The document summarizes the observed structure of the atmospheric boundary layer. It describes the boundary layer as the lowest part of the troposphere directly influenced by the Earth's surface. The boundary layer typically ranges from 100m to 3km deep. It is more turbulent than the free atmosphere above due to friction and rapid dispersion of pollutants. Vertically, it consists of an interfacial layer, surface layer, mixed layer, and entrainment zone. Turbulence is generated via shear and convective instabilities driven by surface forcings. Boundary layer depth varies based on land/ocean differences and weather systems like high/low pressure regions.