Short-term effect of coarse particles on daily mortality rate in a tropical city, Kaohsiung, Taiwan

Many studies examined the short-term effects of air pollution on frequency of daily mortality over the past two decades. However, information on the relationship between exposure to levels of coarse particles (PM_2.5-10) and daily mortality rate is relatively sparse due to limited availability of monitoring data and findings are inconsistent. This study was undertaken to determine whether an association exists between PM_2.5-10 levels and rate of daily mortality in Kaohsiung, Taiwan, a large industrial city with a tropical climate. Daily mortality rate, air pollution parameters, and weather data for Kaohsiung were obtained for the period 2006-2008. The relative risk (RR) of daily mortality occurrence was estimated using a time-stratified case-crossover approach, controlling for (1) weather variables, (2) day of the week, (3) seasonality, and (4) long-term time trends. For the single-pollutant model without adjustment for other pollutants, PM_2.5-10 exposure levels showed significant correlation with total mortality rate both on warm and cool days, with an interquartile range increase associated with a 14% (95% CI = 5-23%) and 12% (95% CI = 5-20%) rise in number of total deaths, respectively. In two-pollutant models, PM_2.5-10 exerted significant influence on total mortality frequency after inclusion of sulfur dioxide (SO₂) on warm days. On cool days, PM_2.5-10 induced significant elevation in total mortality rate when SO₂ or ozone (O₃) was added in the regression model. There was no apparent indication of an association between PM_2.5-10 exposure and deaths attributed to respiratory and circulatory diseases. This study provided evidence of correlation between short-term exposure to PM_2.5-10 and increased risk of death for all causes.