Concept for a New Cloud Condensation Nucleus (CCN) Spectrometer

The design of a new cloud condensation nucleus (CCN) spectrometer based on modifications to the original design of Fukuta and Saxena (1979a) is presented. The key modifications include introducing a trapezoidal geometry and orienting the chamber vertically. A series of simulations demonstrate the broadening of the effective range of the instrument to include supersaturations lower than those reported for the original instrument, without reducing the maximum resolvable supersaturation. A design criterion is developed to eliminate configurations that would result in secondary flows in the growth chamber resulting from buoyancy effects. Using instrument configurations that satisfy this criterion, the effects of variations in the chamber geometry, the imposed temperature gradient, and the total volumetric flow are evaluated. A new configuration is identified that could produce real-time CCN spectra with an effective range including at least supersaturations between 0.07% and 1.2%.