Timelapse footage of smoke from a brush fire revealing the planetary boundary layer (PBL) in the atmosphere. The PBL is the region of the atmosphere where wind, temperature and other variables are affected by the ground below. This causes constant mixing of the air in this region. Above the PBL, the air flow is affected only by pressure and the Coriolis effect, and is much faster. This has the effect of trapping pollutants like this smoke near the ground. Filmed in Colorado, USA, in autumn.