Research on Characteristics of Economic Development and Environmental Pollution in Typical Energy Regions

Abstract

The data on economic development quality and environmental pollution intensity from 2001 to 2021 was selected by taking Shanxi province, a typical energy region of the country, as the research object was analyzed in the evolution characteristics of economic development quality and environmental pollution intensity in Shanxi province over the past two decades by using linear regression, numerical fitting, and Pearson correlation coefficient, and was explored on their mutual relationship. The results show that Shanxi province has made long-term progress in economic development since 2001, with GDP increasing nearly 10 times and maintaining an average annual growth of about 7%. The main pollutants in the last 20 show a trend of steady change, first ascending and then descending, with the turning point occurring in the 12th Five-Year Plan period (2011–2015), which shows that the environmental policies and investments made by China and Shanxi governments in the last 10 years of the new era have taken effect. The results of the numerical fitting curve suggest that the per capita GDP shows a classical inverted “U” curve relationship with wastewater and SO₂ emissions, respectively. The turning point occurs at around 20,000 yuan per capita GDP, while the relationship between chemical oxygen demand and ammonia nitrogen emissions is monotonically decreasing. The relationship with solid waste generation is monotonically increasing without the turning point. The results of the correlation analysis further supported the conclusion of the fitted curve.

1. Introduction

Since the establishment of the People’s Republic of China, it has transformed from an agricultural to an industrial country. In the process of industrialization and urbanization, like most developed countries, rapid economic development is at the expense of excessive consumption of natural resources and destruction of the ecological environment. While human beings enjoy a large number of benefits brought by economic progress, they also have to suffer from various injuries caused by environmental issues [1].

Faced with the ever-growing intense environmental pollution problems, China has abandoned the outdated concept of treatment after development and continuously increased the protection of the ecology to coordinate the promotion of ecological environment and economic development and take the path of sustainable development as well. The construction of an ecological civilization was incorporated into the Five-sphere Integrated Plan at the 18th CPC National Congress, promoting environment-friendly development as the first step in the reform of the ecological civilization system, which was elaborated key during the 19th CPC National Congress and the 20th CPC National Congress; the latter of which proposed one of the important features of socialist modernization, namely, the modernization of the harmonious coexistence between humans and nature, and they emphasized the synchronous promotion of civilization construction of material and ecology [2,3,4]. Since the outbreak of COVID-19, in order to stop the spread of the epidemic, different degrees of containment measures have been adopted across the country, which have seriously affected human activities and industrial–commercial activities. The need for worldwide participation in sustainable development has become more urgent than ever.

The coupling relational model of economic growth and ecological environment has always been one of the hot issues in global studies [5,6,7,8,9]. While most studies focus on coastal cities or first-tier developed areas [10,11,12,13], relatively few related studies take typical energy regions into consideration. Shanxi Province, a typical energy region in China, with coal, energy, and chemical industries as the leading industries, is an important industrial and energy base in northern China. Its economic development and environmental pollution issues have also attracted scholars’ attention. On the basis of reviewing previous research results, this study explores the evolution characteristics of economic development and environmental pollution in typical energy regions of Shanxi Province. This is the first time linear regression, Pearson correlation coefficient, and numerical simulation methods have been used to study the changing characteristics and dominant factors of regional economic development and environmental pollution. This is of great significance for improving residents’ urban environmental quality and living standards. Moreover, it can serve scientific basis and theoretical reference for achieving sustainable development in typical energy regions.

2. Data and Methods

2.1. Data Sources

The economic development quality data were collected through the Shanxi Statistical Yearbook (2001–2021). At the same time, the environmental pollution intensity data were sorted out from the people’s government website and the National Bureau of Statistics website, etc. The missing data were fitted and supplemented by establishing a linear regression equation according to the existing data.

