air pollution

(ecology) The presence in the outdoor atmosphere of one or more contaminants such as dust, fumes, gas, mist, odor, smoke, or vapor in quantities and of characteristics and duration such as to be injurious to human, plant, or animal life or to property, or to interfere unreasonably with the comfortable enjoyment of life and property.

The presence in the atmospheric environment of natural and artificial substances that affect human health or well-being, or the well-being of any other specific organism. Pragmatically, air pollution also applies to situations where contaminants impact structures and artifacts or esthetic sensibilities (such as visibility or smell). Most artificial impurities are injected into the atmosphere at or near the Earth's surface. The lower atmosphere (troposphere) cleanses itself of some of these pollutants in a few hours or days as the larger particles settle to the surface and soluble gases and particles encounter precipitation or are removed through contact with surface objects. Unfortunately, removal of some pollutants (for example, sulfates and nitrates) by precipitation and dry deposition results in acid deposition, which may cause serious environmental damage. Also, mixing of the pollutants into the upper atmosphere may dilute the concentrations near the Earth's surface, but can cause long-term changes in the chemistry of the upper atmosphere, including the ozone layer. See also Atmosphere; Troposphere.

Types of sources

Sources may be characterized in a number of ways. First, a distinction may be made between natural and anthropogenic sources. Another frequent classification is in terms of stationary (power plants, incinerators, industrial operations, and space heating) and moving (motor vehicles, ships, aircraft, and rockets) sources. Another classification describes sources as point (a single stack), line (a line of stacks), or area (city).

Different types of pollution are conveniently specified in various ways: gaseous, such as carbon monoxide, or particulate, such as smoke, pesticides, and aerosol sprays; inorganic, such as hydrogen fluoride, or organic, such as mercaptans; oxidizing substances, such as ozone, or reducing substances, such as oxides of sulfur and oxide s of nitrogen; radioactive substances, such as iodine-131; inert substances, such as pollen or fly ash; or thermal pollution, such as the heat produced by nuclear power plants.

Air contaminants are produced in many ways and come from many sources; it is difficult to identify all the various producers. Also, for some pollutants such as carbon dioxide and methane, the natural emissions sometimes far exceed the anthropogenic emissions.

Both anthropogenic and natural emissions are variable from year to year, depending on fuel usage, industrial development, and climate. In some countries where pollution control regulations have been implemented, emissions have been significantly reduced. For example, in the United States sulfur dioxide emissions dropped by about 30% between 1970 and 1992, and carbon monoxide (CO) emissions were cut by over 30% in the same period. However, in some developing countries emissions continually rise as more cars are put on the road and more industrial facilities and power plants are constructed. In dry regions, natural emissions of nitrogen oxides (NO_x), carbon dioxide (CO₂), and hydrocarbons can be greatly increased during a season with high rainfall and above-average vegetation growth.

The anthropogenic component of most estimates of the methane budget is about two-thirds. Ruminant production and emissions from rice paddies are regarded as anthropogenic because they result from human agricultural activities. The perturbations to carbon dioxide since the industrial revolution are also principally the result of human activities. These emissions have not yet equilibrated with the rest of the carbon cycle and so have had a profound effect on atmospheric levels, even though emissions from fossil fuel combustion are dwarfed by natural emissions.

Effects

The major concern with air pollution relates to its effects on humans. Since most people spend most of their time indoors, there has been increased interest in air-pollution concentrations in homes, workplaces, and shopping areas. Much of the early information on health effects came from occupational health studies completed prior to the implementation of general air-quality standards.

Air pollution principally injures the respiratory system, and health effects can be studied through three approaches, clinical, epidemiological, and toxicological. Clinical studies use human subjects in controlled laboratory conditions, epidemiological studies assess human subjects (health records) in real-world conditions, and toxicological studies are conducted on animals or simple cellular systems. Of course, epidemiological studies are the most closely related to actual conditions, but they are the most difficult to interpret because of the lack of control and the subsequent problems with statistical analysis. Another difficulty arises because of differences in response among different people. For example, elderly asthmatics are likely to be more strongly affected by sulfur dioxide than the teenage members of a hiking club. See also Epidemiology.

Damage to vegetation by air pollution is of many kinds. Sulfur dioxide may damage field crops such as alfalfa and trees such as pines, especially during the growing season (Fig. 1). Both hydrogen fluoride (HF) and nitrogen dioxide (NO₂) in high concentrations have been shown to be harmful to citrus trees and ornamental plants, which are of economic, importance in central Florida. Ozone and ethylene are other contaminants that cause damage to certain kinds of vegetation.

Air pollution can affect the dynamics of the atmosphere through changes in longwave and shortwave radiation processes. Particles can absorb or reflect incoming short-wave solar radiation, keeping it from the Earth's surface during the day. Greenhouse gases can absorb long-wave radiation emitted by the Earth's surface and atmosphere.

Carbon dioxide, methane, fluorocarbons, nitrous oxides, ozone, and water vapor are important greenhouse gases. These represent a class of gases that selectively absorb long-wave radiation. This effect warms the temperature of the Earth's atmosphere and surface higher than would be found in the absence of an atmosphere (the greenhouse effect). Because the amount of greenhouse gases in the atmosphere is rising, there is a possibility that the temperature of the atmosphere will gradually rise, possibly resulting in a general warming of the global climate over a time period of several generations. See also Greenhouse effect.

Researchers are also concerned with pollution of the stratosphere (10–50 km or 6–30 mi above the Earth's surface) by aircraft and by broad surface sources. The stratosphere is important, because it contains the ozone layer, which absorbs part of the Sun's short-wave radiation and keeps it from reaching the surface. If the ozone layer is significantly depleted, an increase in skin cancer in humans is expected. Each 1% loss of ozone is estimated to increase the skin cancer rate 3–6%. See also Stratosphere.

Visibility is reduced as concentrations of aerosols or particles increase. The particles do not just affect visibility by themselves but also act as condensation nuclei for cloud or haze formation. In each of the three serious air-pollution episodes discussed above, smog (smoke and fog) were present with greatly reduced visibility.

Chemistry

Air pollution can be divided into primary and secondary compounds, where primary pollutants are emitted directly from sources (for example, carbon monoxide, sulfur dioxide) and secondary pollutants are produced by chemical reactions between other pollutants and atmospheric gases and particles (for example, sulfates, ozone). Most of the chemical transformations are best described as oxidation processes. In many cases these secondary pollutants can have significant environmental effects, such as acid rain and smog.

Smog is the best-known example of secondary pollutants formed by photochemical processes, as a result of primary emissions of nitric oxide (NO) and reactive hydrocarbons from anthropogenic sources such as transportation and industry as well as natural sources. Energy from the Sun causes the formation of nitrogen dioxide, ozone (O₃), and peroxyacetalnitrate, which cause eye irritation and plant damage.

It has been shown that when emissions of sulfur dioxide and nitrogen oxide from tall power plant and other industrial stacks are carried over great distances and combined with emissions from other areas, acidic compounds can be formed by complex chemical reactions. In the absence of anthropogenic pollution sources, the average pH of rain is around 5.6 (slightly acidic). In the eastern United States, acid rain with a pH less than 5.0 has been measured and consists of about 65% dilute sulfuric acid, 30% dilute nitric acid, and 5% other acids.

The addition of harmful chemicals to the atmosphere. The most serious air pollution results from the burning of fossil fuels, especially in internal-combustion engines.

Human exposures to airborne chemicals vary widely among inhalation microenvironment categories, which include workplaces, residences, outdoor ambient air, transportation, recreation areas, and public spaces. There are also wide variations in exposure within each category, depending on the number and strength of the sources of the airborne chemicals, the volume and mixing characteristics of the air within the defined microenvironment, the rate of air exchange between indoor and outdoor air, and the rate of loss to surfaces within the microenvironment.

Exposures to airborne chemicals in the workplace are extremely variable in terms of composition and concentration, depending on the materials being handled, the process design and operation, the kinds and degree of engineering controls applied to minimize releases to the air, work practices followed, and personal protection provided. Airborne chemicals in residential microenvironments are attributable to their presence in the air infiltrating from out of doors and to their release from indoor sources, such as unvented cooking stoves and space heaters, cigarettes, and consumer products, including volatile emissions from wallboard, textiles, carpets, and other materials. Indoor sources can release nitrogen dioxide (NO₂), fine particle mass (FPM), and formaldehyde (HCHO) to such an extent that indoor concentrations for these chemicals can be much higher than those in ambient outdoor air.

