U7 FRQ Practice
Master Unit 7 air-pollution FRQs on the AP Environmental Science exam with strategy, worked examples, calculation tips, and sample free-response questions.
What you'll do in this lesson
A voice-first session with the Crimsora tutor on U7 FRQ Practice, then targeted practice and FRQs — with the tutor adapting to where you get stuck.
What this lesson covers
Unit 7 covers air pollution, and the AP Environmental Science exam loves to test it with free-response questions (FRQs) that mix identification, explanation, calculation, and proposed solutions. This lesson does not re-teach smog, acid rain, or mitigation — you already know those mechanisms. Instead, it trains you to convert that knowledge into points.
FRQs reward precise verbs, clear reasoning, and correct units. Here you will learn how to decode command words, structure each answer, avoid the mistakes that cost easy points, and handle the math that shows up in air-quality prompts. By the end you should be able to attack any Unit 7 FRQ with a repeatable method.
FRQs reward precise verbs, clear reasoning, and correct units. Here you will learn how to decode command words, structure each answer, avoid the mistakes that cost easy points, and handle the math that shows up in air-quality prompts. By the end you should be able to attack any Unit 7 FRQ with a repeatable method.
How Unit 7 FRQs Are Structured
AP Environmental Science includes three FRQs worth 10 points each: one design-an-investigation question, one analyze-an-environmental-problem-and-propose-a-solution question, and one document-based question. Air-pollution content can appear in any of them, but it most often shows up in the analyze-and-propose format because pollution has clear causes, effects, and solutions.
Each FRQ has multiple parts, usually labeled (a) through (e) or with subparts like (b)(i). Every subpart is scored independently, so a wrong answer early does not sink the rest. Read all parts before writing — later parts sometimes hint at what earlier parts expect.
The command word tells you what earns the point. Here is how the common verbs differ:
Match your effort to the verb. Writing a paragraph for an "identify" wastes time; writing one word for an "explain" loses points.
Each FRQ has multiple parts, usually labeled (a) through (e) or with subparts like (b)(i). Every subpart is scored independently, so a wrong answer early does not sink the rest. Read all parts before writing — later parts sometimes hint at what earlier parts expect.
The command word tells you what earns the point. Here is how the common verbs differ:
| Command word | What earns the point |
|---|---|
| Identify / State | A correct term or fact, no explanation needed |
| Describe | A detailed account of a feature or process |
| Explain | A cause-and-effect chain with reasoning |
| Calculate | The setup, work, and a final answer with units |
| Propose / Justify | A specific solution plus why it works |
Attacking Explain and Describe Prompts
Most Unit 7 points come from explaining pollution processes. The single most common mistake is stopping halfway through the causal chain. An "explain" answer must connect a cause to an effect with a mechanism in between.
Consider a prompt asking you to explain how a thermal inversion worsens photochemical smog. A weak answer says "the inversion traps pollutants." A full-credit answer traces the chain: a layer of warm air sits above cooler surface air, so the normal upward mixing of air is prevented, which traps primary pollutants like and VOCs near the ground, allowing sunlight to drive their reaction into ozone and other smog components that accumulate to harmful levels.
Use this template for explain answers: name the cause, state the mechanism, and end with the specific consequence. For describe answers, add concrete, observable detail rather than reasoning.
A second frequent error is vagueness. "Pollution hurts people" earns nothing; "ground-level ozone inflames lung tissue and reduces respiratory function in asthmatics" earns the point. Always name the specific pollutant, the specific effect, and the specific receptor (human health, crops, buildings, aquatic life). Precision is the difference between a blank score and a full one.
Consider a prompt asking you to explain how a thermal inversion worsens photochemical smog. A weak answer says "the inversion traps pollutants." A full-credit answer traces the chain: a layer of warm air sits above cooler surface air, so the normal upward mixing of air is prevented, which traps primary pollutants like and VOCs near the ground, allowing sunlight to drive their reaction into ozone and other smog components that accumulate to harmful levels.
Use this template for explain answers: name the cause, state the mechanism, and end with the specific consequence. For describe answers, add concrete, observable detail rather than reasoning.
A second frequent error is vagueness. "Pollution hurts people" earns nothing; "ground-level ozone inflames lung tissue and reduces respiratory function in asthmatics" earns the point. Always name the specific pollutant, the specific effect, and the specific receptor (human health, crops, buildings, aquatic life). Precision is the difference between a blank score and a full one.
Handling Calculation Parts
Air-quality FRQs frequently include a calculation worth two to three points. These reward showing work even when the final number is wrong, so never skip the setup.
Common calculation types include dimensional analysis (converting emission rates and units), percent change in pollutant concentration after a mitigation measure, and using given rate data over time. Always write the equation, substitute numbers with units, and box a final answer that carries the correct unit.
A useful relation for percent reduction is . Watch for scientific notation and metric prefixes; a factor-of-1000 slip is the most common lost point. If a question gives more data than you need, that is intentional — identify the relevant values before computing.
