AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Calibration of an Optical Particle Counter for low concentrations of 3 µm particles using a Wafer Surface Scanner
LIN LI, Laura Windmuller, George Mulholland, Miles Owen, David Pui, University of Minnesota
Abstract Number: 251 Working Group: Instrumentation and Methods
Abstract Optical particle counters (OPCs) are widely used to measure aerosol size distribution and number concentration in the size range of approximately 0.1 to 30 micro-meter by means of light scattering from single particles. They are applied to low concentration measurements such as clean room or ambient PM monitoring, and to high concentration industrial aerosols, e.g. industrial filtration. The US Army has a requirement to calibrate an OPC at low concentrations of 3 micro-meter particles with traceability to SI units realized by the National Institute of Standards and Technology (NIST) in support of fielded and future biological agent detectors. Most of the previous studies were focused on the particle sizing accuracy for particles of different size, shape, and refractive index. The OPC number concentration has been measured by comparison with a Condensation Particle Counter (CPC) for particles small than 1 micro-meter, an Aerodynamic Particle Sizer (APS), or a reference OPC. Limited study was conducted concerning OPC calibration at low concentrations.
In this study, we proposed a method for OPC calibration with 3 micro-meter PSL particles at the concentration from 10 to 100 #/L using a Wafer Surface Scanner (WSS) as reference. To have stable NIST traceable calibration for OPCs at low concentration, we nebulized a suspension of NIST traceable 3 micro-meter PSL spheres, evaporated the droplets leaving 3 micro-meter spheres, used a virtual impactor to concentrate the 3 micro-meter particles, and then used a differential mobility analyzer (DMA) to remove residue and select 3 micro-meter particles only. The aerosol stream exiting the DMA was split into two: half was deposited on a wafer and half sent to the OPC. By depositing a controlled number of particles on the wafer surface using a settling chamber, we calibrated the OPC based on the WSS analysis of the deposited particles. The details of this study will be given during the conference.