Atmospheric Pollution — Free AP Environmental Science Review Games.
This unit covers smog, acid rain, ozone depletion and indoor air quality — essential concepts for AP Environmental Science. Use our interactive study games to test your understanding, or review questions in traditional format below.
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This unit covers smog, acid rain, ozone depletion and indoor air quality — essential concepts for AP Environmental Science. Use our interactive study games to test your understanding, or review questions in traditional format below.
Key Concepts Breakdown
1 Smog
Students must distinguish between industrial (sulfurous) smog and photochemical smog, including their formation pathways and primary pollutants. Photochemical smog is the more commonly tested type and involves NOx and VOCs reacting under UV light to produce ground-level ozone. Understanding health and environmental impacts, as well as sources, is essential.
Key Points
- Photochemical smog forms when NOx + VOCs + sunlight → ground-level ozone (O3) + PAN + other secondary pollutants
- Primary pollutants (NOx, VOCs) come from vehicle exhaust and industrial sources; ozone and PAN are secondary pollutants
- Industrial smog results from burning coal and contains SO2 and particulate matter — associated with temperature inversions
- Temperature inversions trap pollutants near the surface by preventing vertical mixing of air
A city experiences heavy traffic congestion on a sunny, calm day. By afternoon, residents report eye irritation and reduced visibility. Explain the chemical process responsible.
NOx emitted from vehicle exhaust reacts with VOCs in the presence of UV sunlight through a photochemical reaction, producing ground-level ozone and PAN. The calm conditions (low wind) and stable atmosphere prevent dispersal, concentrating the secondary pollutants. This is classic photochemical smog — the key distinction from industrial smog is the role of sunlight and the secondary nature of ozone as a product, not a direct emission.
2 Acid Rain
Students must know the chemical reactions that transform SO2 and NOx into sulfuric acid and nitric acid in the atmosphere, and how these acids deposit onto ecosystems. Both wet deposition (rain, snow) and dry deposition (particulates) are tested. Impacts on aquatic ecosystems, forests, soils, and infrastructure are high-frequency exam content.
Key Points
- SO2 + H2O → H2SO3 → H2SO4 (sulfuric acid); NOx + H2O → HNO3 (nitric acid) — primary sources are coal combustion and vehicle exhaust
- Normal rain pH ≈ 5.6 (due to dissolved CO2); acid rain pH < 5.6, often 4–4.5
- Acid rain mobilizes aluminum ions in soil, which are toxic to fish and tree roots; lakes acidify and lose biodiversity
- Buffering capacity of bedrock matters: granite watersheds (low buffering) are more vulnerable than limestone watersheds (high buffering)
Two lakes receive the same amount of acid rain. Lake A sits over granite bedrock; Lake B sits over limestone. Which lake will acidify more rapidly, and why?
Lake A (granite) will acidify more rapidly because granite lacks carbonate minerals and has low buffering capacity — it cannot neutralize incoming acid. Lake B (limestone) contains calcium carbonate (CaCO3), which reacts with acids to form neutral products, effectively neutralizing the acid rain. This concept tests students' understanding that vulnerability to acid deposition depends not just on emission levels but on the receiving ecosystem's chemistry.
3 Ozone Depletion
Students must understand the stratospheric ozone layer's role in absorbing UV-B radiation, the mechanism by which CFCs catalytically destroy ozone, and the difference between stratospheric ozone (beneficial) versus tropospheric ozone (harmful). The Montreal Protocol is the key policy response tested on the exam.
Key Points
- CFCs release chlorine atoms in the stratosphere via UV radiation; each Cl atom catalytically destroys thousands of O3 molecules: Cl + O3 → ClO + O2
- Ozone depletion increases UV-B reaching Earth's surface, raising rates of skin cancer, cataracts, and immune suppression; also harms phytoplankton
- The Antarctic ozone hole forms in spring due to polar stratospheric clouds that accelerate CFC-driven reactions during cold, dark winters
- The Montreal Protocol (1987) phased out CFC production — ozone layer is slowly recovering, demonstrating effective international environmental policy
A scientist measures a 10% decrease in stratospheric ozone over a populated region. Predict two specific environmental or human health consequences and explain the mechanism linking ozone loss to each.
First, increased UV-B radiation reaching the surface elevates the incidence of melanoma and other skin cancers in humans, because UV-B damages DNA in skin cells. Second, marine productivity declines as elevated UV-B penetrates surface waters and damages phytoplankton DNA and photosynthetic pigments, disrupting the base of aquatic food chains. Both consequences trace directly to ozone's role as a UV-B absorber — its depletion removes this shield.
4 Indoor Air Quality
Students must identify major indoor air pollutants, their sources, and health effects. Radon, VOCs, asbestos, carbon monoxide, and secondhand smoke are the most frequently tested. The concept that indoor air is often more polluted than outdoor air due to poor ventilation is a key exam point.
Key Points
- Radon: naturally occurring radioactive gas from uranium decay in soil/rock; seeps into basements; leading cause of lung cancer among non-smokers
- VOCs (formaldehyde, benzene) off-gas from building materials, furniture, paints, and cleaning products; cause headaches, respiratory irritation, and long-term cancer risk
- Carbon monoxide (CO) from incomplete combustion (gas stoves, fireplaces, cars in garages) binds hemoglobin with greater affinity than O2, causing hypoxia
- Sick Building Syndrome results from inadequate ventilation concentrating pollutants; solutions include increased air exchange rates and low-VOC materials
A family installs new carpeting and furniture in a newly weatherized, tightly sealed home. Within weeks, members experience headaches, eye irritation, and fatigue. Identify the most likely pollutant class and explain why the tightly sealed home worsened the problem.
The most likely culprits are VOCs (particularly formaldehyde) off-gassing from new carpet adhesives, pressed-wood furniture, and synthetic fibers. The tightly sealed home, while energy-efficient, dramatically reduces air exchange with the outside, allowing VOC concentrations to build to symptomatic levels rather than being diluted. This illustrates the trade-off between energy efficiency and indoor air quality — a classic AP exam tension — and the solution is increased mechanical ventilation or use of low-VOC materials.
Questions, answered.
What is Atmospheric Pollution?
Atmospheric Pollution is Unit 7 of AP Environmental Science, covering smog, acid rain, ozone depletion and indoor air quality.
How to study for AP Environmental Science Unit 7?
Start with the Quick Summary above, review the Key Concepts, then test yourself with our interactive study games. Aim for 80%+ accuracy before moving on.
How many questions are in this unit?
This unit has 30+ review questions across 5 different game modes.