Air pollution comes from many different sources such as factories, power plants, dry cleaners, cars, buses, trucks and even windblown dust and wildfires. Air pollution can threaten the well-being of humans, trees, lakes, crops, and animals, as well as damage the ozone layer and buildings. Air pollution also can cause haze, reducing visibility in national parks and wilderness areas.

• Sample and measure the particulate matter in the air at various locations and/or elevations in the schoolyard 1
  
• Sample and measure the particulate matter in the air at various locations and/or elevations in the schoolyard 2
  
• Air Pollution Science Fair Projects and Experiments
  
• Find out how dirty (polluted) the air is in your neighborhood
  

This power plant in New Mexico releases sulfur dioxide and particulate matter into the air.

Air pollution is a broad term applied to all physical (particulate matter), chemical, and biological agents that modify the natural characteristics of the atmosphere.

Some definitions also consider physical perturbations such as noise pollution, heat, radiation, and light pollution as air pollution. Definitions commonly include the term harmful as a requisite to consider a change to the atmosphere as pollution.

Air pollutants are classified as either primary or secondary. A primary air pollutant is one that is emitted directly to the air from a given source, such as the Carbon monoxide (CO) produced as a byproduct of combustion; whereas a secondary air pollutant is formed in the atmosphere through chemical reactions involving primary air pollutants. The formation of ozone in photochemical smog is an example of a secondary air pollutant.

The atmosphere is a complex, dynamic and fragile system. Concern is growing about the global effects of air pollutant emissions, especially global warming. Stratospheric ozone depletion due to air pollution has long been recognized as a threat to human health.

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

Casualties

It is estimated that three million people indirectly die of air pollution each year worldwide. About 90% of these mortalities are largely attributable to indoor air pollution in developing nations. In the U.S. between 50,000 and 100,000 deaths per year are linked to air pollution, more people than die from car accidents. Research published in 2005 suggests that 310,000 Europeans die from air pollution annually. Direct causes of air pollution related deaths include aggravated asthma, bronchitis, emphysema, lung and heart diseases, and other respiratory allergies. The US EPA estimates that a proposed set of changes in diesel engine technology (Tier 2) standards 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 US.

The worst short-term civilian event from pollution in India was the 1984 Bhopal Disaster. Leaked industrial vapors 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. 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. The United Kingdom suffered its worst air pollution event when the December 4th Great Smog of 1952 formed over London. In six days more than 4,000 died, and 8,000 more died within the following months. 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.

Intentional air pollution in combat is called chemical warfare. Poison gas as a chemical weapon was principally used during World War I, and resulted in an estimated 91,198 deaths and 1,205,655 injuries. Various treaties have sought to ban its further use. Non-lethal chemical weapons, such as tear gas and pepper spray, are widely used.

Pollution Sources

Dust storm approaching Stratford, Texas

Anthropogenic Sources related to burning different kinds of fuel - human activity

• Combustion-fired power plants.
• Vehicles with internal combustion engines.
• Devices powered by two-stroke engines.
• Stoves and incinerators, especially ones that are coal or wood-fired.
• Farmers burning their crop waste.
• Wood fires, which usually burn inefficiently.

Other Anthropogenic Sources

• Aerosol sprays and refrigeration.
• Arsenic and chlorine found in drinking water and inhaled in bathroom showers.
• Dust and chemicals from farming, especially of erodible land, see Dust Bowl.
• Fumes from paint, varnish, and other solvents.
• Industrial activity in general.
• Military actions, including the use and testing of nuclear bombs, poison gases, and germ warfare.
• Oil refining.
• Waste deposition in landfills, which generate methane (CH₄)
• Rocketry, which produces many tons of exotic emissions quickly and which deposits some of them directly into the tenuous upper atmosphere.

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, namely cattle.
• Pine trees, which emit volatile organic compounds (VOCs) and oxygen.
• Radon gas from earth minerals.
• Smoke and carbon monoxide (CO) from wildfires.
• Volcanic activity, which produce sulfur, chlorine, and ash particulates.

Contaminants

Contaminants of air can be classified as particulates and gases.

Particulates are small particles, classified by their sizes. Atmospheric particles are usually measured as TSP, PM10 or PM2.5. (TSP stands for Total Suspended Particulates. PM stands for Particulate Matter.) The PM10 fraction consists of particles with an aerodynamic diameter of less than 10 micrometres; these are more dangerous to humans than TSP, because they can be breathed deep into the respiratory tract and reach the lungs. PM2.5 particles are even more dangerous because they can pass through the upper airway filtering and into the alveoli, where they can cross the lung/blood stream barrier and transport into the blood. Increasing attention is now focusing on the health impacts of even smaller particles -- the so-called 'nanoparticles'. Smaller particles tend to be more toxic than larger particles and can stay airborne as an 'aerosol' for longer than larger particles, which settle out more quickly.

