The performance and improvements of an aerosol mass spectrometer for the real time analysis of bioaerosol particles is described. The instrument can preselect the biological aerosol particles from non-biological particles, by recording the emitted fluorescence when the particles are irradiated with 266 nm laser light. ne fluorescing particles are further investigated by mass spectrometry. With the current performance of the mass spectrometer the produced mass spectra have high resolution and cover a mass range up to 85 kDalton. The capability of the aerosol mass spectrometer to produce good quality spectra of bacteria particles is shown with a mass spectrum of Erwinia herbicola. For the application of the aerosol mass spectrometer the possible interference of (background) soot particles onto the preselection is investigated and a minor interference is determined.