Exhaust monitoring apparatus

An exhaust monitoring apparatus mounted on a vehicle including an exhaust purification device that is disposed in an exhaust passage of an engine, the exhaust purification device being configured to remove nitrogen oxides contained in exhaust gas, the exhaust monitoring apparatus comprising:

• a nitrogen oxide sensor disposed downstream of the exhaust purification device in the exhaust passage and configured to measure a concentration of nitrogen oxides contained in exhaust gas;
• an air flow meter disposed in an intake passage of the engine and configured to measure an amount of air flowing through the intake passage;
• and
• processing circuitry configured to:
• set a transport delay time, the transport delay time spanning from when air passes through a portion of the intake passage where the air flow meter is provided to when exhaust gas derived from the air that has passed through the air flow meter reaches the nitrogen oxide sensor;
• and
• estimate an emission amount of nitrogen oxides based on an output value of the nitrogen oxide sensor and an output value of the air flow meter that was output earlier than a point in time at which the nitrogen oxide sensor output the output value by the transport delay time.