Summary form only given. Radio frequency driven plasma jets are frequently employed as efficient plasma sources for surface modification and other processes at atmospheric pressure, e.g. in the increasing field of biomedical applications. The radio-frequency driven micro-scaled atmospheric pressure plasma jet (μAPPJ) is a particular variant of that concept. In this work, the characteristics of a μAPPJ operated with a helium-oxygen mixture and its interaction with ambient air are studied by spatially resolved numerical simulation. The density and temperature of the electrons, as well as the concentration of all relevant species are studied in both the discharge itself and its effluent.