An apparatus for treating air from an exhaust port of a building. The apparatus includes an enclosed pathway having an inlet for communication with an exhaust port, a discharge outlet, and a non-linear pathway portion between the inlet and discharge outlet. The non-linear pathway includes air treatment material positioned in communication with a portion of the pathway to expose the air to the air treatment material as it moves through the pathway. The apparatus includes an irrigation system for maintaining the moisture content of the air treatment material.