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

Background Daily 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 PM 2.5 (particles with aerodynamic diameters less than 2.5 μm). The DECH in PM 2.5 was defined as daily total concentration-hours > 25 μg/m 3 . Methods A generalized additive model with a quasi-Poisson link was applied to estimate the associations between day-to-day variation in PM 2.5 DECH and day-to-day variation in cardiovascular mortality in six subtropical cities in Guangdong Province, China. Results The analysis revealed significant associations between PM 2.5 DECHs and cardiovascular mortality. A 500 μg/m 3 ∗ h increase in PM 2.5 DECHs at lag 03 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 PM 2.5 DECHs than daily mean PM 2.5 (6478 (95% CI: 5071, 7917) VS 5136 (95% CI: 3990, 6305)). Conclusion This study reveals that PM 2.5 DECH is one important exposure indicator of ambient PM 2.5 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. [ABSTRACT FROM AUTHOR]