**1. Introduction**

The Yangtze River Economic Belt is one of the most critical contradiction areas between economic development and environmental protection in China [1]. A total 40% of available freshwater resources and more than 20% of its wetland resources in China are concentrated in the Yangtze River Basin, which covers 204 national aquatic germplasm resources protection zones. The River Basin is one of the important ecological security barriers and economic centers in China [2]. The chemical industry is a basic and pillar industry of the national economy, with high dependence on water and energy as well as high safety and environmental risks [3]. China is the largest chemical producer in the world. In 2018, its

**Citation:** Xiang, Y.; Shao, W.; Wang, S.; Zhang, Y.; Zhang, Y. Study on Regional Differences and Convergence of Green Development Efficiency of the Chemical Industry in the Yangtze River Economic Belt Based on Grey Water Footprint. *Int. J. Environ. Res. Public Health* **2022**, *19*, 1703. https://doi.org/10.3390/ ijerph19031703

Academic Editors: Roberto Alonso González Lezcano, Francesco Nocera and Rosa Giuseppina Caponetto

Received: 2 December 2021 Accepted: 28 January 2022 Published: 2 February 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

chemical turnover was 119.8 million EUR, accounting for 35.8% of the global chemical sales for the year [4]. The production value of chemical products in the Yangtze River Economic Belt accounts for more than 40% of the country's total. At present, "chemical industry encircling the river" poses challenges to the Yangtze River Economic Belt. There are more than 400,000 chemical enterprises, 5 steel bases, 7 oil refineries, and many large petrochemical bases along the Yangtze River, leading to a greater risk of environmental pollution [5]. In the "joint efforts to protect" and under the general requirements of "no large-scale development", the green transformation and development of the chemical industry in the Yangtze River Economic Belt is particularly urgent.

The Chinese economy has entered a high-quality development stage from the highspeed growth stage now. The traditional industrial development mode of high energy consumption, high pollution, and high emission has gradually changed to the intensive, efficient, and sustainable green development mode. The Chinese government has attached great importance to the green development of the chemical industry in the Yangtze River Economic Belt. On 14 November 2020, General Secretary Xi Jinping presided over a forum that aimed to promote the comprehensive development of the Yangtze River Economic Belt, stressing the need to make it the main battlefield of Chinese ecological priority and green development. Relevant departments of the state have also issued a series of policies and regulations, such as guiding opinions on strengthening the green development of industries in the Economic Belt, the ecological environment protection plan for the area, the Law of the People's Republic of China on the Protection of the Yangtze River, and so forth. All of these endeavors actively promote the green transformation and upgrading of the chemical industry in the Yangtze River Economic Belt. In the past five years, more than 8000 chemical enterprises along the Economic Belt have been reformed, relocated, transformed, or closed. Remarkable achievements have been made in the green transformation and development of the chemical industry. The ecological environment has been significantly improved. The proportion of excellent water quality sections in the Yangtze River basin increased from 82.3% in 2016 to 91.7% in 2019 and further increased to 96.3% from January to November 2020. The elimination of poor V water bodies achieved for the first time in 2020. It can be seen that comprehensively promoting the green development of the chemical industry and improving its green development efficiency [6] are key to solving the dilemma of the "chemical industry surrounding the river", which ensures environmental and industrial development safety and realizes the sustainable development of the chemical industry. The Yangtze River Economic Belt includes 9 provinces, 2 cities, and 11 provincial administrative units and covers an area of approximately 2.05 million km2 [7]. Due to the differences in resource conditions, economic development levels, innovation abilities, and chemical industry development histories, the spatial distribution and green development level of the chemical industry show spatial heterogeneity, which increases the challenge for the Economic Belt to promote the industrial green development. In order to measure the gray water footprint and green development efficiency of the chemical industry in the Yangtze River Economic Belt, to reveal the spatial differences and their convergence in the green development efficiency of the chemical industry in 11 provinces and cities, and to provide policy support for the green development of the chemical industry in the Yangtze River Economic Belt, this research systematically studied the regional differences and convergence of green development efficiency of the chemical industry in the Yangtze River Economic Belt. The results are expected to be valuable in theoretical reference and practical significance for implementing green development promotion strategy of the chemical industry in different regions and categories.

