Tomb murals conservation in humid regions: hybrid passive-active systems for salt crystallization and condensation mitigation

Open tombs in humid regions are highly susceptible to mural deterioration driven by microclimate fluctuations, especially salt crystallization, condensation, and microbial growth. However, the effectiveness of environmental control strategies in such settings remains insufficiently studied. This study evaluates a buffer space-based environmental control system installed at Qinling Tomb, a 10th-century tomb in southern China. The system comprises three doors and two rooms, one equipped with air conditioning and a dehumidifier, regulating air exchange and incoming air properties. Compared to 2021 (pre-intervention), zones with the largest microclimatic fluctuations showed significant reductions in 2022—60% at 3.0 m in the front chamber for temperature, and 43% at 0.1 m in the back chamber for relative humidity. Moreover, the coverage of surface salt crystallization in winter and condensation in summer was reduced by ~80%. This approach provides a scalable, adaptable solution for preserving open tombs and other vulnerable heritage sites exposed to similar risks.