In industrialized areas, the highest contribution to the fine and ultrafine particles comes from anthropogenic activities, namely from emissions of industrial combustion processes and traffic-related emissions. Peri-urban forests can act as a sink of these compounds through different mechanisms, helping to ameliorate air quality. Here, we present the preliminary results of a study to investigate the patterns of the aerosol particle distribution and their correlations with meteorological parameters. Concentration of particles with size down 2.5 nm in diameter was continuously measured above an evergreen Mediterranean forest from January to June 2014 inside the presidential estate of Castelporziano. Results indicate a strong effect of the boundary layer height on particle dispersion that determines higher particle concentration level at night and then diffusion in cleaner air during the day when turbulence enhances the vertical mixing. We found a pronounced reduction of particle concentration during the rain events, supporting the conclusion that rain events represent the major mechanism of particle deposition. By correlating wind direction and particle concentration, we hypothesize large marine aerosol contribution overlapping the anthropogenic sources, although we cannot discriminate yet between biogenic and anthropogenic origins of particulate.