Optical properties and molecular compositions of water-soluble and water-insoluble brown carbon (BrC) aerosols in northwest China

<p>Brown carbon (BrC) contributes significantly to aerosol light absorption and thus can affect the Earth's radiation balance and atmospheric photochemical processes. In this study, we examined the light absorption properties and molecular compositions of water-soluble (WS-BrC) and water-...

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Main Authors: J. Li, Q. Zhang, G. Wang, C. Wu, L. Liu, J. Wang, W. Jiang, L. Li, K. F. Ho, J. Cao
Format: Article
Language:English
Published: Copernicus Publications 2020-04-01
Series:Atmospheric Chemistry and Physics
Online Access:https://www.atmos-chem-phys.net/20/4889/2020/acp-20-4889-2020.pdf
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language English
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author J. Li
J. Li
Q. Zhang
G. Wang
G. Wang
G. Wang
J. Li
C. Wu
C. Wu
L. Liu
J. Wang
J. Wang
W. Jiang
L. Li
L. Li
K. F. Ho
K. F. Ho
J. Cao
spellingShingle J. Li
J. Li
Q. Zhang
G. Wang
G. Wang
G. Wang
J. Li
C. Wu
C. Wu
L. Liu
J. Wang
J. Wang
W. Jiang
L. Li
L. Li
K. F. Ho
K. F. Ho
J. Cao
Optical properties and molecular compositions of water-soluble and water-insoluble brown carbon (BrC) aerosols in northwest China
Atmospheric Chemistry and Physics
author_facet J. Li
J. Li
Q. Zhang
G. Wang
G. Wang
G. Wang
J. Li
C. Wu
C. Wu
L. Liu
J. Wang
J. Wang
W. Jiang
L. Li
L. Li
K. F. Ho
K. F. Ho
J. Cao
author_sort J. Li
title Optical properties and molecular compositions of water-soluble and water-insoluble brown carbon (BrC) aerosols in northwest China
title_short Optical properties and molecular compositions of water-soluble and water-insoluble brown carbon (BrC) aerosols in northwest China
title_full Optical properties and molecular compositions of water-soluble and water-insoluble brown carbon (BrC) aerosols in northwest China
title_fullStr Optical properties and molecular compositions of water-soluble and water-insoluble brown carbon (BrC) aerosols in northwest China
title_full_unstemmed Optical properties and molecular compositions of water-soluble and water-insoluble brown carbon (BrC) aerosols in northwest China
title_sort optical properties and molecular compositions of water-soluble and water-insoluble brown carbon (brc) aerosols in northwest china
publisher Copernicus Publications
series Atmospheric Chemistry and Physics
issn 1680-7316
1680-7324
publishDate 2020-04-01
description <p>Brown carbon (BrC) contributes significantly to aerosol light absorption and thus can affect the Earth's radiation balance and atmospheric photochemical processes. In this study, we examined the light absorption properties and molecular compositions of water-soluble (WS-BrC) and water-insoluble (WI-BrC) BrC in PM<span class="inline-formula"><sub>2.5</sub></span> collected from a rural site in the Guanzhong Basin – a highly polluted region in northwest China. Both WS-BrC and WI-BrC showed elevated light absorption coefficients (Abs) in winter (4–7 times those in summer) mainly attributed to enhanced emissions from residential biomass burning (BB) for heating of homes. While the average mass absorption coefficients (MACs) at 365&thinsp;nm (MAC<span class="inline-formula"><sub>365</sub></span>) of WS-BrC were similar between daytime and nighttime in summer (<span class="inline-formula">0.99±0.17</span> and <span class="inline-formula">1.01±0.18</span>&thinsp;m<span class="inline-formula"><sup>2</sup></span>&thinsp;g<span class="inline-formula"><sup>−1</sup></span>, respectively), the average MAC<span class="inline-formula"><sub>365</sub></span> of WI-BrC was more than a factor of 2 higher during daytime (<span class="inline-formula">2.45±1.14</span>&thinsp;m<span class="inline-formula"><sup>2</sup></span>&thinsp;g<span class="inline-formula"><sup>−1</sup></span>) than at night (<span class="inline-formula">1.18±0.36</span>&thinsp;m<span class="inline-formula"><sup>2</sup></span>&thinsp;g<span class="inline-formula"><sup>−1</sup></span>). This difference was partly attributed to enhanced photochemical formation of WI-BrC species, such as oxygenated polycyclic aromatic hydrocarbons (OPAHs). In contrast, the MACs of WS-BrC and WI-BrC were generally similar in winter and both showed few diel differences. The Abs of wintertime WS-BrC correlated strongly with relative humidity, sulfate and <span class="inline-formula">NO<sub>2</sub></span>, suggesting that aqueous-phase reaction is an important pathway for secondary BrC formation during the winter season in northwest China. Nitrophenols on average contributed <span class="inline-formula">2.44±1.78</span>&thinsp;% of the Abs of WS-BrC in winter but only <span class="inline-formula">0.12±0.03</span>&thinsp;% in summer due to faster photodegradation reactions. WS-BrC and WI-BrC were estimated to account for <span class="inline-formula">0.83±0.23</span>&thinsp;% and <span class="inline-formula">0.53±0.33</span>&thinsp;%, respectively, of the total down-welling solar radiation in the ultraviolet (UV) range in summer, and <span class="inline-formula">1.67±0.72</span>&thinsp;% and <span class="inline-formula">2.07±1.24</span>&thinsp;%, respectively, in winter. The total absorption by BrC in the UV region was about 55&thinsp;%–79&thinsp;% relative to the elemental carbon (EC) absorption.</p>
