nition, when the gas composition changes in an unresponsive direction in composition space, the sensor response remains constant. When the gas composition changes in an unresponsive direction, the ad sorption of one set of species balances (in mass) the desorption of another set of species, thus, keeping the sensor response fixed. These undetectable gas composition changes generally depend upon the initial composition. The identification of unresponsive directions of gas sensors/sensor arrays is important for understanding their limitations and vulnerabilities to adversarial attacks .