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Air pollution

Air pollution occurs when harmful substances including particulates andbiological 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 orbuilt environment. Human activity and natural processes can both generate air pollution.



Pollutants[edit] Main articles: Pollutant and Greenhouse gas






for hazardous




Substances emitted into the atmosphere by human activity include:

Carbon dioxide (CO 2 ) - Because of its role as a greenhouse gas it has been described as "the leading pollutant" [5] and "the worst climate pollution". [6] Carbon dioxide is a natural component of the atmosphere, essential for plant life and given off by the human respiratory system. [7] This question of terminology has practical effects, for example as determining whether the U.S. Clean Air Act is deemed to regulate CO 2 emissions. [8] CO 2 currently forms about 405 parts per million (ppm) of earth's atmosphere, compared to about 280 ppm in pre- industrial times, [9] and billions of metric tons of CO 2 are emitted annually by burning offossil fuels. [10] CO 2 increase in earth's atmosphere has been accelerating. [11]

Sulfur oxides (SO x ) - particularly sulfur dioxide, a chemical compound with the formula SO 2 . SO 2 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 SO 2 , usually in the presence of a catalyst such as NO 2 , forms H 2 SO 4 , 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 ) - 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 NO 2 . 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 (CH 4 ) 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.


Persistent free radicals connected to airborne fine particles are linked to cardiopulmonary disease. [14][15]



Ammonia (NH 3 ) - emitted from agricultural processes. Ammonia is a compound with the formula NH 3 . 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. [16]

Odours — such as from garbage, sewage, and industrial processes


Secondary pollutants include:

Particulates created from gaseous primary pollutants and compounds in photochemical


Peroxyacetyl nitrate (C 2 H 3 NO 5 ) - similarly formed from NO x and VOCs.

Minor air pollutants include:


under the Clean Air Act and in Europe under the Air Framework Directive A variety of persistent organic pollutants, which can attach to particulates




Anthropogenic (man-made) sources:



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. [17][18] Mobile sources include motor vehicles, marine vessels, and aircraft.






Natural sources:

Dust storm approaching Stratford, Texas.

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


Vegetation, in some regions, emits environmentally significant amounts ofVolatile organic compounds (VOCs) on warmer days. These VOCs react with primary anthropogenic pollutants—specifically, NO x , SO 2 , and anthropogenic organic carbon compounds — to produce a seasonal haze of secondary pollutants. [19] 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 Emission factors[edit] Indoor air quality (IAQ)[edit] Main article: Indoor air quality

Air quality monitoring, New Delhi, India.








including carpetingand plywood emit formaldehyde (H 2 CO)







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. [27] Indoor pollution fatalities may be caused by using pesticides and other chemical sprays indoors without proper ventilation.


The World Health Organization estimated in 2014 that every year air pollution causes the premature death of some 7 million people worldwide. [2] India has the highest death rate due to air pollution. [30] India also has more deaths from asthma than any other nation according to the World Health Organization. In December 2013 air pollution was estimated to kill 500,000 people in China each year. [31] There is a positive correlation between pneumonia-related deaths and air pollution from motor vehicle emissions. [32]

Annual premature European deaths caused by air pollution are estimated at 430,000. [33] An important cause of these deaths is nitrogen dioxide and other nitrogen oxides (NOx) emitted by road vehicles. [33] In a 2015 consultation document the UK government disclosed that nitrogen dioxide is responsible for 23,500 premature UK deaths per annum. [34] Across theEuropean Union, air pollution is estimated to reduce life expectancy by almost nine months. [35] Causes of deaths includestrokes, heart disease, COPD, lung cancer, and lung infections. [2] Cardiovascular disease[edit]

A 2007 review of evidence found ambient air pollution exposure is a risk factor correlating with increased total mortality from cardiovascular events (range: 12% to 14% per 10 microg/m 3 increase). [47]

Air pollution is also emerging as a risk factor for stroke, particularly in developing countries where pollutant levels are highest. [48] A 2007 study found that in women, air pollution is not associated with hemorrhagic but with ischemic stroke. [49] Air pollution was also found to be associated with increased incidence and mortality from coronary stroke in a cohort study in 2011. [50] Associations are believed to be causal and effects may be mediated by vasoconstriction, low- grade inflammation and atherosclerosis [51] Other mechanisms such as autonomic nervous system imbalance have also been suggested. [52] [53] Lung disease[edit]

Research has demonstrated increased risk of developing asthma [54] and COPD [55] from increased exposure to traffic-related air pollution. Additionally, air pollution has been associated with increased hospitalization and mortality from asthma and COPD. [56][57] . Chronic obstructive pulmonary disease (COPD) includes diseases such as chronic bronchitis and emphysema. [58] Cancer[edit]

Cancer mainly the result of environmental factors. [63]

