Unit 7 · 7–10% of the exam Beta

Unit 7 practice test: Atmospheric Pollution

12 exam-style questions from the unit, free, with an explanation for every option. Most have four answer choices, as on the real exam, and a few ask you to type a calculation with its units; sets share one data table, graph, model or passage.

Covers: Introduction to Air Pollution; Photochemical Smog; Thermal Inversion; Atmospheric CO2 and Particulates; Indoor Air Pollutants; Reduction of Air Pollutants; Acid Rain; Noise Pollution.

Model or diagram

Formaldehyde in a new modular classroom over its first year

024681012020406080100120140Months since the classroom openedFormaldehyde (ppb)

1. Describe the trend in formaldehyde in the classroom over the year.

  1. It falls by the same amount each month
  2. It rises at first, then levels off
  3. It falls quickly at first, then more slowly
  4. It stays about the same over the year
Show the answer

Formaldehyde falls quickly at first (120 to 72 ppb in three months) and then more slowly, reaching 30 ppb at 12 months.

  • It falls by the same amount each month: The first months drop by 15 to 20 ppb each, the last ones by 3 to 6, so the rate is not steady.
  • It rises at first, then levels off: Formaldehyde is highest at month 0 and falls from there.
  • Correct: It falls quickly at first, then more slowly: Right: the drop per month shrinks over time.
  • It stays about the same over the year: It falls from 120 to 30 ppb, a large change.

2. Which explanation best fits the shape of the formaldehyde curve?

  1. Students breathe out more formaldehyde as the year goes on
  2. New pressed wood off-gasses fast at first, then slower
  3. Outdoor smog blows in during winter and raises the level
  4. Radon in the soil turns into formaldehyde over time
Show the answer

New pressed-wood furniture, cabinets and glues give off (off-gas) formaldehyde fastest when new. As less is left in the materials, the release slows, so the level falls quickly and then slowly.

  • Students breathe out more formaldehyde as the year goes on: People do not breathe out meaningful formaldehyde.
  • Correct: New pressed wood off-gasses fast at first, then slower: Right: off-gassing is strongest when materials are new.
  • Outdoor smog blows in during winter and raises the level: The level falls steadily; nothing in the graph rises.
  • Radon in the soil turns into formaldehyde over time: Radon is a radioactive gas from rock; it does not turn into formaldehyde.

3. Which step would most directly lower formaldehyde in the classroom during its first months?

  1. Increase ventilation with outdoor air
  2. Seal the windows to keep outdoor smog out
  3. Install a radon fan under the classroom floor
  4. Add more pressed-wood shelves for storage
Show the answer

Bringing in more outdoor air dilutes the formaldehyde that the new materials give off, so the concentration indoors falls.

  • Correct: Increase ventilation with outdoor air: Right: fresh air dilutes and removes the off-gassed formaldehyde.
  • Seal the windows to keep outdoor smog out: Sealing traps the formaldehyde inside and raises its level.
  • Install a radon fan under the classroom floor: A radon fan removes soil gas; it does not remove formaldehyde from furniture.
  • Add more pressed-wood shelves for storage: New pressed wood would add formaldehyde.

Passage

A passage on a sulfur dioxide trading program

A state council is debating a plan to cut sulfur dioxide from its twelve coal power plants. Under the plan, the state sets a total cap on SO2 for all plants together and lowers it by 5% each year. Each plant receives permits for its share. A plant that cuts its emissions below its permits, for example by installing a scrubber or switching to low-sulfur coal, may sell the extra permits to a plant that finds cutting more expensive. Supporters say the cap guarantees the total cut while letting the cheapest cuts happen first. Critics worry that a plant buying many permits could keep polluting its own neighborhood, and they ask the council to add a limit for each plant as well as the total cap.

Invented passage for practice.

4. What is the main claim made by the plan's supporters?

  1. Each plant should be required to install the same scrubber
  2. SO2 should be cut mainly to slow global climate warming
  3. A cap with trading cuts SO2 at low cost
  4. Plants that buy permits will clean up their neighborhoods
Show the answer

Supporters say the cap guarantees the total cut while trading lets plants make the cheapest cuts first.

