Air Pollution and Human Health: From Local to Global Issues

Air pollution from fossil fuel combustion has been known to affect human health for centuries. More detailed insights developed in the 20th century, as a result of studies prompted by severe air pollution episodes such as those in the Meuse Valley, Belgium in 1930, and London, UK in 1952. The focus in the early studies was on local pollution produced by industry, power generation and home heating sources. Later, the emphasis shifted to so-called secondary pollutants, the products of atmospheric reactions producing pollutants such as ozone, sulphates and nitrates. The secondary pollutants typically affected large areas extending hundreds of kilometers downwind from primary sources. Effects of secondary pollutants on human health became evident from population studies and, in case of ozone, also from controlled human laboratory experiments. On an even larger scale, we are now confronted with air pollution masses extending over thousands of kilometers, and occupying several kilometers of the troposphere, the so-called 'brown clouds'. Emissions from megacities, industry, energy production plants, home heating, biomass combustion for cooking and heating in rural areas as well as wildfires contribute to these 'brown clouds'. Adverse effects of such clouds on human health are suspected but have not yet been conclusively proven. On the other end of the spatial scale, it has become convincingly clear that at the very local level, indoor air pollution from biomass combustion and exposure to traffic-related air pollution constitute major health hazards. Developing economies such as in China are confronted with each of these types of air pollution simultaneously, posing tremendous challenges for public health policy.