Comprehensive atmospheric chemistry of volatile organic compounds in high- and mid-latitude urban areas impacted by wood smoke

Atmospheric volatile organic compounds (VOCs) are precursors of tropospheric ozone (O3), carbon monoxide (CO), and secondary organic aerosol (SOA). VOCs play a central role in tropospheric chemistry by affecting radical cycling and thus control the lifetime of most air pollutants. Biomass burning (BB) emissions from open fires and residential wood combustion are important sources of VOCs to the atmosphere, impacting regional air quality and public health particularly in the western U.S. and Alaska. Meanwhile, in urban atmospheres, emissions from volatile chemical products (VCPs) have been suggested to be an important VOC source as mobile emissions have steadily declined. Many fundamental issues related to VOC emissions need to be resolved, limiting our capability for environmental health assessment and management.
This proposal targets the NOAA AC4 Call for Proposals in FY20, and focuses on urban atmospheric chemistry of VOCs including those rarely-measured/understudied species (?missing VOCs?). It is aimed at developing new observational constraints on VOC emissions in two U.S. cities facing serious air pollution challenges. The project will also build on existing FIREX-AQ efforts in Missoula, MT and contribute to the upcoming ALPACA field campaign in Fairbanks, AK. The data analysis will improve mechanistic understanding on VOC emissions and fates:
Q1. How significant are the previously unknown or understudied (?missing?) VOCs present in urban atmospheres?
Q2: How do the fates of these VOCs in cold/dark environments compare to daytime oxidation and how does this vary seasonally and spatially between high- and mid-latitudes?
Q3: How do the emission ratios of air toxics in anthropogenic and biomass burning emission inventories compare to ground field observations? Are there significant discrepancies in oxygenated VOC emissions?
We will deploy a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) in Fairbanks (2021 Jan/Feb) and Missoula (2021 Jul. to 2022 Sept.) to measure VOC mixing ratios across the entire detected mass spectrum every minute. This will provide high-resolution, comprehensive VOC data that includes tens-to-hundreds of rarely reported VOCs for the 2nd or 3rd largest cities in Montana and Alaska. The wintertime data will provide insights into exposures from residential wood stoves and other heating sources in both valleys, and the summer data will examine wildfire smoke impacts. Our source apportionment will further inform mitigation strategies for both cities and the many other similar areas. A chemical box model constrained by observations will examine the seasonal importance of various oxidation loss pathways for VOCs in high vs. mid-latitudes. We will also evaluate emission ratios to diagnose if there are significant errors in the widely used emission inventories for VOCs.