|Year : 2016 | Volume
| Issue : 2 | Page : 43-50
Ongoing progress in cleaning China's air: A novel outlook into pollution
Joshua C Wright1, Zhili Ji2, Xiaokun Geng3, Yuchuan Ding3
1 Department of Neurosurgery, Wayne State University School of Medicine, Detroit, MI, USA
2 Center for Research on Environmental Disease, Luhe Hospital, Capital Medical University, Beijing, China
3 Department of Neurosurgery, Wayne State University School of Medicine, Detroit, MI, USA; Center for Research on Environmental Disease, Luhe Hospital, Capital Medical University, Beijing, China
|Date of Submission||05-Jun-2016|
|Date of Acceptance||16-Jun-2016|
|Date of Web Publication||4-Jul-2016|
No. 82, South Xinhua Road, Tongzhou District, Beijing 101149, China
No. 82, South Xinhua Road, Tongzhou District, Beijing 101149, China
Source of Support: None, Conflict of Interest: None
Over the past 30 years, particulate matter (PM) air pollution has progressively worsened in many of China's urban and suburban areas. This review provides a current picture of the air pollution in China with an emphasis on the history of PM pollution, policies and reduction goals, recent improvements, and known adverse health effects of PM exposure. Several studies have provided the analyses of current PM pollution levels in cities across China using satellite data and air-monitoring stations. These analyses are consistent with the Chinese Ministry of Environmental Protection (MEP) 2015 air pollution report, which concluded that only 8 of 74 (10.8%) cities met the Chinese standards for safe annual average PM 2.5 exposure (35 μg/m 3 ). Even fewer cities met the World Health Organization PM 2.5 guideline of 10 μg/m 3 . The Government of China has acknowledged the public health threat of PM pollution and enacted higher standards and goals through the 12 th five-year plan (FYP) (2010), National Ambient Air Quality Standard (2012), the Air Pollution Prevention and Control Action Plan (2013), and the 13 th FYP (2016). A comparative analysis between 2010 and 2015 satellite data shows that PM pollution decreased by around 17% during this period. This improvement is corroborated by the MEP's report on the State of the Environment in 2014 and the global burden of disease report in 2013. Despite these changes, PM pollution remains a substantial public health challenge. In 2010, an estimated 1.235 million deaths in China were attributed to PM air pollution. Long-term exposure to PM pollution increases the rates of cardiovascular, metabolic, and respiratory mortality. In particular, PM exposure increases the morbidity of respiratory illnesses such as chronic obstructive pulmonary disease (COPD), asthma, and lower respiratory infections (LRIs). Elevated levels of PM have been found to increase the incidence of all of the top five causes of death in 2012: Ischemic heart disease, stroke, COPD, LRI, and lung cancer. In addition, higher PM pollution decreases average birth weight, raises incidence of preterm birth, and increases the prevalence of Type II diabetes mellitus across the population. With the knowledge of these serious health consequences, China must enact greater measures to reduce dangerous PM levels.
Keywords: Disease, environment, particulate matter, particulate matter 10, particulate matter 2.5, public health
|How to cite this article:|
Wright JC, Ji Z, Geng X, Ding Y. Ongoing progress in cleaning China's air: A novel outlook into pollution. Environ Dis 2016;1:43-50
| Introduction|| |
Air pollution is one of the greatest threats to public health. In China, rapid economic growth, urbanization, and heavy dependence on coal have contributed to massive increases in particulate matter (PM) air pollution since the 1970s.  However, recent spikes have caused more dramatic health concerns, bringing the issue to the forefront of public attention.  Both the substantial evidence of negative health effects and improved monitoring of pollution levels have prompted the government to instate several policy changes to reduce the PM haze. Modest improvements in PM annual averages have been recorded in the last 5 years across many Chinese cities. In addition, the 2013 global burden of disease (GBD) study assessed that PM air pollution has dropped from the 4 th to the 8 th , highest out of 88 mortality risk factors in China since 2010.  These improvements are promising signs that China is moving toward a cleaner energy future, but the air in China remains far from clean.
| History of air pollution in china|| |
The advent of air pollution in China can be traced to the start of a planned period of rapid economic development known as the "Economic Reform and Open Door Policy." Beginning in 1978, this period resulted in a 57-fold increase in China's gross domestic product.  China quickly ascended the ranks of global economies, becoming the second largest in the world in 2010. 
The rise of China's economy required exponential increases in energy consumption. Coal became the primary source of energy and currently comprises around two-thirds of energy consumption.  This makes China the largest coal consumer in the world. Coal is an inefficient fuel source, and even with improving technologies, only around 40% of the energy can be extracted from burning coal.  The byproduct of this process is an aerosolized mixture of organic and inorganic PM and high concentrations of SO 2 and CO 2 . Technological improvements have greatly decreased emissions from coal-fired power plants, but these plants remain significant contributors to China's polluted air.  The total energy consumption for China in 2015 was 4.3 billion tons of coal equivalent, and it is still increasing. This high consumption of energy allowed China to unprecedented growth and moved millions out of poverty, but it also caused unintended environmental consequences. 
