09 Apr 2021

09 Apr 2021

Review status: this preprint is currently under review for the journal ACP.

Measurement report: Long emission-wavelength chromophores dominate the light absorption of brown carbon in Aerosols over Bangkok: impact from biomass burning

Jiao Tang1,2,3, Jiaqi Wang1,2,3,7, Guangcai Zhong1,2,3, Hongxing Jiang1,2,3,7, Yangzhi Mo1,2,3, Bolong Zhang1,2,3,7, Xiaofei Geng1,2,3,7, Yingjun Chen4, Jianhui Tang5, Congguo Tian5, Surat Bualert6, Jun Li1,2,3, and Gan Zhang1,2,3 Jiao Tang et al.
  • 1State Key Laboratory of Organic Geochemistry and Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
  • 2CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640, China
  • 3Joint Laboratory of the Guangdong-Hong Kong-Macao Greater Bay Area for the Environment, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
  • 4Department of Environmental Science and Engineering, Fudan University, Shanghai 200092, P.R. China
  • 5Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai 264003, China
  • 6Faculty of Environment, Kasetsart University, Bangkok, 10900, Thailand
  • 7University of Chinese Academy of Sciences, Beijing 100049, China

Abstract. Chromophores represent an important portion of light-absorbing species, i.e. brown carbon. Yet knowledge on what and how chromophores contribute to aerosol light absorption is still sparse. To address this problem, we examined soluble independent chromophores in a set of year-round aerosol samples from Bangkok. The water-soluble chromophores identified via excitation-emission matrix (EEM) spectroscopy and follow-up parallel factor analysis could be mainly assigned as humic-like substances and protein-like substances, which differed in their EEM pattern from that of the methanol-soluble fraction. The emission wavelength of chromophores in environmental samples tended to increase compared with that of the primary combustion emission, which could be attributed to secondary formation or the aging process. Fluorescent indices inferred that these light-absorbing chromophores were not significantly humified and comprised a mixture of organic matter of terrestrial and microbial origin, while these inferences exhibited a refutation with primary biomass burning and coal combustion results. A multiple linear regression analysis revealed that larger chromophores that were oxygen-rich and highly aromatic with high molecular weights, were the key contributors of light absorption, preferably at longer emission wavelength (λmax > 500 nm). Positive matrix factorization analysis further suggested that up to 60 % of these responsible chromophores originated from biomass burning emissions.

Jiao Tang et al.

Status: open (until 04 Jun 2021)

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Jiao Tang et al.


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Short summary
This article provides a combining EEM-PARAFAC and statistical analyses method to explore how the EEM chromophores influence BrC light absorption in soluble organic matter. The application enables us to deduce that the BrC absorption is mainly dependent on the longer emission-wavelength chromophores that were largely associated with biomass burning emissions. This method promotes the application of EEM spectroscopy and helps for understanding the light absorption of BrC in the atmosphere.