Abstract: An electrochemical sensor system for monitoring emissions includes locating first and second electrodes in a position to sense the emissions. At least one of the first and second electrodes is made of a dense electrode material. An ion-conductor material that acts as an electrolyte is operatively connected to the first and second electrodes. The first electrode is excited at a frequency f1, A response is received from the first electrode at frequency f1. A second signal is received base on the emissions and a response is produced indicating the emissions.