*Article* **New Urbanization, Energy-Intensive Industries Agglomeration and Analysis of Nitrogen Oxides Emissions Reduction Mechanisms**

**Yang Yu \* and Tianchang Wang**

School of Economics and Management, Beijing University of Chemical Technology, Beijing 100029, China; 2019200891@mail.buct.edu.cn

**\*** Correspondence: yuyang@mail.buct.edu.cn

**Abstract:** With the deepening of urbanization and industrialization, as well as the exacerbation of energy consumption, China is facing a severe situation in which nitrogen oxide (NOx) emissions reduction is imperative. In this study, it is aimed to put forward countermeasures and suggestions to reduce NOx emissions by analyzing the impact and mechanism of new urbanization, the agglomeration of energy-intensive industries and mutual interactions on China's NOx emissions. By analyzing the data of 30 provinces in China from 2006 to 2017, this paper adopted the system generalized method of moments (SYS-GMM) and intermediary effect model to introduce four variables, such as: energy efficiency, human capital, industrial structure and energy structure, which were for empirical analysis. From the results, it was shown that: (1) NOx emissions in China have an accumulated effect; (2) new urbanization inhibits NOx emissions, whilst the agglomeration of energy-intensive industries intensifies NOx emissions. New urbanization weakens the negative impact of the agglomeration of energy-intensive industries on NOx emissions reduction and, (3) among the impacts of new urbanization on NOx emissions, the energy efficiency and human capital reflect the intermediary effect mechanism. At the same time, in the impact of the agglomeration of energy-intensive industries on NOx emissions, the industrial structure and energy structure show the mechanisms of the intermediary effect and masking effect, respectively.

**Keywords:** air pollution; new urbanization; energy-intensive industries agglomeration; NOx emissions; intermediary effect model; transmission mechanism

## **1. Introduction**

In the "2030 Agenda for Sustainable Development" formulated by the United Nations, 17 sustainable development goals were put forward; among which, SGD11 and SGD13 describe the requirements for building sustainable cities and solving the problems of climate changes, respectively. A key role has been played by new urbanization in promoting urban and ecological sustainable development. In recent years, China's urban air quality has been continuously improved; despite this, there are still some atmospheric pollutants, such as nitrogen oxides, ozone and other gases, that have been emitted at a high level. The emissions reduction effect of these gases is not obvious and brings huge challenges to the prevention and control of air pollution. Nitrogen oxides (NOx = NO + NO2) is one of the most serious air pollutants, and its hazards are reflected in environmental governance and human health. NOx not only directly affects the concentration of nitrogen dioxides in the air but is also the main source of ozone pollutants. In the research on how these gasses harm human health, scholars have discussed the adverse effects of NOx on human life expectancy [1], asthma symptoms [2], mental health disorders complicating pregnancy [3,4] and lung function [5] at birth. In 2018, NOx accounting for the highest proportion of total industrial waste gas emissions, seriously hindering the improvement of China's new urbanization level and the construction of ecological civilization.

**Citation:** Yu, Y.; Wang, T. New Urbanization, Energy-Intensive Industries Agglomeration and Analysis of Nitrogen Oxides Emissions Reduction Mechanisms. *Atmosphere* **2021**, *12*, 1244. https:// doi.org/10.3390/atmos12101244

Academic Editors: Duanyang Liu, Kai Qin and Honglei Wang

Received: 24 August 2021 Accepted: 18 September 2021 Published: 24 September 2021

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In China, NOx emissions are mainly from transportation sources (using automobile engines) and industrial sources (boiler combustion and cement and steel production). It has been pointed out that 75.34% of the NOx emissions from industrial sources focus on nonmetallic mineral products, electric power, thermal power production and supply and ferrous metal smelting and rolling processing industries in energy-intensive industries (Bulletin of the second national survey of pollution sources [6]). It is necessary to reduce NOx emissions from the source, which means that the structure of energy-intensive industries should be upgraded. At present, the view that it is significant to adjust the industrial spatial layout by means of industrial agglomeration give full attention to the technology spillover effect and improve the environment has been recognized by most scholars [7–10]. During the process of actively promoting new urban construction in China, the profound changes are dramatic in the industrial layout. However, it remains to be explored whether the geographical concentration of energy-intensive industries will reduce pollutant emissions. Therefore, it has important guidelines for furthering the construction of new urbanization, optimizing the industrial layout and reducing NOx emissions to clarify the impact and mechanism of new urbanization and energy-intensive industry agglomerations on NOx emissions in China.

