Recommendations: Recommendations of Controlling and Preventing Acute Health Risks of Fine Particulate Matter Pollution — China, 2021

The Global Burden of Disease Study 2019 data showed that ambient fine particulate matter (PM_2.5) is the fourth highest risk factor in the global burden of disease (1). In China, about 1,432,633 premature deaths were attributed to PM_2.5 during 2019 (1). It has an important impact on the occurrence, development, and prognosis of cardiovascular and respiratory diseases in the population. It has been a major environmental problem and an important health issue commonly faced by all countries in the world, especially developing countries (2-4). China currently experiences high levels of ambient air pollution. With rapid industrialization and urbanization, the prevention and control of air pollution is becoming more difficult. To this end, the State Council issued the “Air Pollution Prevention and Control Action Plan” in September 2013, implementing 10 measures for air pollution prevention and control and releasing and implementing the “Three-Year Action Plan to Win the Blue Sky Defense War” in June 2018. After years of continuous efforts, the overall ambient air quality of China has improved significantly. The average annual concentration of PM_2.5 has dropped from 72 μg/m³ in 2013 to 33 μg/m³ in 2020. Ambient inhalable particulate matter (PM₁₀), sulfur dioxide (SO₂), and carbon monoxide (CO) all showed remarkable downward trends, and the people’s sense of the blue sky was significantly enhanced (5-6).

As an important measure to implement the “Air Pollution Prevention and Control Action Plan,” the Ministry of Science and Technology released the national key research and development plan “Research on Air Pollution Causes and Control Technologies” special project in 2015, which aims to strengthen research and development on several aspects, including (1) the formation mechanism, source analysis, migration law, monitoring and early warning of air pollution; (2) the relationship between air pollution and human health; (3) air pollution control technologies such as desulfurization, denitrification, and high-efficiency dust removal; and (4) the transformation and application of technological achievements, providing scientific and technological support for pollution control. The implementation of this special project has strongly encouraged scholars to conduct extensive, in-depth, and systematic research on the scientific issue of “the relationship between air pollution and population health.” The task force conducted a comprehensive review and in-depth discussion on the important innovative achievements in the field of acute health risks of ambient PM_2.5 pollution in recent years and formed this expert consensus in order to provide scientific evidence for the government and relevant professional institutions to develop relevant policies and/or strategic measures. It also aims to provide scientific information for clinicians, public health and environmental protection professionals to understand the acute health hazards of ambient PM_2.5 pollution, and to reduce air pollution exposure for the general public, including patients.

PM_2.5 refers to particulate matter with an aerodynamic equivalent diameter of less than or equal to 2.5 μm in ambient air. Its main sources include primary particulates and secondary particulate matter generated from the conversion of SO₂, nitrogen oxides (NO_x), ammonia, and volatile organic compounds emitted from fossil fuels (such as coal, gasoline, and diesel) and biomass combustion, metallurgy and chemical industries, vehicle exhaust, road dust, etc. The chemical composition of ambient PM_2.5 is very complex, usually consisting of carbon-containing components such as organic carbon and inorganic carbon, inorganic salt ions such as sulfate, nitrate and ammonium salt, and organic matters such as polycyclic aromatic hydrocarbons, metal elements, biological substances, and mineral dust.

The ambient air quality in China was not high a decade ago. In 2012, the first batch of 74 cities that implemented the new air quality standards had an average annual PM_2.5 concentration of 72 μg/m³, which exceeded 106% of the secondary standard limit (annual average concentration of 35 μg/m³) of the “Ambient Air Quality Standard” (GB 3095–2012) (5). With the release and implementation of the “Air Pollution Prevention and Control Action Plan,” ambient PM_2.5 pollution has been effectively controlled. As of 2017, the annual average concentration of ambient PM_2.5 in 74 cities dropped to 47 μg/m³, a decrease of 34.7% compared to 2013. The average number of days with air quality reaching the standard increased from 60.5% to 72.7%; the average concentration of ambient PM_2.5 in key regions such as Beijing-Tianjin-Hebei, the Yangtze River Delta, and the Pearl River Delta decreased by 39.6%, 34.3% and 27.7%, respectively (7). Due to the effective implementation of 6 important measures from 2013 to 2017, including upgrading the industrial sector, upgrading industrial boilers, eliminating outdated industrial production capacity, promoting the use of clean fuels in residents’ lives, shutting down small polluting factories, and strengthening vehicle emission control, SO₂, NO_x, and primary PM_2.5 emissions in China decreased by 16.4 million, 8 million and 3.5 million tons, respectively (8). In 2020, the national ambient PM_2.5 pollution situation was further improved, and 87% of the 337 prefecture-level or higher cities met the air quality standard on average. The average annual concentration of PM_2.5 was 33 μg/m³, lower than the secondary standard limit of “Ambient Air Quality Standards” (GB 3095–2012) (6).

