Natural and man-made. Natural sources include smoke from forest fires, largescale volcanic eruptions, wind blown dust etc. Man-made sources include emission from stationary or mobile sources. For obvious reasons, pollution from man-made sources is more abundant in urban and industrial areas than in the rural areas. The most common air pollutants are Sulphur dioxides (SO2), Nitrogen (NOX), Particulate Matter (SPM), Hydrocarbons (HCs), Carbon Monoxide (CO), Lead (Pb) and other trace compounds.

The quality of the ambient air in a few urban areas of our state, like Hyderabad, Visakhapatnam, Vijayawada and some others, has been deteriorating over the past few years due to various factors like emissions from vehicles, thermal plants and industries.

Theoretically speaking the level of pollution in most of our cities is still within the permissible limits. However, there are exceptions. Hyderabad, Visakhapatnam, Vijayawada and Tirupati where there is very high automobile pollution, are showing a dangerous trend with the levels of Carbon Monoxide and SPM increasing perilously.

It is clear that the major source of air pollution in our cities is automobile pollution. The total vehicular pollution load in the twin cities of Hyderabad and Secunderabad and in other urban areas is increasing with the population. This has resulted in the formation of slums and industrial clusters. The variations in urban climate due to increased building and industrial activity is an established fact and is referred to as Urban Heat Island (UHI) effect.