Important pollutant gases include:

• Carbon monoxide (CO), which is primarily emitted from combustion process, particularly from petrol vehicle exhausts due to incomplete combustion; the highest concentrations are generally found at roadside locations - more at signal light junctions. Inhalation of high levels of carbon monoxide can cause headaches, fatigue and respiratory problems. According to the EPA (as presented in the 2002 World Almanac), 97,441 thousand short tons of carbon monoxide were released in the United States during the year 1999, 75,151 of those caused by transportation related exhaust.
• Chlorofluorocarbons, which destroy the stratospheric ozone layer. Examples of chlorofluorocarbons: methane (CH₄), ethane(C₂H₆), propane (C₃H₈), butane (C₄H₁₀), hexane (C₆H₁₄). see Alkane.
• Hydrocarbon gases.
• Nitrogen oxides (NO_x). Emissions are primarily in the form of NO, which is oxidised by ozone (O₃) from nitric oxide (NO) to Nitrogen dioxide (NO₂). NO₂) is the primary concern for effects on health, and is the species for which WHO's health-based standards are expressed. The various oxides of nitrogen can also react with hydrocarbons in the atmosphere to contribute to photochemical smog. NO_x can also affect ecologically sensitive sites through deposition, causing acidification and eutrophication. In The U.S., 25,393 short tons of nitrogen oxide were released during 1999 [1].
• Sulfur oxide (SO_x), which causes acid rain is derived from the burning of fuel containing sulfur, mostly at power plants, and during metal smelting and other industrial processes. In the U.S., 12.46 tons of sulfur dioxide (SO₂) were released in 1999. [2], however there has been a 33 percent decrease in emissions between 1983 and 2002, due largely to state restrictions.
• Tropospheric ozone, which is ozone in the lower part of the atmosphere. Ozone (O₃) is a secondary pollutant, formed through photochemical reactions involving NO_x and hydrocarbons; it is an irritant gas. In the stratosphere it helps to reduce the amount of ultraviolet radiation from the sun that reaches Earth.
• Volatile organic compounds: gasoline, solvents, cleaning solutions.

Important pollutant particulates (mostly from combustion sources) include:

• hydrocarbon solids (commonly from inefficiently burned fuels)
• suspended oil particles (from aerosol spray sources)
• elemental carbon (soot)
• elemental sulfur
• mineral salts, though these can occur naturally
• lead and other toxic heavy metals
• combinations of ammonia (NH₃) with either sulfuric acid (H₂SO₄) or nitric acid (HNO₃) and water (H₂O) -- secondary emissions
• asbestos fibres

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 to the atmosphere.

• Scrubbers
• Electrostatic precipitators
• Fabric filters such as baghouses
• Carbon adsorption
• Cyclones
• Condensers
• Nonselective catalytic reduction (NSCR) e.g. catalytic converters
• Selective catalytic reduction (SCR)
• Flue gas desulfurization
• Exhaust gas recirculation
• Flares

Indoor air pollution

The lack of ventilation indoors concentrates air pollution where people are most exposed to them. Background pollution comes from such mundane sources as shower water mist containing arsenic or manganese, both of which are damaging to inhale. The arsenic (As³⁺) can be trapped with a shower nozzle filter. Radon (Rn) gas, a carcinogen, is exuded from the Earth and trapped inside houses. Researchers have found that radon gas is responsible for over 1,800 deaths annually in the United Kingdom. These natural radon emissions can be blocked by a layer of aluminum foil under the carpet (according to the U.S. Department of Air Quality Management). 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.

Deaths are often caused by using pesticides and other chemical sprays indoors without proper ventilation, and many homes have been destroyed by accidental pesticide explosions. Second-hand tobacco smoke is now recognized as an indoor air pollutant which accounts for an estimated 3,000 lung cancer deaths annually in the US. Carbon monoxide (CO) poisoning is a quick and silent killer, often caused by faulty vents and chimneys, or by the burning charcoal indoors. 56,000 Americans died from CO in the period 1979-1988. Chronic carbon monoxide poisoning can result even from poorly adjusted pilot lights. Smoke inhalation is a common cause of death in victims of house fires. Traps are built into all domestic plumbing to keep deadly sewer gas, hydrogen sulfide, out of interiors. Clothing emits tetrachloroethylene, or other dry cleaning fluids, for days after dry cleaning.

Biological sources of air pollution can also be found indoors, and include gases, particulates, allergens, and microbes. Pets produce dander, bed mites deposit shells and microscopic droppings, inhabitants emit methane, mold can form in walls and generate spores, air conditioning systems can incubate Legionnaires disease, toilets can emit feces-tainted mists, and houseplants and surrounding gardens can produce pollen, dust, and mold spores.

Asbestos

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, e.g. in mining or in the installation or removal of asbestos-containing materials from 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).

See also

• Air pollution in British Columbia
• Atmospheric chemistry
• Building biology
• Emissions trading
• Global Atmosphere Watch
• Greenhouse effect
• Haze
• Kyoto Protocol
• National Ambient Air Quality Standards
• Smog

Further reading

• Davis, Devra, When Smoke Ran Like Water: Tales of Environmental Deception and the Battle Against Pollution, Basic Books, 2002, hardcover, 316 pages, ISBN 0-465-01521-2

External links

Wikimedia Commons has media related to:

Air pollution

• EPA.org: Information on air pollution from the United States Environmental Protection Agency
• EPA Air Toxics info page
• Scorecard.org: Check how much air pollution exists in your local zipcode (United States)
• Case Studies in Environmental Medicine (CSEM):Environmental Triggers of Asthma
• Natural Resources Defense Council (NRDC): overviews, news and reports on air pollution
• WHO-Europe reports Health Aspects of Air Pollution (2003) (PDF) and "Answer to follow-up questions from CAFE (2004) (PDF)
• Particulate Matter, Ozone and Nitrogen Dioxide Air Pollution — A summary for non specialists of the above WHO reports by GreenFacts.
• British Government Health and Safety Executive: Asbestos

Sources

• SantiagoLimpio.CL - Website of the environmental agency of Chile
• Local air pollution - On a site by the Australian Academy of science
• The UK Air Quality Website - This provides public access to all UK pollution measurements, and emission estimates, as well as much general information on air pollution.
• Report on 2005 air pollution study by the European Commission