A sensor assembly includes a voltage source, a sensor electrode, a grounded assembly, an integration capacitor, and a current meter. The sensor electrode is coupled to the voltage source to receive a voltage. The sensor electrode is disposed within a directed and controlled exhaust flow to facilitate particle agglomeration into particulate matter structures at a surface of the sensor electrode. The grounded assembly is coupled to a ground reference and disposed at a distance from the sensor electrode. The integration capacitor is coupled to a negative side of the voltage source to integrate in time current pulses from charge transfers from the sensor electrode of the particulate matter structures. The current meter is coupled to the voltage source to measure an integrated value of current supplied to the voltage source in response to charge transfers from the sensor electrode to the particulate matter structures in the exhaust flow.