Preprints
https://doi.org/10.5194/acp-2021-465
https://doi.org/10.5194/acp-2021-465

  22 Jun 2021

22 Jun 2021

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

Particle size-dependent fluorescence properties of water-soluble organic compounds (WSOC) and their atmospheric implications on the aging of WSOC

Juanjuan Qin1,2, Jihua Tan1, Xueming Zhou1,3, Yanrong Yang1, Yuanyuan Qin1, Xiaobo Wang1, Shaoxuan Shi1, Kang Xiao1, and Xinming Wang2 Juanjuan Qin et al.
  • 1College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, 100049, China
  • 2Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China
  • 3Faculty of Earth Resources, China University of Geosciences, Wuhan, 430074, China

Abstract. Water-soluble organic compounds (WSOC) are essential in atmospheric particle formation, migration, and transformation processes. Size-segregated atmospheric particles were collected in a rural area of Beijing. Excitation-emission matrix (EEM) fluorescence spectroscopy was used to investigate the sources and optical properties of WSOC. Sophisticated data analysis on EEM data was performed to characteristically estimate the underlying connections among aerosol particles in different sizes. The WSOC concentrations and average fluorescence intensity (AFI) showed monomodal distribution in winter and bimodal distribution in summer, with dominant mode between 0.26 to 0.44 µm for both seasons. The EEM spectra of size-segregated WSOC were different among variant particle sizes, which could be the results of changing sources and/or chemical transformation of organics. Size distributions of fluorescence regional intensity (region Ⅲ and Ⅴ) and HIX indicate that humification degree or aromaticity of WSOC was highest between 0.26 to 0.44 µm. The Stokes shift (SS) and the harmonic mean of the excitation and emission wavelengths (WH) reflected that π-conjugated systems were high between 0.26 to 0.44 µm as well. The parallel factor analysis (PARAFAC) results showed that humic-like substances were abundant in fine particles (< 1 µm) and peaked at 0.26–0.44 µm. All evidence supported that the humification degree of WSOC increased in submicron mode (< 0.44 µm) and decreased gradually. Thus, it was conjectured that condensation of organics still goes on in submicron mode, resulting in the highest humification degree exhibit in particle size between 0.26 to 0.44 µm rather than < 0.26 µm. Synthetically analyzing 3-dimensional fluorescence data could efficiently present the secondary transformation processes of WSOC.

Juanjuan Qin et al.

Status: open (until 12 Aug 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-465', Anonymous Referee #1, 12 Jul 2021 reply
  • RC2: 'Comment on acp-2021-465', Anonymous Referee #2, 28 Jul 2021 reply

Juanjuan Qin et al.

Juanjuan Qin et al.

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Short summary
1. The Excitation-Emission Matrix spectra exhibit macroscopical variation with particle size increase, fluorescence intensity peaked at 0.26–0.44 µm. 2. The aromaticity and humification degree were highest between 0.26 to 0.44 µm. 3. The condensation of organics might occur in submicron particles (< 0.44) and oxidized gradually. 4. Humic-like substances were rich in fine particles and protein-like substances were high in the coarse mode.
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