Abstract: A sensor element for detection of a trace fluid component in a fluid stream or other fluid environment, comprising a piezoelectric crystal having a fundamental resonant frequency in response to an applied oscillating electric field, and an inert porous material coating on the piezoelectric crystal containing a metal species which is reactive with the trace fluid component to yield a solid interaction product of changed mass in relation to initial mass of the metal species interacting with the trace fluid component to yield the solid interaction product.

Abstract: An environmental gas monitor for detection of a trace fluid component in a fluid environment, comprising: a piezoelectric crystal having a fundamental resonant frequency in response to an applied oscillating electric field; a coating on the piezoelectric crystal of a sensor material which is reactive with the trace fluid component to yield a solid interaction product; means for applying an oscillating electric field to the piezoelectric crystal which generates an output resonant frequency therefrom; means for (i) sampling the output resonant frequency of the piezoelectric crystal while the oscillating electric field is applied thereto, (ii) determining the change in resonant frequency from the fundamental resonant frequency that occurs on formation of the solid interaction product when the sensor material interacts with the trace fluid component in the fluid environment, and (iii) generating an output indicative of the presence of the trace fluid component in the environment; means, e.g.