Aerosol Optical Depth over China: effects of Meteorological and Anthropogenic Contributions

<p>The Aerosol Optical Depth (AOD) over China has been increasing from the end of the 20st century due to a multitude of anthropogenic activities contributing to emissions of aerosols and trace gases. The effect of the implementation of a series of policy measures to reduce these emissions is clearly visible in time series of satellite-retrieved AOD. A first maximum was reached in 2007, followed by strong interannual fluctuations until 2011 after which the AOD started to decrease over some provinces in China. However, over many other provinces the AOD decrease did not set in until after 2014. The AOD decrease flattened around 2017/2018 where after it varied within 10%. Clearly, the 2013-2018 Clean Air Action Plan was effective in reducing the AOD, as also shown for PM2.5, but this reduction was not continued during the Three-year Action Plan for Clean Air implemented in 2018. To investigate the reasons for the AOD variation during the last decade, the satellite data were compared with AOD model data simulating only meteorological effects on the AOD. To this end, the model runs were made with emissions fixed to those in 2010, but with actual meteorological data. The model results show that the AOD can change by +10% or -10% due to meteorological influences, the comparison with satellite-derived AOD shows the contributions of anthropogenic effects to the AOD. This study was undertaken over 5 major regions over China, for the years 2010-2022, during which the overall AOD reduction varied between 22% (over the PRD) to 40% over the SCB, with substantial meteorological contributions. The AOD peak in 2014 over part of China was entirely due to meteorological influences. It is recommended to account for meteorological effects to reach the goals of future Action Plans.&#160; &#160; &#160; &#160;</p>