2.2. Research Methods

(1)

Empirical analysis method. The data on the quality of economic development and environmental pollution intensity in Shanxi Province in recent years were collected, including GDP and per capita GDP, permanent population, per capita disposable income, and industrial pollutant emissions, such as wastewater, solid waste, chemical oxygen demand, ammonia nitrogen emissions, nitrogen oxides, smoke, dust, sulfur dioxide, and other indicators. Collected data are analyzed based on the theoretical framework established by normative analysis to build a model of urban economic development and environmental pollution.

(2)

Statistical analysis method. The index of economic development quality and environmental pollution intensity are, respectively, vertical and horizontal coordinates used to draw a scatter plot based on the distribution of the scatter plot to select appropriate fitting curves, such as the exponent, linear, and logarithm curves. The correlation coefficient between the quality of economic development and the intensity of environmental pollution is calculated to determine the correlation between the two. The data processing, analysis, and plotting in the article were calculated and analyzed using Excel 2010 and SPSS Statistics 26.

3. Results and Analysis

3.1. Characteristics of Changes in the Quality of Economic Development

From Figure 1a, it can be seen that the GDP of Shanxi Province has increased from 202.95 billion yuan in 2001 to 2259.02 billion yuan in 2021, with an average annual growth rate of 7% [14]. However, the performance in terms of the fluctuation range of growth rates is not stable. In the past 20 years, its growth rate has shown some cyclical changes. Specifically, the GDP growth rate of Shanxi indicated an upward trend from 2001 to 2003. In 2004, there was a downward trend and a brief stagnation in economic growth. In 2006, the economy rebounded and showed an increase. From 2007 to 2008, due to the global economic crisis, the economy of Shanxi Province also experienced a colossal decline. Until 2010, the economy showed an upward trend, but then the economy declined. Until 2017, when it warmed up again, but it then declined again until an upward trend appeared in 2021. The entire economic growth cycle has gone through multiple fluctuation cycles, with varying degrees of growth and decline. The fluctuations in this economic growth cycle can be interpreted and analyzed from multiple perspectives. For example, changes in various market factors, including changes in internal and external demand, changes in the policy environment, etc., may have a significant impact on economic growth rates. In addition, the special resource environment of Shanxi Province may also have a significant impact on its economic growth. In summary, the economic growth trends presented by the data need to be analyzed based on multiple considerations.

From Figure 1b, over the past 20 years, it can be seen that the per capita GDP of Shanxi has shown an overall growth. The growth rates in other years have been positive, with the exclusion of negative growth rates in 2009 and 2015. From 6226 yuan in 2001 to 64,821 yuan in 2021, the average annual growth rate has reached 12.82%, but the per capita GDP growth rate is unstable, with significant fluctuations, and the trend of change is consistent with GDP, and there was an upward trend from 2001 to 2003 and a downward in 2004. In 2006, the economy warmed up and rose. Due to the impact of the world economic crisis from 2007 to 2008, the economy of Shanxi also declined intensely. It rose with the rise of gross regional product until 2010 and continued to decline. The economic growth rate of Shanxi grew until 2017 and continued to decline. Moreover, in 2021, there was an upward trend.

Figure 1c shows that economic growth shows multiple cyclical fluctuations by analyzing the gross regional product index of Shanxi in the last 20 years. Specifically, the index of the gross regional product of Shanxi showed a great downward from 2002 to 2005. It is obvious that the economic development of it has experienced heavy and great pressure during this stage, which may involve factors such as changes in the market environment and policy adjustments. However, the economic growth of it once again showed an upward between 2006 and 2007, which may be related to factors such as the improvement of the domestic market environment and favorable policies. Afterward, the economic growth situation once again indicated a great downward. More specifically, the gross regional product index of it suggested an obvious downward during the three years from 2007 to 2009, which may be related to the impact of the international financial crisis and other factors. From 2010 to 2015, the economic growth of Shanxi has been in a declining state. It is proved that the economic development of it faced some new structural pressures, such as concentrating on traditional industries and insufficient support for emerging industries. During the 12th Five-Year period, the economic growth of it gradually showed upward, and the indicators stated that the gross regional product index was narrowing; that is, its quality was slowly rising. By 2020, Shanxi’s economic growth declined again, which might be influenced by COVID-19. It should be noted that the GDP of the gross regional product rose again in 2021, which may mean that the economic development of Shanxi has begun to recover and new growth opportunities have been obtained. Overall, we can see the development trend of the economy in Shanxi from these indicator data, and it also reminds us to rationally view the phenomenon of economic growth and fluctuations and take effective measures to strengthen support and ensure its sustainable economic development.

