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Unit 7
7–10% of examAir pollution comes from cars, power plants, factories, nature, and even the inside of your home. This unit covers the main air pollutants, how sunlight turns some of them into smog, how weather can trap pollution near the ground, and how acid rain forms. It also covers the laws and technologies that clean the air.
Longer videos that cover the whole unit. Good for a first pass or a final review.
Burning coal and gasoline releases pollutants like nitrogen oxides, sulfur dioxide, carbon monoxide, particulates and mercury. Primary pollutants come straight from a source, while secondary pollutants, like ground-level ozone, form when primary pollutants react in the air; in the US, the Clean Air Act lets the EPA set limits on the main (criteria) air pollutants.
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Photochemical smog forms when nitrogen oxides and volatile organic compounds (VOCs), mostly from vehicles, react in sunlight to make ground-level ozone. It's worst in warm, sunny cities with heavy traffic, and it irritates your lungs and damages plants.
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Normally air gets cooler as you go up, so warm polluted air near the ground can rise and spread out. In a thermal inversion, a layer of warm air sits on top of cooler air at the surface, trapping pollution near the ground until the weather changes, as in the deadly 1948 Donora, Pennsylvania smog.
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Not all air pollution comes from people: volcanoes, forest fires, dust storms, sea spray and living things also release CO₂, particulates and other gases. Particulate matter is tiny bits of solid or liquid in the air that can cause haze, block sunlight and damage your lungs.
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Indoor air can be more polluted than outdoor air. In developing countries, smoke from burning wood or dung indoors for cooking is a major health threat; in other homes, worries include carbon monoxide from faulty heaters, radioactive radon gas seeping up from soil and rock, asbestos, lead dust, and VOCs like formaldehyde from glues, paints and furniture.
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You can cut air pollution by preventing it (burning less fuel, switching to cleaner fuel) or by catching pollutants before they reach the air. Tools include catalytic converters on cars, scrubbers and electrostatic precipitators at power plants, and vapor recovery nozzles at gas pumps.
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Sulfur dioxide and nitrogen oxides from power plants and vehicles react with water in the air to form sulfuric and nitric acid, which fall as acid rain or dry acid deposition. It lowers the pH of lakes and soils, harms fish and trees, and wears away limestone and marble; areas with limestone bedrock can neutralize some of the acid.
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Noise pollution is sound loud or constant enough to cause stress or harm. Traffic, construction, airports, ships and industry can damage hearing in people and make it harder for animals to communicate, hunt and migrate.
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