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AP Environmental Science Unit 7 Visual Review

An 8-slide visual walkthrough of every Topic 7.1-7.8 concept — primary and secondary pollutants, photochemical smog, thermal inversion, CO2, indoor air quality, pollution reduction, acid rain, and noise pollution — built right into the page.

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TOPIC 7.1 Introduction to Air Pollution Source car, factory, fire Primary pollutant emitted directly + sunlight / reaction Secondary formed in the air Primary pollutants Released directly into the air from a source — CO, SO2, NOx, and particulate matter from vehicle exhaust, power plants, and fires are all textbook primary pollutants. Secondary pollutants Formed when primary pollutants react in the atmosphere — ground-level ozone (7.2) and acid rain (7.7) are both secondary pollutants, never emitted directly by any source. Combustion is the shared root cause behind nearly every pollutant in this unit — vehicle and power plant exhaust. The Review Hub · AP Environmental Science Unit 7 TOPIC 7.2 Photochemical Smog sunlight (UV) NOx + VOCs vehicle exhaust Ground-level O₃ ("smog") The recipe Vehicle exhaust releases nitrogen oxides (NOx) and volatile organic compounds (VOCs). UV sunlight drives a reaction between them, producing ground-level ozone (O₃). Why it's a summer, city problem Needs strong sunlight (worst on hot, sunny afternoons) and heavy traffic (worst in dense cities). Note: this "bad" ground-level ozone is unrelated to the "good" stratospheric ozone layer. Ground-level ozone irritates lungs and airways — the opposite role of the protective ozone layer above it. The Review Hub · AP Environmental Science Unit 7 TOPIC 7.3 Thermal Inversion NORMAL warm air (rises) cool air + pollution pollution disperses upward ✓ INVERSION warm air layer (lid) cool air + trapped pollution ✗ Flipping the usual pattern Normally, air cools with altitude, so warm surface air (and pollution) rises freely. In an inversion, a warm layer sits ABOVE cooler air, acting like a lid that traps pollution below it. Same emissions, worse air quality No new pollution is added — the inversion just prevents dispersal. Common in valleys (Los Angeles, Mexico City) where surrounding hills also block horizontal escape. Weather and geography alone can spike pollution readings — Topic 7.3 tests you on cause, not just chemistry. The Review Hub · AP Environmental Science Unit 7 TOPIC 7.4 Atmospheric CO2 & Particulates CO₂ (ppm) 1960 → today ~420 ppm (2024) PM10 PM2.5 (finer, deeper into lungs) Rising CO2 Fossil fuel combustion and deforestation have pushed atmospheric CO2 from ~315 ppm (1960) past 420 ppm today — the core driver of the enhanced greenhouse effect (Unit 8). Particulate matter (PM) Tiny solid/liquid particles suspended in air. PM10 lodges in airways; PM2.5 (smaller) penetrates deep into lung tissue and even the bloodstream — a leading cause of respiratory illness. The smaller the particle, the deeper it travels into the body — PM2.5 is the size class regulators worry about most. The Review Hub · AP Environmental Science Unit 7 TOPIC 7.5 Indoor Air Pollutants radon (seeps from soil) CO (gas stove/ furnace) asbestos (old insulation) Three pollutants to know Radon — invisible radioactive gas seeping up from soil/rock; the #2 cause of lung cancer. Carbon monoxide — from incomplete combustion; binds hemoglobin, blocking oxygen. Why indoor air can be worse than outdoor Asbestos fibers from old insulation cause lung disease when disturbed. Modern, well-sealed homes trap pollutants indoors more effectively — energy efficiency and air quality can conflict. Radon detectors and simple ventilation are the two cheapest, most effective fixes for indoor air quality. The Review Hub · AP Environmental Science Unit 7 TOPIC 7.6 Reduction of Air Pollutants engine catalytic converter cleaner exhaust smokestack scrubber Technology fixes Catalytic converters use a metal catalyst to convert CO, NOx, and unburned fuel into CO2, N2, and water before exhaust leaves the car. Scrubbers chemically remove SO2 from Policy fixes The Clean Air Act set national air quality standards and forced the adoption of these exact technologies. Cap-and-trade programs for SO2 successfully cut US acid rain (7.7) emissions by letting firms trade pollution permits. Scrubbers exist mainly because industry needed to comply with Clean Air Act limits — technology followed policy. The Review Hub · AP Environmental Science Unit 7 TOPIC 7.7 Acid Rain power plant SO₂ + NOx + H₂O travels 100s of miles falls as acidic rain/snow Formation SO2 (from coal) and NOx (from combustion) react with atmospheric water vapor to form sulfuric and nitric acid, lowering the pH of precipitation well below its normal ~5.6. A transboundary problem Precursor gases can travel hundreds of miles before falling — so the region that emits SO2/NOx often isn't the one that suffers the damage — lakes, forests, and statues. Acid rain acidifies lakes and leaches nutrients from soil — hurting ecosystems far from the smokestack that caused it. The Review Hub · AP Environmental Science Unit 7 TOPIC 7.8 Noise Pollution 30 dB whisper 60 dB conversation 85 dB heavy traffic 110 dB concert / jet each +10 dB ≈ 10x louder The decibel (dB) scale is logarithmic — a jump of 10 dB is roughly a 10x increase in sound intensity, not a small step. Chronic noise raises stress hormones in humans and disrupts wildlife communication, mating, and navigation. The Review Hub · AP Environmental Science Unit 7
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How to use the visual review

Spend 30 seconds per slide before clicking next. Look at the diagram, then ask yourself: "Could I draw this from memory and explain it?"

Use the fullscreen button () on desktop for the best experience. Use arrow keys to navigate. Tap "Show all slides" to jump around.

This covers every one of Unit 7's 8 CED topics, from primary/secondary pollutants through noise pollution.