Performance of a Scanning Mobility Particle Sizer at pressures between 500 - 780 mb

The scanning mobility particle sizer (SMPS) is widely used for measuring particle size distribution in the submicrometer range. For aircraft application there is concern that particle sizing may be flawed because the flows in the SMPS may be compromised due to pressure change at different altitudes. For an aircraft application we have tested the performance of a TSI SMPS model 3936L at various pressures using an altitude/temperature chamber. The sheath and aerosol flows were set at 10 l/min and 1 l/min respectively. The flows in the SMPS were found to be stable at the tested pressure range. Monodisperse aerosol was introduced into the chamber at various pressures and sized by the SMPS. The measured particle size at different pressures agreed within a few percent. One of the shortcomings of the present SMPS is the Aerosol Instrument Manager (AIM) software that controls and processes the data is initiated with a fixed mean free path and viscosity. These values depend on ambient pressure and temperature and thus change for aerosol sampling at different pressures and temperatures. The present instrument can be used since the pressure and temperature can be recorded with an additional serial connection to the classifier. However, this requires post processing.