Aqueous reactions of organic triplet excited states with atmospheric alkenes
<p>Triplet excited states of organic matter are formed when colored organic matter (i.e., brown carbon) absorbs light. While these “triplets” can be important photooxidants in atmospheric drops and particles (e.g., they rapidly oxidize phenols), very little is known about their reactivity towa...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2019-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/5021/2019/acp-19-5021-2019.pdf |
| id |
doaj-37fab17abd4a42e79bbf8abe18504526 |
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| record_format |
Article |
| collection |
DOAJ |
| language |
English |
| format |
Article |
| sources |
DOAJ |
| author |
R. Kaur R. Kaur B. M. Hudson J. Draper J. Draper D. J. Tantillo C. Anastasio C. Anastasio |
| spellingShingle |
R. Kaur R. Kaur B. M. Hudson J. Draper J. Draper D. J. Tantillo C. Anastasio C. Anastasio Aqueous reactions of organic triplet excited states with atmospheric alkenes Atmospheric Chemistry and Physics |
| author_facet |
R. Kaur R. Kaur B. M. Hudson J. Draper J. Draper D. J. Tantillo C. Anastasio C. Anastasio |
| author_sort |
R. Kaur |
| title |
Aqueous reactions of organic triplet excited states with atmospheric alkenes |
| title_short |
Aqueous reactions of organic triplet excited states with atmospheric alkenes |
| title_full |
Aqueous reactions of organic triplet excited states with atmospheric alkenes |
| title_fullStr |
Aqueous reactions of organic triplet excited states with atmospheric alkenes |
| title_full_unstemmed |
Aqueous reactions of organic triplet excited states with atmospheric alkenes |
| title_sort |
aqueous reactions of organic triplet excited states with atmospheric alkenes |
| publisher |
Copernicus Publications |
| series |
Atmospheric Chemistry and Physics |
| issn |
1680-7316 1680-7324 |
| publishDate |
2019-04-01 |
| description |
<p>Triplet excited states of organic matter are formed when colored organic
matter (i.e., brown carbon) absorbs light. While these “triplets” can be
important photooxidants in atmospheric drops and particles (e.g., they
rapidly oxidize phenols), very little is known about their reactivity toward
many classes of organic compounds in the atmosphere. Here we measure the
bimolecular rate constants of the triplet excited state of benzophenone
(<span class="inline-formula"><sup>3</sup>BP<sup>∗</sup></span>), a model species, with 17 water-soluble
<span class="inline-formula">C<sub>3</sub></span>–<span class="inline-formula">C<sub>6</sub></span> alkenes that have either been found in the
atmosphere or are reasonable surrogates for identified species. Measured rate
constants (<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><mi mathvariant="normal">ALK</mi><mo>+</mo><mn mathvariant="normal">3</mn><msup><mi mathvariant="normal">BP</mi><mo>∗</mo></msup></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="47pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="5e244a6573dc648a8ae694306cb94c30"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-5021-2019-ie00001.svg" width="47pt" height="12pt" src="acp-19-5021-2019-ie00001.png"/></svg:svg></span></span>) vary by a factor of 30 and are in the
range of (0.24–7.5) <span class="inline-formula">×10<sup>9</sup></span> M<span class="inline-formula"><sup>−1</sup></span> s<span class="inline-formula"><sup>−1</sup></span>. Biogenic alkenes
found in the atmosphere – e.g., <i>cis</i>-3-hexen-1-ol, <i>cis</i>-3-hexenyl acetate, and
methyl jasmonate – react rapidly, with rate constants above <span class="inline-formula">1×10<sup>9</sup></span> M<span class="inline-formula"><sup>−1</sup></span> s<span class="inline-formula"><sup>−1</sup></span>. Rate constants depend on alkene characteristics
such as the location of the double bond, stereochemistry, and alkyl
substitution on the double bond. There is a reasonable correlation between
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>k</mi><mrow><mi mathvariant="normal">ALK</mi><mo>+</mo><mn mathvariant="normal">3</mn><msup><mi mathvariant="normal">BP</mi><mo>∗</mo></msup></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="47pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="2a58d5ba79f5a7bbe5533d56d95f8683"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-5021-2019-ie00002.svg" width="47pt" height="12pt" src="acp-19-5021-2019-ie00002.png"/></svg:svg></span></span> and the calculated one-electron oxidation potential
(OP) of the alkenes (<span class="inline-formula"><i>R</i><sup>2</sup>=0.58</span>); in contrast, rate constants are not
correlated with bond dissociation enthalpies, bond dissociation free
energies, or computed energy barriers for hydrogen abstraction. Using the OP
relationship, we estimate aqueous rate constants for a number of unsaturated
isoprene and limonene oxidation products with <span class="inline-formula"><sup>3</sup>BP<sup>∗</sup></span>: values are in
the range of (0.080–1.7) <span class="inline-formula">×10<sup>9</sup></span> M<span class="inline-formula"><sup>−1</sup></span> s<span class="inline-formula"><sup>−1</sup></span>, with
generally faster values for limonene products. Rate constants with less
reactive triplets, which are probably more environmentally relevant, are
