Atmospheric particles acting as Ice Forming Nuclei in different size ranges

Abstract

The work presents the results of an experimental campaign performed at a rural site (S. Pietro Capofiume, near Bologna July 2007) concerning measurements of ice nuclei in different size classes of aerosol: PM1, PM2.5, PM10 and total suspended particles (TSP). Simultaneous measurements of particle number concentrations were also performed. Aerosol in the PM1 fraction contributes about 50% of the measured ice nuclei number concentration, and in the PM10 fraction contributes about 70–90%. Consequently, the dominant fraction of aerosol that can be activated as ice nuclei involves particles with aerodynamic diameter less than 10 μm. A positive correlation is observed between higher supersaturation with respect to ice and water ( S ice and S w, respectively) values, and ice nuclei number concentration. The variations of S w from 2 to 10% and S ice from 20 to 32% ( T air = − 15 °C) determine an approximately threefold increase (from 110 to 337 m − 3 ) in the ice nuclei average number concentration. There is no correlation between ice nuclei measured in the different size ranges, either with the particle number concentration measured with the counter spectrometer ( d > 0.3 μm) or with the condensation nuclei counter.