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The light absorption enhancement (E-abs) of black carbon (BC) coated with non-BC materials is crucial in the assessment of radiative forcing, yet its evolution during photochemical aging of plumes from biomass burning, the globe's largest source of BC, remains poorly understood. In this study, plumes from open burning of corn straw were introduced into a smog chamber to explore the evolution of E-abs during photochemical aging. The light absorption of BC was measured with and without coating materials by using a thermodenuder, while the size distributions of aerosols and composition of BC coating materials were also monitored. E-abs was found to increase initially, and then decrease with an overall downward trend. The lensing effect dominated in E-abs at 520 nm, with an estimated contribution percentages of 47.5%-94.5%, which is far greater than light absorption of coated brown carbon (BrC). The effects of thickening and chemical composition changes of the coating materials on E-abs were evaluated through comparing measured E-abs with that calculated by the Mie theory. After OH exposure of 1 x 10(10) molecules cm(-3) s, the thickening of coating materials led to an E-abs increase by 3.2% +/- 1.6%, while the chemical composition changes or photobleaching induced an E-abs decrease by 4.7% +/- 0.6%. Simple forcing estimates indicate that coated BC aerosols exhibit warming effects that were reduced after aging. The oxidation of light-absorbing CxHy compounds, such as polycyclic aromatic hydrocarbons (PAHs), to CxHyO and CxHyO>1 compounds in coating materials may be responsible for the photobleaching of coated BrC. Plain Language Summary Understanding how black carbon (BC) coated with non-BC materials affects light absorption is crucial for assessing its impact on the Earth's climate. However, there is limited knowledge about how this process changes when BC, particularly from biomass burning, is exposed to light. Biomass burning is a significant global source of BC. This study investigated the changes in light absorption of BC from burning corn straw as it aged in a controlled environment. We measured the light absorption of BC with and without its coating materials. Our results showed that the main cause of increased light absorption was the lensing effect of the coating materials, which was more significant than the light absorption by the coating materials themselves. We also discovered that as the coating materials thickened, BC absorbed more light. However, changes in the chemical composition of the coating materials led to a decrease in total absorption. These findings suggest that while coated BC initially has a warming effect on the climate, this effect diminished as the BC ages. The decrease is likely due to the breakdown of light-absorbing compounds in the coating materials, such as polycyclic aromatic hydrocarbons (PAHs).

来源平台：JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES