Evolution of aerosol optical depth over China in 2010–2024: increasing importance of meteorological influences

Abstract. Time series of Collection 6.1 of the MODerate resolution Imaging Spectroradiometer Multi-Angle Implementation of Atmospheric Correction (MODIS/MAIAC C6.1) aerosol optical depth (AOD) and model-simulated AOD were used to determine the contributions of meteorological and anthropogenic effects to spatiotemporal AOD variations over five representative areas in China during the period from January 2010 to September 2024. The time series confirm the effective reduction in AOD between 2010 and 2018, with an additional but smaller reduction thereafter. The overall AOD reduction is mainly attributable to emission reduction policies, although with substantial meteorological effects. The respective total reduction and meteorological contributions during the whole study period and the meteorological contributions before and after 2018 over the five regions were as follows (all in %): 68, 12, 16, and 52 for the North China Plain (NCP); 62, 17, 28, and 14 for the Yangtze River Delta (YRD); 70, 33, 31, and 43 for the Pearl River Delta (PRD); 55, 16, 25, and 21 for Hunan and Hubei (HNB); and 57, 10, 14, and 38 for the Sichuan Basin (SCB). Meteorological effects for each of these periods and each region are discussed in detail. As an example, the above data show that the meteorological effects over the YRD and HNB after 2018 are smaller than before 2018; this can be explained by the occurrence of strong effects in the earlier period and the choice of the period over which effects were calculated. Monthly mean AOD patterns were distinctly different before and after 2016, suggesting that aerosol properties changed in response to the emission reduction policies. In summary, this study highlights the complex interplay between meteorological and anthropogenic factors in shaping AOD variations across China and demonstrates the increasing significance of meteorological conditions in modulating China's AOD.