To measure atmospheric radon-220 (thoron) a device has been developed which uses alpha-alpha coincidences from the decay of radon-220 and its very shortlived decay product polonium-216 (half-life 0.16 sec). The alpha decays are detected in a scintillation chamber of 1340 cm3 effective volume and 2600 cm2 sensitive inner surface. The equipment records all alpha-alpha coincidences with time delays up to 0.32 sec. This time constant has been chosen as an optimal compromise with regard to the half-life of polonium-216 and the rate of chance coincidences for atmospheric air free of aerosol particles flowing through the chamber. Atmospheric thoron concentrations were measured at 0.5 and 1 meter as well as 1 and 6 meters above the ground in Mannheim at the station of the Deutsche Forschungs-Gemeinschaft where the important meteorological parameters are recorded regularly. Correlation and regression calculations were carried out for various parameters. The change of radon-220 content with wind speed in various heights is particularly interesting. A maximum is found for a certain wind speed in each altitude. This result has some consequences for the determination of diffusion coefficients from the ratios of radon-220 concentrations in every two different heights respectively.