By measuring and filtering small ions in aspiration condensers and recording the remaining space charge density in subsequent Obolensky filters, it has been possible to deduce the composition of space charges. The results show clearly that space charges consist of two components: one dominating positive small-ion part generated by the electrode effect and one large-ion part of reverse polarity. The transport mechanism for the two parts differs basically. ¿ American Geophysical Union 1994