Photochemical Reactions of Glyoxal during Particulate Ammonium Nitrate Photolysis: Brown Carbon Formation, Enhanced Glyoxal Decay, and Organic Phase Formation

Ruifeng Zhang, Masao Gen, Zhancong Liang, Yong Jie Li, Chak Keung Chan

Research output: Contribution to journalArticlepeer-review

26 Citations (Scopus)

Abstract

Glyoxal is an important precursor of aqueous secondary organic aerosol (aqSOA). Its photooxidation to form organic acids and oligomers and reactions with reduced nitrogen compounds to form brown carbon (BrC) have been extensively investigated separately, although these two types of reactions can occur simultaneously during the daytime. Here, we examine the reactions of glyoxal during photooxidation and BrC formation in premixed NH4NO3 + Glyoxal droplets. We find that nitrate photolysis and photosensitization can enhance the decay rates of glyoxal by a factor of ∼5 and ∼6 compared to those under dark, respectively. A significantly enhanced glyoxal decay rate by a factor of ∼12 was observed in the presence of both nitrate photolysis and photosensitization. Furthermore, a new organic phase was formed in irradiated NH4NO3 + Glyoxal droplets, which had no noticeable degradation under prolonged photooxidation. It was attributed to the imidazole oxidation mediated by nitrate photolysis and/or photosensitization. The persistent organic phase suggests the potential to contribute to SOA formation in ambient fine particles. This study highlights that glyoxal photooxidation mediated by nitrate photolysis and photosensitization can significantly enhance the atmospheric sink of glyoxal, which may partially narrow the gap between model predictions and field measurements of ambient glyoxal concentrations.

Original languageEnglish
Pages (from-to)1605-1614
Number of pages10
JournalEnvironmental Science & Technology
Volume56
Issue number3
DOIs
Publication statusPublished - 2022 Feb 1

Keywords

  • brown carbon
  • glyoxal
  • nitrate photolysis
  • photosensitization
  • secondary organic aerosol

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