Highly oxygenated organic nitrates formed from NO3 radical initiated oxidation of β-pinene
Abstract
NO3 radical oxidation of biogenic volatile organic compounds (BVOC) is recognized as a significant source of secondary organic aerosols (SOA) and organic nitrate (ON) at night. However, little is known about the highly oxygenated organic molecules formed in the oxidation of this BVOC by NO3. In this study, the reactions of NO3 with β-pinene were performed in SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction) chamber to investigate the highly oxygenated ON using a chemical ionization mass spectrometerwith 15NO3- as the reagent ion. Substantial gas-phase highly oxygenated ON were observed, including monomers (73%) and dimers (27%). Among the monomers, carbonylmononitrates (C10H15NO7-10) were identified as the dominant species. The corresponding hydroxynitrates (C10H17NO8-11) were observed with much lower signals. The concentration of both C10H15NO7-10 and C10H17NO8-11 showed a time profile typical of first generation products, increasing fast with each β-pinene addition and decreasing afterwards. Their corresponding nitrooxyperoxy radicals (NO3-RO2) were also observed; they peaked earlier and decayed faster than corresponding closedshell termination products. Tentative mechanisms for the formation of these ON are discussed, including the self-reaction of NO3-RO2 radicals via the Bennett and Summers mechanism, formation of hydroxycarbonyl via twofold isomerization of NO3-RO2, and the reaction of NO3-RO2 with O2 to form carbonylnitrate. Species with 7 and 9 C-atoms were other important products. They are likely formed by the decomposition of C10H16NOx nitrooxyalkoxy. Second generation dinitrate products, C10H14-16N2O6+x, were also observed, which probably result from the isomerization of hydroxycarbonyls followed by the equilibrium with a substituted dihydrofuran formed by dehydration. Five families of dimers were identified, mainly formed via RO2 + RO2 reaction channel. For the first time to our knowledge, the total molar yield of highly oxygenated ON from NO3 and β-pinene reaction was determined. Their volatility could be low enough to form and contribute to SOA and the converted average mass yield of 11.4% suggests the potential significance.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMA238...06S
- Keywords:
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- 0317 Chemical kinetic and photochemical properties;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0340 Middle atmosphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0394 Instruments and techniques;
- ATMOSPHERIC COMPOSITION AND STRUCTURE