Yungang is located approximately 16km west of the industrial city of Datong near the Inner Mongolian border in northern Shanxi Province, China.

The left photo above shows a cave carving after cleaning in 1986. On the right, the same carving photographed in 1991 shows a visible buildup of deposits, especially on upward-facing horizontal surfaces.

Our research group undertook a study entitled, "Protecting the Yungang Grottoes from Air Pollution Damage" in 1991. Here are some photos of the group.