Meteorological and anthropogenic contributions to changes in the Aerosol Optical Depth (AOD) over China during the last decade.

To reduce air pollution over China, a series of measures to decrease concentrations of aerosols and trace gases has been implemented during the last two decades. The effects of these measures on aerosol concentrations, represented here by satellite-retrieved Aerosol Optical Depth (AOD), were evaluated by comparison of observed AOD time series from 2010 to 2021, over five representative areas, with model simulations using emissions fixed to those in 2010, but with actual meteorological data. Thus, model AOD was only influenced by meteorological conditions and the comparison with satellite AOD allows for the separation of meteorological and anthropogenic contributions to the AOD. The model data shows the influence of meteorological factors on the variation of the AOD, between +10% (unfavorable, leading to AOD increase) and -10% (favorable, leading to AOD decrease). Unfavorable meteorological conditions counteract effects of emission control measures. The satellite data show the occurrence of an AOD maximum in 2014 over three areas due to meteorological effects. The decrease of the AOD, varying between 22% and 40%, is mostly due to anthropogenic effects, but meteorological contributions are substantial and vary between the five focus regions. The satellite and model data also show that during 2017–2021 the AOD reduction flattened and AOD fluctuated within 10% of the average value for these years, with a substantial meteorological contribution. This analysis suggests that the Three-year Action Plan for Clean Air was less effective than the Clean Air Action Plan.