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A thermal gradient diffusion cloud chamber with a supersaturation field that increases along the path of the flow of sample is used as a cloud condensation nucleus (CCN) spectrometer. The CCN spectrum is derived from the final droplet size distribution which has been determined to be related to the nucleus critical super-saturation based on routine calibration procedures using laboratory-produced monodisperse salt particles. The instrument is compared against a previously reported CCN counter on natural and laboratory-produced aerosol and against an absolute CN counter on the monodisperse aerosol. Preliminary results of atmospheric measurements are given. This device produces a CCN spectrum over the entire useful range of interest for cloud physics (0.01% to 1% supersaturation). More than 40 channels of resolution over this range are simultaneously provided. Data can be collected on a continuous basis for integration times as short as 2 seconds. The instrument has obtained data from four different airborne platforms as well as from a mobile surface platform. The number of channels allows the CCN spectrum to be displayed differentially instead of the usual cumulative display traditionally used in cloud physics.
James G. Hudson (Fri,) studied this question.