Abstract Number: 282 Working Group: Instrumentation and Methods
Abstract Visualization of airborne particles is a direct method to analyze the dynamic behavior of aerosol particles and it may be used to obtain the size distribution of particles, the electric charge distribution, etc. When the concentration of aerosol is high, many particles are present in a measurement volume so that we may observe the dynamic behavior. However, when the aerosol concentration is low, the probability of particle existence in the measurement volume is extremely low. In order to capture particles in a measurement volume when sampling aerosol from the ambient air of extremely low particle concentration, we developed a new particle trap system which was activated by the signals from an optical particle counter (OPC). The system consisted of an OPC, a transfer tube (inner diameter: 4.4 mm, length: 0.75 m), solenoid valves, and a visualization cell. When particles were detected by OPC, the solenoid valves at the inlet and outlet of the visualization cell were automatically closed after a certain delay time to trap aerosol particles.
The trap efficiency of system (E) is given by the product of detection efficiency of OPC (E1), the penetration through the transfer tube (E2) and the detection efficiency of visualization cell (E3). These efficiencies were individually measured using monodisperse PSL particles with diameters from 0.5 to 2.0 micro-meter. We found that E1 was nearly 100% and E2 higher than 97% for all particle sizes measured. The maximum visualization efficiency (E3) was about 40% for 2.0 micro-meter PSL particles at the delay time for closing valves of 0.6 s.
The present visualization device is a powerful tool to trap particles which are “suddenly” generated from equipment in a clean room, and we may apply various analyzing techniques to the trapped particles for determining the size, the electric charge, and even the chemical composition.