By 9am, the sun was already quite harsh but the sky was still a cloudy white like fog. However, according to meteorological experts, this was a dry fog phenomenon caused by air pollution. This phenomenon often appears at the beginning of the dry season when there is no more rain to clean the air. Fine dust combined with water vapor remains suspended in the air, creating a cloudy white color all day long. The level of air pollution is at a level that is harmful to health.

According to IQAir, at 8am, Hanoi with the concentration of fine dust in the air was 176 µm/ _m3 (above 150 is red, below 150 is orange and below 100 is yellow) ranked 6th in the world in terms of air pollution while Ho Chi Minh City was 164 ranked 10th.

For Hanoi, today is also the most polluted day of the week. In the previous 3 days, the pollution level was from 113 - 156 µm/m ₃ , and in the next 3 days it will gradually decrease from 123 - 104 µm/m ₃ .

The situation is similar to Ho Chi Minh City but the level is a little milder when only today is red, while 3 days ago, the pollution level of Ho Chi Minh City was 112 - 115 µm/m ₃ equivalent to orange. In the following days, it will return to yellow with the fine dust concentration below 100, corresponding to yellow.

Red air quality corresponds to unhealthy levels for humans and orange corresponds to unhealthy levels for sensitive groups.

Air pollution has been a problem in both cities for many years. One of the main causes is the transportation system, with millions of cars and motorbikes clogging the city streets every day. Many of these vehicles are old and do not comply with emission standards. In addition, there are industrial production activities, construction and people's daily activities.

The average annual PM2.5 dust pollution level of both cities is more than twice as high as the recommended level by the World Health Organization (WHO).