Aerosol mass spectrometer with particle size selection

The invention applies for an aerosol mass spectrometer with particle size selection, wherein the aerosol mass spectrometer can simultaneously select the particle size, the concentration and the chemical component of the atmospheric aerosol. The aerosol mass spectrometer uses a sampling hole with the diameter of 100 micrometers to carry out direct sampling on an aerosol in a natural environment; aerosol particles are focused into a particle beam flow with the 0.5-milimeter diameter by a pneumatic focusing lens; the aerosol particles are selected by a particle size selector that is formed by three coaxial rotating plates with slits, wherein the rotating plates of the particle size selector are driven by a synchronous motor and the frequency of the synchronous motor power supply can be adjusted continuously; an aerosol particle that is selected by the particle size selector is gasified by a gasifier with the high temperature from 600 to 700 degrees; gas after gasification is ionized by an electron collision ionizer; a generated ion is detected by a W type reflection type mass spectrum apparatus so as to obtain the mass spectrum of the aerosol. Therefore, information including the particle size, the concentration and the chemical composition of the organic aerosol can be obtained by analyzing the sampling rate, the frequency of the synchronous motor power supply and the obtained mass spectrum.