It is an important guarantee for sustainable social development to make the development of urbanization and the environment harmonious. The relationship between them has been widely explored by scholars. It is concluded from the research on this topic covering: urbanization improving environmental pollution [11,12], urbanization intensifying environmental pollution [13,14] and the nonlinear relationship between urbanization and environmental pollution [15–17]. Based on a nonlinear relationship, in the early stages of urbanization, with the level of urbanization increasing, pollution intensifies. After that, when urbanization reaches a certain level, pollution will be improved. In some scholars' opinions, they attribute the impact of urbanization on the environment to population growth and industrial agglomeration, holding the opinion that population growth and industrial agglomeration brought about by urbanization have a greater impact on the environment. From the perspective of population factors, as early as 1978, Malthus pointed out that a lack of technology and that population growth will reach the limit because of resource shortage; at the same time, the impact of demographic factors on the environment is also universal [18]. Since then, from the research, large number of scholars have also believed the negative impact of population growth on the environment [19–22].

From the perspective of agglomeration, with the development of urbanization, industrial agglomeration is a form of enterprise agglomeration of organizations with close geographical locations and industrial connections. Some scholars believe that industrial agglomeration has a positive effect on the improvement of environmental pollution. First, most industries gather in specific areas based on unique regional resource conditions, thereby reducing transboundary pollution [23]. Second, industrial agglomeration will attract a large amount of labor force. Meanwhile, specialized equipment can be applied on a large scale, thus promoting the development of specialized investments and services [24]. Third, industrial agglomeration will benefit mutual learning among enterprises and promote the spillover of knowledge and technology [10,25]. In contrast, other scholars believe that industrial agglomeration has exacerbated environmental pollution [26–28], expanding the production scale and output [29,30] and causing crowding effects, as well as environmental damage. Furthermore, other scholars have also verified the nonlinear relationship between industrial agglomeration and environmental pollution [31–33].

NOx is a kind of air pollutant, and manmade NOx emissions mainly come from energy consumption. Considering the seriousness of NOx emissions, large number of scholars have confirmed energy-intensive industries such as iron and steel [34], thermal power [35], cement [36,37] and petrochemicals [38] have bad influences on NOx emissions. After subdividing these industrial sectors, scholars proposed that the emission factors of power generation in the iron and steel industry should be reduced [39], and coal-fired

power plants should implement ultra-low emissions policies [35], strengthen technology research and development [40] and reduce NOx emissions.

By analyzing the literature, it was found as below: firstly, although scholars have conducted deep research into the relationships between urbanization and environmental pollution, industrial agglomeration and environmental pollution, their conclusions are not confirmed. Secondly, the existing literature has covered few researches on the action path of urbanization and industrial agglomeration on the environment, as well as the pollutants rarely involving NOx. Thirdly, with the new urbanization being promoted, the industry has been modified in the original spatial layout; however, few scholars have researched and discussed the relationship between energy-intensive industries and nitrogen oxides from the perspective of agglomeration.

Recently, scholars have paid more attention to evaluating the ecological efficiency [41–44] during the period of measuring the level of urbanization. A new urbanization index system will be constructed, including four dimensions such as population, social development, ecological environment and land, integrating the new urbanization and agglomeration of energy-intensive industries into a unified framework and analyzing their impact on China's NOx emissions by applying the systematic GMM method. In addition, this paper also applied the intermediary effect model to explore the action path of new urbanization and agglomeration of energy-intensive industries on NOx emissions. Finally, some suggestions are put forward to reduce the NOx emissions, in order to provide countermeasures to deal with the air pollution problems during development.
