Estimation of nocturnal.sup.222Rn soil fluxes over Russia from TROICA measurements

In TROICA (TRanscontinental Observations Into the Chemistry of the Atmosphere) campaigns (1999-2008), the simultaneous observations of near surface .sup.222 Rn concentrations and atmospheric boundary layer thermal structure were performed along the Trans-Siberian Railway across northern Eurasia from Moscow to Vladivostok, including central, southern and far eastern parts of Russia. The data on .sup.222 Rn and temperature vertical distribution are used to estimate .sup.222 Rn regional scale soil fluxes based on calculations of nocturnal .sup.222 Rn accumulation rates in the surface layer under inversion conditions. An effect of seasonal soil thawing on 2-4 times surface .sup.222 Rn concentration increase from summer 1999 to autumn 2005 is observed. The estimated .sup.222 Rn regional averaged fluxes vary over Russia from 29 ± 8 mBq m.sup.-2 s.sup.-1 in its so-called European territory to 95 ± 51 mBq m.sup.-2 s.sup.-1 in the southern area of Siberia. The highest .sup.222 Rn fluxes are derived in the regions of high tectonic activity and orogenic belts of central and eastern Siberia and in far eastern Russia. The observed high .sup.222 Rn flux variations in specific events show a strong effect of both soil and atmospheric conditions on .sup.222 Rn near-surface abundance and the derived seasonal patterns over the continent.