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.
"It was difficult for the central government's law enforcers to collect evidence of violations when they make inspection trips outside of Beijing, because locals easily recognise them and polluting factories swiftly suspend production, leaving few traces," said Yang.
The environment ministry recently sent 12 inspection teams to Hebei. A recent report by Southern Weekly said the inspectors were often intercepted by local officials and guided throughout their trips so they could be kept away from some of the biggest pollution hotspots.
"The drones, on the contrary, can catch them off-guard as few people notice their existence," Yang added.
In the fleet's more than 30 flights, numerous violations have been found: an oil refinery in Guangxi had illegally expanded; forests in Hainan had been felled for a mining project; and contractors building the high-speed rail link between Wuhan and Guangzhou had failed to clean up construction waste along the route.
Yang said there was no plan to expand the fleet because of a shortage of flight controllers.
Slow progress in opening up airspace under 1,000 metres had also obstructed the large-scale application of the drones, added Yang.