Xiaoming CHUAI, Gaoyue ZHANG, Haixia ZHOU

1. Safety and Emergency Research Center of Henan University of Technology, Jiaozuo 454000, China; 2. Library of Henan University of Technology, Jiaozuo 454000, China

Abstract At the present stage, China is facing a large number of new risks and challenges in the safety environment, all kinds of environmental pollution problems are widespread, and the atmospheric environmental problems are particularly prominent. According to the discussion and research of a large number of scholars at home and abroad, a series of factors such as the development of urbanization, economic growth and changes in industrial structure, human consumption, and a large number of large-scale enterprises with high energy consumption are the important reasons for the aggravation of air pollution in our country. Starting with the socio-economic factors closely related to human activities, this paper establishes Sustainability Evaluation using Indicators (SEI), and explores the current situation of the research on the causes of air pollution in China through literature research and summary methods. It not only provides a scientific basis for the reasonable formulation of policies and strategies, but also makes it more convenient for the government to carry out accurate governance on this basis, which is of great significance to the construction of a beautiful China.

Key words Air pollution, Influencing factors, Social economy, Air quality

1 Introduction

The great wheel of the industrial revolution has led to great changes in the world economy, and energy such as coal, oil and natural gas has become the golden key for countries all over the world to open the economic Pandora’s box. With the rapid consumption of a large amount of energy, harmful gases are blindly emitted directly into the atmosphere, the degree of air pollution is deepening day by day, and the scope is getting wider and wider, which not only places a stagnant yoke on the economy of various countries, but also seriously threatens people’s health and life. With the acceleration of urbanization and industrialization in China, haze, as a major harmful gas of air pollution, has a great impact on human health, climate environment and urban sustainable development. According to statistics, about 1.2 to 1.6 million people die prematurely due to air pollution every year[1-2], and the economic cost of air quality deterioration reaches 1%-8% of China’s annual GDP[3-4]. Therefore, it is imperative to accurately identify the influencing factors of air pollution and study the relevant causes, so as to provide a scientific basis for the control of air pollution in China.

2 Current research status of urban air pollution

The rapid economic development under the "object-oriented" mode is doomed to take the sacrifice of the regional environment as the price. The problem of urban air pollution is rampant, and the previous research on air pollution mainly focuses on two aspects. One is to explore the temporal and spatial evolution characteristics of air quality through the division of the geographical area where the city is located. For example, based on the national[5-7], urban agglomeration[8-10], provincial[11-12], urban[13-15]scales, a variety of analysis methods[16-18]are used to explore the interannual variation characteristics of air quality in different geographical regions. On the other hand, it focuses on the analysis of the causes of urban air pollution. Urban air quality is affected by a variety of factors, which is more complex. The influencing factors are not isolated individuals, but intertwined to affect the change of air quality[19]. It can be classified into two aspects: natural environmental factors and socio-economic factors. First, the natural environmental factors, such as air temperature[20], precipitation[21], and humidity[22], including natural environmental factors such as vegetation cover[23], topographic conditions[24], altitude[25], as well as sudden natural factors such as volcanic eruptions and forest fires will have a certain impact on urban air quality. The second is about the social and economic aspects. Foreign scholars Grossman and Kreuger first proved that there is an inverted U-shaped relationship between environmental pollution and economic growth, and this quantitative relationship is called Environmental Kuznets Curve (EKC). With the proposal of EKC curve, scholars began to shift their research focus to the verification of EKC curve. Domestic related research began in the eighties of the 20thcentury. Xu Dixin[26]introduced the concept of ecological economy into the development process of China’s economy for the first time, so as to guide China’s economic growth. Then Li Chongyang[27]established a game model to prove that the use of bilateral negotiation to meet the needs of interests between economic development and ecological environment protection can achieve a win-win situation. Fan You[28]took 285 cities in China as the research object, and found that the relationship between environmental pollution and economic growth varies with different income levels. For the low-income areas, the two strongly stimulate each other, but compared with the high-income areas, the effect of the relationship between the two is not obvious. Since then, the analysis of the causes of air pollution has emerged one after another based on the socio-economic perspective. Many scholars believe that urban population agglomeration and growth[29-30], industrial production involved in the secondary industry[31], coal, oil and biomass energy consumption of enterprises above designated size[32], car ownership[33]and so on are the series of culprits that cause air pollution. Additionally, different levels of urbanization[34-35], economic growth rate[36], industrial structure[37], energy use structure and efficiency[38]are also regarded as the main culprits affecting air quality.

