Airborne Pollutants in the Buddhist Cave Temples at the Yungang Grottoes, China

The Buddhist cave temples at the Yungang Grottoes, , experience rapid soiling due to the deposition of particles. Contributing sources include coal and combustion, fugitive road dust, and regional storms. Both particle and gas-phase air pollutants characterized at that site. Annual average coarse (diameter, d_p > 2.1 µm) particle concentrations outdoors 378 µg/m^3, increasing to more than 1200 µg/m^3 peak 24-h periods. These coarse airborne particles crustal dust (e.g., soil dust; over 80% of coarse ) and carbon-containing particles (10 % ). Fine airborne concentrations (d_p ≤ 2.1 µm) outdoors average 130 µg/m^3 and consist mainly of carbon-containing particles (45.5%) and crustal dust (24%). Airborne particle concentrations inside cave 6 average approximately 60% of those outdoors. SO_2 is the principal gas phase air pollutant averaging 31 ppb outdoors and 19 ppb inside cave 6 over the year studied. Other pollutant gases are present at lower average concentrations: NH_3 (4-10 ppb), NO_2 (4-6 ppb), HNO_3 (0.1-0.2 ppb), and HC1(<0.1 PPb).