Spatial And Temporal Evolution Of Smog In "2+26" Cities Around Beijing-Tianjin-Hebei And Evaluation Of The Effectiveness Of Prevention And Control Policies

A good atmospheric environment is the basis for the sustainable development of human society.With the accelerated industrialisation and urbanisation,China is facing a serious air pollution problem along with rapid economic development.For this reason,governments at all levels in China have issued a number of policies on air pollution control since 2012.In the face of the current complex international and domestic situation,there is an urgent need to clarify the role of haze control policies,scientifically assess their effectiveness,assist in the formulation of subsequent policies,and safeguard the healthy socio-economic development of China.This paper uses spatial interpolation algorithms to generate 1*1km raster-scale continuous PM_2.5annual data based on hourly data from national control stations from 2014 to 2020,and analyzes the evolution characteristics of PM_2.5spatial and temporal patterns in the‘2+26’cities around Beijing-Tianjin-Hebei region using trend analysis,spatial feature analysis and center of gravity model.Based on the Regression Discontinuity model（RD）,a Geographical Boundary Discontinuity Model was introduced,and a buffer zone of 10 km inside and outside the administrative boundary of the study area was set as the experimental group and the control group respectively,and Differences-in-Differences（DID）model was constructed to evaluate the haze control policies at the raster scale.Taking into account the potential influence of topographical factors on the assessment results,difference in difference in difference（DDD）model was constructed to evaluate the effectiveness of the policy of the"Three-Year Action Plan to Win the Blue Sky Defense War"on haze pollution in the‘2+26’cities around Beijing-Tianjin-Hebei region.The specific conclusions are as follows:（1）From 2014 to 2020,the overall PM_2.5concentration in the‘2+26’cities around Beijing,Tianjin and Hebei will show a decreasing trend.Beijing,Tianjin and Tangshan,Handan and Xingtai in Hebei Province had the largest decreases in PM_2.5concentrations（all around 40μg/m³）,while Xinxiang,Jiaozuo and Puyang in Henan Province and Heze in Shandong Province had the smallest decreases in PM_2.5concentrations（all less than 25μg/m³）.The rate of reduction in PM_2.5concentrations in the post-policy year（6.30μg/m³）was approximately twice that of the pre-policy year（3.3μg/m³）.The haze pollution concentration levels in the study area show a decreasing trend,showing a change from a high concentration level to a low concentration level,with PM_2.5concentrations in the study area gradually decreasing and air quality gradually improving after the implementation of the policy.（2）The agglomeration effect of PM_2.5concentration in the‘2+26’cities around Beijing-Tianjin-Hebei region has an obvious positive autocorrelation in space,and the agglomeration area has shifted significantly over time.The global autocorrelation results show that the global Moran’s I index of the‘2+26’cities from 2014 to 2020 has a small overall change,with values ranging from 0.37 to 0.55,and there is no"high-low"（H-L）agglomeration and"low-high"（L-H）agglomeration area.Over time,the"high-high"（H-H）agglomeration areas have shifted from the northwestern region to the central and southern regions,from Baoding,Hengshui,Xingtai,and Handan in 2014 to Handan,Anyang,Hebi and Puyang in 2020;the"low-low"（L-L）agglomeration area shifted from the western region to the northern region,from Taiyuan,Changzhi and Jincheng in 2014 to Beijing and Handan in 2020.（3）From the perspective of the concentration and transfer speed of the pollution center of gravity,from 2014 to 2018,the speed of the transfer of the pollution center of gravity was faster,and from 2018 to2020 after the implementation of the policy,the direction and speed of the transfer of the center of pollution were higher than those before the implementation of the policy.Changes have taken place.After the implementation of the policy,the speed of the center of gravity shift gradually slowed down,and the direction shifted from northeast to southwest.（4）The results of the quasi-natural experiment show that the"Three-Year Action Plan for Winning the Blue Sky Defense War"has significantly reduced the haze pollution in the‘2+26’cities around Beijing-Tianjin-Hebei region.After controlling for the influence of terrain factors,the conclusion is still robust.It shows that the implementation of the"Three-Year Action Plan to Win the Blue Sky Defense War"has effectively improved the air quality of the‘2+26’cities around Beijing-Tianjin-Hebei region.