Abstract
Abstract. With the completion of the Beijing Five-year Clean Air Action Plan by the end of 2017, the annual mean PM2.5 concentration in Beijing dropped dramatically to 58.0 µg m−3 in 2017 from 89.5 µg m−3 in 2013. However, controversies exist to argue that favourable meteorological conditions in 2017 were the major driver for such a rapid decrease in PM2.5 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 PM2.5 reduction in Beijing from 2013 to 2017. For these 5 years, the relative contribution of emission reduction to the decrease in PM2.5 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 PM2.5 concentrations in Beijing. WRF-CMAQ revealed that the relative contribution of local and regional emission reduction to the PM2.5 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 PM2.5 reduction respectively. Both models suggested that the control of anthropogenic emissions accounted for around 80 % of the PM2.5 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 PM2.5 concentrations in Beijing.
Highlights
In January 2013, persistent haze episodes occurred in Beijing, during which the highest hourly PM2.5 concentration once reached 886 μg m−3, a historically high record
Meteorological conditions in Beijing were generally favourable for PM2.5 dispersion during the 5-year period, especially in the latter half of 2017, when there was a high frequency of strong northerly winds and much lower wintertime PM2.5 concentrations than in previous years
In November 2017, strong northerly winds in Beijing resulted in the cleanest winter in the past 5 years, raising arguments of whether the favourable meteorological conditions were primarily responsible for PM2.5 reduction or whether the significant improvement in air quality in Beijing was mainly attributed to the control of anthropogenic emissions
Summary
In January 2013, persistent haze episodes occurred in Beijing, during which the highest hourly PM2.5 concentration once reached 886 μg m−3, a historically high record. Cheng et al, 2019) and health effects (Liang et al, 2019) of PM2.5 variations in Beijing from 2013 to 2017 These studies revealed that air quality in Beijing was improved significantly in 2017 in terms of annual mean PM2.5 concentrations, polluted days and pollution durations. Despite different outputs, both source apportionment during pollution episodes based on collected samples (Shao et al, 2019; Xu et al, 2019; Chen et al, 2019) and long-term model simulation based on regional and local emission inventories Cheng et al, 2019) suggested that local and regional anthropogenic emissions (e.g. coal combustion and vehicle emissions) were the major influencing factors for long-term and short-term PM2.5 variations in Beijing Despite different outputs, both source apportionment during pollution episodes based on collected samples (Shao et al, 2019; Xu et al, 2019; Chen et al, 2019) and long-term model simulation based on regional and local emission inventories (J. Cheng et al, 2019) suggested that local and regional anthropogenic emissions (e.g. coal combustion and vehicle emissions) were the major influencing factors for long-term and short-term PM2.5 variations in Beijing
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