  • Each plant should be required to install the same scrubber: The plan lets plants choose how to cut; it does not require one device.
  • SO2 should be cut mainly to slow global climate warming: The passage says nothing of warming; SO2 is cut to protect health and lakes and forests.
  • Correct: A cap with trading cuts SO2 at low cost: Right: that is the supporters' claim.
  • Plants that buy permits will clean up their neighborhoods: That is the opposite of the critics' worry.

5. What assumption underlies the critics' concern?

  1. A cap will fail to lower the total SO2 from the twelve plants
  2. SO2 harms people most near the plant that releases it
  3. Scrubbers do not remove SO2 from a plant's exhaust
  4. Low-sulfur coal costs more than ordinary coal everywhere
Show the answer

The critics assume that SO2 harms people mostly near the plant that releases it, so a plant that buys permits could leave its own neighbors with dirty air even while the state total falls.

  • A cap will fail to lower the total SO2 from the twelve plants: Critics do not dispute the total cut; they worry about where it happens.
  • Correct: SO2 harms people most near the plant that releases it: Right: the worry only makes sense if local emissions matter locally.
  • Scrubbers do not remove SO2 from a plant's exhaust: The passage presents scrubbers as a way to cut SO2.
  • Low-sulfur coal costs more than ordinary coal everywhere: Cost is the supporters' topic; the critics are concerned with local harm.

6. Which evidence would best support the supporters' claim?

  1. A past cap-and-trade plan met its goal for less money
  2. One plant's neighbors had more asthma after it bought permits
  3. Coal plants also release mercury and CO2
  4. Some states use wind farms instead of coal plants
Show the answer

The claim is that trading lowers the cost of a guaranteed cut. Data showing a cap-and-trade program met its target at lower cost than expected would support it directly.

  • Correct: A past cap-and-trade plan met its goal for less money: Right: that tests the cost claim directly.
  • One plant's neighbors had more asthma after it bought permits: That supports the critics, not the supporters.
  • Coal plants also release mercury and CO2: True, but it says nothing about whether trading cuts SO2 cheaply.
  • Some states use wind farms instead of coal plants: That is about energy choices, not the cost of the cap.

7. Is the plan described in the passage a policy or a technology?

  1. A technology, because scrubbers are one way to meet it
  2. A technology, because it uses permits that can be sold
  3. Neither, because it does not name a pollutant to cut
  4. A policy, because it is a rule plants follow
Show the answer

A cap with tradable permits is a rule set by the state, so it is a policy. Scrubbers and low-sulfur coal are the technologies plants may choose to meet it.

  • A technology, because scrubbers are one way to meet it: Scrubbers are a technology a plant may use, but the plan itself is a rule.
  • A technology, because it uses permits that can be sold: A permit is a legal right to emit, part of a rule, not a device.
  • Neither, because it does not name a pollutant to cut: The plan names SO2 directly.
  • Correct: A policy, because it is a rule plants follow: Right: the cap and permits are a rule; scrubbers are the technology.

8. Gasoline contains almost no nitrogen, yet car engines release nitrogen oxides. Why?

  1. Nitrogen fixation by bacteria living in the fuel tank
  2. Sulfur in gasoline turns into nitrogen as it burns
  3. Engine heat makes nitrogen and oxygen in the air combine
  4. Nitrate from fertilizer is mixed into gasoline at refineries
Show the answer

Air is about 78% nitrogen gas. At the high temperature inside an engine, nitrogen and oxygen from the air combine to form NO, which becomes NO2.

  • Nitrogen fixation by bacteria living in the fuel tank: Nitrogen fixation is done by bacteria in soil and roots, not in fuel tanks.
  • Sulfur in gasoline turns into nitrogen as it burns: Burning does not turn one element into another; sulfur becomes SO2.
  • Correct: Engine heat makes nitrogen and oxygen in the air combine: Right: the nitrogen comes from the air drawn into the engine, not from the fuel.
  • Nitrate from fertilizer is mixed into gasoline at refineries: Fertilizer is not added to fuel; the nitrogen comes from the air.

