NOVELTY - A process for improving the quality of indoor air comprises: (a) passing the contaminated air through an adsorbent bed (26); (b) heating the adsorbent bed (26) in a confined space (30) so that the concentrations of the gaseous contaminants that are released into the space (30) are increased; (c) photo-catalytically oxidizing the gaseous contaminants; and (d) repeating the steps a number of times.    USE - The method is used to improve the quality of indoor air (such as air in an office building) by removing the gaseous contaminants. It is particularly used for removing gaseous contaminants from toluene, butane, formaldehyde, methyl ethyl ketone, n-decane, propionaldehyde, 1-butanol, limonene, ethylene, ammonia and phosgene (claimed).    ADVANTAGE - Unlike conventional adsorbent bed technology, the method does not simply transfer the contaminants from the air to an adsorbent, which must be disposed of properly when filled. The method uses photocatalytic oxidation technology which completely destroys gaseous contaminants by oxidizing them to benign products. Because most contaminants are present in building air at quite small levels (less than 0.1 ppm by volume), their rates of oxidation by conventional photocatalytic processes are very slow (the slower the oxidation rate, the larger (and more expensive) the reactor needs to be). However, by releasing the contaminants from the adsorbent bed into a fixed volume of gas, the process increases the concentration of contaminants within that fixed volume to a level much higher than the level in the untreated contaminated air or other gas from which the contaminants are originally removed. The rate of photocatalytic oxidation of these contaminants increases dramatically at higher concentrations. When a sufficient amount of the contaminants within the fixed volume are destroyed by catalytic oxidation, the adsorbent bed is ready to be reused. The whole process allows the use of smaller beds that can be regenerated without the need for removal of the bed or apparatus from its installation. Also, the photocatalytic gas purifier equipment is less costly than would otherwise be required if the external contaminated gas were to be continuously cleaned at low oxidation rates by a single pass through a photocatalytic gas purifier.    DETAILED DESCRIPTION - A process for improving the quality of indoor air by removing the gaseous contaminants, comprises:    (a) passing the contaminated indoor air through an adsorbent bed (26) to adsorb the gaseous contaminants;    (b) heating the adsorbent bed (26) from step (a) in a confined space (30) to release the gaseous contaminants in the confined space (30), and regenerating the spent adsorbent bed (26);    (c) choosing the dimensions of the confined space (30) such that the individual concentrations of the gaseous contaminants released from the adsorbent bed (34) in step (b) are within 0.1-10 ppm by volume;    (d) using linear dependence of the photo-catalytic oxidation rate on concentration in the presence of a photo-catalyst in the concentration range of 0.1-10 ppm by volume to quickly photo-catalytically oxidize the gaseous contaminants; and    (e) repeating steps (a)-(d) a number of times.    DESCRIPTION OF DRAWING(S) - The drawing shows a simplified, partially schematic cross-section of a regenerable system for removing contaminants from a gas stream in accordance with the invention.    Confined space (30)    Photocatalytic air purifier (32)    Adsorbent Catalyst bed (34)