url https://www.atmos-chem-phys.net/20/4889/2020/acp-20-4889-2020.pdf
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spelling doaj-56b92ff34a744e81aa502d9cb41b732e2020-11-25T03:26:00ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242020-04-01204889490410.5194/acp-20-4889-2020Optical properties and molecular compositions of water-soluble and water-insoluble brown carbon (BrC) aerosols in northwest ChinaJ. Li0J. Li1Q. Zhang2G. Wang3G. Wang4G. Wang5J. Li6C. Wu7C. Wu8L. Liu9J. Wang10J. Wang11W. Jiang12L. Li13L. Li14K. F. Ho15K. F. Ho16J. Cao17Key Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, ChinaDepartment of Environmental Toxicology, University of California, Davis, CA 95616, USADepartment of Environmental Toxicology, University of California, Davis, CA 95616, USAKey Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, ChinaKey Laboratory of Geographic Information Science of the Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai 200241, ChinaInstitute of Eco-Chongming, 3663 N. Zhongshan Rd., Shanghai 200062, ChinaKey Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, ChinaKey Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, ChinaKey Laboratory of Geographic Information Science of the Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai 200241, ChinaKey Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, ChinaKey Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, ChinaDepartment of Environmental Toxicology, University of California, Davis, CA 95616, USADepartment of Environmental Toxicology, University of California, Davis, CA 95616, USAKey Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, ChinaDepartment of Environmental Toxicology, University of California, Davis, CA 95616, USAKey Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, ChinaThe Jockey Club School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, ChinaKey Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China<p>Brown carbon (BrC) contributes significantly to aerosol light absorption and thus can affect the Earth's radiation balance and atmospheric photochemical processes. In this study, we examined the light absorption properties and molecular compositions of water-soluble (WS-BrC) and water-insoluble (WI-BrC) BrC in PM<span class="inline-formula"><sub>2.5</sub></span> collected from a rural site in the Guanzhong Basin – a highly polluted region in northwest China. Both WS-BrC and WI-BrC showed elevated light absorption coefficients (Abs) in winter (4–7 times those in summer) mainly attributed to enhanced emissions from residential biomass burning (BB) for heating of homes. While the average mass absorption coefficients (MACs) at 365&thinsp;nm (MAC<span class="inline-formula"><sub>365</sub></span>) of WS-BrC were similar between daytime and nighttime in summer (<span class="inline-formula">0.99±0.17</span> and <span class="inline-formula">1.01±0.18</span>&thinsp;m<span class="inline-formula"><sup>2</sup></span>&thinsp;g<span class="inline-formula"><sup>−1</sup></span>, respectively), the average MAC<span class="inline-formula"><sub>365</sub></span> of WI-BrC was more than a factor of 2 higher during daytime (<span class="inline-formula">2.45±1.14</span>&thinsp;m<span class="inline-formula"><sup>2</sup></span>&thinsp;g<span class="inline-formula"><sup>−1</sup></span>) than at night (<span class="inline-formula">1.18±0.36</span>&thinsp;m<span class="inline-formula"><sup>2</sup></span>&thinsp;g<span class="inline-formula"><sup>−1</sup></span>). This difference was partly attributed to enhanced photochemical formation of WI-BrC species, such as oxygenated polycyclic aromatic hydrocarbons (OPAHs). In contrast, the MACs of WS-BrC and WI-BrC were generally similar in winter and both showed few diel differences. The Abs of wintertime WS-BrC correlated strongly with relative humidity, sulfate and <span class="inline-formula">NO<sub>2</sub></span>, suggesting that aqueous-phase reaction is an important pathway for secondary BrC formation during the winter season in northwest China. Nitrophenols on average contributed <span class="inline-formula">2.44±1.78</span>&thinsp;% of the Abs of WS-BrC in winter but only <span class="inline-formula">0.12±0.03</span>&thinsp;% in summer due to faster photodegradation reactions. WS-BrC and WI-BrC were estimated to account for <span class="inline-formula">0.83±0.23</span>&thinsp;% and <span class="inline-formula">0.53±0.33</span>&thinsp;%, respectively, of the total down-welling solar radiation in the ultraviolet (UV) range in summer, and <span class="inline-formula">1.67±0.72</span>&thinsp;% and <span class="inline-formula">2.07±1.24</span>&thinsp;%, respectively, in winter. The total absorption by BrC in the UV region was about 55&thinsp;%–79&thinsp;% relative to the elemental carbon (EC) absorption.</p>https://www.atmos-chem-phys.net/20/4889/2020/acp-20-4889-2020.pdf