ERRORS IN THE GERDIEN MEASUREMENT OF ATMOSPHERIC ELECTRIC-CONDUCTIVITY

The measurement of conductivity has been an essential part of most atmospheric electricity research programs during the past century. This measurement is known to be vulnerable to a variety of potentially significant errors which can be separated into those resulting from diffusion of ions and those produced by electrical forces. Diffusion errors are caused by inlet tubing, screens, and inlet covers; and electrically produced errors may result from the effect of the accelerating potential or the potential of the apparatus itself. Detection and quantification of these errors has been the subject of several past studies which are discussed in detail. In this paper, a series of measurements and theoretical analyses is described in which the effects of each error mechanism are isolated, measured, and analyzed, and in which prior error reduction schemes are tested. It is shown that diffusive losses in inlet ducting and structures can be significant, and analytical estimations of these losses are presented which agree well with the measurements. The losses produced by electrical forces may also be significant even when plausible ameliorative measures are taken, and operating constraints to avoid this error source are developed. Past measurements of diffusive loss are found to be consistent with these results except in one case where improper operating conditions are indicated.