Air pollution can directly or indirectly affect human health, causing physical discomfort and leading to disease or even death. Studies have shown that when the human body is exposed to highly polluted air for a long time, the mortality rate increases [1
]. Furthermore, air pollution has become the fourth primary risk factor for all deaths in China after heart attack, dietary risk and smoking, according to the latest statistics [3
]. In recent years, there have been frequent haze weather events in many places in China where the air quality was mostly between ‘moderate’ and ‘unhealthy for sensitive groups’. Studies show that under such air conditions, the mortality rate from cardiovascular and cerebrovascular diseases and the prevalence of asthma and respiratory diseases both increase [4
]. In January 2013, a long period of haze hit China and covered a quarter of the land area, affecting nearly half of the population. Because of this, haze days anomalies in the Eastern region lasted more than ten days [5
]. During these years, China strengthened its air quality monitoring and enhanced its air pollution control. For instance, the Chinese government issued a series of air pollution control schemes. In 2013, the government spent three times more money on air pollution than it did in 2012, and this helped to reduce air pollution (air pollution index (API) value declined 10.45 from 2014 to 2013) [6
As for air pollution and control, current research on air pollution and control is focused on four parts, as follows: sources [7
], relationship with health [14
], extreme events [18
] and control methods [23
]. For instance, Ashbaugh [7
] used statistical methods to categorize air pollution sources in the United States. Qiu et al. [9
] showed that emissions from motor vehicles are one of the main sources of air pollution. Li et al. [11
] found that China’s air pollution is correlated with the rapid industrialization; Cong [14
] found that ambient air pollution from waste gas emissions was associated with multiple cancer incidences in Shanghai in a retrospective population-based study; Zhang et al. [19
] used remote sensing data and numerical simulations to analyze a heavy air pollution event in Chengdu, and found the sources and causes of this event; Lawrence et al. [23
] conducted research on air pollution control engineering, and obtained some air pollution control models through an empirical analysis. Through the above studies, it has been found that the research on air pollution mainly focuses on source, methods, cases and the relationships between industry and pollution. Relatively less research has been carried out on the relationship between air pollution and control and the resulting pollution control. In addition, studies on these topic always attract public attention [29
The reason for the scarcity of research is that the relationship between air pollution and control is abstract, and the amount of control investment is the most important factor in China’s air quality improvement [30
], so we used the relationship between air pollution and control investment, which resembles the environmental Kuznets curve between the economy and the environment. The environmental quality metrics in this theory is pollution intensity [31
]. In 1991, the environmental Kuznets curve was proposed by Grossman and Krueger by referring to the Kuznets curve in economics during the study of the environmental impact of the North American Free Trade Agreement [32
]. The environmental Kuznets curve shows that the environment status and the level of per capita income have an inverted U-shaped relationship. As indicated by the curve, at the initial stage, economic development causes environment deterioration. When the per capita income reaches the inflection point, the environmental quality will be improved along with the economic growth. The relationship between the economy and the environment in the environmental Kuznets curve is essentially the relationship between investment in pollution control brought by the economy. Therefore, it is possible to study the relationship between air pollution and control investment based on the environmental Kuznets curve.
In summary, research on air pollution and control investment is of great significance. Therefore, based on the Environmental Theory Model, this study draws attention to the relationship between changes in air pollution and control investment, analyzing the current status of pollution control in China. The objectives of this study are (1) to show the solution to air pollution and control investment by creating a distribution of China’s air pollution index (API) and a distribution map of China’s waste gas control investment from 2005 to 2014; (2) to use the Pearson correlation coefficient to characterize China’s API value and air pollution control investment within a ten-year data set; and (3) to show the inverted U-shaped relationship between air pollution and pollution control. Through the above three objectives, this paper provides a series of suggestions for the Chinese government and offers a new perspective into the study of air pollution in China.
