On the basis of wind direction measurements with 1-s discreteness at the meteorological tower VMM-310 in the town of Obninsk, maximum fluctuations of wind direction are obtained with 10-s averaging over limited time intervals that correspond to the transport of pollutant puffs at distances about 10 km from the source at altitudes up to 300 m. Average values of maximum fluctuations of wind direction decrease with increasing wind speed, level of measurements, and stratification stability. Examples are presented of distributions of maximum fluctuations of wind direction as dependent of these factors. Parameters are given of distributions of maximum fluctuations of wind direction at six levels under different wind speeds and different atmospheric stability. The empirical distributions are approximated by Weibull distribution, and parameters of the latter are presented for separate levels. The results obtained can be used for estimation of an angular size of an area of possible pollution under different conditions of atmospheric stratification, wind speed, and levels of transport of an instantaneous puff of pollutants for the pollutant cloud motion up to a distance of 10 km from the source.

Experimental field and laboratory studies on washout of radionuclides from the snow cover during snow melting were carried out in the winter of 2005/06. In the field studies, a specially equipped runoff site was used. In the laboratory conditions, the experiments were conducted using prepared soil monoliths. In the winter of 2006, 25 g/m 2 of water-free cesium chloride (CsCl) and 25 g/m 3 of strontium chloride (SrCl 2 ) were put onto the snow cover surface of the runoff site. The snow surface of the soil monolith was coated with a 137 Cs-bearing solution, then with SrCl 2 . Under experimental conditions, practically no surface runoff from the runoff site was recorded. The experiments with the soil monoliths demonstrated that the coefficient of the liquid washout of 137 Cs normalized to the runoff layer was within 0.9´10 -6 -1.2´10 -4 mm -1 , and that of 90 Sr normalized to the runoff layer was within 2´10 -6 -1.6´10 -4 mm -1 .