Estimation of nocturnal²²²Rn soil fluxes over Russia from TROICA measurements

Abstract. In TROICA (TRanscontinental Observations Into the Chemistry of the Atmosphere) campaigns (1999–2008), the simultaneous observations of near surface ²²²Rn 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 ²²²Rn and temperature vertical distribution are used to estimate ²²²Rn regional scale soil fluxes based on calculations of nocturnal ²²²Rn accumulation rates in the surface layer under inversion conditions. An effect of seasonal soil thawing on 2–4 times surface ²²²Rn concentration increase from summer 1999 to autumn 2005 is observed. The estimated ²²²Rn 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 ²²²Rn 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 ²²²Rn flux variations in specific events show a strong effect of both soil and atmospheric conditions on ²²²Rn near-surface abundance and the derived seasonal patterns over the continent.