Estimates for SOA production by glyoxal and methylglyoxal have ranged as high as 11 TgC/year.  However, these estimates are very sensitive to the uptake coefficient of methylglyoxal into aqueous aerosol and cloud surfaces, and on whether this uptake is reversible or irreversible.  Since the uptake coefficient for methylglyoxal into aqueous surfaces has never been measured, modelers typically use the uptake coefficient for glyoxal as an approximation.   Our recent efforts to extract uptake coefficients from cloud chamber experiments suggest that methylglyoxal’s aqueous uptake coefficient is larger than that of glyoxal by as much as a factor of 2.  Wet uptake is not the only way that dicarbonyl compounds can influence aerosol properties, however.  Experiments with dry ammonium salt aerosol also show that dicarbonyl exposure can decrease the single-scattering albedo measured at 405 and 450 nm, but without causing a detectable increase in total aerosol mass or in the organic mass fraction.  This “surface browning,” while operating via an unknown mechanism, appears to be fast, reversible, and directly proportional to the dicarbonyl concentration.  We use this proportionality to estimate radiative forcing by surface browning, and find that it is likely responsible for a few percent of the total radiative forcing causing by secondary brown carbon.

Aqueous and dry aerosol processing of dicarbonyls:  Uptake coefficients, SOA production, and radiative forcing

254th National Meeting (2017)

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