GUANGZHOU, April 2 -- Unmanned aerial vehicles (UAVs) are playing an increasingly important role in China's battle against pollution.

During the latest air pollution inspections in Beijing, Tianjin, Hebei Province and surrounding areas, law enforcement officials of the Ministry of Environmental Protection deployed UAVs to check key places.

UAV's were responsible for the discovery of at least one environmental violator in Hebei's Handan City, where the air quality ranks among the worst in China. Two outdated pieces of machinery were found hidden in the Hexin Iron and Steel Company factory. Government inspectors came to the site immediately.

The sintering machines exceeded emissions standards and operation should have stopped before the end of 2013. Workers were also found improperly operating the desulfurization facilities installed in the machines, an inspector said.

Six enterprises including Hexin were found violating pollution control guidelines during the inspections.

With strong determination to fight pollution, UAVs have been frequently used to monitor pollution discharge and the operation of desulfurization facilities of companies related to steel, coking and electricity industries.

As a manufacturing hub, Foshan City of south China's Guangdong Province houses 40,000 sources of industrial pollution and nearly 900 industrial parks scattered in different villages, which are difficult to supervise.

The long-standing problem has pushed Foshan to seek innovative ways to prevent and treat pollution.

When law enforcement officials enter a plant, often illegal behaviors are stopped, making it hard to collect evidence, said Peng Cong'en, head of the city's environmental protection bureau.

The UAVs used for environmental protection collect information with installed remote sensors, including digital cameras in high resolution, infrared and laser scanners and magnetometer. Some are even installed with infrared thermal imager which can show the operation of facilities at night.

Peng told Xinhua that the drones can provide video evidence and record the law enforcement process. "In this way, polluting firms fail to conceal their illegal behaviors," he said.

In addition to Foshan, China's Jilin Province also uses UAVs to monitor the Mudanjiang River, a major waterway in northeast China, in a move to ensure water security.

East China's Zhejiang Province uses UAVs to supervise factories and prevent them from stealthily pumping waste water into rivers or lakes.

UAVs bring a new trend to environmental protection. They also provide technical support in dealing with major environmental emergencies as well as assessment for construction projects, said Wang Qiao, an engineer with the Satellite Environment Center.

Wang said a new system, which could monitor the types, density and diffusion process of pollutants with the help of UAVs once emergencies happen, will be put into use soon.