The city of Linfen in Shanxi province has put stricter controls on emissions of sulfur dioxide, including suspending production at many coal-consuming plants, after residents experienced another bout of alarmingly high pollution on Saturday.

The high level of coal consumption is considered a major source of sulfur dioxide, experts sent by the provincial government and the Ministry of Environmental Protection said after they conducted three days of thorough investigations at plants and heating service providers.

Annual coal consumption increased to 36.6 million metric tons in 2016, up from 30 million tons in 2013, they said, despite many other northern cities cutting consumption.

The city previously said that 70 percent of sulfur dioxide emissions came from households, which drew questions from many residents.

Zhao Suli, a researcher at the city's environment bureau, said coal consumption by households is small, but they discharge sulfur dioxide directly into the air, making them a major source of pollution, according to a report by China News Agency on Monday.

The experts also exposed the failure of governments to promote clean coke for households, and massive violations of rules by some plants that do not operate equipment as required.

The city said it has adopted the experts' suggestions, including replacing low-quality coal and controlling total coal consumption.

Two monitoring stations showed the concentration of sulfur dioxide exceeded 1,000 micrograms per cubic meter at 8 pm on Saturday, the fourth time it has hit that mark since Jan 4, according to data from the China National Environmental Monitoring Center.

The national standard is 60 micrograms.

The World Health Organization said high levels of sulfur dioxide could harm the respiratory system.

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