The Real-time Air Quality Index on aqicn.org on January 29 afternoon ranked pollution in the capital at an "unhealthy" level. The index measured by the Hanoi-based US Embassy hit 154, a level that would require old people and those with heart and respiratory problems to stay indoors.
On January 28, the index measured by the Hanoi’s Department of Natural Resources and Environment at a monitoring station on Pham Van Dong Street, to the west of Hanoi center, reached 202, an alarming pollution level that was classified as "very unhealthy."
The same day, the air quality recorded on Hang Dau Street reached 201 while other tracking stations across the capital recorded figures ranging from 158 to 200.
Aqicn.org uses data collected from the Vietnam Center for Environment Monitoring under the Environment Ministry, the United Nations International School of Hanoi and the US Embassy in Hanoi.
Data from environment agencies in Hanoi showed that the PM2.5 concentration in Hanoi between January 20 and 26 was at a really bad level.
Ambient air pollution is measured by the concentration of particulate matter 2.5 (PM2.5), a fraction of the width of a human hair, which is released from vehicles, industry and natural sources like dust.
The PM2.5 concentration in Hanoi on January 25 was 400 μg/m3, a level that prompted experts to warn local residents to limit outdoor activities so as to prevent respiratory diseases.
The safe concentration limit according to the World Health Organization is 25 μg/m3, so the Hanoi level was 16 times this limit.
Hoang Duong Tung, a senior environment official, told Giao Thong Newspaper that heavy traffic has exacerbated the air pollution level in the capital in recent days.
"High demand for travel in the lead up to Tet, Vietnam’s biggest and most important holiday, has resulted in increasing number of private vehicles on the road, causing dirty air in the capital," he said.
Pham Ngoc Dang, vice chairman of Vietnam Association for Conservation of Nature and Environment, said vehicles' emissions produce around 70 percent of PM2.5 in the air.
"Heavy traffic during the Tet season is the main reason for the serious pollution in Hanoi the past days," he said, as cited by Giao Thong. He added that the cold weather also helped worsen the problem.
Air pollution in Hanoi has been worsening in recent years, with classifications of "unhealthy" and even "hazardous", which means everyone should avoid outdoor exertions.
The 2018 Sustainable Cities Index, commissioned by Arcadis, an Amsterdam-based design and consultancy firm, ranked Hanoi among the least environmentally friendly cities in the world.
Jacques Moussafir, director of French company ARIA Technologies, which specializes in pollutant dispersion and air quality, warned that the number of people suffering from severe respiratory and mental health damage from air pollution would double in 2020 if nothing was done to fix the problem.
The city of eight million people has more than five million motorbikes and 550,000 cars. Data shows the number of private vehicles has been increasing at a rate of 4.6 percent annually, but the amount of land allocated for transportation projects has only been expanding at a rate of 0.4 percent.
In its pollution fight, the Hanoi People’s Council, the municipal legislature, made a controversial decision last July to approve a ban on motorcycles by 2030.
The ostensible aim was to boost use of public transportation, including a new metro system, but this is poorly developed sector in the capital city.
While public buses are cheap and affordable, most vehicles are old and have to share congested roads with cars and motorbikes, making them an unpopular choice for most commuters.
Officials have said that unbridled construction, road works and industrial operations that pay little regard to the environment have also worsened the situation.