Currently, ambient PM_2.5 pollution levels in China are still relatively high, which is higher than the population-weighted annual PM_2.5 concentration in the United Kingdom, the United States, and other countries in the same time period (about 10 μg/m³) (9), and far exceeding the air quality guidelines (5 μg/m³) issued by the World Health Organization (WHO) in 2021. In 2020, 37.1% of the 337 cities (involved prefecture-level and municipality city) nationwide still have an average annual PM_2.5 concentration that does not meet the secondary standard limit of the “Ambient Air Quality Standards” (GB 3095–2012). At the same time, heavy pollution weather still occurs on a large scale across the country. In 2017, 2,311 days of heavy pollution occurred in those cities, and the number of days with heavy PM_2.5 pollution (daily average PM_2.5 concentrations higher than 150 μg/m³) accounted for 74.2% of the days with heavy pollution and above (7). In 2020, the frequency of heavy pollution in the 337 cities was the same as in 2017, and the number of days with heavy PM_2.5 pollution accounted for 77.7% of the days with heavy pollution and above (6). From January to February 2020, the number of days with heavy PM_2.5 pollution in prefecture-level cities across the country was the lowest in the same period in record, which was reduced by 39.2% in the same period since 2015, and the number of hours with hourly PM_2.5 concentration exceeding 300 μg/m³ has decreased by 47.8% compared to 2015. Among them, regional pollution was at a consistently high level in key polluted areas represented by Beijing-Tianjin-Hebei and the Fenwei Plain. In 2020, the average annual PM_2.5 concentration in Beijing-Tianjin-Hebei region was up to 51 μg/m³, the average number of days exceeding the standard was 36.5%, and the number of days with PM_2.5 as the primary pollutant accounted for 48.0% of the total number of pollution days; the average annual concentration of PM_2.5 in the Fenwei Plain was up to 48 μg/m³, the average number of days exceeding the standard was 29.4%, and the number of days with PM_2.5 as the primary pollutant accounted for 56.4% of the total number of days with pollution (6).

The acute health risk of ambient PM_2.5 pollution usually means that short-term exposure to PM_2.5 (exposure duration usually at the level of hours to days) may cause acute damage to the body, trigger the onset of symptoms or diseases (mainly cardiovascular or respiratory disease), and lead to premature death and a series of adverse health effects.

PM_2.5 is the primary air pollutant in China. Short-term exposure to PM_2.5 will significantly increase the risk of non-accidental death of residents in China, especially the risks of death from cardiovascular and respiratory diseases (10-12). A time series study of 272 cities in China found that from 2013 to 2015, the annual average concentration of PM_2.5 across all cities was 56 μg/m³. At this concentration level, the percentage increase in the risk of mortality due to non-accidental causes, cardiovascular diseases, and respiratory diseases per 10 μg/m³ increase in PM_2.5 from lag0 to lag1 was 0.22%, 0.27%, and 0.29%, respectively (10). Compared to similar studies conducted in China and abroad, the relative risk of acute death of people exposed to short-term ambient PM_2.5 in China was lower than that in European and North American countries (2–4,13). A study investigating the association between ambient PM_2.5 and daily population death in 652 cities around the world found that per 10 μg/m³ increase in PM_2.5 from lag0 to lag1, the risk of non-accidental death in the United States, Canada, Spain, and Greece increased by 1.58%, 1.70%, 1.96%, and 2.54%, respectively (13). The reason for the difference in effect estimates may be that the exposure-response relationship between PM_2.5 and death showed a nonlinear trend. The slope of the exposure-response relationship curve was larger at low concentration levels, thus the population death observed was more seriously affected by exposure to unit PM_2.5 concentration. With the increase of exposure level, the slope of the curve gradually decreases, and the curve becomes stable at higher exposure levels, indicating that the relative risk of acute death caused by PM_2.5 increases in a smaller magnitude (13–14). Currently, China is at a high exposure level of global PM_2.5 pollution concentration. For each unit level increase in PM_2.5 concentration, the relative risk of acute death in the Chinese population is relatively lower. In addition, the differences in effects may also be related to the chemical composition of PM_2.5 in different regions, climate characteristics, the health status of the study population, and the degree of socioeconomic development.

