Estimation of nocturnal222Rn 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 Rn-222 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 Rn-222 and temperature vertical distribution are used to estimate Rn-222 regional scale soil fluxes based on calculations of nocturnal Rn-222 accumulation rates in the surface layer under inversion conditions. An effect of seasonal soil thawing on 2-4 times surface Rn-222 concentration increase from summer 1999 to autumn 2005 is observed. The estimated Rn-222 regional averaged fluxes vary over Russia from 29 +/- 8 mBq m(-2) s(-1) in its so-called European territory to 95 +/- 51 mBq m(-2) s(-1) in the southern area of Siberia. The highest Rn-222 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 Rn-222 flux variations in specific events show a strong effect of both soil and atmospheric conditions on Rn-222 near-surface abundance and the derived seasonal patterns over the continent.