AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Aerosol Concentration Calibration and Controlled Delivery for 1 to 8 Micron
VASANTHI SIVAPRAKASAM, Jay D. Eversole, David Silcott, Miles Owen, John E. Tucker, Jesse Linnell, Frank MacDonald, Anthony Woods, Naval Research Laboratory
Abstract Number: 207 Working Group: Instrumentation and Methods
Abstract We describe a calibration method for aerosol instruments that determine particle concentration, such as optical particle counters. Ideally, aerosol samples of a known, fixed concentration would be used to calibrate an instrument that measures concentration. However, until now, traceable aerosol concentration standards, and controlled aerosol generation have not been available.
We have developed and demonstrated a simple device referred to as a constant concentration aerosol generator (CCAG) based on a Collison nebulizer with feedback control from a custom OPC that monitors the total output particle count rate, to adjust the pressure in the nebulizer to achieve homeostasis. Output aerosol concentrations are controlled to a level where the temporal variation in the particle counts is dominated by Poisson statistics. The dynamic output concentration can be controlled over a range of at least a factor of four using this method, while the nominal value can be selected over a wide range based on the polymer bead liquid suspension concentration used. Total flow is controlled, and can be selected over a range from 20 to 60 lpm.
To reference the CCAG output, a pathway for a traceable count concentration standard has also been developed. Essentially monodisperse aerosols of polymer spheres can be generated at a stationary rate and provided simultaneously to an OPC and a reference settling chamber. We will discuss use of a commercially available Wafer Surface Scanner (WSS) to provide a total particle count from the settling chamber, which can be subsequently verified by direct microscopy. Comparison of the total counts on the wafer to the OPC total counts permits a determination of OPC efficiency. Using this method to determine OPC concentration measurement efficiency for particle sizes in the micron range, it is possible to provide a standardized aerosol generator of known, fixed particle concentrations.