Shijiazhuang in North China's Hebei province issued a red alert for heavy air pollution from 7 am on Monday, urging factories and construction sites to reduce emissions so that the pollution might be mitigated.

The conditions for diffusion in the city have deteriorated, and pollutants have continued to accumulate since Sunday, leading to potential moderate to severe air pollution, said a notice by the city's office of emergency command on heavy pollution weather.

Under China's four-tier warning system for air pollution, red is the most severe.

"Although there is a red alert, I haven't felt the heavy pollution yet," said Xing Yafeng, a private business owner in Shijiazhuang, who added that there was still blue sky on Sunday.

According to Wang Xiaoli, director of the Warning Center for Emergency and Heavy Pollution Weather at Hebei Provincial Ecology and Environment Department, the alerts are issued about 48 hours before the predicted heavy pollution, so that emergency measures can be carried out.

"The joint prevention and control in the northern region will also help reduce the pollution," Wang said, adding that multiple cities will take active measures to mitigate the pollution at the same time.

In accordance with the red alert, only certain vehicles are permitted on the road. The neighboring city of Baoding has also taken the same measures for Monday to Sunday.

In Shijiazhuang, construction sites have been ordered to suspend activities that cause heavy dust including demolitions and concrete mixing. All air-related industrial enterprises are required to implement differentiated emission reduction measures.

"Years ago, when red alerts were issued, we could always see heavy smog covering the city. But now it's very different," business owner Xing said.

Expert Wang agreed, saying the province has taken concerted measures in the past decade to curb air pollution, which have led to significant progress in recent years.

In 2022, Hebei had no cities ranked in China's 10 most polluted cities for the first time.

From January to November this year, the average concentration of PM2.5 — fine particulate matter with a diameter of 2.5 micrometers or less — in Handan was 45, the highest in Hebei. The lowest average PM2.5 reading was 18 in Zhangjiakou, according to data from the province.

In 2013, the average PM2.5 reading for Hebei was 108.

According to the Action Plan for Continuous Improvement of Air Quality issued by the State Council earlier this month, by 2025 the PM2.5 concentrations in the Beijing-Tianjin-Hebei region and nearby cities should be reduced by a further 20 percent from 2020.