A filtration system including a novel combination of at least one metal-doped silica-based gel and zeolite materials to trap and/or modify, and remove undesirable gases (such as ammonia, ethylene oxide, formaldehyde, and nitrous oxide, as examples) from an enclosed environment is provided. The gel component exhibits specific porosity requirements and density measurements; the zeolite component is generally acidic and is preferably not reacted with any salts or like substances. Also included is the presence of an oxidizing agent on the gel materials to aid in capturing nitrogen dioxide and preventing conversion of such a product to NO. Methods of using and the application within specific filter apparatuses are also encompassed within this invention.