Single particle mass spectrometers have traditionally been deployed to measure the size and composition of individual particles. The relatively slow sampling rates of these instruments are determined by the rate at which the ionization lasers can fire and/or mass spectra can be recorded. Under most conditions, our single particle mass spectrometer, SPLAT, can detect and size particles at much higher rates than it can record mass spectra. We therefore developed a dual data acquisition mode, in which particle number concentrations, size distributions, and asphericity are measured at a rate determined by particle concentration and the particle detection efficiency, all while the instrument generates and records individual particle sizes and mass spectra at an operator-set rate. Particle number concentrations are calculated from the particle detection rate at the first optical stage and the measured sampling flow rate. We show that SPLAT measured particle number concentrations are in very good agreement with ...