System for sensing particulate matter

A method, comprising:

• adjusting engine operation based on degradation of a particulate filter in an engine exhaust pipe, the degradation determined based on a time interval between a first regeneration and a second regeneration of a curved particulate matter sensor element located in an annular space between concentric, hollow inner and outer tubes;
• wherein
• during a first condition when particulate filter regeneration conditions are met and in response to the time interval being greater than a threshold time interval, regenerating the particulate filter in the engine exhaust pipe via a combination of one or more of retarding spark and decreasing an air/fuel ratio;
• and
• during a second condition and in response to the time interval being less than the threshold time interval, indicating to an operator degradation of the particulate filter and where adjusting engine operation based on degradation of the particulate filter includes adjusting an engine actuator to reduce torque output.