Saying that private vehicles are the biggest source of pollution, Hanoi’s Mayor Nguyen Duc Chung supports the policy to recall old cars and motorbikes.

The people of Ho Chi Minh City awoke to find the southern city under a thick blanket of fog on the morning of October 22, with many of the city’s high-rise buildings being shrouded in mist.

AirVisual, the air quality monitor and information provider, could not be downloaded from both Android and iOS stores in Vietnam for several days.

A Vietnamese Facebook user has apologized to AirVisual for a post that resulted in a “coordinated attack” to discredit the app after its data showed Hanoi has at times topped its list of 90 major cities suffering from air pollution.

A separate annual world ranking elaborated by IQAir (owner of AirVisual) in partnership with Greenpeace in March showed that Hanoi was not in the world’s top 200 most polluted cities last year.

Before "disappearing" from App Store and Play Store stores in Vietnam, AirVisual was the most downloaded air quality monitoring app in the country last week.

Hanoi and HCM City have been named among the top three cities with the most serious air pollution in the world according to the air quality index (AQI) ranking by Air Visual.