Exhaust air containing particulate and gas contaminants is withdrawn from a confined environment, such as a food cooking area, by a circulation system which liquid scrubs some of the contaminants from the exhaust flow, removes mist of the scrubbing liquid from the flow, and then catalyzes or neutralizes gas contaminants into benign gases 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 air to be saved for reuse within the confined environment, rather than discharging the thermal energy into the ambient environment.