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Air pollution

External video
AirVisual Earth – realtime map of global wind and air pollution

Air pollution occurs when harmful substances including particulates and biological molecules are introduced into Earth's atmosphere. It may cause diseases, allergies or death in humans; it may also cause harm to other living organisms such as animals and food crops, and may damage the natural or built environment. Human activity and natural processes can both generate air pollution.

Indoor air pollution and poor urban air quality are listed as two of the world's worst toxic pollution problems in the 2008 Blacksmith Institute World's Worst Polluted Places report. According to the 2014 WHO report, air pollution in 2012 caused the deaths of around 7 million people worldwide, an estimate roughly matched by the International Energy Agency.

An air pollutant is a substance in the air that can have adverse effects on humans and the ecosystem. The substance can be solid particles, liquid droplets, or gases. A pollutant can be of natural origin or man-made. Pollutants are classified as primary or secondary. Primary pollutants are usually produced from a process, such as ash from a volcanic eruption. Other examples include carbon monoxide gas from motor vehicle exhaust, or the sulfur dioxide released from factories. Secondary pollutants are not emitted directly. Rather, they form in the air when primary pollutants react or interact. Ground level ozone is a prominent example of a secondary pollutant. Some pollutants may be both primary and secondary: they are both emitted directly and formed from other primary pollutants.

Major primary pollutants produced by human activity include:

Secondary pollutants include:

Minor air pollutants include:

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 potentially significant impacts on human health and the environment.


Health Risk Air Quality Health Index Health Messages
At Risk population General Population
Low 1-3 Enjoy your usual outdoor activities. Ideal air quality for outdoor activities
Moderate 4-6 Consider reducing or rescheduling strenuous activities outdoors if you are experiencing symptoms. No need to modify your usual outdoor activities unless you experience symptoms such as coughing and throat irritation.
High 7-10 Reduce or reschedule strenuous activities outdoors. Children and the elderly should also take it easy. Consider reducing or rescheduling strenuous activities outdoors if you experience symptoms such as coughing and throat irritation.
Very high Above 10 Avoid strenuous activities outdoors. Children and the elderly should also avoid outdoor physical exertion and should stay indoors. Reduce or reschedule strenuous activities outdoors, especially if you experience symptoms such as coughing and throat irritation.
Most polluted cities by PM
Particulate
matter,
μg/m³ (2004)
City
168 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

