Aerosol pH and chemical regimes of sulfate formation in aerosol water during winter haze in the North China Plain
<p>Understanding the mechanism of haze formation is crucial for the development of deliberate pollution control strategies. Multiphase chemical reactions in aerosol water have been suggested as an important source of particulate sulfate during severe haze (Cheng et al., 2016; Wang et al., 2016...
| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2020-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/20/11729/2020/acp-20-11729-2020.pdf |
| _version_ | 1819111681208352768 |
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| author | W. Tao W. Tao H. Su G. Zheng J. Wang C. Wei L. Liu N. Ma M. Li Q. Zhang U. Pöschl Y. Cheng Y. Cheng |
| author_facet | W. Tao W. Tao H. Su G. Zheng J. Wang C. Wei L. Liu N. Ma M. Li Q. Zhang U. Pöschl Y. Cheng Y. Cheng |
| author_sort | W. Tao |
| collection | DOAJ |
| description | <p>Understanding the mechanism of haze formation is crucial for the development
of deliberate pollution control strategies. Multiphase chemical reactions in
aerosol water have been suggested as an important source of particulate
sulfate during severe haze (Cheng et al., 2016; Wang et al., 2016). While
the key role of aerosol water has been commonly accepted, the relative
importance of different oxidation pathways in the aqueous phase is still
under debate mainly due to questions about aerosol pH. To investigate the
spatiotemporal variability of aerosol pH and sulfate formation during
winter in the North China Plain (NCP), we have developed a new aerosol water
chemistry (AWAC) module for the WRF-Chem model (Weather Research and
Forecasting model coupled with Chemistry). Using the WRF-Chem-AWAC model, we
performed a comprehensive survey of the atmospheric conditions
characteristic for wintertime in the NCP focusing on January 2013. We find
that aerosol pH exhibited a strong vertical gradient and distinct diurnal
cycle which was closely associated with the spatiotemporal variation in
the abundance of acidic and alkaline fine particle components and
their gaseous counterparts. Over Beijing, the average aerosol pH at the
surface layer was <span class="inline-formula">∼5.4</span> and remained nearly constant around
<span class="inline-formula">∼5</span> up to <span class="inline-formula">∼2</span> km above ground level; further
aloft, the acidity rapidly increased to pH <span class="inline-formula">∼0</span> at
<span class="inline-formula">∼3</span> km. The pattern of aerosol acidity increasing with altitude
persisted over the NCP, while the specific levels and gradients of pH varied
between different regions. In the region north of <span class="inline-formula">∼41</span><span class="inline-formula"><sup>∘</sup></span> N, the mean pH values at the surface level were typically
greater than 6, and the main pathway of sulfate formation in aerosol water
was S(IV) oxidation by ozone. South of <span class="inline-formula">∼41</span><span class="inline-formula"><sup>∘</sup></span> N, the
mean pH values at the surface level were typically in the range of 4.4 to 5.7,
and different chemical regimes and reaction pathways of sulfate formation
prevailed in four different regions depending on reactant concentrations
and atmospheric conditions. The <span class="inline-formula">NO<sub>2</sub></span> reaction pathway prevailed in the
megacity region of Beijing and the large area of Hebei Province to the south
and west of Beijing, as well as part of Shandong Province. The transition
metal ion (TMI) pathway dominated in the inland region to the west and the
coastal regions to the east of Beijing, and the <span class="inline-formula">H<sub>2</sub>O<sub>2</sub></span> pathway
dominated in the region extending further south (Shandong and Henan
provinces). In all of these regions, the <span class="inline-formula">O<sub>3</sub></span> and TMI pathways in aerosol
water, as well as the gas-particle partitioning of <span class="inline-formula">H<sub>2</sub>SO<sub>4</sub></span> vapor,
became more important with increasing altitude. Sensitivity tests show that the rapid
production of sulfate in the NCP can be maintained over a wide range of
aerosol acidity (e.g., pH <span class="inline-formula">=4.2</span>–5.7) with transitions from dominant TMI pathway regimes
to dominant <span class="inline-formula">NO<sub>2</sub>∕O<sub>3</sub></span> pathway regimes.</p> |
| first_indexed | 2024-12-22T04:01:29Z |
| format | Article |
| id | doaj.art-b0de543bcf44456bb3aec0e56d4a264f |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-22T04:01:29Z |
