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For more than 15 years, the Chinese government has invested billions of dollars to clean up its deadly air pollution, with an intense focus on reducing sulfur dioxide emissions from coal-fired plants.
These efforts have reduced sulfur dioxide emissions, but extreme pollution episodes remain a normal phenomenon in winter, and experts estimate that more than 1 million people die each year in China from particulate air pollution.
A new Harvard research may explain why. It shows that reducing formaldehyde emissions rather than sulfur dioxide could be a way to reduce extreme air pollution in winter.
The research is published in Letters of geophysical research.
"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, John A graduate student. Paulson School of Engineering at Harvard. Applied Sciences (SEAS) and first author of the article. "Our research suggests ways to more quickly reduce air pollution.This could help save millions of lives and steer billions of dollars worth of investment in reducing pollution from the air. air."
Moch is also a subsidiary of the Department of Earth Sciences and Harvard Planets.
This research was the result of a collaboration between Harvard University, Tsinghua University and Harbin Institute of Technology.
Measurements made in Beijing from days with particularly high particulate pollution, known as PM2.5, showed a sharp increase in sulfur compounds, which were generally interpreted as sulphate. On the basis of these measures, the Chinese government focused on reducing sulfur dioxide (SO2 ), a source of sulphate, as a means of reducing air pollution. As a result of these efforts, SO2 eastern China has declined considerably since 2005. The problem is that PM air pollution has not followed the same path.
Moch collaborated with Eleni Dovrou, a graduate student of SEAS, and Frank Keutsch, Stonington Chair Professor of Engineering and Atmospheric Science and Professor of Chemistry and Chemical Biology. They discovered that the instruments used to analyze mist particles can easily misinterpret sulphate compounds as sulphate, while in fact it is a molecule called hydroxymethane sulphonate (HMS). HMS is formed by the reaction of SO2 with formaldehyde in clouds or droplets of fog.
Using computer simulation, researchers have shown that HMS molecules could be a major part of the sulfur compounds observed in PM2.5 in a winter fog, which would help to explain the persistence of extreme air pollution events despite the reduction of SO emissions.2.
"By including this neglected chemistry in air quality models, we can explain why the number of extremely polluted days in Beijing's winter has not improved between 2013 and January 2017, despite the success major gain in reducing sulfur dioxide, "said Moch. "The sulphide-formaldehyde mechanism may also explain why policies appeared to suddenly reduce extreme pollution last winter.This winter, significant restrictions on SO emissions2 emissions led to lower concentrations for the first time than formaldehyde and2 the limiting factor for the production of HMS. "
The main sources of formaldehyde emissions in East China are vehicles and large industrial facilities such as chemical and oil refineries. The researchers recommend that policymakers focus their efforts on reducing emissions from these sources in order to reduce the extreme veil in the Beijing area.
Next, the team aims to directly measure and quantify the HMS in Beijing using modified observing systems. The team will also implement sulfur-formaldehyde chemistry in an atmospheric chemistry model to quantify the potential significance of the sulfur-formaldehyde chemistry that creates HMS throughout China.
"Our work suggests that this little-known chemical path plays a key role during episodes of extreme pollution in Beijing," said Loretta J. Mickley, Senior Researcher at SEAS.
This research was co-authored by J. William Munger, Senior Researcher in Atmospheric Chemistry and Daniel J. Jacob, Full Professor of the Vasco McCoy Family of Atmospheric Chemistry and Engineering. 39, environment at SEAS. It was also co-written by Yuan Cheng, Jingkun Jiang, Meng Li, Xiaohui Qiao and Qiang Zhang.
The work was funded by Harvard Global Institute's Harvard-China Project Award, the National Science Foundation Senior Research Fellowship, and the Robert and Patricia Switzer Foundation.
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