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Characterization of Urban Aerosol Sulfate Sources in Summer Using High-Resolution Aerosol Mass Spectrometry
FANGZHOU GUO, Alexander Bui, Benjamin Schulze, Henry Wallace, Matthew H. Erickson, Sergio Alvarez, Sujan Shrestha, Subin Yoon, Rebecca J. Sheesley, Sascha Usenko, James Flynn, Robert Griffin, Rice University
Abstract Number: 164
Working Group: Urban Aerosols
Abstract
Currently the seventh most populous city in the United States and the second-most populous city in Texas, San Antonio has been one of the most rapidly growing large cities in the country over the past decade. To understand the sources of particulate matter that contributes to the degradation of San Antonio’s air quality, a mobile air quality laboratory was deployed and operated in the southeast (Traveler’s World RV Park) and northwest (University of Texas at San Antonio campus) of downtown San Antonio in May 2017. Chemical characterization of non-refractory submicron PM (NR-PM1) was conducted using an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Additional measurements included meteorological parameters and trace gas mixing ratios. Results from HR-ToF-AMS indicate large organic (2.96±1.74 µg/m3, 54% of the total on average) and sulfate (1.78±1.23 µg/m3, 33%) contributions at the Traveler’s World site. By further categorizing the campaign into Oceanic, Near Inland, and Continental periods based on backward trajectory cluster analysis, it was observed that high sulfate concentrations were related primarily to air masses coming from the Gulf of Mexico. Utilizing empirical parameterizations from previous laboratory experiments and the ISORROPIA-II model, the contributions of methanesulfonic acid (MSA) and of organosulfates (conservative lower-bound estimate, OSmin) to the total sulfate signal were estimated, as were aerosol liquid water content (LWC) and inorganic aerosol pH values. The biogenic portion of the sulfate was largely influenced by the meteorological conditions, as inferred from a positive correlation between MSA concentration and LWC. However, no significant trends of OSmin with LWC or inorganic aerosol pH were observed. These results reveal the relative contributions of biogenic marine sources and regional anthropogenic activities to urban sulfate loadings.