Due to the small particle size and large specific surface area of ambient PM_2.5, it can enter the respiratory tract or be deposited in the alveoli, causing respiratory system damage and increasing the incidence of disease (15-17). Each 10 μg/m³ increase in PM_2.5 (lag0 day) was associated with a 0.34% increase in the risk of hospitalization for respiratory diseases (including pneumonia, acute bronchitis, upper respiratory tract infection, chronic obstructive pulmonary disease, and bronchiectasis) in 252 cities in China (15); and each 10 μg/m³ increase in moving average PM_2.5 (lag0–2 days) was associated with a 0.31% increase in the risk of hospitalization for pneumonia (16). Inhaled PM_2.5 enters the blood through macrophage phagocytosis and pulmonary capillaries and acts on the body’s circulatory system, increasing the risk of cardiovascular diseases such as ischemic heart disease, stroke, and heart failure (18-20). A time series study of 184 cities in China from 2014 to 2017 found that a 10 μg/m³ increase in the same-day PM_2.5 exposure was significantly associated with 0.26%, 0.31%, 0.27%, and 0.29% increases of hospital admissions for cardiovascular disease, ischemic heart disease, heart failure, and arrhythmia, respectively (18). A time series study of 248 cities in China from 2013 to 2017 found that a 10 μg/m³ increase in PM_2.5 concentration was significantly associated with a 0.26% increase in same-day hospital admissions for ischemic stroke and transient ischemic attack (TIA) (19).

Heavy air pollution weather in China is usually characterized by persistent high concentrations of PM_2.5. Existing epidemiological evidence shows that prolonged heavily PM_2.5-polluted weather will greatly increase the risk of morbidity and mortality and cause more serious health problems (21-23). A study based on the continuous heavily polluted weather of ambient PM_2.5 occurred in Beijing from January 10 to 17, 2013, the average daily concentration of PM_2.5 was 231 μg/m³, showed that compared with other periods in winter in 2013, emergency and outpatient risk of respiratory illness increased by 74% and 16%, respectively, during prolonged heavily polluted weather, indicating that continuous exposure to high concentrations of PM_2.5 has caused a substantial increase in the number of patients with respiratory diseases (21). Another time-stratified case-crossover study observed that persistent heavily or extremely heavily PM_2.5-polluted weather was associated with increased risk of cardiovascular disease hospitalization among Beijing residents. The odds ratios (ORs) associated with extremely heavy PM pollution events (PM concentration ≥150 μg/m³ for 3 days or more) were 1.085, 1.112, 1.068, 1.071, and 1.060 for total cardiovascular disease, angina, myocardial infarction, ischemic stroke, and heart failure, respectively (22). The study also showed that the higher the concentration and the longer the duration of heavy pollution events, the greater the impact was on hospitalizations for various cardiovascular diseases (22). Among them, the risks of angina pectoris and ischemic stroke were more pronounced. However, existing research has not yet formed a unified standard for the definition of prolonged heavily PM_2.5 polluted weather (21-23), and the specific role of pollution concentration and duration in the health impacts of heavily polluted weather requires more researches.

