Analysis of the aerosol number size distribution variability and characterization of new particle formation events at Monte Cimone GAW global station

The aim of this thesis is to obtain long-term information on aerosol number size distribution and new particle formation at the Mt. Cimone GAW global station (CMN, 2165 m a.s.l.) to better assess how aerosols impact on Earth system. The size distribution of particles ranging from 9nm to 500nm was continuously observed with a DMPS from November 2005 to July 2013 in the framework of EUSAAR and ACTRIS projects. Size distribution and number concentration are studied at different time scales, together with occurrences of new particle formation (NPF). CMN typical aerosol number size distribution is bimodal while the average total number concentration of 1534±1332/cm^3. The number concentration shows large seasonal variations with higher values during warm months, almost four times higher than those observed in winter. On a daily time-scale, the maximum of total particles occurs in the afternoon. When classifying aerosol number size distribution into nucleation mode, Aitken mode, and accumulation mode, Aitken mode is the main contributor to the total number concentration for about 53%, followed by particles in the accumulation and nucleation modes with 31% and 16%, respectively. NPFs are identified, by classifying each day following standardized classification criteria. CMN is characterized by a NPF events frequency of 26.7%, with the highest event occurrence in May and August, while non-events are more frequent during winter. The growth of nucleation mode particles and the time evolution of their number concentration begin around local noon. The first one lasts almost three hours, with a mean growth rate of 4.65±1.97nm/h, while the latter lasts more than one hour and a half, with a rate of 0.50±0.56/(cm^3 ·s). The average condensation sink (CS) is 0.280 ·10^-3/s during a typical non-event day, and 0.483·10^-3/s during a typical event day. However, low CS observed before the nucleation onset time can be an important factor triggering NPFs, except during winter season.