Data from the environment department’s VNAir monitoring app showed Hanoi’s air quality index reached 191 at the Hanoi University of Science and Technology station at 7.30 am, close to very poor levels. Readings stood at 162 on Nguyen Van Cu Street in Long Bien, while Thanh Xuan Park recorded an unhealthy AQI of 134.

Air quality in Haiphong, Hung Yen and nearby areas also deteriorated on Wednesday morning, with AQI readings largely between 151 and 200, posing health risks to the public.

According to the department’s 48-hour air quality forecast, pollution is expected to worsen and spread on December 18. Hanoi, Hung Yen, Bac Ninh, Ninh Binh and Haiphong could see AQI levels rise to very poor, in the 201-300 range.

Thai Nguyen, Phu Tho, Lang Son and Quang Ninh may also face severe pollution, with impacts potentially extending to north-central provinces including Thanh Hoa, Nghe An, Ha Tinh and Quang Binh.

Earlier, from November 27 to December 12, northern localities, particularly Hanoi, experienced a prolonged air pollution episode, with levels ranging from poor to very poor. Some monitoring points briefly exceeded an AQI of 300, considered hazardous, prompting advice for residents to remain indoors.

The ministry of agriculture and environment has urged authorities in Hanoi, Haiphong, Bac Ninh, Hung Yen, Phu Tho, Thai Nguyen and Ninh Binh to implement urgent measures to curb pollution.

The ministry of education and training has instructed local education departments to advise schools to limit outdoor activities when air quality reaches poor levels or worse.

Hanoi has halted road and pavement digging, tightened oversight of construction sites and enforced dust-control measures, requiring construction waste to be fully covered during storage and transport.

Northern Vietnam typically enters its air pollution season from October to April, driven mainly by traffic, construction, industrial activity, craft villages and household burning.