Ambient PM_2.5 has a very complex chemical composition. Affected by factors such as local industrial pollution sources and energy structure, there are significant spatiotemporal differences in the chemical compositions of PM_2.5 across China. Current epidemiological studies believe that carbon-containing components (including organic carbon and elemental carbon or black carbon), some inorganic salts (mainly sulfates and nitrates), and metal elements [such as nickel (Ni), zinc, chromium, and lead] are closely related to health hazards caused by PM_2.5 (24-28). For example, a study on the acute effects of PM_2.5 chemical components on mortality in Xi’an found that organic carbon, elemental carbon, sulfate, and nitrate increased by an interquartile range (IQR) for 1-day lag, which were 19.3 μg/m³, 8.8 μg/m³, 27.8 μg/m³, and 15.4 μg/m³, respectively, will increase the risk of non-accidental, cardiovascular, and respiratory deaths in the population by more than 1%. An IQR increase of 0.01 µg/m³ in 1-day lagged Ni was associated with 0.4%, 0.6%, and 0.9% increases in the risk of non-accidental death, cardiovascular, and respiratory mortality, respectively (24). A study on the acute effects of PM_2.5 chemical components on mortality in Beijing found that for a 0-day lag, an IQR (10.11 μg/m³) increase in organic carbon was associated with 2.65% increase in respiratory mortality and an IQR (20.10 μg/m³) increase in sulfate was associated with a 1.57% increase in cardiovascular disease mortality, and the acute death effect in the cold season was strengthened (25). The above chemical components mainly come from fossil fuel combustion (including coal combustion and vehicle emissions) and secondary particulate matters formed by ambient SO₂/NO_x. Their toxic effects are mainly produced by inducing oxidative stress and inflammatory responses. Greater PM_2.5-related acute health hazards could be observed when the content of these toxic chemical components was high (24-28).

Epidemiological studies of the Chinese population have shown that ambient PM_2.5 mainly produces damage by causing oxidative stress and inflammatory responses in the body, as well as autonomic dysfunction. After PM_2.5 is inhaled through the respiratory tract, changes in biomarkers of lung inflammation could be observed in a short period of time, followed by systemic inflammatory response and oxidative stress, resulting in changes in the levels of biomarkers related to cardiovascular effects such as coagulation, vasoconstriction, and vascular endothelial function (27-33). Short-term exposure to PM_2.5 could also activate the human “hypothalamus-pituitary-adrenal axis,” affecting cardiovascular health through the neuro-endocrine pathway (31). In a fixed panel study of healthy and prediabetic people (50–65 years old), increased PM_2.5 exposure was associated with an increment in exhaled nitric oxide (FeNO) (34). In a randomized double-blind controlled intervention trial of healthy college students, the reduction of PM_2.5 exposure significantly reduced the level of exhaled FeNO (35). The possible mechanism of cardiovascular system damage caused by short-term exposure to ambient PM_2.5 is relatively complex. In addition to triggering a systemic inflammatory response and oxidative stress, it can also cause autonomic dysfunction and changes in coagulation function, destroy vascular endothelial structure, and damage endothelial function (35-38). A randomized double-blind controlled intervention trial found that high PM_2.5 exposure can cause an increase in inflammatory markers such as soluble CD40 ligand (sCD40L), interleukin-1β (IL-1β), and C-reactive protein (CRP), as well as blood pressure in healthy college students (31). With the decrease of PM_2.5 exposure, soluble sCD40L, IL-1β, and blood pressure of healthy college students were significantly reduced (35). Another randomized double-blind cross-over controlled trial conducted during a typical haze event found that a 10 μg/m³ increase in time-weighted individual PM_2.5 exposure concentration was significantly associated with an increment of 1.31%–5.33% in cytokine concentrations of IFN-α2, GM-CSF, IL-1RA, sCD40L, IL-4, MIP-1α, MCP-1, Eotaxin, and FGF-2, respectively, in circulatory system (39). A study on air pollution and cardiovascular dysfunction in healthy adults in Beijing found that short-term PM_2.5 exposure was associated with increased levels of atherosclerotic plaque damage or thrombosis-related markers such as fibrinogen, CRP, and IL-1β (33). Due to the wide range of health effects of PM_2.5 exposure, in addition to the cardiovascular and respiratory systems, it may also act on the genitourinary system, causing a decrease in glomerular filtration rate (40) and the total number and concentration of sperm (41).

