Brown carbon (BrC) is a part of organic aerosol (OA) and can absorb solar radiation in near-ultraviolet (UV) to visible (Vis) light. It has been widely recognized that BrC has a significant effect on radiative forcing at both regional and global scales. PM2.5 loading in the Tianjin area is extremely high, with a greater abundance of organic matter (OM). In such an environment, BrC is likely to become an important light-absorbing component of atmospheric aerosols.
Professor Chandra Mouli Pavuluri's research group at our institute employed three-dimensional fluorescence spectroscopy and UV-Vis spectroscopy to investigate the optical properties of water-soluble brown carbon (WSBrC) and water-insoluble but methanol-soluble brown carbon (WI-MSBrC) in PM2.5 from Tianjin. This study systematically examined the light absorption properties and direct radiative effects of brown carbon, elucidating the composition, sources, and seasonal variations of its main chromophores.
Figure 1. Temporal variations of the light absorption coefficient of water-soluble brown carbon (BrC) at 365 nm (Abs365(WSBrC)), water insoluble but methanol-soluble BrC (Abs365(WI-MSBrC)) and the mass concentrations of WSOC and WIOC in PM2.5 in Tianjin, North China.
This study revealed significant seasonal variations in the light absorption characteristics of WSBrC and WI-MSBrC, with higher absorption coefficients in autumn and winter due to richer sources of BrC compared to spring and summer. The lower mass absorption efficiency (MAE365) values of WSBrC and WI-MSBrC in summer and autumn could be attributed to biogenic or secondary brown carbon and/or photobleaching. The correlation between the optical properties of BrC and aerosol chemical composition indicated that biomass burning and fossil fuel combustion (primarily coal) significantly influenced winter BrC content, while primary biological emissions and secondary processes played a notable role in summer BrC content. The absorption of light by WSBrC and WI-MSBrC in the 300-400 nm range accounted for approximately 40% of the absorption across the full 300-700 nm range, highlighting the significant role of BrC in climate warming within the UV-Vis spectrum. These results illustrated the light absorption properties of BrC in metropolis aerosols and emphasized its significant contribution to radiative forcing.
This study has recently been published in the Journal “Atmospheric Chemistry and Physics”. The first author of the paper is Dong Zhichao, a Ph.D. student of School of Earth System Science, and the corresponding author is Professor Chandra Mouli Pavuluri. This research has been supported by the National Natural Science Foundation of China (grant nos. 41775120 and 42277090) and the National Key Research and Development Program of China (grant no. 2017YFC0212700).
Citation: Dong, Z., Pavuluri, C. M., Li, P., Xu, Z., Deng, J., Zhao, X., Zhao, X., Fu, P., and Liu, C.-Q.: Measurement report: Optical characterization, seasonality, and sources of brown carbon in fine aerosols from Tianjin, North China: year-round observations, Atmos. Chem. Phys., 2024, 24, 5887–5905. https://doi.org/10.5194/acp-24-5887-2024
