In the 1980s the comfortable belief that air pollution was no longer a public health issue was shaken by the appearance of the Six Cities study from the USA which revealed dose-related health effects (ranging from symptoms to mortality) at levels of air pollutants at that time considered to be safe.1 Since then there has been a dramatic rise in the number of publications on air pollution from all parts of the world which have resulted in two broad outcomes: a far better understanding of the mechanisms by which ostensibly “low” concentrations of pollutants impact on the lung and increasing awareness within governments of the need to tighten air quality standards. Most epidemiological studies over this time have considered the effects of day-to-day changes in air pollution on daily events such as deaths and hospital admissions (so-called time-series studies).2 While these studies are in theory easy to undertake, being based on routinely collected data, they usually lack individual information other than cause of death or admission, age and gender. Using this information, in 1998 the UK’s Committee on Medical Effects of Air Pollutants (COMEAP) quantified the health impact of air pollution3 as a stepping stone towards determining the cost effectiveness of further pollution control measures. However, at that time they were unable to quantify the impact of long-term exposures—which even then were thought likely to be far greater than the day-to-day effects—for lack of …