: Invite friends, family, or classmates to investigate with you! By getting sample data from other parts of your own city or even from far away, there will be more to compare. Ideally, you’ll want the sample size of the area with jelly to be the same. For example, test squares of 2 by 2 inches on each catcher. You can also ask kids to keep track of each day’s AQI in your area and record that in the notebook to compare the pollution levels over the experiment with friends’ and families’ results, and make hypotheses.
Ideas for Discussion
- How many particles did you see with just your eyes? How many with the magnifying glass or under the microscope? What did the particles look like?
- Think about where the catcher was hung. What do you think the particles might be made of, and where do you think they came from?
- If you used more than one catcher, how do you think the area where the catcher was hung affected the results? Which catcher(s) had the most particles? Why do you think there were more or less in some areas?
- What are some ways people can reduce adding more particles to the air?
What Can You Do to Reduce Air Pollution?
There are many ways we can try to limit our impact on the environment. The Bay Area’s mass transit options offer drivers ways to lessen their reliance on cars and reduce exhaust and emissions from daily commutes. Shopping locally and placing fewer online orders can also help reduce emissions and particle pollution in our cities and on our highways, which are clogged by delivery vehicles.
While air pollution and the health effects it causes are frightening, they are also worthwhile topics of investigation that kids can explore while learning more about the environment and people’s effects on it. For more ways to integrate science into your child’s life, sign your child up for one of STEMful’s programs, and help prepare them to tackle the world’s biggest problems tomorrow with fun STEM learning today.
- “40th Anniversary of the Clean Air Act,” US Environmental Protection Agency, last updated May 17, 2024, https://www.epa.gov/clean-air-act-overview/40th-anniversary-clean-air-act.
- “What Is the AQI?,” AirNow, accessed February 13, 2025, https://www.airnow.gov/education/students/what-is-the-aqi/.
- US Environmental Protection Agency, “What Is Particle Pollution?,” last updated June 20, 2024, https://www.epa.gov/pmcourse/what-particle-pollution.
- National Institute of Environmental Health Sciences, “Air Pollution and Your Health,” National Institute of Health, last reviewed January 27, 2025, https://www.niehs.nih.gov/health/topics/agents/air-pollution.