NASA - National Aeronautics and Space Administration

The GV Scanning Mobility Particle Sizer (SMPS) measures the particle size distribution over the mobility diameter range of 3 to 500 nm (pressure-dependent). It consists of two components: an electrostatic classifier (EC) and a condensation particle counter (CPC). The EC samples aerosol-laden ambient air, places a well-defined charge distribution on the particles, and then selects a narrow range of particle “mobility diameter” (approx. equal to cross-sectional area-to-charge ratio) using a differential mobility analyzer (DMA). The selected diameter can be scanned by a time-varying high voltage applied to the DMA; following this particles are counted by the CPC. The total scan time and the number of counting intervals, the latter of which determines the number of diameter bins in the size distribution, are selected based on ambient particle concentrations and altitude. The raw data (particle counts over each counting interval as a function elapsed time during the linear diameter scan) is mathematically inverted during post-processing to obtain the particle size distribution.