For pollutants having National Ambient Air Quality Standards (NAAQS), such as particulate matter, NO₂, carbon monoxide (CO), ozone (O₂), lead (PB), and sulfur dioxide (SO₂), there is an extensive network of fixed-site monitors, generally on rooftops. Although these devices generate large volumes of data, the concentrations at these sites may differ substantially from the concentrations that people breathe, especially for tailpipe pollutants such as carbon monoxide.

Transportation sources represent a significant source of exposures. Many people spend up to three hours each day in autos or buses as they go to work, to school, or shopping. Inhalation exposures to CO in vehicles and garages can represent a significant fraction of total CO exposures. Recreational exposure while exercising may also be important to total daily exposure because the increased respiratory ventilation associated with exercise can produce much more than proportional increases in delivered dose and functional responses.

Current concern regarding community air quality, is focused on particulate matter (PM) and ozone. A broad variety of processes produce suspended particulate matter (PM) in the ambient air in which we live and breathe, and there are statistically significant associations between the concentrations of airborne PM and the rates of mortality and morbidity in human populations. The PM concentrations have almost always been expressed in terms of mass. Also, in studies that reported on associations between health effects and more than one mass concentration, the strength of the association generally improves as one goes from total suspended particulate matter (TSP) to thoracic particulate matter (PM10 microns or less in aerodynamic diameter [PM10]), to fine particulate matter (PM2.5 microns or less in aerodynamic diameter [PM2.5]).

(SEE ALSO: Airborne Particles; Carbon Monoxide; Clean Air Act; Hazardous Air Pollutants; Inhalable Particles [Sulfates]; Lead; National Ambient Air Quality Standards; Smog [Air Pollution]; Sulfur-Containing Air Pollutants [Particulates]; Total Suspended Particles [TSP])

Bibliography

Lippmann, M., ed. (2000). Environmental Toxicants, 2nd edition. New York: Wiley.

U.S. Environmental Protection Agency (2001). Air Quality Criteria for Particulate Matter. EPA 600/P-99/002. Washington, DC: Author.

— MORTON LIPPMANN

The presence in the earth's atmosphere of man-caused, or man-made, contaminants which may adversely affect property, or the lives of plants, animals, or humans. Common air pollutants include: carbon dioxide, carbon monoxide, lead, nitrogen oxides, ozone, smoke, and sulphur dioxide. In 1988 the EC adopted a directive to limit emissions of sulphur dioxide, nitrogen oxides and dust from power stations above a certain capacity, and the most rigorous environmental protection targets in the 1990s have been set by the six founding states of the EC, together with Denmark. See ambient air standard. See also pollution.

For more information on air pollution, visit Britannica.com.

Air Pollution became a matter of concern in the United States in the nineteenth century, when population growth and industrialization increased the number of wood and coal furnaces, which generated enough smoke to overwhelm natural air-filtering processes and threaten human health. Coal-burning facilities in industrial centers like Pittsburgh, Pennsylvania, and smelter towns like Butte, Montana, spewed tons of smoke, soot, ash, and gases into the atmosphere. Boosters often applauded the smoke as a sign of prosperity. But by the late nineteenth century the hazards of smoke were better understood. Airborne pollutants became especially dangerous when a so-called thermal inversion occurred, trapping the pollutants and allowing them to build up for days in warm air overlaid by a cold air mass. In these cases, human exposure could and did cause respiratory illnesses and deaths. As early as 1815 some local governments required that manufacturers control emissions, and during the Progressive Era most major cities passed ordinances to control the "smoke nuisance." However, events such as the Donora smog of 1948, a thermal inversion in which twenty residents of Donora, Pennsylvania, died and more than five thousand fell ill, suggested that local efforts to abate air pollution were not sufficiently safeguarding public health.

In 1955, Congress enacted the first federal air-quality legislation, providing research and technical assistance to states. States and localities remained responsible for regulating factory emissions and the brown automobile-induced "photochemical smog" over urban basins, but this act expanded federal authority over air-quality control. With the Clean Air Act of 1963 Congress increased aid to states and for the first time allowed federal control over automobile emissions. In 1965 Congress enacted a law requiring automakers to install emissions-reducing devices on all cars built and sold in the United States after 1967.

The Air Quality Act of 1967 dramatically expanded federal control. It authorized federal regulation of stationary as well as mobile pollution sources, required states to impose air-quality standards in problem regions, and allowed federal controls where states failed to act. The Clean Air Act of 1970, a centerpiece of the burgeoning environmental movement, directed the Environmental Protection Agency (EPA), established the previous year, to set National Ambient Air Quality Standards (NAAQS). Under this law the EPA identified the principal air pollutants (particulates, sulfur dioxide, carbon monoxide, hydrocarbons, nitrogen dioxide, ozone, and, after 1978, lead), set maximum allowable levels for each, and required that states draft plans for meeting the federal standards. The act also required that stationary polluters secure federal permits contingent on their use of "best available" abatement technology and mandated that automakers achieve a 90 percent decrease in vehicle emissions by 1985 (a timetable relaxed somewhat by amendments in 1977).

In general these laws set maximum pollutant levels but left it to the polluters to find ways to meet them. This tactic, called "technology forcing," spurred automakers to adopt catalytic converters in the 1970s and compelled the

"big three" automakers (GM, Ford, and Chrysler) in 1993 to launch their Clean Car Initiative, a joint pledge to develop vehicles averaging ninety miles per gallon by 2003. When California insisted that zero-emission vehicles account for 10 percent of all new cars in the state by 2003, setting a precedent that other large states like New York were likely to follow, automakers stepped up efforts to develop new emissions technology. Much research focused on the "hybrid," an electric car with a small, supplementary fuel-burning motor that could radically cut emissions and reduce gasoline consumption. The first mass-produced hybrid, a Honda, was available in the United States in 1999. Other research focused on hydrogen-fed fuel cells, whose only exhaust is water vapor.

Industrial interests pleaded for less-stringent standards, claiming air-pollution control is expensive and economically damaging. Industries blamed the soaring inflation of the 1970s on environmental-protection legislation. In response the EPA delayed requirements and devised strategies for reducing pollution without placing undue burdens on manufacturers. For example, the "bubble" concept, formally adopted in a 1979 amendment to the Clean Air Act, placed an imaginary bubble over an entire region and required the air in the bubble to meet NAAQS levels. Firms in the same bubble could trade pollution rights with each other, allowing excess pollution at one source as long as it was offset by lower emissions at another. (The previous approach had forced each individual "stack" to meet national standards.) By defining each factory as part of a larger air shed, the bubble concept was a step toward an ecosystem-oriented approach. Along these lines, the Clean Air Act of 1990 capped the nation's total sulfur oxide emissions and allowed firms to set up a nationwide market in pollution permits.

By the late 1990s, such measures had significantly reduced major air pollutants in most metropolitan areas. However, haze in scenic nonurban areas such as the Grand Canyon caused by nearby urban areas and power plants had emerged as a growing problem. Moreover, as environmentalists adopted an increasingly global perspective, they identified new air pollution issues. Among the issues was acid precipitation, sulfur dioxide and other chemicals that originate in industrial areas, drift across political borders, and wash out of the atmosphere with rain, snow, or fog, causing acid deposits in lakes and forests. Another new issue, especially following the discovery in 1985 of an "ozone hole" over Antarctica, was depletion of the Earth's ozone layer caused by chlorofluorocarbons (CFCs) used in aerosol propellants, foam plastics, refrigerants, and industrial processes. A third issue that entered environmental debates in the 1980s concerned the emission of "greenhouse gases," especially carbon dioxide, that trap heat in the Earth's atmosphere and, according to many scientists, cause global-scale climate changes. These transnational and global air-quality issues stoked the fears of the industrial interests regarding greater government intervention in their affairs. Such reactions reflect the "out of sight, out of mind" axiom that long characterized responses to air pollution. Efforts to control visible pollution, like smoke or smog, traditionally won widespread support. But the less visible and more theoretical problems attracted detractors, who questioned the scientific methods of pollution-control proponents and raised the specter of economic stagnation to forestall stricter regulations.

Along with global air quality, attention focused on indoor air quality. Radon, a naturally occurring radioactive gas that collects in basements across much of the nation, was identified as a significant carcinogen. Secondary tobacco smoke raised substantial alarm in the 1990s, when many businesses, municipalities, and even states (notably California in 1994) banned Smoking in indoor workplaces. Mold spores, chemical fumes, and other invisible pollutants that circulate indoors were identified as health hazards in the 1980s, giving rise to the term "sick building syndrome" and forcing businesses to listen more carefully when employees complained of "bad air" in the workplace. Thus despite massive government intervention and the hopes of some environmentalists, air pollution did not disappear. The most visible pollutants generally lessened, but research revealed that air pollution was more complex, widespread, and intimate than previously thought.

