A contaminated gas that is to be cleaned, such as contaminated air, is passed through an adsorbent bed to remove gaseous contaminants. An enclosure having a fixed volume is then created around the adsorbent bed. Included within the enclosure is a photocatalytic gas purifier. The adsorbent bed is heated to release the contaminants into the fixed volume to create a high concentration of contaminants in the gas within the fixed volume. The now highly contaminated fixed volume of gas is recirculated through the heated adsorbent bed and photocatalytic gas purifier. The gas purifier oxidizes the contaminants at a high oxidation rate due to the high contaminant concentration level. The enclosure is then opened and the adsorbent bed, now regenerated and at its original temperature, is ready to again receive and clean contaminated gas.