A bird’s-eye view of Yuquan Mountain Forest Park and its reservoir. [Photo provided to chinadaily.com.cn]

Zhang's decision to adopt the mountain also traces back to his deep bond with trees in childhood. A primary school dropout, Zhang worked as a forest ranger for about six years before joining the army. "That's how I developed my love for trees," Zhang recalled.

Zhang left the army in 1998 and started his business a year later, capitalizing on the area's rich, cheap coal resources. Zhang's heating company held the lion's share of the city's heating market during its heyday.

However, the Taiyuan government turned to greener power such as natural gas for building the city's central heating system a decade later, posing a threat to Zhang's business.

"My company, like many others, had polluted the city for so long. It's about time for us to make up for our mistakes and make our city green and clean again," said Zhang. "That's what I thought at the time."