FATE OF ATMOSPHERIC PARTICLES WITHIN THE BUDDHIST CAVE TEMPLES AT YUNGANG, CHINA

The Yungang Grottoes are a collection of manmade cave temples dating f rom the 5th century A.D. that now are situated in the middle of one of China's largest coal mining regions. Air pollutant particles enter th ese caves and deposit onto the more than 50 000 stone carvings contain ed within the caves, leading to rapid soiling of the sculptures. In or der to study this problem, computer-based models have been combined th at simulate the air flow into the caves and particle deposition within the caves. The evolution of the airborne particle concentration and s ize distribution is tracked as outdoor air is drawn into the caves by a natural convection flow that is driven by the temperature difference between the outdoor air and the interior walls of the caves. Particle deposition rates are computed from the boundary layer flows along the surfaces within the caves. Predicted coarse airborne particle (diamet er > 2.3 mu m) size distribution and coarse particle deposition fluxes to horizontal surfaces within caves 6 and 9 at Yungang compare closel y to experimental observations made during the period April 15-16, 199 1. It is found that horizontal surfaces within caves 6 and 9 at Yungan g would become completely covered by a full monolayer of particles in only 0.3-0.5 yr under the April conditions studied here and will be so iled even more rapidly under annual average conditions. The model deve loped here can be used in the future to compute the effects of particl e filtration systems and/or altered ventilation rates on soiling withi n the grottoes.