3.2. Characteristics of Changes in the Three Major Industries

From Figure 2a, in the past 20 years, it can be concluded that the total output value of three major industries in Shanxi province has shown an upward. The output value of the primary sector of the economy in Shanxi increased from 17.109 billion in 2001 to 128.687 billion in 2021, with an average annual growth rate of 11.09%. The total output value of the secondary sector increased from 95.6 billion in 2001 to 112.131 billion in 2021, with an average annual growth rate of 14.31%. The total output value rose from 90.243 billion in 2001 to 100.906 billion in 2021, with an average annual growth rate of 12.95%. Over time, the total output value of the primary sector of the economy has shown a downward trend year by year, while the secondary sector of the economy has gradually increased and fluctuated in recent years. Moreover, the gross output value also continued to grow and accounted for an increasingly important proportion of the entire GDP. The proportion of gross output value of the primary sector of the economy in GDP fluctuates greatly, indicating that agricultural development is not stable enough. The total output value of the three major industries in Shanxi Province has increased in absolute terms. The growth rate of the primary sector of the economy is relatively slow but has been growing steadily. The average annual growth rate of the secondary sector of the economy is relatively large, but the growth is unstable. The tertiary sector of the economy shows relatively stable and rapid growth.

From Figure 2b, in the past 20 years, it can be observed that the industrial structure of Shanxi has undergone a series of changes. According to the data, the proportion of the gross output value of the primary sector of the economy in GDP has remained relatively stable and basically flat. The proportion of gross output value of the secondary sector of the economy in GDP has experienced a wave of the rise and then began to decline gradually, which has been strengthened in recent years. Moreover, the proportion of gross output value of the tertiary sector of the economy in GDP also shows volatility, which has experienced a wave of decline and then began to rise. Overall, the industrial structure of Shanxi has undergone critical changes in the past 20 years. The secondary sector of the economy has always accounted for the main proportion of the total GDP, while the primary sector of the economy and the tertiary sector of the economy are always in the secondary position. However, with the change of the times, the industry of it is also gradually transforming into a light industry, which makes the proportion of the secondary sector of the economy gradually decline. Also, the tertiary sector of the economy has begun to emerge gradually, and has now become a very important part of Shanxi’s GDP with the vigorous development of the service industry. Yet, we found that the proportion of the secondary sector of the economy has actually increased by a small margin in 2021. This trend may be caused by unstable factors in the world economy and fluctuations in international raw material prices.

3.3. Characteristics of Changes in Environmental Pollution Intensity

It can be seen from Figure 3 that the intensity of major pollutants, including wastewater, solid waste, chemical oxygen demand, ammonia nitrogen emissions, nitrogen oxides, smoke, dust, and sulfur dioxide in Shanxi province for nearly two decades has shown a tendency of first rising and then stabilizing. The turning point occurred around 2012 during the “12th Five-Year Plan” period. The change in pollutants from 2001 to 2012 showed a stable upward and basically a steady downward after the “12th Five-Year Plan” period.

