AP Environmental Science Unit 7 practice questions
Try 10 multiple-choice questions from Unit 7 here. Pick an answer to see why it's right or wrong, then take the timed test above for a full AP-style set.
Question 1
NOx and VOCs react in sunlight to form ground-level ozone in urban areas. Why is ozone considered a secondary pollutant rather than a primary pollutant?
It forms in the atmosphere from NOx and VOCs under sunlight.
Its toxicity does not determine whether it is primary or secondary.
Requiring multiple precursors does not by itself make it secondary.
Atmospheric lifetime alone does not define a pollutant as primary or secondary.
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Answer: (A)
Ozone forms in the atmosphere when emitted NOx and VOCs react under sunlight. Secondary pollutants are defined by formation through atmospheric chemical reactions rather than direct emission.
Question 2
A coal plant emits carbon dioxide, sulfur dioxide, mercury, and particulate matter. Nitrogen oxides react in the atmosphere to form nitric acid. Which statement best explains how these pollutants differently affect air quality?
Carbon dioxide, sulfur dioxide, mercury, and particulates are primary and nitric acid is secondary.
Sulfur dioxide, particulate matter, and nitric acid are secondary because they visibly degrade air quality.
All five are primary pollutants because they are directly emitted from the same source.
Sulfur dioxide and mercury are primary while the others are secondary due to persistence.
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Answer: (A)
Primary pollutants are emitted directly while secondary pollutants form by atmospheric chemistry. Nitric acid results from NOx reacting in the atmosphere, so it is secondary while the others are emitted directly.
Question 3
Diesel combustion emits sulfur dioxide near highways, yet sulfuric acid often peaks 50–100 kilometers downwind. Which best explains this pattern?
SO2 is emitted directly at the source while sulfuric acid forms downwind
SO2 disperses faster because it is more volatile than sulfuric acid
SO2 deposits to soil and vegetation near roads while sulfuric acid forms downwind
SO2 comes from diesel combustion near roads while sulfuric acid is not directly emitted
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Answer: (A)
SO2 is a primary pollutant released at the emission source. Sulfuric acid is a secondary pollutant produced by atmospheric oxidation of SO2 during transport, so concentrations peak downwind.
Question 4
The Clean Air Act and its amendments sharply reduced atmospheric lead in the United States after regulations removed lead from gasoline in the 1970s. Lead is still emitted by some industries and by natural weathering. Why did atmospheric lead concentrations drop so dramatically despite continued non-fuel sources?
Gasoline emitted most atmospheric lead, so removing it cut total concentrations.
Industrial and natural lead are less toxic, so they contributed less previously.
The Clean Air Act eliminated industrial or natural lead sources completely.
Atmospheric chemistry converted gasoline lead into harmless compounds, improving air quality.
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Answer: (A)
Removing leaded gasoline eliminated the largest source of airborne lead. Remaining industrial and natural sources were minor, so total atmospheric concentrations dropped over 90 percent.
Question 5
Particulate matter from combustion and industrial sources ranges from 0.1 to 100 micrometers. Larger particles (PM10) settle out within days, while smaller particles (PM2.5) can remain suspended for weeks or months. Why does PM2.5 pose a greater air quality concern than PM10 despite lower emission amounts?
PM2.5 remains suspended longer and reaches deep into the lungs.
PM2.5 is more toxic because it contains more hazardous chemicals.
PM2.5 is emitted in larger quantities than PM10 so it accumulates.
PM2.5 is lighter so stays aloft but poses equal health risk as PM10.
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Answer: (A)
PM2.5 has longer atmospheric residence and deposits in the alveoli, increasing exposure and health risk. Its small size allows long-range transport so lower emissions can still produce harmful concentrations.
Question 6
A coal-fired power plant burns sulfur-containing coal to generate electricity. Which of the following best describes how sulfur dioxide released from this plant can lead to acid rain formation?
Sulfur dioxide reacts with water vapor in the atmosphere to form sulfuric acid, which falls as precipitation
Sulfur dioxide directly dissolves in rainwater without undergoing chemical transformation
Sulfur dioxide combines with nitrogen oxides to form a compound that acidifies precipitation
Sulfur dioxide is absorbed by plants and converted to sulfuric acid in soil, which then contaminates groundwater
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Answer: (A)
Recognizing the chemical transformation from primary to secondary pollutant requires understanding the multi-step process. Sulfur dioxide undergoes oxidation and hydration in the atmosphere, converting to sulfuric acid—a secondary pollutant that precipitates as acid rain. This demonstrates the distinction between primary pollutants (directly emitted) and secondary pollutants (formed through atmospheric reactions).
Question 7
Lead was historically added to gasoline as an anti-knock additive in vehicles. After the Clean Air Act regulations restricted lead in fuels, atmospheric lead concentrations decreased dramatically. Which of the following best explains why regulating the lead content in gasoline was an effective approach to reducing atmospheric lead pollution?
