CLOUD CONDENSATION NUCLEI CONCENTRATIONS IN SOUTHERN ARIZONA - INSTRUMENTATION AND EARLY OBSERVATIONS

During an ongoing study to measure cloud condensation nuclei (CCN) con centrations, a new automated thermal diffusion CCN counter was operate d during the months January through June 1994 near the summit of Mt. L emmon in the Catalina Mountains at about 2700 m elevation. The instrum ent records data continuously at 5-minute intervals 24 hours a day. Th e status of the instrument and the data are monitored remotely by tele phone modem. For the 123-day, continuous study the average CCN concent ration was found to range between a few tens and a few hundred nuclei per cm(3) at supersaturations between 0.3 and 0.7%. Diurnal variations were observed, as well as other possible influences, such as wind spe ed, wind direction and mixing depth. At a constant supersaturation of 0.35% the CCN concentration is typically on the order of 50 to 150 nuc lei per cm(3). A description of the instrumentation and early observat ions are presented and discussed. (C) 1997 Elsevier Science B.V.