Of all the different types of pollution affecting human health, by far the most important is air pollution (both outdoor and indoor). Of all the major EPA statute areas (air, water, pesticides, conservation, drinking water, toxic control, liability), and even by the agency's own reckoning, 86–96 percent of all social benefits stem from the regulation of air pollution. Equally, in a 1999 consolidation of 39 regional, state and local comparative risk analysis studies, air pollution almost invariably came out as the most important environmental problem for human health. We shall therefore start by looking at the problem of air pollution.

We often assume that air pollution is a modern phenomenon, and that it has got worse and worse in recent times. However, as will become clear, the air of the Western world has not been as clean as it is now for a long time. Moreover, there is good reason to assume that air pollution in the developing world will also improve with time.

Air pollution in times past

Air pollution from lead can be documented as far back as 6,000 years ago, reaching its first maximum in the time of the Greeks and Romans. As long ago as 500 BCE, the lead content of the air above Greenland was four times higher than before the European civilizations began smelting metals. In ancient Rome, the statesman Seneca complained about “the stink, soot and heavy air” in the city.