A three-stage cloud impactor for size-resolved measurement of cloud drop chemistry

A new cloud sampler has been designed that is capable of simultaneously collecting three independent portions of the cloud drop size spectrum for chemical analysis. The instrument, known as the IESL cloud impactor, features three jet impaction stages in series, each of which removes droplets above a predetermined cut size. Several interchangeable stages are available, with 50% lower cut sizes of 3, 4, 10, 12, 15, 20, and 30 μm based on drop diameter, permitting numerous combinations of cut sizes to be selected. Calibration experiments indicate the instrument performs according to design. Initial cloudwater samples collected with the impactor at Mt. Mitchell, North Carolina and La Jolla Peak, California reveal ion concentrations in large and small cloud drops higher than those found in intermediate sized drops. The long-term goal for use of the impactor is to evaluate implications of variations in cloud drop chemistry across the drop size spectrum on a variety of processes including aqueous phase sulfur oxidation, precipitation scavenging of pollutants, and pollutant deposition to forests during cloud interception.