Several studies have confirmed that children, the elderly, and patients with cardiovascular and respiratory diseases are vulnerable groups for ambient PM_2.5 pollution (10-11,42-43). The respiratory system of children was more susceptible to the harm of ambient PM_2.5 than that of adults, and short-term exposure to PM_2.5 could result in an increase of FeNO exhaled by children (30,43-46) and increased airway resistance, causing asthma attacks (44). The reduction of PM_2.5 exposure would greatly reduce the level of exhaled FeNO (30). Short-term exposure to PM_2.5 can also cause an increase in heart rate and norepinephrine in preschool children, resulting in damage to the sympathetic-adrenal medulla (44). Both time series studies conducted in 272 cities and 130 districts and counties in China found that short-term exposure to PM_2.5 significantly increased the risk of non-accidental deaths and cardiovascular disease deaths in the elderly over 75 years old, and its increased risk of death exceeded the acute effect of PM_2.5 on death in the general population (10-11). In addition, patients with cardiovascular and respiratory diseases are particularly sensitive to PM_2.5 exposure, and short-term exposure will cause oxidative stress damage to their cardiovascular and respiratory systems, causing dysfunction and reduction, and subsequently increasing their incidence rates. In patients with chronic obstructive pulmonary diseases, a 10 µg/m³ increase in daily average PM_2.5 concentrations was associated with a 26 mL decrease in forced vital capacity (FVC), a 26 mL decrease in forced expiratory volume in 1 second (FEV₁), and a 0.96% decrease in FEV₁% (46). PM_2.5 exposure for 0–6 hours significantly increased the levels of serum fibrinogen, CRP, tumor necrosis factor-α (TNF-α), and other biomarkers in patients with chronic obstructive pulmonary disease (32). The results of a cohort study of 4 cities (Beijing, Shanghai, Wuhan, and Xi’an) in high-risk groups of cardiovascular disease showed that an increase of 1- to 9-hour moving average PM_2.5 concentration was associated with 0.22 to 0.39 mmHg increase in systolic pressure, while the effect of PM_2.5 was attenuated in patients with controlled blood pressure (47).

During the implementation of the “Air Pollution Prevention and Control Action Plan,” air pollution represented by PM_2.5 was effectively controlled, and the health benefits of the population were significant (48-52). A study on the health benefits of emission reduction scenarios based on short-term exposure-response relationships estimated that if the average daily concentration of ambient PM_2.5 reached the current ambient air quality secondary standard (75 μg/m³), a total of 69,000 years of life lost could be avoided and increase life expectancy by 0.06 years among residents of 72 cities in China. Reaching the WHO-recommended transitional target 2 (25 μg/m³) could avoid a total of 168,000 years of life lost each year and increase life expectancy by 0.14 years (48). A study simulating the annual ambient PM_2.5 concentration via chemical transport model and estimating the health benefits under emission reduction policy scenarios during 2013–2017, considering the chronic exposure-response relationship, demonstrated that the deaths due to the PM_2.5 were reduced from 1.389 million in 2013 to 1.102 million in 2017 in China, of which, 88.7% of contributions were from emission reductions (49). A long-term health benefits study focusing on emissions reduction policies in 74 cities across the country estimated that the PM_2.5 pollution was reduced by 33.3%, the death number of people due to the PM_2.5 pollution was reduced by 47,000, and the years of life lost were avoided by 710,000 years. The number of the deaths attributable to PM_2.5 pollution decreased by 26,000 premature deaths, and the years of life lost attributable to PM_2.5 were avoided by 390,000 years in Beijing-Tianjin-Hebei, the Yangtze River Delta, and the Pearl River Delta regions (50). Other studies have pointed out that measures such as civilian clean energy replacement will reduce indoor and outdoor PM_2.5 pollution levels simultaneously and further improve human health (51). For example, the integrated population-weighted exposure to PM_2.5 (IPWE) in China decreased by 47% from 2005 to 2015; 90% of the reduction was attributed to the reduction in the use of household solid-fuel, and the resulting health benefits were the avoidance of around 0.40 million premature deaths annually. If we replaced the remaining household solid fuels with clean fuels, an additional 0.51 million premature deaths would be avoided (51). It is worth noting that the potential benefits of emissions reduction with end-of-pipe control will be exhausted by 2030. In order to reduce the air pollution level in China to the value recommended by the WHO and effectively protect public health from pollution effects, a deep transformation of low-carbon energy under the goal of the carbon neutrality is crucial (52).

