An experimental system to collect cloud condensation nuclei (CCN) onto filters in amounts sufficient for chemical analysis is described. This experimental apparatus is designed to process ambient air at a rate of more than 1 m3/min. Two identical systems have been built. One is installed in a laboratory at Rolla, MO. The other is installed on an 11 m long trailer. The system isolates three size classes of CCN, having mass median diameters of 0.27, 0.12, and 0.075 μm, respectively, and mass collection rates of 11.5, 1.28, and 0.13 mg/day, respectively. The above sizes and collection rates are obtained from a computer simulation that does not account for particle evaporation, but tests of the system indicate that there is particle evaporation which produces some change in the sizes and collection rates. The system components were tested by sampling laboratory-generated CCN of different selected sizes, and the test results were used as inputs for the computer simulation of the system performance.