Number of people that visit the Taj Mahal each year. Commissioned in 1632 by the Mughal emperor, Shah Jahan, to house the tomb of his favourite wife, Mumtaz Mahal, it was designated a UNESCO World Heritage Site in 1983. Toxic air from nearby factories and refineries, belching pollution and excrement from swarms of insects have turned the mausoleum’s pearly-white exterior to shades of greyish-black, yellow and green.