Exhaust air containing particulate and carbon monoxide gas contaminants is withdrawn from a confined environment, such as a food cooking area, by a circulation system which liquid scrubs particulate contaminants from the exhaust flow, removes liquid mist from the flow, and then catalyzes or neutralizes the carbon monoxide gas contaminants into benign carbon dioxide before discharging the flow back into the confined environment. Removing contaminants in this manner allows a substantial amount of the thermal energy content of the exhaust air to be saved and reused within the confined environment, rather than discharging the thermal energy into the ambient environment.