Daily exceedance concentration hours: A novel indicator to measure acute cardiovascular effects of PM2.5 in six Chinese subtropical cities

Abstract

BackgroundDaily mean concentration cannot fully address the hourly variations of air pollution within one day. As such, we proposed a new indicator, daily exceedance concentration hours (DECH), to explore the acute cardiovascular effects of ambient PM2.5 (particles with aerodynamic diameters less than 2.5μm). The DECH in PM2.5 was defined as daily total concentration-hours >25μg/m3. MethodsA generalized additive model with a quasi-Poisson link was applied to estimate the associations between day-to-day variation in PM2.5 DECH and day-to-day variation in cardiovascular mortality in six subtropical cities in Guangdong Province, China. ResultsThe analysis revealed significant associations between PM2.5 DECHs and cardiovascular mortality. A 500μg/m3∗h increase in PM2.5 DECHs at lag03 was associated with an increase of 4.55% (95% confidence interval (CI): 3.59%, 5.52%) in cardiovascular mortality, 4.45% (95% CI: 2.81%, 6.12%) in ischemic cardiovascular mortality, 5.02% (95% CI: 3.41%, 6.65%) in cerebrovascular mortality, and 3.00% (95% CI: 1.13%, 4.90%) in acute myocardial infarction mortality. We further observed a greater mortality burden using PM2.5 DECHs than daily mean PM2.5 (6478 (95% CI: 5071, 7917) VS 5136 (95% CI: 3990, 6305)). ConclusionThis study reveals that PM2.5 DECH is one important exposure indicator of ambient PM2.5 to measure its cardiovascular mortality effects in Pearl River Delta region; and that using daily mean concentration could under-estimate the mortality burden compared with this new indicator.