a multiple stage filter assembly which combines a permanently framed particulate filter media layer with an odor and particulate removal filter media layer which is removably mounted to the particulate permanent filter frame in overlying relationship to the outer surface of the particulate layer . the odor removal filter media layer is held in position by a plurality of filter retaining members which cooperate with the main frame structure to provide support for the gaseous filter layer . the retaining members function in a manner which permits simple removal and replacement of the gaseous filter layer without disturbing the permanently framed particulate filter layer .