Morphology and elemental composition of dustfall particles inside emperor qin's terra-cotta warriors and horses museum

Indoor dustfall samples were collected in Pit 1 and Pit 2 of Emperor Qin's Terra-cotta Warriors and Horses Museum in Xi'an, Shaanxi Province, China. The morphological and elemental analysis for long-term (>10 years) and short-term (∼0.5 year) dustfall particles and lacquer pieces on the faces of partly assembled warriors were performed with scanning electron microscopy with energy dispersive X-ray spectrometer (SEM/EDX). The results showed that the majority of dustfall samples appeared to be composed of mineral dust particles, fly ash, and biological particles with different elemental compositions. Most of the mineral particles had irregular shapes with smooth edges. Small floccules of calcium sulfate were more frequently observed in long-term dustfall samples than in short-term samples, implying a progressive chemical reaction between continuous dustfall particles and atmospheric sulfur dioxide. Crystals of calcium sulfate were also found near pits on both inner and outer surfaces of lacquer pieces, revealing an acid chemical reaction between sulfur dioxide and lacquer material as the cause of the formation of erosion pits and cracks on surface of lacquer pieces.