Ice nuclei measurements in a rural area and at a high altitude remote station

The majority of ice in clouds is formed via heterogeneous nucleation involving aerosol particles known as ice forming nuclei (IN). Ice nuclei can form ice through different thermodynamic mechanisms or modes: deposition, condensation-freezing, immersion and contact. It is generally agreed that ice will form on nuclei in response to different kinds of thermodynamic forcing, the primary variables being temperature, and saturation ratio with respect to ice and water (Sice and Sw, respectively). A wide variety of measurement techniques have been developed for detecting IN and measuring their characteristics. An experimental campaign was carried out at a rural site of S.Pietro Capofiume (SPC), near Bologna, in the period 07-21 February 2014, and on the top of Monte Cimone (MC) in the Northern Apennines (19-28 May 2014, 2165 m asl). Aerosol fractions (PM1 and PM10) were sampled on nitrocellulose membrane filters, by means of sampler heads two times a day at SPC (9 am and 2 pm), while at MC the samplings were uneven. Simultaneous measurements of particle number concentration in 15 different size classes starting from 0.3 mm (Grimm, Mod.1.108) were also performed. Meteorological data were recorded. Concentrations of IN were detected by the membrane filter technique, using a continuous diffusion chamber (Langer and Rodgers, 1975). Measurements were made at Sice = 1.12; Sw = 0.94 (SPC); Sice = 1.21 and Sw = 1.01 (MC).