An air purifier is a device which removes contaminants from the air. These air purifiers residential used are particularly beneficial to allergy sufferers & asthmatics and eliminating second hand tobacco smoke. The air purifiers are manufactures by small scale industries as well as large scale industries. The use of air purifier are dust, pollen, pet dander, mold spores, and dust mite feces can act as allergens, triggering allergies in sensitive people. The purifying techniques are Ultraviolet germicidal irradiation, Filter based purification traps, Activated carbon is a pororus material, Photocatalytic Oxidation, Ionizer purifiers and Liquid Ioniser purifiers. The medical, industrial and commercial industries HVAC are mainly used.