Why is it yellow?

The reason why the sky turns yellow is sandstorm.

During the sandstorm weather, the atmosphere is full of large particles of dust. At this time, the scattering characteristics of solar light are mainly non-selective, that is, when the size of scattered particles is much larger than the wavelength, the scattering intensity is independent of the wavelength. Large particles of dust make non-selective scattering dominant, and the sky is no longer blue because of Rayleigh scattering, but the color of dust-khaki.

Definition:

Sandstorm refers to the weather phenomenon that strong winds blow up dust on the ground, making the air very turbid and the horizontal visibility less than 1km. Sandstorm is a weather phenomenon in wind erosion and desertification, and its formation is influenced by both natural factors and human activities.

Natural factors include strong wind, decreased precipitation and its sand source. Human activity factor refers to the increase of sandstorm frequency after vegetation destruction in the process of economic development.