Preprints
https://doi.org/10.5194/acp-2022-139
https://doi.org/10.5194/acp-2022-139
 
22 Feb 2022
22 Feb 2022
Status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Elucidating the critical oligomeric steps in secondary organic aerosol and brown carbon formation

Yuemeng Ji1,2, Qiuju Shi1,2, Xiaohui Ma1,2, Lei Gao1,2, Jiaxin Wang1,2, Yixin Li3, Yanpeng Gao1,2, Guiying Li1,2, Renyi Zhang3, and Taicheng An1,2 Yuemeng Ji et al.
  • 1Guangdong-Hong Kong-Macao Joint Laboratory for Contaminants Exposure and Health, Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, Institute Environmental Health and Pollution control, Guangdong University of Technology, Guangzhou 510006, China
  • 2Guangzhou Key Laboratory of Environmental Catalysis and Pollution Control, Key Laboratory of City Cluster Environmental Safety and Green development (Department of Education), School of Environmental Science and Engineering, Guangdong University of Technology, Guangzhou 510006, China
  • 3Department of Atmospheric Sciences, Texas A&M University, College Station, Texas 77843, United States

Abstract. Small α-dicarbonyls represent the major precursors for secondary organic aerosol (SOA) and brown carbon (BrC) in the atmosphere, but the chemical mechanisms leading to their formation remain unclear. Here we elucidate the fundamental kinetics and mechanisms for aqueous-phase oligomerization of glyoxal (GL) using quantum chemical and kinetic rate calculations. Our results identify several essential isomeric processes for GL, including protonation to yield diol/tetrol and carbenium ions, nucleophilic addition of carbenium ions to diol/tetrol as well as to free methylamine/ammonia (MA/AM), and deprotonation to propagate oligomers and N-heterocycles. Both protonation and nucleophilic addition occur without activation barriers and are dominantly driven by electrostatic attraction. Deprotonation proceeds readily via water molecules in the absence of MA/AM but corresponds to the rate-limiting step for N-containing cationic intermediates to yield N-heterocycles. On the other hand, the latter occurs readily via a catalytic process by acidic anions (eg., SO42-). A carbenium ion-mediated reaction rate of GL is 4.62 × 10-3 s-1 under atmospheric conditions, in good agreement with the experimental data. Our results provide essential mechanistic and kinetic data for accurate assessment of the role of small α-dicarbonyls in SOA and BrC formation.

Yuemeng Ji et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-139', Anonymous Referee #1, 04 Mar 2022
    • AC1: 'Reply on RC1', Taicheng An, 26 Mar 2022
  • RC2: 'Comment on acp-2022-139', Deming Xia, 05 Mar 2022
    • AC3: 'Reply on RC2', Taicheng An, 26 Mar 2022
  • RC3: 'Comment on acp-2022-139', Anonymous Referee #3, 07 Mar 2022
    • AC2: 'Reply on RC3', Taicheng An, 26 Mar 2022
  • CC1: 'Comment on acp-2022-139', Jan-Hendrik Peters, 06 Apr 2022
    • AC4: 'Reply on CC1', Taicheng An, 15 Apr 2022

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-139', Anonymous Referee #1, 04 Mar 2022
    • AC1: 'Reply on RC1', Taicheng An, 26 Mar 2022
  • RC2: 'Comment on acp-2022-139', Deming Xia, 05 Mar 2022
    • AC3: 'Reply on RC2', Taicheng An, 26 Mar 2022
  • RC3: 'Comment on acp-2022-139', Anonymous Referee #3, 07 Mar 2022
    • AC2: 'Reply on RC3', Taicheng An, 26 Mar 2022
  • CC1: 'Comment on acp-2022-139', Jan-Hendrik Peters, 06 Apr 2022
    • AC4: 'Reply on CC1', Taicheng An, 15 Apr 2022

Yuemeng Ji et al.

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Short summary
Formation mechanism of secondary organic aerosol (SOA) and brown carbon (BrC) from small α-carbonyls are still unclear. Thus, the mechanisms and kinetics of aqueous-phase reaction of glyoxal were investigated using quantum chemical and kinetic rate calculations. Several essential isomeric processes were identified, including protonation to yield diol/tetrol and carbenium ions, nucleophilic addition of carbenium ions to diol/tetrol and free methylamine/ammonia.
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