Brown Carbon from Photo-Oxidation of Glyoxal and SO2 in Aqueous Aerosol

Author(s)

David O. De Haan, University of San Diego
Lelia N. Hawkins, Harvey Mudd College
Praveen D. Wickremasinghe, University of San Diego
Alyssa D. Andretta, University of San Diego
Juliette R. Dignum, University of San Diego
Audrey C. De Haan, University of San Diego
Hannah G. Welsh, Harvey Mudd College
Elyse A. Pennington, Harvey Mudd College
Tianqu Cui, University of North Carolina at Chapel Hill
Jason D. Surratt, University of North Carolina at Chapel Hill
Mathieu Cazaunau, Laboratoire Inter-Universitaire des Systèmes Atmosphériques
Edouard Pangui, Laboratoire Inter-Universitaire des Systèmes Atmosphériques
Jean-François Doussin, Laboratoire Inter-Universitaire des Systèmes Atmosphériques

Document Type

Article

Publication Date

4-27-2023

Journal Title

ACS Earth and Space Chemistry

Volume Number

2023

DOI

https://doi.org/10.1021/acsearthspacechem.3c00035

Version

Publisher PDF: the final published version of the article, with professional formatting and typesetting

Creative Commons License

This work is licensed under a CC BY License.

Disciplines

Chemistry

Abstract

Aqueous-phase dark reactions during the co-oxidation of glyoxal and S(IV) were recently identified as a potential source of brown carbon (BrC). Here, we explore the effects of sunlight and oxidants on aqueous solutions of glyoxal and S(IV), and on aqueous aerosol exposed to glyoxal and SO₂. We find that BrC is able to form in sunlit, bulk-phase, sulfite-containing solutions, albeit more slowly than in the dark. In more atmospherically relevant chamber experiments where suspended aqueous aerosol particles are exposed to gas-phase glyoxal and SO₂, the formation of detectable amounts of BrC requires an OH radical source and occurs most rapidly after a cloud event. From these observations we infer that this photobrowning is caused by radical-initiated reactions as evaporation concentrates aqueous-phase reactants and aerosol viscosity increases. Positive-mode electrospray ionization mass spectrometric analysis of aerosol-phase products reveals a large number of C_xH_yO_z oligomers that are reduced rather than oxidized (relative to glyoxal), with the degree of reduction increasing in the presence of OH radicals. This again suggests a radical-initiated redox mechanism where photolytically produced aqueous radical species trigger S(IV)–O₂ auto-oxidation chain reactions, and glyoxal-S(IV) redox reactions especially if aerosol-phase O₂ is depleted. This process may contribute to daytime BrC production and aqueous-phase sulfur oxidation in the atmosphere. The BrC produced, however, is about an order of magnitude less light-absorbing than wood smoke BrC at 365 nm.

Notes

Original publication information: 'Brown Carbon from Photo-Oxidation of Glyoxal and SO2 in Aqueous Aerosol', D. O. De Haan, L. N. Hawkins, P. D. Wickremasinghe, A. D. Andretta, J. R. Dignum, A. C. De Haan, et al. ACS Earth and Space Chemistry, 2023. DOI: 10.1021/acsearthspacechem.3c00035

Published open access with Creative Commons Attribution 4.0 International (CC BY 4.0)

Digital USD Citation

De Haan, David O.; Hawkins, Lelia N.; Wickremasinghe, Praveen D.; Andretta, Alyssa D.; Dignum, Juliette R.; De Haan, Audrey C.; Welsh, Hannah G.; Pennington, Elyse A.; Cui, Tianqu; Surratt, Jason D.; Cazaunau, Mathieu; Pangui, Edouard; and Doussin, Jean-François, "Brown Carbon from Photo-Oxidation of Glyoxal and SO2 in Aqueous Aerosol" (2023). Chemistry and Biochemistry: Faculty Scholarship. 44.
https://digital.sandiego.edu/chemistry_facpub/44