3 Study on the socio-economic factors influencing air pollution in China

Based on the socio-economic factors closely related to human activities, such as population development, urban construction, industrial structure and energy consumption, this paper establishes Sustainability Evaluation using Indicators (SEI), which is divided into three modules: urban development and population growth (UDPG), economic growth and industrial structure (BGCIS), industrial energy growth and consumption structure (IECGSC) (Table 1). Based on the past scholars’ research on urban population, traffic exhaust, residents’ living consumption, industrial structure innovation and energy consumption of enterprises above designated size, this paper makes an analysis of the causes of urban air pollution.

Table 1 SEI system for air pollution factors

3.1 Impact of urban development and population growth modules on air pollution

3.1.1Demographic variables. The rapid increase of urban population is often accompanied by the continuous deterioration of environment, land and resources. According to the statistics from theChinaStatisticalYearbook, the number of permanent residents in key cities across the country has shown an overall upward trend in the past few years. A large number of reviews at home and abroad have discussed the impact of population on air pollution. Tong Yufen and Han Qian believe that related polluting gas emissions based on large-scale human life and productive activities are important factors affecting air quality[39]. Du Hui explored the relationship between population factors and air pollution from the perspective of population size and structure[40]. In addition, Zhang Yinjun also explored the impact of population aggregation behavior on ambient air quality based on samples of 74 key cities in China[41]. It is proved that there is a significant positive correlation between the increase of population density and the deterioration of urban air quality. It is suggested that urban population concentration should be adjusted and urban air quality should be improved by gradually promoting population urbanization. Peng Lisietal.used spatial metrology to prove that there is a significant spatial effect of PM10pollution in China’s provinces[42]. The increase of population density will significantly worsen urban air quality. In recent decades, China’s population growth has gradually slowed down, and the impact of changes in population structure on air pollution has become more and more prominent. Based on this, many scholars have gradually expanded their research to factors such as population aging and urbanization rate.

3.1.2Urbanization. On the one hand, through the analysis and comparison of the temporal and spatial distribution characteristics of haze weather in a certain area of Jiangsu Province and the influence of urbanization on annual haze days[43], Song Juan found that rapid urbanization and the number of days with haze increased in the same direction, and there was a significant positive correlation between them, which confirmed that the process of urbanization could aggravate air pollution. On the other hand, according to the behavior of human winter heating, Zhang Jingetal.analyzed and compared the concentration of air pollutants produced by two heating modes in Tianjin and Shanghai during the heating period and non-heating period[44], and found that the mass concentrations of air pollutants such as PM2.5, PM10, NO2, SO2and CO in the heating period were higher than those in the non-heating period.

3.1.3Car ownership. Li Xiaodan and Wei Yurui found that there was a high correlation between motor vehicle ownership and air PM2.5index in Beijing[45]. Wangetal.measured the factors of air pollution from the perspective of multi-resolution emission inventory[46], and found that it was transportation that ranked first in the list of the contribution of air pollution. Zhou Wenhua[47]and Zhang Juetal.[48]screened and studied the sources of air pollutants and found that industrial emissions, traffic exhaust and domestic waste combustion were on the list. Compared with the emission data, it was found that there was a difference between coal-fired pollution and motor vehicle pollution. Some studies have shown that vehicle exhaust emissions will increase under acceleration, deceleration or idling compared with uniform speed.

The process of urbanization in China is accelerating, and the urban population density continues to rise. Automobile traffic exhaust, urban construction dust, industrial waste gas, a large amount of infrastructure needed by residents, housing construction under construction, a large amount of building dust have become an important cause of air pollution, which has an important impact on the air environment and quality.

3.1.4GDP. Economic development will restrict the potential of environmental quality improvement, indicating that economic factors are the most direct factors affecting air quality. Zhang Zheetal.compared the relationship between air quality and per capita GDP in 64 key cities of environmental protection in China from 1990 to 2003[49]. It was found that urban economic development was often based on environmental pollution, and confirmed that PM10was the primary pollutant affecting urban air quality. Shao Shuai verified the positive correlation between economic growth and environmental pollution in the effect of energy saving and emission reduction of economic agglomeration[50]. Wu Xuepingetal.confirmed that economic growth did have a certain impact on air quality through the analysis of panel data of 30 provinces and cities from 2001 to 2014. Since the Environmental Kuznets Curve (EKC) was proposed, economic growth and environmental pollution have become classic research topics in the field of environmental economics. Grossman and Kruegeretal.conducted empirical research on the relationship between per capita GDP and environmental degradation based on this theory[52], and put forward one of the most important hypotheses about EKC: EKC is not inevitable, developing countries can avoid environmental degradation caused by economic development through new technologies, new energy and other ways.

