Why does the airflow sink in inversion weather?

In general, the temperature in the middle and lower troposphere is high, the air pressure is relatively low and the density is small; The upper temperature is low, the air pressure is relatively high and the density is high. In this way, there will be convection up and down.

When the temperature is reversed, the lower layer temperature is low and the density is relatively high; The upper temperature is high, the density is relatively low, and the air is not easy to convection, so the pollution will be more serious.