Photolysis and oxidation by OH radicals of two carbonyl nitrates: 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone
<p>Multifunctional organic nitrates, including carbonyl nitrates, are important species formed in <span class="inline-formula">NO<sub><i>x</i></sub></span>-rich atmospheres by the degradation of volatile organic compounds (VOCs). These compounds ha...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/20/487/2020/acp-20-487-2020.pdf |
| Summary: | <p>Multifunctional organic nitrates, including carbonyl nitrates, are important
species formed in <span class="inline-formula">NO<sub><i>x</i></sub></span>-rich atmospheres by the degradation of volatile organic compounds (VOCs). These
compounds have been shown to play a key role in the transport of reactive
nitrogen and, consequently, in the ozone budget; they are also known to be important
components of the total organic aerosol. However, very little is known about
their reactivity in both the gas and condensed phases. Following a previous
study that we published on the gas-phase reactivity of <span class="inline-formula"><i>α</i></span>-nitrooxy
ketones, the photolysis and reaction with OH radicals of
4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone (which are a <span class="inline-formula"><i>β</i></span>-nitrooxy ketone and <span class="inline-formula"><i>γ</i></span>-nitrooxy ketone, respectively) were investigated for the
first time in simulation chambers. The photolysis frequencies were directly
measured in the CESAM chamber, which is equipped with a very realistic
irradiation system. The <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>j</mi><mi mathvariant="normal">nitrate</mi></msub><mo>/</mo><msub><mi>j</mi><mrow class="chem"><msub><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="2651b9abc7d3261168a3beec41f3fe22"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-487-2020-ie00001.svg" width="54pt" height="16pt" src="acp-20-487-2020-ie00001.png"/></svg:svg></span></span> ratios were found to be <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mn mathvariant="normal">5.9</mn><mo>±</mo><mn mathvariant="normal">0.9</mn><mo>)</mo><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">3</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="85pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="0d9ceaa8d3dea35aa95cbb34be525c6d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-487-2020-ie00002.svg" width="85pt" height="15pt" src="acp-20-487-2020-ie00002.png"/></svg:svg></span></span> for 4-nitrooxy-2-butanone and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mn mathvariant="normal">3.2</mn><mo>±</mo><mn mathvariant="normal">0.9</mn><mo>)</mo><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">3</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="85pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="15216b418260229af3a13563eca50989"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-487-2020-ie00003.svg" width="85pt" height="15pt" src="acp-20-487-2020-ie00003.png"/></svg:svg></span></span> for 5-nitrooxy-2-pentanone under our experimental
conditions. From these results, it was estimated that ambient photolysis
frequencies calculated for typical tropospheric irradiation conditions
corresponding to the 1 July at noon at 40<span class="inline-formula"><sup>∘</sup></span> N (overhead ozone column of 300 and albedo of 0.1) are <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mn mathvariant="normal">6.1</mn><mo>±</mo><mn mathvariant="normal">0.9</mn><mo>)</mo><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">5</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="85pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="d61cd6cbe98419f6d15a4bedf98ad312"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-487-2020-ie00004.svg" width="85pt" height="15pt" src="acp-20-487-2020-ie00004.png"/></svg:svg></span></span> s<span class="inline-formula"><sup>−1</sup></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mn mathvariant="normal">3.3</mn><mo>±</mo><mn mathvariant="normal">0.9</mn><mo>)</mo><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">5</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="85pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="ab7920105c9d29568efadb0874f336c2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-487-2020-ie00005.svg" width="85pt" height="15pt" src="acp-20-487-2020-ie00005.png"/></svg:svg></span></span> s<span class="inline-formula"><sup>−1</sup></span> for 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone, respectively.
These results demonstrate that photolysis is a very efficient sink for these
compounds with atmospheric lifetimes of few hours. They also suggest that,
similarly to <span class="inline-formula"><i>α</i></span>-nitrooxy ketones, <span class="inline-formula"><i>β</i></span>-nitrooxy ketones have
enhanced UV absorption cross sections and quantum yields equal to or close to
unity and that <span class="inline-formula"><i>γ</i></span>-nitrooxy ketones have a lower enhancement of cross
sections, which can easily be explained by the larger distance between the
two chromophore groups. Thanks to a product study, the branching ratio between
the two possible photodissociation pathways is also proposed. Rate
constants for the reaction with OH radicals were found to be <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mn mathvariant="normal">2.9</mn><mo>±</mo><mn mathvariant="normal">1.0</mn><mo>)</mo><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">12</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="89pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="c0c8f87180aeb915b755fca0c875464a"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-487-2020-ie00006.svg" width="89pt" height="15pt" src="acp-20-487-2020-ie00006.png"/></svg:svg></span></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mn mathvariant="normal">3.3</mn><mo>±</mo><mn mathvariant="normal">0.9</mn><mo>)</mo><mo>×</mo><msup><mn mathvariant="normal">10</mn><mrow><mo>-</mo><mn mathvariant="normal">12</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="89pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="c07aa1ee0cbca59df7a859463b75f1ac"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-487-2020-ie00007.svg" width="89pt" height="15pt" src="acp-20-487-2020-ie00007.png"/></svg:svg></span></span> cm<span class="inline-formula"><sup>3</sup></span> molecule<span class="inline-formula"><sup>−1</sup></span> s<span class="inline-formula"><sup>−1</sup></span>,
respectively. These experimental data are in good agreement with rate
constants estimated by the structure–activity relationship (SAR) of Kwok and Atkinson (1995) when using the
parametrization proposed by Suarez-Bertoa et al. (2012) for carbonyl
nitrates. Comparison with photolysis rates suggests that the OH-initiated
oxidation of carbonyl nitrates is a less efficient sink than
photodissociation but is not negligible in polluted areas.</p> |
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| ISSN: | 1680-7316 1680-7324 |