Transmission Efficiency of Two Pumped Counterflow Virtual Impactors of the Same Kind for Cloud-aerosol Interactions Studies

SHREYA JOSHI, Lynn Mazzoleni, Will Cantrell, Raymond Shaw, Simeon Schum, Thusitha Divisekara, Ian Helman, Gourihar Kulkarni, Timothy Onasch, Kyle Gorkowski, Arthur J. Sedlacek, Ogochukwu Enekwizu, Claudio Mazzoleni, Michigan Technological University

     Abstract Number: 317
     Working Group: Instrumentation and Methods

Abstract
The Pumped Counterflow Virtual Impactor (PCVI) is a cost-effective and compact tool that separates large from small aerosol particles based on their momentum. Therefore, PCVIs are often used for separating droplets and non-activated aerosol particles in clouds and fog. Several previous studies utilized PCVIs to understand the interactions of aerosols with a cloud’s droplets or ice crystals. However, most studies do not report the particles’ transmission efficiencies (TE), and for those that do, the range of values is very wide going from 45% up to 95%. We report on the TE of two PCVIs of the same kind, performing comparative analysis under controlled laboratory conditions with a range of particle types and sizes including several dry aerosols, as well as cloud droplets. We found that both units performed very well for rejecting particles below the selected particle size cut (e.g. interstitial aerosol in cloud studies); however, we also found significant differences in TEs for larger particles, with variations especially pronounced under higher add flow conditions and during water droplet transmission experiments. We hypothesize that minor manufacturing differences in the PCVI units or differences in wear and tear might have substantially impacted their performances. These results underline the usefulness of PCVIs, but also emphasize the need for careful unit-specific characterization and calibration before use in field and laboratory settings to enhance the reliability of quantitative aerosol measurements and advance our understanding of aerosol-cloud interactions.