EXHAUST AIR SENSOR

A sensor element (2A) in an exhaust air sensor (1) has a solid electrolyte body (31A) provided with a reference electrode (312) and a detection electrode (311) exposed to a detection target gas (G). A porous protective layer (37) is provided on the outer surface (301) of the solid electrolyte body (31A), which includes the surface of the detection electrode (311). The porous protective layer (37) is constituted from a plurality of aggregate particles bonded to one another. When the cross section of a plurality of crystal particles constituting an aggregate particle is observed, the number, per unit surface area, of crystal particle boundary intersections wherein three or more crystal particles intersect is within a range of 1 to 10,000/[mu]m2. 排气传感器(1)的传感器元件(2A)具有：设置有暴露在检测对象气体(G)中的检测电极(311)及基准电极(312)的固体电解质体(31A)。在包含检测电极(311)的表面的固体电解质体(31A)的外侧面(301)上上，设置有多孔质保护层(37)。多孔质保护层(37)由互相结合的多个骨材粒子构成。观察构成骨材粒子的多个晶粒的截面时，3个以上晶粒相交的晶粒交界点在每单位面积中的数量在1～10000个/μm2的范围内。