The Theoretical Model And Application For Aerosol Mass Concentration By The Single Particle Scattering Method

The single particle scattering method is widely employed due to fast,high precision, nonintrusive and suitable for on-line measurement.In this paper,the theory for aerosol mass concentration by using the single particle scattering method is investigated combining with experiments.The innovation achievements are listed as following:The concepts of the average mass of particles in a voltage channel,the equivalent number of spherical particles and the optical equivalent diameter of a particle are presented, respectively,which reveal inherent law between the pulse height distribution of particles and mass.The theoretical model for inversion aerosol mass concentration is then established,which provides theoretical basis for inversion aerosol mass concentration using the pulse height distribution of particles measured by an optical particle counter.Combining the theoretical model for aerosol mass concentration by using the single particle scattering method and the relationship between the pulse height distribution of particles and particle shape,the conception of fractal dimension of scattering equivalent section is put forward by taking the fractal characteristic of particles into account,then the relationship between the average mass of particles in a voltage channel and the signal amplitude of corresponding voltage channel is given.It is found that inversion algorithm of aerosol mass concentration using the single particle scattering method has two characteristic parameters needed to be calibrated,that is,the sensitivity coefficient k and the fractal dimension of scattering equivalent sectionα.The calibration method of the two characteristic parameters in the inversion algorithm for aerosol mass concentration is further researched theoretically and experimentally.The relationship of inversion precision of aerosol mass concentration and fractal dimension of scattering equivalent sectionα_l of a small sample aerosol is analyzed,and it is found that fractal dimension of scattering equivalent sectionαof aerosol cannot be replaced byα_l obtained by the minimum method.Through analyzing the inherent relation betweenαandα_l,the conclusion that the intersection point ofα_l for different small samples is equal toαof aerosol is obtained,thus,the calibration problem of characteristic parameters are solved.The experimental results demonstrate that mass concentrations measured by an optical particle counter agree well with actual mass concentrations in the range from 0.001 to 5 mg/m~3. In order to evaluate the optimization problem of voltage channels of an optical particle counter,the information theory is applied to analyze the reason for the difference of the stable velocities of inversion accuracy of mass concentration obtained using linear and non-linear division methods,respectively.The result indicates that in the case of same number of voltage channels,the information entropy of non-linear division method is obviously larger,leading to the number of voltage channels is fewer when the inversion accuracy of mass concentration is stable.This conclusion indicates that information entropy of the pulse height distribution of particles directly determines the stable velocity of inversion accuracy of mass concentration.In this paper,an overall theory for aerosol mass concentration by using the single particle scattering method is established,whose validity is justified by experiments,and the research of this paper provides a valuable reference for the further development of the single particle scattering method.The method in this paper can be applied to measure aerosol mass concentration in real time.