9. How does the presence of VOCs let ozone build up near the ground during the day?

  1. VOCs split in sunlight into ozone molecules directly
  2. VOCs cool the air so the ozone sinks down to the ground
  3. VOCs block sunlight so ozone is not broken apart
  4. VOCs react with NO, so NO no longer breaks ozone down
Show the answer

Without VOCs, NO reacts with ozone and breaks it back down. VOCs react with the NO instead, forming photochemical oxidants, so ozone is not used up and accumulates.

  • VOCs split in sunlight into ozone molecules directly: VOCs do not break into ozone; ozone forms from an oxygen atom freed from NO2.
  • VOCs cool the air so the ozone sinks down to the ground: VOCs do not cool the air; the effect is chemical.
  • VOCs block sunlight so ozone is not broken apart: VOCs are gases that do not block sunlight; smog forms in strong sun.
  • Correct: VOCs react with NO, so NO no longer breaks ozone down: Right: the NO that would destroy ozone is tied up by VOC reactions.

10. During a five-day thermal inversion over an industrial town, hospitals see many more patients with breathing problems. Which explanation is most complete?

  1. Emissions piled up in the trapped air day after day
  2. Cold air itself irritates the lungs more than polluted air does
  3. Factories released more pollution because of the cold
  4. Warm air from above pushed the ozone layer down to the town
Show the answer

The town's smoke and gases kept being added to the same shallow layer of air, so their concentration rose day after day and irritated people's lungs.

  • Correct: Emissions piled up in the trapped air day after day: Right: same sources, no escape, so the levels climbed.
  • Cold air itself irritates the lungs more than polluted air does: Cold air alone does not explain the steady rise over five days.
  • Factories released more pollution because of the cold: The sources stayed about the same; the air stopped clearing.
  • Warm air from above pushed the ozone layer down to the town: The ozone layer stays in the stratosphere; the cause was trapped emissions.

11. Which natural process releases CO2 when organisms break down dead leaves on a forest floor?

  1. Photosynthesis
  2. Sedimentation
  3. Decomposition
  4. Condensation
Show the answer

Decomposers break down dead matter and release the carbon as CO2 through cellular respiration.

  • Photosynthesis: Photosynthesis takes CO2 in; it does not release it.
  • Sedimentation: Sedimentation buries carbon in rock over long times; it does not release CO2 from leaves.
  • Correct: Decomposition: Right: decomposers respire, releasing CO2.
  • Condensation: Condensation is water vapor turning to liquid; it releases no CO2.

12. Ordinary, unpolluted rain has a pH of about 5.6. Why is it slightly acidic?

  1. Lightning adds sulfur dioxide to the raindrops
  2. Clouds absorb acids from the ozone layer
  3. Water is naturally acidic at pH 5.6 before it evaporates
  4. CO2 in the air dissolves in it and forms a weak acid
Show the answer

CO2 in the air dissolves in raindrops and forms a weak acid, so even clean rain is a little below neutral pH 7. Acid rain is rain below about 5.6.

  • Lightning adds sulfur dioxide to the raindrops: Lightning makes a little NOx, but CO2 is why clean rain is about 5.6.
  • Clouds absorb acids from the ozone layer: The ozone layer does not add acid to rain.
  • Water is naturally acidic at pH 5.6 before it evaporates: Pure water is neutral at pH 7.
  • Correct: CO2 in the air dissolves in it and forms a weak acid: Right: that is why clean rain is about 5.6, not 7.

Keep going

Practice the whole unitTake a timed unit testPrint the unit sheet

Practice has every question in the unit, with feedback after each one; the notes for every topic are free. Other units: Unit 1 · Unit 2 · Unit 3 · Unit 4 · Unit 5 · Unit 6 · Unit 7 · Unit 8 · Unit 9.