In Vietnam, the northeast monsoon usually arrives in the northern part of Vietnam, including Hanoi, in the transition between summer and fall. The phenomenon of temperature inversion with some seasonal breeze makes the northern provinces’ air quality poorer.
Hanoi’s low air quality is the result of the transition between summer and fall. Photo: Baochinhphu
Data from automatic air monitoring points in recent days show that air quality in many northern provinces of Vietnam, especially in Hanoi, is at an alarming level. In Hanoi, during the past few days, the level of air pollution measured at more than 20 locations was always above 100 (bad level).
Deputy Director of the National Center for Hydro-Meteorological Forecast Hoang Phuc Lam said that temperature inversion is one of the factors causing poor air quality in recent days.
Hanoi’s current low air quality is the result of little air circulation in the atmosphere during the transition between summer and fall, Lam added.
Le Thanh Hai, former deputy head of the Vietnam Meteorological and Hydrological Administration, told VnExpress that Hanoi’s ongoing low air quality is the result of little air circulation in the atmosphere during the transition between summer and fall.
Temperature inversion also contributed to the capital’s poor air quality as thermal radiation is dispersed from the ground into the atmosphere, which causes fog at low altitude, he noted.
“Air masses in the city remain static instead of spreading in various shapes and sizes,” Hai explained the high pollution indexes measured in the air of Hanoi in recent days.
“Air could not rise high by convection, so there was no cloud formation to produce rain and cleanse the atmosphere. There was also no wind to disperse the polluted air,” Hai stressed.
Echoing Hai, Hoang Duong Tung, president of the Vietnam Clean Air Partnership, said temperature inversion at night prevents air from rising up into the atmosphere and confines them at the low altitude, which leads to air pollution.
“In the past, we used to pay less attention to the phenomenon of temperature inversion because there was not much dust pollution. Nowadays, air quality is automatically monitored every day, air pollution is obvious and draws people’s attention” Tung said.
“It is recommended that in order to protect yourself from exposing to the dangers of ultrafine dust, adults and children should wear masks when going out. They should not travel on crowded roads, and avoid areas which are often polluted like industrial parks and highways,” Tung added.
Hanoi, which has eight million people, more than five million motorbikes and 550,000 cars, was ranked the second most polluted city in Southeast Asia by the World Air Quality report released by IQAir AirVisual earlier this year.
IQAir AirVisual, a Switzerland-based air quality monitoring facility that generates data from public, ground-based and real-time monitoring stations, recorded Hanoi’s AQI level at 152 on September 18, making it the seventh most polluted city in the world. It used data from three monitoring stations in the city.
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