Effects of ambient air particles on mortality in Seoul: Have the effects changed over time?

Background: Several studies have shown that there may be temporal variation in PM short-term effect on mortality. This temporal pattern may play an important role in evaluating air quality policies. Objectives: We investigated temporal variation in the association between PM and mortality in Seoul, Korea, 1998-2011. Methods: We adopted a generalized additive model and a series of time windows of five years to analyze temporal variation in associations between PM and all-cause, cardiovascular, and respiratory mortality. This time-window approach offers not only a comparison between one and the other half period but also successive variation. Time-varying associations were estimated only for days without Asian dust (dust storm blown from the Gobi desert) intrusion. Results: Annual average PM₁₀ and PM_2.5 total mass decreased from 70.0 to 46.9μg/m³ and 44.4 to 23.4μg/m³, respectively, during 2001-2011. A 10μg/m³ increase in PM₁₀ was associated with 0.16% (95% CI=-0.03% to 0.35%) additional all-cause deaths in 2002-2006 and it increased to 0.26% (95% CI=0.05-0.48%) in 2007-2011. For PM_2.5, the association increased from 0.35% (95% CI=-0.02% to 0.71%) to 0.48% (95% CI=0.08-0.88%). For cardiovascular and respiratory mortality, increasing trends with stronger estimates were found. Conclusions: The present study showed temporally increasing trends in associations between PM and mortality.