Preprints
https://doi.org/10.5194/acp-2022-483
https://doi.org/10.5194/acp-2022-483
 
18 Jul 2022
18 Jul 2022
Status: this preprint is currently under review for the journal ACP.

Concurrent photochemical whitening and darkening of ambient brown carbon

Qian Li1, Dantong Liu1, Xiaotong Jiang1, Ping Tian2, Yangzhou Wu1, Siyuan Li1, Kang Hu1, Quan Liu3, Mengyu Huang2, Ruijie Li2, Kai Bi2, Shaofei Kong4, and Deping Ding2 Qian Li et al.
  • 1Department of Atmospheric Science, School of Earth Science, Zhejiang University, Hangzhou, 310027, China
  • 2Beijing Key Laboratory of Cloud, Precipitation and Atmospheric Water Resources, Beijing Meteorological Service, Beijing, 100089, China
  • 3State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing, 100081, China
  • 4Department of Atmospheric Science, School of Environmental Science, China University of Geosciences, Wuhan, 430074, China

Abstract. The light-absorbing organic aerosol (OA), known as brown carbon (BrC), has important radiative impacts, however its sources and evolution after emission remain to be elucidated. In this study, the light absorption at multiple wavelengths, mass spectra of OA and microphysical properties of black carbon (BC) were characterized at a typical sub-urban environment in Beijing. The absorption of BC is constrained by its size distribution and mixing state, being subtracted from total absorption to obtain the absorption of BrC, then by applying the least-correlation of BC absorption with secondary BrC, the absorption contributed by BC, primary BrC and secondary BrC was apportioned. The multi-linear regression analysis on the factorized OA mass spectra indicated the OA from traffic and biomass burning emission contributed to primary BrC. Importantly, the moderately oxygenated OA (O/C=0.62) was revealed to highly correlate with secondary BrC. These OA had higher nitrogen content, in line with the nitrogen-containing functional groups detected by the Fourier transform infrared spectrometer. The photooxidation was found to result in reduced contribution of primary BrC about 20 % but enhanced contribution of secondary BrC by 30 %, implying the concurrent whitening and darkening of BrC. This provides field evidence that the photochemically produced secondary nitrogen-containing OA can considerably compensate some bleaching effect on the primary BrC, hereby causing radiative impacts.

Qian Li et al.

Status: open (until 31 Aug 2022)

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Qian Li et al.

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Short summary
By attributing the shortwave absorption from black carbon, primary and secondary organic aerosol in a sub-urban environment, we firstly observed the photochemically produced nitrogen-containing secondary organic aerosol may contribute to the enhancement of brown carbon absorption, partly compensating some bleaching effect on the absorption of primary organic aerosol, hereby exerting radiative impacts.
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