Bibliography

Andrews, Richard N. L. Managing the Environment, Managing Ourselves: A History of American Environmental Policy. New Haven, Conn.: Yale University Press, 1999.

Bailey, Christopher J. Congress and Air Pollution: Environmental Policies in the USA. Manchester, U.K., New York: Manchester University Press, 1998.

Grant, Wyn. Autos, Smog, and Pollution Control: The Politics of Air Quality Management in California. Aldershot, U.K., Brook-field, Vt.: Edward Elgar, 1995.

Hays, Samuel P. Beauty, Health, and Permanence: Environmental Politics in the United States, 1955–1985. New York: Cambridge University Press, 1987.

Miller, E. Willard, and Ruby M. Miller. Indoor Pollution: A Reference Handbook. Santa Barbara, Calif.: ABC–CLIO, 1998.

Stradling, David. Smokestacks and Progressives: Environmentalists, Engineers, and Air Quality in America, 1881–1951. Baltimore: Johns Hopkins University Press, 1999.

Switzer, Jacqueline Vaughn. Environmental Politics: Domestic and Global Dimensions. New York: St. Martin's Press, 1994.

—Dennis Williams/W. P.

Air pollution has plagued communities since the industrial revolution and even before. Airborne pollutants, such as gases, chemicals, smoke particles, and other substances, reduce the value of and ability to enjoy affected property and cause significant health and environmental problems. Despite the long history and significant consequences of this problem, effective legal remedies are relatively recent. Though some cities adopted air quality laws as early as 1815, air pollution at that time was seen as a problem best handled by local laws and ordinances. Only as the United States' cities continued to grow, and pollution and health concerns with them, did federal standards and a nationwide approach to air quality begin to emerge.

The earliest cases involving air pollution were likely to be brought because of a noxious smell, such as from a slaughterhouse, animal herd, or factory, that interfered with a landowner's ability to enjoy his or her property. These disputes were handled through the application of the nuisance doctrine, which provides that the possessor of land has a duty to make a reasonable use of his or her property in a manner that does not harm other individuals in the area. A person who polluted the air and caused harm to others was liable for breaching this duty and was required to pay damages or was enjoined (stopped through an injunction issued by a court) from engaging in the activities that created the pollution. In determining whether to enjoin an alleged polluter, courts balanced the damage to the plaintiff landowner's property against the hardship the defendant polluter would incur in trying to eliminate, or abate, the pollution. Courts often denied injunctions because the economic damage suffered by the defendant — and, by extension, the surrounding community, if the defendant was essential to the local economy — in trying to eliminate the pollution often outweighed the damage suffered by the plaintiff. Thus, in many cases, the plaintiff was left only with the remedy of money damages — a cash payment equal to the estimated monetary value of the damage caused by the pollution — and the polluting activities were allowed to continue.

Using the nuisance action to control widespread air pollution proved inadequate for other reasons as well. At common law, only the attorney general or local prosecutor could sue to abate a public nuisance (one that damages a large number of persons) unless a private individual could show "special" damage that was distinct from and more severe than that suffered by the general public. The private plaintiff with special damage had the necessary standing (legally protectible interest) to seek injunctive relief. The problem of standing has been corrected in some states through laws that allow a private citizen to sue to abate public nuisances such as air pollution, though these laws are by no means the norm. Yet another difficulty with the nuisance doctrine is the plaintiff's burden of showing that the harm she or he has experienced was caused by a particular defendant. Pollutants can derive from many sources. As a result, it can be difficult, if not impossible, to prove that a particular polluter is responsible for a particular problem. Lastly, nuisance law was useful only to combat particular polluters; it did not provide an ongoing and systematic mechanism for the regulation and control of pollution.

Early in the nineteenth century, a few U.S. cities recognized the shortcomings of common-law remedies and enacted local laws that attempted to address the problem of air pollution. Pittsburgh, in 1815, was one of the first to institute air quality laws. Others, like Chicago and Cincinnati, passed smoke control ordinances in 1881, and by 1912, twenty-three U.S. cities with populations of over two hundred thousand had passed smoke abatement laws.

Though the early court cases usually addressed polluted air as an interference with the enjoyment of property, scientists quickly discovered that air pollution also poses significant health and environmental risks. It is believed to contribute to the incidence of chronic diseases such as emphysema, bronchitis, and other respiratory illnesses and has been linked to higher mortality rates from other diseases, including cancer and heart disease.

The shortcomings associated with the common-law remedies to control air pollution and increasing alarm over the problem's long-range effects finally resulted in the development of state and federal legislation. The first significant legislation concerning air quality was the Air Pollution Control Act, enacted in 1955 (42 U.S.C.A. § 7401 et seq. [1955]). Also known as the Clean Air Act, it gave the secretary of health, education, and welfare the power to undertake and recommend research programs for air pollution control. Amendments passed during the 1960s authorized federal agencies to intervene to help abate interstate pollution in limited circumstances, to control emissions from new motor vehicles, and to provide some supervision and enforcement powers to states trying to control pollution. By the end of the 1960s, when it became clear that states had made little progress in combating air pollution, Congress toughened the Clean Air Act through a series of new laws, which were known as the Clean Air Act Amendments of 1970 (Pub. L. No. 91-604, 84 Stat. 1676 [Dec. 31, 1970]).

The 1970 amendments greatly increased federal authority and responsibility for addressing the problem of air pollution. They provided for, among other things, uniform national emissions standards for the hazardous air pollutants most likely to cause an increase in mortality or serious illness. Under the amendments, the states retained some regulatory authority, having "primary responsibility for assuring air quality within the entire geographic area comprising such state." Thus, states could not "opt out" of air pollution regulation and for the first time were required to attain certain air quality standards within a specified period of time. In addition, the amendments directed the administrator of the Environmental Protection Agency (EPA), which was also established in 1970, to institute national standards regarding ambient air quality for air pollutants endangering public health or welfare, in particular sulfur dioxide, carbon monoxide, and photochemical oxidants in the atmosphere. The EPA was also granted the authority to require levels of harmful pollutants to be brought within set standards before further industrial expansion would be permitted.

Despite the ambitious scope of the 1970 legislation, many of its goals were never attained. As a result, the Clean Air Act was extensively revised again in 1977 (Pub. L. No. 95-95, 91 Stat. 685 [Aug. 7, 1977]). One significant component of the 1977 amendments was the formulation of programs designed to inspect, control, and monitor vehicle emissions. The 1977 revisions also sought to regulate parking on the street, discourage automobile use in crowded areas, promote the use of bicycle lanes, and encourage employer-sponsored carpooling. Unlike the goals of several of the 1970 amendments, many of the 1977 reforms have become reality. Many states, with the help of federal funding, have developed programs that require automobiles to be tested regularly for emissions problems before they can be licensed and registered. The 1977 amendments also directed the EPA to issue regulations to reduce "haze" in national parks and other wilderness areas. Under these regulations the agency has sought to improve air quality in a number of areas, including the Grand Canyon in Arizona.

During the 1980s and 1990s, several environmental issues, including acid rain, global climate change, and the depletion of the ozone layer, gave rise to further federal regulation. Acid rain, which has caused significant damage to U.S. and Canadian lakes, is created when the sulfur from fossil fuels, such as coal, combines with oxygen in the air to create sulfur dioxide, a pollutant. The sulfur dioxide then combines with oxygen to form sulfate, which, when washed out of the air by fog, clouds, mist, or rain, becomes acid rain, with potentially catastrophic effects on vegetation and water. Amendments to the Clean Air Act in 1990 (Pub. L. No. 101-549, 104 Stat. 2399 [Nov. 15, 1990]) sought to address the challenges posed by acid rain by commissioning a number of federally sponsored studies, including an analysis of Canada's approach to dealing with acid rain and an investigation of the use of buffering and neutralizing agents to restore lakes and streams. The 1990 laws also directed the EPA to prepare a report on the feasibility of developing standards related to acid rain that would "protect sensitive and critically sensitive aquatic and terrestrial resources." In addition, the amendments provided for a controversial system of "marketable allowances," which authorize industries to emit certain amounts of sulfate and which can be transferred to other entities or "banked" for future use.

The problem of global climate change is linked to the accumulation of gases, including carbon dioxide and methane, in the atmosphere. Scientists disagree over the net effect of this pollution on the global climate: some argue that it produces global warming; others maintain that it gradually cools global temperatures. Scientists do agree that a sustained climate change in either direction could significantly affect the environment.

