Air Pollution

At ground level, Earth’s average atmosphere is made up of about 78 percent nitrogen, 21 percent oxygen, and less than 1 percent argon. The remaining 0.04 percent includes several trace gases, some of which are critical. Air pollution is a concentration of trace substances at a greater level than occurs in average air. Concentrations of these trace gases in the air can damage property and adversely affect the health of people, other animals, and plants.

Most air pollution is generated from factories and power plants, as well as from motor vehicles. Factories and power plants produce sulfur dioxides and solid particulates, primarily from burning coal. Burning petroleum in motor vehicles produces carbon monoxide, hydrocarbons, and nitrogen oxides.

Air Pollution by Country

The most countries with the highest concentrations of particulate matters are clustered in Asia and Africa.

Local-Scale Air Pollution

At the local scale, air pollution is especially severe in places where emission sources are concentrated, such as in urban areas. The air above urban areas may be polluted because a large number of factories, motor vehicles, and other polluters emit residuals in a concentrated area. Most of the cities with the worst air pollution are in Asia, especially China and India (Figures 11-58 and 11-59).

Air Pollution, Lahore, Pakistan

One of the world’s most polluted cities.

Urban air pollution has three basic components:

• Carbon monoxide. Breathing carbon monoxide reduces the oxygen level in blood, impairs vision and alertness, and threatens those with breathing problems.

• Hydrocarbons. In the presence of sunlight, hydrocarbons, as well as nitrogen oxides, form photochemical smog, which causes respiratory problems, stinging in the eyes, and an ugly haze over cities.

• Particulates. They include a combination of dust and smoke particles. The dark plume of smoke from a factory stack and the exhaust of a diesel truck are examples of particulate emission.

The worst urban air pollution occurs when winds are slight, skies are clear, and a temperature inversion exists. When the wind blows, it disperses pollutants; when it is calm, pollutants build. Sunlight provides the energy for the formation of smog. Air is normally cooler at higher elevations, but during temperature inversions—in which air is warmer at higher elevations—pollutants are trapped near the ground.

Regional-scale Air Pollution

At the regional scale, air pollution may damage a region’s vegetation and water supply through acid deposition, which is the accumulation of acids, including sulfuric acid and nitric acid, on Earth’s surface. Especially affected by acid deposition are the world’s principal industrial regions (Figure 11-60).

Acid Precipitation

Sulfur oxides and nitrogen oxides, emitted by burning fossil fuels, enter the atmosphere, where they combine with oxygen and water. When dissolved in water, the acids may fall as acid precipitation (rain, snow, or fog) or be deposited in dust. Before they reach the surface, these acidic droplets might be carried hundreds of kilometers.

Acid precipitation damages lakes, killing fish and plants. On land, concentrations of acid in the soil can injure plants by depriving them of nutrients and can harm worms and insects. Buildings and monuments made of marble and limestone have suffered corrosion from acid rain.

Geographers are particularly interested in the effects of acid precipitation because the worst damage is not experienced at the same location as the emission of the pollutants. Within the United States the major generators of acid deposition are in industrial states along the southern Great Lakes. However, the severest effects of acid rain are felt in several areas farther east. The United States reduced sulfur dioxide emissions significantly during the late twentieth century.

Global-scale Air Pollution: Climate Change

At the global scale, the average temperature of Earth’s surface has increased by 1°C (2°F) since 1880. This temperature increase is directly linked to human actions, especially the burning of fossil fuels in factories and vehicles, according to an international team of U.N. scientists.

Global Warming and Carbon Dioxide Concentrations

Since 1880, carbon dioxide concentration has increased by more than one-third and Earth has warmed by about 1°C (2°F).

When fossil fuels are burned, carbon dioxide is discharged into the atmosphere. Plants and oceans absorb much of the discharge, but increased fossil fuel burning during the past 200 years has caused the level of carbon dioxide in the atmosphere to rise by more than one-fourth, according to the U.N. Intergovernmental Panel on Climate Change. The concentration of trace gases in the atmosphere can delay the return of some of the heat leaving Earth’s surface heading for space, thereby raising Earth’s temperatures. The increase in Earth’s temperature, caused by carbon dioxide trapping some of the radiation emitted by the surface, is called the greenhouse effect.

As a country’s per capita income increases, its per capita carbon dioxide emissions generally increase. Some of the wealthiest countries, located primarily in Europe, with GNI per capita between $30,000 and $50,000, show declines in pollution. However, the world’s richest countries, including the United States and several countries in Southwest Asia, display the highest pollution levels.

Gni and Pollution

Global-scale Air Pollution: Ozone Damage

Ozone is a gas that absorbs ultraviolet radiation in the stratosphere, a zone between 15 and 50 kilometers (nine to 30 miles) above Earth’s surface. Were it not for the ozone in the stratosphere, UV rays would damage plants, cause skin cancer, and disrupt food chains.

Earth’s protective ozone layer is threatened by pollutants called chlorofluorocarbons (CFCs). CFCs such as Freon were once widely used as coolants in refrigerators and air conditioners. When they leak from these appliances, the CFCs are carried into the stratosphere, where they break down Earth’s protective layer of ozone gas. In 2007, nearly all countries agreed to cease using CFCs by 2020 in developed countries and by 2030 in developing countries.

Pause & Reflect 11.3.1

What gas is now most commonly used as a coolant instead of CFC? Use a search engine to find the answer.