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Collett Research Group

Atmospheric Chemistry / Air Quality Program
Department of Atmospheric Science
Colorado State University
Fort Collins, Colorado USA

Cloud / Fog Sampling Instrumentation

The CASCC2 bulk fog/cloud sampler

The Caltech Active Strand Cloud Collector Version 2 (CASCC2) is a small, active collector designed for collection of bulk fog and cloud samples (i.e., all drop sizes are collected in one bulk sample). Drops are collected by inertial impaction on Teflon strands of diameter 508 µm. The 50% lower size cut for the CASCC2 is approximately 3.5 µm drop diameter. The flow rate through the CASCC2 is approximately 5.8 m3/min. The CASCC2 is described in more detail in Demoz et al. (1996). The CASCC2 is shown installed here in Fresno, California (left) and on the 430 meter Candelabra Tower near Walnut Grove, California (right) during the 1995 Integrated Monitoring Study (IMS95).

The Caltech Heated Rod Cloud Collector (CHRCC)

The Caltech Heated Rod Cloud Collector (CHRCC) is designed for collection of bulk fog/cloud samples from supercooled clouds or fogs. It is similar in design to the CASCC2 except that stainless steel rods replace the Teflon strands of the CASCC2 as impaction surfaces. The rods can be internally heated at the end of each sample interval (typically 30-60 minutes) to remove accumulated rime. The 50% size cut for the CHRCC is approximately 9 µm drop diameter. The CHRCC is depicted here (left) on Mt. Rigi, Switzerland (Collett et al., 1993). An automated version of the CHRCC (above right) was used extensively in Sequoia and Yosemite National Parks (Collett et al., 1990). The automated version incorporates pneumatically actuated covers and an infra-red backscatter fog/cloud detector..

The Size-Fractionating Active Strand Cloud Collector (sf-CASCC)

The size-fractionating CASCC collects cloud/fog drops in two size ranges via inertial impaction on two banks of Teflon rods/strands arranged in series. The division between small and large drops occurs at a drop size of approximately 20 microns. The flow rate through this sampler is approximately 19 m3/min. Demoz et al. (1996) describe the collector in detail.

The Colorado State University 5-Stage Cloud Collector

The Colorado State University 5-stage cloud collector was developed with support from the National Science Foundation to permit simultaneous collection of 5 independent drop size fractions suitable for chemical analysis. The collector features 5 jet impaction stages arranged in series. The entire collector is constructed of plastic to prevent contamination of collected samples by metal parts. The inlet of the collector is at the left in the photograph. Air is drawn through the collector at 2000 lpm, providing 50% size cuts for the 5 stages that range from approximately 4 to 35 microns drop diameter. Numerical modeling and experimental calibration of the collector are described by Straub and Collett (1999).

The FROSTY Supercooled Cloud Collector

The FROSTY Supercooled Cloud Collector was developed at CSU with joint support from USEPA and NSF. It features 3 jet impaction stages designed to simultaneously collect 3 independent drop size fractions for chemical analysis. Like the CSU 5-stage collector, it is constructed entirely of plastic. FROSTY, whose name derives from the similarity between its cross-section and a famous snowman, has been used to collect supercooled winter clouds at Storm Peak Laboratory in the Rocky Mountains of northern Colorado (Xu et al., 1999). A blower draws drop laden air through the sampler at 1500 lpm. A 2-D section of the collector (see sketch) was modeled using the commercial computational fluid dynamics code FLUENT. The numerically predicted performance matched well with results from a laboratory calibration study (Straub and Collett, 1999). 50% size cuts for operation at design conditions (3000 m elevation, -4 degrees C) were determined to be approximately 17. 10.5, and 4.5 µm.

The CSU-NCAR Airborne Cloudwater Collector

The CSU-NCAR Airborne Cloudwater Collector was developed jointly by Colorado State University and NCAR. Development, testing, and application of this instrument formed the basis for the PhD dissertation of Derek J. Straub. Partial support for this effort was provided by the National Science Foundation through grant ATM-0084696. The collector features an axial flow cyclone design, is capable of collectinng multiple cloudwater samples per research flight, and is designed for deployment in a PMS canister on the NCAR C-130 aircraft. The collector could readily be deployed on other aircraft with similar flight speeds and suitable mounting locations. The collector flew in the 2001 DYCOMS-II field campaign, to investigate the chemical composition of marine stratiform clouds in the NE Pacific (SW of San Diego), and in the 2008 VOCALS Regional Experiment off the coast of Chile to explore cloud composition in the SE Pacific.

The Caltech Passive Cloud Sampler

This passive sampler was used to study cloud interception in Sequoia and Yosemite
National Parks (Collett et al., 1991). Inertial impaction of cloud drops relies on ambient winds.

Instruments for measuring cloud microphysical properties

The Model 100 Particulate Volume Monitor (PVM, above left), manufactured by Gerber Scientific, is used to measure cloud liquid water content and particle surface area. It is shown here deployed in a recent study at Whiteface Mountain, New York. The Particle Measurement Systems CSASP-100-HV (above right) is an optical probe used to measure cloud/fog drop size distributions. It is shown here deployed in a fog study in California's San Joaquin Valley. We have recently replaced the CSASP with a Fog Monitor (FM-100) manufactured by Droplet Measurement Technologies.

Last updated
Dec. 31, 2012