Sulfur oxide detection system

A sulfur oxide detection system comprising;

• an element part which includes a sensor cell having a solid electrolyte layer having oxide ion conductivity, a first electrode arranged on one side surface of the solid electrolyte layer so as to be exposed to a measured gas, and a second electrode arranged at the other side surface of the solid electrolyte layer to be exposed to an atmosphere and includes a diffusion regulating layer regulating diffusion of the measured gas and which is arranged in an exhaust passage of an internal combustion engine;
• a voltage application circuit configured to apply a voltage to the sensor cell so that a potential of the second electrode becomes higher than a potential of the first electrode;
• a current detection circuit configured to detect a current flowing between the first electrode and the second electrode;
• and
• a controller communicatively coupled with the voltage application circuit and the current detection circuit, wherein the controller is configured to:
• perform first control making the voltage applied to the sensor cell rise from a first voltage less than a decomposition start voltage of water and sulfur oxide to a second voltage higher than the decomposition start voltage so that a voltage of the decomposition start voltage or more is applied to the sensor cell for a first period of time, after the first control, perform second control making the voltage applied to the sensor cell rise from the first voltage to the second voltage so that the voltage of the decomposition start voltage or more is applied to the sensor cell for a second period of time different from the first period of time, and, between the first control and the second control, perform poisoning recovery control applying a voltage enabling desorption of decomposition products of sulfur oxide adsorbed at the first electrode to the sensor cell;
• and
• to estimate a sulfur oxide concentration in the measured gas based on a difference or a ratio of a first current detected by the current detection circuit when the first control is performed and a second current detected by the current detection circuit when the second control is performed.