A balloon seller walks across a street in Shijiazhuang, Hebei province, on New Year's Day. But it wasn't a particularly good day for families to go out as the city had issued a red alert for air pollution. [Photo by Chen Jianyu/China Daily]

By Sunday, a total of 26 cities issued top red alerts for the coming days

After Monday morning's brief break from lingering smog, Beijing residents saw it return in the evening.

The smog is forecast to last until Sunday in Beijing, Tianjin, and Hebei, as well as other neighboring regions.

Authorities said they have found many factories producing and discharging pollutants in violation of government restrictions, warning that they would be punished severely.

Northern parts of Beijing, such as Yanqing, experienced blue sky and good air quality on Monday morning, but air pollution returned to hazardous levels in the capital, said the Ministry of Environmental Protection.

Cities such as Hebei's Shijiazhuang experienced concentration levels of PM2.5－hazardous particulate matter with a diameter of less than 2.5 micrometers－that exceeded the Air Quality Index's upper limit of 500 during the holiday.

In addition, heavy fog lowered visibility to 50 meters in certain regions, which disrupted transport in the region, with flights canceled or delayed and expressways closed.

Dai Wei, the mother of a 6-year-old girl living in Hebei's Baoding, was stranded for hours on the expressway when driving to Shijiazhuang on Dec 31, doubling the length of their journey to more than six hours.

"The lingering smog frustrated me, especially when I heard my daughter coughing due to the poor air quality," Dai said. "When will we see real improvements in air quality?"