A 2-STAGE IMPACTOR FOR FOG DROPLET COLLECTION - DESIGN AND PERFORMANCE

A two-stage fog water impactor was designed for the measurement of siz e-dependent cloud droplet solute concentrations. The instrument achiev es isokinetic sampling conditions by using a variable inlet as well as by using a rotating stand in connection with a wind Vane to keep the impactor aligned with the actual mean wind direction. These features a re important for reliable results, especially at the high wind velocit ies which frequently occur at mountain stations. The instrument operat ed successfully during the Great Dun Fell Cloud Experiment in spring 1 993. The results of field measurements, as well as of cloud chamber ex periments to test the performance of the instrument are presented. (C) 1997 Elsevier Science Ltd.