Development Of Small Atmosphere Ultrafine Particle Size Spectrometer

Since the reform and opening up,with the rapid development of the national economy,energy consumption has been rising,resulting in a large number of emissions into the atmosphere,resulting in serious air pollution.Atmospheric particulate matter,especially small-sized particulate matter,has become an important source of air pollution.Medical research has found that the smaller the particle size,the deeper it can penetrate into the human body,the greater the probability of deposition in the alveoli,and the greater the probability of respiratory diseases and heart diseases.Therefore,it is more important to strengthen the particle size detection in aerosols in modern society.At present,the main international measurement methods of particle size spectrum include optical method,aerodynamic method and electromigration method.For optical and aerodynamic measurements,only a few hundred nanometer particle size can be measured,but for tens or even a few nanometers particle size can not be measured.It is these small particle size that cause serious harm to human body.Therefore,this paper proposes a measurement method of ultra-fine particle size spectrometer based on micro-current detection of electromigration.The following aspects are carried out:(1)Determining the design scheme of miniaturized particle size spectrometer.For the measurement of particle size spectrum of ultrafine particles,it needs three parts: particle charge,particle grading and particle concentration measurement.In this paper,unipolar charger,flat-panel DMA and Faraday cup electrometer are used to realize the measurement.Firstly,the unipolar diffusion charger is used to charge particles instead of the existing radioactive neutralizer,because the common radioactive neutralizer contains radiation source,which requires qualifications to hold and has large volume and is not easy to be integrated in miniaturization.Flat-panel DMA is used instead of traditional cylindrical DMA,because cylindrical DMA requires high processing and assembly accuracy and costs a lot.Lady cup electrometer replaces the condensed particle counter to ensure that there are no optical devices inside the particle size spectrometer,reduce the difficulty of maintenance and broaden the use environment.(2)Design and calibration of plate differential electromigration classifier.Based on the theory of electromigration of charged particles,a theoretical model of flat-panel DMA is established and its working principle and process are described in detail.A flat-panel DMA is designed and fabricated.According to the existing instruments in the laboratory,an experimental scheme of deflection voltage of ultrafine particulate matter is designed.The performance of the flat-panel DMA is analyzed and compared with the deflection voltage calculated theoretically.(3)Design and calibration of small Faraday cup.According to the detection principle of Faraday Cup,a miniaturized Faraday Cup measurement module is designed,and the mechanical structure design of Faraday Cup is introduced in detail.By optimizing the structure design of Faraday cup,the interference of external noise and vibration on weak electric signal is reduced.According to the existing instruments in the laboratory,a series of tests are designed to calibrate the performance of Faraday cup.(4)According to the design scheme of particle size spectrometer,the key modules are integrated.The hardware circuit and control system of ultra-fine particle size spectrometer are developed based on STM32 single chip computer.The main parameters of the system are controlled and monitored,including real-time control of aerosol sampling gas and sheath gas flow velocity in the airway,the hierarchical voltage of DMA and the feedback voltage of micro-current amplifier.Through internal inversion,the concentration of particulate matter is calculated by measuring voltage,and the particle size spectrum of the measured particulate matter in the sample gas is displayed in real time on the screen of the prototype.After completing the prototype integration of the ultrafine particle size spectrometer,the field observation experiments were carried out.