APES Unit 7 Notes: Air Pollution Sources and Effects (Foundations to Mechanisms)

Air pollution

The presence of chemicals or particles in the atmosphere at concentrations high enough to harm living organisms, damage materials, or disrupt ecosystems and climate.

Primary pollutant

A pollutant emitted directly from a source (e.g., CO from incomplete combustion, SO2 from coal burning, PM from diesel exhaust).

Secondary pollutant

A pollutant that forms in the atmosphere when primary pollutants react (often with sunlight, water, or oxygen), such as tropospheric ozone or acids in acid deposition.

Photochemical smog

A brownish haze produced when sunlight drives reactions among NOx and VOCs, creating secondary pollutants such as tropospheric ozone (O3) and PANs.

Ozone precursor

A chemical input that helps form tropospheric ozone; mainly nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight.

Tropospheric ozone (ground-level O3)

A harmful secondary pollutant formed from NOx + VOCs + sunlight; a strong oxidant that damages lung tissue and plants.

Stratospheric ozone

Ozone high in the atmosphere that protects life by absorbing ultraviolet (UV) radiation; beneficial unlike ground-level ozone.

Peroxyacetyl nitrates (PANs)

Secondary pollutants formed in photochemical smog; irritate eyes and can harm vegetation.

Nitrogen oxides (NOx)

Primary pollutants (NO and NO2) mainly from vehicles and power plants; cause respiratory irritation and help form ozone and nitric acid (acid deposition).

Volatile organic compounds (VOCs)

Carbon-containing gases from fuel vapors, solvents, and industry (and some plants) that react with NOx in sunlight to form ozone and PANs.

Carbon monoxide (CO)

A primary pollutant from incomplete combustion (e.g., vehicles); reduces oxygen delivery by binding to hemoglobin.

Sulfur dioxide (SO2)

A primary pollutant from burning sulfur-containing coal and smelting; forms sulfuric acid and sulfate particles and contributes to respiratory problems.

Particulate matter (PM)

A mixture of solid particles and liquid droplets suspended in air; harms health, reduces visibility (haze), and can affect climate.

PM2.5

Fine particulate matter (≤2.5 µm) often from combustion and secondary formation; can penetrate deep into lungs and is strongly linked to respiratory and cardiovascular harm.

PM10

Coarser particulate matter (≤10 µm) often associated with dust and larger particles; generally penetrates less deeply into the lungs than PM2.5.

Secondary particulate matter

Particles formed in the atmosphere when gases react to create particles (e.g., SO2 and NOx forming sulfate and nitrate particles).

Black carbon (soot)

A particulate from incomplete combustion that absorbs sunlight (warming effect) and can accelerate melting when deposited on snow/ice.

Sulfate aerosols

Particles often formed from SO2 that tend to reflect sunlight, contributing to cooling and also to haze/visibility reduction.

Thermal inversion

A condition where warm air sits above cooler air near the ground, reducing vertical mixing and trapping pollutants at breathing level.

Radiation inversion

A nighttime inversion that forms when the ground cools quickly on clear, low-wind nights, cooling the air at the surface while warmer air remains above.

Subsidence inversion

An inversion associated with high-pressure systems where sinking air warms as it compresses, creating a warm layer aloft that suppresses mixing for days.

Dry deposition

Removal of pollutants when particles and gases settle onto or stick to surfaces without precipitation.

Wet deposition

Removal of pollutants by rain, snow, or fog; can transfer pollution to ecosystems and may occur as acidic deposition.

Carbon dioxide (CO2)

A naturally occurring gas that becomes a pollutant when human activities increase its concentration, driving greenhouse warming and long-term climate change.

Ocean acidification

A decrease in ocean pH caused by CO2 dissolving into seawater and forming carbonic acid, reducing carbonate availability for corals and shell-forming organisms.