As a critical indicator of environmental quality, air is a natural resource that humans cannot live without. Therefore, air pollution is one of the primary environmental risks that affects human health. According to the World Health Organization’s “World Health Statistics Report 2021”, air pollution, as an environmental risk factor, is associated with various acute and chronic diseases, such as cardiovascular disease, stroke, respiratory disease, and cancer; air pollution caused approximately 7 million deaths globally in 2016 [1]. Since the implementation of its reform and opening-up policy, China has experienced rapid economic development, which significantly improved the living standards of its people. However, the resulting extensive economic development has led to persistent environmental pollution problems, particularly severe air pollution. The health risks and hazards caused by air pollution have become a public concern. China’s ecological civilization construction emphasizes solving prominent environmental problems that harm public health, and the National 14th Five-Year Plan and 2035 Vision Goal emphasize the establishment of a public health impact assessment system. Therefore, revealing the impact of air pollution on residents’ health in China is of practical significance for assessing the health risks of air pollution and promoting healthy living environments.

In recent years, research on public health and air pollution has received increasing attention. Firstly, the health risks associated with air pollution are gradually increasing. According to a global burden of disease study published in The Lancet in 2017, China is one of the countries that is most severely affected by air pollution, with 1.1 million deaths caused by atmospheric PM_2.5 pollution each year, indicating an increase of 17.5% compared to 1990 [2]. A Chinese burden of disease study published in The Lancet in 2019 showed that air pollution is the fourth largest health risk factor in China [3]. Secondly, air pollution has effects on both physical and mental health. In terms of the impact on physical health, existing medical evidence indicates that both short-term and long-term exposure to air pollution can lead to acute and chronic health issues [4]. In terms of mental health, some studies have shown that air pollution factors, including NO₂, SO₂, PM₁₀, and PM_2.5 concentrations, have significant negative effects on people’s happiness and mental health ^{[5][6][7][8][9][10]}[5,6,7,8,9,10] and can also increase the incidence of depressive symptoms [11]. Recently, some studies have reported that indicators of self-reported health status, such as disease severity and depressive symptoms, are associated with perceived air pollution rather than measured air pollution [12]. Scholars have conducted extensive research on the relationship between air pollution and health. However, there are still some shortcomings and areas for further research. Firstly, scholars have mostly studied the health effects of air pollution from a physiological perspective; even though there has been discussion around mental health in recent years, it is still relatively limited. Additionally, the effects of air pollution on physical and mental health are generally discussed separately. Overall, research on the health effects of air pollution is not yet systematic and comprehensive. Secondly, current research mainly focuses on developed countries [13], and there is less research on developing countries. Influenced by factors such as differences in air quality standards, the explanatory power of research results in developing countries is still limited [14]. China is promoting the construction of a healthy and beautiful China, hoping to achieve the goal of safeguarding public health as well as protecting and improving the environment. This requires more academic attention. Thirdly, the health assessment field related to air pollution perception should be optimized. In recent years, with the rise of risk perception research, air pollution as an environmental risk has also attracted some scholars’ attention ^[15][16][15,16]. Currently, only a few studies have applied air pollution perception to health impact assessments, and more in-depth empirical research is needed.

Deguen et al. [17] proposed that a comprehensive assessment of the health effects of air pollution must include both physiological and mental impacts. This study measured residents’ health status from two aspects: self-rated health and mental health. Existing research has shown that self-rated health can comprehensively reflect individual health status, and scholars generally use self-rated health as a proxy indicator of physical health status ^{[18][19][20][21][22][23][24]}[18,19,20,21,22,23,24].

