HR: 1340h
AN: A33B-1194    [Abstracts]
TI: Water Condensation Growth Cells for Ultrafine Particle Collection Onto Concentrated Spots
AU: * Lewis, G S
EM: greg@aerosol.us
AF: Aerosol Dynamics Inc., 935 Grayson Street, Berkeley, CA 94705, United States
AU: Hering, S V
EM: susanne@aerosol.us
AF: Aerosol Dynamics Inc., 935 Grayson Street, Berkeley, CA 94705, United States
AU: Kreisberg, N
EM: nathan@aerosol.us
AF: Aerosol Dynamics Inc., 935 Grayson Street, Berkeley, CA 94705, United States
AB: A laminar flow, condensation method, analogous to that employed in the water-based condensation particle counters, is utilized to provide concentrated, low-pressure drop collection of fine and ultrafine particles. With the laminar flow water condensation approach, the aerosol flow is first chilled by a cold walled conditioner, and then introduced into a hot wet-walled condenser. Because water vapor diffuses more rapidly then heat, the air vapor is supersaturated resulting in particles large enough to be collected by impaction. Several types of collectors have been designed and tested. A compact system utilizing a single TED as a heat pump to provide a ~ 25 ° C temperature difference provides collection at 0.4 L/min with a lower cutpoint of 10 nm, a pressure drop of 1 kPa, and a power consumption of 1 Watt. A larger, parallel plate system samples at 10 L/min, and yields a cutpoint of 20 nm. The design of these systems was guided by numeric modeling of the saturation ratios, particle activation and growth. The model includes the heat release from condensation, and the associated warming of the flow that reduces the supersaturation and particle growth at high particle number concentrations. By controlling the system geometry (either plate separation or tube diameter), we are able to activate at small particle sizes while minimizing concentration effects. Our method of particle collection provides a number of other advantages. Particle bounce off the impaction surface can be eliminated by controlling the temperature of the impaction surface so as to maintain a thin film of water on the surface. Particles can also be collected into a small liquid vial containing less then 1 ml of fluid, which eliminates the need for particle extraction from filters or resuspension from surface, it minimizes the total volume of the sample, and it allows for continuous automated collection and analysis.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting