Evolution of water-soluble organic carbon in neglected coal dust particles influenced by ozone aging

Abstract. Coal mining and utilization generate substantial amounts of coal dust, of which the portion in fine particles can travel long distances and further impact climate and air quality through atmospheric aging processes. However, the evolutionary behavior of water-soluble organic carbon (WSOC) in fine coal dust remains unclear. In this study, the aging of coal dust particles and their WSOC processed by ozone (O₃) under dark conditions was investigated in a flow tube reactor. Results show that O₃ aging significantly enhanced the hydrophilicity, light absorption, and fluorescence intensity of WSOC. During the aging process, both carbon loss and gain were observed in WSOC, with the amount of carbon gain exceeding lost through the generation of volatile species. Although the mass absorption efficiency (MAE₃₆₅) of fresh WSOC was initially low, the O₃ aging process significantly increased the MAE₃₆₅ of WSOC by a factor of 8.8 to 18.2 through the formation of strongly absorbing hydrophilic conjugated compounds. The radiative forcing of WSOC may be underestimated if WSOC absorption linked to atmospheric aging is not accounted for in models. These findings suggest that the long-term O₃ aging effect on coal dust may become prevalent in the background of the complex atmospheric particulate matter and O₃ pollution in China, policymakers should reconsider air quality improvement strategies.