From Figure 3a, it can be seen that the total amount of wastewater discharge in Shanxi has remained relatively stable, except for a great decrease from 2014 to 2017. The output of solid waste has shown an upward trend, with only a brief decline in 2008 and 2014 and a certain increase in other years. The change in chemical oxygen demand is more obvious, and the emission of chemical oxygen demand decreased massively from 78,806.9 tons in 2013 to 4515 tons in 2021. The total amount of ammonia nitrogen emissions has remained comparatively smoothly and steadily descending for nearly 20 years. From Figure 3b, it can be seen that from 2001 to 2015, the emissions of nitrogen oxides ascended from 86.36 × 10⁴ tons in 2013, and they reduced to 17.37 × 10⁴ tons in 2021, with an annual growth rate of −79.85%. From 2001 to 2010, the emission of smoke and dust showed a decrease from 0.832 millon tons in 2001 to 0.432 millon tons in 2010. The emission of dust decreased from 2001 to 2002, and it had a slight increase from 2002 to 2005 but maintained a relatively stable downward until 0.365 million tons in 2010. The emission of sulfur dioxide remained stable at around 1 million tons, with a significant descent in 2016 from around 0.9 million tons to around 0.38 million tons. After that, it showed a slow declining trend.

3.4. Analysis of Fitting Characteristics between Economic Development Quality and Environmental Pollution Intensity

According to the previous research [15], the per capita GDP of Shanxi province was selected as an indicator to measure the quality of economic development, wastewater (WW), solid waste (SW), chemical oxygen demand (COD), ammonia nitrogen emissions (NH₃–N) and sulfur dioxide (SO₂) emissions were taken as environmental pollution intensity indicators to conduct numerical simulation research. The research time axis is from 2001 to 2021, a total of 21 years.

(1)

Fitting curve between per capita GDP and wastewater discharge

The fitting results are shown in Figure 4a. The results show that the fitting effect between per capita GDP and wastewater discharge brings about striking results, showing a classic inverted-U curve.The regression fitting equation is y = 1 × 10⁻⁹x³ − 0.0001x² + 4.5777x + 2145.4, R² = 0.7122. From the curve, it can be seen that with the growth of per capita GDP, the wastewater discharge in Shanxi Province shows a trend of first increasing and then decreasing. The more ambiguous turning point appears at around 20,000 yuan per capita GDP. The more ambiguous turning point appears at about 20,000 yuan per capita GDP. The wastewater discharge in Shanxi descended with the continued growth of per capita GDP around 2014.

(2)

Fitting curve between per capita GDP and solid waste production

The fitting results are shown in Figure 4b; the fitting, which is per capita GDP and solid waste production, shows a monotonic increase. The regression fitting equation is y = 1 × 10⁻⁹x³ – 4 × 10⁻⁵x² + 0.9333x + 3046.3, R² = 0.9907. From the curve, it can be seen that with the growth of per capita GDP, the production of solid waste in Shanxi province shows a gradual upward trend, which can be roughly described as the left side of the inverted U-shaped curve and is still in a monotonic upward stage, namely, the production of solid waste also gradually increases, and there has not been a turning point within the data range of this article with the development of the economy in Shanxi and increase of per capita GDP.

(3)

Fitting curve between per capita GDP and chemical oxygen demand

The fitting results are shown in Figure 4c, which shows a monotonically decreasing relationship between per capita GDP and COD. The regression fitting equation is y = −1 × 10⁻⁸x³ + 0.0016x² − 81.631x + 1 × 10⁶, R² = 0.757. It can be seen from the curve that with the growth of per capita GDP, chemical oxygen demand in Shanxi Province shows a downward trend. According to the inverted U-shaped curve theory, it can be considered that the turning point of the fitting curve of chemical oxygen demand in Shanxi Province is around 2013. As per capita GDP continues to grow, COD emissions will decline.

(4)

Fitting curve between per capita GDP and ammonia nitrogen emissions

The fitting results are shown in Figure 4d, which shows a monotonically decreasing relationship between per capita GDP and ammonia nitrogen emissions. The regression fitting equation is y = −8 × 10⁻¹⁰x³ + 0.0001x² − 7.0359x + 124,547, R² = 0.7832. This curve can be roughly regarded as the right side of the inverted U-shaped curve, with the turning point occurring before 2013. From the curve, it can be seen that with the growth of per capita GDP, the ammonia nitrogen emissions in Shanxi Province show a downward trend, which is basically consistent with the COD change curve.

