Atmospheric particles acting as Ice Forming Nuclei in different size ranges

摘要

The work presents the results of an experimental campaign performed at a rural site (S. PietrornCapofiume, near Bologna July 2007) concerning measurements of ice nuclei in different sizernclasses of aerosol: PM1, PM2.5, PM10 and total suspended particles (TSP). Simultaneousrnmeasurements of particle number concentrations were also performed.rnAerosol in the PM1 fraction contributes about 50% of the measured ice nuclei numberrnconcentration, and in the PM10 fraction contributes about 70-90%. Consequently, therndominant fraction of aerosol that can be activated as ice nuclei involves particles withrnaerodynamic diameter less than 10 μm.rnA positive correlation is observed between higher supersaturation with respect to ice andrnwater (S_(ice) and S_w, respectively) values, and ice nuclei number concentration. The variations ofrnS_w from 2 to 10% and S_(ice) from 20 to 32% (T_(air) = -15 ℃) determine an approximately threefoldrnincrease (from 110 to 337 m~(-3)) in the ice nuclei average number concentration.rnThere is no correlation between ice nuclei measured in the different size ranges, either with thernparticle number concentration measured with the counter spectrometer (d>0.3 μm) or withrnthe condensation nuclei counter.