GAS SENSING APPARATUS

摘要

A method of selectively sensing the concentration of a target gas in polluted ambient air comprises the steps of: providing a target gas sensor (220) sensitive to the target gas; providing a first gas flow derived from the ambient air from which first flow the target gas is substantially removed; providing a second gas flow derived from the ambient air substantially comprising the same target gas concentration as the ambient air; exposing the target gas sensor to the first gas flow during a first time interval and obtaining from the sensor a first output signal (Smf); exposing the target gas sensor to the second gas flow during a second time interval not overlapping with the first time interval and obtaining a second output signal (Smu); calculating the difference (S?) between the first and the second output signals; calculating the concentration of the target gas from the calculated signal difference (S?).