(5)

Fitting curve between per capita GDP and SO₂ emissions

The fitting results are shown in Figure 4e. The results show that the fitting effect of per capita GDP and SO₂ has a good result, showing a classic inverted-U relation. The regression fitting equation is y = 4 × 10¹²x³ – 4 × 10⁻⁷x² + 0.0119x + 25.803, R² = 0.7903; as can be seen from the curve, the sulfur dioxide emissions in Shanxi Province show a trend of first increasing and then decreasing with the growth of per capita GDP. The more ambiguous turning point appears at around 20,000 yuan per capita GDP. The sulfur dioxide emissions decreased with the continued growth of per capita GDP around 2013.

In summary, the fitting curve between the quality of economic development and the intensity of environmental pollution can be classified into three categories. The first type shows a classic inverted-U curve between per capita GDP and wastewater and SO₂ emissions, with a turning point occurring at around 20,000 yuan per capita GDP. The second one shows the per capita GDP is monotonically decreasing with chemical oxygen demand and ammonia nitrogen emissions, and the turning point is before 2013. The third category shows a monotonically increasing relation between per capita GDP and solid waste generation with no turning point yet.

4. Discussion and Summary

4.1. Analysis of Economic Development and Environmental Pollution Issues

According to Figure 1, Figure 2, Figure 3 and Figure 4, it can be seen that the rapid economic growth in Shanxi Province in the past 20 years has brought serious environmental problems, which can be summarized as follows:

(1)

Excessive energy consumption exacerbates resource dependence. From 2.2, it can be seen that during the “Tenth Five-Year Plan” (2001–2005) and “Eleventh Five-Year Plan” (2006–2010) periods, the environmental pollution intensity in Shanxi was relatively severe. Shanxi has abundant coal reserves, and its reserves can reach 27 billion tons, which capacity is second only to Xinjiang and Inner Mongolia. Also, its rank in China is third, and coal production accounts for about 1/4 of the country. Meanwhile, there are ample mineral resources, and 120 types of minerals have been discovered, including 63 minerals with useable resource reserves and 230.4 billion cubic meters of coalbed methane recoverable reserves [16]. And also, Shanxi is a well-known heavy industry base in China, and the steel industry is one of the prominent pillar industries. There are many large-scale iron and steel enterprises in it, such as TAI YUAN IRON & STEEL (GROUP) Co., Ltd. (Taiyuan, China), SHOU GANG CHANG ZHI IRON & STEEl Company Co., Ltd. (Changzhi, China). The scale of iron and steel production capacity ranks at the forefront of the country, focusing on the development of iron and steel, metallurgy, electricity, coke, and other industries. These traditional “three high” (high pollution, high energy consumption, and high emissions) industries bring high industrial output but also produce deadly environmental problems, mainly air pollution, soil pollution, and water pollution. According to statistics, the average annual rate of increase in energy consumption in the province from 2007 to 2017 hit 3.52%, increasing from 146.1976 million tons of standard coal to 200.5723 million tons of standard coal [17]. In energy structure, coal consumption takes up over 88% of the energy consumption in the industrial industry, forming a typical feature of Shanxi in the process of economic development, which is dominated by coal. It can be seen from Figure 1a that the gross regional product (1552.84 billion yuan) of Shanxi in 2017 ranked 23 among the 31 provinces and cities in China, while the per capita gross regional product (40,557 yuan) ranked 18, indicating that the per capita income level of residents in Shanxi is low, and the level of economic development is relatively backward, which reduced the expectations of environmental quality.

