AP Environmental Science, AP exams, 7–10%

Unit 7: Atmospheric Pollution

Unit 7 covers the sources, chemistry, and control of air pollutants. Photochemical smog, thermal inversions, particulates, indoor air pollutants, and acid deposition are the recurring topics, along with the technologies and regulations used to reduce them. Noise pollution appears here as well.

Position: 7 of 9 units
Published weighting: 7–10% in the official framework
Topics covered: 6 topics in this guide

What is covered

Topics inside this unit.

These topics describe the scope students most often review for this part of AP Environmental Science. Treat them as a study checklist rather than an exhaustive list of what a single exam form can sample.

Introduction to air pollution: Primary and secondary pollutants, their major sources, and the criteria pollutants that are regulated.
Photochemical smog: How nitrogen oxides and volatile organic compounds react in sunlight to form ground-level ozone.
Thermal inversion: The temperature profile that traps pollutants near the surface and the geography that favors it.
Particulates and indoor air pollutants: Sources and health effects of particulate matter, plus radon, asbestos, carbon monoxide, and combustion smoke.
Acid deposition: Sulfur and nitrogen oxide sources, downwind effects on soil and water, and buffering capacity.
Reducing air pollutants: Scrubbers, catalytic converters, electrostatic precipitators, and the regulations that require them.

Study tips

How to practice Atmospheric Pollution.

Section-specific guidance that follows from how this material is usually tested.

Trace each pollutant from source through chemistry to effect to control technology as one linked chain.
Distinguish stratospheric ozone from ground-level ozone explicitly; conflating them is a frequent error.
Attach a specific control technology to each pollutant so solution questions have a concrete answer.

Where this fits

Unit 7: Atmospheric Pollution is 7 of 9 units in the AP Environmental Science guide, and it carries a published weighting of 7–10% in the official framework. Use the full guide to balance it against everything else you have to review.

Back to the AP Environmental Science guide Official exam information

Sample Atmospheric Pollution questions

Practice questions, not yet expert-reviewed

Original practice questions written to the published framework for this section. No expert has reviewed them, and they are not taken from any official exam. Try each one before you open the answer.

Question 1Foundational
Which naturally occurring radioactive gas seeps from uranium-bearing rock into basements and is a leading cause of lung cancer?
1. ARadon
2. BCarbon monoxide
3. CAsbestos
4. DOzone
Show answer
Answer: A. Radon
Radon is a colorless, odorless gas produced by the radioactive decay of uranium in soil and bedrock, and it accumulates in enclosed lower levels of buildings where ventilation is poor. Carbon monoxide is the tempting distractor because it is also an invisible indoor hazard, but it comes from incomplete combustion and kills by binding hemoglobin rather than by radiation. Asbestos is a mineral fiber, not a gas.
Key insight: Radon is an indoor air problem tied to geology, so testing and sub-slab ventilation are the standard fixes.
Question 2Foundational
Which emission control device converts nitrogen oxides, carbon monoxide, and unburned hydrocarbons in vehicle exhaust into less harmful gases?
1. AThe electrostatic precipitator
2. BThe catalytic converter
3. CThe wet scrubber
4. DThe baghouse filter
Show answer
Answer: B. The catalytic converter
A catalytic converter uses metal catalysts to convert nitrogen oxides into nitrogen gas and to oxidize carbon monoxide and hydrocarbons into carbon dioxide and water. Electrostatic precipitators and baghouse filters capture particulate matter, and scrubbers remove sulfur dioxide, so all three belong to smokestacks rather than tailpipes. Requiring catalytic converters also forced the phase-out of leaded gasoline, because lead poisons the catalyst.
Key insight: Match the control device to the pollutant: converters for tailpipe gases, precipitators and filters for particulates, scrubbers for sulfur dioxide.
Question 3Intermediate
Which two classes of pollutants react in the presence of sunlight to produce the ground-level ozone in photochemical smog?
1. ASulfur dioxide and particulate matter
2. BCarbon dioxide and methane
3. CNitrogen oxides and volatile organic compounds
4. DChlorofluorocarbons and water vapor
Show answer
Answer: C. Nitrogen oxides and volatile organic compounds
Nitrogen oxides from combustion and volatile organic compounds from fuels and solvents react under sunlight to build ground-level ozone, which makes ozone a secondary pollutant rather than something emitted directly. Sulfur dioxide and particulates cause different problems, mainly acid deposition and respiratory irritation. This is also why smog peaks on hot, sunny, still afternoons in traffic-heavy cities.
Key insight: Primary pollutants are emitted; secondary pollutants such as ground-level ozone are manufactured in the air.
Question 4Intermediate
What is the name of the condition in which a layer of warm air sits above cooler surface air and traps pollutants near the ground?
1. AA cold front
2. BThe Coriolis effect
3. CAdiabatic cooling
4. DA thermal inversion
Show answer
Answer: D. A thermal inversion
Normally air cools with altitude so warm surface air rises and disperses pollutants, but in an inversion the warm layer above acts as a lid and the cool surface air cannot rise. Pollutants therefore accumulate until the inversion breaks, which is why valley cities surrounded by mountains suffer severe smog episodes. Adiabatic cooling describes the temperature drop of rising air rather than the trapping layer itself.
Key insight: An inversion reverses the normal temperature profile, and that reversal is what stops vertical mixing.
Question 5Advanced
Two lakes receive the same amount of acid deposition, but the lake in a granite watershed acidifies while the lake in a limestone watershed does not. What explains the difference?
1. ALimestone neutralizes incoming acid, giving that lake greater buffering capacity
2. BGranite dissolves in acid much faster than limestone does
3. CThe granite watershed is exposed to more sulfur dioxide emissions
4. DLimestone releases sulfate ions that raise the acidity of runoff
Show answer
Answer: A. Limestone neutralizes incoming acid, giving that lake greater buffering capacity
Limestone is calcium carbonate, which reacts with and consumes hydrogen ions, so the lake's pH barely moves even as acid keeps arriving. Granite is composed of slow-weathering silicate minerals that supply almost no neutralizing capacity, leaving that lake defenseless. Buffering capacity, not the amount of deposition, is what determines which lakes acidify first in the same region.
Key insight: Identical acid inputs give different outcomes because the surrounding bedrock decides how much acid the water can absorb.

Continue through AP Environmental Science

Practice Atmospheric Pollution deliberately.

Create your Arcade Academy workspace to turn this topic list into spaced-repetition reviews, linked notes, and progress you can act on.

Create your account

Unit 7: Atmospheric Pollution