Preprints
https://doi.org/10.5194/egusphere-2022-585
https://doi.org/10.5194/egusphere-2022-585
 
06 Sep 2022
06 Sep 2022
Status: this preprint is open for discussion.

Winter brown carbon over six China’s megacities: Light absorption, molecular characterization, and improved source apportionment revealed by multilayer perceptron neural network

Diwei Wang1, Zhenxing Shen1, Qian Zhang2, Yali Lei3, Tian Zhang1, Shasha Huang1, Jian Sun1, Hongmei Xu1, and Junji Cao4 Diwei Wang et al.
  • 1Department of Environmental Science and Engineering, Xi’an Jiaotong University, Xi’an 710049, China
  • 2Key Laboratory of Northwest Resource, Environment and Ecology, MOE, Xi’an University of Architecture and Technology, Xi’an 710055, China
  • 3Key Lab of Geographic Information Science of the Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai 200241, China
  • 4Key Lab of Aerosol Chemistry & Physics, SKLLQG, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, China

Abstract. Brown carbon (BrC) constitutes a large fraction of organic carbon and exhibits strong light absorption properties, thus affecting the global radiation budget. In this study, we investigated the light absorption properties, chemical functional bonds, and sources of BrC in six megacities in China, namely Beijing, Harbin, Xi’an, Chengdu, Guangzhou, and Wuhan. The average values of the BrC light absorption coefficient and the mass absorption efficiency at 365 nm in northern cities were higher than those in southern cities by 2.5 and 1.8 times, respectively, demonstrating the occurrence of abundance of BrC in northern China’s megacities. Fourier transform–infrared (FT-IR) spectra revealed sharp and intense peaks at 1640, 1458–1385, and 1090–1030 cm−1, which were ascribed to aromatic phenols, confirming the contribution of primary emission sources (e.g., biomass burning and coal combustion) to BrC. In addition, we noted peaks at 860, 1280–1260, and 1640 cm−1, which were attributed to organonitrate and oxygenated phenolic groups, indicating that secondary BrC also existed in six megacities. Positive matrix factorization (PMF) coupled with multilayer perceptron (MLP) neural network analysis were used to apportion the sources of BrC light absorption. The results showed that primary emissions (e.g., biomass burning, tailpipe emissions, and coal combustion) made a major contribution to BrC in six megacities. However, secondary formation processes made a greater contribution to light absorption in the southern cities (17.9 %–21.2 %) than in the northern cities (2.1 %–10.2 %). These results can provide a basis for the more effective control of BrC to reduce its impacts on regional climates and human health.

Diwei Wang et al.

Status: open (until 18 Oct 2022)

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  • RC1: 'Comment on egusphere-2022-585', Anonymous Referee #2, 20 Sep 2022 reply
  • RC2: 'Comment on egusphere-2022-585', Anonymous Referee #1, 26 Sep 2022 reply

Diwei Wang et al.

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Winter brown carbon over six China's megacities: Light absorption, molecular characterization, and improved source apportionment revealed by multilayer perceptron neural network Wang Diwei https://doi.org/10.5281/zenodo.6790321

Diwei Wang et al.

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Short summary
The optical properties and molecular structure of atmospheric brown carbon (BrC) in winter of several megacities in China were analyzed, and the source contribution of brown carbon was improved by using positive matrix factorization coupled with multilayer perceptron neural network. These results can provide a basis for the more effective control of BrC to reduce its impacts on regional climates and human health.