The 1990 amendments implemented a number of strategies to address changes in the global climate, including the commissioning of studies on options for controlling the emission of methane. The amendments also contain provisions to deal with the depletion of the ozone layer, which shields the earth from the harmful effects of the sun's radiation. Though the long-term consequences are hard to determine at this time, damage has already been seen in the form of a "hole" in the ozone layer over Antarctica. The destruction of the ozone layer is believed to be caused by the release into the atmosphere of chlorofluorocarbons (CFCs) and other similar substances. The 1990 laws include a ban on "nonessential uses" of ozone-depleting chemicals, and the placement of conspicuous warning labels on certain substances, indicating that their use harms public health and the environment by destroying the ozone in the upper atmosphere.

In the 1990s, the battle to control air pollution moved indoors, into homes and businesses. Studies have shown that people are exposed to higher concentrations of air pollution for longer periods of time inside buildings than out-of-doors. Furthermore, evidence indicates that this exposure is contributing to a rapidly increasing incidence of illness, thus costing businesses, taxpayers, and the government billions of dollars in health care costs and lost work time. The typical U.S. home contains many hazardous chemicals and substances, including radon, which has been linked to lung cancer and other ailments. Congress has responded to public concern about indoor air quality by requiring the EPA, with the Superfund Amendments and Reauthorization Act (SARA), to establish a program to study the problem and make appropriate recommendations (Superfund Amendments and Reauthorization Act of 1986, Pub. L. No. 99-499, 100 Stat. 1613 [codified as amended in scattered sections of 10 U.S.C.A., 26 U.S.C.A., 29 U.S.C.A., 33 U.S.C.A., and 42 U.S.C.A.]).

One contentious air pollution issue is the effect of smoking in public places, especially as it concerns the rights and health of nonsmokers. Many states have enacted legislation designed to protect nonsmokers in public places, and the battle between smokers and nonsmokers is also making its way into the courts. An increasing number of restaurants, airlines, and other public facilities have dealt with the problem by banning smoking completely.

See: Automobiles; Environmental Law; Environmental Protection Agency; Pollution; Surgeon General; Tobacco.

The addition of harmful chemicals to the atmosphere. The most serious air pollution results from the burning of fossil fuels, especially in internal-combustion engines.

Air pollution from World War II production.

Smog over Santiago

Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or damages the natural environment, into the atmosphere.

The atmosphere is a complex, dynamic natural gaseous system that is essential to support life on planet Earth. Stratospheric ozone depletion due to air pollution has long been recognized as a threat to human health as well as to the Earth's ecosystems.

Contents 1 Pollutants 2 Sources 2.1 Emission factors 3 Indoor air quality (IAQ) 4 Health effects 4.1 Effects on cystic fibrosis 4.2 Effects on COPD 4.3 The Great Smog of 1952 4.4 Effects on children 4.5 Health effects in relatively "clean" areas 5 Reduction efforts 5.1 Control devices 6 Legal regulations 6.1 Canada 6.2 European Union 6.2.1 United Kingdom 6.3 United States 7 Statistics 7.1 Most polluted cities 7.2 Carbon dioxide emissions 8 Atmospheric dispersion 9 Environmental impacts of greenhouse gas pollutants 10 See also 11 References 12 External links

Pollutants

Main articles: Pollutant and Greenhouse gas

Before flue gas desulfurization was installed, the emissions from this power plant in New Mexico contained excessive amounts of sulfur dioxide.

An air pollutant is known as a substance in the air that can cause harm to humans and the environment. Pollutants can be in the form of solid particles, liquid droplets, or gases. In addition, they may be natural or man-made.^[1]

Pollutants can be classified as either primary or secondary. Usually, primary pollutants are substances directly emitted from a process, such as ash from a volcanic eruption, the carbon monoxide gas from a motor vehicle exhaust or sulfur dioxide released from factories.

Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or interact. An important example of a secondary pollutant is ground level ozone — one of the many secondary pollutants that make up photochemical smog.

Note that some pollutants may be both primary and secondary: that is, they are both emitted directly and formed from other primary pollutants.

About 4 percent of deaths in the United States can be attributed to air pollution, according to the Environmental Science Engineering Program at the Harvard School of Public Health.

Major primary pollutants produced by human activity include:

• Sulfur oxides (SO_x) - especially sulfur dioxide, a chemical compound with the formula SO₂. SO₂ is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide. Further oxidation of SO₂, usually in the presence of a catalyst such as NO₂, forms H₂SO₄, and thus acid rain.[2] This is one of the causes for concern over the environmental impact of the use of these fuels as power sources.
• Nitrogen oxides (NO_x) - especially nitrogen dioxide are emitted from high temperature combustion. Can be seen as the brown haze dome above or plume downwind of cities.Nitrogen dioxide is the chemical compound with the formula NO₂. It is one of the several nitrogen oxides. This reddish-brown toxic gas has a characteristic sharp, biting odor. NO₂ is one of the most prominent air pollutants.
• Carbon monoxide - is a colourless, odourless, non-irritating but very poisonous gas. It is a product by incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide.
• Carbon dioxide (CO₂) - a greenhouse gas emitted from combustion but is also a gas vital to living organisms. It is a natural gas in the atmosphere.
• Volatile organic compounds - VOCs are an important outdoor air pollutant. In this field they are often divided into the separate categories of methane (CH₄) and non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming. Other hydrocarbon VOCs are also significant greenhouse gases via their role in creating ozone and in prolonging the life of methane in the atmosphere, although the effect varies depending on local air quality. Within the NMVOCs, the aromatic compounds benzene, toluene and xylene are suspected carcinogens and may lead to leukemia through prolonged exposure. 1,3-butadiene is another dangerous compound which is often associated with industrial uses.

• Particulate matter - Particulates, alternatively referred to as particulate matter (PM) or fine particles, are tiny particles of solid or liquid suspended in a gas. In contrast, aerosol refers to particles and the gas together. Sources of particulate matter can be man made or natural. Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes also generate significant amounts of aerosols. Averaged over the globe, anthropogenic aerosols—those made by human activities—currently account for about 10 percent of the total amount of aerosols in our atmosphere. Increased levels of fine particles in the air are linked to health hazards such as heart disease, altered lung function and lung cancer.

• Toxic metals, such as lead, cadmium and copper.
• Chlorofluorocarbons (CFCs) - harmful to the ozone layer emitted from products currently banned from use.
• Ammonia (NH₃) - emitted from agricultural processes. Ammonia is a compound with the formula NH₃. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to foodstuffs and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceuticals. Although in wide use, ammonia is both caustic and hazardous.
• Odors — such as from garbage, sewage, and industrial processes
• Radioactive pollutants - produced by nuclear explosions, war explosives, and natural processes such as the radioactive decay of radon.

Secondary pollutants include:

• Particulate matter formed from gaseous primary pollutants and compounds in photochemical smog .Smog is a kind of air pollution; the word "smog" is a portmanteau of smoke and fog. Classic smog results from large amounts of coal burning in an area caused by a mixture of smoke and sulfur dioxide. Modern smog does not usually come from coal but from vehicular and industrial emissions that are acted on in the atmosphere by sunlight to form secondary pollutants that also combine with the primary emissions to form photochemical smog.
• Ground level ozone (O₃) formed from NO_x and VOCs. Ozone (O₃) is a key constituent of the troposphere (it is also an important constituent of certain regions of the stratosphere commonly known as the Ozone layer). Photochemical and chemical reactions involving it drive many of the chemical processes that occur in the atmosphere by day and by night. At abnormally high concentrations brought about by human activities (largely the combustion of fossil fuel), it is a pollutant, and a constituent of smog.
• Peroxyacetyl nitrate (PAN) - similarly formed from NO_x and VOCs.

Minor air pollutants include:

• A large number of minor hazardous air pollutants. Some of these are regulated in USA under the Clean Air Act and in Europe under the Air Framework Directive.
• A variety of persistent organic pollutants, which can attach to particulate matter.

Persistent organic pollutants (POPs) are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Because of this, they have been observed to persist in the environment, to be capable of long-range transport, bioaccumulate in human and animal tissue, biomagnify in food chains, and to have potential significant impacts on human health and the environment.

Sources

Main article: AP 42 Compilation of Air Pollutant Emission Factors

Dust storm approaching Stratford, Texas

Controlled burning of a field outside of Statesboro, Georgia in preparation for spring planting

Sources of air pollution refer to the various locations, activities or factors which are responsible for the releasing of pollutants in the atmosphere. These sources can be classified into two major categories which are:

Anthropogenic sources (human activity) mostly related to burning different kinds of fuel

• "Stationary Sources" include smoke stacks of power plants, manufacturing facilities (factories) and waste incinerators, as well as furnaces and other types of fuel-burning heating devices

• "Mobile Sources" include motor vehicles, marine vessels, aircraft and the effect of sound etc.

