A method of optimising operating conditions in an abatement apparatus configured to treat an effluent stream from a processing tool and an abatement apparatus are disclosed. The method of optimising operating conditions in an abatement apparatus configured to treat an effluent stream containing PFC from a processing tool comprise: changing an operating parameter which controls an operating condition of the abatement apparatus; determining a change in a PFC concentration present in an exhaust stream of the abatement apparatus; and determining whether to retain the operating parameter based on the change in the PFC concentration. In this way, the concentration of PFC present in the exhaust can be used to determine whether the abatement apparatus is operating under the correct operating conditions or not.