Hanoi's air quality stays at unhealthy levels

Switzerland-based air quality monitoring facility IQAir AirVisual recorded the air quality index (AQI) at over 200 in many places in Hanoi on Friday morning.

At noon, it dropped to 149 on average.

According to AirVisual, the AQI ranges from 0 to 500, though air quality can be indexed beyond 500 when there are higher levels of hazardous air pollution. Good air quality ranges from 0 to 50.

The index staying between 201 and 300 is classified as "very unhealthy," which means the "general public will be noticeably affected and sensitive groups should restrict outdoor activities."

When it ranges from 101 to 150, it is categorized as "unhealthy for sensitive groups" which means "general public and sensitive individuals in particular are at risk to experience irritation and respiratory problems."

In IQAir city ranking, Hanoi was ranked the fourth most polluted city on Thursday morning, but dropped to 26th in the afternoon.

Vietnamese environment monitoring app PAM Air also measured the AQI of Hanoi at hazardous levels, ranging between 151-200 early Friday morning in particular stations, including those placed at Vietnam National University, Hanoi in Cau Giay District and on Nguyen Thi Minh Khai Street in Hai Ba Trung District and on Giang Vo Street of Ba Dinh District.

The PM 2.5 level of the capital city has stayed at 49 µg/m3, which is 9.8 times the WHO annual air quality guideline value.

PM2.5 is defined as ambient airborne particulate that measures up to 2.5 microns in size, just a fraction of the width of a human hair. Their microscopic size allows these particles to be absorbed deep into the bloodstream upon inhalation, potentially causing health issues such as asthma, lung cancer, and heart disease.

Hoang Duong Tung, chairman of the Vietnam Clean Air Partnership, said air pollution was a serious issue in Hanoi for several years due to vehicle emission, industrial operation, construction and the daily activities of local people, including burning fields.

He said the worst air pollution normally lasts from October to March because it is winter when there is little wind and sunshine, yet humidity is high.

He said the air pollution recorded Friday morning was abnormal, which could be caused by thick fog and high humidity following days of heavy rains.