• the non-injectivity of the sensor array operating in this gaseous environment. Fundamentally, it is impossible to distinguish between certain sets of ternary gas compositions from the response of a two-sensor array. Treating C 2 H 6 and CO 2 as the chief analytes, we measure the effect of non-injectivity through the variance in the background humidity concentration, σ H 2 O , which interferes with the response to changes in C 2 H 6 and CO 2 we wish to detect.