A 3-STAGE CLOUD IMPACTOR FOR SIZE-RESOLVED MEASUREMENT OF CLOUD DROP CHEMISTRY

A new cloud sampler has been designed that is capable of simultaneousl y collecting three independent portions of the cloud drop size spectru m for chemical analysis. The instrument, known as the IESL cloud impac tor, features three jet impaction stages in series, each of which remo ves droplets above a predetermined cut size. Several interchangeable s tages are available, with 50% lower cut sizes of 3, 4, 10, 12, 15, 20, and 30 mum based on drop diameter, permitting numerous combinations o f cut sizes to be selected. Calibration experiments indicate the instr ument performs according to design. Initial cloudwater samples collect ed 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 goa l for use of the impactor is to evaluate implications of variations in cloud drop chemistry across the drop size spectrum on a variety of pr ocesses including aqueous phase sulfur oxidation, precipitation scaven ging of pollutants, and pollutant deposition to forests during cloud i nterception.