• 54 questions

APES Unit 7 Study Guide

Unofficial study guide for APES Unit 7, Atmospheric Pollution: the eight topics, with practice questions on each.

See all 54 with answers
Which set of air pollutants does the course description list for coal combustion?

Pick an answer, then press Check answer. Then you see Correct or Not quite, with the reason. Keys: A to D pick, Enter checks.

Print covers the next 25 questions. Share this set copies a link to the same questions in the same order.

More options

Unofficial practice questions, not affiliated with the College Board. Bank checked October 14, 2026.

Next step Next unit: APES Unit 8 practice testAll nine units: APES practice test

All 54 questions with answers

Topic 7.1: Introduction to air pollution 7

  • Besides nitrogen oxides, which pollutants does fossil fuel combustion produce, by the course description? Answer: Carbon monoxide, hydrocarbons and particulate matter. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.1, essential knowledge STB-2.A.2
  • The Clean Air Act requires the EPA to set national air quality standards for six commonly found pollutants. What are these pollutants called? Answer: Criteria air pollutants. Source: U.S. Environmental Protection Agency, "Criteria Air Pollutants"; course topic 7.1
  • How does a secondary air pollutant differ from a primary one? Answer: It is not emitted directly; it forms in the air. Source: Wikipedia, "Air pollution"; course topic 7.1; U.S. Environmental Protection Agency, "Ground-level Ozone Basics"
  • In the atmosphere, the nitrogen oxides from burning fossil fuels convert to which acid? Answer: Nitric acid. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.1, essential knowledge STB-2.A.2
  • On the Air Quality Index, values at or below which number are generally thought of as satisfactory? Answer: 100. Source: AirNow (U.S. Environmental Protection Agency and partner agencies), "AQI Basics"; course topic 7.1
  • Which pollutant fell dramatically in the atmosphere after the EPA regulated its use in fuels under the Clean Air Act? Answer: Lead. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.1, essential knowledge STB-2.A.4; U.S. Environmental Protection Agency, "Basic Information about Lead Air Pollution"
  • Which set of air pollutants does the course description list for coal combustion? Answer: Carbon dioxide, sulfur dioxide, toxic metals and particulates. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.1, essential knowledge STB-2.A.1
Show all 54 questions (47 more)

Topic 7.2: Photochemical smog 9

  • A city wants less photochemical smog. Emissions of which two kinds of pollutant must it reduce? Answer: Nitrogen oxides and VOCs. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.2, essential knowledge STB-2.B.6
  • At what time of day do ozone concentrations in photochemical smog peak? Answer: In the afternoon. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.2, essential knowledge STB-2.B.3
  • In which season are ozone concentrations in photochemical smog higher? Answer: Summer. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.2, essential knowledge STB-2.B.3; U.S. Environmental Protection Agency, "Ground-level Ozone Basics"
  • What makes photochemical smog "photochemical"? Answer: Sunlight drives the reactions that form it. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.2, essential knowledge STB-2.B.1
  • What property do volatile organic compounds (VOCs) such as formaldehyde and gasoline share? Answer: They evaporate or sublimate at room temperature. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.2, essential knowledge STB-2.B.4; U.S. Environmental Protection Agency, "Volatile Organic Compounds' Impact on Indoor Air Quality"
  • Which health effects of photochemical smog does the course description name? Answer: Respiratory problems and eye irritation. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.2, essential knowledge STB-2.B.7
  • Which is a natural source of volatile organic compounds? Answer: Trees. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.2, essential knowledge STB-2.B.4; Wikipedia, "Volatile organic compound"
  • Why does photochemical smog often form in urban areas? Answer: They have large numbers of motor vehicles. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.2, essential knowledge STB-2.B.5
  • The word "smog" was coined in the early 20th century from which two words? Answer: Smoke and fog. Source: Wikipedia, "Smog"; course topic 7.2

Topic 7.3: Thermal inversion 4

  • How does air temperature normally change with altitude in the lower atmosphere, and what happens in a thermal inversion? Answer: It normally falls with height; in an inversion the surface air is cooler than the air above. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.3, essential knowledge STB-2.C.1
  • In which kind of place is the build-up of pollutants under an inversion often more pronounced? Answer: Valleys, basins and areas surrounded by mountains. Source: Wikipedia, "Inversion (meteorology)"; course topic 7.3
  • Which pollutants does the course description say a thermal inversion especially traps close to the ground? Answer: Smog and particulates. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.3, essential knowledge STB-2.C.2
  • Why do pollutants build up under a temperature inversion? Answer: The inversion inhibits vertical mixing of surface air with the air above. Source: Wikipedia, "Inversion (meteorology)"; course topic 7.3

