*3.3. Mechanism Analysis*

Based on the benchmark study in Table 4, it is found that China's new urbanization has a strong inhibitory effect on NOx emissions; however, energy-intensive industries agglomeration has a strong promotion effect on NOx emissions. In this section, the transmission mechanism of new urbanization and energy-intensive industries agglomeration on NOx emissions is explored with the intermediary effect model.

During the period of exploring the transmission mechanism between new urbanization and NOx emissions, it should be considered whether new urbanization can affect NOx emissions with energy efficiency and human capital. It can be seen from Table 5 that, when energy efficiency was taken as the intermediary variable into the model, the absolute value of the estimated coefficient of the impact of new urbanization on NOx emissions in Equation (5) was less than Equation (3), the impact of new urbanization on the energy efficiency was positive and the impact of the energy efficiency on NOx was negative, which was significant at the level of 1%. At the same time, it showed that energy efficiency is the intermediary variable of new urbanization affecting NOx emissions. New urbanization will benefit the improvement of energy efficiency, which not only reduces the level of unit energy consumption but also produces additional economic benefits, leading to reduce NOx emissions. Therefore, new urbanization reduces NOx emissions by improving the energy efficiency. When human capital is introduced into the model as an intermediary variable, the estimation coefficient of new urbanization on NOx emissions in Equation (5) was less than Equation (3), the impact of new urbanization on human capital was positive and the impact of human capital on NOx was negative. It is shown that human capital is the intermediary variable of the new urbanization affecting NOx emissions. With the improvement of new urbanization, better educational opportunities will be provided for more people, in order to promote human capital. At the same time, as the human capital level improves, it contributes to the enhancement of residents' awareness of environmental protection, playing a positive role in pollutant emissions reduction [71,72], which means that the human capital in new urbanization will improve the reduction of NOx emissions.


**Table 5.** Research results on the mechanism of NOx emissions by new urbanization.

Note: \*, \*\* and \*\*\* indicate significance at the levels of 10%, 5% and 1%, respectively; the values in parentheses for the variable and constant items represent the standard errors.

> In the process of exploring the transmission mechanism between the agglomeration of energy-intensive industries and NOx emissions, it should be considered whether energyintensive industries agglomerations can affect NOx emissions with the industrial structure and energy structure. It can be seen from Table 6 that, when the industrial structure is taken as the intermediary variable into the model, the estimation coefficient of the agglomeration of energy-intensive industries on NOx emissions was positive, and Equation (5) was less than Equation (3). The impact of agglomeration of energy-intensive industries on the industrial structure was positive, and the impact of the industrial structure on NOx was positive, which were significant at the confidence level of 1%. At the same time, it also showed that the industrial structure is an intermediary variable for the agglomeration of energy-intensive industries agglomeration to affect NOx emissions. The agglomeration of energy-intensive industries will intensify NOx emissions with the proportion of secondary industry increasing. When the energy structure is taken as the intermediary variable into the model, the estimated coefficient of agglomeration of energy-intensive industries on NOx in Equation (5) is greater than that in Equation (3), and the coefficient signs of the direct and indirect effects of agglomeration of energy-intensive industries on NOx emissions are different. It seemed that the energy structure showed the masking effect. At this time, agglomeration will benefit the upgrading of energy-saving technologies and the transformation of energy-saving equipment and the large-scale use of new energy fuels, so it greatly reduces the proportion of coal in the energy consumption, thus reducing the

pollutant emissions [73]. The agglomeration of energy-intensive industries has a positive impact on NOx emissions; however, the agglomeration of energy-intensive industries will reduce this adverse impact by optimizing the energy structure.


**Table 6.** Research results on the mechanism of NOx emissions by energy-intensive industries agglomeration.

Note: \*, \*\* and \*\*\* indicate significance at the levels of 10%, 5% and 1%, respectively; the values in parentheses for the variable and constant items represent the standard errors.

> From the above, the impact mechanism of new urbanization and agglomeration of energy-intensive industries on NOx through intermediary variables is tested. It is found that the increase of the level of new urbanization not only directly promotes the reduction of NOx but also reduces NOx pollution by improving the energy efficiency and human capital. At present, the high proportion of China's secondary industry is still the key factor, leading to an increase in NOx emissions. Although the agglomeration of energyintensive industries can reduce NOx emissions through the reduction of coal consumption, its masking effect is less than the direct effect of the agglomeration of energy-intensive industries on NOx emissions. Therefore, the total effects of the agglomeration of energyintensive industries on NOx emissions still showed a positive correlation. In order to grasp the inspection results comprehensively, all the inspection results are summarized in Table 7.


**Table 7.** Summary of the mechanism analysis.
