  Detailed tropospheric ion measurements are needed to improve understanding of
the electrical microphysics affecting clouds. Additionally, atmospheric ion
mobility spectra can be used to identify ion growth processes leading to
condensation nucleus formation. However these measurements are rare,
particularly in the troposphere where the majority of clouds form. Developments
in the operating theory of the classical instrument for ion measurement, the
aspirated cylindrical capacitor, are described, which enable ion mobility
spectrum information to be extracted from the rate of voltage decay of the
aspirated capacitor in air. In this paper, data from historical balloon-borne
ion counter ascents will be reanalysed to extract new ion mobility spectra from
simple voltage time series. Such data recovery will increase the amount of
atmospheric ion spectra available for analysis.
