The Effects of Coarse Particles on Daily Mortality: A Case-Crossover Study in a Subtropical City, Taipei, Taiwan

Many studies have examined the effects of air pollution on daily mortality over the past two decades. However, information on the relationship between levels of coarse particles (PM2.5-10) and daily mortality is relatively sparse due to the limited availability of monitoring data. Furthermore, the results are inconsistent. In the current study, the association between coarse particle levels and daily mortality in Taipei, Taiwan's largest city, which has a subtropical climate, was undertaken for the period 2006-2008 using a time-stratified case-crossover analysis. For the single pollutant model (without adjustment for other pollutants), PM2.5-10 showed statistically significant association with total mortality both on warm and cool days, with an interquartile range increase associated with a 11% (95% CI = 6%-17%) and 4% (95% CI = 1%-7%) rise in number of total deaths, respectively. In two-pollutant models, PM2.5-10 remained significant effects on total mortality after the inclusion of SO₂ and O₃ both on warm and cool days. We observed no significant associations between PM2.5-10 and daily mortality from respiratory diseases both on warm and cool days. For daily mortality from circulatory diseases, the effect of PM2.5-10 remained significant when SO₂ or O₃ was added in the regression model both on warm and cool days. Future studies of this type in cities with varying climates and cultures are needed.