• air pollution

It is now generally accepted that the health of many people is affected by exposure to air pollution on a day to day basis. The effects occur at varying levels of severity from mortality through hospital admissions to less serious morbidity such as increased use of inhalers in asthma. The quantification report¹ of the United Kingdom Department of Health estimated that particles contribute to around 8500 deaths a year in the United Kingdom when considering the information available on these day to day effects. But there is evidence that exposure over time to polluted air can cause chronic effects either by initiating disease in otherwise healthy people or by enhancing the long term deterioration of a person's disease,² and separating the two, if possible, is important for determination of the effects on public health.

Important evidence about chronic effects comes from three cohort studies (the Six Cities study,³ the American Cancer Society study⁴ and the Seventh Day Adventist study⁵) but cohort studies are expensive and take time to produce answers. As a result they are much treasured and considerable use has been made of the effect size coefficients from these studies to estimate the overall health impacts of air pollution in other countries, in particular as a step towards costing these impacts. But they have their shortcomings. For …