With increasing height, the temperature normally decreases. In case the temperature rises this is called a temperature inversion. Most common are the ones related due to subsidence in an area of high pressure, or strong surface cooling. During the winter season both can produce a very pronounced inversion. Below, all the moist and industrial dust remains trapped and when thick enough this is referred as smog (smoke and fog). With no synoptic changes, this polluted air can persist for several days.  

Taken at a height of 35 meter, this tele shot shows the top of an inversion: below a rimed landscape with hazy conditions due to industrial dust, and above crisp clear skies. In front at a distance of 3,5 km the church of Perk, in the back at a distance of 12,5 km only the upper part of an 143 meter high water tower located at Mechelen Zuid is visible.