The LIBS Detection System And Its Application Of The Atmospheric Aerosol

In recent years,the environmental pollution is getting serious,the disaster weather occurs frequently,human life is affected by the increasing change of the ecological problems.Among the causes of climate and environmental problems,the role of atmospheric aerosols cannot be ignored.Harmful substances in aerosols can cause air pollution and affect human health.Therefore,accurate characterizing the properties of atmospheric aerosols is particularly important for assessing the magnitude of aerosol hazards.The atmosphere is dynamically changing,and the aerosol detection method requires rapid analysis and detection.Laser Induced Breakdown Spectroscopy（LIBS）as an emerging spectrum detection technology,has been rapidly developed in recent years.LIBS technology is not limited to the shape of the sample to be tested,and it has the advantages of fast online analysis,full element detection,and no pretreatment.Based on this,a laser induced breakdown spectroscopy device was built in this paper.A spectral on-line detection system based on LabVIEW was designed.The system was used to detect the air and aerosol samples which collected on the filter.In this paper,the delay time of the plasma spectral intensity variation at 0.5-5μs was studied.The optimal delay time was determined to be 2μs by time-resolved spectroscopy.The plasma spectral intensity was studied by the modulation of the pump source operating voltage and Q-switch.With the variation of laser power density,the plasma shielding phenomenon that occured when the laser power density reaches a certain value,and the reasons were analyzed and explained.Using the Boltzmann method and the Stark broadening method to solve the plasma electron temperature and electron density at different power densities,the appearance of plasma shielding phenomenon was verified,and the operating parameters of the laser in the LIBS detection system were determined.The plasma spectral data analysis method was studied.The regional polynomial fitting method was applied to the baseline correction of the spectrum,and the wavelet was used to denoise the plasma spectrum.The spectral noise reduction effect under different wavelet bases and different decomposition layers was analyzed.The spectral noise reduction effect was verified by the calculation of peak signal-to-noise ratio.The second-order differential method was used to realize auto spectral line identification.In order to improve the recognition accuracy,six limiting rules are proposed for spectral peak identification and determining the element attribution of the spectral line.It can avoid some interference such as overlapping peaks and sudden peaks.Therefore,the LIBS spectrum on-line detection system based on LabVIEW was designed,and the spectral detection system was verified by plasma spectroscopy of iron-nickel alloy.Finally,the air and aerosol filters were detected by using the LIBS spectral online detection system.N,H,O,and C elements were detected in the air,and metal elements such as Al,Ca,Mg,K,Na,and Ba,and Si elements were also detected in the aerosol filter,and the electrons of the aerosol plasma were obtained by calculation.The temperature was 19871 K,the electron density was 4.74×10¹⁷cm^-3,and the source of the detected elements in the aerosol was analyzed.