Air Quality Experiment for Kids: The Sticky Slide

Most versions of this activity end with a child saying “wow, the air is dirty”. This air quality experiment for kids is better than that, because it ends with them knowing what they measured and what they did not. Sticky cards catch settling dust: pollen grains, skin flakes, soot specks, fibres, bits of tyre and brake wear. Under a hand lens those are countable and the differences between a bedroom and a kerbside are obvious within 48 hours. But the particles that actually drive health warnings, PM2.5, are 2.5 micrometres and smaller, and you will never see one. A human hair is about 70 micrometres across, which the EPA points out is thirty times larger than the biggest fine particle. Saying that out loud is the lesson.

Key Takeaways

• You will coat index cards with petroleum jelly, expose five of them in different places for 48 hours, and count particles in a measured area under a lens.
• The concept is particle deposition: larger airborne particles settle out under gravity, and the rate at which they land is a real measurable quantity.
• Best for ages 8 to 14. Younger kids compare cards by eye; older ones calculate particles per square millimetre per day.
• The usual failure is handling. A fingerprint on the jelly or a card dropped face-down ruins a sample, and there is no recovering it.
• This method sees coarse particles, not PM2.5. Pair it with a real AQI reading rather than pretending it replaces one.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
White index cards	6, A6 size	Stationery drawer	Cut-up cereal box, white side out
Petroleum jelly	A small tub	Bathroom cabinet	Clear double-sided tape, or clear packing tape sticky-side out
Hole punch or 1 cm template	1	Drawer	Draw a 1 cm square with a fine pen
Permanent marker	1	Drawer	—
Hand lens, 10×	1	Toy box or hardware shop	Phone macro mode, or a drop of water on clear plastic as a lens
Clothes pegs or tape	6	Laundry	String and paperclips
Ruler and graph paper	1 each	School bag	Printed 1 mm grid
Phone with internet	1	Pocket	A local air-quality monitor reading from a news site

Time: prep 20 min, 48 hours of waiting, counting 30 min Cost: everything is probably in your house Mess level: low, but petroleum jelly gets on fingers

Do the Experiment

Step 1 — Draw the counting window before you add jelly

On each card, draw a 1 cm square in the middle with a fine permanent pen and label the card with a location and a date. The square is your sampling area and everything you count comes from inside it. Doing this first matters, because you cannot draw a clean line on greased card.

Step 2 — Spread a thin, even film

Smear petroleum jelly over the square and about a centimetre beyond it, then wipe most of it off with a fingertip so what remains is a film you can see through. Thick blobs trap everything including each other and become uncountable. Keep one card jelly-free as a control to prove that your counting is not picking up card texture.

Step 3 — Place five cards in genuinely different places

Pick locations that differ in one obvious way each: a bedroom, the kitchen near the hob, an outdoor spot facing a busy road, a sheltered spot in a garden or park, and a windowsill. Mount them horizontally, jelly side up, at about the height of a child’s face, where nothing will be sprayed, rained on or brushed past. Note the exact placement time.

Step 4 — Record what the air was doing

While the cards are out, write down the weather each day and look up your local AQI on a government monitor. The AirNow scale runs from 0 to 500 across six categories, with 0 to 50 counted as Good, and an AQI of 100 corresponding roughly to the short-term national standard for a pollutant. These numbers are your real air-quality data; the cards are your deposition data.

Step 5 — Collect at 48 hours and count a grid

Bring the cards in flat, jelly side up, without stacking them. Lay graph paper under each card, or place the card on a 1 mm grid printed on paper, and count particles inside the 1 cm window under the lens. Count in strips so you do not double-count, and record totals separately for dark specks, pale flakes, fibres and spheres. Divide by two to get particles per day.

What you should see: The kerbside card is visibly dirtier than the garden card to the naked eye, usually by a factor you can see from across the room. Counts in a 1 cm square typically run from a few dozen in a clean bedroom to several hundred beside a road over two days. Under the lens you will find three recognisable families: angular black specks, which are mostly combustion soot agglomerates and brake and tyre debris; pale irregular flakes, which are skin, textile and plant fragments; and occasional near-spherical yellow grains, which are pollen. The kitchen card often surprises people by beating the garden card, because cooking is a major indoor particle source.

