Five officials in the northwestern Chinese city of Xian have been detained after they were found to have tampered with air quality monitoring equipment and to have falsified data, official media reported.
The move comes as the ruling Chinese Communist Party tries to set up a real-time air pollution monitoring system in the face of widespread falsification of data, state news agency Xinhua reported.
Falsification of data was included as an offense in environmental legislation that went into effect at the start of the year, in a bid to address the "airpocalypse" smog that chokes cities in northern and eastern China in winter.
Five officials are facing charges after staff at a local monitoring station were accused of stuffing sensors with cotton to lower emission readings and removing surveillance camera recordings to eliminate evidence of malpractice, the report said.
Veteran Xi'an journalist Ma Xiaoming said a culture of fakery is all-pervasive in China's bureaucracy.
"They'll stop at nothing, putting fake figures in their reports to get past inspections," Ma said. "All I feel about this is anger about why there has been no tangible improvement in China's environment."
"There is considerable investment in environmental protection in China, but all you get out at the other end is fakery and more environmental damage," he said.
"And that is damaging to everyone who is in that environment."
According to the World Health Organization (WHO), more than a million people in China died untimely deaths because of air pollution in 2012 alone.
China's cabinet, the State Council, announced on Tuesday that it would set up the "strictest environmental protection system" to oversee construction, noise and atmospheric pollution, soil and water quality, and the rural environment.
The plan is to identify high-risk pollution zones and establish a unified disclosure platform for environmental information, according to the "Healthy China 2030" plan.
The U.S. Embassy in Beijing, which monitors air pollution unofficially, tweeted that PM2.5 particulate matter concentrations were at "unhealthy" levels on Thursday, before improving to "moderate" levels later in the day.
Long-time environmental activist Cui Sheng said the Xi'an detentions are likely just the tip of the iceberg.
"This isn't just an isolated case," Cui told RFA. "There's a pollution monitoring station right next to me which is run by the environmental protection department, and it's surrounded by water sprinklers so as to influence the figures."
"I guess they had no way of interfering with the electronics under the cover," he said.
He said the central government has taken back control of some environmental monitoring stations after local officials meddled with the results by computer.
"The local officials now have no way to mess with [the equipment], so they resort to manual operations," Cui said. "This is happening everywhere."
'Brink of collapse'
But he said the data isn't the most important factor at work. "The entire environmental protection regime in China lacks credibility; it's pretty much on the brink of collapse," he said.
The central government's Ministry of Environmental Protection has hit out repeatedly at local governments for hiding the true pollution figures.
It said in June that local governments "act as both the player and the referee" when it comes to monitoring emissions, and that "administrative interference" is on the increase.
A recent inspection in the northern province of Hebei found that a polluting coking plant had also tampered with emissions-monitoring equipment to avoid sanctions.
Greenpeace campaigner Dong Liansai told Agence France-Presse that the detentions in Xi'an should serve as a warning that Beijing is serious about punishing such practices.
"The [ministry] must continue to investigate such cases of falsified readings and ensure that local governments fully implement central government policy," Dong said.
Reported by Yang Fan for RFA's Mandarin Service, and by the Cantonese Service. Translated and written in English by Luisetta Mudie.