HARBIN – Straw burning is the main culprit in the recent severe pollution in north-east China, according to experts from the National Joint Research Centre for Tackling Key Problems in Air Pollution Control, China Youth Daily reported on Thursday.

North-eastern China has been experiencing heavy PM2.5 pollution – health-damaging particulate matter with a diameter of 2.5mm or less – since Oct 28.

According to the National Environmental Air Quality Monitoring Network, the cities of Daqing in Heilongjiang province and Chaoyang in Liaoning province have experienced severe PM2.5 pollution since 4pm on Tuesday, while Harbin and Suihua in Heilongjiang have experienced moderate pollution.

Eleven cities in north-east China recorded PM2.5 concentrations of 150 micrograms (mcg) per cubic m per hour, with Harbin and Suihua recording more than 500mcg per cubic m.

Peak concentration in Suihua reached 735mcg per cubic m at 8am on Tuesday.

From Oct 28 to 30, satellites detected a large number of open straw burning points in north-eastern China, mainly concentrated in central Jilin province, central Liaoning and southern Heilongjiang. Cities such as Harbin and Suihua; Changchun and Jilin in Jilin province; and Liaoyuan and Fushun in Liaoning had many straw burning areas.

Experts from the centre said the intensity of open straw burning resulted in the accumulation of pollutants at night, which exacerbated the PM2.5 pollution.

They said the straw burning took place most heavily from noon to 6pm daily, with the greatest number of burning points reached at 3pm on Monday.

Around three to four hours after the concentrated burning of straw, pollutants were rapidly accumulated and transported by air currents in the region, leading to varying degrees of air quality deterioration in cities.

Unfavourable topography and meteorological conditions facilitate the accumulation of pollutants, experts said.

Moreover, the strong temperature inversion in the early morning within a range of zero to 500m from the ground can also cause the accumulation of pollutants.

From Friday to Tuesday, influenced by cold air, most parts of the region are expected to have good air quality because of better diffusion conditions. CHINA DAILY/ ASIA NEWS NETWORK