What’s Actually Going On

Particles in air fall, but slowly and at a rate that depends sharply on size. A 50 micrometre grain settles in seconds; a 10 micrometre particle takes minutes to drift down across a room; a 1 micrometre particle can stay aloft for hours or days because random collisions with air molecules keep knocking it back up. The practical consequence is that a horizontal sticky surface is a selective sampler. It collects almost all of the coarse fraction that happens to pass over it, a little of the mid-range, and essentially none of the fine fraction. When your child counts 300 specks, they have counted deposition, not concentration, and the unit is particles per square millimetre per day.

The health-relevant distinction is exactly the one your card misses. The EPA defines PM10 as inhalable particles generally 10 micrometres and smaller, and PM2.5 as fine particles generally 2.5 micrometres and smaller. The smaller class penetrates deeper into the lung, stays suspended far longer, and travels much further from its source, which is why air-quality standards and public warnings are built around it. Regulatory monitors measure it by drawing a known volume of air through a weighed filter or by optical scattering, neither of which you can do with jelly and an index card. Saying this plainly does not weaken the activity. It teaches that every instrument has a response range, which is an idea most people never get taught at all.

One more correction, because it comes up constantly: indoors is not automatically cleaner. The EPA’s guidance notes that in homes without smoking or other strong sources, indoor PM would be expected to be the same as or lower than outdoors, but also that indoor levels have the potential to exceed outdoor levels and the national standards. Cooking, candles, fireplaces, unvented heaters and some hobbies all generate particles directly. Your kitchen card is the one most likely to disrupt a child’s assumption that “outside” is where pollution lives.

How to Explain It to Your Kid

Ages 5–8: The air is not empty

Hold a torch beam in a dark room and look at the dust drifting through it. Tell them that air is full of tiny bits, most far too small to see, and that sticky cards work like flypaper for the big ones. Let them choose the five locations and make their own prediction about which card will be dirtiest. Guessing before you look is what turns dust into an experiment.

Ages 9–12: Deposition has units

Introduce particulate matter and the idea of a rate. Three hundred particles is meaningless on its own; three hundred particles per square centimetre in 48 hours is a measurement you can compare with another place. Have them do the arithmetic and build a bar chart of the five sites. Then introduce the size problem with the hair comparison: a hair is about 70 micrometres, and the fine particles that matter are thirty times smaller than the largest of them.

Ages 13+: Settling velocity and instrument response

Give them the physics. Stokes’ law makes settling velocity scale roughly with the square of particle diameter, so a tenfold drop in size means roughly a hundredfold drop in settling speed. That single relationship explains why your sampler is blind to PM2.5 and why fine particles travel hundreds of kilometres from wildfires. Then have them compare their site ranking against the official monitor’s PM2.5 record for the same two days and explain any disagreement.

The question to ask: “Our kerbside card had five times as many specks as the park card. If a smoke plume from a fire a hundred kilometres away passed over the whole town on day two, which cards would show it?”

Why Teaching This Early Pays Off

Air pollution is one of the few environmental topics where children routinely encounter real numbers — a school closing on a smog day, an app showing a colour — without ever being told what the numbers are. This experiment hands them the vocabulary and, more importantly, the idea that a measurement has a range of things it can detect. That is the single most useful concept in interpreting any sensor, from a smartwatch to a home CO2 monitor, and it is transferable in a way that a fact about pollution is not.

The learning research supports a narrow version of the claim. Chi and Wylie’s ICAP framework predicts the largest gains when learners are constructing explanations and arguing rather than observing, and the structure here — predict, sample, count, then explain a disagreement with the official monitor — is built to force that. White and Gunstone’s Predict-Observe-Explain routine is the same engine. What none of this supports is a promise about outcomes. One set of cards does not change anything measurable about a child’s education. It gives them a correct mental model of one instrument.

