"Agriculture has been a vital industry in China for hundreds, if not thousands, of years, and it is the tradition in rural areas to burn straw after autumn harvest and plough to bury the ashes in the ground as fertilizer," said a Weibo user nicknamed Sunflower. "But why we didn't have smog in the past?"

At such criticism, Wang Yu, head of the energy ecology department of the Beijing Agricultural Bureau, admits pollutants were mainly from motor vehicle exhausts, coal burning, industrial production and dust, rather than burning straw.

"But this is the season for burning straw, coinciding with a special climate which features high humidity and lack of wind," he said. "It was like the straw that breaks the camel's back, worsening the air pollution."

Beijing and its surrounding provinces have banned straw burning. And anti-smog measures didn't stop there.

In addition to the straw ban, the city pledged to replace coal with cleaner burning energy like electricity and natural gas for domestic use. They also hope to curb coal sales and use by the end of 2020, as well as other high-pollution fuels, such as fuel oil, petroleum coke, combustible waste and some biomass fuel.

Beijing has also raised the discharging fees for major pollutants such as sulphur dioxide and nitrogen oxide this year.

Li Lixin noted that it might take time to see the achievements of such measures, but the government has attached great importance to the issue, and people's awareness of environmental protection has improved.

In the meantime, Beijingers are avoiding the outdoors and doling out thousands to protect themselves indoors.

An old man surnamed Cheng said his friends with asthma and bronchitis would remind each other not to go out in smoggy days.

Wang Xia's school has stopped outdoor activities for students. "What if we could have air cleaners installed in each classroom," she said.

According to a Mr. Zhang, a sales representative of electrical appliance brand SHARP on e-commerce platform JD.com, sales of air purifiers almost doubled in the past two days.

Fu Baoling, a retired worker, just bought a purifier for 2,100 yuan (about 342.6 U.S. dollars). "My granddaughter is young, so I bought this especially for her," she said. "I don't know whether this is effective or not. I just hope the sky could clear up soon."