Source Apportionment of Sulfate Aerosol at the ASCENT Cheeka Peak Observatory Site

OLIVIA HAKAN, Odelle Hadley, Courtney Winck, Roya Bahreini, Ann M. Dillner, Armistead G. Russell, Nga Lee Ng, Joel A. Thornton, University of Washington

     Abstract Number: 120
     Working Group: Source Apportionment

Abstract
Cheeka Peak Observatory (CPO) is a remote atmospheric measurement field site located on the Olympic Peninsula of Washington, roughly 75 miles from the nearest city of Port Angeles and less than 5 miles from the Pacific Ocean. As part of the Atmospheric Science and Chemistry mEasurement NeTwork (ASCENT), the site is equipped with an aerosol chemical speciation monitor (ACSM), an aethalometer (AE33), an Xact multi-metals monitor (Xact 625i), and a size mobility particle scanner (SMPS) to measure aerosol concentration and composition in near-real time. These instruments measure non-refractory mass loading and composition, light-absorbing particle concentration, concentrations of 46 different elements, and the total particle number concentration and size distribution, respectively. With low wintertime average concentrations of 0.17 μg m-3 organics, 0.03 μg m-3 sulfate, 0.04 μg m-3 nitrate, 0.05 μg m-3 ammonia, and 0.01 μg m-3 chloride at CPO, it is often possible to identify episodic events with relatively low concentration perturbations and analyze their potential sources. Here we analyze speciated aerosol data collected by the ACSM to characterize sulfate sources in the remote Pacific Northwest over several months during the 2023-2025 time period. In this analysis, we have identified several major events, including transported biomass burning from wildfires across the US and Canada, and long-range transport of volcanic sulfate plumes from Kamchatka across the Pacific Ocean. Additionally, we use positive matrix factorization (PMF, SoFi) to apportion the aerosols into distinct sources over several month-long periods of data collection. During this time, we have also observed impacts from maritime vessel traffic, marine-originating methanesulphonic acid, and new particle formation.