A portable air filter and method of use are provided. The portable air filter includes a semi-permeable air filter, optionally disposed within a frame. An attachment surface, such as an adhesive, is disposed on the frame, for attaching the portable air filter to an air vent. In certain embodiments, a second air filter and frame are slidably connected to the frame. If the portable air filter is not disposed within a frame, the portable air filter is cut to fit over an air vent, and an adhesive, such as tape, is provided for a user to attach the cut filter to fit over the air vent. The method includes attaching the portable air filter to an air vent by pressing the adhesive to a wall, ceiling, or floor such that the portable air filter covers the air vent. The invention is useful for improving air quality in a variety of spaces, including in an airplane, in a hotel, on a cruise ship, on a travel bus, and other public spaces.