Date of Award

January 2025

Document Type

Thesis

Degree Name

Master of Public Health (MPH)

Department

School of Public Health

First Advisor

Daniel Carrión

Second Advisor

Kai Chen

Abstract

Wildfire activity has intensified across the United States due to climate change, contributing to rising levels of smoke-attributable fine particulate matter (PM2.5) in ambient air. Wildfire-specific PM2.5 is linked to adverse health outcomes, including increased risk of preterm birth, a leading cause of infant morbidity and mortality. Despite growing concern, few studies have applied quasi-experimental methods to evaluate the causal effects of wildfire-attributable PM2.5 on preterm birth across large, diverse populations and geographical areas. This study estimated the effect of wildfire-specific PM2.5 exposure on preterm birth rates across all counties in the contiguous United States from 2006 to 2020 using the generalized synthetic control method. County-level natality data were merged with wildfire-specific PM2.5 estimates, and exposure was defined using threshold exceedance (5, 10, or 20 µg/m³) across five gestational windows. Generalized synthetic control models estimated average treatment effects on the treated (ATTs) and individual treatment effects (ITEs). Across all thresholds and windows, ATTs were small and statistically insignificant, with most point estimates near zero or slightly negative, suggesting marginally lower preterm birth rates in exposed counties. ITE distributions showed post-exposure heterogeneity but no consistent evidence of harm. These findings diverge from prior studies and may reflect limitations in exposure assessment, residual confounding, or the ecological design. Nonetheless, this study demonstrates the utility of quasi-experimental methods for evaluating environmental exposures and highlights the need for future research using finer-resolution data to better characterize the reproductive health risks of wildfire smoke.

Comments

This thesis is restricted to Yale network users only. It will be made publicly available on 12/16/2025

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