Any of several devices that measure the number concentration of atmospheric particles upon which water vapor condenses at low values of supersaturation that are equivalent to those that occur with the formation of tropospheric liquid clouds. The supersaturations produced in the condensation chambers of these devices can normally be set within a range from a few tenths of one percent to several percent. However, clouds or haze can begin to form on very hygroscopic particles at saturation levels well below 100%, so some devices also allow for a range of measurements at subsaturation. The concentrations of cloud condensation nuclei (CCN) are normally reported as the number per cubic centimeter of air activated at a specified super- or subsaturation with respect to water. Compare condensation nuclei counter.