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

- We explored time-varying short-term effect of PM on mortality in Seoul, Korea.
- PM mass concentration drastically decreased over time.
- The effect size of PM on mortality may increase over time.
- The toxicity of PM or bias in time-series analysis may change over time.
- Air quality policies may not play desirable role in reducing health risks as expected.

BackgroundSeveral 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.ObjectivesWe investigated temporal variation in the association between PM and mortality in Seoul, Korea, 1998-2011.MethodsWe 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.ResultsAnnual average PM10 and PM2.5 total mass decreased from 70.0 to 46.9 µg/m3 and 44.4 to 23.4 µg/m3, respectively, during 2001-2011. A 10 µg/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 PM2.5, 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.ConclusionsThe present study showed temporally increasing trends in associations between PM and mortality. Current policies may not be as effective to reducing health risks attributable to PM as expected. Air quality interventions should be encouraged in terms of causal factors for time-varying association between PM and mortality.