| publishDate | 2020-10-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-b0de543bcf44456bb3aec0e56d4a264f2022-12-21T18:39:44ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242020-10-0120117291174610.5194/acp-20-11729-2020Aerosol pH and chemical regimes of sulfate formation in aerosol water during winter haze in the North China PlainW. Tao0W. Tao1H. Su2G. Zheng3J. Wang4C. Wei5L. Liu6N. Ma7M. Li8Q. Zhang9U. Pöschl10Y. Cheng11Y. Cheng12Multiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, GermanyMinerva Research Group, Max Planck Institute for Chemistry, 55128 Mainz, GermanyMultiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, GermanyMinerva Research Group, Max Planck Institute for Chemistry, 55128 Mainz, GermanyMinerva Research Group, Max Planck Institute for Chemistry, 55128 Mainz, GermanyMultiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, GermanyMinerva Research Group, Max Planck Institute for Chemistry, 55128 Mainz, GermanyInstitute for Environmental and Climate Research, Jinan University, Guangzhou 511443, ChinaMultiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, GermanyDepartment of Earth System Science, Tsinghua University, Beijing 100084, ChinaMultiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, GermanyMultiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, GermanyMinerva Research Group, Max Planck Institute for Chemistry, 55128 Mainz, Germany<p>Understanding the mechanism of haze formation is crucial for the development of deliberate pollution control strategies. Multiphase chemical reactions in aerosol water have been suggested as an important source of particulate sulfate during severe haze (Cheng et al., 2016; Wang et al., 2016). While the key role of aerosol water has been commonly accepted, the relative importance of different oxidation pathways in the aqueous phase is still under debate mainly due to questions about aerosol pH. To investigate the spatiotemporal variability of aerosol pH and sulfate formation during winter in the North China Plain (NCP), we have developed a new aerosol water chemistry (AWAC) module for the WRF-Chem model (Weather Research and Forecasting model coupled with Chemistry). Using the WRF-Chem-AWAC model, we performed a comprehensive survey of the atmospheric conditions characteristic for wintertime in the NCP focusing on January 2013. We find that aerosol pH exhibited a strong vertical gradient and distinct diurnal cycle which was closely associated with the spatiotemporal variation in the abundance of acidic and alkaline fine particle components and their gaseous counterparts. Over Beijing, the average aerosol pH at the surface layer was <span class="inline-formula">∼5.4</span> and remained nearly constant around <span class="inline-formula">∼5</span> up to <span class="inline-formula">∼2</span> km above ground level; further aloft, the acidity rapidly increased to pH <span class="inline-formula">∼0</span> at <span class="inline-formula">∼3</span> km. The pattern of aerosol acidity increasing with altitude persisted over the NCP, while the specific levels and gradients of pH varied between different regions. In the region north of <span class="inline-formula">∼41</span><span class="inline-formula"><sup>∘</sup></span> N, the mean pH values at the surface level were typically greater than 6, and the main pathway of sulfate formation in aerosol water was S(IV) oxidation by ozone. South of <span class="inline-formula">∼41</span><span class="inline-formula"><sup>∘</sup></span> N, the mean pH values at the surface level were typically in the range of 4.4 to 5.7, and different chemical regimes and reaction pathways of sulfate formation prevailed in four different regions depending on reactant concentrations and atmospheric conditions. The <span class="inline-formula">NO<sub>2</sub></span> reaction pathway prevailed in the megacity region of Beijing and the large area of Hebei Province to the south and west of Beijing, as well as part of Shandong Province. The transition metal ion (TMI) pathway dominated in the inland region to the west and the coastal regions to the east of Beijing, and the <span class="inline-formula">H<sub>2</sub>O<sub>2</sub></span> pathway dominated in the region extending further south (Shandong and Henan provinces). In all of these regions, the <span class="inline-formula">O<sub>3</sub></span> and TMI pathways in aerosol water, as well as the gas-particle partitioning of <span class="inline-formula">H<sub>2</sub>SO<sub>4</sub></span> vapor, became more important with increasing altitude. Sensitivity tests show that the rapid production of sulfate in the NCP can be maintained over a wide range of aerosol acidity (e.g., pH <span class="inline-formula">=4.2</span>–5.7) with transitions from dominant TMI pathway regimes to dominant <span class="inline-formula">NO<sub>2</sub>∕O<sub>3</sub></span> pathway regimes.</p>https://acp.copernicus.org/articles/20/11729/2020/acp-20-11729-2020.pdf |
| spellingShingle | W. Tao W. Tao H. Su G. Zheng J. Wang C. Wei L. Liu N. Ma M. Li Q. Zhang U. Pöschl Y. Cheng Y. Cheng Aerosol pH and chemical regimes of sulfate formation in aerosol water during winter haze in the North China Plain Atmospheric Chemistry and Physics |
| title | Aerosol pH and chemical regimes of sulfate formation in aerosol water during winter haze in the North China Plain |
| title_full | Aerosol pH and chemical regimes of sulfate formation in aerosol water during winter haze in the North China Plain |
| title_fullStr | Aerosol pH and chemical regimes of sulfate formation in aerosol water during winter haze in the North China Plain |
| title_full_unstemmed | Aerosol pH and chemical regimes of sulfate formation in aerosol water during winter haze in the North China Plain |
| title_short | Aerosol pH and chemical regimes of sulfate formation in aerosol water during winter haze in the North China Plain |
| title_sort | aerosol ph and chemical regimes of sulfate formation in aerosol water during winter haze in the north china plain |
| url | https://acp.copernicus.org/articles/20/11729/2020/acp-20-11729-2020.pdf |
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