Exhaust gas control apparatus for internal combustion engine

An exhaust gas control apparatus for an internal combustion engine, comprising:

• a NOx storage reduction catalyst which is provided in an exhaust passage for an internal combustion engine;
• a concentration detector whose detection state can be changed between a first detection state in which a total concentration of sulfur oxide and hydrogen sulfide in exhaust gas that has passed through the NOx storage reduction catalyst is detected, and a second detection state in which a concentration of the sulfur oxide in the exhaust gas is detected;
• and
• a controller which performs a poisoning recovery process that controls an operating state of the internal combustion engine such that the sulfur oxide is released from the NOx storage reduction catalyst, wherein
• the detection state of the concentration detector is alternately changed between the first detection state and the second detection state after the concentration dectector which is in the second detection state detects release of the sulfur oxide from the NOx storage reduction catalyst during the poisoning recovery process performed by the controller, whereby the concentration detector obtains the concentration of the sulfur oxide and a concentration of the hydrogen sulfide.