What is the main wind direction when sand and dust weather occurs in Beijing in spring?

It is dominated by the northwest wind.

There are three main sand sources affecting Beijing: Mu Us and Kubuqi Desert, Wulanbuhe Sandy Land and Hunshandake Sandy Land. The first route is: from Shandake Sandy Land in Inner Mongolia to Heihe River Basin in Hebei Province, and finally to Beijing. The second route is from Zhu Rihe in Inner Mongolia to Yanghe River Basin in Hebei, and then to Yongding River Basin in Beijing. The third path is: Sanggan River Basin in Hebei to Yongding River Basin in Beijing.

Beijing is located in the northeast of North China, at the southern foot of Yanshan Mountain and east of Taihang Mountain. Mainly composed of loess and sandy land, there is no large area of desert. The desert in northwest China is dominated by sand, which is not the source of dust. Besides, there are Yanshan Mountain and Taihang Mountain as barriers in North China, and the desert is not a concern. What's more, the dust structure in Beijing is very different from the sandy structure in the northwest desert.