Calibration of the QCM Impactor for Stratospheric Sampling

Abstract

The performance of the QCM impactor (Model 3000, California Measurements, Sierra Madre, CA) has been evaluated at inlet pressures of 59 and 88 Torr, corresponding to the conditions of stratospheric sampling aboard the U-2 aircraft. Impactor mass flow rates and stage operating pressures were measured as a function of inlet pressure. The collection efficiencies of monodisperse liquid oleic acid aerosols were measured for individual impactor stages by counting particle penetration with an optical particle counter. Modification of the optical counter for this low pressure application is described. Response of the assembled QCM to near-mono-disperse Apiezon grease aerosols was measured using the signal from the quartz crystal impaction substrates. Aerodynamic cutoff diameters as a function of inlet pressure agree with impaction theory for most stages. Good comparison is found between the response of the QCM microbalance impaction plates and the optical particle counter data. For solid particles the QCM collection is poor due to rebound of the particles off the uncoated surface.