(2)

The industrial structure is single, and the economic structure is fragile. With the acceleration of industrialization, the proportion of the tertiary sector of the economy in GDP will inevitably surpass the primary and secondary sectors of the economy and become the main force leading the healthy development of the national economy. It can be seen from Figure 2 that during the period from the “Tenth Five-Year Plan” to the “Twelfth Five-Year Plan”, among the three major industrial output values of Shanxi, the secondary sector of the economy has the highest output value, ranked second one is a tertiary sector, and the last one is primary sector. Also, the proportion of the secondary sector of the economy in GDP exceeded 50%. The economic development was mainly driven by the secondary sector of the economy. The proportion of the tertiary sector of the economy in GDP was overtaking until the beginning of 2015, becoming the pillar of the social economy in Shanxi. From the perspective of the proportion of the three industries in GDP, the contribution rate of the primary sector of the economy has been essentially steady. Before 2015, the changing trend of the contribution rate of the secondary sector of the economy and the tertiary sector of the economy was basically smooth. Since the “13th Five Year Plan”, the contribution rate of the tertiary sector of the economy in Shanxi has continued to grow and exceeded the contribution rate of the secondary sector of the economy in 2015. The industrial structure is gradually changing from the secondary sector being the heavyweight, the tertiary sector is in the middle, and the primary sector is in the last one to the tertiary sector ranked first, the secondary sector is in the middle, and the primary sector is still in last one. The main reason for this change is that the People’s Government of Shanxi Provincial take the initiative to vigorously develop the cultural service industry [18] and adjust the proportion of the three major industries. Moreover, it optimizes industrial layout and upgrades and transforms industrial structure to gradually reverse the traditional extensive economic development model. Nevertheless, the extensive development approach still leads to an unreasonable industrial structure, with a high proportion of resource-based industries with high energy consumption and pollution, such as coal, steel, and electricity. There are fewer green and low-carbon emerging strategic projects, and there is still a difficult situation where environmental protection lags behind economic and social development.

(3)

Backward development level and insufficient investment in environmental protection funds. According to statistics [19], during the 11th Five-Year Plan period in Shanxi province, the total amount of environmental protection investment was 16.51 billion yuan. While within 7 years after entering the 12th Five-Year Plan and 13th Five-Year Plan periods, the total amount of environmental protection investment in Shanxi province has reached 18.59 billion yuan, of which only 15% is used to treat industrial three wastes (industrial wastewater, waste gases, and residues), and the majority is used for environmental infrastructure construction. Obviously, the investment is far from enough. For typical energy regions, the space for improving environmental pollution control is becoming increasingly small, and tackling challenges is becoming increasingly difficult. In the past 10 years of the new era, China’s industrial added value has doubled, from 20.9 trillion yuan to 45.1 trillion yuan. During the epidemic period, the output value had a positive increase, and China has been the world’s largest manufacturing country for 12 consecutive years [20]. From Figure 3, it can be seen that the discharge of solid waste in Shanxi has deadly decreased since 2012. After taking control measures, the discharge of industrial wastewater and sulfur dioxide in Shanxi has been decreasing year by year, and the compliance rate and sulfur dioxide removal rate of industrial wastewater discharge treatment has been increasing year by year. After 2012, industrial sulfur dioxide emissions considerably dropped, which was mainly due to the government’s significantly higher investment in exhaust gas treatment compared to other pollution control fields [21]. Moreover, during the “12th Five-Year Plan” period, the Shanxi government actively transformed its economic development mode from extensive to intensive, eliminated excess production capacity, and seized the construction opportunity of the “Yellow River Golden Triangle Demonstration Area” [22]. It aims to further optimize the industrial structure, which can strengthen regional economic cooperation between Shaanxi and Henan provinces, give full play to the advantages of cultural resource management, and actively explore new development models focusing on culture, tourism, finance, real estate, etc.

In summary, in the past 20 years, the main pollutants have shown a trend of increasing first and then decreasing steadily, with a turning point occurring during the “12th Five Year Plan” period. It can be seen that the environmental policies and investments of the Chinese and Shanxi provincial governments in the new era have been effective in the past 10 years, and the environmental pollution problem has been effectively improved.

4.2. Correlation Analysis

Correlation analysis refers to the analysis of multiple variables related to the quality of economic development and the intensity of environmental pollution in order to measure the degree of correlation between economic development and environmental pollution. From Figure 5, it can be seen that there are different degrees of correlation between economic development quality data and environmental pollution intensity data.

