Preprints
https://doi.org/10.5194/egusphere-2024-3419
https://doi.org/10.5194/egusphere-2024-3419
08 Nov 2024
 | 08 Nov 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

HOMs and SOA formation from the oxidation of α- and β-phellandrenes by NO3 radicals

Sergio Harb, Manuela Cirtog, Stéphanie Alage, Christopher Cantrell, Mathieu Cazaunau, Vincent Michoud, Edouard Pangui, Antonin Bergé, Chiara Giorio, Francesco Battaglia, and Bénédicte Picquet-Varrault

Abstract. Nighttime NO3-initiated oxidation of monoterpenes plays a crucial role as source of organic nitrates (ONs) and secondary organic aerosols (SOA), impacting climate, air quality, and human health. Nevertheless, monoterpene reactions with NO3 remain poorly understood. This study provides an in-depth investigation of the NO3-initiated oxidation of α- and β-phellandrenes, through simulation chamber experiments and a combination of various analytical techniques (FTIR, PTR-ToF-MS, ACSM, nitrate-CI-APi-ToF-MS, Orbitrap, SMPS). SOA yields were measured, and oxidation products, including highly oxygenated organic molecules (HOMs), were investigated in gas and aerosol phases. Numerical simulations were also performed to investigate the dominant chemical regimes for RO2 radicals. We found that α- and β-phellandrenes are efficient SOA precursors with yields reaching up to 35 % and 60 %, respectively, with b-phellandrene generating significantly more SOA than α-phellandrene. Both monoterpenes produce large amounts of ONs in gas and aerosol phases with total molar yields of 40–60 %. Similar gas-phase products were detected for α- and β-phellandrenes. In particular, carbonyl nitrates, dicarbonyl nitrates and dicarbonyls were detected as first-generation products. Autooxidation processes were also shown to occur with numerous gas-phase HOM monomers and dimers detected. Chemical mechanisms have been proposed to explain products formation. Since gas-phase products were similar for both monoterpenes, they do not explain the differences in SOA yields. However, some differences in aerosol-phase composition were observed which may explain why β-phellandrene is a more efficient SOA precursor. This study is the first mechanistic investigation of the reactions of α- and β-phellandrenes with NO3 radical.

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Sergio Harb, Manuela Cirtog, Stéphanie Alage, Christopher Cantrell, Mathieu Cazaunau, Vincent Michoud, Edouard Pangui, Antonin Bergé, Chiara Giorio, Francesco Battaglia, and Bénédicte Picquet-Varrault

Status: open (until 22 Dec 2024)

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Sergio Harb, Manuela Cirtog, Stéphanie Alage, Christopher Cantrell, Mathieu Cazaunau, Vincent Michoud, Edouard Pangui, Antonin Bergé, Chiara Giorio, Francesco Battaglia, and Bénédicte Picquet-Varrault
Sergio Harb, Manuela Cirtog, Stéphanie Alage, Christopher Cantrell, Mathieu Cazaunau, Vincent Michoud, Edouard Pangui, Antonin Bergé, Chiara Giorio, Francesco Battaglia, and Bénédicte Picquet-Varrault

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Short summary
We investigated the reactions of α- and β-phellandrenes (from vegetation emissions) with NO3 radicals, a major nighttime oxidant from human activities. Using lab-based simulations, we examined these reactions and measured particle formation and by-products. Our findings reveal that α- and β-phellandrenes are efficient particle sources and enhance our understanding of biogenic-anthropogenic interactions and their contributions to atmospheric changes affecting climate and health.