Common calculation types include dimensional analysis (converting emission rates and units), percent change in pollutant concentration after a mitigation measure, and using given rate data over time. Always write the equation, substitute numbers with units, and box a final answer that carries the correct unit.
| Step | Why it matters |
|---|---|
| Write the formula | Shows the grader your method; often worth a point alone |
| Substitute with units | Prevents unit errors and earns setup credit |
| Cancel units carefully | Confirms the answer's unit is correct |
| State final answer with unit | The answer point requires a unit |
Proposing and Justifying Solutions
The final parts of an analyze-and-propose FRQ ask you to suggest a mitigation strategy and justify it. Two points are typically available: one for a specific, feasible solution and one for correct reasoning about why it reduces the pollutant or its impact.
Generic answers like "reduce pollution" or "use less energy" fail. Instead name a mechanism: install catalytic converters to chemically convert and CO into , , and water; require scrubbers on smokestacks to remove before it forms acid rain; expand public transit to cut the number of combustion-engine vehicles emitting primary pollutants.
Your justification must link the solution back to the problem in the prompt. If the FRQ is about acid rain damaging a lake, propose scrubbers or switching to low-sulfur fuel AND explain that reducing emissions lowers the formation of sulfuric acid in precipitation, raising the lake's pH toward tolerable levels for aquatic organisms.
When a part asks for an environmental OR economic drawback of your solution, give a real trade-off: scrubbers are expensive to install and produce sludge that requires disposal. Balancing benefit and cost signals the analytical thinking graders reward.
Generic answers like "reduce pollution" or "use less energy" fail. Instead name a mechanism: install catalytic converters to chemically convert and CO into , , and water; require scrubbers on smokestacks to remove before it forms acid rain; expand public transit to cut the number of combustion-engine vehicles emitting primary pollutants.
Your justification must link the solution back to the problem in the prompt. If the FRQ is about acid rain damaging a lake, propose scrubbers or switching to low-sulfur fuel AND explain that reducing emissions lowers the formation of sulfuric acid in precipitation, raising the lake's pH toward tolerable levels for aquatic organisms.
When a part asks for an environmental OR economic drawback of your solution, give a real trade-off: scrubbers are expensive to install and produce sludge that requires disposal. Balancing benefit and cost signals the analytical thinking graders reward.
Time Management and Point-Maximizing Habits
You have roughly 22 minutes per FRQ. Budget time by point value, not by how much you know. A part worth one point should not consume five minutes.
Label every answer with its exact part letter and number. Graders look for (a), (b)(i), and so on; unlabeled prose is easy to miss. Answer in the same order the question asks.
Do not restate the question — it earns nothing and wastes time. Start directly with your answer. When a part says "identify TWO," give exactly two clearly separated responses; if you list four and two are wrong, some rubrics grade only the first two.
Finally, use correct Unit 7 vocabulary: primary versus secondary pollutant, , VOCs, tropospheric versus stratospheric ozone, thermal inversion, and the AQI. Using the right term often IS the point. Leave nothing blank — an educated guess on an identify part costs nothing and may score.
Label every answer with its exact part letter and number. Graders look for (a), (b)(i), and so on; unlabeled prose is easy to miss. Answer in the same order the question asks.
Do not restate the question — it earns nothing and wastes time. Start directly with your answer. When a part says "identify TWO," give exactly two clearly separated responses; if you list four and two are wrong, some rubrics grade only the first two.
Finally, use correct Unit 7 vocabulary: primary versus secondary pollutant, , VOCs, tropospheric versus stratospheric ozone, thermal inversion, and the AQI. Using the right term often IS the point. Leave nothing blank — an educated guess on an identify part costs nothing and may score.
Key terms
- Command word.
- The action verb in an FRQ (identify, describe, explain, calculate, propose) that dictates how much reasoning an answer must contain to earn credit.
- Primary pollutant.
- A pollutant emitted directly into the air from a source, such as , CO, or from combustion.
- Secondary pollutant.
- A pollutant formed by reactions in the atmosphere, such as ground-level ozone produced when and VOCs react in sunlight.
- Thermal inversion.
- A condition where a warm air layer sits above cooler surface air, preventing vertical mixing and trapping pollutants near the ground.
- Scrubber.
- A device on smokestacks that removes pollutants like from exhaust gases before they are released, reducing acid rain formation.
- Catalytic converter.
- A vehicle emission-control device that chemically converts , CO, and unburned hydrocarbons into less harmful gases.
- Percent change.
- A calculation of relative change given by , common in mitigation-effectiveness FRQ parts.
- AQI.
- The Air Quality Index, a scale that reports daily air pollution levels and associated health risks to the public.
Worked example
A metropolitan area in a valley experiences frequent winter smog episodes. A coal-burning power plant and heavy vehicle traffic are the main pollution sources. (a) Identify one primary pollutant emitted by the vehicles. (b) Explain how a thermal inversion contributes to smog buildup in the valley. (c) The plant emits 8,000 kg of per day. After installing a scrubber that removes 90% of , calculate the new daily emission. (d) Propose one additional strategy to reduce vehicle-related pollution and justify how it works.
