Unit 7: Atmospheric Pollution
AP Environmental Science: 50 practice questions with detailed explanations.
Unit Study Guide
Executive Summary
Unit 7 covers outdoor and indoor air pollution: how smog forms, what acid rain does, and how regulation cleaned the air.
Photochemical smog
Sunlight drives NOx + VOCs to form tropospheric ozone and smog, worst in sunny cities with traffic (Los Angeles). Thermal inversions trap it: a warm layer sits above cool air, blocking dispersal — common in valley cities.
Primary and secondary pollutants
Primary pollutants are emitted directly (CO, particulates, SO₂, NOx, VOCs). Secondary pollutants form in the air: ozone, sulfuric and nitric acids, PANs. Particulate matter (PM2.5, PM10) penetrates lungs.
Acid deposition
SO₂ (coal) and NOx form sulfuric and nitric acids that fall as acid rain, lowering pH of lakes and soils and leaching nutrients. Lime can buffer lakes; scrubbers remove SO₂ at the source.
Indoor air
Radon (radioactive soil gas) causes lung cancer; formaldehyde, VOCs, asbestos, and carbon monoxide threaten indoors. Ventilation is the cheapest fix.
Regulation
The Clean Air Act (1970) set national standards for six criteria pollutants and drove catalytic converters and scrubbers. The Montreal Protocol (1987) phased out CFCs, healing stratospheric ozone — the most successful environmental treaty.
Exam traps
Stratospheric ozone is protective; tropospheric ozone is a pollutant — same molecule, different altitude. Thermal inversions worsen smog by trapping it. The Montreal Protocol addressed ozone, not climate (though CFCs are also greenhouse gases).