The main factors determining the radon hazard on the territory of Moscow are analyzed based on the results of research of more than 4000 sites and radon flux density measurements (RTD). The main factor determining the value of the RTD is radon concentration in the first layer of soil from the surface. Maximum values of the RTD are typical for clay massifs with radium concentration from 15 to 45 Bq/kg, the minimum ones for sandy massifs. It is emphasized that the value of RRR in the atmosphere depends on local defects in the near-surface layer. The role of tectonic disturbances in the character of radon distribution in the atmosphere is denied.
