AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Design and Evaluation of a Low Flow Personal Cascade Impactor
MODI CHEN, Francisco Romay, Virgil Marple, MSP Corporation
Abstract Number: 427 Working Group: Instrumentation and Methods
Abstract A very compact cascade impactor with a low sampling flow rate has been developed. Its dimensions are 8.5 cm L x 5.0 cm W x 11.4 cm H, and weighs 0.27 kg. It has ten impaction stages that cover the size range of 60 nm to 9.6 μm at a 2 L/min inlet sampling flow rate. The top eight stages, measuring particle aerodynamic diameter down to 170 nm, can be used as a stand-alone impactor with a portable, battery-powered pump, while the ten stage impactor requires a larger vacuum pump to operate. Particle collection efficiencies for each stage were obtained experimentally with two types of commonly used substrates, aluminum foil and glass fiber filters. Impactor cutpoints for aluminum foil substrates agree well with conventional impactor theory. The efficiency curves are sharp with minimum overlap between them. Thus, the compact design does not compromise its performance when compared with the larger cascade impactors such as the MOUDI, making it suitable for general purpose applications where a lower sampling flow rate provides adequate mass collection. With glass fiber filter substrates, impactor cutpoints are smaller and the efficiency curves are less steep, especially for the last stages. Also, the collection efficiency curves do not drop to near zero at small Stokes numbers. Instead, excess particle collection efficiency of around 10% is observed for the top six stages, and becomes even higher for the last four stages. This is due to the collection of particles by filtration as the impinging jets penetrate the filter substrate. Thus, when using glass fiber filter substrates, only the upper 8 stages of the impactor should be used.