2. Health Risks of Air Pollution

Early research on the health effects of environmental pollution was based on the health production function theory pioneered by Grossman [25]. Subsequently, Gerking et al. [26] incorporated environmental factors into the health production function and examined the impact of environmental factors on health depreciation rates. Existing research has mostly analyzed the effects of pollution on residents’ health from an epidemiological perspective, with pollution mainly causing respiratory, cardiovascular, and heart diseases ^[27][28][27,28]. Air pollution is an important source of environmental pollution, and the health effects of air pollution have been studied and analyzed by scholars in the fields of epidemiology, health economics, sociology, and other related fields. Many scholars have studied the health risks associated with air pollution by examining its relationship with mortality rates and various diseases. Francesca et al. [29] analyzed the relationship between air pollution and mortality rates in 88 of the largest cities in the US from 1987 to 1994 and found that, in most areas, the previous day’s PM₁₀ concentration was positively correlated with total mortality rate. Chen et al. [30] systematically evaluated the health effects of air pollution in China using a regression discontinuity design based on data collected from 1981 to 2000. Their results showed that a 100 μg/m³ increase in Total Suspended Particulate (TSP) concentration in a long-term living environment was associated with a 14% increase in mortality rate and a 3-year reduction in life expectancy. The increase in the mortality rate was mainly due to an increase in cardiovascular and respiratory diseases. Regarding the relationship between air pollution and infant mortality, Chay [31] found that reducing air pollution levels could reduce the number of infant deaths. Currie et al. [32] reached a similar conclusion in their study. Regarding the relationship between air pollution and health, most of the research studies have focused on the effects of air pollution on physical health. However, in recent years, some studies have begun to explore how air pollution affects people’s mental health. Compared to physical illnesses, which have a certain latency and lag, intense and negative psychological experiences are more direct and prominent. In this sense, mental health is an issue that economists, sociologists, and psychologists can and should explore in order to prevent and reduce the harm of environmental problems on mental health. In their studies on air pollution and subjective well-being, Marques et al. [33] used a quasi-experimental design to compare the subjective well-being of residents living in industrial and non-industrial areas. They found that residents living in highly polluted industrial areas not only had lower subjective well-being but also higher levels of anxiety and depression. This was because the air pollution affected individuals’ perception of the risk of illness. Even if they were not ill, individuals exposed to poor air quality for a long time would have increased worries and fears about getting sick, leading to a decrease in their subjective well-being and even anxiety and depression. Some scholars have conducted research on the relationship between air pollution and anxiety and psychological stress ^[34][35][34,35]. Regarding air pollution and depressive symptoms, Block et al. [36] pointed out that air pollution could cause systemic inflammation, cerebrovascular damage, and neurodegenerative changes, thus increasing the risk of depression. Many scholars have empirically analyzed the relationship between the two, and most studies have shown a positive correlation between air pollution and depression. Lim et al. [37] used survey data from Seoul, South Korea, and found that air pollution increased the relative risk of depression in the elderly. Pun et al. [38] used data from the National Social Life, Health, and Aging Project (NSHAP) in the US and studied the relationship between air pollution and depressive and anxiety symptoms in older people. Their results showed that PM_2.5 was significantly positively correlated with depressive and anxiety symptoms in older people, showing a stronger correlation among individuals with lower socioeconomic status and related chronic diseases. However, some studies have found no positive correlation between air pollution and depressive symptoms [39]. In summary, air pollution has negative effects on human health, with research mainly focusing on the physiological aspects and primarily targeting developed countries. There has been relatively little research on the relationship between air pollution and mental health, especially in developing countries. Recently, foreign scholars have begun to pay attention to this relationship. In China, research on the health effects of air pollution is relatively scarce, and descriptive statistical analyses are more common than empirical analyses. Therefore, it is necessary to use China’s empirical data to analyze the health effects of air pollution.

3. Perception of Pollution and Its Health Effects

There has been a significant amount of research on environmental perception, which includes evaluations of the overall environment as well as specific elements, such as water and air quality ^[40][41][40,41]. Perception of environmental pollution refers to an individual’s perception of pollution in their environment. Previous studies have focused on the impact of pollution levels, resident characteristics, and social environments on the perception of environmental pollution. Most studies suggest a positive correlation between pollution perception intensity and pollution levels ^[42][43][42,43]. However, some scholars argue that pollution perception is mainly influenced by individual characteristics rather than the actual pollution levels of their environment [44]. In the field of health effects research, most scholars have not explicitly used the concept of environmental pollution perception and have not distinguished between objective environmental pollution and subjective environmental pollution. However, distinguishing between subjective and objective environmental pollution is important, particularly when examining subjective evaluation indicators, such as happiness, life satisfaction, and health perception. Subjective environmental pollution is a more intuitive reflection of the relationship between environmental pollution and individual perception [45]. Scholars have typically focused on the impact of air pollutants (such as SO₂, NO₂, PM_2.5, or PM₁₀) on individual health from an objective environmental pollution perspective. However, individuals have different levels of sensitivity to environmental pollution, and subjective indicators are more intuitive in reflecting the relationship between environmental pollution and individual health perception. The attention from the fields of sociology and psychology to air pollution extends beyond its psychological effects to include public perceptions of air pollution. Focusing on the subjective judgments and understanding of the general public regarding air pollution (such as their knowledge of its causes, severity, and harms), surveys or attitude polls are used to understand public attitudes (in contrast to objective data or expert opinions), providing powerful references for the formulation and implementation of public policies related to air pollution. Since the mid-twentieth century, researchers have conducted a large number of surveys and studies on public perceptions of air pollution, achieving fruitful research results ^[15][46][15,46]. There is no consensus on which factors are involved in the public’s perception of air pollution in the existing research. Although the existing research lacks dialogue, the conclusions drawn from different studies consistently show that the perception of air pollution is a subjective construction process or result that does not depend entirely on objective air pollution status. On the one hand, public perception of air pollution itself is a subjective judgment based on life experience and intuitive feelings and may, therefore, be inconsistent with objective data or information. Although most people acknowledge the scientific and necessary nature of objective data, the public’s judgment of air quality is mainly based on sensory experiences, such as vision and smell, rather than air quality monitoring data, and there is no significant correlation between the two. Especially when they are inconsistent or conflicting, the public usually refuses objective data and insists on subjective judgment [47]. At the same time, public perception of air pollution has important practical significance: public exposure to air pollution is largely determined by their judgment of air pollution quality, and public attribution of air pollution may also affect their response to relevant public policies; thus, public perception is also one of the evaluation criteria to determine the effectiveness of air pollution control. On the other hand, the impact of objective information on public perception of air pollution is limited. Even with a large amount of available air pollution information, the public’s attention to and recognition of this information is not high [48]. Beaumont et al. [49] further pointed out that the public is not a homogeneous group, and differences in age, gender, social class, culture, and economic status may affect the effectiveness of risk communication strategies, and attention should be paid to the usefulness of relevant information for different groups. In Bush et al.’s [50] view, the public does not just passively receive air quality information in a social vacuum but reflects on and evaluates air pollution information based on their social and cultural backgrounds, local knowledge, and cognitive processes. Furthermore, subjective air quality is a subjective construction that may be influenced by many factors, such as education level, gender, personality traits, and socioeconomic status ^[51][52][53][51,52,53].

