air pollution

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 the amount of discharge gradually and to disperse it as quickly as possible by using a very tall chimney, or by intermittent release.

One major air pollutant is sulphur dioxide (SO₂), produced from the burning of fossil fuels. It dissolves in atmospheric moisture to produce sulphurous acid (acid rain):

SO₂ + H₂O = H₂SO₃

California's Clean Air Act 1988 aimed to reduce exhaust emissions of carbon monoxide, nitrogen oxides, hydrocarbons, and other precursors of smog in increasingly stringent phases. Southern California had unhealthy levels of air pollution, the heaviest levels in the USA, on half of all days during 1993. In August 1996 Canada, Mexico, and the USA agreed to develop a system to monitor transboundary air pollution in North America.

Other major pollutants Oxides of nitrogen (NOx), produced by car exhausts, also contribute to acid rain. The poisonous gas carbon monoxide (CO) results from the partial combustion of fuels and is particularly prevalent where there is heavy traffic, contributing to photochemical smog. The air pollution caused by lead compounds from leaded petrol, particularly tetraethyl lead (Pb(C2H5)4), can cause learning impairment in children living near busy roads. The air pollution caused by small particles (PM10s), which results mainly from vehicle emissions, is also a major health risk.

A 1997 survey of contamination in mosses showed that Slovakia and southern Poland are the most polluted areas in Central Europe, with high levels of heavy-metal pollutants including cadmium, lead, copper, and zinc, caused by chemical and metal smelting industries in Slovakia, the northeastern Czech Republic, and Poland.

The 1997 Kyoto Protocol committed the industrialized nations of the world to cutting their levels of harmful gas emissions. The protocol aims to reduce the greenhouse gas emissions of the industrialized nations to 5% below 1990 levels by 2012. In 2001, the USA pulled out of the agreement, a move that threatened the whole agreement. However, a compromise was reached in June 2002 allowing the other nations to proceed. By November 2003, 84 countries had signed the agreement and 120 countries had ratified or acceded to the Protocol. The treaty was finally ratified by Russia at the 2002 World Summit, enabling it to be brought into effect.