Characterization Of Organic Compounds In Atmospheric Fine Particles By Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

In recent years with the fast development of economy and urbanization, atmospheric pollution, especially haze weather, showed an increased tendency which had previously experienced in the developed nations. Among all the pollutants, aerosol fine particles, also known as PM2.5, are the main components leading to the air pollution. In spite of its low concentration, atmospheric fine particles have significant impacts on air quality. Since the size of atmospheric fine particles is quite tiny, it can easily absorb toxic and harmful substances, leading to significant effect on human health and atmospheric environment quality. The components of atmospheric fine particles are very complex, mainly composed of organic portion and inorganic portion. According to some literature, the organic portion in the atmospheric fine particles accounts for 20%-50% of all the components[1], making it one of the most important parts in atmospheric fine particles. Among all the industrial pollutants, nitrogen oxide and sulphur oxide are the most important indicators. Therefore, we chose the organic compounds as our research subject and tried to identify the organonitrates and organosulfates. The research work was conducted as follows.Firstly, analysis of the organic compounds in atmospheric fine particles was conducted by the ultrahigh resolution and mass accuracy Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Analysis method of atmospheric fine particles extraction flow were established, and all the parameters were optimized in order to improve the ionization efficiency. Compounds with C, H, O atoms were the main class in atmospheric fine particles, while compounds with N and S atoms were less. Meanwhile several methods were applied to comprehensively characterize the compounds in fine particles, including molecular descriptor modified aromaticity index(AI_mod), visualization method van Krevelen diagram and Kendrick mass defect plot, direct comparison of molecules. The aromaticity of all compounds and influences of different extraction solvents were evaluated in the research. It turned out that solvents with polarity tended to detect more compounds and the polarity of solvents were related to the aromaticity. Proper extraction solvents should be chosen according to the characteristics of target compounds.Secondly, considering the potential component contribution of natural organic matter and dissolved organic matter to atmospheric fine particles, the components of natural organic matter were identified using the similar analytical method to atmospheric fine particles. Comparisons were made between atmospheric fine particles and natural organic matter compounds. Results showed that the same compounds identified by the two different matters were not as high as we expected, which means the component contribution of natural organic matter to atmospheric fine particles was limited. The main components of atmospheric fine particles were probably the reaction products of complicated atmospheric interactions.Lastly, given the different selectivity and ionization efficiency of different ionization sources, MALDI and ESI source were applied to the research and the differences were compared in order to comprehensively understand the components of atmospheric fine particles. Results showed that the compounds detected by MALDI and ESI source were quite different from the qualities. MALDI source was easy to detect compounds with high aromaticity, low O/C ratio (<0.3) and low H/C ratio (<1.5), while ESI source was inclined to detect polar compounds with high O/C ratio. Therefore, different ionization sources should be combined to comprehensively detect the components for complex mixtures like atmospheric fine particles.