Topic 7.4: Atmospheric CO2 and particulates 5

  • The course description names three natural sources of carbon dioxide in the atmosphere. Which set is it? Answer: Respiration, decomposition and volcanic eruptions. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.4, essential knowledge STB-2.D.1
  • The EPA describes particulate matter as a mixture of what? Answer: Solid particles and liquid droplets found in the air. Source: U.S. Environmental Protection Agency, "Particulate Matter (PM) Basics"; course topic 7.4
  • Fine particles are the main cause of which air quality problem in parts of the United States, including many national parks? Answer: Reduced visibility, or haze. Source: U.S. Environmental Protection Agency, "Particulate Matter (PM) Basics"; course topic 7.4
  • What does the 2.5 in PM2.5 refer to? Answer: Particle diameters of 2.5 micrometers and smaller. Source: U.S. Environmental Protection Agency, "Particulate Matter (PM) Basics"; course topic 7.4
  • Which of these is a natural source of particulate matter? Answer: Sea spray. Source: Wikipedia, "Particulate matter"; course topic 7.4

Topic 7.5: Indoor air pollutants 9

  • By the EPA's estimate, radon is responsible for about how many lung cancer deaths every year in the United States? Answer: About 21,000. Source: U.S. Environmental Protection Agency, "Health Risk of Radon"; course topic 7.5
  • Carbon monoxide is classified as which kind of indoor air pollutant? Answer: An asphyxiant. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.5, essential knowledge STB-2.E.1; U.S. Environmental Protection Agency, "Carbon Monoxide's Impact on Indoor Air Quality"
  • Formaldehyde in indoor air comes from which sources, by the course description? Answer: Building materials, furniture, upholstery and carpeting. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.5, essential knowledge STB-2.E.5
  • How does radon gas most often get into a home? Answer: It moves up through the soil and enters through the basement or cracks in the foundation. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.5, essential knowledge STB-2.F.1
  • Radon-222 is produced by the decay of which element found in some rocks and soils? Answer: Uranium. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.5, essential knowledge STB-2.E.7; Wikipedia, "Radon"
  • Which indoor air pollutants does the course description classify as particulates? Answer: Asbestos, dust and smoke. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.5, essential knowledge STB-2.E.2
  • Which set lists common combustion air pollutants found indoors? Answer: Carbon monoxide, nitrogen oxides, sulfur dioxide, particulates and tobacco smoke. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.5, essential knowledge STB-2.E.6
  • Which set lists common indoor air pollutants from natural sources? Answer: Radon, mold and dust. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.5, essential knowledge STB-2.E.4
  • Why can people not detect carbon monoxide in a room by themselves? Answer: It is odorless and colorless. Source: U.S. Environmental Protection Agency, "Carbon Monoxide's Impact on Indoor Air Quality"; course topic 7.5

Topic 7.6: Reduction of air pollutants 7

  • How does an electrostatic precipitator clean the gas flowing through it? Answer: It removes fine particles with an induced electrostatic charge. Source: Wikipedia, "Electrostatic precipitator"; course topic 7.6
  • Most gasoline-powered vehicles in the United States have carried catalytic converters starting with which model year? Answer: 1975. Source: Wikipedia, "Catalytic converter"; course topic 7.6
  • What do wet and dry scrubbers remove? Answer: Particulates and gases from industrial exhaust streams. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.6, essential knowledge STB-2.G.4
  • What does a vapor recovery nozzle do? Answer: It keeps fumes from escaping at a gasoline pump during fueling. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.6, essential knowledge STB-2.G.2
  • Which three exhaust pollutants does a catalytic converter act on? Answer: Carbon monoxide, nitrogen oxides and hydrocarbons. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.6, essential knowledge STB-2.G.3
  • Which three kinds of method does the course description list for reducing air pollutants at the source? Answer: Regulatory practices, conservation practices and alternative fuels. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.6, essential knowledge STB-2.G.1
  • Which two devices does the course description name for reducing air pollution from coal-burning power plants? Answer: Scrubbers and electrostatic precipitators. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.6, essential knowledge STB-2.G.5

