Chinese authorities have arrested five local officials after they reportedly stuffed cotton gauze into sensors used to monitor pollution in an attempt to improve air quality readings.
The environmental officials also allegedly tampered with monitoring equipment to alter the results of pollution readings in the northern city of Xian, according to local media reports.
China has vowed to wage a "war on pollution," with Beijing setting targets for local governments to curb smog levels.
The collated emissions data is also being used to identify and punish high-polluting business, although ensuring the information is reliable has proved to be a challenge.
An official from the Environment Protection Bureau in Xian's Chang'an District told the U.K.-based newspaper The Telegraph that local police had detained a group of officials in an investigation into tampered air quality data.
According to the state-owned Global Times newspaper, officials in charge of environmental protection blocked the sampling equipment in an attempt to make the data "look better" and avoid penalties for high pollution in their area of responsibility.
Readings of PM 2.5, which are toxic microscopic particles that penetrate deep into the lungs, have been reported to decrease by 30 percent to 50 percent if cotton is used to cover the air monitoring equipment, an expert cited by the Beijing News as saying.
"Data fraud severely impacts the public's right to know, and air quality data is an important measuring index used by environmental protection bureaus to make decisions," Ma Jun, a Chinese environmental activist, told The Telegraph.
China's Ministry of Environmental Protection (MEP) has promised to crack down on false air quality readings, but cases of falsified date have been reported in the past.
In 2015, local Chinese media reported officials in the northern city of Hanzhong had been altering PM 2.5 readings by spraying the sampling equipment with water from a fire hose.
Pollution has been a major issue in China, with Party leaders repeatedly saying they are making efforts to deal with the toxic haze affecting large swathes of the country.
Approximately 1.6 million people are estimated to have died each year in China as a result of pollution.
"Citizens have a right to know about the quality of the air they breathe, in order to protect their and their family's health. Reliable data is the very starting point of China's 'war on pollution,'" said Dong Liansai, a climate and energy activist with Greenpeace East Asia.