A time-series study of air pollution, socioeconomic status, and mortality in Vancouver, Canada

Abstract

We evaluated the relationship between daily levels of particulate and gaseous phase pollutants and mortality within a dynamic cohort of approximately 550,000 individuals whose vital status was ascertained between 1986 and 1999. Time-series methods were applied to evaluate whether there were differential pollutant effects on daily aggregated numbers of deaths in the cohort that was stratified into quintiles of income as defined by the 1991 and 1996 Canadian censuses. The percent change in all-cause, cardiovascular, respiratory, and cancer daily mortality was calculated in relation to short-term changes in levels of a number of particulate (PM_2.5, PM_10–2.5, total suspended particle co-efficient of haze PM₁₀, SO₄) and gaseous (O₃, CO, SO₂, NO₂) pollutants. The estimated effects of air pollution on mortality were adjusted for day of week effects, and several meteorologic variables including temperature, change in barometric pressure, and relative humidity. Several gaseous pollutants were associated with an increased risk of mortality. Specifically for an increase equivalent to the difference between the 90th and 10th percentiles, the estimated percent change in daily mortality based on the 3-day average of NO₂, and SO₂ was 4.0% and 1.3%, respectively. The corresponding changes in mortality associated with SO₂ were much higher when analyses were restricted to death from respiratory disease. Specifically, a difference between the 90th and 10th percentiles was associated with a 5.6% (95% CI= −0.7% to 12.3%). The daily mean coarse fraction (PM_10–2.5) was associated with increased cardiovascular mortality (estimated change=5.9%, 95% CI=1.1–10.8%). PM_2.5 was not found to be an important predictor of mortality. For NO₂, CO, and SO₂, there was some suggestion of increased risk of all-cause and cardiovascular mortality at lower levels of socioeconomic status. However, these results should be interpreted cautiously due to the small number of deaths observed within each stratum of socioeconomic status.