AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Multiple Charging Correction for SMPS Algorithm
Meilu He, SURESH DHANIYALA, Clarkson University
Abstract Number: 559 Working Group: Instrumentation and Methods
Abstract Critical to accurate calculation of aerosol size distributions from scanning mobility particle spectrometer (SMPS) measurements is the knowledge of particle charge characteristics. If the investigating particles are mostly smaller than 50nm, i.e., nanoparticles, the SMPS data can be accurately inverted considering just the singly-charged fraction. However, when a significant fraction of particles are larger than 100 nm, the role of multiple-charged particles in data inversion cannot be ignored. The SMPS is typically operated with an impactor at the inlet to eliminate the contribution of multiply-charged large sized particles to the mobility distribution. Coupled with an impactor, if the SMPS can be scanned to particle sizes larger than the impactor cutoff size, accurate particle size distributions can be calculated with a multiple-charge corrected inversion algorithm. Sometimes, an impactor cannot be used or the SMPS cannot be scanned to sizes beyond the impactor cut-size, e.g., for particles with low density and hence small aerodynamic diameters or under high altitude operation when the DMA upper voltage limit is reduced. Under such situations, the current multiple-charge correction inversion algorithm may produce incorrect size distribution, often with an artificial large particle mode. To overcome this problem, a new multiple-charge correction data inversion algorithm will be presented. Modeling results show that the new algorithm can produce accurate size distribution from SMPS data even under conditions of partial scanning and without an impactor in place.