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Air pollution has many different aspects. Whether the pollution is likely to cause environmental or
health effects depends on the concentration of pollutants and the amount of time an individual is exposed to them.
Smog
is an often-visible haze made up of thousands of constituents, the most abundant, but not necessarily the most toxic, of which is ozone. Ozone -- made up of three oxygen atoms -- is produced when volatile organic compounds (VOCs) and nitrogen oxides released from natural and human sources combine in the presence of sunlight. Ozone at elevated levels can create breathing problems, particularly in the young, the old, and persons with existing health problems. Exposure to excess ozone reduces lung function by increasing sensitivity to asthma and aging lungs. It may irritate eyes, cause nasal congestion, and reduce resistance to colds and other infections. Ozone at elevated levels is toxic to other living organisms as well; it damages plants and trees by affecting the stability of cell walls.
Particulate matter, which is made up of ash, smoke soot, dust, fibers, and liquid droplets, can be
produced by the burning of wood, diesel, and other fuels; agricultural activities, mining, and industrial processes; and traffic on unpaved roads. Particulate matter produces a haze that can
cause visibility problems. It also dirties and damages buildings and clothes. Smaller particulates can be inhaled deeply and, with elevated concentrations over an extended period of time, can
cause lung damage and bronchitis. Recent studies have linked exposure to these smallest particles to a greater risk of premature death.*
Nitrogen oxides
result from the burning of fossil fuels, such as coal, natural gas, gasoline, and oil. At present, automobiles are the main source of nitrogen oxide emissions in urban areas. Nitrogen oxides, at elevated concentrations, can damage the respiratory system. They can also be a key ingredient in the formation of both ozone and acid rain.
Sulfur dioxide
is released when sulfur-containing fuels, such as coal and oil, are burned. Common sources of sulfur dioxide emissions are electric utilities and certain industrial processes, such as copper smelting. Sulfur dioxide at elevated concentrations can cause respiratory problems and also affects plant and crop production. It also can be a contributing component of acid rain.
Toxic chemicals, which include VOCs such as benzene, toluene and 1,1,1 trichloroethane, when inhaled in
elevated concentrations over time, can cause birth defects, cancer, and various other health problems. Sources of toxic emission include industrial processes, such as refineries and chemical
manufacturers, and small businesses, such as print shops and dry cleaners. VOCs also contribute directly to the formation of ozone, another air pollutant.
Carbon monoxide (CO)
is formed when fuel does not burn completely. Cars and trucks, as well as power plants, are the main contributors. Carbon monoxide interferes with the blood's ability to transport oxygen to cells and tissues. Exposure to elevated levels of carbon monoxide can cause drowsiness, headaches, and sometimes death. Carbon monoxide is particularly hazardous to those who have heart disease or pre-existing lung conditions.
Acid rain
forms when the sulfur dioxide, nitrogen oxides, and carbon dioxide emitted from fossil-fuel-burning industrial plants and other combustion processes combine with rain, fog, or snow in the atmosphere. Over time, with conducive geologic conditions, acid rain can increase the acidities of lakes, streams, and soils, disturbing or destroying local environments. Wind can carry pollutants far away from where they originated, creating problems in other states or countries.
Lead
is a heavy metal that persists in the environment for decades. The former use of leaded gasoline, which is no longer commercially available in most of the United States, the manufacture of lead-based paint, and lead-acid battery reclamation operations are sources of lead in the air. Emissions from metal smelters are another source. Exposure to lead at high levels and over time can cause brain and other nervous system damage, particularly in children. Excess exposure to lead can also harm wildlife and is known to cause cancer in animals.
Carbon dioxide, a compound naturally found in the atmosphere, is produced by humans and animals and
utilized by plants in the photosynthesis process. Carbon dioxide is also produced, however, by electric utilities, cars, petroleum refineries, the burning of wood, and many other sources. The
elevated presence of carbon dioxide, as well as other gases such as methane and nitrous oxide, is believed to influence global climate change by preventing heat from escaping out of the
atmosphere in a phenomenon known as global warming. The implications of global warming over the long term are serious, including catastrophic floods and droughts.
(Source: EPA, The Clean Air Act Amendments: A Guide for Small Businesses [September 1992].)
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