• Chemicals, dust and controlled burn practices in agriculture and forestry management. Controlled or prescribed burning is a technique sometimes used in forest management, farming, prairie restoration or greenhouse gas abatement. Fire is a natural part of both forest and grassland ecology and controlled fire can be a tool for foresters. Controlled burning stimulates the germination of some desirable forest trees, thus renewing the forest.

• Fumes from paint, hair spray, varnish, aerosol sprays and other solvents

• Waste deposition in landfills, which generate methane.Methane is not toxic; however, it is highly flammable and may form explosive mixtures with air. Methane is also an asphyxiant and may displace oxygen in an enclosed space. Asphyxia or suffocation may result if the oxygen concentration is reduced to below 19.5% by displacement

• Military, such as nuclear weapons, toxic gases, germ warfare and rocketry

Natural sources

• Dust from natural sources, usually large areas of land with little or no vegetation.
• Methane, emitted by the digestion of food by animals, for example cattle.
• Radon gas from radioactive decay within the Earth's crust. Radon is a colorless, odorless, naturally occurring, radioactive noble gas that is formed from the decay of radium. It is considered to be a health hazard. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as the basement and it is the second most frequent cause of lung cancer, after cigarette smoking.

• Smoke and carbon monoxide from wildfires.
• Volcanic activity, which produce sulfur, chlorine, and ash particulates.

Emission factors

Main article: AP 42 Compilation of Air Pollutant Emission Factors

Air pollutant emission factors are representative values that attempt to relate the quantity of a pollutant released to the ambient air with an activity associated with the release of that pollutant. These factors are usually expressed as the weight of pollutant divided by a unit weight, volume, distance, or duration of the activity emitting the pollutant (e.g., kilograms of particulate emitted per megagram of coal burned). Such factors facilitate estimation of emissions from various sources of air pollution. In most cases, these factors are simply averages of all available data of acceptable quality, and are generally assumed to be representative of long-term averages.

The United States Environmental Protection Agency has published a compilation of air pollutant emission factors for a multitude of industrial sources.^[2] The United Kingdom, Australia, Canada and many other countries have published similar compilations, as well as the European Environment Agency.^{[3][4][5][6][7]}

Indoor air quality (IAQ)

Main article: Indoor air quality

A lack of ventilation indoors concentrates air pollution where people often spend the majority of their time. Radon (Rn) gas, a carcinogen, is exuded from the Earth in certain locations and trapped inside houses. Building materials including carpeting and plywood emit formaldehyde (H₂CO) gas. Paint and solvents give off volatile organic compounds (VOCs) as they dry. Lead paint can degenerate into dust and be inhaled. Intentional air pollution is introduced with the use of air fresheners, incense, and other scented items. Controlled wood fires in stoves and fireplaces can add significant amounts of smoke particulates into the air, inside and out^[8]. Indoor pollution fatalities may be caused by using pesticides and other chemical sprays indoors without proper ventilation.

Carbon monoxide (CO) poisoning and fatalities are often caused by faulty vents and chimneys, or by the burning of charcoal indoors. Chronic carbon monoxide poisoning can result even from poorly adjusted pilot lights. Traps are built into all domestic plumbing to keep sewer gas, hydrogen sulfide, out of interiors. Clothing emits tetrachloroethylene, or other dry cleaning fluids, for days after dry cleaning.

Though its use has now been banned in many countries, the extensive use of asbestos in industrial and domestic environments in the past has left a potentially very dangerous material in many localities. Asbestosis is a chronic inflammatory medical condition affecting the tissue of the lungs. It occurs after long-term, heavy exposure to asbestos from asbestos-containing materials in structures. Sufferers have severe dyspnea (shortness of breath) and are at an increased risk regarding several different types of lung cancer. As clear explanations are not always stressed in non-technical literature, care should be taken to distinguish between several forms of relevant diseases. According to the World Health Organisation (WHO), these may defined as; asbestosis, lung cancer, and mesothelioma (generally a very rare form of cancer, when more widespread it is almost always associated with prolonged exposure to asbestos).

Biological sources of air pollution are also found indoors, as gases and airborne particulates. Pets produce dander, people produce dust from minute skin flakes and decomposed hair, dust mites in bedding, carpeting and furniture produce enzymes and micrometre-sized fecal droppings, inhabitants emit methane, mold forms in walls and generates mycotoxins and spores, air conditioning systems can incubate Legionnaires' disease and mold, and houseplants, soil and surrounding gardens can produce pollen, dust, and mold. Indoors, the lack of air circulation allows these airborne pollutants to accumulate more than they would otherwise occur in nature.

Health effects

The World Health Organization states that 2.4 million people die each year from causes directly attributable to air pollution, with 1.5 million of these deaths attributable to indoor air pollution.^[9] "Epidemiological studies suggest that more than 500,000 Americans die each year from cardiopulmonary disease linked to breathing fine particle air pollution. . ."^[10] A study by the University of Birmingham has shown a strong correlation between pneumonia related deaths and air pollution from motor vehicles.^[11] Worldwide more deaths per year are linked to air pollution than to automobile accidents.^{[citation needed]} Published in 2005 suggests that 310,000 Europeans die from air pollution annually.^{[citation needed]} Direct causes of air pollution related deaths include aggravated asthma, bronchitis, emphysema, lung and heart diseases, and respiratory allergies.^{[citation needed]} The US EPA estimates that a proposed set of changes in diesel engine technology (Tier 2) could result in 12,000 fewer premature mortalities, 15,000 fewer heart attacks, 6,000 fewer emergency room visits by children with asthma, and 8,900 fewer respiratory-related hospital admissions each year in the United States.^{[citation needed]}

The worst short term civilian pollution crisis in India was the 1984 Bhopal Disaster.^[12] Leaked industrial vapors from the Union Carbide factory, belonging to Union Carbide, Inc., U.S.A., killed more than 2,000 people outright and injured anywhere from 150,000 to 600,000 others, some 6,000 of whom would later die from their injuries.^{[citation needed]} The United Kingdom suffered its worst air pollution event when the December 4 Great Smog of 1952 formed over London. In six days more than 4,000 died, and 8,000 more died within the following months.^{[citation needed]} An accidental leak of anthrax spores from a biological warfare laboratory in the former USSR in 1979 near Sverdlovsk is believed to have been the cause of hundreds of civilian deaths.^{[citation needed]} The worst single incident of air pollution to occur in the United States of America occurred in Donora, Pennsylvania in late October, 1948, when 20 people died and over 7,000 were injured.^[13]

The health effects caused by air pollutants may range from subtle biochemical and physiological changes to difficulty in breathing, wheezing, coughing and aggravation of existing respiratory and cardiac conditions. These effects can result in increased medication use, increased doctor or emergency room visits, more hospital admissions and premature death. The human health effects of poor air quality are far reaching, but principally affect the body's respiratory system and the cardiovascular system. Individual reactions to air pollutants depend on the type of pollutant a person is exposed to, the degree of exposure, the individual's health status and genetics.^{[citation needed]}

A new economic study of the health impacts and associated costs of air pollution in the Los Angeles Basin and San Joaquin Valley of Southern California shows that more than 3800 people die prematurely (approximately 14 years earlier than normal) each year because air pollution levels violate federal standards. The number of annual premature deaths is considerably higher than the fatalities related to auto collisions in the same area, which average fewer than 2,000 per year ^[14].

Diesel exhaust (DE) is a major contributor to combustion derived particulate matter air pollution. In several human experimental studies, using a well validated exposure chamber setup, DE has been linked to acute vascular dysfunction and increased thrombus formation.^[15][16] This serves as a plausible mechanistic link between the previously described association between particulate matter air pollution and increased cardiovascular morbidity and mortality.

