Temperature-dependent aqueous OH kinetics of C<sub>2</sub>–C<sub>10</sub> linear and terpenoid alcohols and diols: new rate coefficients, structure–activity relationship, and atmospheric lifetimes
<p>Aliphatic alcohols (AAs), including terpenoic alcohols (TAs), are ubiquitous in the atmosphere due to their widespread emissions from natural and anthropogenic sources. Hydroxyl radical (OH) is the most important atmospheric oxidant in both aqueous and gas phases. Consequently, the aqueous...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2024-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/24/663/2024/acp-24-663-2024.pdf |
| Summary: | <p>Aliphatic alcohols (AAs), including terpenoic alcohols (TAs), are ubiquitous in the atmosphere due to their widespread emissions from natural and anthropogenic sources. Hydroxyl radical (OH) is the most important atmospheric oxidant in both aqueous and gas phases. Consequently, the aqueous oxidation of the TAs by the OH inside clouds and fogs is a potential source of aqueous secondary organic aerosols (<span class="inline-formula"><sub>aq</sub></span>SOAs). However, the kinetic data, necessary for estimating the timescales of such reactions, remain limited. Here, bimolecular rate coefficients (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>k</mi><mrow class="chem"><msub><mi mathvariant="normal">OH</mi><mi mathvariant="normal">aq</mi></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="9f9f16e16217a8d294acd471a22b5999"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-663-2024-ie00001.svg" width="27pt" height="16pt" src="acp-24-663-2024-ie00001.png"/></svg:svg></span></span>) for the aqueous oxidation of 29 C<span class="inline-formula"><sub>2</sub></span>–C<span class="inline-formula"><sub>10</sub></span> AAs by hydroxyl radicals (OH) were measured with the relative rate technique in the temperature range 278–328 K. The values of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>k</mi><mrow class="chem"><msub><mi mathvariant="normal">OH</mi><mi mathvariant="normal">aq</mi></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="05d730519381fbb0231f432727f62899"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-663-2024-ie00002.svg" width="27pt" height="16pt" src="acp-24-663-2024-ie00002.png"/></svg:svg></span></span> for the 15 AAs studied in this work were measured for the first time after validating the experimental approach. The <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>k</mi><mrow class="chem"><msub><mi mathvariant="normal">OH</mi><mi mathvariant="normal">aq</mi></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="3f1d1957d331842f50e14b71260018d9"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-663-2024-ie00003.svg" width="27pt" height="16pt" src="acp-24-663-2024-ie00003.png"/></svg:svg></span></span> values measured for the C<span class="inline-formula"><sub>2</sub></span>–C<span class="inline-formula"><sub>10</sub></span> AAs at 298 K ranged from 1.80 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>9</sup></span> to 6.5 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>9</sup></span> M<span class="inline-formula"><sup>−1</sup></span> s<span class="inline-formula"><sup>−1</sup></span>. The values of activation parameters, activation energy (7–17 kJ mol<span class="inline-formula"><sup>−1</sup></span>), and average Gibbs free energy of activation (18 <span class="inline-formula">±</span> 2 kJ mol<span class="inline-formula"><sup>−1</sup></span>) strongly indicated the predominance of the H-atom abstraction mechanism. The estimated rates of the complete diffusion-limited reactions revealed up to 44 % diffusion contribution for the C<span class="inline-formula"><sub>8</sub></span>–C<span class="inline-formula"><sub>10</sub></span> AAs.</p>
<p>The data acquired in this work and the values of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M22" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>k</mi><mrow class="chem"><msub><mi mathvariant="normal">OH</mi><mi mathvariant="normal">aq</mi></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="e0e5a12a35f43b69f1ebe53dce74ec81"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-663-2024-ie00004.svg" width="27pt" height="16pt" src="acp-24-663-2024-ie00004.png"/></svg:svg></span></span> for AAs, carboxylic acids, and carboxylate ions available in the literature were used to develop a modified structure–activity relationship (SAR). The SAR optimized in this work estimated the temperature-dependent <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>k</mi><mrow class="chem"><msub><mi mathvariant="normal">OH</mi><mi mathvariant="normal">aq</mi></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="bd899baab315c573475882c72613e1ab"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-663-2024-ie00005.svg" width="27pt" height="16pt" src="acp-24-663-2024-ie00005.png"/></svg:svg></span></span> for all compounds under investigation with much higher accuracy compared to the previous models. In the new model, an additional neighboring parameter was introduced (<span class="inline-formula"><i>F</i>≥</span> (CH<span class="inline-formula"><sub>2</sub></span>)<span class="inline-formula"><sub>6</sub></span>), using the <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M27" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>k</mi><mrow class="chem"><msub><mi mathvariant="normal">OH</mi><mi mathvariant="normal">aq</mi></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="928c9bc541cb653a5d032bef990810c4"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-663-2024-ie00006.svg" width="27pt" height="16pt" src="acp-24-663-2024-ie00006.png"/></svg:svg></span></span> values for the homolog (C<span class="inline-formula"><sub>2</sub></span>–C<span class="inline-formula"><sub>10</sub></span>) linear alcohols and diols. A good overall accuracy of the new SAR at 298 K (slope <span class="inline-formula">=</span> 1.022, <span class="inline-formula"><i>R</i><sup>2</sup>=0.855</span>) was obtained for the AAs and carboxylic acids under investigation. The kinetic database (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M32" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>k</mi><mrow class="chem"><msub><mi mathvariant="normal">OH</mi><mi mathvariant="normal">aq</mi></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="b88a9296a73ff6f30f335109e2f52d74"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-663-2024-ie00007.svg" width="27pt" height="16pt" src="acp-24-663-2024-ie00007.png"/></svg:svg></span></span> values in this work and compiled literature data) was also used to further enhance the ability of SAR to predict temperature-dependent values of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M33" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>k</mi><mrow class="chem"><msub><mi mathvariant="normal">OH</mi><mi mathvariant="normal">aq</mi></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="27pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="fb6a38ff92c89776b35d7bd73fe5988c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-663-2024-ie00008.svg" width="27pt" height="16pt" src="acp-24-663-2024-ie00008.png"/></svg:svg></span></span> in the temperature range 278–328 K.</p>
<p>The calculated atmospheric lifetimes indicate that terpenoic alcohols and diols can react with the OH in aerosol, cloud, and fog water with liquid water content (LWC) <span class="inline-formula">≥0.1</span> g m<span class="inline-formula"><sup>−3</sup></span> and LWC <span class="inline-formula">≥</span> 10<span class="inline-formula"><sup>−4</sup></span> g m<span class="inline-formula"><sup>−3</sup></span>, respectively. The preference of terpenoic diols to undergo aqueous oxidation by the OH under realistic atmospheric conditions is comparable with terpenoic acids, making them potentially effective precursors of <span class="inline-formula"><sub>aq</sub></span>SOAs. In clouds, a decrease in the temperature will strongly promote the aqueous reaction with the OH, primarily due to the increased partitioning of WSOCs into the aqueous phase.</p> |
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| ISSN: | 1680-7316 1680-7324 |