Leveraging Machine Vision in a Liquid Level Controller for Long-Term Aerosol Capture with a Water Condensation Growth Tube Sampler

BRADEN STUMP, Panupoan Xiong, Dominick Heskett, Greg Brandes, Patricia Keady, Arantzazu Eiguren-Fernandez, Nathan Kreisberg, Aerosol Devices Inc.

     Abstract Number: 419
     Working Group: Instrumentation and Methods

Abstract
Aerosol Devices Inc. has developed multiple water condensation growth tube samplers that collect and concentrate aerosol particles into a small volume liquid vial. These samplers have opened many opportunities for bioaerosol capture due to their gentle, high efficiency collection over a wide size range (<10 to 10,000 nm) and the ability to maintain viability. However, with a low concentration of bioparticles in the environment, or the desire to sample over a fixed period (e.g., an 8-hour shift), long sample times are often desired. With longer sample times, the volume of liquid in the sample vial can vary due to (1) ambient temperature fluctuations causing liquid vial temperature to rise above or below the dew point of the aerosol exiting the growth tube causing water vapor to condense or evaporate from the sample; and (2) varying aerosol concentrations (including non-biological particles) that add water to the sample from the collection of condensed particle-droplets. A solution to this sampling challenge is to control the dew point from the condensation growth tube such that the water in the sample vial is condensing or evaporating to maintain a constant volume of liquid over a long sample period. Measuring the liquid level requires a non-invasive solution that cannot contaminate the sample. The Aerosol Devices Liquid Level Controller was developed in response to this user need. In this presentation we discuss the application requirements, design, and performance of this controller in detail. Liquid level is monitored with machine vision paired with control of the condensation growth tube’s moderator and sampler temperatures to maintain a constant liquid level in a non-invasive fashion. We report the efficacy of the device in controlling the liquid volume in a variety of environmental and aerosol conditions, using both the Biospot-GEM™ bioaerosol sampler and the Spot Sampler™ aerosol collector.