likely roughly 25 times slower. Using our predicted rate constants, along
with values for other reactions from the literature, we conclude that
triplets are probably minor oxidants for isoprene- and limonene-related
compounds in cloudy or foggy atmospheres, except in cases in which the triplets
are very reactive.</p> |
| url |
https://www.atmos-chem-phys.net/19/5021/2019/acp-19-5021-2019.pdf |
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doaj-37fab17abd4a42e79bbf8abe185045262020-11-25T00:27:55ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242019-04-01195021503210.5194/acp-19-5021-2019Aqueous reactions of organic triplet excited states with atmospheric alkenesR. Kaur0R. Kaur1B. M. Hudson2J. Draper3J. Draper4D. J. Tantillo5C. Anastasio6C. Anastasio7Department of Land, Air, and Water Resources, University of California, Davis, California 95616, USAAgricultural & Environmental Chemistry Graduate Group, University of California, Davis, California 95616, USADepartment of Chemistry, University of California, Davis, California 95616, USADepartment of Land, Air, and Water Resources, University of California, Davis, California 95616, USAnow at: Fresno Metropolitan Flood Control District, Fresno, California 93727, USADepartment of Chemistry, University of California, Davis, California 95616, USADepartment of Land, Air, and Water Resources, University of California, Davis, California 95616, USAAgricultural & Environmental Chemistry Graduate Group, University of California, Davis, California 95616, USA<p>Triplet excited states of organic matter are formed when colored organic matter (i.e., brown carbon) absorbs light. While these “triplets” can be important photooxidants in atmospheric drops and particles (e.g., they rapidly oxidize phenols), very little is known about their reactivity toward many classes of organic compounds in the atmosphere. Here we measure the bimolecular rate constants of the triplet excited state of benzophenone (<span class="inline-formula"><sup>3</sup>BP<sup>∗</sup></span>), a model species, with 17 water-soluble <span class="inline-formula">C<sub>3</sub></span>–<span class="inline-formula">C<sub>6</sub></span> alkenes that have either been found in the atmosphere or are reasonable surrogates for identified species. Measured rate constants (<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><mi mathvariant="normal">ALK</mi><mo>+</mo><mn mathvariant="normal">3</mn><msup><mi mathvariant="normal">BP</mi><mo>∗</mo></msup></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="47pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="5e244a6573dc648a8ae694306cb94c30"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-5021-2019-ie00001.svg" width="47pt" height="12pt" src="acp-19-5021-2019-ie00001.png"/></svg:svg></span></span>) vary by a factor of 30 and are in the range of (0.24–7.5) <span class="inline-formula">×10<sup>9</sup></span> M<span class="inline-formula"><sup>−1</sup></span> s<span class="inline-formula"><sup>−1</sup></span>. Biogenic alkenes found in the atmosphere – e.g., <i>cis</i>-3-hexen-1-ol, <i>cis</i>-3-hexenyl acetate, and methyl jasmonate – react rapidly, with rate constants above <span class="inline-formula">1×10<sup>9</sup></span> M<span class="inline-formula"><sup>−1</sup></span> s<span class="inline-formula"><sup>−1</sup></span>. Rate constants depend on alkene characteristics such as the location of the double bond, stereochemistry, and alkyl substitution on the double bond. There is a reasonable correlation between <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>k</mi><mrow><mi mathvariant="normal">ALK</mi><mo>+</mo><mn mathvariant="normal">3</mn><msup><mi mathvariant="normal">BP</mi><mo>∗</mo></msup></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="47pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="2a58d5ba79f5a7bbe5533d56d95f8683"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-5021-2019-ie00002.svg" width="47pt" height="12pt" src="acp-19-5021-2019-ie00002.png"/></svg:svg></span></span> and the calculated one-electron oxidation potential (OP) of the alkenes (<span class="inline-formula"><i>R</i><sup>2</sup>=0.58</span>); in contrast, rate constants are not correlated with bond dissociation enthalpies, bond dissociation free energies, or computed energy barriers for hydrogen abstraction. Using the OP relationship, we estimate aqueous rate constants for a number of unsaturated isoprene and limonene oxidation products with <span class="inline-formula"><sup>3</sup>BP<sup>∗</sup></span>: values are in the range of (0.080–1.7) <span class="inline-formula">×10<sup>9</sup></span> M<span class="inline-formula"><sup>−1</sup></span> s<span class="inline-formula"><sup>−1</sup></span>, with generally faster values for limonene products. Rate constants with less reactive triplets, which are probably more environmentally relevant, are likely roughly 25 times slower. Using our predicted rate constants, along with values for other reactions from the literature, we conclude that triplets are probably minor oxidants for isoprene- and limonene-related compounds in cloudy or foggy atmospheres, except in cases in which the triplets are very reactive.</p>https://www.atmos-chem-phys.net/19/5021/2019/acp-19-5021-2019.pdf |