Lanzhou in north-west Gansu ranked last, while Haikou on southern Hainan island was rated with the cleanest air.
In 2008, he was convicted by a court in the western province of Gansu, where the sarcophagus was from.
BBC: Belgian art dealer convicted of smuggling in China dies
Guan Yiquan, a Chinese scholar in Lanzhou, the capital of Gansu, also became convinced that Liqian had links to Rome.
Eager to escape Beijing, he volunteered for a post at the Liujiaxia Hydraulic Power Plant in the northwestern province of Gansu.
In Ningxia, Gansu and Inner Mongolia, for example, they are drawing far more than their fair share of the Yellow River's water.
In Gansu and Qinghai Provinces and throughout north-central China, people of nine different ethnic groups share a music tradition known as Hua er.
Dubs says the Chinese kept the ex-legionaries as frontier guards, installing them in a specially created town called Liqian in what is now Gansu.
He had come the way I had, from Xian, 1, 600km westward down the Gansu corridor between the wastes of the Gobi and the cold heights of the Qilian Shan.
The story begins in 1992, when an army unit from Lanzhou in neighbouring Gansu province, drilling with state permission, made a decent oil find in Jingbian county.
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Raedemaeker was initially held in Gansu but was later allowed to live with his partner in a Beijing hotel because of his poor health, media reports say.
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In the north Ningxia, Shanxi, Hebei and Gansu are drought-stricken.
Wind power is also being experimented with in a small way for power generation in northern and western China, where it could supply electricity to rural villages in windswept and increasingly arid Inner Mongolia and Gansu Province that are still not on the grid.
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