10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Refinements of a Water-Based Condensation Particle Counter for Detection near 1 nm
Gregory Lewis, Steven Spielman, SUSANNE HERING, Aerosol Dynamics Inc.
Abstract Number: 1583 Working Group: Instrumentation
Abstract Reported are refinements and further characterization of a water-based, condensation particle counter for particle detection near 1nm. This instrument operates at an aerosol flow of 0.3L/min, without use of a sheath. It employs a three-stage, laminar-flow growth tube with a cooled conditioner, followed by a short, warm initiator, and longer, cooled moderator. Operating temperatures are in the range of 1°-10°C, 80-95°C, and 10-20°C for the three stages, respectively. Walls are wetted throughout. Within the initiator stage, the transport of water vapor from the warm, wet walls is faster than the transport of heat, thus creating supersaturated conditions. The larger the temperature difference between the conditioner and initiator stages, the higher the supersaturation, and the smaller this particle size that is activated. The final moderator section reduces both water vapor content and temperature while maintaining supersaturated conditions.
As compared with the original prototype instrument, the new instrument has been designed to minimize the heat leak between stages, and to provide for much more rapid changes in operating temperatures. Operating temperatures of 1°C and 95°C are now attained within 3 minutes of start-up. Improvements in the temperature control of the final moderator stage eliminates the need for a water trap on the sample exit flow, as the flow is non-condensing at 20°C. As with the original prototype instrument, operation at an initiator-conditioner temperature difference of less than 84°C makes the instrument blind to ions from a bipolar ion. Calibration data show fifty percent efficiency cut-point varying from 1.5 nm to 2.0 nm depending on operating temperatures and aerosol type. The new system is self-contained with on-board pumps and water injection, and yet fits within the box of a standard water condensation particle counter. Unattended operation of two collocated units over a 4-day period yields a correlation coefficient R=0.99, and a regression slope of 1.02.