Measurement of the mobility distribution of tropospheric ions

Summary The analysis is given for an improved aspiration-type mobility chamber which suppresses the growth of boundary layers and turbulence at the electrodes by employing converging-channel geometry. The distribution of small ions in air as a function of their mobility is determined from data taken with the converging-channel chamber. The results show that the distribution of positive ions is quite stable with an average mobility of about 1.35 cm² volt^–1 sec^–1 (at STP). The negative-ion distribution is broader, less stable, and the average mobility shifts from about 2.1 to 1.7 cm² volt^–1 sec^–1 with the addition of water vapor. The effect of Aitken nuclei upon the mobility distribution is also discussed. The results are compared with previous measurements.