CMAQ-based AOD issues


#1

Dear CMAQ users,

I tried to use CMAQv5.2.1 to simulate AOD outputs and want to evaluate the simulated AOD outputs. The followings are my questions:

  1. Is the CMAQ-based AOD (CCTM_AOD_DIAG) a 2-Dimensional output instead of a 3-D output? According to my test case, the AOD is a 2-dimensional output. Does the CMAQ only generate 2d, or is there any other setting that I can change to get 3d output?

  2. If it is a 2-d, does it represent AOD at surface layer or aggregated AOD through multiple layers (e.g., 35 layers as my METCRO3D file). I didn’t find any detailed information about the CMAQ-AOD output from CMAQ user manual.

  3. How to evaluate CMAQ simulated AOD outputs? As provided by CMAQv5.2.1 Release Notes, the CMAQ model “estimates the light extinction of aerosols at 550nm”. Does it mean that we can compare CMAQ-based AOD with MODIS-derived AOD at 550 nm, or compared to AERONET AOD to evaluate CMAQ model performance?

Thank you for your help,

Best Regards,
Xiangyu


#2

Dear Xiangyu,

The AOD output in v5.2.1 is somewhat confusing. We have made an effort in the release of v5.3 to clarify the processing of AOD and the guidance on how to use it. For a robust evaluation, I recommend upgrading to v5.3_Beta when we release a new interim version this month. That said, here is what you need to know for evaluating AOD with v5.2.1.

The quantity on AOD_DIAG is 2D summed for the entire column. The backend calculation is based on correlations to visibility data at IMPROVE sites, not a rigorous optical calculation. Similar quantities are output on the PMVIS file. There is no way to output this AOD quantity resolved for each layer of the column.

There is another pair of AOD values output on the PHOTDIAG2 file (“TAU_AERO_W294” and “TAU_AERO_W607”). I believe these are closer to what you are looking for. They are calculated based on Mie theory and output for every layer. As the names suggest they are applicable to 294 nm and 607 nm respectively. We have experts on our team who have routinely interpolated between these wavelengths to suit their own evaluation needs (e.g. 550 nm). I will forward this issue to them as well.

Best regards,
Ben


#3

Hi Ben,

Thank you very much for your kind reply! I have a few more questions regarding the AOD_DIAG and PHOTDIAG2 file.

  1. As you mentioned, the AOD_DIAG is estimated based on “correlations to visibility data at IMPROVE sites instead of rigorous optical calculation” but the TAU_AERO outputs are calculated based on Mie theory. So if we want to evaluate CMAQ-AOD outputs, we should not directly compare the observed AOD data (e.g., MODIS-AOD or AERONET-AOD) with AOD_DIAG, but should compare AOD observations with TAU_AERO as it is more accurate? In other words, is theTAU_AERO outputs more representative of the CMAQ-simulated AOD? Or both represent CMAQ-AOD but estimated based on different methods.

  2. If we want to evaluate TAU_AERO by comparing them against the observed AOD (from either satellite or AERONET), do we need to aggregate them over entire layers? If so, can we directly add up the TAU_AERO results over the entire layers or is there any particular formula to do that?

Thank you again! I am looking forward to getting more information about the AOD evaluation and calculation.

Best Regards,
Xiangyu