05 Jul 2022
05 Jul 2022
Status: this preprint is currently under review for the journal ACP.

Chromophores and chemical composition of brown carbon characterized at an urban kerbside by excitation-emission spectroscopy and mass spectrometry

Feng Jiang1,2, Junwei Song1,2, Jonas Bauer2, Linyu Gao1,2, Magdalena Vallon1, Reiner Gebhardt3, Thomas Leisner1,4, Stefan Norra2,5, and Harald Saathoff1 Feng Jiang et al.
  • 1Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, 76344 Eggenstein–Leopoldshafen, Germany
  • 2Institute of Applied Geosciences, Working Group for Environmental Mineralogy and Environmental System Analysis, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
  • 3Institute of Geography and Geoecology, Karlsruhe Institute of Technology, Reinhard-Baumeister-Platz 1, 76131 Karlsruhe, Germany
  • 4Institute of Environmental Physics, Heidelberg University, 69120 Heidelberg, Germany
  • 5Institute of Environmental Sciences and Geography, Chair of Soil Science and Geoecology, University of Potsdam, Karl-Liebknecht-Strasse 24 / 25, 14476 Potsdam, Germany

Abstract. The optical properties, chemical composition, and potential chromophores of brown carbon (BrC) aerosol particles were studied during typical summer and winter time at a kerbside in downtown Karlsruhe, a city in central Europe. The average absorption coefficient and mass absorption efficiency at 365 nm (Abs365 and MAE365) of BrC were lower in the summer period (1.6 ± 0.5 Mm-1, 0.5 ± 0.2 m2 g-1) than in the winter period (2.8 ± 1.9 Mm-1, 1.1 ± 0.3 m2 g-1). Using a Parallel factor (PARAFAC) analysis to identify chromophores, two different groups of highly oxygenated humic-like substances (HO-HULIS) dominated in summer and contributed 96 ± 6 % of total fluorescence intensity. In contrast, less oxygenated-HULIS (LO-HULIS) dominated the total fluorescence intensity in winter with 57 ± 12 %, followed by HO-HULIS with 31 ± 18 %. The statistical analysis of AMS data (positive matrix factorization) and Aqualog excitation-emission spectra (parallel factor analysis) showed that the LO-HULIS chromophores are most likely emitted from biomass burning in winter. Less volatile oxygenated organic aerosol shows good correlations (r > 0.7; p < 0.01, respectively) with HO-HULIS components in summer. The LO-HULIS have a negative correlation (r = -0.6, p < 0.01) with O3, which indicates that the LO-HULIS may be depleted by reaction with ozone. In contrast, the HO-HULIS had a positive correlation (r = 0.7, p < 0.01) with O3, indicating that they may result from oxidation reactions.

Five nitro-aromatic compounds (NACs) were identified by CIMS (C7H7O3N, C7H7O4N, C6H5O5N, C6H5O4N, and C6H5O3N) which contributed 0.03 ± 0.01 % to the total organic mass, but can explain 0.3 ± 0.1 % of the total absorption of methanol-extracted BrC at 365 nm in winter. Furthermore, we identified 316 potential brown carbon molecules which accounted for 2.5 ± 0.6 % of the organic aerosol mass. Using an average mass absorption efficiency (MAE365) of 9.5 m2 g-1 for these compounds, we can estimate their mean light absorption to be 1.2 ± 0.2 Mm-1, accounting for 32 ± 15 % of the total absorption of methanol-extracted BrC at 365 nm. The potential BrC molecules assigned to the LO-HULIS component had a higher average molecular weight (265 ± 2 Da) and more nitrogen-containing molecules (62 ± 1%) than the molecules assigned to the HO-HULIS components. Our analysis shows that the LO-HULIS, with a high contribution of nitrogen-containing molecules originating from biomass burning, dominate aerosol fluorescence in winter and HO-HULIS, with less nitrogen-containing molecules from less volatile oxygenated organic aerosol, dominate in summer.

Feng Jiang et al.

Status: open (until 16 Aug 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-465', Anonymous Referee #1, 16 Jul 2022 reply
  • RC2: 'Comment on acp-2022-465', Anonymous Referee #2, 28 Jul 2022 reply
  • RC3: 'Comment on acp-2022-465', Anonymous Referee #3, 29 Jul 2022 reply

Feng Jiang et al.


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Short summary
We studied the brown carbon aerosol during typical summer and winter periods in downtown Karlsruhe, in southwest Germany. The chromophore and chemical composition of brown carbon were determined by excitation-emission spectroscopy and mass spectrometry. The chromophore types and sources were substantially different in winter and summer. Humic-like chromophores of different degrees of oxidation dominated and were associated with molecules of different molecular weight and nitrogen-content.