Influence of some climatic elements on radon concentration in Saeva Dupka Cave, Bulgaria

This study reveals the influence of some climatic elements on radon concentration in Saeva Dupka Cave, Bulgaria. The research is based mainly on statistical methods. Radon concentration in the cave is determined by two main mechanisms. The first one is through penetration of radon from soil and rocks around the cave (present all year round, but has leading role during the warm half of the year). The second one is through thermodynamic exchange of air between inside of the cave and outside atmosphere (cold half of the year). Climatic factors that affect radon concentration in the cave are temperatures (air, surface, soil) and amount of water, expressed by precipitation or by volumetric water content in the soil. In the cold half of the year, an important factor is the duration and depth of snow cover. Statistical models and projections show that by the year 2070 CE radon concentration in the cave will increase. This increase will occur primarily in the warm half of the year due to the increase in outside air temperatures that will decrease thermodynamic exchange of air between the cave and the atmosphere. By the middle of the 21st century, it is expected that the studied area will no longer have a permanent snow cover and the temperature will remain the only factor for the increase of radon concentration in the cold half of the year. Water content in the soil and precipitation are important factors for radon concentration in the cave, but they have no significant trend and they are not expected to exert any influence in the next 50 years. The projected increase of radon concentration in Saeva Dupka Cave creates a serious risk for the health of the tour guides working there. That is why it is necessary to develop a plan to protect the health of the cave staff. On the other hand, the projected increase of radon concentration does not pose any significant health risk for the tourists visiting the cave