China's skies: a complex recipe for pollution with no quick fix
2013; Elsevier BV; Volume: 381; Issue: 9882 Linguagem: Inglês
10.1016/s0140-6736(13)61186-1
ISSN1474-547X
Autores Tópico(s)Air Quality and Health Impacts
ResumoChina's Government is doing more than ever to address air pollution in the country, but scientists say periodic crises may remain beyond government control for years to come. Ted Alcorn reports. Of all the challenges facing Chinese policy makers, air pollution is uniquely communal. Even in a society of stark divisions and increasing inequality in housing, health care, and education, everyone still breathes the same air when they step outside. Air pollution is also uniquely conspicuous: there is little the government can do to hide the problem. “Seeing is believing”, says Jiang Lin, senior vice president at the Energy Foundation, a partnership of major foundations interested in sustainable energy. “If you can see the air you breathe, it is not good air—no matter what spin you put on it.” Public concern boiled over in Beijing this January when for several days the air quality reached its worst levels in recent memory, pushing the government to act. The concentration of fine particles smaller than 2·5 μm (PM2·5) spiked to 886 μg/m3—35 times the WHO standard for acceptable daily exposure and five times the average concentration in US airport smoking lounges. Though Beijing's skies ultimately cleared and pollution levels haven't returned to those heights, the US Embassy air quality monitor has registered “hazardous” levels on at least 1 day every month since. Nor is the problem limited to Beijing; pollution in several Chinese cities, including Chongqing and Shanghai, have reached the same level in the past month. As science advances, the danger posed by long-term exposure to these particles and their impact on the Chinese population looks increasingly dire, says Aaron Cohen, principal scientist of the Health Effects Institute, MA, USA, and an expert on the effects of air pollution. “We have more information, and that information is telling us that the risks are larger than we thought they were.” Long-term exposure to high levels of PM2·5 is associated with high risks of ischaemic heart disease, stroke, lung cancer, and chronic obstructive pulmonary disease. In view of the severity of pollution in China and the number of inhabitants, the burden of disease is enormous. An expert group cochaired by Cohen estimated that ambient air pollution contributed to 1·2 million premature deaths in China in 2010—nearly 40% of the global total. Air pollution in northeastern China is a long-standing problem. But Beijingers have tolerated poor air quality for decades, seemingly willing to shrug off polluted skies as fog or haze. What made January's episode notable was not its severity, but how the public responded. In response to a previous episode of severe pollution in December, 2011, the Ministry of Environmental Protection had begun reporting PM2·5 levels in real time. When the concentration spiked in January, Chinese internet users had a measure with which to quantify it, and mentions on China's microblogs of the term PM2·5 skyrocketed. For the first time, mainstream newspapers began to criticise the conditions. But if Beijing's soupy skies focused public ire on the problem, they are an imperfect measure. As any Beijing resident will tell you, heavily polluted days may alternate incongruously with so-called blue-sky days. This is because PM2·5 does not simply emerge from smokestacks and tailpipes; many of these particles are produced in the atmosphere by reactions between other pollutants—namely SO2, mono-nitrogen oxides, and volatile organic compounds—in a complex interplay with sunlight, humidity, and temperature. The process is not unlike baking a cake, with mankind providing many ingredients and the weather acting as an unpredictable chef. The weather helps to explain the severe air pollution observed in Beijing this January, says Yuxuan Wang, associate professor at Tsinghua University in Beijing. Wang has built a model to measure how much influence the weather had in producing the recorded PM2·5 levels. Typically, winter conditions in Beijing are shaped by the Siberian High: a body of cold, dry air that builds up over Eurasia and generates winds across northeastern China towards the Pacific. But last winter, perhaps due to long-term changes in the global climate, the Siberian High was weaker than usual. Higher average air temperatures in Beijing produced faster chemical reactions; the higher relative humidity was better for catalysing PM2·5 formation; and there was less wind to blow pollution out to sea. Although Wang says that other factors play a part, her chemical–transport model explains 70% of average PM2·5 levels in January and 50% of concentrations on the days of heaviest pollution. “If the Siberian High continues to weaken in the future, there may be more and more severe pollution episodes in winter, and I think that has significant implications for air quality management in China”, she says. The central part played by the weather means that, just as the Chinese Government can't take credit for every blue-sky day, the public can't