Pollution, Air

Types of Pollution

Air pollution can be categorized as gaseous or particulate matter, primary or secondary, and toxic or nontoxic. Air pollution and related formal and informal prevention measures are also generally divided between outdoor or indoor environments.

One of the most pervasive outdoor pollutants with serious health and environmental risks is particulate matter. Particulate matter is classified in two ways, having a diameter less than 2.5 micrometers (PM2.5) and particulate matter with a diameter less than 10 micrometers (PM10). Although both forms of particulate matter present serious health risks, PM2.5 is generally considered more dangerous because of its small size—approximately 1/30 the width of a human hair. When breathed, PM2.5 can lodge deep in human lung tissue and even enter the bloodstream, causing severe health problems. Smaller particulate matter also tends to have a longer residence time in the atmosphere. As a result, PM2.5 can travel farther and affect a greater population.

The principle sources of PM2.5 and PM10 include combustion from motor vehicles, power plants, and other industrial sources, as well as biomass burning. One of the most severe sources of particulate matter is diesel-powered vehicles. Airborne dust, soils, and salts are other common forms of large particulate matter that occur in areas susceptible to high winds. The combination of these sources can produce a haze in the sky in both urban and rural areas, often in the late afternoon.

The composition of the earth's atmosphere is 78 percent nitrogen (N2), 21 percent oxygen (O2) and [Page 1391].9 percent argon (Ar). The other 0.1 percent of atmosphere consists of trace gasses such as carbon dioxide (CO2), neon (Ne), helium (He), methane (CH4), and water vapor. Except in extreme situations, most pollutants are considered trace gases and do not greatly alter the overall composition of the atmosphere. Even at extremely low levels, however, gaseous pollutants can have serious health and environmental consequences.

Important gas contaminants include: Carbon monoxide (CO), chlorofluorocarbons (CFCs), nitrogen oxides (NOx), hydrocarbons (HC), sulfur dioxide (SO2), and carbon dioxide (CO2).

Carbon monoxide (CO) is formed when carbonbased substances are burned with an insufficient supply of air. The majority of CO in the United States is emitted from motor vehicles due to the incomplete combustion of gasoline. Areas within road and highway corridors are therefore subject to high levels of CO. When inhaled, the health effects of CO include headaches, respiratory illness, and—in extremely high doses—death. Carbon monoxide is a “criteria” pollutant as outlined under the Clean Air Act.

Chlorofluorocarbons (CFCs) were used historically as refrigerants, cleaning solvents, and as propellants in aerosol canisters. CFC use was largely banned under the 1987 Montreal Protocol due to its impact on the ozone layer. The State of Oregon banned CFCs as early as 1975. Their long atmospheric lifetime—ranging from 55 to 140 years—and regenerative capabilities make CFCs particularly devastating to the upper atmosphere.

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