Year of Award

2020

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Chemistry (Analytical/Environmental Option)

Department or School/College

Department of Chemistry and Biochemistry

Committee Chair

Robert Yokelson

Commitee Members

Lu Hu, Mark Cracolice, Michael DeGrandpre, Philip Higuera

Keywords

chemistry, wildfires

Abstract

Wildfire smoke impacts are important in the western US and projected to increase substantially in upcoming decades. It’s impacts on regional and global scale atmospheric chemistry is dependent upon both physical and chemical changes that take place as biomass burning (BB) emissions are transported, diluted, and exposed to oxidation. In turn, evaluation of smoke modeling requires quality, long-term simultaneous measurements of wildfire smoke characteristics that provide both inert tracers to test production and transport (e.g. black carbon (BC) and CO) and reactive species to test chemical mechanisms (e.g. particulate matter (PM), O3, brown carbon (BrC)). During the Fire Influence on Regional to Global Environments and Air Quality Experiment (FIREX-AQ) at the Missoula Fire Sciences Lab, we burned realistic fuel complexes for western wildfire ecosystems to better understand and assess their emissions profiles, and found that the average trace gas emissions were similar across the coniferous ecosystems tested and most of the variability observed in emissions could be attributed to differences in the consumption of components such as duff and litter, rather than the dominant tree species, which may have implications for land management strategies like prescribed burning. Further, our observations show that emissions of BC and BrC and its optical properties are strongly correlated with fuel type. Major findings of over 1000 hours of ambient smoke monitoring in a populated center downwind of multiple fires include a ~50% lower PM2.5/CO at Missoula than commonly observed in previously-published airborne studies of wildfire smoke suggesting that evaporation can dominate secondary organic aerosol (SOA) formation in aged smoke at surface altitudes. O3 was enhanced by dilute smoke and suppressed by thick smoke, and O3 and NO2 were strongly anti-correlated, yielding high NO3 production rates. On average, BrC accounted for about 50% of the aerosol absorption at 401 nm. Finally, in comparing our surface measurements of smoke to recent field campaign measurements, we find additional evidence for lower PM/CO ratios at the surface, compared to high elevation or airborne campaigns, suggesting temperature may play a critical role in the evolution of BB aerosol. These findings may have larger scale implications especially as it relates to land management and the increased implementation of prescribed fires.

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© Copyright 2020 Vanessa Selimovic