One of the Seven Wonders of the World is under attack—and it’s not from extremists or urban rezoning or too many tourists. No, India’s Taj Mahal is being attacked by the tiniest of assailants: air pollution. The monument, once called the White Marvel, is now dingy yellow and brown, thanks to incessant automobile and factory pollution, as well as India’s dependence on coal-burning power, which causes some days of near zero-visibility.

A study conducted by the University of Wisconsin and the Georgia Institute of Technology, in conjunction with the Indian Institute of Technology, Kanpur and the Archaeological Survey of India, set out to determine what was happening and at what rate.

First, the team took air samples around the site for a year, determining there were high concentrations of pollution that could potentially cause the discoloration.

Next, the team placed clean marble samples like the ones used in the surface structure of the Taj Mahal throughout secured areas on the grounds of the monument. That way, the samples could be left for extended periods without the potential of accidental tampering by tourists.

After a prescribed period, the researchers analyzed the samples and found significant deposits of both black and brown carbon. Black carbon is a remnant of fossil fuel burning, like emissions from factories and automobiles. Brown carbon comes from the burning of biomass—garbage and other refuse.

Armed with definitive proof of the pollution, the Indian government has taken steps to curb it, creating a safe zone around the monument and redirecting automobile traffic. Tour buses and cabs taking tourists to the site now are electrically-powered to provide zero emissions. And, the local government has installed air quality monitors to gauge the effectiveness of environmental efforts.

Still, it’s an ongoing battle, since illegal factories and businesses continue to spring up around the city of Agra, the site of the monument. Only time will tell if collective efforts can save the Wonder.