Apparatus and methods for reducing or eliminating undesirable air-borne substances, such as odors, bacteria, viruses, fungi, and toxins, are provided. A filter containing nanocrystalline metal oxide or metal hydroxide particles may be installed within an air handling apparatus such as an existing HVAC unit located within a building, and particularly within a home, or a portable air processor or purifier. The air handling apparatus comprises a blower which pulls air containing various undesirable substances from within the enclosed environment and directs it through a filtering device containing the nanocrystalline particles. The undesirable substances are sorbed by the nanocrystalline particles thereby creating a deodorized stream of air that may then be directed back into various portions of the enclosed environment or vented to the atmosphere.