UMR dual mode CCN counter (modes: CFD plus haze)

The chamber consists of two vertical plates 100 cm long in the vertical direction and 13 cm wide, with a 0.8 cm spacing between the plates. The haze mode is used for the nuclei active at supersaturations (S) from 0.0133 to 0.173%. In this mode the two plates are kept at the same temperature (25 C). In the CFD mode the supersaturation is determined by the temperature difference between the two plates. About 40 minutes is required to obtain a spectrum (5 values of S in the CFD mode, plus 7 values of S in the haze mode). About half of this time is used to adjust the temperatures and flows; the rest is used in actual counting of the nuclei. Comparisons of the counter to other types of counters are reported.