Brown Carbon Production by Aqueous-Phase Interactions of Glyoxal and SO₂

Abstract

Oxalic acid and sulfate salts are major components of aerosol particles. Here, we explore the potential for their respective precursor species, glyoxal and SO 2 , to form atmospheric brown carbon via aqueousphase reactions in a series of bulk aqueous and flow chamber aerosol experiments. In bulk aqueous solutions, UV-and visible-light-absorbing products are observed at pH 3-4 and 5-6, respectively, with small but detectable yields of hydroxyquinone and polyketone products formed, especially at pH 6. Hydroxymethanesulfonate (HMS), C 2 , and C 3 sulfonates are major products detected by electrospray ionization mass spectrometry (ESI-MS) at pH 5. Past studies have assumed that the reaction of formaldehyde and sulfite was the only atmospheric source of HMS. In flow chamber experiments involving sulfite aerosol and gas-phase glyoxal with only 1 min residence times, significant aerosol growth is observed. Rapid brown carbon formation is seen with aqueous aerosol particles at >80% relative humidity (RH). Brown carbon formation slows at 50-60% RH and when the aerosol particles are acidified with sulfuric acid but stops entirely only under dry conditions. This chemistry may therefore contribute to brown carbon production in cloud-processed pollution plumes as oxidizing volatile organic compounds (VOCs) interact with SO 2 and water.

Aging of Atmospheric Brown Carbon Aerosol

“…209 These results indicate that evaporation-driven BrC formation can be important in organic mixtures other than the imine BrC system. BrC formation through aqueous reactions of glyoxal and sulfite leading to organosulfates compounds has also been observed recently 210 and may indicate that these types of reactions can be important even without evaporation. While many laboratory studies have identified the formation of BrC upon droplet or bulk solution evaporation, confirmation of this process has yet to be observed in ambient cloud droplets and aerosol particles.…”

“…These results indicate that evaporation-driven BrC formation can be important in organic mixtures other than the imine BrC system. BrC formation through aqueous reactions of glyoxal and sulfite leading to organosulfate compounds has also been observed recently and may indicate that these types of reactions can be important even without evaporation.…”

Global modeling of heterogeneous hydroxymethanesulfonate chemistry

“…Recently, the quantum chemical calculations by Chen and Zhao (2020) suggested that hydroxymethyl sulfite (HMSi), an isomer of HMS, might also be produced by an aqueous reaction of HCHO and SO 2 . The laboratory experiments of De Haan et al (2020) demonstrated that HMS was one of the major products from the aqueous processing of glyoxal monobisulfite (CH(OH) 2 CH(OH)SO −…”

Multiphase Oxidation of Sulfur Dioxide in Aerosol Particles: Implications for Sulfate Formation in Polluted Environments

“…69 Other aldehydes can also react with SO 2 to produce other hydroxyalkylsulfonate species that may be atmospherically important. For example, De Haan et al 129 observed the formation of HMS, C 2 , and C 3 sulfonates from the reaction between S(IV) and glyoxal in bulk aqueous solutions and aerosol particles at atmospherically relevant pH values. 4.7.…”