Particulate Oxalate-to-Sulfate Ratio as an Aqueous Processing Marker: Similarity Across Field Campaigns and Limitations
Miguel Ricardo A. Hilario1, Ewan Crosbie2,3, Paola Angela Bañaga4,5, Grace Betito4,5, Rachel A. Braun6,†, Maria Obiminda Cambaliza4,5, Andrea F. Corral6, Melliza Templonuevo Cruz4,7, Jack E. Dibb8, Genevieve Rose Lorenzo1, Alexander B. MacDonald6, Claire E. Robinson2,3, Michael A. Shook2, James Bernard Simpas4,5, Connor Stahl6, Edward Winstead2,3, Luke D. Ziemba2, and Armin Sorooshian1,6
1 Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ 85721, USA, 2 NASA Langley Research Center, Hampton, VA, USA, 3 Science Systems and Applications, Inc., Hampton, VA, USA, 4Manila Observatory, Quezon City 1108, Philippines, 5Department of Physics, School of Science and Engineering, Ateneo de Manila University, Quezon City 1108, Philippines, 6Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ 85721, USA, 7 Institute of Environmental Science and Meteorology, University of the Philippines, Diliman, Quezon City 1101, Philippines, 8 Earth Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA
Corresponding author: Armin Sorooshian (armin@email.arizona.edu)
Now at: Healthy Urban Environments Initiative, Global Institute of Sustainability and Innovation, Arizona State University, Tempe, AZ, USA
Key Points:
Abstract
Leveraging aerosol data from multiple airborne and surface-based field campaigns encompassing diverse environmental conditions, we calculate statistics of the oxalate-sulfate mass ratio (median: 0.0217; 95% confidence interval: 0.0154 – 0.0296; R = 0.76; N = 2948). Ground-based measurements of the oxalate-sulfate ratio fall within our 95% confidence interval, suggesting the range is robust within the mixed layer for the submicrometer particle size range. We demonstrate that dust and biomass burning emissions can separately bias this ratio towards higher values by at least one order of magnitude. In the absence of these confounding factors, the 95% confidence interval of the ratio may be used to estimate the relative extent of aqueous processing by comparing inferred oxalate concentrations between air masses, with the assumption that sulfate primarily originates from aqueous processing.