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Air pollution is the introduction of particulates, biological molecules, or other harmful materials into the Earth's atmosphere, possibly causing disease, death to humans, damage to other living organisms such as food crops, or the natural or built environment.

Indoor air pollution and urban air quality are listed as Indoor air pollution and urban air quality are listed as two of the world's worst toxic pollution problems in the two of the world's worst toxic pollution problems in the 2008 2008 Blacksmith InstituteBlacksmith Institute World's Worst Polluted World's Worst Polluted Places report.Places report.[1][1]

According to the 2014 According to the 2014 WHOWHO report, air pollution in 2012 report, air pollution in 2012 caused the deathscaused the deaths of around of around 7 7 millionmillion people worldwide people worldwide.

Air pollution is a significant risk factor for a number of health conditions including respiratory infections, heart disease, COPDCOPD, stroke and lung cancer.[2]

In India in 2014, it was reported that air pollution had cut crop yields in the most affected areas by almost half in 2010 when compared to 1980 levels.[56] effect of air pollution on plants Air pollution injury to plants can be evident in several ways. Injury to foliage may be visible in a short time and appear as necrotic lesions (dead tissue), or it can develop slowly as a yellowing or chlorosis of the leaf. There may be a reduction in growth of various portions of a plant.

AgriculturalAgricultural effectseffects

In general, there are two types of air quality standards. The first class of standards (such as the U.S. National Ambient Air Quality StandardsNational Ambient Air Quality Standards and E.U. Air Quality DirectiveAir Quality Directive) 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 IndexAir 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

Some air pollution is not directly caused by humans: for example, animals emit carbon dioxide when they breathe, and volcanoes release sulfur oxide. However, most air pollution is linked directly or indirectly to human activity. This means that air pollution can be best controlled by modifying human activity to burn a smaller quantity of fossil fuels.