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China is not known for its respect for the environment and its capital, Beijing, has always been one of the most polluted cities in the world. But over the last fifteen years or so, the Chinese government has invested billions of dollars in cleaning up air pollution, which would result in more than a million deaths a year.
Leaders focus more specifically on reducing sulfur dioxide (SO2) emissions from coal-fired power plants – one of the main sources of particulate air pollution that causes many casualties. Although their efforts have reduced these emissions, there are still extreme pollution events that occur mainly in winter. A new study from Harvard University, published in Letters of geophysical research, may have found the reason why.
The study finally revealed that reducing formaldehyde emissions – not just sulfur dioxide – was a key factor in reducing extreme winter air pollution.
"We show that policies to reduce formaldehyde emissions can be much more effective at reducing extreme winter fog than policies aimed at reducing sulfur dioxide alone, "said Jonathan M. Moch, a graduate student in Harvard John A. Paulson School of Engineering and Applied Science (SEAS) and first author of the paper. "Our research indicates ways to more quickly eliminate air pollution. This would save millions of lives and direct billions of dollars of investment in reducing air pollution. "
The measurements taken in Beijing on days when air pollution by particulates (PM2.5) was particularly high showed a sharp increase in sulfur compounds. These are the measures that led the Chinese government to reduce SO2. However, despite the decrease in sulfur dioxide emissions compared to East China, airborne particle pollution has not been reduced in the same way.
It has been determined that the instruments used to analyze the haze particles can easily misinterpret sulphate compounds as sulphate, whereas it is actually a molecule called hydroxymethane sulfonate (HMS). HMS is formed by the reaction of sulfur dioxide with formaldehyde in clouds or droplets of fog.
"By integrating this neglected chemistry into the air quality models, we can explain why the number of extremely polluted days in winter in Beijing did not improve between 2013 and January 2017, despite the success major won by the reduction of sulfur dioxide, "said Moch. "The sulphide-formaldehyde mechanism may also explain why policies seemed to suddenly reduce extreme pollution last winter. During this winter, significant restrictions on the SO2 emissions led to lower concentrations for the first time than formaldehyde and2 the limiting factor for the production of HMS. "
Formaldehyde emissions come mainly from vehicles and major industrial facilities – such as chemical and oil refineries – located in eastern China. It is therefore not surprising that researchers are recommending that policy makers strive to reduce emissions from these sources in order to improve the public health of their country.
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By Connor Ertz, Earth.com Editor
Image credit: Jonathan M. Moch / SEAS from Harvard
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