Volatile Organic Compounds in a Western Montana Valley: Roles of Residential Wood Burning and Impacts of SARS-CoV-2 Shutdowns

Abstract:

We present ongoing atmospheric measurements of volatile organic compounds (VOCs) by a proton transfer reaction – time of flight – mass spectrometer (PTR-ToF-MS) in Missoula, Montana for the 2020 Spring, covering the periods before, during, and post SARS-CoV-2 shutdowns. We will interpret the data in terms of how sudden shifted anthropogenic activities affect atmospheric composition in a Western intermountain valley, which ranked 7^th out of 216 metropolitan areas in the U.S. for short-term particle pollution by the American Lung Association. Compared to pre-shutdowns and the same period in 2019, we find that mixing ratios of benzene and toluene, which are commonly associated with vehicle emissions, decreased by up to 48% during the shutdowns. D5 siloxane, a tracer for personal care products, fell by 75%, likely driven by a reduction in the Missoula population due to Spring break followed by the university’s transition to distance learning. Observations of diurnal profiles, for vehicle emissions related species, indicate transportation patterns were altered during shutdowns. Diurnal patterns of benzene and toluene exhibit a distinct modification during the shutdowns, as the enhancement associated with the evening rush hour peak was no longer observed while the morning rush hour peak became markedly shorter and less intense. The morning rush hour peak for D5 siloxane was no longer observed during the shutdowns. The ambient mixing ratios and diurnal profile for furfural, a potential tracer for residential wood burning activities, did not change to any appreciable extent as a result of the shutdowns. Additional analyses such as positive matrix factorization source apportionment will be presented in further detail.