# The role of radical chemistry in the product formation from nitrate radical initiated gas-phase oxidation of isoprene

Philip T. M. Carlsson, Luc Vereecken, Anna Novelli, François Bernard, Birger

Bohn, Steven S. Brown, Changmin Cho, John Crowley, Andreas

Hofzumahaus, Wahid Mellouki, et al.

► To cite this version:

Philip T. M. Carlsson, Luc Vereecken, Anna Novelli, François Bernard, Birger Bohn, et al. The role of radical chemistry in the product formation from nitrate radical initiated gas-phase oxidation of isoprene. vEGU21, 2021, Online, France. 10.5194/egusphere-egu21-7338. insu-03559374

HAL Id: insu-03559374

https://insu.hal.science/insu-03559374

Submitted on 7 Feb 2022

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

# The role of radical chemistry in the product formation from nitrate radical initiated gas-phase oxidation of isoprene

Philip T. M. Carlsson<fnref n="1" />, Luc Vereecken<fnref n="1" />, Anna Novelli<fnref n="1" />, François Bernard<fnref n="2" />,<fnref n="6" />, Birger Bohn<fnref n="1" />, Steven S. Brown<fnref n="3" />,<fnref n="5" />, Changmin Cho<fnref n="1" />, John Crowley<fnref n="4" />, Andreas Hofzumahaus<fnref n="1" />, Abdelwahid Mellouki<fnref n="2" />, David Reimer<fnref n="1" />, Franz Rohrer<fnref n="1" />, Justin Shenolikar<fnref n="4" />, Ralf Tillmann<fnref n="1" />, Li Zhou<fnref n="2" />,<fnref n="7" />, Astrid Kiendler-Scharr<fnref n="1" />, Andreas Wahner<fnref n="1" />, and Hendrik Fuchs<fnref n="1" />

Experiments at atmospherically relevant conditions were performed in the simulation chamber SAPHIR, investigating the reaction of isoprene with NO₃ and its subsequent oxidation. Due to the production of NO₃ from the reaction of NO₂ with O₃ as well as the formation of OH in subsequent reactions, the reactions of isoprene with O₃ and OH were estimated to contribute up to 15% of the total isoprene consumption each in these experiments. The ratio of RO₂ to HO₂ concentrations was varied by changing the reactant concentrations, which modifies the product distribution from bimolecular reactions of the nitrated RO₂. The reaction with HO₂ or NO₃ was found to be the main bimolecular loss process for the RO₂ radicals under all conditions examined.

Yields of the first-generation isoprene oxygenated nitrates as well as the sum of methyl vinyl ketone (MVK) and methacrolein (MACR) were determined by high resolution proton mass spectrometry using the Vocus PTR-TOF. The experimental time series of these products are compared to model calculations based on the MCM v3.3.1,<fnref n="1" /> the isoprene mechanism as published by Wennberg *et al.*<fnref n="2" /> and the newly developed FZJ-NO₃-isoprene mechanism,<fnref n="3" /> which incorporates theory-based rate coefficients for a wide range of reactions.

Among other changes, the FZJ-NO₃-isoprene mechanism contains a novel fast oxidation route through the epoxidation of alkoxy radicals, originating from the formation of nitrated peroxy radicals. This inhibits the formation of MVK and MACR from the NO₃-initiated oxidation of isoprene to practically zero, which agrees with the observations from chamber experiments. In addition, the FZJ-NO₃-isoprene mechanism increases the level of agreement for the main first-generation oxygenated nitrates.

<footnote n="1">¹Institute for Energy and Climate Research, Forschungszentrum Jülich GmbH, Jülich, Germany</footnote>

<footnote n="2">²Institut de Combustion, Aérothermique, Réactivité et Environnement (ICARE), CNRS (UPR 3021)/OSUC, Orléans, France</footnote>

<footnote n="3">³NOAA Chemical Sciences Laboratory, Boulder, USA</footnote>

<footnote n="4">⁴Atmospheric Chemistry Department, Max-Planck-Institut für Chemie, Mainz, Germany</footnote>

<footnote n="5">⁵Department of Chemistry, University of Colorado Boulder, Boulder, USA</footnote>

<footnote n="6">⁶now at: Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Université d'Orléans, Orléans, France</footnote>

<footnote n="7">⁷now at: College of Architecture and Environment, Sichuan University, Chengdu, China.</footnote>
<footnote n="1">¹ M. E. Jenkin, J. C. Young and A. R. Rickard, The MCM v3.3.1 degradation scheme for isoprene, *Atmospheric Chem. Phys.*, 2015, **15**, 11433–11459.</footnote>

<footnote n="2">² P. O. Wennberg *et al.*, Gas-Phase Reactions of Isoprene and Its Major Oxidation Products, *Chem. Rev.*, 2018, **118**, 3337–3390.</footnote>

<footnote n="3">³ L. Vereecken *et al.*, Theoretical and experimental study of peroxy and alkoxy radicals in the NO₃-initiated oxidation of isoprene, *Phys. Chem. Chem. Phys.*, submitted.</footnote>