Health effects of air pollution: Acute and chronic

It took the London smog of 1952 to demonstrate the risk to human health of breathing polluted air in the industrialized cities of the 1940s and 50s.1 At least 4000 (and probably many more) deaths resulted from cardiac and respiratory disease during that episode. The effects of the London smog should have come as no surprise: earlier incidents in the Meuse Valley in 1930 and in Donora, Pennsylvania in 1948 had shown that high concentrations of industrially generated air pollutants could have a serious effect on health. At the time, scientific opinion believed that the impact on health was a result of the combination of particles and sulphur dioxide, and while a later re-examination of the historical data supported a role for the acidity of the aerosol in contributing to the observed mortality,2 this hypothesis has since been questioned, highlighting the difficulty of identifying causal pathways in this whole area.