09 Oct 2023
 | 09 Oct 2023

An observation-constrained estimation of brown carbon aerosol direct radiative effects

Yueyue Cheng, Chao Liu, Jiandong Wang, Jiaping Wang, Dafeng Ge, Caijun Zhu, Jinbo Wang, and Aijun Ding

Abstract. Brown carbon (BrC) is an organic carbon component with noticeable absorption in the ultraviolet and short visible wavelengths, which influences the global radiative balance. However, the assessment of BrC radiative effects remains a challenging task because of the scarcity of direct BrC observations and uncertainties in their chemical and optical properties. This study proposes a convenient method for estimating BrC radiative effects based on concise observational data. The light-absorbing properties of BrC obtained from aethalometer measurements and an optical separation method were combined with the simulated BrC optical properties to determine their mass concentrations. The aerosol optical depth (AOD) and mass concentration of PM10 were used to constrain the total and other aerosol contents, and the optical properties and concentrations were estimated using an optical closure study. Such a state-of-the-art combination of measurements and numerical models provides the primary variables for radiative transfer simulations to estimate the BrC radiative effects. We use observations over four months (from July 1 to November 18, 2021) in Nanjing (a megacity in East China) as an example. During the observational period, BrC absorption constitutes 8.7–34.1 % of the total aerosol absorption at 370 nm. In the atmosphere, BrC plays a warming role with its average instantaneous radiative forcing (RF) and standard deviation of 6.4 ± 3.4 W m-2, 29.2 % that of black carbon (BC). At the surface, the BrC-induced actinic flux (AF) attenuation was comparable to that caused by BC, accounting for over 40 % of BC effects in the UV range and almost 20 % in the visible range. Furthermore, the photosynthetically active radiation (PAR) caused by BrC is about 34.7 ± 9.7 % that caused by BC. These findings provide valuable insights into the understanding of BrC radiative effects and indicate the importance and necessity of better observation and modeling of BrC properties.

Yueyue Cheng 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 egusphere-2023-2122', Anonymous Referee #1, 03 Nov 2023
  • RC2: 'Comment on egusphere-2023-2122', Anonymous Referee #2, 01 Dec 2023

Yueyue Cheng et al.

Yueyue Cheng et al.


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Short summary
Brown carbon (BrC) is an important light-absorbing aerosol influencing the climate change. This study develops a BrC radiative forcing estimation method by a combination of conventional observations and numerical models. We find BrC absorption at 370 nm can be comparable to that of black carbon, and its influences on the radiative forcing, actinic flux and photosynthetically active radiation are unignorable.