5.1.2. The Quantile DID Results

In Table 2, the industrial energy intensities are divided into nine subpoints from low to high. Due to limited space, no other control variable results are shown. Based on the quantile DID method results, the BTH coordinated development strategy tends to restrain industrial energy intensity at the lower quantile levels from 0.1 to 0.4 but tends to promote industrial energy intensity at the higher quantile levels from 0.7 to 0.9. The results indicate that the BTH coordinated development strategy tends to restrain industrial energy intensity in the lower quantile level cities but tends to promote industrial energy intensity in the higher quantile level cities. The reason is perhaps that energy-intensive industries are mainly located in some cities of Hebei province and some of the industries transferred from Beijing are highly polluting, like steel companies, thus increasing the industrial energy intensity in some Hebei cities. However, cities with low energy intensity, such as Beijing and Tianjin, may optimize and upgrade their industries and may reduce their industrial energy intensity after the transfer.


**Table 2.** Regression results by quantile difference-in-difference (DID) method.

Source: Authors' estimation. Notes: *p*-values are in brackets \* *p* < 0.05, \*\* *p* < 0.01.

Specifically, at the city level, Tangshan, Handan, Zhangjiakou, and Chengde of Hebei province rank high in industrial energy intensity and their industrial energy intensities rose in 2015. In the early stage, most of the transferring enterprises from Beijing to Hebei were high-energy-intensive, thus reducing air pollution in Beijing. Moreover, most of these enterprises were relocated to high-intensity industrial cities or nearby cities in Hebei province like the above ones. Therefore, how to improve the technical level of these enterprises transferred to Hebei and to eliminate backward production capacity among them must be of the utmost importance in the future. More environmental policies should be formulated to reduce energy consumption while maintaining corporate interests. For example, China can improve carbon emission trading markets in Beijing and Tianjin, can establish a new carbon emission trading market in Hebei province, and finally can realize carbon emission market integration in the BTH region.
