MODELING OF AMBIENT POLYCYCLIC AROMATIC HYDROCARBON (PAH) CONCENTRATIONS OVER NORTH AMERICA: IMPACTS OF WILDFIRE EMISSIONS

MD Jahidul Islam

Wildfire activity and smoke have increased across North America, becoming a major and growing source of toxic air pollution, including carcinogenic polycyclic aromatic hydrocarbons (PAHs). This thesis examines wildfire-driven PAH exposure across North America through a combination of literature synthesis and original atmospheric modeling research. It first reviews the current state of knowledge on the impacts of wildfires on air quality, wildfire emission inventories, and PAH modeling. This review identifies a persistent gap: existing wildfire PAH emission inventories, and the models built on them, substantially underestimate wildfire's true contribution to ambient PAH concentrations and the resulting cancer risk. Building on this review, the thesis presents original research that develops a new PAH emission inventory for wildfire sources. This inventory integrates dry matter burned estimates from both bottom-up (GFED, FINN) and top-down (GFAS, QFED) global wildfire databases with land cover–specific PAH emission factors that capture fuel-dependent variability. GEOS-Chem Model evaluation against surface observations shows that the updated inventory reduces the systematic underestimation of wildfire-derived PAHs by 5–13% across seasons. Increasing model resolution from 2° × 2.5° (~200 km) to 0.5° × 0.625° (~50 km) further reduces overall bias by approximately 33%, underscoring the importance of resolving spatial heterogeneity in smoke transport. Wildfires are shown to dominate summertime PAH concentrations in fire-prone western regions, contributing 60–80% of total PAH levels in Northern California and the Pacific Northwest, with wildfire contributions rising sharply over the study period even as non-fire sources have declined. At the national scale, wildfire-driven PAHs account for approximately 35% of total PAH-attributable incremental lifetime cancer risk, with localized hotspots in Northern California exceeding EPA risk benchmarks. The thesis closes by discussing the limitations of this modeling framework and outlining directions for future research, including finer-scale emission characterization and the incorporation of satellite-based observational constraints. Together, this work demonstrates that wildfires are an increasingly dominant driver of carcinogenic PAH exposure across North America and establishes an improved modeling foundation for quantifying that risk under a changing climate.

MODELING OF AMBIENT POLYCYCLIC AROMATIC HYDROCARBON (PAH) CONCENTRATIONS OVER NORTH AMERICA: IMPACTS OF WILDFIRE EMISSIONS

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