4.1. Variable Selection and Applicability of the Environmental Kuznets Curve
The environmental Kuznets curve shows that environmental status and level of per capita income have an inverted U-shaped relationship. The capital in environmental Kuznets curve can be divided into two parts: one for production and spoiling the environment; the other for pollution control and improving the quality of the environment [51
]. The pollution control part is similar to environment control investment. So, the environmental Kuznets curve is helpful in the study of air pollution and control investment.
The environmental Kuznets curve’s variable on the study of air environment is income and economic aggregate [52
]. For instance, Selden et al. [53
] used a cross-national panel of data on emissions of four important air pollutants: suspended particulate matter, sulfur dioxide, oxides of nitrogen, and carbon monoxide, and they found that the per capita emissions of all four pollutants exhibit inverted-U relationships with per capita GDP. Orub et al. [54
] proved the existence of an environmental Kuznets curve for air suspended particulate matter through the study of the relationship between per capita income and environmental degradation in Africa. When the per capita income and per capita GDP are variable, under the same conditions of income, there are discrepancies in the control investment in different regions. So, taking the per capita income and per capita GDP as variables, there might be errors.
This paper used Kuznets curve as a reference and extended its scope of application. Instead of using per capita income and per capita GDP, we adopted air pollution control investment as a variable for accuracy. In this way, we were able to see the relationship between pollution control and ecological benefit. In addition, by analyzing the inflection point of the inverted U-shaped curve, we were able to answer the following question: what is the threshold number of control investment that improves air quality? However, a defect may still exist due to the fact that this curve is solely based on data covering the period from 2005 to 2014.
Due to limited resources and data availability, we acknowledge the following limitations. Firstly, in terms of data precision, after 2013, two new indexes were added to China’s air quality monitoring indicators, PM2.5 and ozone (O3), which were not included in this study to allow data continuity. In addition, we only used 34 monitoring sets points, so the interpolation data accuracy still needs to be further improved. For the accuracy problem, this study used 34 sets of API interpolation maps and 74 site interpolation maps from 2013 and 2014 for the correlation analysis and obtained a high level of correlation. It is concluded that the data accuracy of this paper is good.
Secondly, the effect of interference factors presented a limitation. This paper mainly focused on the air pollution control status study in the secondary industry. Apart from industrial air pollution, less ink was given to other sources of air pollution. Still, this paper did not exclude the interference of other pollution sources with air quality. Future research will study how to analyze the status of multi-source air pollution control and investigate how to reduce the interference of irrelevant variables in the analysis.
Despite rapid economic growth, China’s air quality is still lower than developed countries. The air quality and control investment from 2005 to 2014 on a province-wide scale by IDW was analyzed by Pearson correlation. This paper concludes that (1) at present, there is a significant positive correlation between China’s API value and air pollution control with the coefficient of correlation being 0.466 (p-value < 0.01)—the lower air quality in China, the higher the investment put into air pollution control. ‘Treatment after Pollution’ remains a remarkable feature of China’s economy; (2) there is an inverted U-shaped relationship between China’s air pollution and control investment (2005–2014) which approximates the environmental Kuznets curve. In other words, an inflection point exists. Before the inflection point, there is positive correlation between air pollution and control investment. When the inflection point appears in the year of 2013 with the control investment of 2 billion yuan, the correlation turns negative; (3) Air pollution in north China is more serious than that in south China, and the distribution is consistent with the distribution of pollution control investment.
Deficiencies and further study directions in this paper are as follows: (1) This paper selected the air pollutant concentration data from 2005 to 2014. However, after 2013, the air quality monitoring index changed and new indicators were added. We used the API to allow good continuity; (2) this paper was limited by data in terms of studying the current status of air pollution control. It mainly focused on the study of the status of industrial air pollution control and dealt little with the control status of other pollution sources; (3) this paper did not establish an effective study system for air pollution control status due to limitations caused by data and technique. However, this study offers a new perspective into the study of air pollution in China and contributes to the literature on pollution control. Further study will be based on environmental pollution models, such as establishing a relationship model between air pollution and control investment, and the proportional hazards model (COX model) could also be used to conduct an air pollution risk assessment and establish an assessment model for air pollution and human health risk.