Major Air Pollutants

Sulfur dioxide (SO₂)

Combustion of fuels that contain sulfur, including coal, oil, and gasoline

Respiratory irritant, can exacerbate asthma and other respiratory ailments

SO₂ gas can harm stomate and other plant tissue

Converts to sulfuric acid in atmosphere, which is harmful to aquatic life and some vegetation

Power plants, industrial processes, fires, mobile, miscellaneous

Nitrogen oxides (NO_x)

All combustion in the atmosphere including fossil fuel combustion, wood, and other biomass burning

Respiratory irritant, increases susceptibility to respiratory infection

An ozone precursor, leads to formation of photochemical smog

Converts to nitric acid in atmosphere, which is harmful to aquatic life and some vegetation

Contributes to over-fertilization of terrestrial and aquatic systems

Mobile, power plants, industrial processes, biogenic, fires, miscellaneous

Carbon monoxide (CO)

Incomplete combustion of any kind

Malfunctioning exhaust systems and poorly ventilated cooking fires

Bonds to hemoglobin, thereby interfering with oxygen transport in the bloodstream

Causes headaches at low concentrations

Can cause death with prolonged exposure at high concentrations

Mobile, fires, biogenic, fuel combustion, miscellaneous, industrial processes

Particulate matter (PM₁₀, PM_2.5)

Combustion of coal, oil, and diesel, and of biofuels such as manure and wood

Agricultural, road construction, and other activities that mobilize soil, soot, and dust

Can exacerbate respiratory and cardiovascular disease and reduce lung function

May lead to premature death

Reduces visibility and contributes to haze and smog

Fires, agriculture, dust, power plants, mobile, miscellaneous, industrial processes

Lead (Pb)

Gasoline additive, oil and gasoline, coal, old paint

Impairs central nervous system

At low concentrations, can have measurable effects on learning and ability to concentrate

Ozone (O₃)

A secondary pollutant formed by the combination of sunlight, water, oxygen, VOCs, and NO_x

Reduces lung function and exacerbates respiratory symptoms

Degrades plant surfaces

Damages materials such as rubber and plastic

Volatile organic compounds (VOC)

Evaporation of fuels, solvents, paints

Improper combustion of fuels such as gasoline

Precursor to ozone formation

Mercury (Hg)

Coal, oil, gold mining

Impairs central nervous system

Bioaccumulates in food chain

Carbon dioxide (CO₂)

Combustion of fossil fuels and clearing land

Affects climate and alters ecosystems by increasing greenhouse gas concentrations