#### **2. Literature Review**

The concept of "green development" was first proposed by the United Nations Development Programme in 2002. The essence of green development is to regard resources and the environment as endogenous factors of growth and provide a balance between economic growth and ecological environment protection by changing the dynamic mechanism of

economic development to form a new sustainable development model [8,9]. From the perspective of input and output, green development efficiency refers to the proportional relationship between green development output and input. Green development efficiency is an important indicator to analyze the degree of green development of industries and is often used to reflect the completion degree, achievements, and effectiveness of green development. Since data envelopment analysis (DEA) can consider a variety of input and output and does not need to set specific function forms, it has become the mainstream method to measure green development efficiency [10]. Pittman (1983) first included "undesirable" output into the productivity analysis process [11]. Chung et al. (1997) proposed directional distance function and the Malmquist–Luenberger Index (MLI), which carries out productivity evaluation after the "undesirable" output is considered reasonable [12]. Tone (2001, 2002) proposed a SBM model that considers relaxation measures to effectively overcome radial and angular defects [13,14]. A DEA analysis method based on the measurement of slack variables, which puts the input and output slack directly into the objective function so that it can directly measure the inefficiency caused by slack compared to the optimal production frontier, thus solving the problem of input and output slack in the traditional DEA model, removing the inefficiency caused by slack, and also solving the problem of productivity evaluation in the presence of non-expected outputs. Many scholars used the DEA model to discuss the green development efficiency of the chemical industry. Tanzil and Beloff (2006) summarized the sustainability indicators and indicators of the chemical industry, focusing on ecological efficiency and company-specific indicators [15]. Alessandro et al. (2017) measured the environmental economic efficiency of Italian and German chemical enterprises [16]. Yeh Jiahuey et al. (2019) calculated the total factor green energy efficiency of China's chemical industry [17]. Yijun Zhang et al. (2020) used the three-stage SBM–DEA model and MLI to measure the green total factor productivity (GTFP) of China's chemical industry [6]. Sun Honghai (2017) used super-efficiency DEA to calculate the ecological efficiency of 25 petrochemical enterprises in China [18]. Yuan Yaqiong (2018) used DEA and value-driven analysis to evaluate the ecological efficiency of heavy chemical enterprises in Beijing, Tianjin, and Hebei region from 2012 to 2016 [19]. Lu Qiuqin et al. (2020) used the improved three-stage DEA model to evaluate the transformation and upgrading efficiency of China's coal chemical enterprises [20].

When using DEA, researchers usually take labor, capital, and energy as inputs, the output value of the chemical industry as the expected output, and environmental pollutants as the unexpected output to build an evaluation model of green development efficiency of the chemical industry. These indicators do not consider the characteristics of the chemical industry, which has a great impact on water environment. Tony Allan proposed "Virtual Water"; Hoekstra et al. proposed the concept of "Water Footprint". Grey water footprint refers to the volume of freshwater required to dilute certain pollutants on the basis of existing water quality standards and natural background concentration [21]. Given that water footprint and grey water footprint can better represent the water consumption and water pollution accounting of industries [22], they have been gradually incorporated into the evaluation framework of the green development efficiency of regional industries [23,24].

The spatial distribution and environmental risk of the chemical industry in the Yangtze River Economic Belt have always been hot areas of academic concern. For a long time, the spatial layout of the chemical industry in the Economic Belt has reflected two major factors: the proximity to raw materials and market. The chemical industry along the Yangtze River is mainly distributed in the areas of Shanghai and Jiangsu [25]. In recent years, the petrochemical industry had a trend of expansion along the river to the upstream. The environmental pollution load gradient also shifted to the middle and upper reaches, and the environmental risk increased [26,27]. Xiang et al. (2021) found that the spatial differentiation characteristics of green development efficiency of the chemical industry in the Yangtze River Economic Belt were obvious. Economic level, scientific and technological innovation, industrial structure, and industrial agglomeration are the main factors affecting the spatial differentiation of green development efficiency of the chemical industry in the

Economic Belt. The impact of foreign investment intensity and environmental regulation is relatively weak [28]. Therefore, it is necessary to guide the chemical industry of the Yangtze River Economic Belt to gather in large coastal bases and raw material producing or consumption areas, improve the rate of chemical enterprises entering the park, and optimize the spatial layout of the chemical industry [29]. Some scholars also studied the negative effects of the development of the chemical industry on the ecological environment. Zhu Deming et al. (2006) showed that the development of the chemical industry along the Yangtze River in Jiangsu threatened the drinking water source and water supply safety [30]. Intensive chemical enterprises and unreasonable industrial layout along the Yangtze River Economic Belt have brought some potential environmental risks to the environmental protection of the Yangtze River Basin [31,32]. Dong et al. (2020) found that the division level of heavy chemical industry in the middle and upper reaches of the Yangtze River Economic Belt decreased, which promoted the decline of the regional pollution level [33].

The contribution of this research is mainly reflected in the following aspects. Firstly, it makes up for the industry characteristics that little considered the impact of the chemical industry on the water environment in previous studies. In this study, water footprint and grey water footprint are included in the green development efficiency measurement index system of the chemical industry, and the green development efficiency of the chemical industry is established by using DEA, which was calculated from 2002 to 2016 in the Yangtze River Economic Belt. Secondly, Dagum Gini coefficient and its decomposition method are used to decompose the regional differences of green development efficiency of the chemical industry in the Economic Belt. Lastly, the convergence characteristics of green development efficiency of the chemical industry in the Economic Belt and its upstream, middle, and lower reaches are tested with the coefficient of variation method and panel data regression model from three aspects, i.e., convergence, absolute convergence, and conditional absolute convergence.
