Propylene glycol and ethanol: A replacement for glycometh as an antifreeze in precipitation gauges

Federal and state agencies have used a 40 percent ethylene glycol-60 percent methanol solution (glycometh) as an antifreeze solution in precipitation gauges for over 25 years. Current and future disposal regulations, however, make the continued use of the toxic glycometh unfeasible. Propylene glycol (PG) and denatured ethanol have been identified as likely substitutes for glycometh because they have similar characteristics but have low toxicity levels. This paper reports on cold room experiments (0 to -40 degrees C) to ascertain the freezing point of five different mixing ratios of PG and ethanol (PGE) in ten dilutions (1:0 to 1:7) with water. Little difference in freezing point was found across the five mixing ratios, so solution density and cost are important in recommending the best mixing ratio. An equation combines factors such as annual precipitation and minimum January temperature to predict the quantity of PGE that is required as a 'charge' at a precipitation gauging site.