Preprints
https://doi.org/10.5194/acp-2023-4
https://doi.org/10.5194/acp-2023-4
02 Mar 2023
 | 02 Mar 2023
Status: a revised version of this preprint is currently under review for the journal ACP.

Measurement report: Brown Carbon Aerosol in Polluted Urban Air of North China Plain: Day-night Differences in the Chromophores and Optical Properties  

Yuquan Gong, Ru-Jin Huang, Lu Yang, Ting Wang, Wei Yuan, Wei Xu, Wenjuan Cao, Yang Wang, and Yongjie Li

Abstract. Brown carbon (BrC) aerosol is light-absorbing organic carbon that affects radiative forcing and atmospheric photochemistry. The BrC chromophoric composition and its linkage to optical properties at the molecular level, however, are still not well characterized. In this study, we investigate the day-night differences in the chromophoric composition (38 species) and optical properties of water-soluble and water-insoluble BrC fractions (WS-BrC and WIS-BrC) in aerosol samples collected in Shijiazhuang, one of the most polluted cities in China. We found that the light absorption contribution of WS-BrC to total BrC at 365 nm was higher during the day (62 ± 8 %) than during the night (47 ± 26 %), which is in line with the difference in chromophoric polarity between daytime (more polar nitrated aromatics) and nighttime (more less-polar polycyclic aromatic hydrocarbons, PAHs). The high polarity and water solubility of BrC in daytime suggests the enhanced contribution of secondary formation to BrC during the day. There was a decrease of the mass absorption efficiency of BrC from nighttime to daytime (2.88 ± 0.24 vs. 2.58 ± 0.14 for WS-BrC and 1.43 ± 0.83 vs. 1.02 ± 0.49 m2 gC-1 for WIS-BrC, respectively). Large polycyclic aromatic hydrocarbons (PAHs) with 4–6-rings PAHs and nitrophenols contributed to 76.7 % of the total light absorption between 300–420 nm at night time, while nitrocatechols and 2–3-ring oxygenated PAHs accounted for 52.6 % of the total light absorption at day. The total mass concentrations of the identified chromophores showed larger day-night difference during the low-pollution period (day-to-night ratio of 4.3) than during the high-pollution period (day-to-night ratio of 1.8). The large day-night difference in BrC composition and absorption, therefore, should be considered when estimating the sources, atmospheric processes and impacts of BrC.

Yuquan Gong 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-2023-4', Anonymous Referee #3, 06 Jun 2023
  • RC2: 'Comment on acp-2023-4', Anonymous Referee #1, 11 Jun 2023
  • AC1: 'Comment on acp-2023-4', Ru-Jin Huang, 21 Jul 2023

Yuquan Gong et al.

Data sets

Measurement report: Brown Carbon Aerosol in Polluted Urban Air of North China Plain: Day-night Differences in the Chromophores and Optical Properties Yuquan Gong, Ru-Jin Huang, Lu Yang, Ting Wang, Wei Yuan, Wei Xu, Wenjuan Cao, Yang Wang, and Yongjie Li https://doi.org/10.5281/zenodo.7690230

Yuquan Gong et al.

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Short summary
This study reveals the large day-night differences in BrC chromophores composition, which has far from been known previously. The results provide insights into the effects of atmospheric processes and emissions on BrC composition.
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