Impact of HO<sub>2</sub>∕RO<sub>2</sub> ratio on highly oxygenated <i>α</i>-pinene photooxidation products and secondary organic aerosol formation potential
<p>Highly oxygenated molecules (HOMs) from the atmospheric oxidation of biogenic volatile organic compounds are important contributors to secondary organic aerosol (SOA). Organic peroxy radicals (RO<span class="inline-formula"><sub>2</sub>)</span> and hydroper...
| Main Authors: | , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2024-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/24/4789/2024/acp-24-4789-2024.pdf |
| Summary: | <p>Highly oxygenated molecules (HOMs) from the atmospheric oxidation of biogenic volatile organic compounds are important contributors to secondary organic aerosol (SOA). Organic peroxy radicals (RO<span class="inline-formula"><sub>2</sub>)</span> and hydroperoxy radicals (HO<span class="inline-formula"><sub>2</sub>)</span> are key species influencing the HOM product distribution. In laboratory studies, experimental requirements often result in overemphasis on RO<span class="inline-formula"><sub>2</sub></span> cross-reactions compared to reactions of RO<span class="inline-formula"><sub>2</sub></span> with HO<span class="inline-formula"><sub>2</sub></span>. We analyzed the photochemical formation of HOMs from <span class="inline-formula"><i>α</i></span>-pinene and their potential to contribute to SOA formation under high (<span class="inline-formula">≈1</span>/1) and low (<span class="inline-formula">≈1</span>/100) <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">HO</mi><mn mathvariant="normal">2</mn></msub><mo>/</mo><msub><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="2b4018409b4ed76ade91ea8e966f8959"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-4789-2024-ie00004.svg" width="50pt" height="14pt" src="acp-24-4789-2024-ie00004.png"/></svg:svg></span></span> conditions. As <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">HO</mi><mn mathvariant="normal">2</mn></msub><mo>/</mo><msub><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="8cd9c354b6d3062297ae8c19001649cf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-4789-2024-ie00005.svg" width="50pt" height="14pt" src="acp-24-4789-2024-ie00005.png"/></svg:svg></span></span> <span class="inline-formula">></span> 1 is prevalent in the daytime atmosphere, sufficiently high <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">HO</mi><mn mathvariant="normal">2</mn></msub><mo>/</mo><msub><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="2eb9e90b0bd9aa84933ade8700ded6ca"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-4789-2024-ie00006.svg" width="50pt" height="14pt" src="acp-24-4789-2024-ie00006.png"/></svg:svg></span></span> is crucial to mimic atmospheric conditions and to prevent biases by low <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">HO</mi><mn mathvariant="normal">2</mn></msub><mo>/</mo><msub><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="e1d7ab50b5885ac2f66055485c5143cf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-4789-2024-ie00007.svg" width="50pt" height="14pt" src="acp-24-4789-2024-ie00007.png"/></svg:svg></span></span> on the HOM product distribution and thus SOA yield. Experiments were performed under steady-state conditions in the new, continuously stirred tank reactor SAPHIR-STAR at Forschungszentrum Jülich. The <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">HO</mi><mn mathvariant="normal">2</mn></msub><mo>/</mo><msub><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="87d1411523dfc82614bf68f0ff2f9588"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-4789-2024-ie00008.svg" width="50pt" height="14pt" src="acp-24-4789-2024-ie00008.png"/></svg:svg></span></span> ratio was increased by adding CO while keeping the OH concentration constant. We determined the HOM's SOA formation potential, considering its fraction remaining in the gas phase after seeding with (NH<span class="inline-formula"><sub>4</sub>)<sub>2</sub></span>SO<span class="inline-formula"><sub>4</sub></span> aerosol. An increase in <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M20" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">HO</mi><mn mathvariant="normal">2</mn></msub><mo>/</mo><msub><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="e5e8e165accc4799514d6e5795966a13"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-4789-2024-ie00009.svg" width="50pt" height="14pt" src="acp-24-4789-2024-ie00009.png"/></svg:svg></span></span> led to a reduction in SOA formation potential, with the main driver being a <span class="inline-formula">∼</span> 60 % reduction in HOM-accretion products. We also observed a shift in HOM-monomer functionalization from carbonyl to hydroperoxide groups. We determined a reduction of the HOM's SOA formation potential by <span class="inline-formula">∼</span> 30 % at <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">HO</mi><mn mathvariant="normal">2</mn></msub><mo>/</mo><msub><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="66226eec0ca5d58aa351b18e8a3becd8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-4789-2024-ie00010.svg" width="50pt" height="14pt" src="acp-24-4789-2024-ie00010.png"/></svg:svg></span></span> <span class="inline-formula">≈1</span>/1 compared to <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M25" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">HO</mi><mn mathvariant="normal">2</mn></msub><mo>/</mo><msub><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="866241d0f96f6d46374a213dee573c58"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-4789-2024-ie00011.svg" width="50pt" height="14pt" src="acp-24-4789-2024-ie00011.png"/></svg:svg></span></span> <span class="inline-formula">≈</span> 1/100. Particle-phase observations measured a similar decrease in SOA mass and yield. Our study shows that too low <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M27" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">HO</mi><mn mathvariant="normal">2</mn></msub><mo>/</mo><msub><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="50pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="edf73373e907de77c0d0711e75bc50a3"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-4789-2024-ie00012.svg" width="50pt" height="14pt" src="acp-24-4789-2024-ie00012.png"/></svg:svg></span></span> ratios compared to the atmosphere can lead to an overestimation of SOA yields.</p> |
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| ISSN: | 1680-7316 1680-7324 |