Air pollution is caused by smoke emitted from a variety of sources in a region. There are number of sources (like transport, industries, DG sets, road dust, biomass burning) which contribute substantially to the air pollution. Meteorology plays an important role in dispersion of these pollutants and could be responsible for very high pollution in some specific location. The variety of sources include :-
Point sources : Which are represented by stacks and their dimensions are insignificant in comparison to the region they are emitting their smoke to. E.g. industries, power plants etc
Line sources : which are more in one dimension and insignificant in the other dimension and act as a line . E.g. road transport
Area sources : which have significant two- dimensional structure. This include emissions from a forest, dust emissions from an area, emissions form an industrial estate, etc.
While sources such as vehicles, domestic cook stoves emit at a lower height, stacks of industries emit the pollution load at an higher altitude. Higher stack are provided to reduce the direct exposure of pollutant to the humans, and provision of more dispersion time.