Light absorption enhancement of black carbon and its impact factors during winter in a megacity of the Sichuan Basin, China

• Published in: The Science of the total environment Vol. 918; p. 170374
• Main Authors: Lan, Yuting, Zhou, Li, Liu, Song, Wan, Ruilin, Wang, Ning, Chen, Dongyang, Li, Yi, Jiang, Yan, Rao, Zhihan, Jiang, Wanting, Song, Danlin, Tan, Qinwen, Yang, Fumo
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 25.03.2024
• Subjects: absorption; aerosols; air pollution control; basins; Black carbon coating; carbon; Carbonaceous aerosols; China; cities; climate; environment; environmental quality; Light absorption enhancement; Mixing state; nitrates; particle size distribution; particulate emissions; particulates; PM2.5; shrinkage; Sichuan basin; wavelengths; winter; China; Light absorption enhancement; Sichuan basin; Mixing state; Carbonaceous aerosols; PM2.5; Black carbon coating; PM(2.5)
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.170374

Carbonaceous aerosols play a vital role in global climate patterns due to their potent light absorption capabilities. However, the light absorption enhancement effect (Eabs) of black carbon (BC) is still subject to great uncertainties due to factors such as the mixing state, coating material, and particle size distribution. In this study, fine particulate matter (PM2.5) samples were collected in Chengdu, a megacity in the Sichuan Basin, during the winter of 2020 and 2021. The chemical components of PM2.5 and the light absorption properties of BC were investigated. The results revealed that secondary inorganic aerosols and carbonaceous aerosols were the dominant components in PM2.5. Additionally, the aerosol filter filtration-dissolution (AFD) treatment could improve the accuracy of measuring elemental carbon (EC) through thermal/optical analysis. During winter in Chengdu, the absorption enhancement values of BC ranged between 1.56 and 2.27, depending on the absorption wavelength and the mixing state of BC and non-BC materials. The presence of internally mixed BC and non-BC materials significantly contributed to Eabs, accounting for an average of 68 % at 405 nm and 100 % at 635 nm. The thickness of the BC coating influenced Eabs, displaying an increasing-then-decreasing trend. This trend was primarily attributed to the hygroscopic growth and dehydration shrinkage of particulate matter. Nitrate, as the major component of BC coating, played a crucial role in the lensing effect and exhibited fast growth during variation in Eabs. By combining the results from PMF, we identified the secondary formation and vehicle emission as the primary contributors to Eabs. Consequently, this study can provide valuable insights into the optical parameters, which are essential for assessing the environmental quality, improving regional atmospheric conditions, and formulating effective air pollution control strategies. [Display omitted] •Using a thermal/optical carbon analyzer would underestimate around 16 % of EC.•Eabs ranges from 1.56 to 2.27 across 405–980 nm during winter in Chengdu.•Internal mixing and lensing effect dominate Eabs at wavelengths >635 nm.•Secondary formation and vehicle emission contribute the most to Eabs.