China's top environmental watchdog reiterated its zero-tolerance policy against falsifying environmental monitoring data on Monday, summoning the head of Linfen, Shanxi province, after discovering that air quality monitoring had been altered for almost a year.

Six automatic air quality monitoring stations in Linfen were tampered with more than 100 times from April 2017 to March this year, resulting in severely inaccurate monitoring data.

It was an intentional criminal activity that was well organized and planned, the Ministry of Ecology and Environment said, as it summoned Liu, according to a statement from the ministry.

The false data not only misled decision-making on environmental policies but also infringed upon the public's right to know and severely damaged the credibility of the government, the ministry said.

As required by the central authorities, local government heads should be responsible for establishing a mechanism to prevent manipulation and falsification of environmental data and also develop a penalty mechanism.

Heads of Linfen, however, failed to establish such mechanisms and didn't attach adequate importance to the work, even though someone had previously been detained for interfering with environmental monitoring in the city.

The Linfen government has been ordered to rectify the problem and report to the ministry and the Shanxi provincial government before Sept 30.

Liu said his government will draw a lesson from the incident and make every effort to rectify the problem, the ministry said.

In March 2017, Zhang Wenqing, former head of Linfen's environmental protection bureau, asked an official to find ways to "beautify" air quality data in the city, which was in the spotlight because of its frequently alarming concentrations of sulfur dioxide.

In January 2017, the Linfen government was summoned by the ministry for contributing to air pollution.

The perpetrators were promised 3,000 yuan ($460) per month and were given masks, hats, helmets and gloves to hide their identities.

On May 30, a court in Jinzhong, Shanxi, sentenced five people－including Zhang－to prison sentences of six months to two years for tampering with air quality monitoring equipment and falsifying data.

Another 11 people, who had been found guilty of "damaging the computer information system", received four-to six-month terms in a detention house.