Research on composite evaluation index of karst cave health effects: A case study of Tianyuan cave in Hongguoshu area of Guizhou

Air negative anion, known as "air vitamin", has biological effects such as regulating nerve centers and promoting metabolism, and is beneficial to physical and mental health. At the same time, negative ions also have antibacterial and bactericidal effects. The content of negative ions in Karst caves is high, and clean air in the cave is also created. Karst cave's natural health care is a series of activities that are beneficial to physical and mental health based on the cave environment and microclimate.It has more leisure and health care functions than speleotherapy. This paper uses index analysis method to select human climate comfort, air cleanliness and air anion enrichment from the perspective of human feeling and environmental hygiene to construct the cave health function index (CRFI), the weights of the three indicators are 0.142, 0.286, 0.572. The evaluation results of the cave health function index were divided into four grades, above 0.8 is very suitable for health activities, and less than 0.2 is not suitable. According to Tianyuan cave environment monitoring data from August 2017 to July 2018, found the cave within the annual average temperature of 14 ℃, relative humidity of 88.88%, human body comfort level is relatively low. The annual radon concentration in the cave is 610.26 Bq.m-3, which meets the international radiation safety requirements. Positive and negative ions content have a significant change in time and space, and negative ion concentration spatial distribution takes TY-4 underground lake as the center and gradually decreases towards two holes of the cave. Air negative ions content is higher in the whole cave from April to September, and the air cleanliness index are higher than 1.00, belongs to the most clean air, very beneficial to human body health. From December to January, the negative ion content in each monitoring site was less than 1,000?cm-3. The health function index of Tianyuan cave shows that the best health care time is may and September, and the best health care site is near the underground lake of TY-4, and only December and January are not suitable for cave health activities.