Radial Differential Mobility Analyzer

A differential mobility analyzer in which particles are classified in a radial flow toward the center of parallel disk electrodes, termed the Radial Differential Mobility Analyzer (RDMA), has been developed. Its classifying characteristics have been determined experimentally using both standard polystyrene latex spheres and mobility-classified aerosol particles over the size range of 3-200 nm. The idealized transfer function for the RDMA differs from that of the conventional cylindrical DMA only by a group of geometrical constants. The RDMA is designed specifically for the measurement of ultrafine aerosol particles, achieving a transmission efficiency of 0.85 to 0.90 in the 3-10-nm size range and having a short residence time to limit diffusional broadening of the transfer function. The simple design of the RDMA reduces the number of precision parts that must be fabricated below that for cylindrical DMAs, resulting in a compact, relatively lightweight, and low-cost instrument.