A Safe Air Quality Experiment for Kids: What Parents Should Know

Best age	8 to 14. Younger children can place and compare cards but the per-area arithmetic is where the value sits
Supervision	Minimal. An adult chooses the outdoor kerbside location and goes along to place it
Real hazards	None beyond normal care. Do not stand a child near traffic to mount a card; pick a kerbside spot behind a fence or railing. Petroleum jelly is harmless on skin but is not for eyes or mouths. Keep cards away from under-3s, who will put them in their mouth
Don’t	Do not place a card where it will be rained on, do not use cooking oil instead of petroleum jelly as it goes rancid and attracts insects, and do not describe your particle count as an air-quality index reading. It is a deposition count

When It Doesn’t Work

• Every card looks identical. Either the jelly was too thin to hold anything or 48 hours was not long enough in calm, damp weather. Run it for a week, and make sure the film is thick enough to catch a light reflection.
• The cards are unreadably crowded. Too much jelly, or a very dusty site. Wipe the film thinner next time, or shrink the counting window to 5 mm × 5 mm and multiply by four.
• A card went face-down or got rained on. It is gone. Always expose six cards for five sites so you have a spare, and mount outdoor cards under a small overhang that shields rain without blocking the sky.
• You cannot tell particles from card texture. This is what the blank card is for. Count the blank, and if it has anything on it, your lens or your lighting is the problem. Side-lighting at a low angle makes real particles cast shadows.
• The counts disagree with the official AQI. Expected, and interesting rather than wrong. You measured coarse deposition at one point for two days; the monitor measured fine particle concentration continuously. Work out which one a wildfire would move.

Take It Further

• Height as the variable. Four cards on the same post at 0.3, 0.9, 1.5 and 2.1 metres, same 48 hours. Road dust and brake debris are heaviest near the ground, and the gradient is usually clear. This is the version that wins science fairs because it isolates one variable cleanly.
• Before and after an activity. Card in the kitchen during a week of normal cooking versus a week where the extractor fan runs every time. Same for vacuuming, or for a candle-free week. The EPA’s indoor-PM advice becomes testable in your own house.
• Pollen season tracking. Repeat the same five sites monthly for three months and count only the spherical grains. You will see the seasonal curve, and it maps onto local pollen forecasts. For the long-term biological version of the same idea, see using lichen as a pollution sensor on your street.

What to Watch For Over the Next 3 Months

• Week 4: They check an air-quality app and ask what the number means rather than just reading the colour. That is the shift from signal to measurement.
• Month 2: The size idea reappears somewhere unexpected: why a mask matters, why smoke smells for days after a fire a long way off, why dust makes some people sneeze and not others. Our explainer on kids, air quality and wildfire smoke is a good place to take those questions.
• Month 3: The follow-up worth encouraging is wanting a real sensor. Low-cost PM2.5 monitors are imperfect but genuinely useful, and comparing one against a government monitor is a strong next project. Several of the projects in our guide to citizen-science environmental monitoring accept that kind of data.

Frequently Asked Questions

Does this measure PM2.5?

No. Fine particles are 2.5 micrometres and smaller and stay airborne for hours to days, so almost none land on a sticky card, and none are visible under a hand lens. The card measures coarse-particle deposition. Use a government monitor for PM2.5.

How long should we leave the cards out?

Forty-eight hours is the sweet spot for a visible difference between sites without overcrowding. In still, damp weather extend to a week. Keep the exposure time identical across all cards or the comparison means nothing.

Can we use tape instead of petroleum jelly?

Yes. Clear packing tape fixed sticky-side-out over a card window works well and is less messy, though it collects slightly fewer particles. Whichever you choose, use the same method on every card.

Why was the kitchen card dirtier than outside?

Because cooking is a significant indoor particle source, along with candles, fireplaces and unvented heaters. The EPA notes indoor PM can exceed outdoor levels in homes with strong sources. Running the extractor fan is the usual fix, and it is testable.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

1. U.S. Environmental Protection Agency. “Particulate Matter (PM) Basics.” https://www.epa.gov/pm-pollution/particulate-matter-pm-basics
2. U.S. Environmental Protection Agency. “Indoor Particulate Matter.” https://www.epa.gov/indoor-air-quality-iaq/indoor-particulate-matter
3. AirNow (U.S. EPA and partners). “Air Quality Index (AQI) Basics.” https://www.airnow.gov/aqi/aqi-basics/
4. Chi, M. T. H., & Wylie, R. (2014). “The ICAP Framework: Linking Cognitive Engagement to Active Learning Outcomes.” Educational Psychologist, 49(4), 219-243. https://doi.org/10.1080/00461520.2014.965823
5. National Research Council. (2012). A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas. National Academies Press. https://doi.org/10.17226/13165
6. White, R., & Gunstone, R. (1992). Probing Understanding. Falmer Press. (Predict-Observe-Explain.)