Preprints
https://doi.org/10.5194/acp-2021-396
https://doi.org/10.5194/acp-2021-396

  17 May 2021

17 May 2021

Review status: a revised version of this preprint was accepted for the journal ACP.

Aqueous SOA formation from the photo-oxidation of vanillin: Direct photosensitized reactions and nitrate-mediated reactions

Beatrix Rosette Go Mabato1, Yan Lyu1, Yan Ji1, Dan Dan Huang2, Xue Li3, Theodora Nah1, Chun Ho Lam1, and Chak K. Chan1 Beatrix Rosette Go Mabato et al.
  • 1School of Energy and Environment, City University of Hong Kong, Hong Kong, China
  • 2Shanghai Academy of Environmental Sciences, Shanghai 200233, China
  • 3Institute of Mass Spectrometry and Atmospheric Environment, Jinan University No. 601 Huangpu Avenue West, Guangzhou 510632, China

Abstract. Vanillin (VL), a phenolic aromatic carbonyl abundant in biomass burning emissions, forms triplet excited states (3VL*) under simulated sunlight leading to aqueous secondary organic aerosol (aqSOA) formation. This direct photosensitized oxidation of VL was compared with nitrate-mediated VL photo-oxidation under atmospherically relevant cloud and fog conditions, through examining the VL decay kinetics, product compositions, and light absorbance changes. The majority of the most abundant products from both VL photo-oxidation pathways were potential Brown carbon (BrC) chromophores. In addition, both pathways generated oligomers, functionalized monomers, and oxygenated ring-opening products, but nitrate promoted functionalization and nitration, which can be ascribed to its photolysis products (OH, NO2, and N(III), NO2- or HONO). Moreover, a potential imidazole derivative observed from nitrate-mediated VL photo-oxidation suggested that ammonium may be involved in the reactions. The effects of secondary oxidants from 3VL*, pH, the presence of volatile organic compounds (VOCs) and inorganic anions, and reactants concentration and molar ratios on VL photo-oxidation were also explored. Our findings show that the secondary oxidants (1O2, O2•-/HO2, OH) from the reactions of 3VL* and O2 play an essential role in VL photo-oxidation. Enhanced oligomer formation was noted at pH < 4 and in the presence of VOCs and inorganic anions, probably due to additional generation of radicals (HO2 and CO3•-). Also, functionalization was dominant at low VL concentration, whereas oligomerization was favored at high VL concentration. Furthermore, guaiacol oxidation by photosensitized reactions of VL was observed to be more efficient relative to nitrate-mediated photo-oxidation. Lastly, potential VL photo-oxidation pathways under different reaction conditions were proposed. This study indicates that the direct photosensitized oxidation of VL, which nitrate photolysis products can further enhance, may be an important aqSOA source in areas influenced by biomass burning emissions.

Beatrix Rosette Go Mabato et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-396', Anonymous Referee #1, 05 Jun 2021
    • AC1: 'Reply on RC1', Beatrix Rosette Go Mabato, 02 Sep 2021
  • RC2: 'Referee comment on acp-2021-396', Anonymous Referee #2, 20 Jun 2021
    • AC2: 'Reply on RC2', Beatrix Rosette Go Mabato, 02 Sep 2021
  • RC3: 'Comment on acp-2021-396', Anonymous Referee #3, 22 Jun 2021
    • AC3: 'Reply on RC3', Beatrix Rosette Go Mabato, 02 Sep 2021

Beatrix Rosette Go Mabato et al.

Beatrix Rosette Go Mabato et al.

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Short summary
Biomass burning (BB) is a global phenomenon that releases large quantities of pollutants such as phenols and aromatic carbonyls into the atmosphere. These compounds can form secondary organic aerosols (SOA) which play an important role in the Earth’s energy budget. In this work, we demonstrated that the direct irradiation of vanillin (VL) could generate aqueous SOA (aqSOA) such as oligomers. In the presence of nitrate, VL photo-oxidation can also form nitrated compounds.
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