Ambient air pollution in China

Ambient air pollution is a global problem of increasing concern to governments and the public. Air pollution causes more than 4.2 million deaths annually, and this figure is likely to exceed 6.3 million deaths by 2050 unless there is a significant intervention.1 As the world's largest developing country, China's rapid economic growth has come at a cost of dangerous ambient air pollution, which threatens human health and sustainable social and economic development. Rapid industrialization and urbanization over the last three decades in China has created one of the highest disease burdens in the world. In 2017, 81% of Chinese people were living in places where PM2.5 (particulate matter with aerodynamic diameter ≤2.5μm) concentrations were higher than the Interim Target-1 limit (35 μg/m3) set by the World Health Organization (WHO), and 50% of Chinese people were exposed to annual-average PM2.5 concentrations of >48.2 μg/m3.2 China has the world's second largest economy and many sources of harmful emissions when compared to other developed countries (e.g. USA and Europe). China consumes roughly 50% of the world's coal due to outdated technology and poorly maintained coal facilities. The number of on-road vehicles adds to this burden, as the civilian fleet has increased from 16 million vehicles in 2000 to 229 million vehicles in 2018. China's widespread industrial development, coal-dependent energy utilization and vast number of personal vehicles have led to compound air pollution which is a blend of coal smoke and motor vehicle emissions. What health impacts does this ambient air pollution have on the population of China? For a large majority of the exposed population, disease burden and economic loss due to ambient air pollution in China are greater than in other countries. For example, according to economic loss calculations estimated using the Global Burden of Disease framework, ambient air pollution is the fifth leading risk factor for all-cause disease mortality in China and caused 1.1 million deaths in 2015, which contributes to 26% of estimated deaths associated with air pollution globally.3 According to the China Pulmonary Health Study,4 8.6% of the Chinese population (or nearly 100 million people) have chronic obstructive pulmonary disease (COPD) and 18.7% of total COPD deaths can be attributed to ambient PM2.5 exposure.2 However, it may be more meaningful and informative to compare mortality associated with ambient air pollution with cigarette smoking habits. For example, as a standard, one cigarette per day is roughly equivalent to 22 μg/m3 of PM2.5. In 2015, Beijing had pollution levels at about 85 μg/m3 of PM2.5 which was equivalent to roughly four cigarettes per day. Whereas in 2016, levels of PM2.5 in Beijing shot to 550 μg/m3, equivalent to 25 cigarettes per day for every man, woman and child living in the city. Taking into consideration the nonlinear exposure–effect relationship between air pollution and health effects, along with the unique socio-demographic characteristics of China (e.g. age structure, disease pattern and socio-economic status), studies pertaining to Chinese subjects may provide a better understanding about the role of potential modifiers of adverse health effects of ambient air pollution (Fig. 1). For example, in 2013, the International Agency for Research on Cancer (IARC), a branch of the WHO, conducted a meta-analyses of 18 studies to examine the exposure–effect relationship of ambient particulate matter (PM) and found that the meta-relative risk for lung cancer was 1.09 (95% CI: 1.04–1.14) for PM2.5 and 1.08 (95% CI: 1.00–1.17) for PM10 (particulate matter with aerodynamic diameter ≤10μm), per 10 μg/m3 increase in exposure to PM.5 However, most of these 18 studies were from regions of North America and Europe, with only one study from China. Furthermore, the only study in China was conducted 20 years ago using total suspended particulate (TSP) concentrations to estimate levels of PM2.5 exposure. So, this exposure–effect relationship reported from IARC does not accurately depict the effects of air pollution in China. The results from the China Four Cities Study, a 12-year retrospective cohort of 39 054 participants, showed that each 10 μg/m3 increase in PM10 concentration was associated with a 65% (95% CI: 1.527–1.791) increase in lung cancer mortality,6 which was higher than those reported from IARC, indicating that findings based on Chinese populations are essential to understand and improve the assessment of the global health hazards of air pollution. In recent years, China has made substantial progress in reducing air pollution, and monitoring data show that national average PM2.5 concentrations decreased by 46% from 72 μg/m3 in 2013 to 39 μg/m3 in 2018.7 However, prevention and control of air pollution seems to have decreased, due to the government's low priority for environmental issues, lack of cooperation among various agencies and most of all inadequate government funding. In this context, China has developed strict environmental regulations such as the newly enacted China Air Pollution Prevention and Control Law that holds the local government responsible for areas under its administration for a cleaner and better environment. However, local government may not be the most suitable agency to deliver and enforce change, as no clear set of guidelines are present on how to implement the policy. It is not clear what to do and who should be accountable if air quality standards are not implemented. Furthermore, rural areas of China are also facing great challenges in migration and diffusion of air pollutants due to the transfer of highly polluting industries from central cities to suburban or rural districts. This transfer may cause much more serious environmental pollution due to the lack of supervision in rural areas. To correct this problem, in 2018, the ‘Ministry of Ecology and Environment’ was established to formulate policies to achieve environmental protection on a national scale using statutory power. The current status of China as one of the major global polluters makes the success of these initiatives of great importance, with the overall goal of improving human health alongside sustainable social and economic growth. This work was supported by National Key Research and Development Program of China (2016YFC0207000) and the National Natural Science Foundation of China (81872582).