Impacts of the 2023 Canadian Wildfires on VOC Speciation and Chemical Reactivity in the New York Metropolitan Area

The 2023 wildfire season was the most intense biomass burning season on record for Canada, breaking the previous records for area burned in both Canadian and North American history. In June 2023, ongoing wildfires in Quebec, Canada, transported smoke thousands of miles to the Northeastern United States affecting air quality for millions of Americans. The New York metropolitan area (e.g., New York City and Long Island) is commonly affected by summertime air pollution events characterized by O₃ exceedance days, making it an important region to study O₃ and its precursors (i.e., VOCs). In June 2023, New York City (NYC) and Long Island were significantly impacted by the long-range transport of Canadian wildfire smoke, enduring multiple days of air quality advisories and hazy, smoke-filled skies. Here, we present what are, to our knowledge, the first observations of VOCs in the New York metropolitan area during the June 2023 Canadian wildfire smoke events, utilizing a high-resolution proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) 8000 (Ionicon Analytik GmbH, Austria). We investigate the impact of the advected biomass burning plumes on local VOC speciation and atmospheric chemical reactivity at the Flax Pond Marine Laboratory, a rural site on Long Island, situated roughly 60 miles downwind of New York City. This study focuses on the urban-rural interface and understanding how the transported Canadian wildfire smoke influenced air quality and VOC speciation at this transitional zone. We also investigate how these wildfire plumes have impacted the long-term trends of VOCs and chemical reactivity through comparison to previous years’ data (i.e., 2022), which had no biomass burning influence. Additionally, we apply positive matrix factorization (PMF) to resolve the sources of VOCs at Flax Pond during the influx of aged Canadian wildfire smoke, providing a better understanding of the various VOC sources at the urban-rural interface. During June 2023 and the Canadian wildfire events, the PTR-ToF-MS detected several oxygenated VOCs (OVOCs), such as acetaldehyde, formic acid, and formaldehyde, all of which had atmospheric concentrations ~5-10x above background. The VOC speciation at Flax Pond was altered by the influence of Canadian wildfire smoke, with OVOCs comprising ~78% of the total observed VOC concentration, compared to ~54% from OVOCs in the local rural plume. The contribution of VOCs to the total chemical reactivity during the advected wildfire plumes from Canada was dominated by OVOCs (~58%) whereas the local rural chemical reactivity at Flax Pond is typically dominated by biogenic VOCs (BVOCs; 94%). This shift in chemical reactivity at Flax Pond highlights the need for further observation and analysis of VOCs, particularly in wildfire plumes, due to the high reactivity of several oxygenated species that can lead to secondary pollutant formation in the New York metropolitan area. The Canadian wildfire events in June 2023 had significant impacts on air quality and trace gas speciation at a site thousands of miles away. As wildfires are expected to become more frequent with increasing global temperatures, continuously monitoring VOCs and air pollutants in densely populated regions is crucial.