To remove gaseous contaminants, a variety of sorbent materials are used. Activated carbon, which is made from sieved coconut-shell carbon, removes many gases and vapors from an airstream by adsorption. The carbon granules have an enormous surface area per mass. Gas molecules diffuse to the surface where they are retained. Sorbent "filters" (charcoal, permanganate/ alumina, or other materials) are typically available for HVACs in refillable 1 to 1 and 1/8-inch refillable panels. Depending on the packing and mesh size, sorbent panels can be 90 to 95% effective in removing most organic compounds.
To use - sprinkle carbon granules into the "valleys" formed by the pleats on secondary filter on top of unit.