Gas sensor and nitrogen oxide sensor

A nitrogen oxide sensor for measuring an amount of a nitrogen oxide component in a to-be-measured gas present in an external space, which sensor comprises:

• a main body made of an oxygen ion-conductive solid electrolyte, which is in contact with the external space,
• a first internal space formed in the solid electrolyte, communicating with an external space via a gas inlet,
• an upstream-side diffusion resistance portion formed as a slit for introducing the to-be-measured gas into the first internal space at a given diffusion resistance,
• a pumping means which has a first, inside, pumping electrode formed inside the first internal space and a first, outside, pumping electrode formed outside the first internal space and which subjects the oxygen contained in the to-be-measured gas introduced from the external space, to a pumping treatment based on a controlling voltage applied between the two electrodes, to control the oxygen partial pressure in the first internal space to a given level at which NO is not decomposed substantially,
• a second internal space communicating with the first internal space,
• a downstream-side diffusion resistance portion formed as a slit for introducing the atmosphere subjected to the pumping treatment in the first internal space, into the second internal space at a given diffusion resistance,
• a gas component-measuring means which has a second, inside, pumping electrode formed inside the second internal space and a second, outside, pumping electrode formed outside the second internal space and further has a detection electrode for decomposing the NO contained in the atmosphere introduced from the first internal space, by either of catalysis and electrolysis and measuring the to-be-measured gas component in the to-be-measured gas based on the oxygen generated by the decomposition,
• a porous, protective layer for detection electrode, formed so as to cover the detection electrode of the gas component-measuring means, and
• a harmful substance-trapping layer made of a porous material capable of trapping a harmful substance, which is formed apart from and upstream of the detection electrode, in a gas passage formed inside the solid electrolyte so as to enable the flowing of the to-be-measured gas, wherein the harmful substance-trapping layer is in contact with at least an upper surface of the gas passage and a lower surface of the gas passage, which are directly opposed to each other, and extends between the gas inlet and the upstream-side diffusion resistance portion and between the upstream-side diffusion resistance portion and the downstream-side diffusion resistance portion.