Real-time Rain Conductivity as a Surrogate for pH: Development of a Field-deployable Instrument

Alfred M. Moyle and Dennis Lamb
Meteorology Department, 503 Walker Building, The Pennsylvania State University
University Park, PA 16802


The “daily” protocol of AIRMoN, compared with the “weekly” sampling of NTN, represents a significant improvement in the temporal resolution of wet-deposition data. Still, the single measurement of pH that AIRMoN currently provides on a given day represents only the broadest average of rain acidity; all the natural variability of the weather system is masked by the collection of a single rain sample. The fine temporal signature of individual storms at a given location, which might well reveal mechanistic information about cloud processes, is not available with the current monitoring strategy. In order to address the need for higher-resolution data, we have developed an economical, real-time, single-parameter monitor of precipitation quality.

Electrical conductivity, unlike pH, is relatively easy to measure, and its variations can be monitored continuously in time to give data representative of rain pH throughout a storm. In a presentation at the Fall 2006 NADP Technical Meeting, we described a manually-operated prototype instrument designed to measure the conductivity of precipitation in real-time and presented measurements made during a convective precipitation event in State College, PA on 28 September 2006. The prototype system has now been converted to an automatic, field-deployable form and is undergoing testing at our Scotia (PA15) field site. Initial results reveal that convective storms yield rain with highly variable conductivity (hence pH). It is hoped that routine measurements of conductivity may help unravel the temporal signature of rain pH and yield a wealth of new data about the chemical evolution of acidic storms.