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The data from observations made in the Hyytiälä background station over the period 1997–2003 were analyzed in order to investigate the possible links between physical, chemical and meteorological parameters for event and nonevent days during different seasons. The seasonal patterns of average trace gas (O3, H2O, NOx = NO + NO2, SO2) concentrations, UV-A irradiation intensity, temperature, relative humidity and condensation sink were established and used for evaluating their influence on the seasonal dependence of the formation and growth rates of particles in the nucleation mode. For the forest region at Hyytiälä, an estimate was made on the contribution of the oxidation products of SO2 and volatile organic compounds (VOCs) by O3 and OH to the formation and growth of the nucleation mode particles. The condensation sink was shown to play a crucial role in the chemical dynamics of gaseous precursors and aerosol particles. The variability of the sink was attributed mainly to the humidification of the pre-existing aerosol particle population, depending thus strongly on the relative humidity. Our results indicate that the observed growth rate of new particles is connected with condensation of secondary organic compounds originating from the oxidation of terpenes.

The International Geophysical Year (IGY) was the most significant international scientific event in geophysical sciences in the history of mankind. This was the largest international experiment that brought together about 300 000 scientists from 67 countries. Well-planned activity of national and international committees was organized for the first time. The history of the IGY organization and complex international experiments in planetary geophysics conducted within its program are discussed in this article. Special attention is given to the estimation of the significance of this project for developing worldwide geophysical research.

We present one-year data on atmospheric aerosol particle size distributions covering the ultrafine size range from two measurement stations situated in central Siberia: Tomsk and Listvyanka. The size distributions were measured using Diffusion Aerosol Spectrometers (DAS), which are able to detect particles as small as 3 nm in diameter. The analysis of the size distribution time series revealed about 30 new-particle formation and growth events at both stations. The events occurred predominantly during the springtime. The average particle formation rates were 0.4 cm–3 s–1 at both stations, whereas the particle growth rates were on average 5.5 nm h–1 at Tomsk and 1.8 nm h–1 at Listvyanka. The formation and growth rates were comparable with those observed in the western part of the Eurasian boreal forest.