China's pollution problem is not new. But despite some signs of hope, air pollution continues to plague much of the country, particularly the northeast.
One recent study, published in the journal PLOS One, found that air pollution is linked to about one in six premature deaths, killing 1.6 million Chinese a year.
In China, PM 2.5 levels tend to peak during the winter months, and local officials linked the pollution in Shenyang to the fact that city recently switched on the heat.
But the advent of winter - and the start of heating season - comes as no surprise, which led many Chinese to question why officials did not do more to prevent the seasonal surge.
On Chinese social media, people vented about the even-worse-than-usual weather, worrying about the prospect of lung cancer and lamenting the limits of the state response. "Waiting for the wind to change is how the Government deals with air pollution," one person wrote.
China's leaders say they share the concern and have vowed, repeatedly, to wage war on bad air. In November last year, as China welcomed world leaders to an Apec summit, President Xi Jinping conceded that he checked pollution readings every day.
"These days the first thing I have been doing after getting up in the morning is check how Beijing's air quality is and hope there is less smog so that all these guests from distant places will feel more comfortable," he said in a televised speech.
His team managed to clear the air for visiting dignitaries.
Not so in Shenyang.
