Oxygenated products formed from OH-initiated reactions of trimethylbenzene: autoxidation and accretion
<p>Gas-phase oxidation pathways and products of anthropogenic volatile organic compounds (VOCs), mainly aromatics, are the subject of intensive research, with attention paid to their contributions to secondary organic aerosol (SOA) formation and potentially new particle formation (NPF) in the...
| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/20/9563/2020/acp-20-9563-2020.pdf |
| Summary: | <p>Gas-phase oxidation pathways and products of anthropogenic
volatile organic compounds (VOCs), mainly aromatics, are the subject of
intensive research, with attention paid to their contributions to secondary
organic aerosol (SOA) formation and potentially new particle formation
(NPF) in the urban atmosphere. In this study, a series of OH-initiated
oxidation experiments of trimethylbenzene (TMB, <span class="inline-formula">C<sub>9</sub>H<sub>12</sub></span>) including
1,2,4-TMB, 1,3,5-TMB, 1,2,3-TMB, and 1,2,4-(methyl-D3)-TMBs
(<span class="inline-formula">C<sub>9</sub>H<sub>9</sub>D<sub>3</sub></span>) were investigated in an oxidation flow reactor
(OFR) in the absence and presence of <span class="inline-formula">NO<sub><i>x</i></sub></span>. Products were measured using
a suite of state-of-the-art instruments, i.e. a nitrate-based chemical
ionization–atmospheric pressure interface time-of-flight mass spectrometer
(nitrate CI-APi-TOF), an iodide-adduct chemical ionization time-of-flight
mass spectrometer (iodide CI-TOF) equipped with a Filter Inlet for Gases and
AEROsols (FIGAERO), and a Vocus proton-transfer-reaction mass spectrometer
(Vocus PTR). A large number of <span class="inline-formula">C<sub>9</sub></span> products with 1–11 oxygen atoms and <span class="inline-formula">C<sub>18</sub></span>
products presumably formed from dimerization of <span class="inline-formula">C<sub>9</sub></span> peroxy radicals were
observed, hinting at the extensive existence of autoxidation and accretion
reaction pathways in the OH-initiated oxidation reactions of TMBs. Oxidation
products of 1,2,4-(methyl-D3)-TMBs with deuterium atoms in different methyl
substituents were then used as a molecular basis to propose potential
autoxidation reaction pathways. Accretion of <span class="inline-formula">C<sub>9</sub></span> peroxy radicals is the most
significant for aromatics with meta-substituents and the least for aromatics
with ortho-substituents if the number and size of substituted groups are
identical. The presence of <span class="inline-formula">NO<sub><i>x</i></sub></span> would suppress the formation of highly oxygenated molecules (HOMs) of <span class="inline-formula">C<sub>18</sub></span> and enhance the formation of
organonitrates and even dinitrate organic compounds. Our results show that
the oxidation products of TMB are much more diverse and could be more
oxygenated than the current mechanisms predict.</p> |
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| ISSN: | 1680-7316 1680-7324 |