Exposure assessment
Daily mean PM10, PM2.5, NO2 and O3 concentrations derive from the archives of the Regional Environmental Protection Agency (ARPA Lombardia) that collects results of the simulations, on a regional scale, of the FARM (Flexible Air quality Regional Model) chemical-physical model of air quality [19], a three-dimensional Eulerian model simulating dispersion and chemical reactions of atmospheric pollutants available at municipality resolution (www.arpalombardia.it/Pages/Aria/Modellistica/I-sistemi-modellistici-in-ARPA.aspx). A variability in exposures between subjects exists due to spatial and temporal variability, as each patient was assigned the daily concentration of all pollutants at the municipality in which they live, the day of evaluation and back to 14 days (i.e. from day 0 to day -14) and the mean of one week before enrolment (i.e. week-1 is the mean of the day 0-to day-7). Only patients from the Lombardy region (located in the north of Italy) were considered for the study.