3.2 Economic growth and industrial structure module

3.2.1Output value of primary industry. The study found that the three industries classified according to the national economic sector have a certain impact on urban regional air pollution from different aspects. The unreasonable treatment of a large amount of crop straw in agricultural production in China, such as open-air burning, causes serious stress to the atmospheric environment. According to the investigation of Li Qing[53], it is found that the number of straw burning points that can be monitored in China from 2013 to 2016 was as high as 4 000 annually, and both the number of burning points and the burning area are increasing year by year. Xiong Zhunan also discussed the impact of repeated ban on straw burning, huge pollution by bulk coal combustion and increased motor vehicle exhaust emissions on air quality in rural areas of China[54]. Straw burning, chemical fertilizer use and livestock and poultry breeding are all important emission sources of air pollution in the primary industry. On the one hand, a large quantity of primary particles emitted directly during crop straw combustion is an important cause of air pollution[55]. On the other hand, other primary pollutants (SO2, NOx, VOCx) and volatile organic compounds (VOCs) are generated through chemical reactions to produce a large number of secondary particles such as aerosols and PM2.5, further aggravating air pollution[56]. However, Mo Caifenetal.investigated the air quality pollution sources in Wuhan and found that the effects of agricultural straw combustion on motor vehicle exhaust, industrial exhaust emissions and construction dust on air quality are decreasing year by year[57]. This may be related to the introduction of policies such as the modernization of agricultural production and the prohibition of straw burning in China in recent years.

3.2.2Output value of secondary industry. The industrial revolution in Western countries started early, and frequent air pollution events such as London smog and photochemical pollution in Los Angeles in North America at the beginning of the 20thcentury are all manifestations of the serious impact of industrialization on air quality. When Xu Zhengsongetal.[58]explored the relationship between economic development level, industrial structure and environmental pollution, they found that there was a significant positive correlation between the proportion of industrial added value in GDP and heavy industry output value in total industrial output value and the comprehensive index of environmental pollution. The higher the proportion of heavy industry is, the more serious the environmental pollution is. Li Shixiang, Shi Dan and Liu Changetal.[59-61]believe that the phase of China’s industrialization development is mainly characterized by inefficient energy use and obvious overcapacity in high energy-consuming industries. The secondary industry, as the main body of energy consumption, deserves to be the main emission source of a large quantity of smoke and dust, sulfur dioxide and nitrogen oxides in the country. If the economic growth depends too much on heavy industry and it lacks the adjustment of industrial structure, the gas emissions from industrial production and construction dust, as the main sources of air pollution, will seriously negatively affect the air quality.

3.2.3Output value of tertiary industry. Xu Zhengsongetal.[58]found that although industrial development had a strong impact on the atmospheric environment, the tertiary industry as a whole had no significant impact on environmental pollution. However, Sun Genjin, Qian Qi, Tang Guilinetal.studied the impact of air pollution on the development of tourism in China’s tertiary industry[62]and found that tourism was highly sensitive to air pollution and air pollution had a significant negative impact on tourism. Transportation in the tourism industry can not be ignored. The primary particulate matter emitted by motor vehicle exhaust and the secondary particulate matter produced by the reaction of NOX and hydrocarbon (CHX) in the air are the important sources of regional PM2.5. Thus it can be seen that tourism income, as an important part of local GDP, must have a great impact on urban air quality.

3.3 Industrial energy growth and consumption structure module

3.3.1Domestic energy consumption. Atmospheric environment, as one of the important factors that can restrict the sustainable development of China’s economy, often exists with residents’ high-carbon consumption patterns. The study shows that under the same heat generation efficiency, the pollutant emission of residential raw coal is much higher than that of industrial coal, heating and electric power industry. Wang Litaoetal.pointed out that the emission factor of some civil manual-fired furnaces was 2 to 15 times higher than that of the corresponding electric power industry furnaces, because the content of carbon monoxide in the waste gas was obviously on the high side due to insufficient coal burning for civil use[63]. Pan Taoetal.also found that during the winter and spring heating period, the average daily emissions of sulfur dioxide, nitrogen oxides, fine particulate matter (PM2.5) and respirable particulate matter (PM10) from civil coal burning were about 7, 1.2, 5 and 8 times higher than those of the electric power industry[64].

3.3.2Energy consumption of enterprises above designated size. There are many researches on "energy-environment-economy" by foreign scholars. Paoetal used the Lotka-Volterra model to study the competitive interaction among energy, environment and economy in the United States, pointing out that there was an interaction between energy and environmental quality, and that there was an environmental Kuznets curve. It is suggested that in developed markets like the United States, strengthening energy security and improving energy efficiency, developing low-carbon clean energy and mitigating climate change should be the primary task. Tiba and Omri studied the "energy-ecology-economy" relationship from 1978 to 2014, and concluded that while energy consumption stimulated economic growth, the subsequent increase in pollutant emissions would further increase the damage to the environment, the three showed a dynamic cycle and interacted with each other. Domestic scholars mainly study the impact on air quality from the two aspects of total energy consumption and structure. Liu Zhixiong[65]pointed out that energy consumption, as one of the main causes of environmental deterioration, should be controlled from the scale of consumption. Mai Chaopingetal.[66]analyzed the dynamic relationship between energy consumption structure and ambient air quality and pointed out that coal-based energy consumption structure brought economic benefits, but at the same time harmful gases produced in the production process are the main sources of air pollutants.

