Development And Application Of Wide Range Single Particle Mass Spectrometry Sampling System

Single Particle Mass Spectromtry（SPMS）is an online aerosol analysis instrument with high spatial and temporal resolution,which can analyze the aerodynamic particle size and chemical components of individual particles within millisecond level.However,limited by the existing sampling technology,the particle sizing range of most SPMS is around 0.1～3μm,which makes the detection capability of SPMS for coarse particles such as mineral dust,sea salt,fungi and spores significantly insufficient.In addition,the conventional SPMS sampling flow rate is only～100 m L/min,which limits the application of SPMS in ultra-low concentration environments such as the North and South Poles and air background stations.How to achieve simultaneous high-throughput detection of fine and coarse particulate matter is one of the technical bottlenecks facing SPMS at present.In this paper,by analyzing the performance of the international mainstream SPMS sampling systems for different particle sizes and combining with the numerical simulation technology of computational fluid dynamics,we conducted a gas-phase and particle-phase two-phase flow field evaluation and optimization of the Single Particle Aerosol Mass Spectrometry（SPAMS）sampling system developed by our team.Numerical simulations were performed to evaluate and optimize the system.The results of numerical simulation show that the reasons for the loss of large particles can be summarized as follows:1)the peripheral particles near the tube wall upstream of the critical orifice,especially those larger than 2μm in size,are easily accelerated by the contraction of the airflow and deposited on the surface of the orifice plate by inertial collision;2)the particles above 0.4μm are easily dispersed by the acceleration of the supersonic airflow after the critical orifice and inertially hit the relaxation chamber.（3）The small aperture of the first and second lens,as well as the large or small upstream air pressure,will cause an unreasonable distribution of the overall lens particle Stokes number,making the transmission efficiency and focusing effect of fine or coarse particulate matter lower.In order to improve the detection time resolution of SPMS in ultra-low concentration environment,this thesis combines the working principle of virtual impactor and the acceleration of critical orifice airflow,and designs a virtual impact concentration device upstream of the lens,and increases the critical orifice aperture from 0.11 mm to 0.22 mm.The experimental results show that the concentration device can increase the inlet sample The experimental results show that the concentration device can increase the sample flow rate to～340 m L/min,and also reduce the deposition loss of coarse particles to a certain extent,and the concentration times of particles larger than 0.8μm can be 8-9 times.To address the challenge of efficient sampling and detection of SPMS in a wide particle size range,this thesis presents a comprehensive improvement of the sampling structure of the critical orifice,relaxation chamber,and aerodynamic lens,and proposes for the first time a pre-focused sampling interface that can effectively reduce the collisional deposition loss of coarse particulate matter at the critical orifice plate,and the theoretical calculation shows that the particle transfer efficiency is 100%in the range of 0.2～15μm.Secondly,the critical orifice diameter of the virtual impact concentration device was further increased to 0.25 mm,and the flow rate was increased to～480 ml/min.Meanwhile,the fluid structure of the downstream separation cone and buffer chamber was optimized.According to the particle Stokes number as a function of particle size distribution curve of the lens,a 7-Stage aerodynamic lens was designed.The working pressure was 210 Pa,and the diameter of the lens cylinder was 40 mm,The lens spacing is 40 mm,and the aperture is 19mm,11 mm,8.5 mm,6.5 mm,5 mm and 4 mm respectively.The numerical characterization of the improved overall inlet flow field was carried out based on FLUENT software,and the numerical results showed that the particle transfer efficiency could reach 100%in the particle size range of 0.15～10μm.A wide range aerosol sampling system was installed on the existing SPAMS and its sampling performance was characterized using monodisperse standard microspheres of known particle size.Preliminary experimental results show that the particle transfer efficiency is around 100%in the range of 0.2～10μm,which is in good agreement with the theoretical value,but the particle transfer efficiency below0.2μm is reduced compared to the theoretical efficiency due to the limitation of the optical sizing system,and the overall highest performance of the existing single particle mass spectrometry aerodynamic sampling In addition,20 common microbial samples were selected in this thesis to carry out the exploration of bioaerosol applications.The experimental results show that the overall particle size of bacteria is small,with a linear mean particle size of about 0.8μm,while the linear mean particle size of fungi is about 1.8μm,especially for Pseudomonas tropicalis and Aspergillus brasiliensis,with a large proportion of particle size distribution in the range of 0.1～10μm.In addition,the ability to distinguish bioaerosols from biomass combustion products,etc.was explored based on the ion peak area ratios of PO₃^-/PO₂^-to CNO^-/CN^-in the mass spectra,and the results showed that there were significant differences in the ion peak area ratio distributions of PO₃^-/PO₂^-to CNO^-/CN^-between bioaerosols and biomass combustion products and automobile exhaust,which can be attempted as SPAMS to distinguish The ion peak area distribution of PO₃^-/PO₂^-and CNO^-/CN^-is significantly different from that of biomass combustion products and automobile exhaust.Subsequently,the sample types can be further enriched,and other ion peak area ratio relationships,such as organic nitrogen and phosphate or amino acid decarboxylate ions,can be clustered to improve the discrimination ability of SPAMS for biological aerosols.