Effects on cystic fibrosis

Main article: Cystic fibrosis

A study from 1999 to 2000 by the University of Washington showed that patients near and around particulate matter air pollution had an increased risk of pulmonary exacerbations and decrease in lung function.^[17] Patients were examined before the study for amounts of specific pollutants like Pseudomonas aeruginosa or Burkholderia cenocepacia as well as their socioeconomic standing. Participants involved in the study were located in the United States in close proximity to an Environmental Protection Agency.^{[clarification needed]} During the time of the study 117 deaths were associated with air pollution. A trend was noticed that patients living closer or in large metropolitan areas to be close to medical help also had higher level of pollutants found in their system because of more emissions in larger cities. With cystic fibrosis patients already being born with decreased lung function everyday pollutants such as smoke emissions from automobiles, tobacco smoke and improper use of indoor heating devices could add to the disintegration of lung function.^[18]

Effects on COPD

Main article: COPD

Chronic obstructive pulmonary disease (COPD) include diseases such as chronic bronchitis, emphysema, and some forms of asthma.^[19]

A study conducted in 1960-1961 in the wake of the Great Smog of 1952 compared 293 London residents with 477 residents of Gloucester, Peterborough, and Norwich, three towns with low reported death rates from chronic bronchitis. All subjects were male postal truck drivers aged 40 to 59. Compared to the subjects from the outlying towns, the London subjects exhibited more severe respiratory symptoms (including cough, phlegm, and dyspnea), reduced lung function (FEV₁ and peak flow rate), and increased sputum production and purulence. The differences were more pronounced for subjects aged 50 to 59. The study controlled for age and smoking habits, so concluded that air pollution was the most likely cause of the observed differences.^[20]

It is believed that much like cystic fibrosis, by living in a more urban environment serious health hazards become more apparent. Studies have shown that in urban areas patients suffer mucus hypersecretion, lower levels of lung function, and more self diagnosis of chronic bronchitis and emphysema.^[21]

The Great Smog of 1952

Main article: Great Smog of 1952

Early in December 1952, a cold fog descended upon London. Because of the cold, Londoners began to burn more coal than usual. The resulting air pollution was trapped by the inversion layer formed by the dense mass of cold air. Concentrations of pollutants, coal smoke in particular, built up dramatically. The problem was made worse by use of low-quality, high-sulphur coal for home heating in London in order to permit export of higher-quality coal, because of the country's tenuous postwar economic situation. The "fog", or smog, was so thick that driving became difficult or impossible.^[22]. The extreme reduction in visibility was accompanied by an increase in criminal activity as well as transportation delays and a virtual shut down of the city. During the 4 day period of fog, at least 4,000 people died as a direct result of the weather.^[23]

Effects on children

Cities around the world with high exposure to air pollutants have the possibility of children living within them to develop asthma, pneumonia and other lower respiratory infections as well as a low initial birth rate. Protective measures to ensure the youths' health are being taken in cities such as New Delhi, India where buses now use compressed natural gas to help eliminate the “pea-soup” smog.^[24] Research by the World Health Organization shows there is the greatest concentration of particulate matter particles in countries with low economic world power and high poverty and population rates. Examples of these countries include Egypt, Sudan, Mongolia, and Indonesia. The Clean Air Act was passed in 1970, however in 2002 at least 146 million Americans were living in areas that did not meet at least one of the “criteria pollutants” laid out in the 1997 National Ambient Air Quality Standards.^[25] Those pollutants included: ozone, particulate matter, sulfur dioxide, nitrogen dioxide, carbon monoxide, and lead. Because children are outdoors more and have higher minute ventilation they are more susceptible to the dangers of air pollution.

Health effects in relatively "clean" areas

Even in areas with relatively low levels of air pollution, public health effects can be substantial and costly. This is because effects can occur at very low levels and a large number of people can potentially breathe in such pollutants. A 2005 scientific study for the British Columbia Lung Association showed that a 1% improvement in ambient PM2.5 and ozone concentrations will produce a $29 million in annual savings in the region in 2010^[26]. This finding is based on health valuation of lethal (mortality) and sub-lethal (morbidity) effects.

Reduction efforts

There are various air pollution control technologies and land use planning strategies available to reduce air pollution. At its most basic level land use planning is likely to involve zoning and transport infrastructure planning. In most developed countries, land use planning is an important part of social policy, ensuring that land is used efficiently for the benefit of the wider economy and population as well as to protect the environment.

Efforts to reduce pollution from mobile sources includes primary regulation (many developing countries have permissive regulations),^{[citation needed]} expanding regulation to new sources (such as cruise and transport ships, farm equipment, and small gas-powered equipment such as lawn trimmers, chainsaws, and snowmobiles), increased fuel efficiency (such as through the use of hybrid vehicles), conversion to cleaner fuels (such as bioethanol, biodiesel, or conversion to electric vehicles).

Control devices

The following items are commonly used as pollution control devices by industry or transportation devices. They can either destroy contaminants or remove them from an exhaust stream before it is emitted into the atmosphere.

• Particulate control
  • Mechanical collectors (dust cyclones, multicyclones)
  • Electrostatic precipitators An electrostatic precipitator (ESP), or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulate matter such as dust and smoke from the air stream.
  • Baghouses Designed to handle heavy dust loads, a dust collector consists of a blower, dust filter, a filter-cleaning system, and a dust receptacle or dust removal system (distinguished from air cleaners which utilize disposable filters to remove the dust).

• • Particulate scrubbersWet scrubber is a form of pollution control technology. The term describes a variety of devices that use pollutants from a furnace flue gas or from other gas streams. In a wet scrubber, the polluted gas stream is brought into contact with the scrubbing liquid, by spraying it with the liquid, by forcing it through a pool of liquid, or by some other contact method, so as to remove the pollutants.

• Scrubbers
  • Baffle spray scrubber
  • Cyclonic spray scrubber
  • Ejector venturi scrubber
  • Mechanically aided scrubber
  • Spray tower
  • Wet scrubber

• NOx control
  • Low NOx burners
  • Selective catalytic reduction (SCR)
  • Selective non-catalytic reduction (SNCR)
  • NOx scrubbers
  • Exhaust gas recirculation
  • Catalytic converter (also for VOC control)

• VOC abatement
  • Adsorption systems, such as activated carbon
  • Flares
  • Thermal oxidizers
  • Catalytic oxidizers
  • Biofilters
  • Absorption (scrubbing)
  • Cryogenic condensers
  • Vapor recovery systems

• Acid Gas/SO₂ control
  • Wet scrubbers
  • Dry scrubbers
  • Flue gas desulfurization

• Mercury control
  • Sorbent Injection Technology
  • Electro-Catalytic Oxidation (ECO)
  • K-Fuel

• Dioxin and furan control

• Miscellaneous associated equipment
  • Source capturing systems
  • Continuous emissions monitoring systems (CEMS)

Legal regulations

The examples and perspective in this article may not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page.

Smog in Cairo

In general, there are two types of air quality standards. The first class of standards (such as the U.S. National Ambient Air Quality Standards) set maximum atmospheric concentrations for specific pollutants. Environmental agencies enact regulations which are intended to result in attainment of these target levels. The second class (such as the North American Air Quality Index) take the form of a scale with various thresholds, which is used to communicate to the public the relative risk of outdoor activity. The scale may or may not distinguish between different pollutants.

Canada

In Canada, air quality is typically evaluated against standards set by the Canadian Council of Ministers of the Environment (CCME), an inter-governmental body of federal, provincial and territorial Ministers responsible for the environment. The CCME has set Canada Wide Standards(CWS).^[27][28] These are:

• CWS for PM2.5 = 30 µg/m3 (24 hour averaging time, by year 2010, based on 98th percentile ambient measurement annually, averaged over 3 consecutive years).

• CWS for ozone = 65 ppb (8-hour averaging time, by year 2010, achievement is based on the 4th highest measurement annually, averaged over 3 consecutive years).

Note that there is no consequence in Canada to not achieving these standards. In addition, these only apply to jurisdictions with populations greater than 100,000. Further, provinces and territories may set more stringent standards than those set by the CCME.

European Union

A report from the European Environment Agency shows that road transport remains Europe’s single largest air polluter ^[29] .

National Emission Ceilings (NEC) for certain atmospheric pollutants are regulated by Directive 2001/81/EC (NECD).^[30] As part of the preparatory work associated with the revision of the NECD, the European Commission is assisted by the NECPI working group (National Emission Ceilings – Policy Instruments).^[31]

Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on ambient air quality and cleaner air for Europe (the new Air Quality Directive) has entried into force 2008-06-11 ^[32].

Individual citizens can force their local councils to tackle air pollution, following an important ruling in July 2009 from the European Court of Justice (ECJ). The EU’s court was asked to judge the case of a resident of Munich, Dieter Janecek, who said that under the 1996 EU Air Quality Directive (Council Directive 96/62/EC of 27 September 1996 on ambient air quality assessment and management ^[33]) the Munich authorities were obliged to take action to stop pollution exceeding specified targets. Janecek then took his case to the ECJ, whose judges said European citizens are entitled to demand air quality action plans from local authorities in situations where there is a risk that EU limits will be overshot. ^[29] .

United Kingdom

Air quality targets set by the UK's Department for Environment, Food and Rural Affairs (DEFRA) are mostly aimed at local government representatives responsible for the management of air quality in cities, where air quality management is the most urgent. The UK has established an air quality network where levels of the key air pollutants^[34] are published by monitoring centers.^[35] Air quality in Oxford, Bath and London^[36] is particularly poor. One controversial study^[37] performed by the Calor Gas company and published in the Guardian newspaper compared walking in Oxford on an average day to smoking over sixty light cigarettes.

More precise comparisons can be collected from the UK Air Quality Archive^[38] which allows the user to compare a cities management of pollutants against the national air quality objectives^[39] set by DEFRA in 2000.

