A Direct Estimate of the Impact of PM(2.5), NO(2), and O(3) Exposure on Life Expectancy Using Propensity Scores

Many studies have reported associations of air pollutants and death, but fewer examined multiple pollutants, or used causal methods. We present a method for directly estimating changes in the distribution of age at death using propensity scores. METHODS: We included all participants in Medicare from 2000 to 2016 (637,207,589 person-years of follow-up). We fit separate logistic regressions modeling the probability of death at each year of age from 65 to 98 or older as a function of exposure to particulate matter less tha 2.5 µM in diameter (PM(2.5)), NO(2), and O(3), using separate propensity scores for each age. We estimated the propensity score using gradient boosting. We estimated the distribution of life expectancy at three counterfactual exposures for each pollutant. RESULTS: The estimated increase in mean life expectancy had the population been exposed to 7 versus 12 µg/m(3) PM(2.5) was 0.29 years (95% CI = 0.28, 0.30). The change in life expectancy had the population been exposed to 10 versus 20 ppb of NO(2) was −0.01 years (95% CI = −0.015, −0.006). The increase in mean life expectancy had the population been exposed to 35 versus 45 ppb of O(3) was 0.15 years (95% CI = 0.14, 0.16). Each of these effects was independent and additive. CONCLUSIONS: We estimated that reducing PM(2.5) and O(3) concentrations to levels below current standards would increase life expectancy by substantial amounts compared with the recent increase of life expectancy at age 65 of 0.7 years in a decade. Our results are not consistent with the hypothesis that exposure to NO(2) decreases life expectancy.