After enjoying cleaner air briefly in 2014 when offices and factories were closed for several days as Beijing hosted the APEC Summit, residents of the capital city are back to wearing face masks.

Smog has worsened with pollution levels going up to hazardous levels 20 times the limits set by the World Health Organization (WHO).

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According to the U.S. Embassy, PM 2.5 particulates soared to 568 micrograms per cubic meter on Thursday. The WHO standard places a cap of 25 micrograms to distinguish between acceptable and dangerous pollution levels, BBC reports.

At a municipal monitoring station in east Beijing, the reading was even higher at 621 micrograms per cubic meter.

To cut the smog, the central government prohibited the construction of new oil refining facilities, steel, cement and thermal power plants beginning March, reports China Daily.

It also promised to reduce coal use in some areas and passed in 2014 the first amendment to China's environment protection law in a quarter of a century by placing tougher fines on polluters.

Meanwhile, the Beijing Meteorological Bureau placed the city on yellow pollution alert on Saturday. It is the third-highest level in the bureau's four-tier system.

Lower pollution levels were expected in Tiamjin, Heibei province and parts of Shanxi and Sichuan provinces.

Rao Bing, a local environment official in Dazhou, Sichuan blamed the province's smog on residents' use of a traditional preservation method for pork and sausage.

However, residents made fun of Rao for blaming a preservation method that has been used for hundreds of years. One Chinese posted on Sina Weibo, the country's most popular microblogging site, "The people who discovered this should win the Nobel."

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