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https://doi.org/10.5194/egusphere-2024-891
https://doi.org/10.5194/egusphere-2024-891
15 Apr 2024
 | 15 Apr 2024

Measurement report: Formation of tropospheric brown carbon in a lifting air mass

Can Wu, Xiaodi Liu, Ke Zhang, Si Zhang, Cong Cao, Jianjun Li, Rui Li, Fan Zhang, and Gehui Wang

Abstract. An enhanced formation of brown carbon (BrC) with a non-negligible warming effect at the tropopause has recently been found. However, its formation mechanism is unclear. Here we report a BrC formation process that happens during air mass upward transport by conducting simultaneously a 4-hour time resolution of measurement on atmospheric BrC at the mountain foot (MF, 400 m a.s.l.) and mountainside (MS, 1120 m a.s.l.) of Mt. Hua, China in 2016 summer. Our results showed that the daytime light-absorption (Abs365nm) of BrC at MS is approximately 60 % lower than that at MF due to a dilution effect caused by the planetary boundary layer expansion, but the daytime light-absorption of BrC relative to black carbon at MS is about 30 % higher than that at MF, suggesting a significant formation of secondary BrC in the lifting process of air mass from MF to MS. Such a secondary formation accounted for >50 % of BrC at MS but only 27 % of BrC at MF. Moreover, N:C elemental ratio of the daytime BrC was 15 % higher at MS than that at MF, mainly due to an aerosol aqueous phase formation of water-soluble organic nitrogen (WSON) compounds. Stable nitrogen isotope composition further indicated that such light-absorbing WSON compounds were produced from the aerosol aqueous-phase reaction of carbonyls with NH4+. Our work for the first time revealed that ammonia -induced aerosol aqueous reactions can significantly promote BrC formation during the air mass lifting process, which is probably responsible for an enhanced light absorption of BrC in the upper troposphere.

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Can Wu, Xiaodi Liu, Ke Zhang, Si Zhang, Cong Cao, Jianjun Li, Rui Li, Fan Zhang, and Gehui Wang

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-891', Anonymous Referee #1, 04 May 2024
  • RC2: 'Comment on egusphere-2024-891', Anonymous Referee #2, 07 May 2024
  • RC3: 'Comment on egusphere-2024-891', Anonymous Referee #3, 08 May 2024
Can Wu, Xiaodi Liu, Ke Zhang, Si Zhang, Cong Cao, Jianjun Li, Rui Li, Fan Zhang, and Gehui Wang

Data sets

C. Wu Observation of Brown carbon and its optical properties on Mt. Hua https://doi.org/10.5281/zenodo.10926469

Synchronous observation of aerosol at Mt. Hua W. Can https://doi.org/10.5281/zenodo.7413640

Can Wu, Xiaodi Liu, Ke Zhang, Si Zhang, Cong Cao, Jianjun Li, Rui Li, Fan Zhang, and Gehui Wang

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Short summary
Brown carbon (BrC) is prevalent in the troposphere, and can efficiently absorb solar and terrestrial radiation. Our observations manifested that the enhanced light-absorption of BrC relative to black carbon at the tropopause can be attributed to the formation of nitrogen-containing organic compounds through the aqueous-phase reactions of carbonyls with ammonium.