Spatial and temporal changes in microclimate affect disease distribution in two ancient tombs of Southern Tang Dynasty

Two tombs of the Southern Tang Dynasty (Qinling Tomb and Shunling Tomb), the most important cultural heritages in China, were built for emperors 1000 years ago and decorated with murals and stone sculptures. After their excavation in the 1950s, it was found that drastic fluctuations in the environment within the tombs had caused multiple diseases, such as salt efflorescence, powdering, and biodeterioration, which led to irreversible damage to the murals. This research comprised long-term (yearly) environmental monitoring and short-term (monthly) investigation into the distribution of salt crystallization and microbial growth within the two tombs. The objective was to unveil the relationship between the temporal and spatial distributions of the mural diseases and environmental characteristics while proposing a promising environmental regulation strategy for relic conservation. The results showed a gradual reduction in temperature fluctuation from the entrance to the back chamber and a distinct vertical stratification in relative humidity. The relative humidity in the upper areas of the tombs reached 100% during summer, while it averaged around 40-50% in the lower areas during winter. Consequently, significant condensation was observed on the ceiling in summer, whereas salt crystallization occurred on the murals in the lower space in winter. The distribution of these diseases was influenced by the airflow exchange between the interior and exterior. Furthermore, the structural disparities between the two tombs contributed to higher relative humidity and greater microorganism coverage in the Shunling Tomb compared to the Qinling Tomb. From the abovementioned findings, we suggest that microclimate control is essential for mitigating mural deterioration and should be paid more attention in the future.