Part (a) asks only to identify, so give one term: nitrogen oxides () are emitted directly from vehicle combustion. Carbon monoxide would also earn the point. No explanation is needed.
Part (b) requires a full causal chain. State the mechanism: during an inversion a layer of warm air settles over the cooler valley air, and because warm air is less dense it stays on top, preventing the cooler polluted surface air from rising and dispersing. The primary pollutants from traffic and the plant are therefore trapped near the ground, where sunlight drives them into secondary pollutants, and concentrations climb to unhealthy levels. Notice how cause, mechanism, and consequence are all present.
Part (c) is a calculation. Set up: removed amount kg. Remaining emission kg per day. Alternatively, new emission kg per day. Always show the setup and keep the unit: the answer is 800 kg of per day.
Part (d) needs a specific solution plus justification: expand public transit such as buses or light rail. Justification: this reduces the number of individual combustion-engine vehicles on the road, lowering direct emissions of and VOCs, which are the precursors to photochemical smog, thereby cutting secondary pollutant formation.
Part (b) requires a full causal chain. State the mechanism: during an inversion a layer of warm air settles over the cooler valley air, and because warm air is less dense it stays on top, preventing the cooler polluted surface air from rising and dispersing. The primary pollutants from traffic and the plant are therefore trapped near the ground, where sunlight drives them into secondary pollutants, and concentrations climb to unhealthy levels. Notice how cause, mechanism, and consequence are all present.
Part (c) is a calculation. Set up: removed amount kg. Remaining emission kg per day. Alternatively, new emission kg per day. Always show the setup and keep the unit: the answer is 800 kg of per day.
Part (d) needs a specific solution plus justification: expand public transit such as buses or light rail. Justification: this reduces the number of individual combustion-engine vehicles on the road, lowering direct emissions of and VOCs, which are the precursors to photochemical smog, thereby cutting secondary pollutant formation.
Practice questions
An FRQ part states: "Explain how sulfur dioxide emissions lead to the acidification of a downwind lake." Which response would earn full credit?
- Sulfur dioxide is bad for the environment and lowers lake pH.
- released from combustion reacts with water and oxygen in the atmosphere to form sulfuric acid, which falls as acid precipitation and lowers the lake's pH, harming aquatic life.
- Acid rain is caused by pollution from factories.
- Lakes become acidic when it rains a lot near power plants.
Answer: released from combustion reacts with water and oxygen in the atmosphere to form sulfuric acid, which falls as acid precipitation and lowers the lake's pH, harming aquatic life.
An explain prompt requires a complete cause-and-effect chain. Only this choice names the pollutant, the atmospheric reaction forming sulfuric acid, the deposition as acid precipitation, and the consequence of lowered pH. The other options are vague, restate the phenomenon, or omit the mechanism, so they would not earn the reasoning point.
A factory emits 5,000 kg of particulate matter per day. A new filter reduces emissions by 75%. Calculate the new daily emission and show your work.
Answer: 1,250 kg per day.
Removed amount is kg. New emission is kg per day, or directly kg per day. Show the setup and include the unit; on the exam the setup and the final answer with correct units are scored separately, so writing the equation protects partial credit even if the arithmetic slips.
A prompt asks you to propose ONE strategy to reduce ground-level ozone in a smoggy city and justify it. Write a full-credit response.
Answer: Require catalytic converters on all vehicles, because they convert and unburned hydrocarbons into less reactive gases, reducing the precursor pollutants that react in sunlight to form ground-level ozone.
A propose-and-justify part needs a specific, feasible strategy plus reasoning that links it to the pollutant in the prompt. This answer names a concrete technology and explains the mechanism: fewer and VOC precursors means less secondary ozone formation. A vague answer like 'drive less' without linking to ozone precursors would likely miss the justification point.
FAQ
- How many points is each AP Environmental Science FRQ worth?
- Each of the three FRQs is worth 10 points, and together they make up the entire free-response section. Every subpart is graded independently, so a mistake on one part does not lower your score on the others.
- Do I lose points for writing extra wrong information on an FRQ?
- Generally graders score the correct content you provide, but contradictory or clearly incorrect statements can negate a point, and for 'identify TWO' prompts some rubrics grade only the first responses listed. Answer precisely and avoid padding with guesses that contradict your correct work.
- How do I know when to show math versus just explain?
- Follow the command word. 'Calculate' requires you to show the equation, substitute numbers with units, and give a final answer with units. 'Explain' or 'describe' requires written reasoning, not computation. Doing the wrong one wastes time and misses the point.
- What vocabulary should I use on Unit 7 FRQs?
- Use precise terms: primary versus secondary pollutant, , VOCs, , , tropospheric versus stratospheric ozone, thermal inversion, catalytic converter, scrubber, and AQI. Using the correct term often earns the point directly, so avoid vague phrasing like 'bad chemicals.'
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