Three Xi’an officials have been detained by police after it was found that an air quality monitoring station sampling unit in Central China had been stuffed with cotton material in an effort to cheat the sensors.

An official at the Chang’an branch of the Xi’an Environmental Protection Bureau reportedly made a copy of the key to the monitoring station and memorised the passcode to the restricted area, reported Xi’an newspaper Huashangbao. Staff then repeatedly snuck into the station to stuff cotton into the sampling unit.

The monitoring unit. Photo: The Paper.

Air quality monitors typically draw in air then measure the amount of particles present. A source familiar with the matter told the newspaper that stuffing cotton material into the sampling unit would act as an air filter.

The China National Environmental Monitoring Center (CNEMC), which is overseen by the Ministry of Environmental Protection, noticed the change in the data. Following an investigation by the police, those suspected to be involved were detained by police, reported The Paper.

Three officials at the branch were taken by police and another is on leave, it reported.

The Paper’s source said that the government punishes officials whose responsible areas are rated to be at the bottom of environmental rankings. To avoid punishment, the officials took steps to improve the air quality readings, the source said.

City wall in Xi’an. Photo: Wikicommons.

China’s vice minister of environmental protection announced a two-year inspection campaign to root out fake air quality data in April 2015. At the time, the minister accused some local governments of fabricating or tampering with air quality data and told national news agency Xinhua that monitoring stations affiliated with the ministry would help cross check data from other stations.

The Chang’an monitoring station was one of the two stations in the city that directly fed data to the CNEMC, according to the local paper’s source.

The Chang’an branch of the Xi’an Environmental Protection Bureau has not yet responded to HKFP’s request for comment.