Observation and modeling of atmospheric OH and HO<sub>2</sub><sup>∗</sup> radicals at a subtropical rural site and implications for secondary pollutants
<p><span class="inline-formula">HO<sub><i>x</i></sub></span> radicals (<span class="inline-formula">OH</span> and <span class="inline-formula">HO<sub>2</sub></span>) are crucial oxidants that...
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| Main Authors: | , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/8147/2025/acp-25-8147-2025.pdf |
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| Summary: | <p><span class="inline-formula">HO<sub><i>x</i></sub></span> radicals (<span class="inline-formula">OH</span> and <span class="inline-formula">HO<sub>2</sub></span>) are crucial oxidants that determine atmospheric oxidation capacity and the production of secondary pollutants; however, their sources and sinks remain incompletely understood in certain rural, forest, and maritime environments. This study measured <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">HO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="16a5119f850650e91518d92f5e605c09"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-8147-2025-ie00004.svg" width="23pt" height="14pt" src="acp-25-8147-2025-ie00004.png"/></svg:svg></span></span> (<span class="inline-formula">HO<sub>2</sub></span> <span class="inline-formula">+</span> contribution from <span class="inline-formula">RO<sub>2</sub></span>, organic peroxyl radicals) and <span class="inline-formula">OH</span> concentrations using a chemical ionization mass spectrometer at a subtropical rural site in southern China from 12 November to 19 December 2022. The average peak concentrations were 3.50 <span class="inline-formula">±</span> 2.47 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>6</sup></span> <span class="inline-formula">cm<sup>−3</sup></span> for <span class="inline-formula">OH</span> and 1.34 <span class="inline-formula">±</span> 0.93 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>8</sup></span> <span class="inline-formula">cm<sup>−3</sup></span> for <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M20" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">HO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="dc19ee8d3b1067dde070fac7e2890a95"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-8147-2025-ie00005.svg" width="23pt" height="14pt" src="acp-25-8147-2025-ie00005.png"/></svg:svg></span></span>. Model-estimated contribution from <span class="inline-formula">RO<sub>2</sub></span> to <span class="inline-formula">HO<sub>2</sub></span> during the measurement period ranged from 44 % to 69 % of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">HO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="7ea210efdc007f6cda21857ee3b28272"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-8147-2025-ie00006.svg" width="23pt" height="14pt" src="acp-25-8147-2025-ie00006.png"/></svg:svg></span></span>. Calculations based on an observation-constrained chemical model revealed an overestimation of <span class="inline-formula">HO<sub>2</sub></span> and <span class="inline-formula">OH</span> concentrations during warm periods of the field study. Sensitivity tests suggest that adding <span class="inline-formula">HO<sub><i>x</i></sub></span> sinks or an <span class="inline-formula">HO<sub>2</sub></span> recycle process to the model could improve the model performance. Over-simulation of <span class="inline-formula">HO<sub><i>x</i></sub></span> in the model resulted in overestimations of midday (10:00–15:00 UTC) production rates by more than 79 % for ozone and a factor of 1.88 for nitric acid. Our study highlights the need for further improving understanding of the sources and sinks of <span class="inline-formula">OH</span> and <span class="inline-formula">HO<sub>2</sub></span> and representation of them in air quality models.</p> |
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| ISSN: | 1680-7316 1680-7324 |