The control of anthropogenic emissions contributed to 80 % of the decrease in PM.sub.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.sub.2.5 concentration in Beijing dropped dramatically to 58.0 µg m.sup.-3 in 2017 from 89.5 µg m.sup.-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.sub.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.sub.2.5 reduction in Beijing from 2013 to 2017. For these 5 years, the relative contribution of emission reduction to the decrease in PM.sub.2.5 concentrations calculated by KZ filtering and WRF-CMAQ 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.sub.2.5 concentrations in Beijing. WRF-CMAQ revealed that the relative contribution of local and regional emission reduction to the PM.sub.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.sub.2.5 reduction respectively. Both models suggested that the control of anthropogenic emissions accounted for around 80 % of the PM.sub.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.sub.2.5 concentrations in Beijing.