China uses cameras on drones to catch industrial polluters unaware

The mainland's environmental watchdogs have long been criticised for their alleged lax supervision of industrial polluters. Even when the agencies did crack down, their inspections were obstructed by local officials.

Now the Ministry of Environmental Protection is mobilising a fleet of drones to record images of factories discharging untreated pollutants into the atmosphere. The drones can fly virtually undetected.

Three videos shot last month over the cities of Tangshan , Xingtai and Handan in Hebei , three of the mainland's most polluted cities known for their steel mills, cement factories and coal-fired power stations, explain why smog has hung so persistently over the region.

"You can easily tell from the colour of the smoke - black, purple and brown - that the pollution is over the limit, because if smokestack scrubbers are operating properly, only white smoke is emitted," said the ministry's Yang Yipeng, showing pictures from the flight over Tangshan. "There were too many chimneys like these, and the drones also captured pictures of flames in the open air … and that is still only the tip of the iceberg."

According to Yang, the ministry's four drones, introduced in 2012 at a cost of around 8 million yuan (HK$10.1 million), are used primarily to gather evidence of environmental breaches, to monitor pollution following accidents, and to evaluate the performance of local governments in protecting the environment.

The high-resolution images were used as evidence against polluters who breached emission limits, he said.