To evaluate the performance of gas sensing methods or gas sensors, several indicators should be
considered: (1) sensitivity: the minimum value of target gases’ volume concentration when they could
be detected; (2) selectivity: the ability of gas sensors to identify a specific gas among a gas mixture;
(3) response time: the period from the time when gas concentration reaches a specific value to that
when sensor generates a warning signal; (4) energy consumption; (5) reversibility: whether the sensing
materials could return to its original state after detection; (6) adsorptive capacity (also affects
sensitivity and selectivity); (7) fabrication cost. More indicators for different sensing methods will be
listed and compared in Section 4.