The nature and degree of air pollution have varied over time and the attitude of man towards it has also changed. As the human population grew, so did the levels of environmental pollution. There is little evidence that suggests that air pollution was perceived as a major health problem up to the end of the 13th century. By that time coal was used extensively, and gases emitted from the burning became the most important air pollutant. As early as 1900 the irritating combination of coal smoke and fog, commonly known as smog, became associated with significant increases in urban death rates. The potential hazards associated with the exhaust gases of the internal combustion engine were reported as early as 1915. During the second world war the levels of air pollution in industrial and urban areas increased dramatically but it has only been in the past few years that substantial evidence has been accumulated on the adverse effects of air pollution on human health and well being. It is now understood that air pollution can be disseminated over vast areas by contaminating the atmosphere, resulting in adverse human health effects, and contaminating the environment far away from the original source.