The short-term implementation of air pollution control policies has greatly improved air quality and brought certain population health benefits. During the 2008 Beijing Olympic Games, a series of measures to control industrial emissions and traffic pollution were implemented, and the concentration of ambient particulate matter was significantly reduced. Consequently, the economic costs associated with human health decreased by 38% and 16% before and after the Beijing Olympic Games, respectively (53). During the meeting of Asia-Pacific Economic Cooperation (APEC) held in November 2014 (12 days) and the military parade to commemorate the 70th anniversary of the victory of the Chinese People’s War of Resistance against Japanese Aggression in September 2015 (15 days), the short-term air pollution control policies have also been carried out in Beijing. During the 2 events, the ambient PM_2.5 concentration was decreased by more than 40% compared with that before the event in Beijing. According to estimates, 39–63 and 41–65 deaths were avoided due to the decrease in PM_2.5 concentration during the APEC meeting and the military parade, respectively (54).

With the deepening of awareness of the health hazards of the PM_2.5 pollution, the utilization rate and popularization range of personal protective measures such as air purification devices and wearing masks have increased and expanded significantly. A number of current intervention studies have shown that the proper wearing of masks or using air purifiers can reduce individual PM_2.5 exposure effectively, thereby reducing their health hazards to varying degrees (30-31,37,55-57). A randomized double-blind controlled intervention trial using N95 masks as an intervention measure showed that the use of masks for protection in heavily polluted weather could reduce the levels of serum inflammatory markers and PM_2.5-related airway inflammatory responses in healthy young people (55). Another randomized crossover study of healthy young adults observed that the wearing particulate-filtering respirators in a short-term might reduce cardiovascular risks through enhancing the function of autonomic nervous and decreasing blood pressure (56).

A randomized double-blind crossover study which took healthy college students as the research object found that the PM_2.5 average concentration in the environment with air purifiers was much lower than that in the environment without air purifiers, and higher PM_2.5 environmental exposure might induce metabolic alterations associated with the hypothalamus-pituitary-adrenal and sympathetic-adrenal-medullary axes activations, indicating that air purification measures could effectively reduce the health damage caused by PM_2.5. A randomized double-blind crossover experiment on school-aged children also observed that air purifiers had a good removal effect on indoor particles of different sizes and could protect the respiratory health of children by increasing energy production and anti-inflammatory and antioxidant capacities (30,57).

At present, the situation of air pollution in China is still severe, the ambient PM_2.5 concentration is still relatively high, and the ozone (O₃) pollution has not been effectively controlled and even has an upward trend in some areas. Exposure to various air pollutants together threatens the health of local residents. Air pollution is a clear hazard to human health, and when measures are taken to reduce air pollution, it can bring significant health benefits. This complies with the primary prevention requirements of the three categories of the prevention strategy. Therefore, the task force recommends that the policies for preventing and controlling air pollution should be formulated by reducing source emissions and strengthening regional control to further reduce the level of air pollution and promote the continuous improvement of the health of residents by focusing on the national strategic goals of beautiful China and healthy China in combination of the mission requirements of carbon peaking and carbon neutrality.

First, the widespread use and efficient development of clean energy should be continuously strengthened. It is necessary to strengthen source control through energy structure reform, reduce the proportion of fossil energy consumption, and build a new energy system with hydropower, nuclear power, solar power, and wind power as the main components. Energy coupling technology should be vigorously developed to increase energy efficiency, and at the same time, the application of clean energy for civilian use should be promoted. As a result, a green and efficient energy system should be ultimately formed, which will control source emissions of air pollution and improve the health benefits brought by energy structure improvement.

Second, the promotion of industrial upgrading should be continued. Measures should be taken to strictly limit high energy consumption and high emission enterprises and accelerate the development of low energy consumption and low emission enterprises. The research and promotion of cleaner production technology should be increased to provide assistance for industrial upgrading. Rational industrial structure composition should be planned to enhance regional pollution control benefits.

Third, pollution in the transportation sector should be effectively controlled. According to the development characteristics of large cities, the number of vehicles should be controlled and the proportion of energy-saving and environmentally-friendly vehicles should be expanded via planning. It is necessary to gradually improve the fuel quality and emission standards of vehicles, vigorously develop urban green transportation, and increase the proportion of clean transportation. The health benefits of urban populations would be increased by comprehensively improving the level of cleanliness in the transportation field through multiple measures and reducing the proportion and level of pollution from transportation sources.

