To obtain mobility of air ions under atmospheric pressure conditions, a simple measuring method of drift veloc-ity of positive air ions produced by pulsed corona discharge was demonstrated. The drift region was formed by two disc electrodes. The ions were produced at the tip of a needle electrode where a high-voltage pulse with duration of 10 μs and pulse height of 3 kV was applied with repetition rate of 25 Hz. A time of flight of ions from the needle to an ring electrodes was obtained from the waveform of iuduction current due to movement of ions. There is zero-crossing in the waveform of the induction current. The zero-crossing time was detected automatically by a fabri-cated circuit and a counterboad connected to a personal computer. In this system, 400 data of the drift velocity of ions obtained for the period of 16 seconds were avaraged and ion mobility were calculated. The drift velocity of ions depends on the electric field strength in the drift region. The ion mobility under atmopheric pressure was obtained as 1.95×10-4 m2/V•s.
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