Utilizing daily excessive concentration hours to estimate cardiovascular mortality and years of life lost attributable to fine particulate matter in Tehran, Iran

Background: Evidence for associations between fine particulate matter (PM2.5) and cardiovascular diseases (CVDs) in Iran is scarce. Given large within-day variations of PM2.(5) concentration, using the daily mean of PM2.5 (PM(2.5)mean) as exposure metric might bias the health-related assessment. This study applied a novel indicator, daily excessive concentration hours (DECH), to evaluate the effect of ambient PM2.5 on CVD mortality and years of life lost (YLL) in Tehran, the capital city of Iran. Methods: Hourly concentration data for PM2.5, daily information for meteorology and records of registered cardiovascular deaths from 2012 to 2016 were obtained from Tehran, Iran. Daily excessive concentration hours of PM2.5 (PM2.5DECH) was defined as daily total concentration-hours exceeding 35 mu g/m(3). Using a time-series design, we applied generalized linear models to assess the attributable effects of PM2.5DECH and PM(2.5)mean on CVD mortality and YLL. Results: For an interquartile range (IQR) rise in PM2.5DECH, total CVD mortality at lag 0-10 days and YLL at lag 0-8 days increased 2.26% (95% confidence interval (CI): 0.85-3.69%) and 23.24 (6.07-40.42) person years, respectively. Corresponding increases were 3.45% (1.44-5.49%) and 35.21 (10.85-59.58) person years for an IQR rise in PM(2.5)mean. Significant associations between PM2.5 pollution (i.e., PM(2.5)mean and PM2.5DECH) and cause-specific cardiovascular health (i.e., mortality and YLL) were only identified in stroke. Subgroup analyses showed that male and people aged 0-64 years suffered more from PM2.5 pollution. Furthermore, we attributed a greater CVD burden to PM2.5DECH (1.67% for mortality and 2.67% for YLL) than PM2.5mean (0.63% for mortality and 0.70% for YLL) during the study period. Conclusions: This study strengthened the evidence for the aggravated CVD mortality burden associated with short-term exposure to PM2.5. Our findings also suggested that PM2.5DECH might be a potential alternative indicator of exposure assessment in PM2.5-related health investigations. (C) 2019 Elsevier B.V. All rights reserved.