Pollution of the air.
Contamination of the atmosphere caused by the discharge, accidental or deliberate, of a wide range of toxic airborne substances. Often the amount of the released substance is relatively high in a certain locality, so the harmful effects become more noticeable. The cost of preventing any discharge of pollutants into the air is prohibitive, so attempts are more usually made to reduce gradually the amount of discharge and to disperse this as quickly as possible by using a very tall chimney, or by intermittent release.
California's Clean Air Act 1988 aims to reduce exhaust emissions of carbon monoxide, nitrogen oxides, hydrocarbons and other precursors of smog in increasingly stringent phases. S California had unhealthy levels of air pollution, the heaviest levels in the US, on half of all days during 1993.