A SPATIAL CAUSAL ANALYSIS OF WILDLAND FIRE-CONTRIBUTED PM 2.5 USING NUMERICAL MODEL OUTPUT.

Wildland fire smoke contains hazardous levels of fine particulate matter (PM _2.5 ), a pollutant shown to adversely effect health. Estimating fire attributable PM _2.5 concentrations is key to quantifying the impact on air quality and subsequent health burden. This is a challenging problem since only total PM _2.5 is measured at monitoring stations and both fire-attributable PM _2.5 and PM _2.5 from all other sources are correlated in space and time. We propose a framework for estimating fire-contributed PM _2.5 and PM _2.5 from all other sources using a novel causal inference framework and bias-adjusted chemical model representations of PM _2.5 under counterfactual scenarios. The chemical model representation of PM _2.5 for this analysis is simulated using Community Multiscale Air Quality Modeling System (CMAQ), run with and without fire emissions across the contiguous U.S. for the 2008-2012 wildfire seasons. The CMAQ output is calibrated with observations from monitoring sites for the same spatial domain and time period. We use a Bayesian model that accounts for spatial variation to estimate the effect of wildland fires on PM _2.5 and state assumptions under which the estimate has a valid causal interpretation. Our results include estimates of the contributions of wildfire smoke to PM _2.5 for the contiguous U.S. Additionally, we compute the health burden associated with the PM _2.5 attributable to wildfire smoke.