Forests have sanitary influences upon environment through the degradation and purification of sulfur dioxide, fluoride and nitrogen oxides as well as solid dust and heavy metal ions by the forest ecosystem after absorption, filtration, blocking and decomposition. Forests also help reduce noise and release negative ions and terpenoid substances (e.g. phytoncide) to improve the air quality. In brief, forests can absorb air pollutants, block dust away, increase negative oxygen ions in the air, and reduce noise.

Negative ions in high concentrations have powerful health benefits. They are good for lung, myocardial mechanics, autonomic nerves, sterilization, and can activate a variety of enzymes in the body. Therefore, negative ions are reputed as “Air Cleaners” and also called “Vitamins of Air”. At present, the concentration of negative air ions in the air has been regarded as an important parameter to measure air quality.

Medical studies have shown that negative ions, with the concentration reaching over 1,000 ions/cm³, can prevent or treat diseases; if the concentration stands at around 500 ions/cm³, they can meet the basic needs for health; about 200 ions/cm³ can merely secure a minimum threshold of physical health, putting people at the risk of sub-health problems; and in the case of less than 50 ions/cm³, physiological disorders, diseases or even cancer may occur. The normal concentration of negative ions for fresh air is 1,000-1,500 ions/cm³, according to the World Health Organization.

The lush tropical rainforest in Hainan makes this place a natural oxygen bar and a perfect destination for travel, leisure and rehabilitation. The mean concentration of negative ions in tropical rainforest areas such as BaWang Ling, JianFeng Ling, WuZhi Shan and DiaoLuo Shan reaches 6,000 ions/cm³, and the transient peak can even amount to 110,000 ions/cm³, 35-220 times more than that of the urban areas in Guangzhou.