Point Sources of Pollution

Point sources of pollution are individual, localized facilities that emit air and/or water pollution into the environment. Point sources can also emit thermal, light, and noise pollution. Point sources of air pollution are often also called stationary sources and are usually industrial facilities (e.g., coal-fired power plants, chemical plants, steel mills, paper mills, copper and aluminum smelters, oil refineries). A related category, area sources, refers to small, stationary sources of air pollution such as dry cleaners, bakeries, fast-food restaurants, home fireplaces, landfills, and gasoline stations. The other major source of air pollution is transportation, or mobile sources, which has accounted for a growing share of air pollution as increasingly strict standards have been implemented in many nations for stationary sources and as the automobile fleet size has increased. In the water pollution arena, the major point sources are publicly owned sewage treatment plants and industrial effluent dischargers. The other major sources of water pollution are nonpoint, diffuse sources such as runoff from agriculture, silviculture, storm water, and cities.

Point sources of pollution are usually regulated by government requirements to control emissions or effluents from smokestacks, pipes, vents, ditches, tunnels, or conduits, either by limiting the emission rate over a short time period or by controlling the total emissions into the ambient air or water. Permits are often issued that specify these requirements for the emission source (usually a private business), including the type of pollution being controlled, which could be one or more categories. For large industrial sources, these requirements can become complicated and expensive, involving dozens of point sources and many categories of air and water pollution. Since the 1980s, governments have increasingly turned to emissions trading systems to control point sources of pollution, especially in the United States. These approaches, such as emission offsets and “cap-and-trade” systems for sulfur dioxide and nitrogen oxides, are more cost-effective and flexible for industry. In the case of water pollution, effluent trading in watersheds even allows for trading between point and nonpoint sources.

In addition to the regulation of air pollution from individual point sources, atmospheric dispersion modeling is often required to determine the effects of individual sources on ambient air quality, particularly in urban areas. Such modeling requires mathematical simulation by computer programs to determine the atmospheric concentration of pollutants downwind from a range of sources. These models are important to the efforts of government air pollution agencies to design control strategies and plans. For water pollution, water quality simulation and waste load allocation models are used to similarly determine how multiple-point source dischargers can best meet ambient standards and total maximum daily load requirements.