According to the results from 18 automatic environment monitoring stations in the cities of Hanoi, Viet Tri, Ha Long, Hue, Da Nang, Nha Trang and Ho Chi Minh City, most urban areas across the country had 24-hour parameters of PM2.5 within the permitted threshold of Vietnamese standards.
The number of days with good air quality index (AQI) during 24 hours was higher than in previous months.
Hanoi was always more polluted than other cities but still had up to 90% of the days with good AQI.
However, in some areas of Pham Van Dong, Hang Dau and Minh Khai streets, the AQI exceeded the threshold.
The department said that May is the beginning of the rainy season so the air quality in many provinces and cities, especially Hanoi and the northern region, improved compared to the dry season's moths.
However, according to the National Centre for Hydro-meteorological Forecasting, the number of hot days this summer would be higher than normal.
The prolonged heat wave would have significant impacts on air quality, especially in urban areas, the centre said.