Research On The Seasonal Variation Of Organic Nitrates In The Atmospheric Particulate Phase Of Beijing And Their Formation Mechanism

Organic Nitrates are esters and derivatives containing nitrate groups,and also an important pool of nitrogen oxides?NOx?in the atmosphere.ONs in the gas phase are mainly produced through the oxidation process of OH,NO3 free radicals and VOCs.ONs not only consume oxidants in the atmosphere,but may also release NOx in subsequent reactions,affecting photochemical reactions as well as ozone generation.In addition,ONs contribute to the organic matter in particle phase to a certain extent.ONs has various types due to their different precursors VOCs,and there are also different types of composition and distribution in urban areas and suburbs.In this study,an efficient GC-MS/MS method for determining organic nitrates in atmospheric fine particles?PM2.5?was established using synthesized standards.,and the qualitative and quantitative ion pairs of straight-chain alkyl nitrates and methyl-phenyl,ethyl phenyl and p-dimethyl-phenyl nitrates were determined.And the instrument method was optimized.The repeatability and recovery of the method are verified by standard recovery experiment,and the method is further applied to the detection of actual environment samples.In the environmental samples,the total detection frequency of the 7 substances was 87%.This study choose the Minzu University of China as a sampling point,using the established detective method to analyzed the PM2.5 samples of September,November,2018 and January,march and may,2019.C₈-C₁₂ straight-chain alkyl nitrates were detected,and using the same qualitative quantitative ions we detected 8 kinds of C₈-C₁₂ alkyl nitrates isomers and C₁₃-C₁₆ straight-chain alkyl nitrates.The seasonal and diurnal concentrations tendency of organic nitrates was analyzed.We compared the concentrations tendency of ONs and PAN and O3,the results showed that C₈-C₁₆ straight-chain alkyl nitrates may have a different formation mechanism with PAN.The data showed that ONs concentration peaks in winter and is significantly higher than that in other seasons,which is related to the burning of fossil fuels during winter heating period in Beijing.In terms of seasonal composition differences,the average proportion of C₈-C₁₂ straight-chain alkyl nitrates was the highest in summer,while the average proportion of C₁₃-C₁₆ straight-chain alkyl nitrates was the highest in winter.In this study,the correlation of C₈-C₁₂ and C₁₃-C₁₆ alkyl nitrates with NOx and particle phase NO3-was discussed,and it was found that some monomers and particle phase NO3-had similar concentration variation tendency.And because of low volatility of C₈-C₁₆ alkane in the winter,it may be difficult to generate C₈-C₁₆ straight-chain alkyl nitrates in the gas phase.And because alkanes can react with nitric acid directly to form alkyl nitrates in the presence of metal catalysts.Therefore,it is speculated that C₈-C₁₆ straight-chain alkyl nitrates may be more from the reaction of NO3-generated by heterogeneous reaction and alkanes on the surface of particulate matter.Due to the relatively low detection rate or concentration of individual monomer,the variation trend of its concentration does not have obvious regularity,so it is necessary to further explore the influencing factors of its formation.