Single-sided natural ventilation in deep caves: field evidence and implications for microclimate management at the Mogao Grottoes

Door opening is a common low-intervention strategy to regulate cave microclimates, yet its effectiveness in deep caves remains poorly understood. This study investigates the ventilation behavior of 12 representative caves at the Mogao Grottoes through field experiments, combining multi-point measurements of air velocity, temperature, and humidity with CO 2 tracer-gas decay tests across different seasons. Results show that single-sided natural ventilation is highly spatially constrained, decaying rapidly with depth and leaving the main chamber nearly stagnant. A persistent bidirectional flow structure exists at the doorway, driven by wind and thermal pressures. Open-door air exchange rates reach 9–13/h, whereas closed-door infiltration drops to 1.6/h. Ventilation intensity depends heavily on indoor–outdoor temperature differences and opening sizes. These findings demonstrate that door opening does not ensure whole-space ventilation, providing a quantitative basis for the preventive conservation of grotto heritage.