Technical Note: Characterization of a static thermal-gradient CCN counter

[摘要] The static (parallel-plate thermal-gradient) diffusion chamber (SDC) was oneof the first instruments designed to measure cloud condensation nuclei (CCN)concentrations as a function of supersaturation. It has probably also beenthe most widely used type of CCN counter. This paper describes the detailedexperimental characterization of a SDC CCN counter, including calibrationwith respect to supersaturation and particle number concentration. Inaddition, we investigated the proposed effect of lowered supersaturationbecause of water vapor depletion with increasing particle concentration. Theresults obtained give a better understanding why and in which way it isnecessary to calibrate the SDC CCN counter. The calibration method isdescribed in detail and can, in parts, be used for calibrations also forother types of CCN counters.

We conclude the following: 1) it is important to experimentally calibrateSDC CCN counters with respect to supersaturation, and not only base thesupersaturation on the theoretical description of the instrument; 2) thenumber concentration calibration needs to be performed as a function ofsupersaturation, also for SDC CCN counter using the photographic technique;and 3) we observed no evidence that water vapor depletion lowered thesupersaturation.

[学科分类] 大气科学