Temporal variability of short term effects of PM₁₀ on mortality in Seoul, Korea

Health effects of PM₁₀ on mortality have been studies worldwide. However, not many studies have questioned possibility that short-term effects of PM₁₀ can be changed over time. Identifying temporal variability of the effects would be of help to getting more valid PM₁₀ effect estimates which are a major basis for public health policies. In this study, temporal variability of short-term effects of PM₁₀ for mortality was investigated from 2001 to 2015 in Seoul, Korea. A time series analysis was used to estimate the effects of PM₁₀ on all-cause, circulatory, and respiratory mortality. Study period was divided into five years of moving time window, and relative risks and its 95% confidence intervals were estimated using distributed lag model for each time window. The annual average of PM₁₀ in Seoul decreased from 52.6 μg/m³ in 2001 to 40.5 μg/m³ in 2015. There were significant temporal trends in PM₁₀ effects regarding each mortality. The effects of PM₁₀ tend to slightly increase in early of the study period and then dropped in recent years. An increase of 2 days of cumulative exposure of PM₁₀ was associated with 0.31% (95% confidence interval: 0.15, 0.46) increase in all-cause mortality for 2001–2005 period, 0.61% (95% confidence interval: 0.34, 0.89) increase in 2005–2009 period, and −0.06% (95% confidence interval: −0.38, 0.25) increase in 2011–2015 period. We found evidence that short-term effects of PM₁₀ on mortality have been changed over time in Seoul, Korea. The observed temporal trend might attributable from two factors which are change of PM₁₀ compositions and population vulnerability. If effects of PM₁₀ vary over time, considering its change would be necessary not only in the estimation of the PM₁₀ effect but also its application for a variety of public health policies.