The Impact of Particulate Matter on Daily Mortality in Bangkok, Thailand

Several studies conducted in U.S. cities report an association between acute exposures to particulate matter (PM), usually measured as PM_10, and mortality. Evidence of high concentrations of PM₁₀ in Eastern Europe and in large metropolitan areas outside of the United States, such as Mexico City and Bangkok, underscores the need to determine whether these same associations occur outside of the United States. In addition, conducting studies of mortality and air pollution in regions that have distinctly different seasonal patterns than those of the United States provides an effective opportunity to assess the potentially confounding aspects of seasonality. Over the last few years, daily measures of ambient PM₁₀ have been collected in Bangkok, a tropical city of over 6 million people. In this metropolitan area, PM₁₀ consists largely of fine particles generated from diesel- and gasoline-powered automobiles, and from two-stroke motorcycle engines. Our analysis involved the examination of the relationship between PM₁₀ and daily mortality for 1992 through 1995. In addition to counts of daily natural mortality (total mortality net of accidents, homicides, and suicides), the data were compiled to assess both cardiovascular and respiratory mortality, and natural mortality by age group. A multivariate Poisson regression model was used to explain daily mortality while controlling for several covariates including temperature, humidity, day of the week, season, and time. The analysis indicated a statistically significant association between PM10 and all of the alternative measures of mortality. The results suggest a 10-µg/m³ change in daily PM₁₀ is associated with a 1-2% increase in natural mortality, a 1-2% increase in cardiovascular mortality, and a 3-6% increase in respiratory mortality. These relative risks are generally consistent with or greater than those reported in most studies undertaken in the United States.