The Taj Mahal was threatened by air pollution from nearby factories that caused "Marble Cancer". Over 1700 factories were polluting the air and endangering the marble structure. Efforts were made to reduce pollution through closing factories, applying protective treatments to the marble, banning polluting activities like brick kilns, and introducing electric buses to reduce traffic and carbon monoxide levels. However, the effects of these efforts are still uncertain as pollution remains a significant problem due to the large local population and tourism.