Beyond size classification: The dynamic-aerosol-size electrical mobility spectrometer

Abstract

This paper overviews an alternative operation mode of the Electrical Mobility Spectrometer (EMS), herein termed as the “Dynamic-aerosol-size Electrical Mobility Spectrometer (DEMS)” where the size of aerosol particles evolves during mobility classification in response to any chemical/physical processes taking place within the device's classification region. Unlike the conventional EMS designed to classify the aerosol particle size, the function of the DEMS is to probe the kinetics (in terms of corresponding growth/shrinkage rates) of aerosol related chemical/physical processes. This is achievable because the particle trajectory in the device's classification region contains full information about the particle size change history. A theoretical framework is developed for analyzing the transmission of size-changing particles in the device's classification region. Expressions for the particle mobility at the device outlet and size change rate are derived based on known initial mobility and DEMS response, using the evaporation of monodisperse and single-component aerosols as an example. The theoretical framework is applicable to the entire Knudsen number range and is compared against simulations and experiments, demonstrating excellent validity in the test conditions.