This is the replacement TiO2 filter for Air Cleaner model: AC-2102. TiO2 (titanium Oxide) Filter with UV Light: Photo catalytic oxidation is achieved when UV ray combines with a TiO2-coated filter. This process creates hydroxyl radicals and super-oxide ions, which are highly reactive electrons. These electrons aggressively combine with other elements in the air, such as bacteria and volatile organic compounds (VOC), which are harmful pollutants. Once bound together, the chemical reaction takes place between the super-charges ion and the pollutant, effectively �??oxidizing�?� or burning the pollutant. This breaks the pollutant down into harmless carbon dioxide and water molecules.