American Association for Aerosol Research - Abstract Submission

AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA

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Validation of the CPMA-Electrometer Suspended Mass Standard against Gravimetric Measurements

JONATHAN SYMONDS, Kingsley Reavell, Jason S. Olfert, Cambustion

     Abstract Number: 33
     Working Group: Instrumentation and Methods

Abstract
The Centrifugal Particle Mass Analyser (CPMA, Olfert and Collings 2005) classifies particles by their mass to charge ratio, using opposing centrifugal and electric forces.

For singly-charged particles passing through the CPMA of mass m, there may also be doubly-charged particles of mass 2m, etc. It then follows, by counting the number of charges post-CPMA, we count the number of quanta of mass m. Thus by placing an aerosol electrometer downstream of the CPMA, the mass concentration post-CPMA is given by multiplying the measured charge concentration by the single-charge mass of the CPMA (Symonds et al., 2011). This stream of particles of known mass concentration can be split to provide a calibration source for real-time instruments which infer a mass concentration measurement by less traceable means. A correction may be required for any uncharged particles which pass through the CPMA, but this can be made negligible by the use of a unipolar charger to place a high level of charge on the particles.

A silicon oil with low vapour pressure was nebulised, highly charged with a Unipolar Diffusion Aerosol Charger (UDAC, Cambustion), and passed through a CPMA. The flow was then split, one half passing to an aerosol electrometer, the other half collecting on a filter paper, which was weighed before and after loading. Mass flow meters were used downstream of the filter paper and electrometer. By varying the single-charge mass setting of the CPMA, the mass concentration post-CPMA was varied and plotted versus filter mass concentration. In this experiment, the two methods agreed to within 6%.

Olfert J.S. & Collings, N., New method for particle mass classification—the Couette centrifugal particle mass analyser. J. Aerosol Science v36 1338–1352 (2005)
Symonds, J.P.R. et al., Behaviour of non- and multiply- charged aerosols in the centrifugal particle mass analyzer, AAAR Conference (2011)