Recent Increases in Air Pollution: Evidence and Implications for Mortality

After a decade of improvement, annual average fine particulate matter (PM2.5) in the United States increased in both 2017 and 2018. These increases are worrisome, because studies have shown that PM2.5 increases premature mortality risk (e.g., Lelieveld et al. 2015), and this risk accounts for the largest share of monetary damages from air pollution (US EPA 1999, 2010a; Muller, Mendelsohn, and Nordhaus 2011). Based on data for 2009–2018, this article documents US trends in PM2.5 and their implications for mortality. We find that nationally, PM2.5 levels fell by 27.4 percent from 2009 to 2016 and then increased 5.7 percent from 2016 to 2018. We explore channels through which the PM2.5 increases may have occurred, including increases in economic activity, increases in wildfires, and decreases in Clean Air Act enforcement actions. The evidence suggests that all three may have played roles in the observed increase. Although further research is needed on the causes of the increase in PM2.5, we find that these trends have significant health implications, with premature deaths from PM2.5 rising by 9,700 between 2016 and 2018, representing damages of $89 billion (in $2018). In the remainder of the article, we present our results concerning trends in PM2.5; discuss our analysis of the contribution of economic activity, wildfires, and regulatory enforcement actions to these trends; and identify the implications of these trends for mortality.