Effects of air pollution on emergency room visits for respiratory illnesses in Montreal, Quebec.

As an approach to evaluating the public health burden from current air pollution levels, we examined the relationship of daily emergency room (ER) visits for respiratory illnesses (25 hospitals, average 98 visits/d) to air pollution in Montreal, Canada, from June through September, 1992 and 1993. Air pollutants measured included ozone (O3), particulate matter diameter < 10 microm (PM10) and < 2.5 microm (PM2.5), the sulfate fraction of PM2.5 (SO4), and aerosol strong acidity (H+). Temporal trends, autocorrelation, and weather were controlled for in time-series regressions. For 1992, no significant associations with ER visits were found. However, 33% of the particulate data were missing. For 1993, 1-h maximum O3, PM10, PM2.5, and SO4 were all positively associated with respiratory visits for patients over 64 yr of age (p < 0.02). An increase to the mean level of 1-h maximum O3 (36 ppb) was associated with a 21% increase over the mean number of daily ER visits (95% confidence interval [CI]: 8 to 34%). Effects of particulates were smaller, with mean increases of 16% (4 to 28%), 12% (2 to 21%) and 6% (1 to 12%) for PM10, PM2.5, and SO4, respectively. Relative mass effects were PM2.5 > PM10 >> SO4. Ozone and PM10 levels never exceeded 67 ppb and 51 microg/m3, respectively (well below the U.S. National Ambient Air Quality Standards of 120 ppb and 150 microg/m3, respectively). The present findings have public health implications with regard to the adverse health effects of urban photochemical air pollution on older individuals.