Change in aerosol optical depth in Chinese urban agglomerations during the early phase of dual-carbon actions

Abstract

Dual-carbon policies were implemented by Chinese government to mitigate climate warming; however, changes in aerosol optical depth (AOD) during early phases of these actions (2020-2022) remain unclear. Thus, AOD variations during this period were investigated compared to the baseline (2015-2019 mean) across seven urban agglomerations (UAs) using multi-source data. Significant temporal variations in AOD anomalies (ΔAOD) were observed at annual and seasonal scales, with varying magnitudes. On average, AOD decrease by -0.210, -0.225, -0.180, and -0.038 in Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD), Guanzhong Plain (GZP), and Liaozhongnan (LZN), respectively. In contrast, increases of 0.041 and 0.057 were observed in Pearl River Delta (PRD) and Tianshan Mountains northern foothills (TSBP), while Lhasa metropolitan area (LS) remain stable (0.0001). In 2021, the most significant decrease in AOD was recorded in YRD, whereas the greatest declines in other urban areas were noted in 2022. The largest ΔAOD in LZN, BTH, and YRD occurred in autumn, while the peak ΔAOD in GZP was observed in spring. In contrast, the highest ΔAOD in PRD, TSBP, and LS occurred in summer. These temporal variations in ΔAOD can be attributed to dual-carbon policies, natural and meteorological anomalies, along with the impacts of stringent lockdown policies and abrupt dust events. Path analysis indicated that the effects of various drivers on ΔAOD were interconnected. When interactions among these factors were considered, their influences on ΔAOD were found to be either amplified or altered, highlighting the importance of accounting for interactions within the human-nature-meteorological system in formulation of atmospheric pollution policies. These findings contribute to a deeper understanding of ΔAOD variation mechanisms and provide valuable insights for the development of air pollution reduction strategies at the UA scale.