4. Other Factors

Health is related to demographic characteristics, such as age, gender, marital status, education, and socioeconomic status ^[54][55][55,56]. Wilkinson ^[56][57] proposed that people determine their relative position by comparing themselves to others around them, and a lower relative position can make people feel disadvantaged, which can lead to health problems, such as cardiovascular disease and depression. Since the 1970s, socioeconomic status has received increasing attention in research on resident health. There is not only a significant correlation between socioeconomic status and resident health, but socioeconomic status differences are also one of the important causes of health inequality. Socioeconomic status is a concept with complex connotations, which is usually measured by indicators such as income, years of education, and occupational status; a socioeconomic status index can also be constructed based on differences in occupational status ^[57][58]. A study on the health of residents in 22 European countries showed a robust and sustained relationship between socioeconomic status and resident health ^[58][59]. The same conclusion has also been verified in China ^[59][60][60,61]. Based on existing research, the impact of socioeconomic status differences on resident health advantages mainly comes from the following aspects: an increase in income can improve personal living environments and increase the ability to obtain medical resources; a good educational background makes it more advantageous in obtaining medical knowledge and economic and social resources ^[61][62]; and upward mobility in occupational status is often accompanied by improvements in work environment and physical activity, which reduce health risks ^[62][63]. In the literature on environmental health risks, some studies have further examined the issue of health inequality caused by environmental pollution, and the main view is that groups with low socioeconomic status bear higher health risks due to their greater exposure to environmental pollution ^[63][64]. It is not difficult to see that environmental pollution is still an important transmission mechanism for affecting health inequality. Due to the different abilities of individuals with different socioeconomic status to avoid environmental risks, the differentiated exposure level of environmental pollution becomes a source of health and social inequality. This also means that increasing the intensity of environmental regulation is one of the important breakthroughs to reduce pollution exposure risks and achieve environmental health equity. Although air pollution has negative impacts on health, the severity of these impacts is influenced by the social vulnerability of specific groups ^[64][65][65,66]. The interplay between air pollution and social factors in affecting health has led scholars to explore the “triple jeopardy” of health, social, and environmental inequalities ^[66][67]. Research on the differential health impacts of air pollution exposure and environmental justice is a popular topic in health geography ^[67][68]. Scholars are concerned with issues of environmental justice and health inequalities arising from the uneven distribution of products, services, pollution exposure, and other factors related to social and economic development ^[68][69]. Studies on the relationship between PM_2.5 and mortality risk have focused on vulnerable groups, such as infants, pregnant women, and the elderly ^[69][70][70,71]. The impact of PM_2.5 on population health in China varies significantly between urban and rural areas ^[71][72]. Air pollution has a more severe impact on the health of vulnerable groups with a lower socioeconomic status, such as those with low income and education levels with poor working conditions and living in environments with high indoor pollution levels ^[72][73]. When environmental pollution interacts with health, socioeconomic factors, and inequality issues, it can lead to an environmental health poverty trap, resulting in a vicious cycle of pollution exposure and health hazards ^[73][74]. Socioeconomic factors can modulate the relationship between air pollution and health.