[Assessment of Emergency Emission Reduction Effect During the Heavy Air Pollution Episodes in Beijing, Tianjin, Hebei, and Its Surrounding Area("2+26" Cities) from October to December 2019].

To evaluate the effect of emergency emission reduction measures during the heavy air pollution episodes in Beijing, Tianjin, Hebei, and its surrounding areas, a scenario simulation method was used. The concentrations of PM, PM, SO, NO, CO, and O-8h, air quality index (AQI), characteristics of heavy air pollution, and climate and meteorological factors were analyzed using the observation data available from October to December 2019. The 24 h, 72 h, and 144 h prediction results of NAQPMS model were analyzed. The uncertainties of the assessment and model prediction were discussed. The results showed that the average PM concentration in Beijing, Tianjin, and its surrounding 26 cities ("2+26" cities) from October to December 2019 was 64 μg ·m, indicating a decrease of 10 μg ·m as compared with that during the same period in 2018. There were 4 occurrences of regional heavy air pollution episodes, with the average PM concentration of 156 μg ·m of affected cities. The value of evaluation on meteorological condition index of PM pollution (EMI) of "2+26" cities ranged from -15.6%-16.8%. The meteorological conditions of 12 cities, including Beijing, Tianjin, and Shijiazhuang, deteriorated as compared with those during the same period in 2018, and the changes ranged from 3.2%-16.8%. However, the emergency emission reduction measures effectively reduced the occurrence of regional heavy air pollution episodes, the peak concentration of PM was decreased significantly, and no severe regional pollution episode occurred. The daily PM concentrations reduced by 2% to 9% in Beijing, Shijiazhuang, Baoding, Tangshan, and other cities during a typical heavy air pollution period. The quarterly average concentrations of PM in the "2+26" cities reduced by 1 to 3 μg ·m. The regional emergency emission reduction measures have played an active role in protecting the health of the people and improving the quality of ambient air.