"Within 10, 20, or 100 years, these hieroglyphics will disappear if we don't do anything about it," Bravo said.
Bravo and his colleagues spent several years simulating the effects of polluted air and acid rain on El Tajin's soft limestone buildings.
He blamed the erosion on contaminants like chlorine, sulfates, and nitrates in the air from power stations and oil refineries.
Acid rain causes erosion on ancient monuments because the sulfuric and nitric acid chemically reacts with the calcium carbonate in the stones to create gypsum, which then flakes off.
Acid rain forms when pollutants in the air become trapped inside water droplets in a cloud. The pollution is then carried down to earth with the rain.
"The Veracruz region has some of the highest acid levels in the air in Mexico," Bravo said.
Other scholars expressed similar alarm at the detrimental effects of pollution on El Tajin.
"The art of El Tajin is crucial to our understanding of the ancient history of the Gulf coast," said John Machado, a pre-Columbian art historian at Chaffey College in Rancho Cucamonga, California.
"It gives evidence of a powerful and complex civilization that had broad interaction with Mesoamerican cultures in both central Mexico and Maya-controlled regions but still cultivated its own unique Veracruz style and iconography."
"The loss of these images would be devastating to the cultural heritage of the area," said Machado, who has done extensive research at El Tajin.
But the problem of pollution affects archaeological sites throughout Mexico.
The sources of degradation vary, said Maria Lourdes Gallardo, chief conservator at the main Aztec temple, Templo Mayor, in Mexico City.
"The pollutants in the archaeological zone of Templo Mayor range from the smog to water filtrations underground," Gallardo said.
"We found that there had been a significant change in the rate of pollutants derived from sulfur, which had diminished considerably, compared to an increase in the quantity of chloride and heavy metal pollutants."
(Read related story: "Aztec Temple Found in Mexico City 'Exceptional,' Experts Say" [October 5, 2006].)
David Grove, a professor emeritus of anthropology at the University of Illinois at Urbana-Champaign, has worked extensively at the site of Chalcatzingo in Morelos, 60 miles (97 kilometers) south of Mexico City.
The site is noted for its Olmec-style bas-relief carvings dating back to 700 B.C. in granodiorite, a rock much harder than limestone.
"I can document with 30 years of photographs just how acid rain is destroying those magnificent works of art," he said. "The details are slowly disappearing."
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