As clouds of polluted air enveloped Hanoi on Wednesday, a hazy atmosphere descended onto the capital.

Air quality in Vietnam’s capital city has been extremely poor over the past few days, with the situation exacerbated on Wednesday by a phenomenon called temperature inversion.

In such districts as Ha Dong, Trung Yen, My Dinh, and Cau Giay, where roads are often congested and many construction projects dot the landscape, the air quality index (AQI) ranged from 150 to 200 yesterday. Any index above 150 is considered unhealthy for local residents.

According to Hoang Duong Tung, president of the Vietnam Clean Air Partnership (VACP), air quality typically worsens when temperature inversion occurs.

Temperatures are normally lower at higher altitudes, Tung elaborated, adding that temperature inversion happens when mecury at those altitudes heats up.

Polluted air is, as the result, prevented from spreading to high altitudes and thus gets trapped in the lower layers, hence the dark shadow is cast over the city.

The cloud of dust is expected to linger over the city for the next two to three days before a cold spell brings rains on March 31, said Tran Qang Nang, an official from the National Center for Hydro-meteorological Forecasting.

It is highly recommended that citizens monitor the city’s air quality at hanoi.gov.vn and properly prepare themselves before heading outside.

Reports from local authorities show that there are currently 5.8 million motorbikes and 700,000 automobiles registered in the capital and an additional 1.2 million vehicles currently in the city but registered to other provinces.

Air quality is poorest during the morning and evening rush hours.

Like us on Facebook or follow us on Twitter to get the latest news about Vietnam!