  • Carbon dioxide (CO2) - This is by far the most emitted form of human caused air pollution. Although CO2 is currently only about 405 parts per million in earth's atmosphere, billions of metric tons of CO2 are emitted annually by burning of fossil fuels. CO2 increase in earth's atmosphere has been accelerating.
  • Sulfur oxides (SOx) - particularly sulfur dioxide, a chemical compound with the formula SO2. SO2 is produced by volcanoes and in various industrial processes. Coal and petroleum often contain sulfur compounds, and 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 (NOx) - Nitrogen oxides, particularly nitrogen dioxide, are expelled from high temperature combustion, and are also produced during thunderstorms by electric discharge. They can be seen as a brown haze dome above or a plume downwind of cities. Nitrogen dioxide is a chemical compound with the formula NO2. It is one of several nitrogen oxides. One of the most prominent air pollutants, this reddish-brown toxic gas has a characteristic sharp, biting odor.
  • Carbon monoxide (CO) - CO is a colorless, odorless, toxic yet non-irritating gas. It is a product of incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide.
  • Volatile organic compounds (VOC) - VOCs are a well-known outdoor air pollutant. They are categorized as either methane (CH4) or non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming. Other hydrocarbon VOCs are also significant greenhouse gases because of their role in creating ozone and prolonging the life of methane in the atmosphere. This effect varies depending on local air quality. The aromatic NMVOCs benzene, toluene and xylene are suspected carcinogens and may lead to leukemia with prolonged exposure. 1,3-butadiene is another dangerous compound often associated with industrial use.
  • Particulates, alternatively referred to as particulate matter (PM), atmospheric particulate matter, or fine particles, are tiny particles of solid or liquid suspended in a gas. In contrast, aerosol refers to combined particles and gas. 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 worldwide, anthropogenic aerosols—those made by human activities—currently account for approximately 10 percent of 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.
  • Persistent free radicals connected to airborne fine particles are linked to cardiopulmonary disease.
  • Toxic metals, such as lead and mercury, especially their compounds.
  • Chlorofluorocarbons (CFCs) - harmful to the ozone layer; emitted from products are currently banned from use. These are gases which are released from air conditioners, refrigerators, aerosol sprays, etc. On release into the air, CFCs rise to the stratosphere. Here they come in contact with other gases and damage the ozone layer. This allows harmful ultraviolet rays to reach the earth's surface. This can lead to skin cancer, eye disease and can even cause damage to plants.
  • 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. In the atmosphere, ammonia reacts with oxides of nitrogen and sulfur to form secondary particles.
  • Odours — such as from garbage, sewage, and industrial processes
  • Radioactive pollutants - produced by nuclear explosions, nuclear events, war explosives, and natural processes such as the radioactive decay of radon.
  • Particulates created from gaseous primary pollutants and compounds in photochemical smog. Smog is a kind of air pollution. 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 ultraviolet light from the sun to form secondary pollutants that also combine with the primary emissions to form photochemical smog.
  • Ground level ozone (O3) formed from NOx 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 (C2H3NO5) - similarly formed from NOx and VOCs.
  • 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. In developing and poor countries, traditional biomass burning is the major source of air pollutants; traditional biomass includes wood, crop waste and dung.
  • Mobile sources include motor vehicles, marine vessels, and aircraft.
  • Controlled burn practices in agriculture and forest 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 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 resources, such as nuclear weapons, toxic gases, germ warfare and rocketry
  • 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
  • Vegetation, in some regions, emits environmentally significant amounts of Volatile organic compounds (VOCs) on warmer days. These VOCs react with primary anthropogenic pollutants—specifically, NOx, SO2, and anthropogenic organic carbon compounds — to produce a seasonal haze of secondary pollutants. Black gum, poplar, oak and willow are some examples of vegetation that can produce abundant VOCs. The VOC production from these species result in ozone levels up to eight times higher than the low-impact tree species.
  • Volcanic activity, which produces sulfur, chlorine, and ash particulates
  • Combustion of fossil fuels for space heating can be replaced by using ground source heat pumps and seasonal thermal energy storage.
  • Electric power generation from burning fossil fuels can be replaced by power generation from nuclear and renewables.
  • Motor vehicles driven by fossil fuels, a key factor in urban air pollution, can be replaced by electric vehicles.
  • 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 particulates 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 scrubbers Wet 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.
  • Brimblecombe, Peter. The Big Smoke: A History of Air Pollution in London Since Medieval Times (Methuen, 1987)
  • Brimblecombe, Peter. "History of air pollution." in Composition, Chemistry and Climate of the Atmosphere (Van Nostrand Reinhold (1995): 1-18
  • Brimblecombe, Peter; Makra, László (2005). "Selections from the history of environmental pollution, with special attention to air pollution. Part 2*: From medieval times to the 19th century". International journal of environment and pollution. 23 (4): 351–367. doi:10.1504/ijep.2005.007599. 
  • Cherni, Judith A. Economic Growth versus the Environment: The Politics of Wealth, Health and Air Pollution (2002) online
  • Corton, Christine L. London Fog: The Biography (2015)
  • Currie, Donya. "WHO: Air Pollution a Continuing Health Threat in World's Cities," The Nation's Health (February 2012) 42#1 online
  • Dewey, Scott Hamilton. Don't Breathe the Air: Air Pollution and US Environmental Politics, 1945-1970 (Texas A & M University Press, 2000)
  • Gonzalez, George A. The politics of air pollution: Urban growth, ecological modernization, and symbolic inclusion (SUNY Press, 2012)
  • Grinder, Robert Dale (1978). "From Insurgency to Efficiency: The Smoke Abatement Campaign in Pittsburgh before World War I.". Western Pennsylvania Historical Magazine. 61 (3): 187–202. 
  • Grinder, Robert Dale. "The Battle for Clean Air: The Smoke Problem in Post-Civil War America" in Martin V. Melosi, ed., Pollution & Reform in American Cities, 1870-1930 (1980), p83-103.* Mosley, Stephen. The chimney of the world: a history of smoke pollution in Victorian and Edwardian Manchester. Routledge, 2013.
  • Peebles, Graham. Worldwide Air Pollution is Making us Ill (December 2016)
  • Schreurs, Miranda A. Environmental Politics in Japan, Germany, and the United States (Cambridge University Press, 2002) online
  • Thorsheim, Peter. Inventing Pollution: Coal, Smoke, and Culture in Britain since 1800 (2009)
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