Response of dissolved organic carbon in rainwater during extreme rainfall period in megacity: Status, potential source, and deposition flux

Abstract

Air pollution and related wet deposition process (rainfall) caused environmental hazards under the climate change, particularly in urban regions, attracting global concern and challenges. Atmospheric dissolved organic carbon (DOC) deposition is not only the major removal pathway of OC from atmosphere, but also a significant influence factor of urban haze pollution and local climate. Although the significance of DOC deposition to carbon budgets is confirmed, the extreme rainfall influenced OC transfers from the atmosphere to land is poorly understood. This study systematically investigated the rainwater DOC in Beijing during the extreme rainfall period of 2021 to explore its status, source, and flux. The results showed that the rainwater DOC concentration level is close to the Asian and global mean level, while the DOC deposition flux was relatively high due to high rainfall amount and rainfall scouring, and the overall declined trend of DOC concentrations was identified. Source identification revealed that human OC emissions (municipal wastes, agricultural and traffic emission) are the primary sources of DOC, whereas ocean and crust source contributed negligibly. This research clarified the extreme rainfall-driven rainwater DOC dynamics in a megacity and supported the evaluation of global carbon budgets.