Fourth, the modernization of the air pollution control system should be continuously enhanced. Regular capacity building such as laws and regulations, policy mechanisms, monitoring, and supervision should be further deepened from a scientific perspective. Combined with carbon peaking and carbon neutral policy situations to optimize the construction framework of the system, carbon emission control and related contents should be included in the current air pollution control chain. The coordinated management should be strengthened to realize the dual reduction goal of carbon emission and air pollution. In the meantime, it is necessary to guide and encourage the public to adopt a green and low-carbon lifestyle and increase the participation of the whole society in pollution reduction and carbon reduction policies.

Fifth, the formulation and revision of relevant air quality standards need to be carried out gradually. Compared with the air quality guidelines issued by the WHO, combined with the latest research evidence on the health impacts of air pollution, and according to the actual situation in China, the current standards for air quality should be revised. Air pollution prevention and control should be ensured by gradually tightening the standard limits of air pollutants and increasing the protection of human health from a legal perspective.

Sixth, effects after the implementation of clean air actions and policies should be estimated, including the health benefits assessment after the implementation of relevant policies. The policies formulated and implemented by various localities for the prevention and control of air pollution should be evaluated regularly. The prevention and control policy can be optimized by screening the level of pollution concentration reduction and the degree of health benefits. Local governments are encouraged to prioritize measures that maximize population health benefits when formulating air pollution control programs.

Combined with the existing evidence of the impact of air pollution on human health, the research advances of human health protection, and the new air quality guideline value issued by the WHO, multiple measures should be taken to improve the public’s awareness of the health hazards of PM_2.5 pollution, strengthen scientific protection capabilities, improve the overall health literacy of the public, and reduce health damage caused by PM_2.5 exposure.

First, the release of air pollution monitoring and relevant information should be strengthened and the formulation of protection policies should be promoted to ensure that the public is informed. Accurately and promptly release pollution and health-related information to ensure that the public could grasp information on changes in pollution and can take timely health protection measures and change outdoor activities. Based on the continuously strengthened air pollution monitoring network, more valid data can be obtained. By comprehensively analyzing these environmental data and health impact data, it is possible to formulate effective pollution control and health protection policies in China.

Second, the propagation of air pollution health hazards should be enhanced to help the public to understand the health hazards of air pollution and the benefits of prevention and control, and improve their relevant knowledge base. Knowledge of air pollution health hazards should be widely publicized through health education via new media dissemination, communities, healthcare institutions, primary medical staff and other channels and forms. In addition, scientific measures of health protection against air pollution should be demonstrated to promote the public to understand relevant information and strengthen risk awareness. Improve the public’s awareness of the health hazards of air pollution, and improve their knowledge reserve for taking timely and effective health protection behaviors.

Third, air pollution health protection guidance and recommendations should be clarified and the operability should be improved to ensure the effectiveness of public health protection. According to the air quality forecast or warning information released by relevant agencies and combined with the results of some pollution prevention studies, different air pollution health protection guidance and suggestions could be given. These suggestions include formulating reasonable outdoor travel arrangements, correctly wearing masks that filter PM_2.5 when going out, opening windows for indoor ventilation in a timely and appropriate manner according to air quality conditions, and using purification equipment to reduce indoor PM_2.5 concentrations when the air pollution is heavy. Through the above practical guidance and suggestions, the protection skills of the public against air pollution can be effectively improved.

Fourth, it is necessary to strengthen the health protection of sensitive groups who are vulnerable to air pollution and reduce the exposure risk of the PM_2.5 for sensitive groups. For vulnerable groups such as children, the elderly, and patients with cardiovascular and respiratory diseases, the guidance and recommendations for individual protection should be targeted. The risk prevention awareness and self-protection ability of vulnerable groups should be improved through continuous health education and information dissemination in specific locations (such as hospitals, communities, kindergartens, nursing homes, and schools). This will enable these vulnerable groups to take correct protective measures based on air quality forecasts and their own characteristics to reduce health hazards caused by air pollution.

