A self-calibrating programable mobility spectrometer for atmospheric ion measurements

Ion measurements in atmospheric air allow atmospheric ion-aerosol charge exchange to be investigated, which is thought to be important in cloud processes. Classical aspiration ion measurement techniques have been significantly improved by the use of electronic switching systems to permit the selection of different mobilities, with adjacent instruments using the combination of Voltage Decay and ion current techniques used for calibration. An integrated programable ion mobility spectrometer using the same collection electrodes in both modes is described here, with which high-resolution measurements (1 s sampling) of ion concentration fluctuations have been made. Mobility spectrum information has also been extracted by varying the bias voltage under full computer control. The integrated system can determine small ion concentrations to +/-1%, to a minimum mobility mu similar to0.1 cm(2) V-1 s(-1) (corresponding to a particle radius of similar to2 nm). (C) 2001 American Institute of Physics.