A major threat to Taj Mahal is from the Mathura oil refinery due to polluting gases like sulphur dioxide, hydrogen sulphide and nitrogen oxides. When moisture gets accumulated in a polluted environment, the oxides of sulfur, carbon and nitrogen form weak sulfuric, carbonic and nitric acids which are corrosive of stone, metals, paints and textiles. Many priceless works of art have suffered more damage in the last 20 years due to increased sulfur-dioxide in the atmosphere.