SMOKE needs information on layer structures for processing elevated point sources’ plume rise in the Laypoint program and creating the ASCII elevated-point-source file (ELEVTS_L or ELEVTS_S) with the Smkmerge program. The way SMOKE obtains the layer information differs depending on whether you are creating emissions using a CMAQ-based or UAM-based approach (see Section 2.4.3, “Model-ready files”). For the CMAQ-based approach, SMOKE determines the layer structure from the structure included in the header of the GRID_CRO_3D meteorology file. For the UAM-based approach, SMOKE does not really need to know the layer structure, except to output it to the ASCII elevated-point-source file. In this case, there are many settings obtained by Smkmerge from environment variable names starting with UAM_.