First Year of Aerosol Characterization at the ASCENT-Atlanta Site: Temporal and Seasonal Variations of Aerosol Chemical Composition and Sources

RUIZHE LIU, Alison Fankhauser, Yutong Liang, David Pando, Roya Bahreini, Ann M. Dillner, Armistead G. Russell, Nga Lee Ng, Georgia Institute of Technology

     Abstract Number: 336
     Working Group: Coast to Coast Campaigns on Aerosols, Clouds, Chemistry, and Air Quality

Abstract
Fine aerosol in the southeastern U.S. is often characterized by strong interactions of biogenic and anthropogenic emissions. Results from prior short intensive campaigns have shown that biogenic hydrocarbons contribute substantially to organic aerosol (OA) in the greater Atlanta area, especially in summer. However, seasonal variation of aerosol composition in Atlanta remains complex and poorly understood. In this work, we conduct continuous measurements at the South Dekalb site in Atlanta from April 2023 to May 2024, which is part of the Atmospheric Science and Chemistry mEasurement NeTwork (ASCENT). A Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM; non-refractory aerosol), an aethalometer (AE33; black carbon and brown carbon), an XRF-based trace metal monitor (Xact-625i; metals), and a Scanning Mobility Particle Sizer (SMPS, particle size distribution) are deployed. All instruments have a PM2.5 inlet except for SMPS which is PM1. We report temporal and seasonal variations of aerosol composition and sources from our first year of measurements. Overall, the data thus far show that fine aerosol is dominated by organics (72%), followed by black carbon (8%), sulfate and nitrate (6-7% each), ammonium and metals (3-4% each), and a negligible amount of chloride. Positive Matrix Factorization (PMF) analysis shows distinct OA subtypes and contributions. Less-oxidized and more-oxidized oxygenated OA (LO-OOA, MO-OOA) consistently display the highest mass concentrations across all seasons. The mass fractions of other factors exhibit seasonal variability, with primary OA such as cooking OA (COA), biomass burning (BBOA), and hydrocarbon-like OA (HOA) increasing in colder months. Potential sources of OOAs are investigated, including biomass burning, oxidation of biogenic hydrocarbons, and long-range transport. Lastly, we compare these ASCENT measurements with our decade long (2012-2022) intensive summer campaigns in Atlanta, showing how continued decreases in NOx and SO2 have impacted aerosol composition and sources in this region.