The reason is due to the phenomenon of radiation temperature-inversion in combination with high air humidity leading air pollutants to result in blindness of photochemical smog.
The photochemical blindness occurs 6-7 days in September and October annually when weak southwest monsoon in combination with the cold air mass moving from the North to the South causes a range of tropical convergence.
According to Director of Environmental Monitoring and Analysis Center Cao Tung Son, the phenomenon has been frequently happening in five recent years.
With the current limitation conditions of the manual monitoring, data sharing and reports about the radiation temperature-inversion from meteorological agencies as well as assessment and recommendations for people are also limited.
