Koninklijke Philips Corporation N.V.

Peter Van Der Linde

Johan Hendrik Klootwijk

Nico Maris Adriaan De Wild

Johan Marra

Jacobus Bernardus Giesbers

Rogier Adrianus Henrica Niessen

Marcel Bulder

A method of selectively sensing the concentration of a target gas in polluted ambient air comprises the steps of: &#x2014;providing a target gas sensor () sensitive to the target gas; &#x2014;providing a first gas flow derived from the ambient air, from which first flow the target gas is substantially removed; &#x2014;providing a second gas flow derived from the ambient air, substantially comprising the same target gas concentration as the ambient air; &#x2014;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); &#x2014;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); &#x2014;calculating the difference (S&#x394;) between the first and the second output signals; calculating the concentration of the target gas from the calculated signal difference (S&#x394;).

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Amersfoort, Netherlands

Peter Van Der Linde