Abstract: An apparatus and technique for measuring a concentration of radical particles within a gas sample obtained from a location within a semiconductor processing system having a process chamber while a process is being performed within the process chamber includes obtaining radical data corresponding to the measured concentration of radical particles, comparing the obtained radical data to at least one threshold and outputting a control signal when a result of the comparing indicates that the obtained radical data has a predetermined relationship with the at least one threshold. The first control signal can be configured to cause a chamber recovery process to be performed within the process chamber or indicate that a chamber recovery process should be performed within the process chamber.