Sino-German researchers announce the mystery of cracking the main components of severe haze in Beijing and North China

Chinese and German researchers said on the 21st that they cracked the mystery of the formation of sulphates, the main components of smog in Beijing and North China, and found that the chemical reaction of nitrogen dioxide and sulphur dioxide in the water adsorbed by atmospheric fine particles is the current fog. The main route of formation of sulfate during radon. This finding highlights the importance of giving priority to increasing nitrogen oxide emission reductions to mitigate air pollution while continuing to implement emission reduction measures.

In recent years, haze has become more frequent in Beijing and North China. Studies have shown that sulfate is the main driver of heavy pollution. In terms of absolute contribution, the sulfate accounted for 20% of PM2.5 in the atmospheric fine particulate matter during heavy pollution, which is the highest proportion of monomer; in relative trend, with the increase of PM2.5 pollution degree, sulfuric acid Salt is the fastest growing component of PM2.5. Therefore, the study of the source of sulfate is a key scientific problem to explain the formation of haze.

Academician He Kebin of Tsinghua University, Prof. Zhang Qiang, Dr. Zheng Guangjie, Prof. Cheng Yafang of the Max Planck Institute for Chemistry in Germany, Prof. Ulrich Perschul, Prof. Su Hang and others in the new issue of American “Scientific Progress” The magazine reported that they used field observations, model simulations, and theoretical calculations to find that during the haze in Beijing and North China, sulfate was mainly composed of particulate matter-bound water dissolved in the air by sulfur dioxide and nitrogen dioxide. In the special neutral environment of northern China, rapid response is generated. Particulate matter-bound water refers to the moisture that PM2.5 deliquescents in a relatively high relative humidity environment.

This conclusion is quite different from the commonly thought sulphate formation mechanism. The existing classical atmospheric chemistry theory based on Europe and the United States and other regions believes that sulfate is mainly formed in the cloud water environment. Since the liquid water content in the cloud is much higher than the particulate matter-bound water, it is usually 1000 to 100,000 times higher than that of the cloud. Compared with the sulphate formation reaction in water, the reaction in particulate matter-bonded water is negligible; theoretical calculations also show that in the cloud-water reaction route, the contribution of nitrogen dioxide to oxidation of sulphur dioxide to sulfate formation is also negligible.

During the haze in Beijing and North China, on the one hand, due to the sharp increase in particulate matter concentration and relatively high relative humidity in quiet weather conditions, the particulate matter-bound water content is much higher than that of the classic scenario, and the total amount of reaction in particulate matter-bound water is greatly improved; On the other hand, the concentration of nitrogen dioxide during severe haze is more than 50 times that of the classical cloud water scenario, which directly changes the relative importance of nitrogen dioxide oxidation pathways. In addition, the presence of large amounts of ammonia, mineral dust, and other alkaline substances in Beijing and North China makes the pH of the local particulate matter-bound water much higher than in the United States and other places, presenting a unique neutral neutral environment, and the reaction rate of the nitrogen dioxide oxidation mechanism. It will increase dramatically with rising pH.

Based on this, the researchers pointed out in the paper that giving priority to reducing the emission of nitrogen oxides may help to significantly reduce the level of sulphate pollution in Chinese haze.

"This study shows the specificity of compound pollution in China," Academician He Kebin told Xinhua News Agency reporters. "High sulfur dioxide is mainly from coal-fired power plants, and high nitrogen dioxide is mainly from power plants and motor vehicles, and it plays a basic role in neutralization." Substance ammonia, mineral dust, etc. come from other sources such as agriculture, industrial pollution, dust, etc. These different sources of pollution are emitted at the same time in China with high intensity, resulting in the rapid generation of sulfate by a unique chemical pathway, which is also the concentration of particulates during severe haze. One of the main reasons for rapid growth."

Acid mist in London is generally considered to be caused by coal-burning smoke and primary pollutants such as sulphur dioxide. Los Angeles fog is a kind of photochemical pollution, the main reason is that the motor vehicle exhaust reacts under the sunlight to generate secondary pollutants. In contrast, smog in China is a combination of secondary pollutants.

He Kebin said that the special nature of this compound pollution further demonstrates the importance of multi-pollutant collaborative emission reduction, especially at this stage should be given priority to increase nitrogen oxide emission reduction efforts. “Even though we knew that we needed to reduce emissions, if we couldn't figure out the key chemical mechanisms that formed heavy pollution, we couldn’t carry out effective model quantitative simulation analysis, and we could not accurately assess how to reduce emissions most efficiently and scientifically. The platoon may lead to serious consequences, may have spent a lot of manpower and material resources, but with little success.” (The original title “The study revealed that the mechanism of sulphate formation in Beijing haze suggests increasing nitrogen oxide emissions reduction”)