Levels of hazardous small particles known as PM2.5 in the air in Hanoi were at 187 micrograms per cubic metre late today, the highest among a list of most polluted international cities, according to data from AirVisual, which provides independent global air pollution information via a phone app.

“This is damaging for our health,” said Duong Kim Oanh, a 58-year-old Hanoi resident. “I think Hanoi’s pollution is caused by a large number of personal vehicles and the fine dust from all the construction, plus this cold weather.”

According to a 2021 World Bank report, emissions from Hanoi’s eight million registered vehicles made up 30% of air particulate pollution, and industry emissions another 30%.

The pollution “will affect people’s respiratory system, making people feel sick or even suffocated,” said Pham Thi Phuong, another resident.

Nearly 100 flights to and from the international airport in Hanoi were delayed or diverted to other cities on Feb 2 due to heavy fog and worsening air pollution.