Abstract: A method and system for ozone treatment of air for a vehicle cab where the system monitors the level of ozone in treated air, and is arranged to perform further treatment of the treated air if the detected ozone levels exceed a threshold level. Such further treatment may include adjusting the flow rate of air in the system, recirculating the treated air through an air filter to remove ozone from the treated air; providing an ozone-reducing substance to the treated air to lower the level of ozone in the treated air, and/or ejecting at least a portion of the treated air to the environment.