Short Term Exposure to Air Pollution and Mortality in the US: A Case-Crossover Analysis
Abstract Background: Studies examining the association of short-term air pollution exposure and daily deaths have typically been limited to cities and used citywide averages for exposure. This study aims to estimate the associations between short-term exposures to fine particulate matter (PM2.5), ozone (O3), and nitrogen dioxide (NO2) and all-cause and cause-specific mortality in multiple US states including rural areas.Methods: We conducted a time-stratified case-crossover study examining the entire population of seven US states from 2000-2015, with over 3 million non-accidental deaths. Daily predictions of PM2.5, O3, and NO2 at 1x1 km grid cells across the contiguous US were linked to mortality based on census track and residential address. For each pollutant, we used conditional logistic regression to quantify the association between exposure and the relative risk of mortality conditioning on meteorological variables and other pollutants. Results: A 10 μg/m3 increase in PM2.5 exposure at the moving average of lag 0-1 day and 10 ppb increase in NO2 exposure at lag 0-3 day were significantly associated with a 0.67% (95%CI: 0.34-1.01%) and 0.20% (95%CI: 0.00-0.39%) increase in the risk of all-cause mortality, respectively. A marginally significant association for mortality was observed with each 10 ppb increase in O3 exposure at lag 0-3 day. The adverse effects of PM2.5 on all-cause mortality persisted when restricting the analysis at lower levels.. PM2.5 was also significantly associated with respiratory mortality and cardiovascular mortality. Conclusions: Short-term exposure to PM2.5 and NO2 is associated with increased risks for all-cause mortality. Our findings delivered evidence that risks of death persisted at levels below currently permissible.