Rate coefficients for reactions of OH with aromatic and aliphatic volatile organic compounds determined by the multivariate relative rate technique
<p>The multivariate relative rate method was applied to a range of volatile organic compound (VOC) reactions with OH. This previously published method (Shaw et al., 2018) was improved to increase the sensitivity towards more slowly reacting VOCs, broadening the range of compounds which can be...
| 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/20/9725/2020/acp-20-9725-2020.pdf |
| Summary: | <p>The multivariate relative rate method was applied to a
range of volatile organic compound (VOC) reactions with OH. This previously
published method (Shaw et al., 2018) was improved to increase the
sensitivity towards more slowly reacting VOCs, broadening the range of compounds
which can be examined. A total of 35 room temperature relative rate
coefficients were determined, eight of which have not previously been
reported. Five of the new reaction rate coefficients were for large alkyl
substituted mono-aromatic species recently identified in urban air masses,
likely with large ozone production potentials. The new results (with
<span class="inline-formula"><i>k</i><sub>OH</sub></span> (296 K) values in units of 10<span class="inline-formula"><sup>−12</sup></span> cm<span class="inline-formula"><sup>3</sup></span> molec.<span class="inline-formula"><sup>−1</sup></span> s<span class="inline-formula"><sup>−1</sup></span>) were <span class="inline-formula"><i>n</i></span>-butylbenzene, 11 (<span class="inline-formula">±4</span>); <span class="inline-formula"><i>n</i></span>-pentylbenzene, 7 (<span class="inline-formula">±2</span>); 1,2-diethylbenzene, 14 (<span class="inline-formula">±4</span>); 1,3-diethylbenzene, 22 (<span class="inline-formula">±4</span>);
and 1,4-diethylbenzene, 16 (<span class="inline-formula">±4</span>). Interestingly, whilst results for
smaller VOCs agreed well with available structure–activity relationship (SAR)
calculations, the larger alkyl benzenes were found to be less reactive than
the SAR prediction, indicating that our understanding of the oxidation
chemistry of these compounds is still limited. <span class="inline-formula"><i>k</i><sub>OH</sub></span> (296 K) rate
coefficients (in units of 10<span class="inline-formula"><sup>−12</sup></span> cm<span class="inline-formula"><sup>3</sup></span> molec.<span class="inline-formula"><sup>−1</sup></span> s<span class="inline-formula"><sup>−1</sup></span>) for
reactions of three large alkanes with OH were also determined for the first
time: 2-methylheptane, 9.1 (<span class="inline-formula">±0.3</span>); 2-methylnonane, 11.0 (<span class="inline-formula">±0.3</span>);
and ethylcyclohexane, 14.4 (<span class="inline-formula">±0.3</span>), all in reasonable agreement with
SAR predictions. Rate coefficients for the 27 previously studied
OH <span class="inline-formula">+</span> VOC reactions agreed well with available literature values, lending
confidence to the application of this method for the rapid and efficient
simultaneous study of gas-phase reaction kinetics.</p> |
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| ISSN: | 1680-7316 1680-7324 |