1) Instrument Function.
ER-2 CNC counts particles in the approximate diameter range from 0.006 m
to 2 m. The instrument
operates by exposing the articles to saturated Flourinert vapor at 28 C
and then cooling the sample in a condenser at 5 C.
The supersaturation of the vapor increases as it is cooled and the
vapor condenses on the particles causing them to grow to sizes which are
easily detected. The
resulting droplets are passed through a laser beam and the scattered light
is detected. Individual
particles are counted (Wilson et al., 1983) and are referred to as
condensation nuclei (CN). Two
CN Counters are provided in the instrument.
One counts the particles after sampling from the atmosphere and the
second counts particles that have survived heating to 192C.
Lab experiments show that pure sulfuric acid particles smaller than
are volatilized in the heater. The
heated channel detects when small particles are volatile and permits
speculation about the composition. The
CNC II contains an impactor collector which permits the collection of
particles on electron microscope grids for later analysis.
The collector consists of a two stages.
In the first stage the pressure of the sample is reduced by a
factor of two without loosing particles by impaction on walls.
The second stage consists of a thin plate impactor which collect
efficiently even at small Reynolds numbers.
The system collects particles as small as 0.02 m at WB-57F cruise
altitudes. As many as 25
samples can be collected in a flight.
C. A., P. Hamill, J. C. Wilson, H. H. Jonsson, K. R. Chan,"Particle
formation in the upper tropical troposphere: a source of nuclei for the
stratospheric aerosol," Science,
270, 1650-1653, (1995).
Fahey, D. W., E. R. Keim, K. A. Boering, C. A. Brock, J. C. Wilson, H. H. Jonsson, S. Anthony, T. F. Hanisco, P. O. Wennberg, R. C. Miake-Lye, R. J. Salawitch, N. Louisnard, E. L. Woodbridge, R. S. Gao, S. G. Donnelly, R. C. Wamsley, L. A. Del Negro, S. Solomon, B. C. Daube, S. C. Wofsy, C. R. Webster, R. D. May, K. K. Kelly, M. Loewenstein, J. R. Podolske, K. R. Chan, Emission Measurements of the Concorde Supersonic Aircraft in the Lower Stratosphere, Science, 270,70-74(1995).
P. J., Brock, C. A., Wilson J. C., “Aerosol particles in the upper
troposphere and lower stratosphere: Elemental composition and morphology
of individual particles in northern midlatitudes”
Geophysical Research Letters, 21, 2587-2590, 1994.
J.C., Blackshear E.D., Hyun J.H., "The Function and Response of an
Improved Stratospheric Condensation Nucleus Counter," Journal
of Geophysical Research:
Oceans and Atmospheres 88:6781-6785, 1983.
Wilson, J. C., Lai,W. T., Smith, S. D. "Measurements of condensation nuclei above the jet stream: evidence for cross jet transport by waves and new particle formation at high altitudes", Journal of Geophysical Research, 96:17,415-17,423, 1991