Chinese and German researchers announced to solve the mystery of the formation of major components in heavy haze in Beijing and North China

Researchers from China and Germany said on the 21st that they have solved the mystery of the formation of sulfate, the most important component of haze in Beijing and North China, and found that the chemical reaction of nitrogen dioxide and sulfur dioxide in the water adsorbed by atmospheric fine particles is the main path of sulfate formation during the current haze. This finding highlights the importance of giving priority to NOx emission reduction while continuing to implement emission reduction measures to alleviate air pollution< 1n recent years, haze has occurred frequently in Beijing and North China. Previous studies have shown that sulfate is the main driving factor of heavy pollution. 1n terms of absolute contribution, sulfate accounted for 20% of PM2.5 in heavy pollution period, which was the highest monomer; 1n the relative trend, with the increase of PM2.5 pollution, sulfate is the component with the fastest increase of relative proportion in PM2.5. Therefore, the source of sulfate is the key scientific problem to explain the formation of haze academician he Kebin, Professor Zhang Qiang and Dr. Zheng Guanghui of Tsinghua University, Professor Cheng Yafang, Professor Ulrich boscher and Professor Suhang of Max Planck 1nstitute of chemistry in Germany reported in the new issue of scientific progress that they had found that they had made use of field observation, model simulation and theoretical calculation, During the haze period in Beijing and North China, sulfate is mainly formed by the “particulate matter bound water” of sulfur dioxide and nitrogen dioxide dissolved in the air, which reacts rapidly in the unique neutral environment in North China. Particulate matter bound water refers to the moisture absorbed by PM2.5 deliquescence in high relative humidity environment this conclusion is quite different from the commonly thought sulfate formation mechanism. The existing classical atmospheric chemistry theories based on Europe and America believe that sulfate is mainly formed in cloud water environment. Because the liquid water content in cloud is much higher than that in particulate matter bound water, which is usually 1000 to 100000 times higher than that in cloud water, the reaction in particulate matter bound water can be ignored compared with sulfate formation in cloud water; Theoretical calculation also shows that in the cloud water reaction path, the contribution of nitrogen dioxide oxidation of sulfur dioxide to sulfate is negligible during the haze period in Beijing and North China, on the one hand, due to the sharp rise of particulate matter concentration and the high relative humidity under static and stable weather conditions, the bound water content of particulate matter is much higher than that in the classic scenario, and the total amount of reaction in the bound water of particulate matter is greatly increased; On the other hand, the concentration of nitrogen dioxide during severe haze is more than 50 times of that under the classical cloud water scenario, which directly changes the relative importance of nitrogen dioxide oxidation pathway. 1n addition, a large number of alkaline substances such as ammonia and mineral dust exist in Beijing and North China, which makes the pH value of particulate matter bound water much higher than that in the United States and other places, showing a unique neutral environment, and the reaction rate of nitrogen dioxide oxidation mechanism will increase significantly with the increase of pH value 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 sulfate pollution level in China’s haze “this study shows the particularity of compound pollution in China,” academician he Kebin told Xinhua news agency. “High sulfur dioxide mainly comes from coal-fired power plants, high nitrogen dioxide mainly comes from power plants and motor vehicles, and alkaline substances such as ammonia and mineral dust that play a neutralizing role come from agriculture, industrial pollution, dust and other sources. At the same time, these different pollution sources are discharging at a high intensity in China, leading to the rapid formation of sulfate in a unique chemical generation path, which is one of the main reasons for the rapid growth of particulate matter concentration during severe haze London acid fog is generally considered to be caused by primary pollutants such as soot from coal combustion and sulfur dioxide. Los Angeles haze is a kind of photochemical pollution, which is mainly caused by the reaction of vehicle exhaust under the action of sunlight. The haze in China is caused by the mixture of primary and secondary pollutants he Kebin said that the particularity of this kind of compound pollution shows the importance of collaborative emission reduction of multiple pollutants, especially the priority should be given to increasing the emission reduction of nitrogen oxides at the present stage” Although we know that we need to reduce emissions before, if we can’t understand the key chemical mechanism of heavy haze pollution, we can’t carry out effective model quantitative simulation analysis, and we can’t accurately assess how to reduce emissions most effectively and scientifically. Unscientific emission reduction may lead to serious consequences. 1t may cost a lot of manpower and material resources, but it has little effect. “(The original title is “the study reveals the mechanism of sulfate formation in Beijing haze and suggests to increase the emission reduction of nitrogen oxides”)

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