Air pollution and daily mortality in seven major cities of Korea, 1991-1997

The relationship between ambient air pollution and daily mortality in seven major cities of Korea for the period 1991-1997 was examined. These cities account for half of the Korean population (about 22 million). The observed concentrations of sulfur dioxide (SO₂, mean = 23.3 ppb), ozone (O₃, mean = 23.7 ppb), and total suspended particulates (TSP, mean = 77.9 μg/m³) during the study period were at levels below Korea's current ambient air quality standards. Generalized additive models were applied to allow for the highly flexible fitting of seasonal and long-term time trends in air pollution as well as nonlinear associations with weather variables, such as air temperature and relative humidity. In city-specific analyses, an increase of 50 ppb of SO₂ corresponded to 1-12% more deaths, given constant weather conditions. The risk of all-cause mortality was estimated to increase by 0.5-4%, with an increase in the 2-day moving average of TSP levels equal to 100 μg/m³. In multipollutant models with pooled data, we found that the estimated risk of death by SO₂ was notably unaffected by adding the other two pollutants (TSP and O₃) to the model and was statistically significant in various regression models. The rate ratio (RR) for SO₂ remained elevated, indicating an excess mortality of 3% 50 ppb (RR = 1.03; 95% CI, 1.01-1.05). TSP's effect on mortality maintained its significance with O₃, but not with SO₂. This implies that there may be collinearity problems where TSP and SO₂ are included in the same model or that TSP may function less than SO₂ as a surrogate for fine particles in the ambient air of Korea. In conclusion, increased mortality was associated with air pollution at SO₂ levels below the current recommendation for air quality. Further research is needed to clarify the relationship between SO₂ and fine particles in Korea. (C) 2000 Academic Press.