Air pollution and daily mortality in Seoul and Ulsan, Korea

The relationship between air pollution and daily mortality for the period 1991-1995 was examined in two Korean cities, Seoul and Ulsan. The observed concentrations of sulfur dioxide (SO₂; mean = 28.7 ppb), ozone (O₃; mean = 29.2 ppb), and total suspended particulates (TSP; mean = 82.3 μg/m³) during the study period were at levels below Korea's current ambient air quality standards. Daily death counts were regressed separately in the two cities, using Poisson regression on SO₂, O₃ and/or TSP controlling for variability in the weather and seasons. When considered singly in Poisson regression models controlling for seasonal variations and weather conditions, the nonaccidental mortality associated with a 50-ppb increment in a 3-day moving average of SO₂ concentrations, including the concurrent day and the preceding 2 days, was 1.078 [95% confidence interval (CI), 1.057-1.099] for Seoul and 1.051 (CI, 0.991-1.115) for Ulsan. The race ratio was 1.051 (CI, 1.031-1.072) in Seoul and 0.999 (CI, 0.361-1.039) in Ulsan per 100 μg/m³ for TSP, and 1.015 (CI, 1.005-1.025) in Seoul and 1.020 (0.889-1.170) in Ulsan per 50 ppb for 1-hr maximum O₃. When TSP was considered simultaneously with other pollutants, the TSP association was no longer significant. We observed independent pollution effects on daily mortality even after using various approaches to control for either weather or seasonal variables in the regression model. This study demonstrated increased mortality associated with air pollution at both SO₂ and O₃ levels below the current World Health Organization recommendations.