疫情期间“2+26”城市污染减排成效评估

为评估“2+26”城市在疫情期间的减排效果，基于NAQPMS模式和情景模拟的方法，分析了2020年1~3月及疫情前后空气质量特征，对气象、重污染应急减排措施及社会经济活动对空气质量的影响和研究的不确定性进行了分析讨论.结果表明，2020年1~3月，“2+26”城市空气质量级别优良率为59.6%，同比上升10.9%；PM₁₀、PM_2.5、SO₂、NO₂、O₃-8h-90per和CO-95per平均浓度分别为108，76，14，36，109μg/m³和2.3mg/m³.疫情期间（1月24日~3月31日） PM₁₀、NO₂、PM_2.5和CO浓度比疫情前期（1月1~23日）同比降幅明显.气象条件造成沿燕山和太行山城市PM_2.5浓度约上升1%~8%.重污染减排促使区域性污染过程减少了2次，“2+26”城市PM_2.5季度均值降低约6~26 μg/m³.受春节和疫情综合影响，机动车排放量大幅下降，但焦化、火电等重点行业实际污染排放量变化不大，散煤燃烧对空气质量的负面影响增加.

Assessment of emission reduction effect in Beijing,Tianjin and surrounding 26 cities from January to March in 2020 during the epidemic of COVID-19

In order to evaluate the effect of air pollutions emission reduction in Beijing, Tianjin, Hebei and its surrounding 26 cities ("2 + 26" cities) from January to March in 2020 during the epidemic of COVID-19, the air quality model of nested air quality prediction modeling system (NAQPMS) was applied to conduct a few scenarios. The characteristics of air quality from January to March 2020, and during the periods before and after the epidemic of COVID-19 were investigated. The influences of meteorology, emergency emission reduction measures and social economic activities on ambient air quality as well as the uncertainties were elucidated and discussed. The results showed that the number of days achieving good and moderate air quality standard in "2+26" cities accounted for 59.6%, on average of 10.9% increase relative to the same period last year. The mean concentration of PM₁₀、PM_2.5、SO₂、NO₂、O₃-8h-90 per and CO-95 per in "2 + 26" cities from January to March in 2020 were 108, 76, 14, 109, 36μg/m³, and 2.3mg/m³, respectively. During the epidemic period from January 24 to March 31, the concentrations of PM₁₀, NO₂, PM_2.5, and CO decreased significantly compared with the period prior to the epidemic from January 1to 23. In contrast to January to March in 2019, the PM_2.5 concentrations of the cities along the Yan mountain and Taihang mountain increased by 1%~8% in 2020. However, the model simulations revealed that the emergency emission reduction measures potentially avoided twice of the regional heavy air pollution events, resulting in the quarterly mean PM_2.5 concentration in "2 + 26" cities reduced by 6 to 26μg/m³. Due to the influence of the Spring Festival holiday and epidemic, the traffic emissions were reduced substantially. In contrast, the emissions from the industry such as coking and thermal power did not show large variations, and the negative impact of loose coal combustion on ambient air quality may become even more severe.