THE USE OF RAMAN LIDAR FOR THE CHARACTERIZATIONOF PARTICLE HYGROSCOPICITY: ANALYSIS OF SELECTED CASE STUDIES FROM THE CONVECTIVE AND OROGRAPHICALLY-INDUCED PRECIPITATION STUDY

Aerosol particles tend to grow at large relative humidity values as a result of their hygroscopicity. Raman lidars with aerosol, water vapour and temperature measurement capability are potentially attractive tools for studying aerosol hygroscopicity as in fact they can provide continuous altitude-resolved measurements of particle optical, size and microphysical properties, as well as relative humidity, without perturbing the aerosols or their environment. Specifically, the University of Basilicata Raman lidar system (BASIL) considered in the present study has the capability to perform all-lidar measurements of relative humidity based on the combined application of the rotational and the vibrational Raman lidar techniques in the UV. BASIL was operational in Achern (Black Forest, Lat: 48.64 ° N, Long: 8.06 ° E, Elev.: 140 m) between 25 May and 30 August 2007 in the framework of the Convective and Orographically-induced Precipitation Study (COPS). The present analysis is focused on selected case studies characterized by the presence of different aerosol types with different hygroscopic behaviour. The observed behaviour, dependent upon aerosol composition, ranges from hygrophobic to hygroscopic, with monotonic (smoothly varying) or deliquescent (step change) growth.