Air Quality and Climate Impacts of Western U.S. Wildfires
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University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 2020 Air Quality and Climate Impacts of Western U.S. Wildfires Vanessa Selimovic University of Montana, Missoula Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Selimovic, Vanessa, "Air Quality and Climate Impacts of Western U.S. Wildfires" (2020). Graduate Student Theses, Dissertations, & Professional Papers. 11634. https://scholarworks.umt.edu/etd/11634 This Dissertation is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. AIR QUALITY AND CLIMATE IMPACTS OF WESTERN US WILDFIRES By VANESSA SELIMOVIC B.A. Chemistry, Concordia University, Portland, OR, 2014 Dissertation presented in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Chemistry The University of Montana Missoula, MT August 2020 Approved by: Scott Whittenburg, Dean of The Graduate School Graduate School Dr. Robert Yokelson, Committee Chair Department of Chemistry and Biochemistry Dr. Lu Hu, Committee Member Department of Chemistry and Biochemistry Dr. Mark Cracolice, Committee Member Department of Chemistry and Biochemistry Dr. Michael DeGrandpre, Committee Member Department of Chemistry and Biochemistry Dr. Philip Higuera, Committee Member Department of Forestry i Selimovic, Vanessa, PhD, Summer 2020 Chemistry Air quality and climate impacts of western US wildfires Advisor: Dr. Robert Yokelson, Department of Chemistry 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. ii ACKNOWLEDGEMENTS My deepest gratitude extends to anyone and everyone who has supported me throughout my graduate studies and doctoral pursuits. Specifically, I am incredibly thankful to my advisor Bob Yokelson for the insight, patience, and time he devoted to me as my mentor. This work would be impossible without his support and guidance, and the support and guidance from my committee members: Lu Hu, Mark Cracolice, Michael DeGrandpre, and Philip Higuera. I also extend my thanks to Ted Christian and Chelsea Stockwell for their advice, encouragement, and friendship as group members. Although there are too many names to list here, I am incredibly grateful for those whom I worked alongside with and befriended during field campaigns—you made the long days not only bearable, but also enjoyable. In the same regard, I want to extend my gratitude to all those who provided data, advice, and meaningful considerations during my grad school career and in this work. Finally, thank you to my friends, family, and loved ones for their continued support, compassion, and words of encouragement, and to my dog Molly for her unconditional love (and fluffiness) throughout this journey. iii ABSTRACT…………………………………………………………………………………….ii ACKKNOWLEDGEMENTS ……………………………………………………………..….iii TABLE OF CONTENTS………………………………………………………………………iv LIST OF FIGURES…………………………………………………………………………..viii LIST OF TABLES………………………………………………………………………….…xii TABLE OF CONTENTS Chapter 1: Introduction ................................................................................................................................. 1 1.1 Western wildfire impacts and background .......................................................................................... 1 1.2 Motivation and Goals .......................................................................................................................... 4 1.3 Thesis Outline ..................................................................................................................................... 5 1.4 Literature Review ................................................................................................................................ 7 1.4.1 Atmospheric processes and biomass burning emissions .............................................................. 7 1.4.2 Aerosol Absorption and Scattering ............................................................................................ 10 1.4.3 Sampling Considerations ........................................................................................................... 14 Chapter 2: Biomass burning general information and useful ratios ............................................................ 16 2.1 Emission Inventories ......................................................................................................................... 16 2.2 Emission ratios and emission factors ................................................................................................ 17 2.3 Modified Combustion Efficiency...................................................................................................... 18 2.4 Single scattering albedo and absorption Ångström Exponent .......................................................... 18 2.5 Mass Scattering and Mass Absorption Coefficients ......................................................................... 19 Chapter 3: The Fire Influence on Regional and Global Environments Experiment (FIREX) Missoula Fire Sciences Lab Experiment ............................................................................................................................ 20 3.1 FIREX Lab Introduction: .................................................................................................................. 20 3.2 FIREX Lab configurations ................................................................................................................ 21 3.2.1: US Forest Service Fire Sciences Laboratory ............................................................................ 21 3.2.2: Stack burn configuration ........................................................................................................... 21 3.2.3: Room burn configuration .......................................................................................................... 22 3.3 Fuels overview .................................................................................................................................. 22 3.4 Instrument overview ......................................................................................................................... 23 3.4.1 OP-FTIR introduction ................................................................................................................ 24 iv 3.4.2 OP-FTIR data collection ............................................................................................................ 25 3.4.3 FTIR Measurement Strategy ...................................................................................................... 26 3.4.4 Emission ratio and emission factor determination ..................................................................... 27 3.4.5 Photoacoustic extinctiometers (PAX) at 870 and 401 nm ........................................................