Many epidemiological studies have demonstrated the importance of air pollution as a risk factor and characterised dose-response relationships between health endpoints and pollutants.The association between particulate matter (PM) and health is generally regarded as causal, and a nonthreshold linear relationship with, for example, mortality and hospital admission has been observed in several settings.The ubiquitous PM air pollution is likely to have a large overall impact on human health, even if risks are relatively small. There have recently been a large number of papers reporting quantitative estimations of the health impact of PM on health, as measured by the proportion of excess events that are attributable to PM exposures in the general population, mainly in industrialised countries. For example, in the eight largest Italian cities it has been estimated that concentrations beyond 30 mg?m -3 are responsible for about 3,500 extra deaths per year. A similar study has been carried out for France, Austria and Switzerland.These evaluations fill a knowledge gap between the laboratory and clinical studies on the pathophysiological mechanisms, the epidemiological research on the nature and strength of the association at the population level, and the risk management needs for developing appropriate preventive policies.Some The scientific evidence on the health effects of ambient air pollution has been growing in recent years. Several questions remain open, but many epidemiological studies have demonstrated the importance of air pollution as a risk factor for mortality and morbidity [1][2][3][4][5][6][7][8][9]. For several specific health endpoints and pollutants, the associations have been quantified and concentration-response relationships have been characterised. Among these pollutants, the role of suspended particulate matter (PM) has been especially investigated with regard to its short-and long-term effects on mortality and morbidity. Most of the scientific evidence available to date concerns PM10 and PM2.5 (particles with a 50% cut-off aerodynamic diameter ofv10 and v2.5 mm, respectively), although the role of finer particles is of increasing interest. This evidence has prompted the World Health Organization (WHO) to include air pollution and its health effects in its agenda [10][11][12].Although the biological mechanism of action is not yet fully understood, the association between PM and health is generally regarded as causal [13], and a nonthreshold concentrationresponse relationship with, for example, mortality and hospital admission has been observed in several settings. Cohort studies conducted in the USA found increase in total and cardio-respiratory mortality in populations of cities with higher long-term mean PM10 concentrations [14][15][16]. Shortterm studies have demonstrated effects occurring shortly after elevated concentration days: hospital admission [17][18][19][20][21], incidence of new cases of bronchitis and occurrence of respiratory symptoms and asthma exacerbation [22][23][24], fo...