Air Pollution

Pollution (Latin : Pollutus) which means made foul, unclean, or dirty. Some authors limit the use of the term to damaging materials that are released into the environment by human activities. There are, however, many natural sources of air quality degradations. Volcanoes spew out ash, acid mists, hydrogen sulfide, and other toxic gases. Sea spray and decaying vegetation are major sources of reactive sulfur compounds in the air.pollen, spores, viruses, bacteria, and other small bits of organic material in the air cause widw spread suffering from allergies and airborne infections.

In many case, the chemical compositions of pollutants from natural and human related sources are identical, and their effects are inseparable. Sometimes, however, materials in the atmosphere are considered innocuous at naturally occuring levels, but when humans add to these levels, overloading of natural cycles or disruption of essential processes. While the natural sources of suspended particulate materials in the air outweigh human sources at least tenfold worlwide, in many cities more than 90 percent of the airborne particulate matter is anthropogenis (human-caused).

Primary pollutants are those directly into the air in a harmful form. Secondary pollutants, by contrast, are modified to hazardous form after they enter the air or are formed by chemical reactions as components of the air mix and interact. Solar radiation often provides the energy for these reactions. Photochemical oxidants and atmospheric acids formed by these mechanisms are probably the most important secondary pollutants in terms of human health and ecosystem damage.

The Clean Air Act of 1970 designated seven major pollutants (sulfur dioxide, carbon monoxide, particulates, hydrocarbons, nitrogen oxide, photochemical oxidants and lead) for which maximum ambient air (air all around us) levels are mandated. These seven conventional or criteria pollutants contribute the largest volume of air quality degradation and also are considered the most serious threat of all air pollutants to human health and welfare.

Estimated fluxes of pollutants and trace gases to the atmosphere

Species	Major sources	Approximate annual flux (million of tons)	Average half life in atmosphere (days)
Carbon dioxide	Respirations	100.000	2500
Carbon dioxide	Biomass, fossil fuel burning	10.000	2500
Carbon monoxide	Biomass, fossil fuel burning	1000	75
Methane	Wetlands, rice paddies, termites, ruminant animals	400	3600
Volatile organic compounds	Human-made	100	1-1000
Nitrogen oxides	Soils, burning biomass, fossil fuels	100	4
Nitrous oxide	Fertilizer, tropical forest	100	60000
Sulfur dioxide and sulphate	Sea spray, fossil fuels, smelting	90	1-4
Ammonia	Industrial and biological nitrogen-fixation	100	9
H2S and organic sulfur	Biogenic, anthropogenic	90	1-900
Suspended particulate materials	Wind erosion, fires, volcanoes, human sources	10000	1-1000
Metals	Leaded gasoline, coal, industrial waste	3	1-30