Calculated OH Reactivity of Western U.S. Wildfires Measured During WE-CAN

Wildfires can be a dominant source of atmospheric volatile organic compounds (VOCs) in the western U.S. during the fire season, emitting hundreds of reactive organic species. Here we build upon emissions data from the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) aircraft campaign to calculate OH reactivities for 161 VOCs measured in western U.S. wildfires. OH reactivities are used to examine how VOC and total gas profiles vary between fresh wildfire emissions, aged smoke, smoke and non-smoke impacted urban areas, and the free troposphere. We find that VOCs account for ~75 % of the total calculated plume OH reactivity upon emission when considering all measured gas-phase species, including 161 VOCs, NO2, NO, CO, O3, CH4, PAN, and NH3. Of those, the top ten species make up ~60 % of the total calculated VOC OH reactivity: formaldehyde, acetaldehyde, propene, ethane, butadienes, C2-substituted furans, furan, monoterpenes, furfural, and 5-methylfurfural/benzene diols. Commonly used chemical transport models (CTMs) such as GEOS-Chem only accounts for 4 out of these top 10 species in smoke plumes, and may also miss the remaining 40 % of VOC OH reactivity which is spread across ~150 more rarely reported/measured species. As smoke plumes age, the total calculated OH reactivity is found to decrease due to loss of NOx and oxidation of reactive primary VOCs. This in turn leads to a larger proportion of aldehydes and other oxygenated VOCs in the total OH reactivity as plumes age. Smoke plume emission and aged OH reactivities are further discussed in the context of VOC emissions represented in the GEOS-Chem CTM, and species treated in the Master Chemical Mechanism (MCM). We will examine the consistency between the observed evolution of OH reactivity in smoke plumes and the simulated one by MCM, and draw conclusions on our overall understanding of the gas-phase OH reactions for organic compounds.