In terms of the quality of economic development, there is a positive correlation between GDP and per capita GDP, permanent population, and per capita disposable income. Among these data, the correlation between GDP and per capita GDP is the most powerful. Also, these data with a correlation coefficient of per capita disposable income is 0.981 and 0.742 with a permanent population. This means that population growth has a critical impact on GDP, and the level of economic development is closely related to per capita disposable income.

In the aspect of environmental pollution intensity, it can be seen that there is a strong positive correlation between wastewater discharge and chemical oxygen demand, ammonia nitrogen discharge, and sulfur dioxide discharge, which correlation coefficients of 0.757, 0.764, and 0.855, respectively. This indicates that the amount of wastewater discharge may affect the level of these pollutant emissions, and there is no significant correlation between the amount of wastewater discharge and the amount of solid waste generated or exhaust gas emissions. There is a strong correlation between the amount of solid waste generated, chemical oxygen demand emissions, and ammonia nitrogen emissions; the coefficients are 0.519 and 0.513, respectively. The correlation coefficient between chemical oxygen demand and ammonia nitrogen emissions reached 0.998, suggesting that the higher the concentration of ammonia nitrogen, the higher the COD when other components in industrial wastewater remain unchanged. The correlation coefficient between chemical oxygen demand and sulfur dioxide emissions is 0.642, showing a certain correlation, and the changing trend is basically the same under certain conditions. The correlation coefficient between ammonia nitrogen emissions and solid waste emissions, and sulfur dioxide emissions is greater than 0.5, showing a certain positive correlation.

The correlation between economic development quality and environmental pollution intensity indicators show that the correlation coefficients between GDP (per capita GDP) and wastewater emissions and sulfur dioxide emissions are −0.4 and −0.7, respectively. It shows that as economic indicators rise, wastewater emissions and sulfur dioxide emissions gradually decrease, which is consistent with the curve-fitting results in Figure 4a,e. The correlation coefficient between GDP (per capita GDP) and COD emissions and ammonia nitrogen emissions is −0.3, while the correlation coefficient between COD and ammonia nitrogen emissions exceeds 0.9, indicating that with the ceaseless development of the economy, COD emissions and ammonia nitrogen emissions slowly decrease. The fitting curves in Figure 4c,d further support this conclusion. The correlation coefficient between GDP (per capita GDP) and solid waste production exceeds 0.5, showing a positive correlation, which is consistent with the conclusion of the fitting curve in Figure 4b; namely, the two show a monotonically increasing relationship. In addition, the correlation coefficient between GDP (per capita GDP) and waste gas emissions exceeds 0.7, indicating that the level of economic development is also closely related to exhaust emissions.

In other indicators, the permanent resident population has the greatest correlation with the amount of solid waste generated, with a coefficient of 0.841, and a strong correlation with the amount of exhaust gas emissions, with a coefficient of 0.450. There is no obvious correlation with other pollutants (wastewater emissions, chemical oxygen demand emissions, ammonia nitrogen emissions, and sulfur dioxide emissions). The per capita disposable income has a strong correlation with the generation of solid waste and exhaust gas emissions, with coefficients of 0.513 and 0.714, respectively, while it has a remarkable negative correlation with sulfur dioxide (coefficient of −0.799) and has no remarkable correlation with other pollutants (wastewater emissions, chemical oxygen demand emissions, and ammonia nitrogen emissions).

In summary, the trend of correlation between the quality of economic development and the intensity of environmental pollution is basically consistent, and GDP (per capita GDP) shows moderate and strong negative correlations with wastewater emissions and sulfur dioxide emissions. GDP (per capita GDP) shows a moderate negative correlation with COD emissions and ammonia nitrogen emissions, while GDP (per capita GDP) shows a strong positive correlation with solid waste production. The correlation analysis results further support the fitting curve results.

4.3. Comparison of Evolution Characteristics in Different Periods

From

Table 1. Comparison of evolution characteristics in different periods.