Increasing population numbers, especially within urban centers, have exacerbated the expansion of Chinese air pollution. During the last three decades, the number of people living in China's urban centers has tripled.  Areas with high populations experience an amplification of pollution due to transportation, cooking, and other processes of daily living. In addition, the number of cars throughout China has increased exponentially in the last decade, creating a new source of hazardous emissions.
Public awareness of the severity of pollution in China reached a critical point during the first quarter of 2013.  During this time, a haze composed of aerosolized pollutants lingered over many cities. The region affected was approximately 1.3 million km 2 and contained 800 million people.  Concentrations of dangerous fine PM (PM 2.5 ) were recorded as high as 772 μg/m 3 , which is more than ten times greater than the Chinese limit for safe at 24 h exposure (75 μg/m 3 ) [Table 1]. This smog was persistent throughout January 2013. The average daily PM 2.5 concentration exceeded 75 μg/m 3 for 69% of January across 74 cities.  For reference, a World Health Organization (WHO) analysis concluded that every increase of 10 μg/m 3 of PM 2.5 concentration for a 24 h period resulted in a 0.5% increase in all-cause mortality.  These levels of PM caused a significant public concern and prompted several policy changes and reduction goals. 
|Table 1: Particulate matter air pollution standards from various governments and organizations|
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Current Chinese policy indicates that monitoring and decreasing PM 2.5 is a high priority. China's State Council released the Air Pollution Prevention and Control Action Plan in September 2013. The plan requires 15-25% reductions of PM 2.5 levels in targeted regions of China by 2017. The 2015 Ministry of Environmental Protection (MEP) report on pollution in the specified regions suggests that pollution levels are on track to surpass these goals by 2017.  China also releases air pollution goals as part of five-year plans (FYPs), which contain economic, environmental, and energy conservation goals for the subsequent 5-year period. The 11 th FYP (2006-2010) and 12 th FYP (2010-2015) contained stringent goals for limiting SO 2 emission. These were largely met due to flue gas desulfurization of coal plants.  The 13 th FYP (2016-2020) was released in March 2016. This plan includes China's first cap on total energy consumption. The cap is placed at 5 billion tons of coal equivalent, which allows for a 16% increase from the 2015 energy consumption level.  The plan also set a goal of having "good air quality" (<50 μg/m 3 PM 2.5 ) on 80% of days by 2020. 
| Particulate matter air pollution standards|| |
Air pollution can be classified generally into aerosol PM of various aerodynamic diameters or by specific harmful molecules. Negative health effects have been associated with aerosols <10 μm in diameter (PM 10 ), aerosols <2.5 μm in diameter (PM 2.5 ), NO 2 , SO 2 , CO, and ozone (O 3 ). This review examines aerosol pollution because it poses the largest immediate threat to public health in China, and recent clean air policies have focused on decreasing these pollutants.
PM pollution consists of various aerosolized particles of sizes ranging from <0.1 to >10 μm in diameter. The smaller particles make up the largest fraction of PM by number, but they make a negligible contribution to the mass of PM. In contrast, the large particles are fewer in number, but make up the bulk of PM mass.  PM has been categorized into coarse PM (PM 10 ), fine PM (PM 2.5 ), and ultrafine PM (PM 0.1 ). One important qualification is that coarse PM also includes the fine and ultrafine particles as it represents every particle <10 μm in diameter. Particles between 2.5 and 10 μm in diameter are referred to as the coarse fraction (PM c ) and particles between 0.1 and 2.5 μm in diameter make up the fine fraction (PM f ).  Most studies examining the health risks associated with PM have focused on PM 10 and PM 2.5 concentrations.
PM 10 particle composition varies depending on the location and specific pollution sources in the vicinity. A recent study of industrial sites in Shenzhen, China, found that local PM 10 composition was predominantly organic materials, followed by secondary inorganic aerosols, dust, elemental carbon, and sea salt.  The current guideline for safe annual average PM 10 levels in China's Ambient Air Quality Standard in 2012 (AAQS-2012) is 40 μg/m 3 in residential areas (I) and 70 μg/m 3 in commercial areas (II) [Table 1]. As a comparison, the WHO sets the safe annual average at 20 μg/m 3 . In developing countries, the PM 2.5 /PM 10 ratio is approximately 0.5, while PM 10 , a more widely reported indicator, values are often used to estimate PM 2.5 , which is a greater threat to public health. 
