Gas sensor and concentration measurement method using gas sensor

A concentration measurement method of measuring concentrations of a plurality of sensing target gas components contained in a measurement gas using a gas sensor, the measurement gas at least containing water vapor and carbon dioxide, wherein

• the gas sensor includes a sensor element having an elongated planar structure formed of an oxygen-ion conductive solid electrolyte,
• the sensor element comprises:
• a gas inlet through which the measurement gas is introduced;
• an internal chamber communicating with the gas inlet via a diffusion control part;
• an adjustment electrode, a first measurement electrode, and a second measurement electrode each provided to face the internal chamber and arranged in order of proximity to the gas inlet while being spaced apart at predetermined intervals;
• an adjustment pump cell including the adjustment electrode, an out-of-space pump electrode provided at a location other than a location in the internal chamber, and a portion of the solid electrolyte present between the adjustment electrode and the out-of-space pump electrode;
• a first measurement pump cell including the first measurement electrode, the out-of-space pump electrode, and a portion of the solid electrolyte present between the first measurement electrode and the out-of-space pump electrode;
• a second measurement pump cell including the second measurement electrode, the out-of-space pump electrode, and a portion of the solid electrolyte present between the second measurement electrode and the out-of-space pump electrode;
• and
• a heater heating the sensor element, and
• the concentration measurement method using the gas sensor comprises:
• a) pumping, using the adjustment pump cell, oxygen into the internal chamber from an external space so that, when the measurement gas having reached the adjustment electrode contains a hydrocarbon gas component, the hydrocarbon gas component is oxidized;
• b) pumping, using the first measurement pump cell, oxygen out of the measurement gas having reached the first measurement electrode so that substantially all water vapor and carbon dioxide contained in the measurement gas having reached the first measurement electrode are reduced;
• c) pumping, using the second measurement pump cell, oxygen into the internal chamber to selectively oxidize hydrogen generated by reduction of water vapor and contained in the measurement gas having reached the second measurement electrode;
• d) identifying a concentration of water vapor contained in the measurement gas based on a value of a hydrocarbon equivalent current as an oxygen pump current flowing between the adjustment electrode and the out-of-space pump electrode when the hydrocarbon gas component is oxidized with oxygen pumped in using the adjustment pump cell and a value of a water vapor equivalent current as an oxygen pump current flowing between the second measurement electrode and the out-of-space pump electrode when hydrogen is oxidized with oxygen pumped in using the second measurement pump cell;
• and
• e) identifying a concentration of carbon dioxide contained in the measurement gas based on the value of the hydrocarbon equivalent current, the value of the water vapor equivalent current, and a value of a total reducing current as an oxygen pump current flowing between the first measurement electrode and the out-of-space pump electrode when water vapor and carbon dioxide are reduced by pumping out oxygen using the first measurement pump cell.