The control of anthropogenic emissions contributed to 80 % of the decrease in PM_2.5 concentrations in Beijing from 2013 to 2017

With the completion of the Beijing Five-year Clean Air Action Plan by the end of 2017, the annual mean PM_2.5 concentration in Beijing dropped dramatically to 58.0 μgm^-3 in 2017 from 89.5 μgm^-3 in 2013. However, controversies exist to argue that favourable meteorological conditions in 2017 were the major driver for such a rapid decrease in PM_2.5 concentrations. To comprehensively evaluate this 5-year plan, we employed a Kolmogorov-Zurbenko (KZ) filter and WRF-CMAQ (Weather Research and Forecasting and the Community Multi-scale Air Quality) to quantify the relative contribution of meteorological conditions and the control of anthropogenic emissions to PM_2.5 reduction in Beijing from 2013 to 2017. For these 5 years, the relative contribution of emission reduction to the decrease in PM_2.5 concentrations calculated by KZ filtering and WRFCMAQ was 80.6% and 78.6% respectively. KZ filtering suggested that short-term variations in meteorological and emission conditions contributed majorly to rapid changes in PM_2.5 concentrations in Beijing. WRF-CMAQ revealed that the relative contribution of local and regional emission reduction to the PM_2.5 decrease in Beijing was 53.7% and 24.9% respectively. For local emission-reduction measures, the regulation of coal boilers, increasing use of clean fuels for residential use and industrial restructuring contributed 20.1 %, 17.4% and 10.8% to PM_2.5 reduction respectively. Both models suggested that the control of anthropogenic emissions accounted for around 80% of the PM_2.5 reduction in Beijing, indicating that emission reduction was crucial for air quality enhancement in Beijing from 2013 to 2017. Consequently, such a long-term air quality clean plan should be continued in the following years to further reduce PM_2.5 concentrations in Beijing.