Air pollution in India is increasing at an alarming rate and must be controlled both at the individual and the policy making level. Polluted air contains a lot of harmful substances which are listed and explained below:

Sulphur dioxide:

This substance has an odour that is unpleasant and can be detected at a concentration of more than 1ppm (parts per million), although with more than 3ppm the sense of smell is lost rapidly. Sulphur dioxide causes irritation in the respiratory passages and can also cause shortness of breath and chronic lung disease.

Oxides of Nitrogen:

The three oxides of Nitrogen are considered to be major pollutants; nitrous oxide (dinitrogen oxide, N20), nitric oxide (NO) and nitrogen dioxide (NO2). Nitrous oxide is different from others, is a green house gas and hence is a contributor to global warming.


Hydrocarbons are substances that contain carbon as well as hydrogen. One of the simplest of these is methane, which originates from various sources in nature. These are produced entirely by micro-organisms under anaerobic conditions.

Oxides of Carbon:

Carbon dioxide and carbon monoxide are major pollutants. Carbon dioxide is a greenhouse gas and contributes to global warming. The other harmful gas Carbon monoxide is produced by the atmospheric oxidation of hydrocarbons and is also generated biologically both on land and sea.

Compounds of Lead:

Ninety per cent of the lead present in the atmosphere is due to human activities. Lead is a major pollutant; high levels of lead in the air we breathe are known to cause serious health hazards.

The levels of some major air pollutants need to be monitored strictly and kept in check so that we may have good air quality. The levels of various air pollutants in India over time are given below: