Snow scavenging of ultrafi ne particles: fi eld measurements and parameterization

Snow scavenging of sub-micrometre aerosol particles is poorly known, even though it is an important aerosol removal mechanism in the polar and mountainous regions as well as in the upper troposphere and in mid-latitudes in winter. In our study, snow scavenging coeffi cients were calculated using four years of particle number concentration spectra measurements together with meteorological measurements. The obtained experimental median scavenging coeffi cients varied between 8.7 ¥ 10 s and 5.2 ¥ 10 s in the 10 nm to 1 μm size range. A parameterization of the results is presented and its functionality is tested using University of Helsinki Multicomponent Aerosol model (UHMA). The parameterization applies to snowfall types of slight continuous snowfall and snow grains with intensities of the order of 0.1 mm h.