Topic 7.7: Acid rain 8

  • Acid deposition is due to oxides of which two elements in the atmosphere? Answer: Nitrogen and sulfur. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.7, essential knowledge STB-2.H.1
  • The course description names two sources for the nitrogen oxides behind acid deposition and one for the sulfur dioxide. Which source is named for the nitrogen oxides only? Answer: Motor vehicles. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.7, essential knowledge STB-2.H.2
  • In what the EPA calls wet deposition, how do sulfuric and nitric acids reach the ground? Answer: Mixed with rain, snow, fog or hail. Source: U.S. Environmental Protection Agency, "What is Acid Rain?"; course topic 7.7
  • Normal rain has a pH of about 5.6. What pH does acid rain usually have, by the EPA? Answer: Between 4.2 and 4.4. Source: U.S. Environmental Protection Agency, "What is Acid Rain?"; course topic 7.7
  • Two lakes receive the same acid rain. One sits on limestone bedrock and one on granite. What does the course description say about the lake on limestone? Answer: The limestone can neutralize the effect of the acid rain. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.7, essential knowledge STB-2.I.3
  • Which communities does acid deposition mainly affect? Answer: Those downwind from coal-burning power plants. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.7, essential knowledge STB-2.I.1; U.S. Environmental Protection Agency, "What is Acid Rain?"
  • Which effects of acid rain and deposition does the course description list? Answer: Acidification of soils and bodies of water, and corrosion of human-made structures. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.7, essential knowledge STB-2.I.2; U.S. Environmental Protection Agency, "Effects of Acid Rain"
  • Why is even normal, unpolluted rain slightly acidic? Answer: Carbon dioxide dissolves in it and forms weak carbonic acid. Source: U.S. Environmental Protection Agency, "What is Acid Rain?"; course topic 7.7

Topic 7.8: Noise pollution 5

  • How does the course description define noise pollution? Answer: Sound at levels high enough to cause physiological stress and hearing loss. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.8, essential knowledge STB-2.J.1; U.S. Environmental Protection Agency, "Clean Air Act Title IV - Noise Pollution"
  • In 1981 the federal government concluded that noise issues in the United States were best handled at which level? Answer: The state and local level. Source: U.S. Environmental Protection Agency, "Clean Air Act Title IV - Noise Pollution"; course topic 7.8
  • Which effect of noise pollution on animals does the course description list? Answer: Masking of the sounds they use to communicate or hunt. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.8, essential knowledge STB-2.J.3
  • Which sources of noise pollution in urban areas does the course description list? Answer: Transportation, construction, and domestic and industrial activity. Source: College Board, AP Environmental Science Course and Exam Description, topic 7.8, essential knowledge STB-2.J.2
  • Why are whales and dolphins particularly vulnerable to ship noise and sonar? Answer: They rely on sound for echolocation. Source: Wikipedia, "Noise pollution"; course topic 7.8

How this list was compiled: Our own questions, written to Unit 7 (Atmospheric Pollution, topics 7.1 to 7.8) of the College Board's AP Environmental Science Course and Exam Description, effective fall 2026, https://apcentral.collegeboard.org/media/pdf/ap-environmental-science-course-and-exam-description.pdf, read 2026-10-14. Each fact was read on 2026-10-14 in the public page named under its question: an essential knowledge statement of the course description; a page of the U.S. Environmental Protection Agency or of AirNow; or a Wikipedia article. Licence: Own work.

How it works

This APES Unit 7 study guide sets out the eight topics of Atmospheric Pollution and tests each with practice questions, 54 of our own in all. It is unofficial and not affiliated with the College Board, which owns AP.

Read the full guide

The eight topics of Unit 7

7.1 Air pollution: what coal and other fossil fuels release, lead, primary and secondary pollutants. 7.2 Photochemical smog: nitrogen oxides and VOCs in sunlight, with ozone peaking in the afternoon. 7.3 Thermal inversion: cool surface air capped by warmer air. 7.4 Natural sources of CO2 and particulates. 7.5 Indoor air: carbon monoxide, radon, asbestos, formaldehyde. 7.6 Controls: catalytic converters, scrubbers, electrostatic precipitators, vapor recovery nozzles. 7.7 Acid rain: nitrogen and sulfur oxides, and limestone that neutralizes. 7.8 Noise pollution.

Where the answers come from

Each question cites the College Board's course description (effective fall 2026, read October 14, 2026), a page of the Environmental Protection Agency or AirNow, or a Wikipedia article.

  • Sort every pollutant three ways: primary or secondary, indoor or outdoor, natural or human-made.
  • Match each control to its target: catalytic converter for engine exhaust, scrubber and precipitator for smokestacks, vapor recovery for gasoline pumps.
  • Ozone is harmful at ground level and protective in the stratosphere. Unit 7 is about the ground.

Questions and answers

What is Unit 7 in APES?

Atmospheric Pollution. Its eight topics are an introduction to air pollution, photochemical smog, thermal inversion, atmospheric CO2 and particulates, indoor air pollutants, reduction of air pollutants, acid rain and noise pollution.

How long is Unit 7 of AP Environmental Science?

About 11 to 12 class periods, by the course description. Its Progress Check, assigned by teachers in AP Classroom, has about 20 multiple-choice questions and one free-response question on designing an investigation.

How much of the AP Environmental Science exam is Unit 7?

Atmospheric Pollution carries 7 to 10% of the multiple-choice section, which has 80 questions and counts for 60% of the exam score, by the College Board's course and exam pages.

Are these the College Board's Unit 7 questions?

No. The College Board keeps its questions in AP Classroom and on its exams. The 54 here were written for this page from the unit's published topics and the public pages named under each answer.

More tests

Show 8 more

Browse Civics and Law