Development Of Aerosol Mass Spectrometer Sampling Interface Based On Water-based Growth Tube

Aerosol particles are the main composition of atmospheric pollutants,which affects the global climate,air quality and human health.According to the particle size,aerosol particles can be divided into two categories: coarse particles(Dp > 2.5 ?m)and fine particles(Dp ? 2.5 ?m),and new particles with smaller particle size/ultrafine nanoparticles(Dp ? 100 nm).The concentration of the new particles in the atmosphere is very high,and its proportion accounts for 80% or even higher of the total number of particles.Many artificial and natural processes result in a large amount of ultrafine nanoparticles.This thesis focuses on the sampling interface of ultrafine nanoparticle aerosol mass spectrometer.Based on the principle of heterogeneous condensation and growth of water vapor,a three-stage water-based growth tube for the growth of ultrafine nanoparticles is developed.The nanoparticles grow rapidly from nanometer scale to sub-micron or micron.The aerodynamic lens is designed to efficiently transmit and focus the growing particles into the aerosol mass spectrometer,so as to realize the chemical composition measurement of ultrafine nanoparticles,and the device has applied in laboratory model aerosol particles and flow tube nucleation aerosol systems.The main research work and results of this thesis are as follows:1.Numerical calculation of physical field of water-based growth tube.Through the heat and mass transfer model of qualitative parameters,the temperature and pressure fields inside the water-based growth tube were calculated using numerical software,and then the supersaturation distribution was obtained.In addition,the effects of activation efficiency and system flow on the supersaturation field were also calculated.The results show that the growth tube first reaches supersaturation inside and outside the tube wall radially,the supersaturation in the supersaturation zone reaches the peak on the center line,and the supersaturation in the equilibrium zone reaches the peak near the tube wall;The temperature has a significant effect on supersaturation.The higher the temperature,the higher the supersaturation peak,and the peak corresponding to the axial position is biased toward the entrance of the growth tube;when the temperature difference is large,the particle activation efficiency is higher,and the activated limit particle size is smaller;Increasing the system flow,the change trend of supersaturation remains unchanged,but the position of the peak of supersaturation deviates from the entrance of the growth tube,the peak of supersaturation remains unchanged,and the average supersaturation shows a clear increasing trend.2.Experimental research on the design and growth characteristics of water-based growth tubes.The supersaturated water vapor environment is constructed by using water as a working fluid and the combination of cold air flow-hot wall phase and hot air flow-cold wall,which is used to rapidly increase the particle size of ultrafine nanoparticles.Taking the sodium chloride and pyrene as research objects,the effects of parameters such as the placement position of the water-based growth tube,the temperature,the air flow rate,and the initial particle number concentration on the particle size growth of the nanoparticles were experimentally investigated.The results show that: the vertical placement of the growth tube has a significant increase in particle size growth compared to the horizontal placement;the temperature difference in the growth tube is positively related to the growth performance of the particles;the higher the airflow of the particle,that is,the shorter the residence time,the growth of the particle The smaller the probability,the smaller the average particle size after growth;too high initial particle number concentration has a suppressive effect on the particle size growth.3.Preliminary application of water-based growth tube combined with vacuum ultraviolet photoionization aerosol mass spectrometer.An aerodynamic lens is designed to transport particles that have grown in diameter through the water-based growth tube.Using aerosol atomizer and SMPS,several kinds of nanoparticles were generated and selected;through the ozonation reaction of ?-pinene in the laminar flow tube,polydisperse nanoparticles were generated,and the whole system was investigated for monodisperse nanoparticles and polydispersity The effect of nanoparticles.The results show that the aerosol generator produces monodisperse model particles of water vapor nucleation and condensation growth.Taking oleic acid as an example,the signal intensity of the mass spectrum can be increased by 2.7-8 times.Taking pinene as an example,the signal intensity of mass spectrometry can be increased by 2-3 times..