Hanoi (VNS/VNA) - Many studies in Hanoi haveshown that heat inversion is one of the main causes for recent sharp rises inpollutants, according to the Ministry of Natural Resources and Environment(MoNRE).

In a report released on September 4, the MoNRE said that inorder to comprehensively assess air quality in a certain area, it is necessaryto analyse and evaluate the monitoring data of many parameters continuously ondifferent days throughout the year.

The report was released after Hanoi’s air quality has beenreported at harmful levels over recent days.

The monitoring results showed that the air pollution ismainly dust, especially PM2.5, a single particle that has a diameter of lessthan 2.5 micrometres.

Other parameters such as sulfur dioxide, nitrogen dioxide,carbon monoxide and ozone are still within permissible limits, except for somespots near roads with elevated levels of nitrogen dioxide.

The report said that during summer months in the rainy season,air quality is the best of the year. However, sometimes abnormal meteorologicalconditions led to increases in dust concentration.

On September 2, the PM2.5 dust concentration increased, thusair quality remained at a harmful level at air monitoring stations in thecapital city.

The PM2.5 dust concentration reached the highest level atnight and dawn on September 2, possibly because of a lack of wind limiting thecirculation of pollutants, according to the report.

In order to explain the meteorological conditions that causethe dust concentration to increase suddenly, it is necessary to conduct furtherstudies.

Recent research by the Hanoi University of Natural Resourcesand Environment said that heat inversion was an atmospheric phenomenon thatoccurred when the temperature of the upper atmosphere is greater than thetemperature of the lower atmosphere.

Heat inversion occurs at different times of the year, oftenwith high frequency in the winter when the air is stable, the nights are longand cold air is flowing in.

When heat inversion occurs, it stops the atmospheredisturbance process leaving pollutants trapped in the atmosphere.

This process raises the concentration of pollutants andaffects human health.

In developing countries, many studies have shown that humanhealth is affected by polluted air during the days of heat inversion. Heatinversion also causes acute respiratory diseases.

The MoNRE believes that to improve polluted air in Hanoi,it’s necessary to limit the number of personal vehicles in the city andencourage environmentally-friendly public transportation.

Industrial enterprises should be moved to suburban areas andreduce waste from construction work.

More inspections should also be conducted on vehicles.-VNS/VNA