An ASI official said that the spots were initially cleaned using a mudpack, but stains have been reappearing biannually, with an exception in 2020 when pollution levels in Agra were unusually low. An archaeologist at ASI, Rajkumar Patel, said that brown-green spots appear on the monument’s north face adjoining River Yamuna. Archaeological Survey of India To Undertake Extensive Study To Prevent Green-Coloured Stains on Taj Mahal.