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Air pollution is due to human influences that contaminate the air with chemicals, particulate matter, and biological matter.

There are two types of air pollution:

1. ozone (i.e., smog) and
2. particulate matter (i.e., soot).

Both types of air pollution pose health risks and environmental dangers to people, plants, and animals. Ozone is an invisible gas that vapors emitted from fuel (e.g., cars, trucks, factories, power plants) interacts with sunlight. Particle pollution is comprised up of ash, soot, diesel exhaust, chemicals, metals and aerosols released into the atmosphere. Of the two forms of air pollution, particle pollution is more dangerous.

American Lung Association: State of the Air ReportEdit

Each year, the American Lung Association releases a nationwide report that documents the amount of ozone and particulate-matter pollution in the atmosphere. In their report, they list the most cleanest and most polluted cities in the U.S. Below is a list of the top-5 cities in both categories.

Most Polluted CitiesEdit

Most polluted cities by short-term particulate pollution:

1. Pittsburgh-New Castle, PA
2. Los Angeles-Long Beach-Riverside, CA
3. Fresno-Madera, CA
4. Bakersfield, CA
5. Birmingham-Hoover-Cullman, AL

Most polluted cities by year-round particulate pollution:

1. Los Angeles-Long Beach-Riverside, CA
2. Pittsburgh-New Castle, PA
3. Bakersfield, CA
4. Birmingham-Hoover-Cullman, AL
5. Visalia-Porterville, CA

People at risk for most ozone pollution:

1. Los Angeles-Long Beach-Riverside, CA
2. Bakersfield, CA
3. Visalia-Porterville, CA
4. Houston-Baytown-Huntsville, TX
5. Fresno-Madera, CA

Several cities, including Los Angeles, CA and Atlanta, GA, frequently report smog alerts when conditions are particularly dangerous to children and adults suffering from diabetes, heart disease, or sensitive lung conditions.

Cleanest CitiesEdit

Cleanest cities for short-term particle pollution:

1. Alexandria, LA
2. Amarillo, TX
3. Bismarck, ND
4. Brownsville-Harlingen-Raymondville, TX
5. Cheyenne, WY

Cleanest cities for year-round particle pollution

1. Cheyenne, WY
2. Santa Fe-Espanola, NM
3. Honolulu, HI
4. Great Falls, MT
5. Farmington, NM

Health RisksEdit

People with asthma and other chronic lung diseases, senior citizens, and children are particularly vulnerable to experiencing negative effects from exposure to smog. Prolonged exposure to smog can cause asthma attacks, coughing and wheezing, shortness of breath, chest pain when inhaling deeply, and even premature death. Breathing high levels of smog over the long term can also lead to impaired lung function, inflamed lung lining, and increased breathing problems.

Breathing particle pollution also poses very serious consequences to one's health. Breathing particle pollution year-round can shorten life by one to three years. Particle pollution can trigger heart attacks, strokes, irregular heartbeats. It also causes lung cancer, premature births, and can worsen serious respiratory disorders, including asthma and causes wheezing and coughing.

"Ambient particulate matter and nanoparticles have been shown to translocateto the brain, and potentially influence the central nervous system. No data are available whether this may lead to functional changes in the brain."Particle and Fibre Toxicology 2008, 5:4 [1]

delete pageExposure_to_Diesel_Ehaust_On_Humans

Air pollution is the human introduction into the atmosphere of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or damages the environment. Air pollution is often identified with major stationary sources, but the greatest source of emissions is mobile sources, mainly trees. Gases such as carbon dioxide, that come from trees and their leaves, contribute to global warming, have recently gained recognition as pollutants by climate scientists, while they also recognize that carbon dioxide is essential for plant life through photosynthesis.

PollutantsEdit

There are many substances in the air which may impair the health of plants and animals (including humans), or reduce visibility. These arise both from natural processes and human activity. Substances not naturally found in the air or at greater concentrations or in different locations from usual are referred to as pollutants.

Pollutants can be classified as either primary or secondary. 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 doixide 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.