3.3.3Raw coal consumption of enterprises above designated size. As the energy pillar of China, coal has occupied an important strategic position in the energy consumption structure for a long time. 90% of SO2, 85% of CO2, 70% of smoke dust and 60% of NOx in urban air pollution in China come from coal combustion. Liu Dan used grey correlation analysis method to study the relationship between the main air pollutants and energy consumption structure in Xi’an[67]. It is found that the proportion of raw coal and oil in the energy consumption structure has the highest correlation with the concentration of each pollutant. By comparing the sources of PM2.5before and after the large-scale implementation of the "coal to gas" and "coal to electricity" policies in Beijing, Cao Junji[68]found that in the total PM2.5generated by local pollution, coal burning, accounting for 22.4%, has become the second largest pollution source after traffic exhaust pollution, accounting for 31.1%, having an obvious impact on environmental quality. In 2013, the State Council issued theAirPollutionPreventionandControlActionPlan(also known asTenArticlesoftheAtmosphere) as a national action program for air pollution control in the following five years. According to the final assessment results of the implementation announced by the Ministry of Ecology and Environment, the implementation of theTenArticlesoftheAtmospherehas significantly reduced the emissions of major air pollutants throughout the country. By decomposing the contribution of various measures to emission reduction, it is found that the control of coal-fired boilers is indeed one of the three major measures that make the most significant contribution to emission reduction, which fully proves the close relationship between raw coal combustion and atmospheric pollutant emissions.

3.3.4Power consumption of enterprises above designated size. Power is the "industrial blood", the power consumption above the scale is restricted by economic factors, and the impact on air quality should not be underestimated. Zhu Shuai, Huang Qingetal.believe that China’s atmospheric environment has changed from a single local soot pollution to a regional compound pollution[69-70]. The electric power industry above designated size has become a major emitter of pollutants such as SO2, NOx and smoke. The emission chimneys of electric power enterprises are relatively high, and the pollutants emitted can be transmitted over a long distance and in a large area. As a result, the electric power industry has become the main industry of regional compound air pollution. And with the diversification and complexity of atmospheric environmental problems related to enterprise power energy consumption, it is urgent for researchers to change the research and control means of air pollution from single pollutant control to multi-pollutant integrated control. Based on the CMAQ air quality model, Xue Wenboetal.evaluated the effects of multi-pollutant cooperative control in the power industry on the treatment of regional compound air pollution[71], and found that the reduction of NOx and SO2emissions in the power industry can reduce the concentration of secondary fine particles such as nitrate and sulfate, thus indirectly alleviating PM2.5and air pollution. Studying the relationship between the changes of pollutant factors and environmental quality benefits to prove the correlation between large-scale electric power industry and air pollution, is of great significance for formulating and optimizing multi-pollutant control strategies in electric power industry.

4 Conclusions

Air pollution is not caused by a single factor, and the causes of air pollution are different in different countries and regions. Summarizing the causes of air pollution in different places is of great practical significance for the control of air pollution. In accordance with the research of scholars, it is found that the indicators of each module under the socio-economic category are inextricably linked to the air pollution. First of all, with the influx of a large rural population into the cities, the population density of various cities in China has soared, and the urbanization rate has increased significantly, and the air quality has been significantly affected by population size and urbanization. Due to the substantial increase in human production and living activities in cities, the AQI index has not decreased but increased. In the process of urbanization, the traffic situation has been improved, and the number of motor vehicles has continued to increase, followed by a large quantity of vehicle exhaust emissions, which has become the main factor threatening the urban ambient air quality. Secondly, the primary industry and the secondary industry are still the main sources of polluting gas emissions, and the impact of the secondary industry is more significant, which is mainly related to the increase of air pollutants caused by the massive combustion of fossil energy such as coal and oil in the development of industrial enterprises in China. With the advancement of urbanization and industrialization, the human factors from economy, society, population development, urban construction, energy consumption and so on have a more concentrated impact on urban air quality. Although the government has achieved results in the treatment of environmental problems and the overall air quality has been improved, formulating relevant policies and programs in accordance with local conditions and vigorously taking corresponding measures are the effective strategies for sustainable improvement of urban air environment.