Spatio-temporal variability of the ultrafine and fine particle formation over Siberia is discussed. An estimate of foreground processes in the nanoparticle formation has been done. Analysis of the nucleation processes in the free atmosphere shows that nucleation events were observed in 85% of all airborne soundings performed over Siberia. In 80% of cases, nanoparticle layers are formed between heights of 4 and 7 km. The layer thickness mainly varies between 0.5 and 2.0 km and sometimes it can reach 4 km. A simultaneous increase in concentrations of nanoparticles and ozone, stated earlier, appears with an equal probability of coincidence or non-coincidence of nanoparticle and ozone layers at all heights. The horizontal length of nanoparticle layers varies between tens and 600 km. The most probable length is 100–300 km (> 50% of cases). Minimum of monthly mean values of both total nano- and nucleation mode particle concentrations in the ground layer is observed in summer. Concentration of particles with diameters between 3 and 70 nm in free troposphere varies from 300 in summer to 30 cm-3 in winter. The number density of bigger particles (70 < d < 200 nm) varies between 10 (in winter) and 30 cm-3 (in summer). Nucleation in the atmospheric boundary layer and free troposphere occurs absolutely independently. Main sources of nanoparticle formation in the free atmosphere are nucleation and photochemical processes. Contributions of nucleation, photochemical and advective processes in the atmospheric boundary layer are comparable.
nanoparticles, spatial distribution, nucleation, season cycle