Photo: CFP

A sandstorm gradually drifted out of Beijing on Sunday afternoon after it had enveloped the Chinese capital for about 12 hours, just 13 days after the city was hit by the largest sandstorm for the first time in a decade. 

Although Mongolia was still the largest source of this latest sandstorm, sand from North China also played a part. Experts said that the lower density and smaller size of this sandstorm, compared with the previous one roughly two weeks ago, was a result of the shelterbelts, set up in North China's Inner Mongolia Autonomous Region, that helped reduce the amount of dust and prevented sand from drifting in.

There were few pedestrians or vehicles on Beijing's roads on Sunday, due to low visibility. The Air Quality Index reached the severest level.

The storm was accompanied by ferocious winds. The city experienced gusts of force 7 to 8, and gusts in mountainous areas soared to levels of force 8 to 10. 

Visibility in Beijing ranged from 1 to 2 kilometers, and it was below 1 kilometer in some parts of the southern districts of Tongzhou and Daxing. 

The PM10 index at one point exceeded 3,000 micrograms per cubic meter in Beijing's northern Yanqing district, indicating air quality reached a severe pollution level. 

According to a statement by the National Forestry and Grassland Administration (NFGA), this storm swept across 13 province-level regions in China, spanning an area of 1.8 million square kilometers  and affecting 240 million people.

China's Central Meteorological Observatory activated yellow sandstorm warnings on Saturday morning.

The wave of strong sand and dust would last about12 hours from morning until nightfall on Sunday, equivalent to the duration of the sandstorm that hit the city on March 15. But this wave of sandstorms coming from Mongolia and northern China is lower in intensity and smaller in scope, as shelterbelts in Inner Mongolia have reduced the amount of dust and prevented sand from drifting, analysts said.

The NFGA said that the reason why sandstorms now frequently hit Beijing and sweep across parts of China is that a continuous dry climate in Mongolia and northwestern China tends to loosen soil, which forms sand and dust, and easily follows the development of air convection and the exchange of air flows. 

Satellite imagery showed a large area of sand and dust forming in Mongolia on Saturday morning due to the impact of the Mongolian cyclone, and the air quality of Ulaanbaatar, the capital of Mongolia, deteriorated.

While temperatures in Mongolia and northwestern China were significantly higher, precipitation was lower and the surface had gradually thawed, making it easier for dust particles to drift, analysts said.

But unlike the last strong sandstorm, which drifted into some provinces in southern China, this sandstorm carried sand from the western and central parts of Inner Mongolia in North China. It had a lower intensity and affected a smaller area due to the protection from shelterbelts there, Wang Gengchen, a research fellow at the Institute of Atmospheric Physics of the Chinese Academy of Sciences, told the Global Times on Sunday.

Wang explained to the Global Times on Sunday that as some sand sources were from Inner Mongolia, shelterbelts in the autonomous region have reduced the amount of dust and prevented sand from drifting, making the intensity of sand and dust lower than the last storm. Wang said that this sandstorm will not sweep central and southern China like the last one did.

Experts said shelterbelts will reduce the amount of dust within the shelterbelt area, preventing sand from drifting, but they play limited role in stopping sand and dust from other remote desert and Gobi areas.

Experts also noted that fundamentally, any move to overcome dusty weather lies in global cooperation on the prevention and control of sand sources, as rapidly expanding desertification in Mongolia and elsewhere will result in sand drifting into China's territory, whipped up by strong winds.