Image copyright Weibo/Qing Xiaojuan Image caption Qing Xiaojuan took part in the online protest campaign. The board she's holding reads: "I love Chengdu. Please let me breathe!"

It's winter in China, and that means smog - and it also means a cat-and-mouse game between online protestors and Chinese censors who feel touchy about air pollution.

Chengdu is a huge city and the capital of Sichuan province in south western China. It's particularly known for its giant pandas. But this week it appeared in a list of top censored searched terms on the website Free Weibo - because of its high levels of smog.

For the past two weeks, air pollution has resulted in a yellow smog alert - the lowest level - and a temporary closure of the city's airport due to poor visibility.

On microblogging site Sina Weibo, people demanded that the government do more to deal with the pollution. But not all of the posts are currently visible, because, as in previous years, censors have cracked down on smog talk.

Image copyright Weibo Image caption This image appeared on Weibo. The panda's mask reads: "Chengdu, please let me breathe"

"Many of my posts about smog had been deleted on Sina Weibo," Chengdu resident Qing Xiaojuan tells BBC Trending. "I have no hope. I don't expect anything could be improved."

Xiaojuan joined an online campaign by posting a picture of herself wearing a face mask and holding a board reading "I love Chengdu, please let me breathe."

Despite the fact that some of her other posts have been deleted, that particular picture remained online - although Xiaojuan says she suspects it will be deleted soon.

The authorities have also clamped down in other ways. A planned protest didn't happen because the square where it was scheduled to be held was closed. "Police prevented people from entering," Xiaojuan told Trending.

Another protest in the city did go ahead when a group of artists gathered wearing face masks. The silent protest was stopped and the artists were arrested by police, but released a few hours later.

One of the participants told the BBC that the protest was planned with very little notice over the messaging app WeChat.

Image caption This picture of the artists being questioned by police was widely circulated on social network Weibo

Chatter about the protest and arrests was deleted by censors, according to messages which later appeared on Free Weibo.

Some Weibo users complained that the smog wasn't mentioned in local news reports. "Look at the news these days in Chengdu, we are suffering from the smog so badly, but this topic is not covered on any media platforms. Isn't it odd?" one user said.

Another commented: "Because Chengdu is in a basin located in a lowland region, even strong wind can't blow away the smog. The government really needs to solve this fundamental problem."

Follow BBC Trending on Facebook

Join the conversation on this and other stories here.

Some Weibo users blamed a nearby petrochemical plant for causing the pollution, although the Chengdu environmental protection bureau released figures stating that emissions from the plant are below official limits.

On the Chengdu city government's official Weibo account, an article about the causes of air pollution stated that the local government was trying to be transparent about the situation. But some citizens aren't impressed.

Weibo user "ding cuiling" wrote: "If everyone in Chengdu uses Weibo and WeChat to express their demands about dealing with smog, then it will become impossible to delete all of them.

"Once it becomes a hot topic... that will work well," he wrote.

Next story: Top tips for an arranged marriage

Image copyright Nazreen Fazal

A Facebook post by 24-year-old Indian woman on her dos and don'ts for those embarking on arranged marriages has resonated with many - it's been shared more than 2,000 times.READ MORE

You can follow BBC Trending on Twitter @BBCtrending, and find us on Facebook. All our stories are at bbc.com/trending.