Authorities in the southwestern Chinese province of Sichuan are clamping down on spontaneous public protests after several days of heavy smog hit the provincial capital, Chengdu. Schools have slapped a ban on face-masks in the classroom, while the ruling Chinese Communist Party's propaganda machine has issued strict guidelines on coverage of the pollution protests. And online activist Liu Ermu was detained after he penned an article protesting the government's response to air pollution in China. "I hope that soldiers and armed police will think about the fact that the people whose interests they protect have sent their families to live overseas, while their own wives and children have to breathe in this smog," the article said. "They should shake off the[mental] fog that surrounds them and act to protect their families' interests," it said. Liu's wife said he still hadn't returned by Tuesday afternoon, local time. But she declined to give an interview. "I don't want the foreign media involved," she said, before hanging up. A source close to Liu said he had been detained by officers from the Puyang police station in Chengdu's Wuhou district. "It's to do with the article he wrote about military police wearing face-masks," the source said. "The article was posted the day before yesterday ... He has been writing a lot of very cutting articles that really hit their mark." A journalist surnamed Wen said Liu is likely still being questioned inside the same police station. "It was to do with an article he wrote about the smog a couple of days ago," Wen said. An employee who answered the phone at the Puyang police station on Tuesday hung up when contacted by RFA. Students warned Meanwhile, screenshots of text messages sent out to students at Chengdu's Jiaxiang Foreign Languages School warned students not to take part in any protest activities. "Please do not believe in rumors, and do not spread them," the text message, sent on Monday, said. "You must put your trust in the government to carry out anti-pollution work." "No teachers or students in our school will wear face-masks, without exception," the message said. An employee who answered the phone at the Jiaxiang school denied that students were being forced not to wear masks, but declined to comment further on Monday. The Sichuan provincial propaganda office also issued a set of censorship instructions to the media, imposing a "unified" message on all coverage of the smog ahead of an official press conference. "Journalists invited to take part should submit scripts to the Chengdu environmental protection bureau for checking," the press conference communique, a copy of which was posted on the China Digital Times website, said. "Drafts are subject to approval and should not be rushed to publication, while headlines that encourage to speculation or negative reactions should be avoided," it said. It said all media outlets, including individual social media accounts, should only use official reports from the local government. "Do not carry out independent reporting or take photos or video," it said. Online activist Xiucai Jianghu said the government's actions are part of a coordinated "stability maintenance" strategy. "It's really draconian to ban students from wearing face-masks, but these arbitrary school rules are a response to the smog," he said. "The education minister has called for ideology to enter the classroom, and for any negative news to be excluded from it," he said. "They mustn't say anything negative about the government." Sporadic protests The clampdown follows sporadic protests, on and offline, last week that included the placing of face-masks on sculptures in downtown Chengdu, after which police threw a security cordon around the city's central Tianfu Square. Authorities in the southwestern province of Sichuan on Friday deployed riot police to clamp down on spontaneous anti-smog protests in the provincial capital, Chengdu. Chengdu residents, unused to the toxic brown haze that regularly engulfs more northern cities like Beijing, were quick to complain about the smog that engulfed their city. Police have also warned local businesses to report anyone buying bulk orders of face-masks. "You have to register[with ID] now even if you are just buying a face-mask," a local journalist surnamed Huang told RFA. "They're afraid people will use them to incite unrest." He said the authorities are more concerned about maintaining their grip on power than with the long-term health of Chinese people. "They won't allow anyone to form a unified public opinion ... They are terrified that environmental issues will become the basis for a popular movement," Huang said. "So the more public pressure they get on the environment, the more they'll suppress it, and pretend it isn't happening," he said. 'Ridiculous approach' Xiucai Jianghu said the government's approach is "ridiculous," however, and accused officials of seeking to cover up their own mistakes. "The smog is the disaster; it is fundamentally negative," he said. "How can you report smog in a positive light?" "Are we supposed to love the smog? Be proud of it? They think they can make it go away by not letting people talk about it." Police on Sunday briefly detained eight mask-wearing protesters for questioning, the Hong Kong-based South China Morning Post reported. The demonstrators were artists staging a brief sit-in after a mass protest planned for the weekend was scuppered by police, the paper said.