Short-term association between sulfur dioxide and daily mortality: The Public Health and Air Pollution in Asia (PAPA) study ★

Sulfur dioxide (SO2) has been associated with increased mortality and morbidity, but only few studies were conducted in Asian countries. Previous studies suggest that SO2 may have adverse health effects independent of other pollutants. In the Public Health and Air Pollution in Asia (PAPA) project, the short-term associations between ambient sulfur dioxide (SO2) and daily mortality were examined in Bangkok, Thailand, and three Chinese cities: Hong Kong, Shanghai, and Wuhan. Poisson regression models incorporating natural spline smoothing functions were used to adjust for seasonality and other time-varying covariates. Effect estimates were obtained for each city and then for the cities combined. The impact of alternative model specifications, such as lag structure of pollutants and degree of freedom (df) for time trend, on the estimated effects of SO2 were also examined. In both individual-city and combined analysis, significant effects of SO2 on total non-accidental and cardiopulmonary mortality were observed. An increase of 10 μg/m3 of 2-day moving average concentrations of SO2 corresponded to 1.00% [95% confidence interval (CI), 0.75–1.24], 1.09% (95% CI, 0.71–1.47), and 1.47% (95% CI, 0.85–2.08) increase of total, cardiovascular and respiratory mortality, respectively, in the combined analysis. Sensitivity analyzes suggested that these findings were generally insensitive to alternative model specifications. After adjustment for PM10 or O3, the effect of SO2 remained significant in three Chinese cities. However, adjustment for NO2 diminished the associations and rendered them statistically insignificant in all four cities. In conclusion, ambient SO2 concentration was associated with daily mortality in these four Asian cities. These associations may be attributable to SO2 serving as a surrogate of other substances. Our findings suggest that the role of outdoor exposure to SO2 should be investigated further in this region.