The temperature effect on atmospheric circulation is called an inversion. Basically, air near the ground is normally warmer than that above it so rises buoyantl

The temperature effect on atmospheric circulation is called an inversion. Basically, air near the ground is normally warmer than that above it so rises buoyantly, mixing the atmosphere through convection. When the air near the ground is colder than the air above it (the gradient is "inverted") the air no longer rises, causing polluted air generated at the surface to linger. There are several circumstances that can lead to colder air at the surface than above it, including cold, cloud-free nights.