Types of Air Pollutants

The most significant pollutants include oxides of carbon, sulfur, and nitrogen; hydrocarbons; particulate matter; and chlorofluorocarbons.

By the mid-1980's, scientific studies had shown that the air inside homes and office buildings is often more polluted than the air outdoors. Air pollutants originating indoors include oxides of carbon and nitrogen, particulate matter, radon, and vapors from such household chemicals as insecticides and paint strippers. The construction of well-sealed buildings to lower heating and cooling costs has contributed to the problem of indoor air pollution.

Carbon oxides make up the largest single group of pollutants. Carbon monoxide, a colorless and odorless poison, is a gas produced when fuel is incompletely burned in engines, furnaces, and space heaters. Automobiles and other vehicles are the major source of this pollutant. Another gas, carbon dioxide, is a product of all normal combustion (burning). Although carbon dioxide is not a serious pollutant in itself, some scientists believe that a long-term buildup of this gas in the atmosphere could cause what they call a “greenhouse effect” by reducing the flow of heat from the earth back into space, thus causing a potentially dangerous warming of the earth.

Sulfur oxides—notably sulfur dioxide—are among the most dangerous and irritating of all air pollutants. Factories and electric power plants that use sulfur-containing coal or oil as fuel are major sources of sulfur oxides. In the air, some sulfur dioxide is converted to sulfuric acid, which is then deposited on the earth's surface, usually by rain. Such acid rain has caused serious damage to the environment in many parts of the world.

Nitrogen oxides are produced in automobile engines and other devices where combustion takes place. Indoors, gas ranges are a major source of nitrogen oxides. Chemical reactions between nitrogen oxides and hydrocarbon pollutants in sunlight produce ozone, a major constituent of an irritating mixture of pollutants and fog known as smog. Some nitrogen oxides in the air are converted to nitric acid, which contributes to the formation of acid rain.

Hydrocarbon pollutants are products of unburned fuel, and are emitted mostly by motor vehicles. Like nitrogen oxides, hydrocarbons contribute to smog.

Particulate matter consists of tiny liquid or solid particles in the air. Particulate matter includes smoke, dust, and soot, which may contain such toxic substances as asbestos, fluorides, lead, and mercury. Indoors, tobacco smoke is a major source of particulate matter.

Chlorofluorocarbons (CFC's) are chemically stable synthetic substances that have had a variety of industrial uses. Some scientists believe that CFC's, like carbon dioxide, can contribute to a “greenhouse effect” resulting in a warming of the earth. Some scientists also believe that CFC's are destroying ozone that absorbs potentially harmful ultraviolet radiation from the sun.

Radon is a naturally occurring radioactive gas found in varying concentrations in the ground. The decay products of radon are also radioactive; if they are inhaled and become attached to the lining of the lungs, they can cause cancer. Radon enters buildings from the ground; in areas where the soil contains high concentrations of radon, dangerous levels of the gas may accumulate in a building without adequate ventilation.