At this stage, studies focusing on acute health risks of the PM_2.5 pollution in China have basically clarified the impact of short-term exposure to PM_2.5 on local residents’ health. Since the air pollution level in China is much higher than the air quality guidelines recommended by the WHO, and the health consequences of air pollution are a long-term and complex process, it is of great social and economic benefits to continue to carry out in-depth scientific research in this field. Based on the current research hotspots and technical difficulties, the task force recommends that the related research on air pollution and population health should be strengthened from the following six aspects during “the Fourteenth Five-Year Plan” period.

First, strengthen the research on air pollutant monitoring technology and monitoring system based on the promotion of accurate exposure assessment. Combined with new technologies and methods, high-density, high-precision, and real-time air pollution monitoring stations should be established; research on population and individual exposure assessment and monitoring methods should be strengthened, and the research and development of exposure model simulation and source apportionment technologies should be promoted. Based on the current monitoring system, the refined exposure data should be gradually included, and the types of air pollutants that can be monitored could be expanded. This enables monitoring systems to include both large-scale regional data and nationally mandated pollutant data, as well as small-scale individual exposure data and key pollutant data. The monitoring system can provide data support for subsequent identification and traceability of key toxic components of different types of air pollutants, as well as carrying out research on air pollution-related health effects.

Second, a full-spectrum identification and correlation study of air pollutants and health effects should be systematically carried out. Through targeted and non-targeted high-throughput screening technologies, the analysis of the PM_2.5 pollution spectrum should be carried out in-depth, and the identification of gaseous pollutants including volatile organic compounds (VOCs) should be gradually carried out. The acute and chronic health effects of air pollution in China on different human systems and the joint effects of the PM_2.5 and the O₃ should be further explored. It should be concentrated on sorting out the full health effect spectrum of PM_2.5 and gaseous pollutants and carrying out correlation research to support further identification of typical health hazards and degrees of specific substances in the pollution spectrum.

Third, studies on key toxic components and early biomarker inventory of air pollution health effects should be carried out. Based on the obtained full spectrum of the association between air pollution and health, systematic evaluation and toxicological verification studies of key components and effect biomarkers should be carried out via population epidemiological survey methods. Health impact assessment indicators should be established to dynamically monitor the health effects of the PM_2.5 and its components. And carried out stepwise and cross validation for potential key components and biomarkers through research methods at different levels of evidence. Key components and early health effect biomarkers with high sensitivity and specificity that have been consistently validated in the cell, animal, and human studies could be included in the inventory. It can provide a scientific basis for the early detection and early intervention of the health effects of air pollution in China.

Fourth, the toxicity mechanism of key toxic components of air pollutants should be explored. Based on multi-omics technologies such as genome, epigenome, transcriptome, metabolome, proteome, and gut microbiome, research on the molecular mechanism of the impact of air pollution on human health should be systematically carried out. It can also explain the relationship between key toxic components of air pollutants and related diseases, key toxic pathways, and molecular mechanisms, in order to provide a possible toxicological mechanism basis for explaining the causal relationship between air pollution and health effects in China.

Fifth, research on health risk assessment and early warning of combined exposure to air pollutants should be carried out. In view of the characteristics of complex ambient pollution in China, combined with high-precision exposure assessment, the health risk characteristics of regional air pollution should be accurately quantified to reveal regional risk levels for different types of air pollutants. It is necessary to actively carry out research on air pollution health risk early warning, further promote health risk intervention research after the early warning is released, provide the public with risk warning according to local conditions, improve public health service capabilities, and reduce health risks caused by air pollution. Research on disease prevention and control closely related to air pollution should be strengthened to accurately assess and estimate the health benefits of the population under air pollution reduction measures, and to promote the formulation of air pollution and health prevention and control strategies focusing on “health risk control.”

Sixth, research on the health and economic benefits of pollution reduction and carbon reduction under the carbon neutrality and beautiful China strategies should be carried out. Economy, energy, and emissions scenarios for China to achieve carbon neutrality and beautiful China strategies should be established. At the same time, by coupling the global change assessment model, global climate model, and regional meteorological-chemical model, the regional air pollution and climate change trends in China under different scenarios could be predicted. The acute health impacts of air pollution from various emergencies, including the COVID-19 pandemic and policy responses, should be assessed. Combined with the latest epidemiological evidence, the health benefits from improved air quality and climate change mitigation could be quantified, and the comprehensive economic costs of pollution and carbon reduction and health co-benefits could be estimated.

No conflict of interest.