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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 16 Mar 2020

Submitted as: research article | 16 Mar 2020

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This preprint is currently under review for the journal ACP.

Glyoxal's impact on dry ammonium salts: fast and reversible surface aerosol browning

David O. De Haan1, Lelia N. Hawkins2, Kevin Jansen3, Hannah G. Welsh2, Raunak Pednekar2,, Alexia de Loera1, Natalie G. Jimenez1, Margaret A. Tolbert3, Mathieu Cazaunau4, Aline Gratien4, Antonin Bergé4, Edouard Pangui4, Paola Formenti4, and Jean-François Doussin4 David O. De Haan et al.
  • 1Department of Chemistry and Biochemistry, University of San Diego, 5998 Alcala Park, San Diego CA 92110 USA
  • 2Department of Chemistry, Harvey Mudd College, 301 Platt Blvd, Claremont CA 91711 USA
  • 3Department of Chemistry / Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder CO 80309 USA
  • 4Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR7583, CNRS, Université Paris-Est-Créteil (UPEC) et Université de Paris, Institut Pierre Simon Laplace (IPSL), Créteil, France
  • deceased

Abstract. Alpha-dicarbonyl compounds are believed to form brown carbon in the atmosphere via reactions with ammonium sulfate (AS) in cloud droplets and aqueous aerosol particles. In this work, brown carbon formation in AS and other aerosol particles was quantified as a function of relative humidity (RH) during exposure to gas-phase glyoxal (GX) in chamber experiments. Under dry conditions (RH < 5 %), solid AS, AS/glycine, and methylammonium sulfate aerosol particles brown within minutes upon exposure to GX, while sodium sulfate particles do not. When GX concentrations decline, browning goes away, demonstrating that this dry browning process is reversible. Declines in aerosol albedo are found to be a function of [GX]2, and are consistent between AS and AS/glycine aerosol. Dry methylammonium sulfate aerosol browns 4x more than dry AS aerosol, but deliquesced AS aerosol browns much less than dry AS aerosol. Optical measurements at 405, 450, and 530 nm provide an estimated Ångstrom absorbance coefficient of −16 ± 4. This coefficient and the empirical relationship between GX and albedo are used to estimate an upper limit to global radiative forcing by brown carbon formed by 70 ppt GX reacting with AS (+7.6 × 10−5 W/m2). This quantity is < 1 % of the total radiative forcing by secondary brown carbon, but occurs almost entirely in the ultraviolet range.

David O. De Haan et al.

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Status: open (until 11 May 2020)
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David O. De Haan et al.

David O. De Haan et al.


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Short summary
When exposed to glyoxal in chamber experiments, dry ammonium or methylammonium sulfate particles turn brown immediately and reversibly without increasing in size. Much less browning was observed on wet aerosol particles, and no browning was observed with sodium sulfate aerosol. While estimated dry aerosol light absorption caused by background glyoxal (70 ppt) is insignificant compared to that of secondary brown carbon overall, in polluted regions this process could be a source of brown carbon.
When exposed to glyoxal in chamber experiments, dry ammonium or methylammonium sulfate particles...