Localized peak values are often cited, but average values are also important to human health. The UK National Air Quality Information Archive offers almost real-time monitoring of "current maximum" air pollution measurements for many UK towns and cities.^[40] This source offers a wide range of constantly updated data, including:

• Hourly Mean Ozone (µg/m³)
• Hourly Mean Nitrogen dioxide (µg/m³)
• Maximum 15-Minute Mean Sulphur dioxide (µg/m³)
• 8-Hour Mean Carbon monoxide (mg/m³)
• 24-Hour Mean PM₁₀ (µg/m³ Grav Equiv)

DEFRA acknowledges that air pollution has a significant effect on health and has produced a simple banding index system^[41] is used to create a daily warning system that is issued by the BBC Weather Service to indicate air pollution levels.^[42] DEFRA has published guidelines for people suffering from respiratory and heart diseases.^[43]

United States

Looking down from the Hollywood Hills, with Griffith Observatory on the hill in the foreground, air pollution is visible in downtown Los Angeles on a late afternoon.

In the 1960s, 70s, and 90s, the United States Congress enacted a series of Clean Air Acts which significantly strengthened regulation of air pollution. Individual U.S. states, some European nations and eventually the European Union followed these initiatives. The Clean Air Act sets numerical limits on the concentrations of a basic group of air pollutants and provide reporting and enforcement mechanisms.

In 1999, the United States EPA replaced the Pollution Standards Index (PSI) with the Air Quality Index (AQI) to incorporate new PM2.5 and Ozone standards.

The effects of these laws have been very positive. In the United States between 1970 and 2006, citizens enjoyed the following reductions in annual pollution emissions:^[44]

• carbon monoxide emissions fell from 197 million tons to 89 million tons
• nitrogen oxide emissions fell from 27 million tons to 19 million tons
• sulfur dioxide emissions fell from 31 million tons to 15 million tons
• particulate emissions fell by 80%
• lead emissions fell by more than 98%

In an October 2006 letter to EPA, the agency's independent scientific advisors warned that the ozone smog standard “needs to be substantially reduced” and that there is “no scientific justification” for retaining the current, weaker standard. The scientists unanimously recommended a smog threshold of 60 to 70 ppb after they conducted an extensive review of the evidence. ^[45]

The EPA has proposed, in June 2007, a new threshold of 75 ppb. This is less strict than the scientific recommendation, but is more strict than the current standard.

Some industries are lobbying to keep the current standards in place. Environmentalists and public health advocates are mobilizing to support the scientific recommendations.^{[citation needed]}

The National Ambient Air Quality Standards are pollution thresholds which trigger mandatory remediation plans by state and local governments, subject to enforcement by the EPA.

An outpouring of dust layered with man-made sulfates, smog, industrial fumes, carbon grit, and nitrates is crossing the Pacific Ocean on prevailing winds from booming Asian economies in plumes so vast they alter the climate. Almost a third of the air over Los Angeles and San Francisco can be traced directly to Asia. With it comes up to three-quarters of the black carbon particulate pollution that reaches the West Coast. ^[46]

Libertarians typically suggest propertarian methods of stopping pollution. They advocate strict liability which would hold accountable anyone who causes polluted air to emanate into someone else's airspace. This offense would be considered aggression, and damages could be sought in court under the common law, possibly through class action suits.^[47] Since in a libertarian society, highways would be privatized under a system of free market roads, the highway owners would also be held liable for pollution emanating from vehicles traveling along their property. This would give them a financial incentive to keep the worst polluters off of their roads.

Statistics

This section requires expansion.

Most polluted cities

Air pollution is usually concentrated in densely populated metropolitan areas, especially in developing countries where environmental regulations are relatively lax or nonexistent. However, even populated areas in developed countries attain unhealthy levels of pollution.

Carbon dioxide emissions

Most Polluted World Cities by PM[48]
Particulate matter, μg/m³ (2004)	City
169	Cairo, Egypt
150	Delhi, India
128	Kolkata, India (Calcutta)
125	Tianjin, China
123	Chongqing, China
109	Kanpur, India
109	Lucknow, India
104	Jakarta, Indonesia
101	Shenyang, China

Total CO₂ emissions

Main article: List of countries by carbon dioxide emissions

Countries with the highest CO2 emissions
Country	Carbon dioxide emissions per year (106 Tons) (2006)	Percentage of global total
China	6,103	21.5%
United States	5,752	20.2%
Russia	1,564	5.5%
India	1,510	5.3%
Japan	1293	4.6%
Germany	805	2.8%
United Kingdom	568	2.0%
Canada	544	1.9%
South Korea	475	1.7%
Italy	474	1.7%

Per capita CO₂ emissions^[49]

Main article: List of countries by carbon dioxide emissions per capita

Countries with the highest per capita CO2 emissions
Country	Carbon dioxide emissions per year (Tons per person) (2006)
Qatar	56.2
United Arab Emirates	32.8
Kuwait	31.2
Bahrain	28.8
Trinidad and Tobago	25.3
Luxembourg	24.5
Netherlands Antilles	22.8
Aruba	22.3
United States	19
Australia	18.1

Atmospheric dispersion

Main article: Atmospheric dispersion modeling

The basic technology for analyzing air pollution is through the use of a variety of mathematical models for predicting the transport of air pollutants in the lower atmosphere. The principal methodologies are:

• Point source dispersion, used for industrial sources.
• Line source dispersion, used for airport and roadway air dispersion modeling
• Area source dispersion, used for forest fires or duststorms
• Photochemical models, used to analyze reactive pollutants that form smog

Visualization of a buoyant Gaussian air pollution dispersion plume as used in many atmospheric dispersion models

The point source problem is the best understood, since it involves simpler mathematics and has been studied for a long period of time, dating back to about the year 1900. It uses a Gaussian dispersion model for buoyant pollution plumes to forecast the air pollution isopleths, with consideration given to wind velocity, stack height, emission rate and stability class (a measure of atmospheric turbulence).^[50][51] This model has been extensively validated and calibrated with experimental data for all sorts of atmospheric conditions.

The roadway air dispersion model was developed starting in the late 1950s and early 1960s in response to requirements of the National Environmental Policy Act and the U.S. Department of Transportation (then known as the Federal Highway Administration) to understand impacts of proposed new highways upon air quality, especially in urban areas. Several research groups were active in this model development, among which were: the Environmental Research and Technology (ERT) group in Lexington, Massachusetts, the ESL Inc. group in Sunnyvale, California and the California Air Resources Board group in Sacramento, California. The research of the ESL group received a boost with a contract award from the United States Environmental Protection Agency to validate a line source model using sulfur hexafluoride as a tracer gas. This program was successful in validating the line source model developed by ESL inc. Some of the earliest uses of the model were in court cases involving highway air pollution, the Arlington, Virginia portion of Interstate 66 and the New Jersey Turnpike widening project through East Brunswick, New Jersey.

Area source models were developed in 1971 through 1974 by the ERT and ESL groups, but addressed a smaller fraction of total air pollution emissions, so that their use and need was not as widespread as the line source model, which enjoyed hundreds of different applications as early as the 1970s. Similarly photochemical models were developed primarily in the 1960s and 1970s, but their use was more specialized and for regional needs, such as understanding smog formation in Los Angeles, California.

Environmental impacts of greenhouse gas pollutants

Main articles: Ocean acidification and Greenhouse effect

The greenhouse effect is a phenomenon whereby greenhouse gases create a condition in the upper atmosphere causing a trapping of heat and leading to increased surface and lower tropospheric temperatures. Carbon dioxide from combustion of fossil fuels is the major problem. Other greenhouse gases include methane, hydrofluorocarbons, perfluorocarbons, chlorofluorocarbons, nitrogen oxides, and ozone.

This effect has been understood by scientists for about a century, and technological advancements during this period have helped increase the breadth and depth of data relating to the phenomenon. Currently, scientists are studying the role of changes in composition of greenhouse gases from natural and anthropogenic sources for the effect on climate change.

A number of studies have also investigated the potential for long-term rising levels of atmospheric carbon dioxide to cause increases in the acidity of ocean waters and the possible effects of this on marine ecosystems.

