AP Environmental Science Unit 7 Cheatsheet: Atmospheric Pollution

Start with the first 3 sections of the Unit 7 one-page cheatsheet below. The full sheet is a PDF you can print.

Primary & Secondary Pollutants from Fossil Fuels

Primary pollutants are released directly into the atmosphere.

Secondary pollutants form when primary pollutants react in the atmosphere.

Fuel Type	Primary Pollutants Released
Coal	CO₂, SO₂, toxic metals, particulates
All fossil fuels	NOₓ, CO, hydrocarbons, particulates
Diesel	SO₂ (especially high)

Key reaction: NOₓ + sunlight + VOCs → ozone + photochemical smog

Photochemical Smog Formation & Timing

Forms when NOₓ and volatile organic compounds (VOCs) react with heat and sunlight.

Daily pattern:

Early morning: NOₓ levels peak (from traffic)
Afternoon: Ozone concentrations peak (chemical reactions need sunlight)
Summer: Higher ozone (more sunlight, warmer temperatures)

VOC sources: gasoline, formaldehyde, trees (natural)

Why urban areas? High motor vehicle traffic = more NOₓ and VOCs

Thermal Inversion & Pollution Trapping

Normal atmosphere: Temperature decreases with altitude.

Thermal inversion: Warmer air layer sits above cooler surface air.

Effect: Acts as a lid—traps smog and particulates near ground level, preventing dispersion.

Result: Pollution concentrations increase dramatically in affected areas.

Common confusion: Inversion doesn't create pollution; it traps existing pollution and prevents it from rising and dispersing.

The rest of the Unit 7 sheet

6 more sections are on the one-page PDF:

Indoor Air Pollutants: Sources & Classification
Radon: Entry & Health Impact
Acid Deposition: Formation & Regional Impact
Pollution Control Devices & Methods
Reducing Photochemical Smog & Lead Regulation
Noise Pollution: Sources & Ecological Effects

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Unit 7: Atmospheric Pollution on one page, aligned to the 2026-2027 course. Made and checked by the Fiveable Content Team.

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