The Ministry of Environmental Protection found 11 companies in Handan of Hebei province had been emitting excessive pollutants into the air during the night throughout March, thanks to drone inspections, which will play an increasing role in pollution inspections, the supervision bureau head said on Monday.

Since September, a coal chemical plant in Handan city did not use its dust-removing facilities as stipulated for 43 nights , thinking they could escape daily inspection by the authorities. However, data and statistics collected by drones revealed this, the ministry said.

As a result, two managers of the plant have been detained for 15 days, and the plant has received a fine of 50,000 yuan ($8,000) for pollution.

Besides, the deputy head of the county government where the plant is located has been punished for not controlling the pollution.

Drones will play an important role in inspecting polluting companies for the ministry, becoming regular inspection tools and controlling pollution more efficiently, said Zou Shoumin, head of the supervision bureau under the ministry.

In addition to inspection from drones, the ministry has also conducted inspections in 52 cities of 17 provinces and municipalities in March, exposing 88 cases of pollution control violations such as illegal emissions from companies and excessive vehicle exhausts.