Effects of the emergency control measures in Beijing on air quality improvement

Emergency air pollution control measures were successfully implemented in Beijing many times, such as during the Asia-Pacific Economic Cooperation (APEC) conference in 2014 and the Red Alert (RA) in 2015. Given that air quality was largely affected by wind speed, the efficiency of control measures and wind speed must be quantified to adjust the control measures under different wind speeds. During APEC and RA, source apportionment of organic carbon (OC) was conducted using chemical mass balance receptor model (CMB) with organic tracers to reveal PM2.5 source reductions caused by control measures. In the APEC control period, mobile sources contribution to organic carbon (OC) and dust contribution to PM2.5 decreased from 3.7 μg/m3 (63.7%) to 3.3 μg/m3 (38.8%) and from 5.1 μg/m3 (16.6%) to 3.8 μg/m3 (6.9%), respectively. For the RA day, coal combustion source contribution to OC decreased from 11.3 μg/m3 (53.2%) to 2.3 μg/m3 (6.2%), while mobile sources contribution changed from 8.9 μg/m3 (41.7%) to 14.7 μg/m3 (40.3%). These data suggest that the vehicle restriction rule was not truly implemented. Control measures should be announced in advance to achieve the expected result. In addition, the effectiveness of control measures would decrease with the increase of wind speed, and the critical wind speeds for sustaining an excellent PM2.5 level (35 μg/m3) and daily PM2.5 concentration standard of China (75 μg/m3) were determined by a power function as 11 km/h and 7 km/h, respectively. So wind speed should be considered before the selection of anthropogenic control measures.