Particulate Oxalate-to-Sulfate Ratio as an Aqueous Processing Marker:
Similarity Across Field Campaigns and Limitations
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.