Abstract Body
Background: Epidemiologic studies of air pollution and mortality have primarily investigated long- and short-term exposures separately, have used multiplicative models, and have been associational studies.
Methods: We analyzed 1.5 million Medicare beneficiaries living in Massachusetts with 3.9 billion person-days of follow-up during 2000-2012. We implemented a generalized propensity score adjustment approach, which accounted for joint confounding by the concurrent exposures, individual- and area-level covariates, meteorological covariates, seasonal variations, and long-term time trend, to evaluate causal effects of long- (one-year moving average) and short-term (two-day moving average) exposures to PM2.5, O3, and NO2 on all-cause mortality. By modeling the binary outcome of death with linear probability model, we estimated the potential number of deaths that would occur per unit increase in each air pollutant exposure.
Results: We found that long- and short-term PM2.5, O3, and NO2 were all associated with an increased risk of mortality. Specifically, per 10 million person-days, each 1 µg·m-3 increase in long- and short-term PM2.5 were associated with 35.4 (95% confidence interval [CI], 33.4-37.6) and 3.04 (95% CI, 2.17-3.94) excess deaths, respectively; each 1 ppb increase in long- and short-term O3 were associated with 2.35 (95% CI, 1.08-3.61) and 2.41 (95% CI, 1.81-2.91) excess deaths, respectively; and each 1 ppb increase in long- and short-term NO2 were associated with 3.24 (95% CI, 2.75-3.77) and 5.60 (95% CI, 5.24-5.98) excess deaths, respectively. Importantly, risk differences associated with long-term effects of PM2.5 and O3 increased substantially when the exposure levels went below the increasingly stringent thresholds, including those well below the current National Ambient Air Quality Standards (NAAQS).
Conclusions: The findings suggest that air pollution exposures were causally associated with mortality, even at levels below NAAQS. The estimates on additive probability scale provide clearer insights into the relative magnitude of air pollution effects.