See also

Acid rain Air Hygiene Foundation Air pollutant concentrations Air pollution in British Columbia Air Quality Index Air stagnation AP 42 Compilation of Air Pollutant Emission Factors ASEAN Agreement on Transboundary Haze Pollution Asian brown cloud Atmospheric chemistry Atmospheric dispersion modeling Beehive burner Best Available Control Technology Bibliography of atmospheric dispersion modeling Building biology List of atmospheric dispersion models Critical load Cruise ship pollution Emission standard Emissions & Generation Resource Integrated Database (eGRID) Emission-free zone Environmental agreement

Environmentalism Flue gas desulfurization Flue gas emissions from fossil fuel combustion Global Atmosphere Watch Global dimming Global warming Greenhouse effect Haze Health Effects Institute (HEI) Indicator value International Agency for Research on Cancer Kyoto Protocol Light water reactor sustainability List of natural disasters by death toll#Smog Lowest Achievable Emissions Rate National Ambient Air Quality Standards (USA EPA) NASA Clean Air Study Particulate Polluter pays principle Ship pollution Smog and Haze Spare the Air program (California) Stench Tire fire

References

1. ^ EPA: Air Pollutants
2. ^ AP 42, Volume I
3. ^ United Kingdom's emission factor database
4. ^ European Environment Agency's 2005 Emission Inventory Guidebook
5. ^ Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories (reference manual)
6. ^ Australian National Pollutant Inventory Emissions Estimation Technique Manuals
7. ^ Canadian GHG Inventory Methodologies
8. ^ Duflo, E., Greenstone, M., and Hanna, R. (2008) “Indoor air pollution, health and economic well-being”. S.A.P.I.EN.S. 1 (1)
9. ^ Estimated deaths & DALYs attributable to selected environmental risk factors, by WHO Member State, 2002
10. ^ "Newly detected air pollutant mimics damaging effects of cigarette smoke". www.eurekalert.org. http://www.eurekalert.org/pub_releases/2008-08/acs-nda072308.php. Retrieved 2008-08-17. 
11. ^ "Study links traffic pollution to thousands of deaths" (in English). The Guardian (London, UK: Guardian Media Group). 2008-04-15. http://www.guardian.co.uk/society/2008/apr/15/health. Retrieved 2008-04-15. 
12. ^ Simi Chakrabarti. "20th anniversary of world's worst industrial disaster". Australian Broadcasting Corporation. http://www.abc.net.au/worldtoday/content/2004/s1257352.htm. 
13. ^ Davis, Devra (2002). When Smoke Ran Like Water: Tales of Environmental Deception and the Battle Against Pollution. Basic Books. ISBN 0-465-01521-2. 
14. ^ http://www.sacbee.com/378/story/1393268.html , http://www.latimes.com/features/health/la-me-pollute13-2008nov13,0,5432723.story , http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/11/13/MNQP143CPV.DTL
15. ^ Diesel exhaust inhalation increases thrombus formation in man† Andrew J. Lucking1*, Magnus Lundback2, Nicholas L. Mills1, Dana Faratian1, Stefan L. Barath2, Jamshid Pourazar2, Flemming R. Cassee3, Kenneth Donaldson1, Nicholas A. Boon1, Juan J. Badimon4, Thomas Sandstrom2, Anders Blomberg2, and David E. Newby1
16. ^ Persistent Endothelial Dysfunction in Humans after Diesel Exhaust Inhalation Ha°kan To¨rnqvist1*, Nicholas L. Mills2*, Manuel Gonzalez3, Mark R. Miller2, Simon D. Robinson2, Ian L. Megson4, William MacNee5, Ken Donaldson5, Stefan So¨derberg3, David E. Newby2, Thomas Sandstro¨m1, and Anders Blomberg1
17. ^ Christopher H. Goss, Stacey A. Newsom, Jonathan S. Schildcrout, Lianne Sheppard and Joel D. Kaufman (2004). "Effect of Ambient Air Pollution on Pulmonary Exacerbations and Lung Function in Cystic Fibrosis". American Journal of Respiratory and Critical Care Medicine 169: 816–821. doi:10.1164/rccm.200306-779OC. PMID 14718248. 
18. ^ Michael Kymisis, Konstantinos Hadjistavrou (2008). "Short-Term Effects Of Air Pollution Levels On Pulmonary Function Of Young Adults". The Internet Journal of Pulmonary Medicine 9 (2). http://www.ispub.com/ostia/index.php?xmlFilePath=journals/ijpm/vol9n2/pollution.xml. 
19. ^ Zoidis, John D. (1999). "The Impact of Air Pollution on COPD". RT: for Decision Makers in Respiratory Care. http://www.rtmagazine.com/issues/articles/1999-10_06.asp. 
20. ^ Holland WW, Reid DD. The urban factor in chronic bronchitis. Lancet. 1965;I:445-448.
21. ^ J. Sunyer (2001). "Urban air pollution and Chronic Obstructive Pulmonary disease: a review". European Respiratory Journal 17: 1024–1033. doi:10.1183/09031936.01.17510240. PMID 11488305. http://erj.ersjournals.com/cgi/content/abstract/17/5/1024. 
22. ^ Nielsen, John (2002-12-12). "The Killer Fog of ’52: Thousands died as Poisonous Air Smothered London". National Public Radio. http://www.npr.org/templates/story/story.php?storyId=873954. 
23. ^ "On this Day: 1952 London Fog Clears After days of Chaos". BBC News. 2005-12-09. http://news.bbc.co.uk/onthisday/hi/dates/stories/december/9/newsid_4506000/4506390.stm. 
24. ^ "Polluted Cities: The Air Children Breathe" (PDF). World Health Organization. http://www.who.int/ceh/publications/en/11airpollution.pdf. 
25. ^ Committee on Environmental Health (2004). "Ambient Air Pollution: Health Hazards to Children". Pediatrics 114 (6): 1699–1707. doi:10.1542/peds.2004-2166. PMID 15574638. 
26. ^ 2005 BC Lung Association report on the valuation of health impacts from air quality in the Lower Fraser Valley airshed
27. ^ Canada-wide Standards
28. ^ Canada-Wide Standards for Particulate Matter (PM) and Ozone
29. ^ ^{a b} http://correu.cs.san.gva.es/exchweb/bin/redir.asp?URL=http://www.transportenvironment.org/Publications/prep_hand_out/lid:516
30. ^ Directive 2001/81/EC of the European Parliament and of the Council of 23 October 2001 on national emission ceilings for certain atmospheric pollutants
31. ^ Terms of Reference, Working Group on the Revision of National Emissions Ceilings and Policy InstrumentsPDF (24.4 KiB)
32. ^ http://eur-lex.europa.eu/JOHtml.do?uri=OJ:L:2008:152:SOM:EN:HTML
33. ^ OJ L 296, 21.11.1996, p. 55. Directive as amended by Regulation (EC) No 1882/2003 of the European Parliament and of the Council (OJ L 284, 31.10.2003, p. 1); Directives 96/62/EC, 1999/30/EC, 2000/69/EC and 2002/3/EC shall be repealed as from 11 June 2010
34. ^ The Department for Environment, Food & Rural Affairs (DEFRA): Air Pollution
35. ^ LAQM Air Quality Management Areas
36. ^ London
37. ^ Taking the Oxford air adds up to a 60-a-day habit (a newspaper article in The Guardian)
38. ^ UK Air Quality Archive
39. ^ UK National Air Quality Objectives
40. ^ Current Air Pollution Bulletin
41. ^ Air Pollution Bandings and Indexes
42. ^ BBC Weather Service
43. ^ Air Pollution - What it means for your health
44. ^ Wall Street Journal article, May 23, 2006
45. ^ American Lung Association, June 2, 2007
46. ^ Wall Street Journal article, July 20, 2007
47. ^ Rothbard, Murray. "Conservation, Ecology, and Growth". For a New Liberty: The Libertarian Manifesto. pp. 256–257. 
48. ^ World Bank Statistics
49. ^ International Carbon Dioxide Emissions and Carbon Intensity Energy Information Administration
50. ^ Turner, D.B. (1994). Workbook of atmospheric dispersion estimates: an introduction to dispersion modeling (2nd ed.). CRC Press. ISBN 1-56670-023-X. 
51. ^ Beychok, M.R. (2005). Fundamentals Of Stack Gas Dispersion (4th ed.). author-published. ISBN 0-9644588-0-2.  www.air-dispersion.com

External links

Wikimedia Commons has media related to: Air pollution

Air quality science and general information

• International Conference on Urban Air Quality.
• UNEP Urban Issues
• European Commission > Environment > Policies > Air >Air Quality.
• UNEP Partnership for Clean Fuels and Vehicles

Air quality modelling

• Stuff in the Air Standard air quality modelling procedure for industrial sources.
• Wiki on Atmospheric Dispersion Modelling. Addresses the international community of atmospheric dispersion modellers — primarily researchers, but also users of models. Its purpose is to pool experiences gained by dispersion modellers during their work.
• Air Dispersion Modeling Conversions and Formulas One of six technical articles devoted to air quality and air pollution dispersion modeling.

Effects on human health

• Air Pollution Triggers Blood Clots
• American Lung Association of New England on air quality.

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