Tourists experience drifting along a canyon at a scenic spot of Wushan County, one "natural oxygen bar," in southwest China's Chongqing, June 30, 2017. As more and more Chinese people are choosing to visit places that have fresh air, thick forests and are rich in negative ions, ecotourism becomes a fresh favoured choice across the country. According to a report by the China Meteorological Service Association, trips to the regions granted as "natural oxygen bars" by the association surged over 200 percent year on year in 2018. (Photo: Xinhua)

A tourist visits the Tianchi Lake in Arxan, one "natural oxygen bar," north China's Inner Mongolia Autonomous Region, Aug. 5, 2018. As more and more Chinese people are choosing to visit places that have fresh air, thick forests and are rich in negative ions, ecotourism becomes a fresh favoured choice across the country. According to a report by the China Meteorological Service Association, trips to the regions granted as "natural oxygen bars" by the association surged over 200 percent year on year in 2018. (Photo: Xinhua)

Cycling lovers ride bikes in Arxan, one "natural oxygen bar," north China's Inner Mongolia Autonomous Region, May 20, 2018. As more and more Chinese people are choosing to visit places that have fresh air, thick forests and are rich in negative ions, ecotourism becomes a fresh favoured choice across the country. According to a report by the China Meteorological Service Association, trips to the regions granted as "natural oxygen bars" by the association surged over 200 percent year on year in 2018. (Photo: Xinhua)

Tourists go sightseeing on a transparent horseshoe-shaped cantilever bridge at the Yunyang Longgang Geological Park, one "natural oxygen bar," in Chongqing, southwest China, April 14, 2018. As more and more Chinese people are choosing to visit places that have fresh air, thick forests and are rich in negative ions, ecotourism becomes a fresh favoured choice across the country. According to a report by the China Meteorological Service Association, trips to the regions granted as "natural oxygen bars" by the association surged over 200 percent year on year in 2018. (Photo: Xinhua)

Tourists enjoy themselves in Xiayu Village of Yinkeng Township in Kaihua County, one "natural oxygen bar," east China's Zhejiang Province, Aug. 25, 2018. As more and more Chinese people are choosing to visit places that have fresh air, thick forests and are rich in negative ions, ecotourism becomes a fresh favoured choice across the country. According to a report by the China Meteorological Service Association, trips to the regions granted as "natural oxygen bars" by the association surged over 200 percent year on year in 2018. (Photo: Xinhua)

Photo taken on July 11, 2017 shows tourists visiting the Qixing Lake Scenic Area of the Saihanba State Forest Park in Weichang Man and Mongolian Autonomous County of Chengde City, one "natural oxygen bar," in north China's Hebei Province. As more and more Chinese people are choosing to visit places that have fresh air, thick forests and are rich in negative ions, ecotourism becomes a fresh favoured choice across the country. According to a report by the China Meteorological Service Association, trips to the regions granted as "natural oxygen bars" by the association surged over 200 percent year on year in 2018. (Photo: Xinhua)

People do morning exercise at the Qingmuchuan ancient town in Ningqiang County of Hanzhong City, one "natural oxygen bar," northwest China's Shaanxi Province, March 19, 2019. As more and more Chinese people are choosing to visit places that have fresh air, thick forests and are rich in negative ions, ecotourism becomes a fresh favoured choice across the country. According to a report by the China Meteorological Service Association, trips to the regions granted as "natural oxygen bars" by the association surged over 200 percent year on year in 2018. (Photo: Xinhua)

Girls play among blossoming flowers in Liuba County of Hanzhong City, one "natural oxygen bar," northwest China's Shaanxi Province, July 12, 2019. As more and more Chinese people are choosing to visit places that have fresh air, thick forests and are rich in negative ions, ecotourism becomes a fresh favoured choice across the country. According to a report by the China Meteorological Service Association, trips to the regions granted as "natural oxygen bars" by the association surged over 200 percent year on year in 2018. (Photo: Xinhua)