Air pollution usually causes slow and gradual effects which are of chronic type. As the main route of entry of pollutants is through respiratory track various chronic, non-specific respiratory diseases such as bronchitis, chronic obstructive ventilatory diseases, pulmonary emphysema, bronchial asthma etc. may be caused by air pollution.

Very large doses of most of the common pollutants of air are required to produce acute toxicities. Such concentrations are very rare. Most of the instances of acute toxicity so far recorded involve industrial emission of toxic gases and vapours which are not usually present in the environment or if present they occur in traces only.

The famous Bhopal tragedy of 1984, in which about 40 tons of methyl isocyanate was accidentally released into the atmosphere, left about 2800 people dead within 15 minutes and many more crippled for life. The release of chlorine gas in a subway tunnel in Brooklyn is another such example. Both these cases were caused by toxic agents who are not commonly found in toxic concentration in the atmosphere and it was only the accidental release of these gases from industries which resulted in the disasters.