Contact-potential and surface-charge effects in atmospheric-electrical instrumentation

Various investigators have noted deleterious effects on atmospheric electrical measurements due to contact potentials between different metal parts of the apparatus. A less familiar error source of comparable magnitude arises from charge patches which apparently can be deposited on thin insulating films common to the surfaces of many metals. These phenomena seem never to have been studied in the atmosphere, where variable humidity and surface contamination complicate the situation. Two laboratory experiments have been conducted to investigate those error sources with a view toward minimizing their effects by suitable choice of materials. The contact potentials between various metal plates before and after weathering were measured by the nulling potentiometer method in an ionization chamber. The local Volta-potential perturbations due to artificially deposited surface-charge patches were measured on several metal plates by spinning them on a lathe. Of the metals tested, stainless steel and rhodium plate were found to be the best in almost all respects. Surprisingly, gold-plated samples exhibited particularly large variability and sensitivity to weathering.