18 Jul 2022
 | 18 Jul 2022
Status: a revised version of this preprint is currently under review for the journal ACP.

Concurrent photochemical whitening and darkening of ambient brown carbon

Qian Li, Dantong Liu, Xiaotong Jiang, Ping Tian, Yangzhou Wu, Siyuan Li, Kang Hu, Quan Liu, Mengyu Huang, Ruijie Li, Kai Bi, Shaofei Kong, and Deping Ding

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: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-483', Anonymous Referee #1, 28 Aug 2022
    • AC1: 'Reply on RC1', Dantong Liu, 20 Oct 2022
  • RC2: 'Comment on acp-2022-483', Anonymous Referee #2, 31 Aug 2022
    • AC2: 'Reply on RC2', Dantong Liu, 20 Oct 2022

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.