Lung function is an excellent operative marker of the effects of air pollution in the general population. It is objective and quantitative, an early predictor of cardiorespiratory morbidity and mortality, able to describe trajectories to the occurrence of chronic obstructive pulmonary disease (COPD) and coherent with experimental data on deposition and accumulation of pollutants in airways and lungs and the resulting systemic inflammation and oxidative stress.1 2

Acute effects of air pollution are well established, whereas long-term effects are less certain. There is strong evidence of long-term effects of current levels of air pollution on lung function growth in children, resulting in deficits of lung function at the end of adolescence.3 However, there are no data about the potential reversibility of the deleterious effect afterwards. In adults, there is only one large long-term follow-up study.4 The strongest evidence for adverse long-term effects of air pollution on lung function in adults comes from cross-sectional investigations. In Europe, these studies were limited to a few residential areas.5 6

Forbes et al have published in this issue (see page 657) the largest cross-sectional study in adults in Europe, comprising four English surveys conducted between the years 1995 and 2001 in 648–720 postcode areas, adding 41 329 subjects older than age 16 and living in around 30 000 households.7 Individual residential exposure to air pollutants was based on dispersion modelling including meteorological and emission data for each postcode. Air pollution levels are moderate (median particulate matter <10 μm (PM₁₀) and NO₂ around 20 and 30 μg/m³, respectively). An increase in 10 μg/m³ of PM₁₀ and NO₂ was associated with a decrease of about 3% and 0.7% in FEV_{1 …}