AP Environmental Science Unit 7 Cheat Sheet: Atmospheric Pollution

The basics

What it covers: Air pollution — sources, chemistry, weather effects, indoor pollutants, and reduction strategies.

Exam weight: About 7–10% of the AP Environmental Science exam.

The big question: Where does air pollution come from, how does weather affect its concentration, and how can it be reduced?

Big Idea covered: Sustainability (STB).

Primary: emitted directly (CO, SO2). Secondary: formed via reactions in the atmosphere (ground-level ozone).

Sunlight + NOx + VOCs (mostly vehicle emissions) → ground-level ozone. Worst on sunny, calm, high-traffic days.

Warm air layer traps cool air (and pollution) near the ground — worsened by valley/mountain geography (e.g., LA, Mexico City).

PM2.5 (fine, more dangerous) vs. PM10 (coarse). Rising CO2 driven by fossil fuels + deforestation.

Radon (radioactive gas, lung cancer risk), CO (binds hemoglobin), asbestos (lung scarring/cancer).

Catalytic converters (vehicles), scrubbers (smokestacks), and the Clean Air Act (regulation).

SO2 + NOx + water vapor → sulfuric/nitric acid precipitation. Damages soil, water, and can travel far from the source.

Disrupts wildlife communication and mating behavior; can damage human hearing at high, sustained levels.

Primary pollutant — emitted directly into the atmosphere.
Secondary pollutant — formed by atmospheric chemical reactions.
Photochemical smog — sunlight-driven reaction of NOx and VOCs producing ground-level ozone.
Thermal inversion — warm air trapping cool, pollutant-laden air near the surface.
Particulate matter (PM2.5/PM10) — suspended solid/liquid particles classified by size.
Radon — radioactive indoor gas linked to lung cancer.
Catalytic converter — vehicle device converting exhaust pollutants to less harmful substances.
Scrubber — smokestack device removing particulates/gases before release.
Acid rain — acidic precipitation from SO2/NOx reacting with water vapor.
Noise pollution — excessive sound disrupting human and wildlife well-being.

Weather and geography amplify pollution. Thermal inversions and valley terrain can trap pollutants that would otherwise disperse.
Most major pollutants trace back to combustion. Vehicles and power plants are the common thread across smog, particulates, and acid rain.
Pollution doesn't respect borders. Acid rain and smog precursors can travel far from their original source.
Indoor air can be more polluted than outdoor air. Radon, CO, and asbestos are unique indoor-specific risks not caused by outdoor sources.
Regulation and technology both reduce pollution. The Clean Air Act (policy) and catalytic converters/scrubbers (technology) work together.

Don't confuse ground-level ozone with stratospheric ozone. One is harmful smog (Unit 7); the other protects against UV (Unit 9 — Global Change).
Thermal inversion reverses the normal pattern — don't describe it as simply "polluted air," but specifically as warm air trapping cool air below.
PM2.5 is more dangerous than PM10, not less — smaller particles penetrate deeper into lungs.
Radon is natural, not industrial — it comes from underlying rock and soil, not from a specific human pollution source.
Acid rain's source and impact location can differ. Don't assume the polluting power plant and the damaged lake are in the same place.
Catalytic converters and scrubbers are not interchangeable terms. Converters are for vehicle exhaust; scrubbers are for stationary sources like smokestacks.