Highly-Oxidized Secondary Organic Aerosol in Coastal Communities Downwind of New York City: Influence of Over-Water Production and Transport

MITCHELL ROGERS, Anandi Williams, Keerthana Chari, Tori Hass-Mitchell, Colby Buehler, Heather LeClerc, Catelynn Soong, Anita Avery, Mitchell Alton, Jo Machesky, Taekyu Joo, Manjula Canagaratna, Andrew Lambe, Drew Gentner, Yale University

     Abstract Number: 286
     Working Group: Coast to Coast Campaigns on Aerosols, Clouds, Chemistry, and Air Quality

Abstract
Emissions of aerosols and their reactive precursors from New York City and other Mid-Atlantic urban areas often travel across the Long Island Sound and undergo over-water oxidative transformations, leading to regional enhancements in secondary pollutants for these downwind communities. Using summer 2023 observations from the Yale Coastal Field Station in Guilford, CT as part of the NYC-METS 2023 (New York City metropolitan Measurements of Emissions and TransformationS) and AEROMMA 2023 (Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas) campaigns, we examine the impacts of reactive anthropogenic, biogenic, and marine emissions and multiphase oxidative chemistry on secondary organic aerosol (SOA) reaching downwind coastal regions. Time-resolved gas and particle-phase measurements via a Proton-Transfer-Reaction Time-of-Flight Mass Spectrometer (PTR-ToF-MS) and Aerosol Chemical Speciation Monitor (ACSM) are used to explore enhancements in oxygenated organic aerosol (OOA) and their variations with emissions and meteorology. The results of online analysis are also compared to the offline analysis of functionalized organic particle-phase compounds using gas and liquid chromatography with tandem mass spectrometry. We examine differences in oxidized aerosol composition and molecular functionalities that vary with on-shore versus off-shore flow, as well as with backward air mass trajectory clusters, and often arrived in single or multi-day events coincident with elevated ozone. For example, periods of on-shore flow brought 1+ μg m^-3 enhancements in OOA concentrations that were more oxidized on average (f₄₄/f₄₃ = 2.7) and represented by a spectrum of OOA source factors as determined via source apportionment with positive matrix factorization. The influence of oxidized SOA downwind of densely-populated urban areas is assessed across the summer 2023 campaign and in the context of changing emissions and climate.