FLASH and Covenant - Thank you for correcting my misstatement re 'hydrocarbons'. The O in ethanol definitely helps to give it that special zing.
My thoughts were distracted in trying to find a general way to describe the behavior of the widely used metal-oxide alcohol sensors (tin oxides being most common) which can have selective sensitivities to a wide variety of hydrocarbons, other organics, and some elemental substances under varying conditions. They DO work, but are somewhat analogous to using a wet finger as a wind direction / velocity sensor.