Determination of Differential Mobility Analyzer Transfer Functions Using Identical Instruments in Series

The differential mobility analyzer (DMA) is an important tool for determining particle size distributions. The physical performance of a DMA is quantified by the concept of the transfer function. Therefore, knowledge of the transfer function is important to interpret the mobility distributions recorded by a DMA. During a calibration workshop in preparation for the Aerosol Characterization Experiment 1 (ACEt) field campaign, the transfer functions of five types of different mobility analyzers (Vienna-type DMA short, medium, and long, CIT radial, and TSI long; CIT = California Institute of Technology, Pasadena, CA; TST = TSI Inc., St. Paul, MN) were experimentally characterized by height, width, and area of their transfer functions. Different particles size ranges between 3 and 200 nm were investigated. The transfer function was determined by scanning a DMA across the mobility distribution produced by another, identical DMA. Subsequently, the data were processed by a deconvolution algorithm assuming a triangular shape for the transfer function. For all DMA types, the area of the transfer function decreased with particle size, especially for ultrafine particles (dp < 20 nm). The gradient with which this area decreases with particle size, however, is different for each of the DMA types investigated. The calibration provides an improved description of the performance of each DMA, particularly in the ultrafine size range.