A few years back, the Leshan Giant Buddha started to weep.
Or so some locals imagined when black streaks appeared on the rose-colored cheeks of the towering 7th-century figure, hewn from sandstone cliffs in the forests of southern China. They worried they had angered the religious icon.
The culprit, it turned out, was the region's growing number of coal-fired power plants. Their smokestacks spew toxic gases into the air, which return to earth as acid rain. Over time, the Buddha's nose and other facial areas turned darkened.
"If this continues, the Buddha will lose its nose and even its ears," said Li Xiao Dong, a researcher who has studied the impact of air pollution in Sichuan Province, the statue's home. "It will become just a piece of rock."
China's ancient buildings, tombs and stone carvings have weathered storms, invading armies and thieves. Now, they face a new threat, a by-product of the rapid economic development that has lifted so many Chinese out of poverty.
More than 80 percent of China's 33 U.N.-designated World Heritage sites, including the Leshan Buddha, have been damaged by air pollution and acid rain, mostly from the burning of coal, according to China's official Xinhua News Agency.
"The level of pollution that China is creating will be devastating to these monuments," said Melinda Herrold-Menzies, a professor of environmental studies at Pitzer College in Claremont, Calif.
Chinese officials are starting to acknowledge the downside of unbridled development. Qiu Baoxing, the vice minister of construction, blamed the devastation of historic sites on "senseless actions" by local officials in pursuit of modernization, the government-run China Daily newspaper reported in June.
"They are totally unaware of the value of cultural heritage," he said, likening the destruction to that of cultural relics during the Great Leap Forward in the late 1950s and the Cultural Revolution from 1966 to 1976.
The 19-story-high Leshan Buddha, with a head that appears lost in the trees, stares down on the confluence of three rivers. Authorities gave it a multimillion-dollar facelift in 2001. Six years later, the seated figure is stained black again, mostly because of acid rain, Li said.
About 750 miles to the north, clouds of black dust coming off coal trucks have damaged the Yungang Grottoes, a World Heritage site in the heart of China's coal belt.
Herrold-Menzies expressed surprise that caves with such historical and archaeological importance would lie so close to "coal mines and an industrial nightmare of a city."
The 250 caves hold more than 50,000 statues of Buddha dating to the 5th century, their heights ranging from less than an inch to 56 feet.
Authorities relocated nearby factories and rerouted truck traffic in 1998. But much of the coal dust has been left on the statues, for fear that the sandstone might not survive a cleaning.
As visitors weave in and out of the caves, the damaged statues are easy to pick out. Their red, blue and yellow paint is faded, and they look as if they are wearing a black trench coat or skirt.
"As you can see, the statues are dirty and it's from coal of course," said Ren Yun Xia, a 21-year-old student from nearby Linfen. "It upsets me. But the whole world is developing and you can't avoid this kind of pollution."