An onsite chemistry air filtration system to remove gaseous contaminants from air is disclosed. The onsite chemistry air filtration system of the present invention comprises: a conventional particulate filtration section, a photochemical filtration section, a static gas phase filtration section and a catalytic filtration section. The conventional particulate filtration section captures solids and condensables. In the photochemical filtration section, UV lamps generate bio-destruction and surface photochemical activity on a semiconductor catalyst material, provide a radiation source to irradiate airborne contaminant molecules and to energize their states to promote reactions and generate airborne ozone and radicals. In the static gas phase filtration section, gas phase filtration media is used to capture contaminants, concentrate them in a relatively confined space and allow airborne generated chemistries to concentrate and react in-situ, thereby creating a regeneration effect on the media. In the catalytic filtration section, catalytic media scavenges and converts airborne radicals and ozone to harmless by-products.