Aerial photo taken on Oct. 18, 2019 shows tourists strolling in Yunlong Lake Tourist Area in Xuzhou, east China's Jiangsu Province. Once faced with the worst air pollution of any city in China, Xuzhou has had to turn its back what has nourished its economy for 130 years: coal. Following an economic transformation, Xuzhou has become a "garden city" with a greener economic base. (Xinhua/Ji Chunpeng)