Characterization of water-soluble brown carbon in atmospheric fine particles over Xi'an, China: Implication of aqueous brown carbon formation from biomass burning

Yali Lei; Ke Zhang; Yeyu Lu; Yiming Qin; Lijuan Li; Jianjun Li; Xiaodi Liu; Can Wu; Si Zhang; Yubao Chen; Junke Zhang; Fan Zhang; Gehui Wang

doi:10.1016/j.scitotenv.2023.163442

Characterization of water-soluble brown carbon in atmospheric fine particles over Xi'an, China: Implication of aqueous brown carbon formation from biomass burning

Sci Total Environ. 2023 Jul 10:881:163442. doi: 10.1016/j.scitotenv.2023.163442. Epub 2023 Apr 12.

Authors

Yali Lei¹, Ke Zhang¹, Yeyu Lu¹, Yiming Qin², Lijuan Li³, Jianjun Li³, Xiaodi Liu¹, Can Wu¹, Si Zhang¹, Yubao Chen¹, Junke Zhang⁴, Fan Zhang¹, Gehui Wang⁵

Affiliations

¹ Key Lab of Geographic Information Science of the Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai 200241, China.
² Department of Chemistry, University of California, Irvine, CA 92697-2025, USA.
³ State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China.
⁴ Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Chengdu 611756, China.
⁵ Key Lab of Geographic Information Science of the Ministry of Education, School of Geographic Sciences, East China Normal University, Shanghai 200241, China; Institute of Eco-Chongming, East China Normal University, Shanghai 202162, China. Electronic address: ghwang@geo.ecnu.edu.cn.

PMID: 37059143
DOI: 10.1016/j.scitotenv.2023.163442

Abstract

Brown carbon (BrC) aerosols can affect not only the climate but also human health, however, the light absorption, chemical compositions, and formation mechanisms of BrC are still uncertain, which leads to uncertainties in the accurate estimation of its climate and health impacts. In this study, highly time - resolved brown carbon (BrC) in fine particles was investigated in Xi'an using offline aerosol mass spectrometer analysis. The light absorption coefficient (b_abs365) and mass absorption efficiency (MAE₃₆₅) at 365 nm of water-soluble organic aerosol (WSOA) generally increased with oxygen-to-carbon (O/C) ratios, indicating that oxidized OA could have more impacts on BrC light absorption. Meanwhile, the light absorption appeared to increase generally with the increases of nitrogen-to-carbon (N/C) ratios and water-soluble organic nitrogen; strong correlations (R of 0.76 for C_xH_yN_p⁺ and R of 0.78 for C_xH_yO_zN_p⁺) between b_abs365 and the N - containing organic ion families were observed, suggesting that the N - containing compounds are the effective BrC chromophores. b_abs365 correlated relatively well with BBOA (r of 0.74) and OOA (R of 0.57), but weakly correlated with CCOA (R of 0.33), indicating that BrC in Xi'an was likely to be associated with biomass burning and secondary sources. A multiple linear regression model was applied to apportion b_abs365 to contributions of different factors resolved from positive matrix factorization on water-soluble organic aerosols (OA) and obtained MAE₃₆₅ values of different OA factors. We found that biomass-burning organic aerosol (BBOA) dominated the b_abs365 (48.3 %), followed by oxidized organic aerosol (OOA, 33.6 %) and coal combustion organic aerosol (CCOA, 18.1 %). We further observed that nitrogen-containing organic matter (i.e., C_xH_yN_p⁺ and C_xH_yO_zN_p⁺) increased with the increase of OOA/WSOA and the decrease of BBOA/WSOA, especially under high ALWC conditions. Our work offered proper observation evidence that BBOA is oxidized through the aqueous formation to produce BrC in Xi'an, China.

Keywords: Aqueous formation; Brown carbon; Light absorption; Sources; Xi'an.