The Association between Daily Mortality and Ambient Air Particle Pollution in Montreal, Quebec: 1. Nonaccidental Mortality

Abstract

This study was undertaken to determine whether variations in concentrations of particles in the ambient air of Montreal, Quebec, during the period 1984 to 1993, were associated with daily variations in nonaccidental mortality. Fixed-site air pollution monitors in Montreal provided daily mean levels of various measures of particulates and gaseous pollutants. Total sulfates were also measured daily (1986–1993) at a monitoring station 150 km southeast of the city (Sutton, Quebec). We estimated associations for PM2.5, PM10, total suspended particles, coefficient of haze (COH), extinction coefficient, and sulfates. We used coefficient of haze, extinction coefficient, and Sutton sulfates to predict fine particles and sulfates for days that were missing. To estimate the associations between nonaccidental mortality and ambient air particles, we regressed the logarithm of daily counts of nonaccidental mortality on the daily mean levels for the above measures of particulates, after accounting for seasonal and subseasonal fluctuations in the mortality time series, non-Poisson dispersion, weather variables, and gaseous pollutants. There were 140,939 residents of Montreal who died during the study period. We found evidence of associations between daily nonaccidental deaths and most measures of particulate air pollution. For example, the mean percentage increase (MPC) for an increase of total suspended particles of 28.57 μg/m3 (interquartile range, IQ), evaluated at lag 0 days, was 1.86% (95% confidence interval (CI): 0.00–3.76%), and for an increase of coefficient of haze (IQ=18.5 COH units per 327.8 linear m) the MPC was 1.44% (95% CI: 0.75–2.14%). These results are similar to findings from other studies (the mean percentage increase in nonaccidental deaths for a 100 μg/m3 increase in daily total suspended particles was 6.7%). We also found increases for fine particles and for inhalable particles, but the confidence intervals included unity. All measures of sulfates showed increased daily mortality; e.g., the MPC for sulfates from fine particles (IQ=3.51 μg/m3) was 1.86% (95% CI: 0.40–3.35%). We generally found higher excesses in daily mortality for persons 65 years of age and for exposures averaged across lags 0, 1, and 2 days. The slope of the association between daily mortality and ambient air particles in Montreal, which has lower levels of pollution than most major urban centers, is similar to that reported in most other industrialized cities. This study therefore provides further evidence that the association is linear and that any threshold effect, should it exist, would be found at lower levels of air pollution than those found in Montreal.