Vertical Layers - CMAQ/WRF/MCIP/EMIS

Hi all,

I have some confusion regarding how vertical layers are determined and defined in CMAQ and its inputs.

  1. From my understanding, the CMAQ grid is defined in WRF. Does this mean that:
    e_vert (in WRF namelist.input) = nz (in CMAQ run script)?

  2. If e_vert need not = nz, must e_vert > nz (as MCIP can “collapse” the meteorological layers)?

  3. What does CMAQ do with emissions input that have fewer vertical layers than the simulation?

  4. Does anyone have suggestions for best practices in defining the various vertical layers?


I think nz in the CMAQ run script is used only for convenience, as a portion of file names. CMAQ determines the number of model layers from the meteorological input data from MCIP.

MCIP can be used to collapse vertical layers, so that there are fewer layers in the MCIP outputs than were present in the original WRF data. This practice is not recommended, and is not typically used at EPA, but I am not aware of any studies that have investigated impacts of layer collapsing.

CMAQ should be able to handle gridded emissions that have fewer layers than are in the model. In recent practice, gridded emissions typically have only one layer, while vertical distribution of point source emissions is calculated using a plume rise algorithm.