An aerial view of Datong city, Shanxi province, on May 17, 2017. Datong once heavily depended on its coal industry and was known as China's "capital of coal" as demand for energy took off in the 1980s. Despite a short economic boom, Datong experienced economic and environmental woes in the 21st century because of its  heavy dependence on coal, when the country's industrial transformation began and its local environment increasingly deteriorated. To improve the local environment, Datong residents have persisted in planting trees over the past decades, which subsequently propelled the city into the top position for air quality in recent years among cities in Shanxi province. [Photo/Xinhua]