Major primary pollutants produced by human activity include:

• Sulfur oxides (SO_x) especially sulfur dioxide are emitted from burning of coal and oil.
• 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.
• Carbon monoxide is 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.
• Volatile organic compounds (VOC), such as hydrocarbon fuel vapors and solvents.
• Particulate matter (PM), measured as smoke and dust. PM₁₀ is the fraction of suspended particles 10 micrometers in diameter and smaller that will enter the nasal cavity. PM_2.5 has a maximum particle size of 2.5 µm and will enter the bronchies and lungs.
• 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.
• Odors, such as from garbage, sewage, and industrial processes
• Radioactive pollutants produced by nuclear explosions and war explosives, and natural processes such as radon.

Secondary pollutants include:

• Particulate matter formed from gaseous primary pollutants and compounds in photochemical smog, such as nitrogen dioxide.
• Ground level ozone (O₃) formed from NOx and VOCs.
• Peroxyacetyl nitrate (PAN) similarly formed from NOx 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.

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

• "Stationary Sources" as smoke stacks of power plants, manufacturing facilities, municipal waste incinerators.
• "Mobile Sources" as motor vehicles, aircraft etc.
• Marine vessels, such as container ships or cruise ships, and related port air pollution.
• Burning wood, fireplaces, stoves, furnaces and incinerators.
• Oil refining, and industrial activity in general.
• Chemicals, dust and controlled burn practices in agriculture and forestry management.
• Fumes from paint, hair spray, varnish, aerosol sprays and other solvents.
• Waste deposition in landfills, which generate methane.
• 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, , for example cattle. -- An important note is that although this is categorized here as a "natural" source, there is nothing natural about livestock. Raising livestock is a human activity. Also important is that methane is 23 times more effective than C02 at trapping heat. This is why livestock are responsible for more climate change effects than all the human transportation systems combined. [2]
• Radon gas from radioactive decay within the Earth's crust.
• Smoke and carbon monoxide from wildfires.
• Volcanic activity, which produce sulfur, chlorine, and ash particulates.

Emission factorsEdit

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.

Indoor air quality (IAQ)Edit

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. 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.

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 Edit

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.

A 2005 study 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 respiratory allergies. The United States Environmental Protection Agency estimates that a proposed set of changes in diesel engine technology could result in 12,000 fewer premature mortalities, 15,000 fewer myocardial 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. The worst short term civilian pollution crisis in India was the 1984 Bhopal Disaster. 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. 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.

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.

Reduction effortsEdit

There are various air pollution control technologies and urban planning strategies available to reduce air pollution. Efforts to reduce pollution from mobile sources includes primary regulation (many developing countries have permissive regulations, 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).

Legal regulationsEdit

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.

United StatesEdit

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 Environmental Protection Agency replaced the Pollution Standards Index (PSI) with the Air Quality Index 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

• 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. The United States Environmental Protection Agency has proposed, in June 2007, a new threshold of 75 ppb. This falls short of the scientific recommendation, but is an improvement over the current standard.

Polluting industries are lobbying to keep the current (weaker) standards in place. Environmentalists and public health advocates are mobilizing to support compliance with the scientific recommendations. 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 of the United States.

StatisticsEdit

Most Polluted CitiesEdit

Most Polluted World Cities by PM
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

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

Carbon dioxide emissionsEdit

Total CO₂ emissions

10⁶ Tons of CO₂ per year:

• United States: 2,790
• China: 2,680
• Russia: 661
• India: 583
• Japan: 400
• Germany: 356
• Australia: 226
• South Africa: 222
• United Kingdom: 212
• South Korea: 185

Per capita CO₂ emissions

Tons of CO₂ per year per capita:^[1]

• Australia: 10
• United States: 8.2
• United Kingdom: 3.2
• China: 1.8
• India: 0.5

Environmental impactsEdit

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. It shares this property with many other gases, the largest overall forcing on Earth coming from water vapour. Other greenhouse gases include methane, hydrofluorocarbons, perfluorocarbons, chlorofluorocarbons, NOx, and ozone. Many greenhouse gases, contain carbon, and some of that from fossil fuels.

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 slight increases in the acidity of ocean waters and the possible effects of this on marine ecosystems. However, carbonic acid is a very weak acid, and is utilized by marine organisms during photosynthesis.

See alsoEdit

• Pollution
• Indoor Air Pollution
• Water pollution
• Soil conservation
• Land Pollution
• Soil contamination
• How to Reduce Air Pollution

External LinkEdit

[American Lung Association State of the Air Report]

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