Air Pollution

Abstract

AbstractAir pollution is the presence of any substance in the atmosphere at a concentration high enough to produce an objectionable effect on humans, animals, vegetation, or materials, or to significantly alter the natural balance of any ecosystem. Substances can be solids, liquids, or gases, and can be produced by anthropogenic activities or natural sources. In this article only nonbiological material is considered and the discussion of airborne radioactive contaminants is limited to radon. The original six criteria pollutants, for which the Environmental Protection Agency is required to summarize published information on each, were sulfur dioxide, SO2; carbon monoxide, CO; nitrogen dioxide, NO2; ozone, O3; suspended particulates; and nonmethane hydrocarbons, NMHC. The NMHC are now referred to as volatile organic compounds (VOC). The NMHC were dropped from the list shortly after the criteria pollutants were so designated. In the late 1970s, lead, Pb, was added to the list and in 1987, so was particulate matter having an aerodynamic diameter of less than or equal to 10 µm, PM10. There have been several developments since the establishment of the criteria pollutants. In the mid‐1970s it was shown that high concentrations of O3and sulfate haze could be transported hundreds of miles, and acid deposition studies in the 1980s clearly illustrated the international and global aspects of this transport. Then stratospheric O3depletion and global warming became issues and air pollution was finally viewed in a global context. Air pollution can be considered to have three components: sources, transport and transformations in the atmosphere, and receptors. The source emits airborne substances. The receptor is the person, animal, plant, material, or ecosystem affected by the emissions. In the United States, the framework for air quality management is the Clean Air Act (CAA), which defines two categories of pollutants; criteria and hazardous. For the criteria pollutants, the CAA requires that EPA establish National Ambient Air Quality Standards (NAAQS) and emissions standards for stationary sources and for motor vehicles. For the hazardous air pollutants, only emissions standards for some sources are required, but the number is growing rapidly. Current air pollution concerns include photochemical smog, volatile organic compounds (VOC), nitrogen oxides (NOx), sulfur oxides (SOx), carbon monoxide (CO), particulate matter, global warming (the greenhouse effect), and stratospheric O3depletion, among others.