• According to the WHO, air pollution is defined as limited to situations in which the outdoor ambient atmosphere contains materials in concentration, which are harmful to the environment and his/her surrounding environment.
  • The nature, dimensions, and magnitude of air pollution depends on a variety of factors such as residence time of pollutants in the atmosphere, sources of pollutants, nature of pollutants, amount of pollutants, etc.
  • The time of pollutants for which it stays in the atmosphere vary considerably depending upon the nature of the pollutant, on meteorological factors (amount of moisture, cloudiness, etc.) and on sink mechanism (vegetation, water bodies, etc.)
AIR POLLUTANTSAir pollutant is a material in the air that can have adverse effects on humans and the ecosystem.
Pollutants are classified asAccording to their existence in nature,

  • Quantitative Pollutants: These occur in nature and become pollutants when their concentration reaches beyond a threshold level. Example: Carbon dioxide, Nitrogen oxide.
  • Qualitative Pollutants: These do not occur in nature and are man-made. Example: fungicides, herbicides, DDT etc.

According to the form in which they persist after release into the environment

  • Primary pollutants: These persist in the form in which they are added to the environment. Examples: ash from a volcanic eruption, carbon monoxide gas from motor vehicle exhausts, Sulphur dioxide released from factories.
  • Secondary pollutants: These are formed by interaction and reaction among the primary pollutants. They are not emitted directly. Examples: peroxyacetyl nitrate (PAN) is formed by the interaction of nitrogen oxides and hydrocarbons; ground-level ozone, etc.


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