Instrument Acronym:
CVI
Instrument Measurements:
a) Trace Gas
b) Cloud Physics/Aerosol
Number of cloud droplet residuals and condensed water content.
Can also be used to measure size distribution and chemical
composition of residual nuclei, as well as volatile gases
besides water vapor.
c) Radiation/Optical/Electrical
d) Additional Capabilities
Resource Person/Developer:
Name: Cynthia Twohy
Affiliation: NCAR/ATD, Oregon State University
Phone: (303) 497-1017 or (541) 737-5690
Email: twohy@oce.orst.edu
Principle of Measurement:
Cloud droplets or ice crystals are impacted into dry N2
and then evaporated. Non-volatile residual particles and
volatile gases are measured downstream.
In situ/Remote/Flux Measurement:
In-situ
Field projects in which the instrument has been used:
Multiple since 1985 (on various aircraft in U.S. and Europe).
Noone, K.J., Ogren, J. A., Heintzenberg, J., Charlson, R. J. and D. S. Covert, 1988: Design and calibration of a counterflow virtual impactor for sampling of atmospheric fog and cloud droplets. Aerosol. Sci. Tech., 8, 235-244.
Aircraft Platform:
NCAR Electra and C-130, NASA DC-8. Others possible.
Inlet Configuration/Location:
Inlet must be special counterflow design and temperature
controlled. Newest design has flow-straightening
shroud.
Calibration/Cross Calibration:
Calibration of flow meters, pressure transducers, and hygrometers
(usually Lyman-alpha) before and after each project.
Operator Requirements:
Requires some hands-on operation, depending on complexity
of project and measurements.
Data Collection:
self
Post-flight Data Validation, Processing, Hours per Flight Hour etc.
Complete processing is time consuming, due to varying
Lyman-alpha baseline and other factors.
Physical Characteristics:
Dimensions: 1/2 of full NASA DC-8/NCAR C-130 style rack.
Weight: about 150 lbs. depending on configuration
Power: 110-120 VAC
Other:
Response Time:
About 1 s, with 3-5 s delay in sampling line and instrument.
Detection Limits:
Particle size: > 3-4 microns radius
Number: About 0.04 cm-3
Cond. water cont.: 1 mg/m3
Accuracy:
About 20% for number, 10% for condensed water content.
Precision:
0.002 cm-3, 0.1 mg/m3
Limitations (such as altitude, airspeed, etc.)
Droplets larger than a few hundred microns diameter may shatter
upon collection. Enhancement or shadowing of some particle sizes
can occur, depending on fuselage location.