Design and theory of a new compact ultrafine particle sizing instrument. called the miniature electrical-mobility aerosol spectrometer (MEAS), was recently introduced [Ranjan, M.. & Dhaniyala. S. (2007). A new miniature electrical spectrometer Theory and design. Journal of Aerosol Science, 39, 950-963]. In the MEAS, electrostatic precipitation technique is used for both generation of sheath flow and classification of particles based on their electrical mobility. An electrometer-array, connected to the collection electrodes in the classifier section. is used to measure the [lumber of particles collected in the different mobility channels, and these data are inverted using MEAS transfer functions to obtain particle number size distributions. Design of a prototype MEAS and the experimental approach to validate the performance of the individual components of the instrument are presented. Particle size distributions obtained from MEAS measurements compare well with those obtained using a scanning mobility particle sizer (SMPS; TS13936), validating theoretical calculations of instrument transfer functions. The operational limits of MEAS are determined from the calculation of error in the inverted size distribution as a function of total particle concentration. This analysis suggests that the designed MEAS can be used for applications such as personal and ambient monitoring under conditions of moderate to high particle concentrations. (C) 2008 Elsevier Ltd. All rights reserved.