Air Quality, Mortality, and Perinatal Health: Causal Evidence from Wildfires

I demonstrate how scientific models of pollution processes can be leveraged in quasi-experimental econometric designs to credibly estimate the impacts of environmental quality on health or other outcomes while also improving precision and external validity over previous approaches. I simulate the geographic distribution of fine particulate matter (PM2.5) caused by wildfires for the entire continental United States during 2004-2010 using a set of scientific models of wildfire emissions and air pollution transport commonly used wildfire and air quality applications. Regressing observed concentrations of PM2.5 at pollution monitoring stations on simulated PM2.5 from wildfires, I find that wildfires can explain at least 15 percent of ambient ground-level PM2.5 and even larger fractions of toxic mercury and lead particulates. I then regress county-level health outcomes on station-measured PM2.5 using simualted wildfire PM2.5 as an instrumental variable. I find that a 10 microgram per cubic meter (approximately 2.3 standard deviation) increase in monthly PM2.5 concentration is associated with one additional premature death per 100,000 individuals. This effect is driven primarily by deaths from cardiovascular and respiratory diseases for individuals over age 65. With a control function approach, I find evidence that dose response is approximately linear below the U.S. ambient air quality standard for PM2.5. In addition, I find that in-utero exposure to PM2.5 is associated with higher rates of prematurity, lower birth weights, and changes in the sex ratio, which I interpret as evidence of fetal attrition. Finally, I show that the estimated health effects of PM2.5 are sensitive to the inclusion of controls for other pollutants. I present suggestive evidence that this sensitivity reflects a heterogeneous response to metallic particulates, which are known to be particularly detrimental to health. These findings contribute to a growing body of evidence on the health dangers of fine particulate matter.