Age	Timeline	Environmental Pollution Intensity Indicators	Quality Indicators of Economic Development	Result	References
2016	1998–2012	WW	PCGDP	N-shaped	[23]
2018	1995–2015	WW, COD, SW, Soot, WG, SO2	PCGDP	Inverted U-shaped, U-shaped, N-shaped	[24]
2020	1985–2017	WG, SO2, COD	PCGDP	N-shaped	[25]
2023	2001–2021	WW, SW, COD, NH3-N, SO2	PCGDP	Inverted U-shaped, Inverted N-shaped, N-shaped	This study

WW—Industrial wastewater discharge; COD—Chemical oxygen demand emissions; SW—Industrial solid waste emissions; WG—Industrial exhaust emissions; SO₂—Emission of sulfur dioxide; NH₃-N—Ammonia nitrogen emissions; PCGDP—Per capita GDP.

, it can be seen that there are slight differences in the research conclusions of different researchers on the relationship between economic development and environmental pollution in Shanxi Province during different periods. The research results from Zhang Rongyan et al. [23] indicate that the fitting curve of Shanxi is like the letter “N”. With economic growth, the industrial exhaust emissions in Shanxi will increase, and there has not yet been a turning point. The research results from Zhang Lin et al. [24] show that wastewater discharge, powdery dust (smoke and dust in the air) emissions, and sulfur dioxide appear like the inverted-U, industrial solid waste, and industrial waste gas are “U” shaped curves, and chemical oxygen demand is “N” shaped curves. Zhu Weixin et al. [25] found that the year with the most critical pollution in Shanxi was 1998, with atmospheric and industrial solid waste pollution being the most severe. In 2011, water pollution reached its peak. The fitting curve shows that the curves of industrial waste gas emissions, SO₂ emissions, and COD emissions conform to the inverted-U feature. The curve of NH₃-N emissions shows an inverted letter “N”. The curve of smoke and dust emissions and industrial solid waste emissions shows the letter “N”.

In this study, it was found that the per capita GDP of Shanxi province showed a classic inverted “U” shaped relationship between wastewater and SO₂ emissions, with a turning point occurring at around 20,000 yuan per capita. It is monotonically decreasing with chemical oxygen demand and NH₃-N emissions and is monotonically increasing with solid waste generation. The reasons for the differences in the above research results may include the following. Firstly, differences in the selection of data intervals and ranges. Different researchers have chosen different research intervals and ranges, which may lead to different results. Secondly, differences in the selection of research variables. Researchers may choose different variables, such as some studies only studying exhaust and wastewater emissions, while others may also study solid waste production, which may lead to different results. Thirdly, differences in research methods: researchers may adopt different research methods, using different statistical or computational methods and resulting in different results.

On the whole, this study focuses on characteristics of economic development and environmental pollution in a typical energy region, Shanxi. Nevertheless, it is necessary to select appropriate variables, research methods, and data intervals as good choices for future research. Only in this way can we obtain more accurate research results.

5. Conclusions

(1)

The GDP of Shanxi Province has shown a certain growth trend in the past 20 years, with an average annual growth rate of 7%. The overall per capita GDP shows a growth trend, with an average annual growth rate of 12.82%. However, the growth rate is unstable and fluctuates significantly.

(2)

In the last 20 years, the intensity of major pollutants (wastewater, solid waste, chemical oxygen demand, ammonia nitrogen emissions, nitrogen oxides, smoke, dust, and sulfur dioxide) in Shanxi Province showed a trend of first rising and then stabilizing. The turning point roughly occurred around 2012 during the “12th Five Year Plan” period.

(3)

The numerical fitting features can be classified into three categories. The first category shows a classic inverted “U” curve relationship between per capita GDP and wastewater and SO₂ emissions, with a turning point occurring at around 20,000 yuan per capita GDP. Second, the per capita GDP is monotonically decreasing with chemical oxygen demand and ammonia nitrogen emissions, and the turning point is before 2013. The third category shows a monotonically increasing relationship between per capita GDP and solid waste generation, with no turning point yet.