HANOI (Bloomberg): Vietnam’s capital has been blanketed in toxic air for weeks with one index briefly making Hanoi the world’s most-polluted city on Friday, putting pressure on authorities to take tougher action to tackle the smog.
Hanoi hit the purple "very unhealthy” level on the IQAir Index for nine out of the last 17 days, which denotes an air quality level of 201 or higher, just below the most dangerous "hazardous.”
The burning of agricultural products and waste by residents, and Hanoi’s daily use of millions of liters of gasoline, have contributed to the extreme pollution, according to a Dec. 11 posting on the government’s website.
Air pollution often spikes during Vietnam’s winters due to a confluence of meteorological, human, and geographical factors, said Theodora Nah, who researches atmospheric chemistry at the City University of Hong Kong.
In the winter, the northeast monsoon brings cool, dry air to Vietnam - and pollutants from neighboring countries like China. Add to that a phenomenon called temperature inversion, which happens when air near the ground cools more quickly than air further aloft, trapping pollution. Greater heating demand as well as crop burning also raises emissions and the mountains that surround Hanoi can also trap pollutants - much like what happens in New Delhi in India.
On top of these seasonal factors, weather systems can also worsen smog conditions in the short-term. Jung-Eun Chu, a climate scientist also at the City University of Hong Kong, said a tropical depression southeast of Vietnam the week of Christmas likely added to the pollution by pushing air down and generating strong easterly winds.
Hanoi city’s government said it plans to step up testing of compliance with emissions regulations and conduct regular water spraying activities on main traffic routes to limit dust dispersion, in a posting on Thursday. It also called for a major push to develop sustainable transport systems, minimize traffic pollution and focus on air pollution management policies.
Hanoi is piloting low-emission zones, which will ban diesel trucks and limit cars, motorbikes and scooters that don’t meet set emission standards from entering certain areas.
The health ministry recommended the public avoid taking part in outdoor activities when the air pollution rate is above 201 and suggested keeping windows and doors shut, according to a report on the website of Suc Khoe Doi Song, a publication under the ministry. Officials also advised citizens to wear masks and use public transport.
Hanoi, which has a population of roughly 9 million residents, consumes about 80 million kilowatt hours of electricity and millions of liters of gasoline and oil per day, the ministry said. The city has 10 industrial parks, more than 7 million motorbikes and 600,000 automobiles.
Air pollution causes at least 70,000 deaths each year in Vietnam, shortening the average lifespan by 1.4 years, according to the United Nations.
--With assistance from Linh Vu Nguyen. -- ©2025 Bloomberg L.P.
