Fine horizontal grid resolution

Hello all,

I wonder whether there is a limit (or a recommended range) to the horizontal grid resolution of CMAQ.

We will be able to obtain meteorological forecasting data of 600m and 200m horizontal grid resolution, for which the 200m data even has LES module turned on. We wish to use them directly as the boundary conditions for CMAQ. We are thus curious whether it is recommended to do so and what may require our special attention.

It is also useful to know whether similar simulations have been previously tested/done.

Any comment is appreciated.


This is not a topic for which I am an expert, but there are several considerations:

  • horizontal and vertical resolutions must be appropriate for each other;
  • neither the cloud nor the vertical diffusion modules are appropriate at LES scales;
  • temporal resolution of the met forcing data must be appropriate (consider wind-speed as a conversion factor between temporal and spatial resolution, and allow for the fact that the met models tend not to resolve features smaller than 5 DX: is 10 M/S a reasonable upper bound? …then 200M horizontal resolution corresponds to a 100 second met-file temporal resolution.

Better to use a chem-enabled version of your LES met-model…

Q1) On the issue of grids, I got an error when running CCTM (CMAQv5.2.1):

This looks like a grid issue to me, but I was wondering if there are any insights regarding these IO/API subroutine errors.

Q2) Is there a regridding function in IO/API to regrid IO/API files?


These are not I/O API errors (and it’s not IO/API by the way…).

They seem to be in CMAQ routnes HGRD_INIT() and GRID_INIT()

I want to simulate air pollution with 500 m resolution. I couldn’t find anything in the user guide of CMAQ about the smallest resolution that CMAQ simulates. Could you tell me what is the smallest resolution in CMAQ, please?
Thank you


In air quality modeling which size of grid is good?
Is there “grid independence” in air quality modeling? How it is done?
Could you guide me, please?

Thank you