Identifying the Temporal Change and Impact of Liquid Water Content, Acidity, and Meteorological Conditions on Fine Particle Concentration and Composition in San Antonio, Texas

FANGZHOU GUO, Alexander Bui, Benjamin Schulze, Chun-Ying Chao, Sergio Alvarez, Subin Yoon, Sujan Shrestha, Rebecca J. Sheesley, Sascha Usenko, James Flynn, Shan Zhou, Robert Griffin, University of Houston

     Abstract Number: 431
     Working Group: Aerosol Chemistry

Abstract
Two field studies were conducted near downtown San Antonio in May 2017 and April-May 2021. Results from a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) indicated large organic (5.89±3.46 and 7.19±3.94 µg m^-3 in 2017 and 2021, respectively) and sulfate (3.55±2.46 and 5.11±4.80 µg m^-3) contributions to the total non-refractory submicron particulate matter (NR-PM₁). Two-day backward trajectories were clustered into “Oceanic,” “Coastal” and “Continental” scenarios for each campaign. In 2017, increased NR-PM₁ was observed in Oceanic scenarios, driven by sulfate (4.87±2.64 µg m^-3) and ammonium (1.57±0.84 µg m^-3). These sulfate and ammonium concentrations are three times as large as in Continental scenarios (1.66±0.56 and 0.55±0.23 µg m^-3, respectively), with those in Coastal scenarios in the middle (2.66±0.98 and 0.88±0.31 µg m^-3, respectively). Organics were relatively consistent, slightly increasing from 5.74±3.67 µg m^-3 in Continental scenarios to 6.25±3.91 µg m^-3 in Oceanic scenarios. In 2021, sulfate and ammonium also increased from Continental scenarios (2.75±1.91 and 1.08±0.68 µg m^-3) to Oceanic scenarios (8.08±5.70 and 3.08±2.13 µg m^-3), but the organics showed a stronger decrease from 8.45±4.13 µg m^-3 to 6.50±3.45 µg m^-3. Using ISORROPIA-II, we investigated the change in aerosol liquid water content (LWC) and acidity. In both years, LWC decreased from Oceanic scenarios (7.89±6.07 and 13.53±10.44 µg m^-3 in 2017 and 2021, respectively) to Coastal scenarios (3.62±3.14 and 10.46±6.25 µg m^-3) and further to Continental scenarios (1.25±1.01 and 3.34±3.71 µg m^-3), while inorganic aerosol pH indicates that NR-PM₁ became more acidic. Compared to 2017, increased LWC and decreased acidity were observed in all scenarios in 2021. Further analysis will be performed to investigate different sources/formation pathways of NR-PM₁ and how air mass history, meteorological factors, and chemical processing impact its level in San Antonio.