THE ROLE OF PARTICULATE SIZE AND CHEMISTRY IN THE ASSOCIATION BETWEENSUMMERTIME AMBIENT AIR-POLLUTION AND HOSPITALIZATION FOR CARDIORESPIRATORY DISEASES

In order to address the role that the ambient air pollution mix, compr ised of gaseous pollutants and various physical and chemical measures of particulate matter, plays in exacerbating cardiorespiratory disease , daily measures of fine and coarse particulate mass, aerosol chemistr y (sulfates and acidity), and gaseous pollution (ozone, nitrogen dioxi de, sulfur dioxide, and carbon monoxide) were collected in Toronto, On tario, Canada, in the summers of 1992, 1993, and 1994. These time seri es,were then compared with concurrent data on the number of daily admi ssions to hospitals for either cardiac diseases (ischemic heart diseas e, heart failure, and dysrthymias) or respiratory diseases (tracheobro nchitis, chronic obstructive lung disease, asthma, and pneumonia). Aft er adjusting the admission time series for long-term temporal trends, seasonal variations, the effects of short-term epidemics, day of the w eek effects, and ambient temperature and dew point temperature, positi ve associations were observed for all ambient air pollutants for both respiratory and cardiac diseases. Ozone was least sensitive to adjustm ent for the gaseous and particulate pollution measures. However, the a ssociation between the health outcomes and carbon monoxide, fine and c oarse mass, sulfate levels and aerosol acidity could be explained by a djustment for exposure to gaseous pollutants. Increases in ozone, nitr ogen dioxide, and sulfur dioxide equivalent to their interquartile ran ges corresponded to an 11% and 13% increase in daily hospitalizations for respiratory and cardiac diseases, respectively. The inclusion of a ny one of the particulate air pollutants in multiple regression models did not increase these percentages. particle mass and chemistry could not be identified as an independent risk factor for the exacerbation of cardiorespiratory diseases in this study beyond that attributable t o climate and gaseous air pollution. We recommend that effects of part iculate matter on health be assessed in conjunction with temporally co varying gaseous air pollutants.