A review of evidence regarding whether ambient air pollution exposure is a risk factor for cancer in 2007 found solid data to conclude that long-term exposure to PM2.5 (fine particulates) increases the overall risk of non-accidental mortality by 6% per a 10 microg/m 3 increase. Exposure to PM2.5 was also associated with an increased risk of mortality from lung cancer (range: 15% to 21% per 10 microg/m 3 increase) and total cardiovascular mortality (range: 12% to 14% per a 10 microg/m 3 increase). The review further noted that living close to busy traffic appears to be associated with elevated risks of these three outcomes --- increase in lung cancer deaths, cardiovascular deaths, and overall non-accidental deaths. The reviewers also found suggestive evidence that exposure to PM2.5 is positively associated with mortality from coronary heart diseases and exposure to SO 2 increases mortality from lung cancer, but the data was insufficient to provide solid conclusions. [64] Another investigation showed that higher activity level increases deposition fraction of aerosol particles in human lung and recommended avoiding heavy activities like running in outdoor space at polluted areas. [65] Children[edit]

In the United States,

despite the passage of

1970, in

2002 at

least 146

million Americans were living innon-attainment areasregions in which the concentration of certain air pollutants exceeded federal standards. [68] These dangerous pollutants are known as the criteria pollutants, and include ozone, particulate matter, sulfur dioxide, nitrogen dioxide,

carbon monoxide, and lead. Protective measures to ensure children's 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. [69] A recent study in Europe has found that exposure to ultrafine particles can increase blood pressure in children. [70]


Ambient levels of air pollution have been associated with preterm birth and low birth weight. A 2014 WHO worldwide survey on maternal and perinatal health found a statistically significant association between low birth weights (LBW) and increased levels of exposure to PM2.5. Women in regions with greater than average PM2.5 levels had statistically significant higher odds of pregnancy resulting in a low-birth weight infant even when adjusted for country-related variables. [71] The effect is thought to be from stimulating inflammation and increasing oxidative stress. "Clean" areas[edit]

Even in the areas with relatively low levels of air pollution, public health effects can be significant and costly, since a large number of people breathe in such pollutants. A 2005 scientific study for the British Columbia Lung Association showed that a small improvement in air quality (1% reduction of ambient PM2.5 and ozone concentrations) would produce $29 million in annual savings in the Metro Vancouver region in 2010. [75] This finding is based on health valuation of lethal (death) and sub-lethal (illness) affects. Central nervous system[edit]

Data is accumulating that air pollution exposure also affects the central nervous system. [76]


Agricultural effects[edit]


Economic effects[edit]


Historical disasters[edit]

The world's worst short-term civilian pollution crisis was the 1984 Bhopal Disaster in India. [85] Leaked industrial vapours from the Union Carbide factory, belonging to Union Carbide, Inc., U.S.A. (later bought by Dow Chemical Company), killed at least 3787 people and injured from 150,000 to 600,000. 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 more recent estimates put the figure at nearer 12,000. [86] An accidental leak of anthrax spores from a biological warfare laboratory in the former USSR in 1979 near Sverdlovsk is believed to have caused at least 64 deaths. [87] The worst single incident of air pollution to occur in the US occurred in Donora, Pennsylvania in late October, 1948, when 20 people died and over 7,000 were injured. [88]

Alternatives to pollution[edit] There are now practical alternatives to the principal causes of air pollution:








Reduction efforts[edit]

There are various air pollution control technologies and strategies available to reduce air pollution. [94][95] 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.





A very effective means to reduce air pollution is the transition to renewable energy. According to a study published inEnergy and Environmental Science in 2015 the switch to 100% renewable energy in the United States would eliminate about 62,000 premature mortalities per year and about 42,000 in 2050, if no biomass were used. This would save about $600 billion in health costs a year due to reduced air pollution in 2050, or about 3.6% of the 2014 U.S. gross domestic product. [96] Control devices[edit]

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

Particulate control Mechanical collectors (dust cyclones, multicyclones)





<a href=Having a Best Friend A story tells that two friends were walking through the desert. During some point of the journey, they had an argument, and one friend slapped the other one in the face. The one who got slapped was hurt, but without saying anything, wrote in the sand “Today my best friend slapped me in the face”. They kept on walking until they found an oasis, where they decided to take a bath. The one who had been slapped got stuck in the mire and started drowning, but the friend saved him. After he recovered from the near drowning, he wrote on a stone “Today my best friend saved my life”. The friend who had slapped and saved his best friend asked him, “After I hurt you, you wrote in the sand and now, you write on a stone, why?” The other friend replied “When someone hurts us we should write it down in the sand where winds of forgiveness can erase it away. But, when someone does something good for us, we must engrave it in stone where no wind can ever erase it.” " id="pdf-obj-13-4" src="pdf-obj-13-4.jpg">



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