On the roads into Baiyin's downtown area, countless small and medium-sized abandoned factories, all with their distinctive high chimneys, stand shoulder to shoulder, covered by thick dust. In winter, the leafless trees and grassless soil give the impression that the outskirts have been painted gray.

In a small, abandoned factory near the city center, four workers were using a plastic drum to remove acid from a large cement pool. They were reluctant to give their names, but said the factory, built 40 years ago, closed in 2012. Most of the facilities are in a state of advanced disrepair. The containers are stained light and dark yellow, indicating that the acid they contain has been leaking for some time.

The factory was one of more than 50 the city government forced to close last year. Early this year, the provincial government approved a budget of 150 million yuan to treat emissions. All the local highly polluting factories were given a stark choice - they could either close or they could improve their waste-recycling systems and update the old facilities to make them environmentally friendly.

In Lanzhou, 5 billion yuan was invested to tackle pollution from 2006 to 2010. A new gas heating system reduced the annual consumption of coal by 650,000 metric tons, almost entirely eradicating the use of the fuel in the downtown area. The airborne concentration of sulfur dioxide was reduced by 20 percent, as was the concentration of inhalable particulate matter. Nearly 70 small and medium-sized factories will be relocated to the suburbs by the end of this year and 13 other highly polluting factories will be closed. Within a year, coal-fired heating will be totally eradicated from the city center.

To meet national environmental protection standards, the provincial authorities have rebuilt or upgraded the facilities at 135 factories. Statistics from Gansu Environment Protection Department show that in 2012 sulfur dioxide emissions fell by 56,2000 tons and nitrogen oxide by 23,600 tons. The effect has been an increase in the number of blue-sky days. Compared with 2011, the five Gansu cities under special supervision recorded a higher number of days with good air quality in 2012. Baiyin registered 41 extra blue-sky days, while Jiayuguan saw an extra 86.

The moves to improve the quality of the air are having a positive effect and the locals realize the process will be long and arduous, but ultimately worthwhile.

"There used to be a saying: 'If you stay in Baiyin for three years, your teeth will no longer be strong enough to eat beans," said the former metals worker Zhao, "I really hope that saying will be thrown into the dustbin of history before I die."