The Evolution Characteristics Of Protein Components In PM_2.5 During Winter Haze Pollution And The Correlation Between Protein And Chemical Components

In recent years,Xi’an has experienced rapid economic development and has successfully ranked among the"new first-tier"cities.The air pollution problem has also become a"stubborn disease"that plagues the sustainable development of the city.At present,there have been many studies on the components of PM_2.5 during the winter haze in Xi’an,but the understanding of its biological components was still very insufficient.The most of previous studies are mostly focused on long-term sampling,and various substances in aerosols are constantly undergoing physical and chemical reactions.Therefore,high time-resolved sampling of PM_2.5 is helpful to more clearly explore the formation and transformation mechanism of each component in particulate matter.This study conducted high time-resolved sampling of PM_2.5 samples under typical polluted conditions in winter in Xi’an from December 2019 to January 2020.Taking the protein substances,water-soluble inorganic ions and Dicarboxylic acids in PM_2.5 as the research objects,the concentration characteristics and short-term continuous changes of different types of pollutants in winter haze days are explored,and the main conclusions are as follows:（1）During winter haze pollution,the average concentration of protein substances in PM_2.5at Xi’an urban area was 5.587μg/m³,which was at a relatively high level compared to other areas in China;the protein concentration showed significant short-term continuous changes,and the concentration of protein at night was higher than that during the day,which was significantly affected by human activities.（2）The concentration of water-soluble inorganic ions also showed short-term continuous changes.NO₃^-and SO₄^2-were the highest concentration of water-soluble inorganic ions.The average value of the ratio of NO₃^-to SO₄^2-was 1.47.The contribution of the mobile sources to the PM_2.5 concentration were higher than that of the fixed sources;while the concentration of PM_2.5 and the ratio of NO₃^-to SO₄^2-rose rapidly at the same time,and the mobile sources had a higher impact on the change of PM_2.5 concentration than the fixed sources.（3）Oxalic acid（C2）was the highest concentration of dicarboxylic acid,with an average concentration of 1671.88 ng/m³,which was also at a higher level compared to other parts of China;as the concentration of PM_2.5 continued to increase on a hazy day,the concentration of oxalic acid showed a rising trend;when the ratio of C3/C4 increased,the degree of oxidation of aerosols was higher than other conditions in the case of high humidity.（4）The concentration of protein was significantly positively correlated with K⁺,indicating that the source of proteins in aerosols at Xi’an were related to biomass combustion;the concentration of protein also showed a significant positive correlation with the concentrations of NO₃^-and SO₄^2-,indicating that proteinaceous substances may be related to the production of NO₃^-and SO₄^2-;the concentration of protein and relative humidity were also significantly positively correlated（p<0.01）,and protein was easy to absorb moisture and grow at high relative humidity.（5）According to the correlation analysis between protein components and other chemical components,the results showed that protein had good hygroscopicity;when the relative humidity in the air was high,the aerosol formed by taking protein as the core to absorb water vapor in the air and gaseous pollutants（O₃,SO₂,NO_X,VOCs,etc.）that were easily soluble in water produced hygroscopic growth and heterogeneous reaction;after that,SO₂ and NO_Xaccelerated the formation of SO₄^2-and NO₃^-in the liquid phase,and the organic matter was easily to be oxidized to\dicarboxylic acids in the acidic aerosol rich in SO₄^2-.