OH measurements in the coastal atmosphere of South China: possible missing OH sinks in aged air masses
<p>The hydroxyl radical (OH) is the main atmospheric oxidant responsible for the removal of many reduced trace gases and the formation of secondary air pollutants. However, due to technical difficulties in measuring OH, the existing measurements of atmospheric OH concentrations are limited, an...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2023-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/7057/2023/acp-23-7057-2023.pdf |
| _version_ | 1827916134196707328 |
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| author | Z. Zou Q. Chen M. Xia Q. Yuan Y. Chen Y. Wang E. Xiong Z. Wang T. Wang |
| author_facet | Z. Zou Q. Chen M. Xia Q. Yuan Y. Chen Y. Wang E. Xiong Z. Wang T. Wang |
| author_sort | Z. Zou |
| collection | DOAJ |
| description | <p>The hydroxyl radical (OH) is the main atmospheric oxidant responsible for
the removal of many reduced trace gases and the formation of secondary air
pollutants. However, due to technical difficulties in measuring OH, the
existing measurements of atmospheric OH concentrations are limited, and its
sources and sinks are not well understood under low-nitrogen-oxide
(NO<span class="inline-formula"><sub><i>x</i></sub></span>) conditions. In this study, we observed the OH concentrations
using chemical ionization mass spectrometry at a coastal site in Hong Kong
from October to November 2020. The average noontime OH concentration over
the study period was measured at <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">4.9</mn><mo>±</mo><mn mathvariant="normal">2.1</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">6</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="72pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="6d519aac96e94f559f12156e51aed359"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7057-2023-ie00001.svg" width="72pt" height="14pt" src="acp-23-7057-2023-ie00001.png"/></svg:svg></span></span> cm<span class="inline-formula"><sup>−3</sup></span>. We found that a box model with comprehensive observational constraints reproduced the observed daytime OH concentrations when air parcels originated from the continental regions. However, this model overpredicted the observed daytime OH concentrations for coastal air parcels by 142 % on average. Unaccounted-for OH sinks in the model are proposed to be the cause of this overprediction. A missing OH reactivity, which is defined as the pseudo-first-order rate coefficient for OH loss by unmeasured trace gases, was estimated as <span class="inline-formula">5.0±2.6</span> s<span class="inline-formula"><sup>−1</sup></span> (lower limit) in the coastal air, and the missing reactivity increased with decreasing concentrations of NO<span class="inline-formula"><sub><i>x</i></sub></span> and volatile organic compounds (VOCs). Further studies are needed to find out the exact cause of the model overestimation and to identify the suspected unmeasured chemical species that contribute to the OH budget, in order to better quantify the formation of secondary air pollutants.</p> |
| first_indexed | 2024-03-13T03:09:41Z |
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| id | doaj.art-436c856f03514ab0a2640d9fa7990f2f |
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| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-03-13T03:09:41Z |
| publishDate | 2023-06-01 |
| publisher | Copernicus Publications |
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| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-436c856f03514ab0a2640d9fa7990f2f2023-06-26T14:43:14ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242023-06-01237057707410.5194/acp-23-7057-2023OH measurements in the coastal atmosphere of South China: possible missing OH sinks in aged air massesZ. Zou0Q. Chen1M. Xia2Q. Yuan3Y. Chen4Y. Wang5E. Xiong6Z. Wang7T. Wang8Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, ChinaDepartment of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, ChinaDepartment of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, ChinaDepartment of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, ChinaDivision of Environment and Sustainability, The Hong Kong University of Science and Technology, Hong Kong SAR, ChinaDepartment of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, ChinaDepartment of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, ChinaDivision of Environment and Sustainability, The Hong Kong University of Science and Technology, Hong Kong SAR, ChinaDepartment of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, China<p>The hydroxyl radical (OH) is the main atmospheric oxidant responsible for the removal of many reduced trace gases and the formation of secondary air pollutants. However, due to technical difficulties in measuring OH, the existing measurements of atmospheric OH concentrations are limited, and its sources and sinks are not well understood under low-nitrogen-oxide (NO<span class="inline-formula"><sub><i>x</i></sub></span>) conditions. In this study, we observed the OH concentrations using chemical ionization mass spectrometry at a coastal site in Hong Kong from October to November 2020. The average noontime OH concentration over the study period was measured at <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">4.9</mn><mo>±</mo><mn mathvariant="normal">2.1</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">6</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="72pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="6d519aac96e94f559f12156e51aed359"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7057-2023-ie00001.svg" width="72pt" height="14pt" src="acp-23-7057-2023-ie00001.png"/></svg:svg></span></span> cm<span class="inline-formula"><sup>−3</sup></span>. We found that a box model with comprehensive observational constraints reproduced the observed daytime OH concentrations when air parcels originated from the continental regions. However, this model overpredicted the observed daytime OH concentrations for coastal air parcels by 142 % on average. Unaccounted-for OH sinks in the model are proposed to be the cause of this overprediction. A missing OH reactivity, which is defined as the pseudo-first-order rate coefficient for OH loss by unmeasured trace gases, was estimated as <span class="inline-formula">5.0±2.6</span> s<span class="inline-formula"><sup>−1</sup></span> (lower limit) in the coastal air, and the missing reactivity increased with decreasing concentrations of NO<span class="inline-formula"><sub><i>x</i></sub></span> and volatile organic compounds (VOCs). Further studies are needed to find out the exact cause of the model overestimation and to identify the suspected unmeasured chemical species that contribute to the OH budget, in order to better quantify the formation of secondary air pollutants.</p>https://acp.copernicus.org/articles/23/7057/2023/acp-23-7057-2023.pdf |
| spellingShingle | Z. Zou Q. Chen M. Xia Q. Yuan Y. Chen Y. Wang E. Xiong Z. Wang T. Wang OH measurements in the coastal atmosphere of South China: possible missing OH sinks in aged air masses Atmospheric Chemistry and Physics |
| title | OH measurements in the coastal atmosphere of South China: possible missing OH sinks in aged air masses |
| title_full | OH measurements in the coastal atmosphere of South China: possible missing OH sinks in aged air masses |
| title_fullStr | OH measurements in the coastal atmosphere of South China: possible missing OH sinks in aged air masses |
| title_full_unstemmed | OH measurements in the coastal atmosphere of South China: possible missing OH sinks in aged air masses |
| title_short | OH measurements in the coastal atmosphere of South China: possible missing OH sinks in aged air masses |
| title_sort | oh measurements in the coastal atmosphere of south china possible missing oh sinks in aged air masses |
| url | https://acp.copernicus.org/articles/23/7057/2023/acp-23-7057-2023.pdf |
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