Description of the cloud condensation nuclei counter

General Operation

The CCN instrument consists of a vertical column with wetted walls which provides the water vapor necessary to produce super-saturations. Particles activate into droplets when exposed to the super-saturated conditions. An optical particle counter measures the resulting droplet size distribution. The CCN at several supersaturations is measured using a DMT CCN counter (Roberts and Nenes, 2005). The percent supersaturation (%SS) of the instrument is stepped in 7 intervals every 30 minutes with 5 minutes at each setting in a pyramid form. We use a heat transfer and fluid dynamics model flow model to calculate the %SS (Lance et al., 2006). The model uses the calibrated temperature, pressure and flows in the instrument to calculate the %SS.

Our CCN instrument comes from Droplet Measurement Technologies (DMT) in Boulder, CO.