measure the government's progress against recorded pollution levels alone. In fact, most experts credit the government for the major steps it has taken to address air pollution thus far. China's dramatic expansion of ground-level monitoring of PM2·5 is a case in point. In 2012, 74 Chinese cities began reporting real-time PM2·5 concentrations and public awareness has risen steeply. India, by contrast—where analyses of satellite data indicate that air pollution may be even more severe than in China—does not have a similar system of ground-level monitors. Angel Hsu, a postdoctoral associate at the Yale School of Forestry, CT, USA, analysed the satellite data and says that with respect to these data, “China is actually ahead of the curve.” This spring, China also introduced several long-discussed changes to the regulation of vehicle emissions. In February, the State Council announced new standards, requiring the country's oil refiners to reduce the sulphur content of diesel from 350 ppm to 10 ppm and that of gasoline from 150 ppm to 10 ppm, the same standard as the European Union. Improved fuel, in turn, will allow China's vehicle fleet to adopt advanced emissions control technologies and greatly reduce their tailpipe emissions. These changes should have a particularly large effect on diesel and heavy-duty trucks, which comprise a small share of total vehicles but account for most of the emissions. David Wagner, an expert in vehicle emission control at the nonprofit International Council for Clean Transportation, applauds these changes but says that they aren't radical when viewed in the context of China's breakneck economic growth. He points out that 20 million new vehicles will be sold in China this year, so the government has to increase environmental standards rapidly just to keep up. Perhaps China's biggest success has been the reduction of SO2, a byproduct of coal-fired power stations and one of the main precursors of PM2·5 and of acid rain. In the 11th Five-Year Plan initiated in 2006, the government committed to reducing SO2 emissions by 10% and the policy was implemented aggressively. In just 2 years, China had installed desulphurisation equipment in more power stations than the USA had equipped in three decades. And, because China's power plants are so new—more than half of its capacity has been installed since 2003—their average efficiency also exceeds that of US power stations. An independent evaluation of the policy led by Chris Nielsen, executive director of the China Project at Harvard University, MA, USA, found that the government exceeded its target. But the policy had a major weakness in that it focused on a single pollutant while leaving others unconstrained: SO2 emissions fell, but mono-nitrogen oxides—mainly from vehicles and heavy industry—rose by 47%, Nielsen says. “We would argue the government has done things to successfully—even aggressively—reduce some forms of PM2·5, but meanwhile others have increased. That doesn't get the government off the hook entirely, but it's a much different story than the government isn't acting.” Advocates hope that the government is learning from this experience. The 12th Five-Year Plan established the first targets for reducing mono-nitrogen oxides, and denitrification equipment is being added to major stationary sources like power stations and steel mills. Volatile organic compounds are still uncontrolled, but insiders say that comprehensive targets for PM2·5 reduction may be on the table for the 13th Five-Year Plan in 2016. Nielsen says that a carbon tax could also be implemented with little effect on the economy and huge benefits for the environment. But the major reductions achieved so far were the low-hanging fruit; the remaining polluters are smaller and far more numerous. Chinese financial magazine Caixin cited a Beijing municipal government plan that said that it would take Beijing 18 years to reach international standards for PM2·5 concentrations. Making headlines may be health and environmental advocates' greatest tools to deepen reforms. “In the past few years, the Ministry of Environmental Protection in particular has been very clever at making sure the rest of the Chinese Government understands the political cost of inaction”, says Deborah Seligsohn, a former US State Department official who has worked in China off and on since 1984. “The Ministry itself has pushed more information out there to the public, and I think they do that because every time the public reacts, it actually helps them make the case to the rest of the government.” Towards better health for people in ChinaThe “Chinese dream”, like the “American dream”, is not only an extremely popular political slogan in China, but also a topic discussed worldwide. According to the Chinese President, Xi Jinping, the Chinese dream is about “realising a prosperous and strong country, the rejuvenation of the nation, and the wellbeing of the people”. The wellbeing of Chinese people is dependent on a range of factors, with health as a key component. China's rapid emergence as a global power has coincided with a series of unprecedented challenges to Chinese people's health. Full-Text PDF
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