PM 2.5 is a heterogeneous mix of organic molecules, inorganic molecules, water vapor, and microorganisms, all of which are suspended in an aerosol with particle diameters of <2.5 microns.  Increases in PM 2.5 concentrations have been linked to cardiovascular disease, cerebrovascular disease, chronic obstructive pulmonary disease (COPD), asthma, changes in lung function, and preterm birth. In contrast to the PM c particles, PM 2.5 particles travel deep into the bronchial tree, and a fraction of these particles may enter the bloodstream.  The smaller PM 2.5 particles also contain a much larger surface area for trapping harmful gaseous molecules than PM c . PM 2.5 may be generated from several sources including vehicle exhaust, biomass burning, cooking, coal burning, and dust production. The generation of PM 2.5 is a combination of primary (direct emission of aerosol) and secondary (emission of particles which react to form the aerosol) formation. A recent study indicates that the sporadic severe haze events in Chinese cities are predominantly the result of secondary aerosol formation. 
The Chinese AAQS in 1996 established standards for natural conservation areas (Grade I), urban residential and commercial areas (Grade II), and industrial districts and high traffic areas (Grade III).  The current guideline for safe annual average PM 2.5 levels in China's AAQS-2012 is 15 μg/m 3 in Grade I and 35 μg/m 3 in Grade II areas, while the WHO issued a more ambitious safe annual average standard of 10 μg/m 3 [Table 1]. ,
| Improved pollution status|| |
Transparency regarding Chinese air pollution data has greatly improved in the past 4 years. The AAQS, implemented in 2012, catalyzed the creation of a national air reporting system. China now contains more than 1500 automated air quality monitoring sites distributed across 940 cities.  These stations publish hourly data to a website accessible to the public, although these sites do not allow access to archived data. Several recent studies have collected this data over periods of time to create a clearer picture of the air pollution dynamics.
A study by Berkeley Earth analyzed all the PM 2.5 data from April 5, 2014, to August 5, 2014.  During this period, 83% of the population-weighted area experienced average PM 2.5 concentrations above 35 μg/m 3 . In addition, over 90% of the observed population experienced unhealthy air for at least 1 day/month and 46% of the population experienced hazardous pollution levels (>250 μg/m 3 ) for at least 1 h during the course of the study.  A 2015 Greenpeace report compiled data from monitoring stations in 366 cities and found similar results. According to their report, 293 cities (80.1%) did not meet the national AAQS limit of 35 μg/m 3 .  However, these numbers did represent a significant improvement from the previous year. The 2014 analysis only contained 189 cities, which is a testament to the rapid expansion of China's monitoring network. One hundred and seventy one cities in the 2014 report (90.5%) experienced PM 2.5 improvements in 2015 with an average change of 10.3%.  This data correlate with the 2015 report from the MEP of the People's Republic of China, which revealed that only 8 of 74 cities analyzed (10.8%) satisfied China's air quality standards (35 μg/m 3 ). The report also enumerated widespread improvements in PM 2.5 pollution from 2014. 
Air monitoring stations on the ground are the most accurate measure of PM, but this tool was developed recently and does not provide data for long-term changes. Detection of PM is also possible through satellite measurements of aerosol optical thickness (AOT).  This system utilizes Moderate Resolution Imaging Spectroradiometer and Multiangle Imaging Spectroradiometer satellite instruments, which can provide an estimate of aerosol concentration with a resolution of approximately 10 km × 10 km.  AOT can be calculated using satellite data collected from as early as 2001. 
Several studies have analyzed AOT data to determine changes in PM levels across China. A recent analysis of NASA satellite data compared the average annual PM 2.5 concentration throughout China between 2010 and 2015. A 17% decrease in AOT correlated with PM 2.5 concentration was observed. This improvement was in contrast to other countries in the region, such as India where the AOT increased by 13% during this period. 
| Health effects|| |
Ambient PM air pollution was responsible for an estimated 1.235 million deaths in China during 2010.  Links have been uncovered between PM air pollution and cardiovascular disease, cerebrovascular disease, COPD, asthma, changes in lung function, diabetes mellitus, and preterm birth. Recent analyses show that PM pollution is also an independent risk factor for all five of the leading worldwide causes of death [Table 2].  In 2012, the leading causes of death were ischemic heart disease (IHD), stroke, COPD, lower respiratory infection, and lung and airway cancers [Table 3],  which are all exacerbated by PM pollution. This section will summarize the recent population level studies in China regarding the effect of PM air pollution on disease morbidity and mortality.
|Table 2: Recent studies on particulate matter air pollution as an independent risk factor for the top five leading causes of death globally|
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|Table 3: Contribution of particulate matter air pollution to the mortality rates of the five leading causes of death globally|
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The GBD report is a comprehensive analysis of epidemiological and demographic data to determine imminent public health threats across 188 countries. The 2010 report revealed the scale at which PM is affecting public health in China [Table 3]. The report included a calculation of disability-adjusted life years (DALY) for 67 risk factors, including PM air pollution. PM air pollution was the 4 th largest contributor to DALYs, causing an estimated 25,227,000 healthy years of life lost across the population of China.  The 2013 GBD report showed that PM air pollution remains a major contributor to DALYs, but recent efforts have successfully decreased its effect. PM air pollution was the 8 th greatest contributor to DALYs of the 88 risk factors estimated using data from 2013. 
