Why is only a small piece of sky next to the sun blue when the weather is polluted?

Air molecules will have Rayleigh scattering. When the weather is polluted, when sunlight passes through the atmosphere, it will Rayleigh scatter with air molecules. Due to the strong Rayleigh scattering of blue light, the sky appears blue. Polluted weather refers to the phenomenon of air pollution caused by the accumulation of pollutants in the air under unfavorable meteorological conditions such as no wind, inversion temperature and high humidity.