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.

A plasma-resistant article is provided in which a surface region of the article to be exposed to plasma in a corrosive atmosphere is formed from a zirconia-based ceramic that contains yttria in an amount of 7 to 17 mol %. The plasma-resistant article exhibits a sufficient resistance against exposure to plasma and is cost-effective. Preferably, the surface region has a centerline average roughness (Ra) of 1.2 to 5.0 .mu.m, which is readily achieved through the use of an etching solution containing hydrofluoric acid. The present invention also provides a production method for such a plasma-resistant article.

Apparatus and method for determining the concentration of NOx in a gas mixture. The gas mixture is supplied to two electrodes at which different NOx decomposition conditions are present. The electrodes may be of different materials or sizes or may be positioned in different gas enclosure environments. The NOx decomposes at different rates at the two electrodes and an emf is thus produced between the electrodes. The concentration of NOx in the gas mixture is determined from the measured emf.

Apparatus and method for determining the concentration of NOx in a gas mixture. The gas mixture is supplied to two electrodes at which different NOx decomposition conditions are present. The electrodes may be of different materials or sizes or may be positioned in different gas enclosure environments. The NOx decomposes at different rates at the two electrodes and an emf is thus produced between the electrodes. The concentration of NOx in the gas mixture is determined from the measured emf.

A sensor system accurately measures nitrogen oxide (NO.sub.x) in a gas mixture via the use of at least one electrochemical sensing cell and differential pulse voltammetry (DPV). The sensor system has a sensor with an electrochemical sensing cell for producing an electrical signal (current, voltage, etc.) indicative of an amount of the nitrogen oxide within the gas mixture. The sensing cell has an electrolyte interposed between an anode electrocatalyst and a cathode electrocatalyst. Significantly, a DPV mechanism is connected to the sensing cell for enhancing the sensitivity and selectivity of the electrolyte associated with the sensing cell. The DPV mechanism has (1) a pulse superimposition mechanism for combining a pulse with a sensing cell bias imposed upon the sensing cell; (2) a measurement mechanism for measuring the electrical signal before and during superimposition of the pulse to derive first and second sample signals; and (3) a concentration derivation mechanism for mathematically combining (preferably, subtraction) the first and second sample signals to derive a DPV signal which is indicative of the NO.sub.x concentration. Optionally, based upon the material structure of the sensing cell, the sensor system may also be equipped with an electrochemical pumping cell for consuming oxygen (O.sub.2) within the gas mixture.