17 Apr 2024
 | 17 Apr 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Nocturnal Atmospheric Synergistic Oxidation Reduces the Formation of Low-volatility Organic Compounds from Biogenic Emissions

Han Zang, Zekun Luo, Chenxi Li, Ziyue Li, Dandan Huang, and Yue Zhao

Abstract. Volatile organic compounds (VOCs) are often subject to synergistic oxidation by different oxidants in the atmosphere. However, the exact synergistic oxidation mechanism of atmospheric VOCs and its role in particle formation remain poorly understood. In particular, the reaction kinetics of the key reactive intermediates, organic peroxy radicals (RO2), during synergistic oxidation is rarely studied. Here, we conducted a combined experimental and kinetic modelling study of the nocturnal synergistic oxidation of α-pinene (the most abundant monoterpene) by O3 and NO3 radicals as well as its influences on the formation of highly oxygenated organic molecules (HOMs) and particles. We find that in the synergistic O3 + NO3 regime, where OH radicals are abundantly formed via decomposition of ozonolysis-derived Criegee intermediates, the production of CxHyOz-HOMs is substantially suppressed compared to that in the O3-only regime, mainly because of the termination of α-pinene RO2 derived from ozonolysis and OH oxidation by those arising from NO3 oxidation. Measurement-model comparisons further reveal that the termination reactions between ozonolysis- and NO3-derived RO2 are on average 10 – 100 times more efficient than those of OH- and NO3-derived RO2. Despite a strong production of organic nitrates in the synergistic oxidation regime, the substantial decrease of CxHyOz-HOM formation leads to a significant reduction in ultralow- and extremely low-volatility organic compounds, which significantly inhibits the formation of new particles. This work provides valuable mechanistic and quantitative insights into the nocturnal synergistic oxidation chemistry of biogenic emissions and will help to better understand the formation of low-volatility organic compounds and particles in the atmosphere.

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Han Zang, Zekun Luo, Chenxi Li, Ziyue Li, Dandan Huang, and Yue Zhao

Status: open (until 29 May 2024)

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  • RC1: 'Comment on egusphere-2024-1131', Anonymous Referee #1, 09 May 2024 reply
  • RC2: 'Comment on egusphere-2024-1131', Anonymous Referee #2, 12 May 2024 reply
  • RC3: 'Comment on egusphere-2024-1131', Anonymous Referee #3, 15 May 2024 reply
Han Zang, Zekun Luo, Chenxi Li, Ziyue Li, Dandan Huang, and Yue Zhao
Han Zang, Zekun Luo, Chenxi Li, Ziyue Li, Dandan Huang, and Yue Zhao


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Short summary
Atmospheric organics are subject to synergistic oxidation by different oxidants, yet the mechanisms of such processes are poorly understood. Here, using direct measurements and kinetic modelling, we probe the nocturnal synergistic oxidation mechanism of α-pinene by O3 and NO3 radicals and in particular the fate of peroxy radical intermediates of different origins, which will deepen our understanding of the monoterpene oxidation chemistry and its contribution to atmospheric particle formation.