There is no doubt that positive and negative ion concentrations are influenced by meteorological conditions. But this dependence on weather is due to the given atmospheric content and size of aerosol particles which the small ions attach to (Lassen and Rau, 1960). Consequently, minimum values are found in fog and low visibility, respectively, high values at high visibility, fair weather without precipitation, but also during foehn conditions. However, the latter are in no way distinguished by special features compared to other weather conditions that favor the increase of ion concentrations. This relates to ion concentrations of both signs as well as the ratio from positive to negative concentrations.