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.