Lead in gasoline was a major source of atmospheric lead emissions, so reducing its use directly decreased the primary source of lead entering the atmosphere
Lead in gasoline was a major source of atmospheric lead emissions, but lead particles persist in the atmosphere for decades, so concentrations decreased slowly rather than dramatically
Lead in gasoline contaminated soil and water when deposited, and reducing gasoline lead prevented these contaminated surfaces from re-releasing lead into the atmosphere
Lead in gasoline was one source of atmospheric lead, but emissions from lead-based paint and industrial sources compensated for the reduction in gasoline lead
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Answer: (A)
Effective pollution control requires identifying and reducing major emission sources. Lead in gasoline was directly combusted in vehicle engines, making it a significant primary source of atmospheric lead. Regulating this source eliminated a major pathway for lead to enter the atmosphere. This demonstrates the principle that controlling primary pollutant sources at their origin is an effective regulatory strategy.
Question 8
A factory near a residential area emits sulfur dioxide, nitrogen oxides, and volatile organic compounds. Residents report that air quality problems are worse on days when the air is stagnant and atmospheric mixing is minimal. Which of the following best explains why atmospheric stagnation exacerbates air quality problems from these emissions?
Stagnant air prevents pollutants from dispersing and diluting, allowing concentrations to accumulate near the emission source
Stagnant air causes the factory to emit more pollutants because equipment operates less efficiently in calm conditions
Stagnant air prevents photochemical reactions from occurring, allowing primary pollutants to accumulate without forming secondary pollutants
Stagnant air causes pollutants to settle rapidly to the ground, removing them from the breathing zone where residents are exposed
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Answer: (A)
Understanding how atmospheric conditions affect pollutant concentrations requires recognizing the role of air movement in dispersal. When atmospheric mixing is minimal, pollutants remain concentrated near their source rather than being transported and diluted over a larger area. This demonstrates how meteorological factors influence the effects of primary pollutant emissions, independent of the amount of pollution being released.
Question 9
An oil refinery releases volatile organic compounds (VOCs) and nitrogen oxides into the atmosphere. In a nearby urban area downwind of the refinery, ground-level ozone concentrations increase significantly on sunny days. Which of the following best describes the relationship between the refinery's emissions and the ozone formation observed in the urban area?
Volatile organic compounds and nitrogen oxides from the refinery are transported downwind where they react with sunlight to form ground-level ozone as a secondary pollutant
The refinery directly emits ground-level ozone, which is then concentrated in the urban area by atmospheric circulation patterns
Volatile organic compounds from the refinery react with atmospheric oxygen to form ozone, while nitrogen oxides are transported away without participating in reactions
The refinery's emissions cause ozone depletion in the stratosphere, which increases ground-level ultraviolet radiation and creates secondary ozone through photochemical reactions
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Answer: (A)
Connecting primary pollutant sources to secondary pollutant formation requires understanding atmospheric transport and photochemical reactions. VOCs and nitrogen oxides are primary pollutants emitted by the refinery; when transported downwind and exposed to sunlight, they undergo photochemical reactions to form ground-level ozone. This demonstrates how primary pollutants can be transformed into secondary pollutants through atmospheric processes, and how pollution sources affect areas beyond their immediate vicinity.
Question 10
A diesel truck emits particulate matter and nitrogen oxides directly. Which statement best describes their pollutant classification and atmospheric behavior?
Particulate matter is emitted as particles, while nitrogen oxides form secondary pollutants.
Particulate matter is a secondary product of nitrogen oxides, while nitrogen oxides are primary.
Both particulate matter and nitrogen oxides are secondary pollutants formed in the atmosphere.
Particulate matter settles faster, while nitrogen oxides are long-lived secondary pollutants.
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Answer: (A)
Particulate matter is released as particles and largely remains in that form. Nitrogen oxides are emitted directly but react in the atmosphere to produce secondary pollutants such as nitric acid and ozone precursors.
What's on the AP Environmental Science Unit 7 practice test
The standard version takes about 70 minutes and follows the timing and directions of the AP exam, sized to one unit:
- 20 Multiple Choice Questions (23 minutes)
- 1 FRQ – FRQ 1 – Design an Investigation (23 minutes)
- 1 FRQ – FRQ 2 – Analyze and Interpret Quantitative Data (23 minutes)
Questions are drawn from 2403 multiple-choice questions and 50 FRQs written for Unit 7, Atmospheric Pollution.
Practice AP Environmental Science Unit 7 FRQs
Answer the unit's free-response questions one at a time and get a score on every part.
- FRQ 1 – Design an Investigation (13 questions)
- FRQ 2 – Analyze and Interpret Quantitative Data (18 questions)
- FRQ 3 – Analyze an Environmental Problem Doing Calculations (19 questions)
Review Unit 7 before you start
- 7.1 Introduction to Air Pollution
- 7.2 Photochemical Smog
- 7.3 Thermal Inversion
- 7.4 Atmospheric CO2 and Particulates
- 7.5 Indoor Air Pollutants
- 7.6 Reduction of Air Pollutants
- 7.7 Acid Rain
- 7.8 Noise Pollution