Integration And Application Of LIBS System Based On Aerosol Composition Analysis

Aerosols are rare in the Earth's atmospheric composition,but their impact on the atmospheric environment and ecosystem is huge.Due to the different sources and formation reasons of aerosols,the chemical composition of aerosols is different,and with the changes of air flow and temperature,aerosols have obvious regional and seasonal characteristics.The rapid and real-time analysis of the chemical composition of aerosols is great significance for traceability of pollution sources and prevention.Laser-Induced Breakdown Spectroscopy(LIBS)is an atomic emission spectroscopy analysis method.Compared with other analysis technologies,LIBS technology has the advantages of fast,in-situ,real-time,and full-element analysis,and is suitable for the atmospheric environment.It is applicable to the detection of element composition and content in the field of atmospheric environment.The background of this paper is the detection of metal elements in atmospheric aerosols.The LIBS experimental device was built first,and then the LIBS principle prototype was designed and integrated.The test results show that the LIBS principle prototype can be applied to the detection of aerosol composition and content.The main research work of this paper is as follows:1.The LIBS experimental equipment was set up,and the selection of LIBS experimental instrument and the test of LIBS system were completed.The internal structure and packaging method of the dual-pulse LIBS principle prototype was designed using Unigraphics NX software.Two sets of imaging systems are integrated in the LIBS principle prototype,which are used to monitor and adjust the coincidence of two pulsed laser spots on the sample surface and to monitor the laser irradiation position and sample status in real time.The control software of the electronically controlled translation stage in the prototype of the LIBS principle was developed to solve the problem of insufficient sampling rate of circular samples.The laser irradiating point can be used to conduct helical irradiating scan on the surface of the sample according to the size of the sample.Finally,each experimental instrument was integrated into a prototype of the double-pulse laser-induced breakdown spectroscopy(DP-LIBS)principle.2.The collection efficiency of four common spectral collection optical paths for plasma light was studied.Based on the most efficient collection method(double-lens combination optical path with a focal length of 100 mm),the spectral excitation and collection optical path systems were optimized.The effects of different delay times on the spectrum are compared.Based on the spectral net intensity and the signal-to-noise ratio,a delay time of 1600 ns is determined as the optimal spectrum acquisition parameter.The effects of preprocessing methods such as Sliding Window Algorithm,Fourier Transform,Gaussian Curve Fitting Method,Continuous Wavelet Transform on noise suppression and spectral line recognition are compared and analyzed.Finally,Wavelet Threshold Denoising Method and Bi-Scale Correlation Method as a spectral preprocessing method.3.Using the LIBS experimental system,an experimental study on the aerosol composition was carried out,and it was found that the aerosol contained metal elements such as Cr,Na,Mg,Al,Ca,Fe,and Ba.Quantitative analysis of the heavy metal elements was carried out.The correlation coefficient R~2 of the experimentally established calibration curve for heavy metal elements was between 0.995 and 0.997,and the detection limit was between1.9 and 3.6 ppm.The inverted heavy metal content was between 2.9 and 142.3 ppm.Normalized fitting of the net intensity of heavy metal element spectral lines with the PM 2.5and PM 10 data published by the China Environmental Monitoring Station,found that the Ba element has a better fit with PM 10 and the Cr element has a better fit with PM 2.5.The experimental results show that the built LIBS system can perform rapid qualitative and quantitative analysis of atmospheric aerosols.