A strong connection has been documented between PM pollution and respiratory illness [Table 2]. Due to the variability in PM composition, the focus of this review is on studies from East Asia. Several recent studies have shown increased admissions to emergency departments (ED) for asthma and COPD-related events during times of high pollution. , In cities across China and Taiwan, studies were conducted after days with high PM pollution. A 2014 study in Shanghai found increased ED admissions of children with asthma-related incidents following periods of increased PM 2.5 levels.  The emergency room admissions peaked 3 days after the rise in PM 2.5 levels. Another study, in Hong Kong, China, found that COPD and asthma hospital admissions spiked during periods of high PM levels.  Four recent studies in Taiwan have found increased COPD and asthma hospital admissions following days with high PM 2.5 levels detected (Cheng et al.;  Tsai et al., 2013; Tsai et al., 2014; and Tao et al., 2014). These provide substantial evidence suggesting that the PM pollution in China increases respiratory illness morbidity.
PM air pollution also affects the cardiovascular system. Several studies have calculated significant increases in cardiovascular mortality risk after long-term exposure to high PM concentrations. A large-scale analysis of patient data collected by the American Cancer Society concluded that mortality risk increases 8-18% with each 10 μg/m 3 rise in PM 2.5 . These increases in mortality were attributable to IHD, dysrhythmia, heart failure, and cardiac arrest.  A recent study in China evaluated a cohort of 71,431 men to determine whether PM pollution increased cardiovascular mortality. They found a 1.8% increase in risk for cardiovascular mortality with each 10 μg/m 3 increase in PM 10 concentration. 
In addition, evidence supports a cardiovascular morbidity and mortality risk associated with short-term exposure to PM pollution. A recent analysis in Shanghai, China, found a 0.56% increase in outpatient cardiac arrhythmia visits for each 10 μg/m 3 increase in PM 10 concentration.  Similarly, a study of mortality in eight Chinese cities found a 0.86% increase in coronary heart disease mortality risk for every 10 μg/m 3 increase in PM 10 concentration.  These studies suggest that both 24 h and long-term exposure to PM pollution in China can negatively affect cardiovascular health.
Stroke has long been associated with PM air pollution. A study in Guangzhou, China, analyzed daily mortality data between 2007 and 2011 and correlated the stroke deaths with data collected from two air-monitoring stations in the area.  They found significant increases in daily stroke mortality with increases in PM 10 and PM 2.5 levels. Their findings also suggested that hemorrhagic stroke mortality risk increases more than ischemic stroke following PM exposure. 
Several studies have linked PM pollution to adverse pregnancy outcomes.  There is substantial support for lower birth weights and increased frequency of preterm delivery due to PM exposure. A WHO Global Survey on Maternal and Perinatal Health (2001-2006) matched PM 2.5 levels with local data from air-monitoring stations. The worldwide results showed decreased birth weights with PM 2.5 elevation, but the preterm birth correlation was insignificant. However, in several highly polluted cities in China, the survey found a significant correlation between PM 2.5 and preterm birth in addition to the low birth weights. 
PM pollution has been positively correlated with population-wide incidence of Type II diabetes mellitus. However, this correlation was found in studies from developed countries with relatively low PM levels.  Few studies have been published on this topic from countries with pollution levels as high as the cities in China, but a recent analysis of 1760 cases in China has reported a significant association. 
| Conclusion|| |
Substantial evidence has revealed severe public health effects from PM air pollution in China. PM pollution increases mortality risk and increases the risk for the top five global causes of death. The PM concentrations in a majority of China's cities are above the national and international standards for yearly and 24 h exposures. The PM haze has prompted policy changes and reduction goals, which have proven effective in recent years. Reduction of PM air pollution has been detected in China between 2010 and 2015, but these modest improvements are little consolation to the millions of people exposed to unsafe pollution levels. China is moving in a positive direction, but pollution reduction efforts must continue improving to adequately relieve this preventable danger to public health.
Financial support and sponsorship
This work was partially supported by the American Heart Association Grant-in-Aid (14GRNT20460246), Merit Review Award (I01RX-001964-01), from the US Department of Veterans Affairs Rehabilitation R & D Service, National Natural Science Foundation of China (81501141), Beijing New-star Plan of Science and Technology (xx 2016061) as well as the Training Program of Beijing Ministry of Science and Technology (Z151100003915134).
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3]
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