A New Size-fractionated Liquid Collection of Viable Airborne Particles: The BioCascade Impactor

Stavros Amanatidis, Nathan Kreisberg, ARANTZAZU EIGUREN-FERNANDEZ, Aerosol Dynamics Inc.

     Abstract Number: 38
     Working Group: Instrumentation and Methods

Abstract
Viral respiratory diseases spread from person to person by droplets coughed or sneezed into the air. Larger particles settle quickly and land on objects and surfaces around the person, while smaller particles (<5μm) remain suspended for longer periods and travel farther distances, thereby prolonging the risk for acquiring an infection and increasing the likelihood of community transmission. Identifying the transmission modes for respiratory viruses is critical to establish effective control protocols to limit transmission.

We have developed a new system, the BioCascade Impactor, for simultaneous liquid collection of viable airborne microorganisms present in three particle size fractions: >10 μm, PM_4-10, PM_1.5-4. The BioCascade combines multiple stage size-classification and particle collection by gentle impaction into liquid. Aerosol samples are collected at a flowrate of 8 L/min and sequentially passed through impaction stages of decreasing size cutpoints. Particles smaller than 1.5 μm can be further collected by passing the sample into a VIVAS, filter or other collection system, operating at the same flowrate. The BioCascade combines established guidelines for impaction on solid, flat surfaces, while maintaining low-enough flow velocities to avoid unstable air jet-liquid interface. To avoid potential liquid transfer between stages, the collection containers are placed on the same planar level and are connected through aerodynamically gentle inter-stage flow passages. The design was optimized with 3D finite element simulations of flows and particle trajectories using COMSOL Multiphysics.

The performance of the BioCascade was be tested in the laboratory following previously established protocols using polystyrene latex spheres with NIST-certified sizes, fluorescein particles and laboratory generated ammonium nitrate particles, in conjunction with an Aerodynamic Particle Sizer (APS) (TSI Model 3021, Minnesota) and water-based Condensation Particle Counters (WCPC) (ADI, California) for monitoring particle size and concentration. The cut-off size of each impactor was first characterized separately, followed by the evaluation of the complete BioCascade.