Unbalanced emissions and ambient concentrations

CMAQ
1

Hi everyone,

In one of my cases, I have constant grid emissions. However, in CONC file, the concentrations at the first (bottom) layer don’t show the constant emission. It seems that at 1-4 hour, the highest emission grids do not emit gas. From 5 to 14hour, the emissions start to work. Afterwards, the produced pollutants moved under meteorological conditions, but the emissions stop. I attached the 24 hours concentration profile and the constant emission below. The chemical from CONC file is ACAJ and the chemical from emission file is PCA. I also checked SO2 and NO2, the temporal change is similar to ACAJ.

24hours
emission

I checked the dry and wet deposition. They are much smaller than the ambient concentrations. The volume of the grid cell and the air density don’t change much.

What other parameters should I check and how can I understand the unbalance?

Thank you very much!
Best,
Feng

2

Hi Feng,
If the boundary layer is growing at the start of your simulation, then the resulting concentrations due to precursor emissions may be diluted as they are ventilated into the atmosphere.

If you wish to confirm that the emissions that you provide are being used in CMAQ, please evaluate the emissions diagnostic file output.

Please review instructions to enable the emissions diagnostic file for the version of CMAQ that you are using, and follow those instructions for how to turn on the emissions diagnostic file.

For the current released version of CMAQ (v5.3.3) the instructions are here:

setenv EMISDIAG T            #> Print Emission Rates at the output time step after they have been
                             #>   scaled and modified by the user Rules [options: F | T or 2D | 3D | 2DSUM ]
3

Thank you very much for the reply. I use CMAQ v5.2 and do not have EMISDIAG option in CCTM run script. Instead I switch on the process analysis and vertical dispersion diagnostic option. The concentration change caused by emissions is almost equal to the change caused by vertical diffusion in the first layer.

I also attached the change of the boundary layer here. At the beginning, the hot spots of high emission do not have a high boundary layer but show no concentration at first layer. later until the boundary layer gets thicker there seems to have some concentration in the ambient.

ezgif-4-b0129d1a02

It is still confusing. Why emission is removed all by the vertical diffusion immediately? I also want to check the eddy diffusivity but cannot find where they stored.

Thanks again for the help!

4

Another two small questions.

  1. Does vertical diffusion in the process analysis include both vertical diffusion and vertical mixing (asymmetrical conventional model)?

  2. Can I interpret what happened is that the vertical diffusion drained all the emissions upward like a chimney at some hot spots of emissions without high ambient concentrations?

Thanks a lot!