*3.2. Regression of the Basic Model*

Considering the robustness of the estimation results, this paper adopted the random effects model, fixed effects model and SYS-GMM model for estimation. From the regression results in Columns 1–3, in Table 4, in addition to the estimated coefficient of ln*fdi*, the influence coefficients of the dependent variables estimated by the random effects model, fixed effects model and SYS-GMM model on NOx emissions were consistent; that is, the robustness of the estimated results was verified. In the estimation of the SYS-GMM method, based on the research of Arellano and Bond [51] and Arellano and Bover [68], the Sargan test and Arellano bond test were applied to determine whether there was a second-order autocorrelation between the effectiveness of the instrumental variables and the error term or not. From the regression results in Table 4, it was shown that, in the Sargan test, the original hypothesis of the effectiveness of the instrumental variables was accepted, and in the statistics of AR (2) in Arellano bond test, the original assumption that the second-order sequence of residual terms had no autocorrelation showed that the model setting was effective.


**Table 4.** Baseline regression results.

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.

> The regression coefficients in all the independent variables wee significant at the 1% level, and the first-order coefficient in the early stage of the NOx emissions was positive; from this, it was indicated that China's NOx emissions had a cumulative effect, which means the increase of NOx emissions in the early stage will result in the increase of NOx emissions during the current period.

> New urbanization, environmental regulation and economic development will promote to reduce NOx emissions. For every 1% increase in the level of new urbanization, the nitrogen oxides emissions can be reduced by 0.4766%, as, for every 1% increase in the environmental regulations, the NOx emissions will be reduced by 0.4251%. For every 1% increase in economic development, nitrogen oxides emissions will be reduced by 0.6537%.

> The agglomeration of energy-intensive industries, industrial structure, technological innovation and foreign direct investment were positively correlated with the increase of

NOx emissions. For every 1% increase in the agglomeration of energy-intensive industries, NOx emissions will be increased by 0.1290%. The industrial structure is the biggest factor affecting NOx emissions, with the elasticity coefficient reaching 2.1128. Therefore, it is the key to realizing China's NOx emissions reduction to optimize the industrial structure. The elastic coefficient of technological innovation is 0.4274, which indicates that there is a positive correlation between technological innovation and NOx emissions. From this result, it is shown that China's technological innovation has not yet played its role in reducing emissions [69,70]. The coefficient of foreign direct investment is 0.1421, indicating that, for every 1% increase in foreign direct investment, the NOx emissions will increase by 0.1421%.

Furthermore, new urbanization will attract similar industries to gather in specific regions, and industrial agglomeration will drive population agglomeration, thereby promoting the development of new urbanization. Therefore, there may be an interaction between the new urbanization and agglomeration of energy-intensive industries. From the regression results in Column 4 in Table 4, it is shown that the new urbanization and agglomeration of energy-intensive industries mutually interact. After adding the interaction terms of the new urbanization and agglomeration of energy-intensive industries, the positive and negative affecting coefficients in each dependent variable on NOx emissions have not been changed and are significant at the level of 1%, which, once again, verifies the robustness of the regression results. The interaction coefficient between the new urbanization and agglomeration of energy-intensive industries is −0.2818, showing that the promotion of NOx emissions by the agglomeration of high-energy-consuming industries decreases as the level of new urbanization increases. With the improvement development of new urbanization, the adverse impact of energy-intensive industries agglomeration on NOx emissions reduction will be weakened gradually.
