A solid state electrochemical cell (10a) for measuring the concentration of
a component of a gas mixture (12) includes first semiconductor electrode
(14) and second semiconductor electrode (16) formed from first and second
semiconductor materials, respectively. The materials are selected so as to
undergo a change in resistivity upon contacting a gas component, such as
CO or NO. An electrolyte (18) is provided in contact with the first and
second semiconductor electrodes. A reference cell can be included in
contact with the electrolyte. Preferably, a voltage response of the first
semiconductor electrode is opposite in slope direction to that of the
second semiconductor electrode to produce a voltage response equal to the
sum of the absolute values of the control system uses measured pollutant
concentrations to direct adjustment of engine combustion conditions.