Short term exposure to air pollution and mortality in the US: a double negative control analysis

Rationale Studies examining the association of short-term air pollution exposure and daily deaths have typically been limited to cities and used citywide average exposures, with few using causal models. Objectives To estimate the associations between short-term exposures to fine particulate matter (PM.sub.2.5), ozone (O.sub.3), and nitrogen dioxide (NO.sub.2) and all-cause and cause-specific mortality in multiple US states using census tract or address exposure and including rural areas, using a double negative control analysis. 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 PM.sub.2.5, O.sub.3, and NO.sub.2 at 1x1 km grid cells were linked to mortality based on census track or 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, other pollutants, and using double negative controls. Results A 10 [mu]g/m.sup.3 increase in PM.sub.2.5 exposure at the moving average of lag 0-2 day was significantly associated with a 0.67% (95%CI: 0.34-1.01%) increase in all-cause mortality. 10 ppb increases in NO.sub.2 or O.sub.3 exposure at lag 0-2 day were marginally associated with and 0.19% (95%CI: -0.01-0.38%) and 0.20 (95% CI-0.01, 0.40), respectively. The adverse effects of PM.sub.2.5 persisted when pollution levels were restricted to below the current global air pollution standards. Negative control models indicated little likelihood of omitted confounders for PM.sub.2.5, and mixed results for the gases. PM.sub.2.5 was also significantly associated with respiratory mortality and cardiovascular mortality. Conclusions Short-term exposure to PM.sub.2.5 and possibly O.sub.3 and NO.sub.2 are associated with increased risks for all-cause mortality. Our findings delivered evidence that risks of death persisted at levels below currently permissible. Keywords: Air pollutant, Particulate matter, PM2.5, Ozone, Nitrogen dioxide, Mortality