Air Pollution

20-1 Structure and Science of the Atmosphere

The atmosphere consists of several layerswith different temperatures, pressures, and compositions, Fig. 20-2

Atmospheric pressure is higher at sea level than in the mountains. Nitrogen and oxygen make up 99% of the air we breathe.Stratospheric ozone acts as a sort of global sunscreen that filters out harmful UV radiation.

20-2 Outdoor Air Pollution

Air pollution harms living organisms, damages materials, and can alterclimate. Primary pollutants may react with one another or with

chemicals in the troposphere to form secondary pollutants.

20-3 Photochemical and Industrial Smog

Photochemical smog begins with the formation of nitric oxide (NO) in automobile engines and industrial plants. Photochemical smog can irritate the eyes and respiratory tract. It is worst in warm, dry cities with lots of motor vehicles, such as Los Angeles, California.

Industrial smog occurs when the burning of coal and heavy oils releases soot, carbon dioxide, carbon monoxide, and sulfur dioxide. Reactions in the troposphere produce sulfur oxides, sulfuric acids, and ammonium oxides. Industrial smog is a problem in many cities in Asia and Eastern Europe.

A temperature inversion can cause pollutants to concentrate in air near the

ground.

20-4 Regional Outdoor AirPollution from Acid

Deposition

Acid deposition or acid rain is a regional problem in several parts of the world. It occurs downwind of coal-burning plants and heavily populated cities. Acid deposition contributes to human respiratory problems, damages buildings, harms forests, and threatens aquatic ecosystems.

20-5 Indoor Air PollutionIndoor air pollution is now a more serious problem than outdoor air pollution, both in buildings and inside cars that are in heavy traffic. Cigarette smoke, formaldehyde, and radioactive radon-222 gas are the three most dangerous indoor pollutants.

20-6 Effects of Air Pollution on Living Organismsand Materials

Smoking and exposure to air pollutants can cause lung cancer, asthma, chronic

bronchitis, and emphysema and lead to large numbers of premature deaths.

20-7 Preventing and Reducing Air Pollution

• The U.S. Clean Air Acts established air pollutionregulations that are enforced by each state and by major cities. The EPA has also set standards for more than100 toxic air pollutants known or suspected to havehealth effects.

• Tougher fuel-efficiency standards would lower smog levels. Between 1990 and 2000, an emissions tradingsystem helped reduce sulfur dioxide emissions in theUnited States by 30%. Similar cap-and-trade programsmay be used to control three substances emitted by coal-burning plants (sulfur dioxide, nitrogen oxides, andmercury) at the same time.