Air pollution in Hanoi soared to the most hazardous level on the day. According to VEA, air quality index (AQI) in Hanoi was recorded from 160 to 220 while the index in adjoining city and provinces of Hai Phong, Hung Yen , Hai Duong, Ninh Binh, Thai Binh, Thai Nguyen was 151 to 200 respectively.

The level of particulate matter considered most harmful to human health skyrocketed to 150-200 micrograms per cubic meter.

According to VEA, air pollution is really bad in the morning and the evening and better in the afternoon in the capital city. The large difference between day and night temperatures in Hanoi caused warmer air to be held above cooler air.

The PM2.5 particles or fine dust concentration was rising in the midnight when the warmer air was held above cooler air, a phenomenon known as inversion.

Pollution has reached unbearable levels. Therefore, medical experts advised people specially children, elderly people and those suffering respiratory diseases to stay at home, not to open window and wear facemask when outside.