Fluorescence And Electrochemical Characteristics Of PAHs In Atmospheric Particulate Matter And Their Photochemical Conversion

Polycyclic aromatic hydrocarbons（PAHs）are important components in atmospheric particulates,and they are attracting more and more attention because of their wide sources,high damage and long-lasting pollution.Based on the attention paid to PAHs organic pollutants in recent years,it is gradually found that the analysis of PAHs in environmental media has complex pretreatment process,large amount of organic solvent,and long time for instrument analysis,which cannot meet the real-time performance of sample analysis.The development of simple and fast analysis methods has become an urgent problem.In this study,a combination of indoor simulation and external field monitoring was used to establish a fluorescence characteristic spectrum method and a rapid analysis and testing technique for electrochemical sensors for preferential control of PAHs.The established method was used to study the photochemical conversion of PAHs in the atmosphere.The results are as follows:1 By comparing traditional single-wavelength excitation/emission fluorescence spectra with constant energy synchronous fluorescence spectroscopy,the optimal excitation wavelength,optimal emission wavelength and optimal detection energy difference of each PAHs are determined,and establishing a characteristic map library of 15 preferentially controlled PAHs in atmospheric particulate matter.Under the optimal conditions,the PAHs were quantitatively studied.The LOD and LOQ of the remaining PAHs were 0.058～3.18ng/m L and 0.232～12.7 ng/m L,respectively.The recoveries in the blank and a certain concentration ranged from 82.8%to 120%,and the relative standard deviations（n=7）ranged from 0.51%to 5.87%,indicating that the sample preparation procedure was simple and the instrument analysis time was short（40～50s）and can reduce the use of environmentally unfriendly solvents.This method was applied to set up sampling points in Lanzhou City to analyze the distribution characteristics of 15 PAHs in atmospheric particulate matter in Lanzhou.2 Based on the electrochemically modified multi-walled carbon nanotubes,an acidified carbon nanotube-glass-carbon modified electrode was prepared based on the electrochemical analysis test method.The electrochemical sensors of five common PAHs were constructed by using the modified electrode.Electrochemical characterization studies were carried out in comparison with bare glassy carbon electrodes,indicating good electrical conductivity,stability and reproducibility.The electrochemical behaviors of five PAHs were studied by cyclic voltammetry（CV）and linear voltammetry（LSV）.The qualitative correlation between the standard curves was between 0.9910 and 0.9998,and the LOD and LOQ were 0.105ng/m L-0.354 ng/m L,0.420 ng/m L-1.061 ng/m L.The recoveries in the blank and a certain concentration ranged from 86.7%to 117.3%,and the relative standard deviations（n=7）ranged from 0.88%to 3.98%.The method has good stability and the method of collecting atmospheric particulate samples is verified.3 In the closed smoke chamber,five kinds of PAHs were atomized,and the atmospheric pollution process was simulated under static conditions,and add ultraviolet photolysis PAHs.The simulated photolysis experiments showed that the three PAHs of Ant,Bk F and Bap could undergo degradation reaction,and the degradation rates were 90.2%,79.8%and 87.6%,respectively.It is speculated that the degradation mechanism of PAHs in this experiment is that under ultraviolet irradiation,PAHs absorb energy from a stable ground state to an excited state,and water molecules and O₃ produced·OH radicals attack PAHs molecules in an excited state.Causes degradation and transformation of PAHs.In the experimental simulation,the concentration of·OH radicals is large,and the PAHs are directly mineralized into carbon dioxide and water,so the degradation rate obtained is high and no byproducts are detected.At the same time,it was found that the two PAHs,Ft and Bghi P,could hardly react due to photolysis experiments.The reaction was simulated in the smoke chamber,which caused a certain part of the·OH radical oxidative chain reaction to be impossible.Explain the diversity of light conversion pathways and reaction mechanisms of PAHs in the actual atmosphere.