Air Quality

The standard composition of a well-mixed atmosphere is approximately 78 percent nitrogen, 21 percent oxygen, 0.93 percent argon, and 0.038 percent carbon dioxide, plus water vapor (spatially and temporally variable) and numerous trace constituents. Because of the negative impacts of poor air quality, such as acid precipitation or compromised human health, an understanding of both normal and disturbed atmospheric conditions is necessary. Air quality is an assessment of the state of the atmosphere that uses a combination of various characteristics describing the ambient atmosphere, including concentration of pollutants, visibility, turbidity, and thermal pollution. [Page 11]Air quality problems are often common to urbanized regions, where people engage in industrial activities, vehicular traffic is concentrated, and other conditions that deteriorate the ambient atmosphere exist. Efforts to mitigate compromised air quality range from international treaties and protocols to local regulations and ordinances.

Photochemical smog, most commonly associated with Los Angeles, is caused by the interaction of solar radiation with pollutants like nitrogen oxides, peroxyacytyl nitrate, and volatile organic compounds

Source: iStockphoto

Pollutants that compromise the “clean” characteristics of the air may come from nonhuman or human (anthropogenic) sources. Nonhuman sources of pollutants include volcanic eruptions, which send ash and sulfurous gases into the atmosphere, diminishing local visibility and possibly contributing to cooling on a global scale. Lightning-caused forest fires create airborne particulates, or soot, and anaerobic decomposition in wetlands is a source of methane. Because there is little that can be done with respect to natural sources of air pollutants, efforts to restore and maintain air quality usually focus on reducing anthropogenic sources of pollution. Anthropogenic sources of air pollutants include particulate matter caused by combustion engines, chemicals released by industrial and agricultural processes, and the use of consumer products.