"Despite a red alert for bad weather, the cities failed to enforce emergency measures to reduce emissions ... which missed the opportunity to ease pollution," the MEP said in a statement on Tuesday.
The cities of Harbin, Jiamusi, Shuangyashan and Hegang were covered in a blanket of chocking smog on Oct.18-20, with concentrations of hazardous particles, known as PM 2.5, reaching over 400 micrograms.
China's official air quality standard is 35 micrograms, while the recommended level set by the World Health Organization should be no more than 10 micrograms.
To combat air pollution, Beijing has issued guidelines for temporary measures to curb emissions. Some industrial plants in the steel, aluminium, cement and ceramics sectors in northern part of the country were asked to limit production by up to 50 percent during the winter season.
Illegal crop straw burning, which was believed to be the main cause of the air pollution in four cities, was detected by the MEP using remote satellite sensors during the night.
The MEP also found utilisation data for crop straw in the cities had been forged. Almost 90 percent and 70 percent of the data reported by Shuangyashan and Hegang respectively in 2016 was found to have been exaggerated.
Some coal-fired power utilities such as plants controlled by state-backed China Huadian Corporation and Harbin Hatou Investment Co as well as some steel mills and coal producers were found not to be enforcing capacity cuts during red alerts.
Officials at the four cities have been given 20 working days to make improvement plans, the MEP said.
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