A mountain reborn

When Zhang first visited Yuquan Mountain, then known as the most polluted area around the city, he found exposed rock faces towering like cliffs, garbage scattered on the ground, ash from coal combustion permeating the air and hundreds of crows flying around, cawing.

Excessive quarrying and mining for coal and gypsum left the mountain with nearly 200 gigantic holes.

The area was so desolate it was used as a dumping ground for household and industrial waste. There were seven major landfills, drawing countless scavengers.

What's worse, upwind of the city, the mountain could pollute as much as half of the urban area once the wind blew, sending soot and dust everywhere.

"I never saw stars or a clear sky during the first 20 years," Zhang recalled. "Standing atop the mountain, you could see the whole city was just like under a huge black pot cover, really a horrible scene."