Negative values at high altitude in FLOOR file

CMAQ
1

Hi all,

I am using CMAQ-5.4 to run the 12US1 case for July 2021. I downloaded emissions and BCs from the website (https://2021platform.s3.amazonaws.com/index.html#2021platform/12US1/) and used the hemispheric output as ICs (https://drive.google.com/drive/folders/11G3eAcs7WFKuRP1AhzD4PWBsslPZrL6Q). I used the cb6mp_ae6_aq and ae6_mp mechanism. I run the model on NCAR derecho. The model can run but generated the FLOOR files showing negative values at high altitude:

 Concentrations less than, but reset to  0.000E+00 in           VDIFF
     Date:Time     Col  Row Layer Species             Value before reset
  2021182:002100   14   74   32  184 (ASO4K           )  -1.250E-06
  2021182:002100   15   74   32  184 (ASO4K           )  -1.355E-06
  2021182:002100   16   74   32  184 (ASO4K           )  -1.458E-06
  2021182:002100   17   74   32  184 (ASO4K           )  -1.544E-06
  2021182:002100   18   74   32  184 (ASO4K           )  -1.622E-06
  2021182:002100   19   74   32  184 (ASO4K           )  -1.693E-06
  2021182:002100   20   74   32  184 (ASO4K           )  -1.771E-06
  2021182:002100   21   74   32  184 (ASO4K           )  -1.868E-06
  2021182:002100   22   74   32  184 (ASO4K           )  -1.962E-06
  2021182:002100   23   74   32  184 (ASO4K           )  -2.045E-06
  2021182:002100   24   74   32  184 (ASO4K           )  -2.102E-06
  2021182:002100   25   74   32  184 (ASO4K           )  -2.149E-06
  2021182:002100   26   74   32  184 (ASO4K           )  -2.191E-06
  2021182:002100   27   74   32  184 (ASO4K           )  -2.370E-06
  2021182:002100   28   74   32  184 (ASO4K           )  -2.411E-06
  2021182:002100   29   74   32  184 (ASO4K           )  -2.454E-06
  2021182:002100   30   74   32  184 (ASO4K           )  -2.496E-06
  2021182:002100   31   74   32  184 (ASO4K           )  -6.515E-07
  2021182:002100   14   74   32  190 (ANO3K           )  -2.264E-08
  2021182:002100   15   74   32  190 (ANO3K           )  -3.038E-08
  2021182:002100   16   74   32  190 (ANO3K           )  -3.748E-08
  2021182:002100   17   74   32  190 (ANO3K           )  -4.348E-08
  2021182:002100   18   74   32  190 (ANO3K           )  -4.869E-08
  2021182:002100   19   74   32  190 (ANO3K           )  -5.282E-08
  2021182:002100   20   74   32  190 (ANO3K           )  -5.691E-08
  2021182:002100   21   74   32  190 (ANO3K           )  -6.183E-08
  2021182:002100   22   74   32  190 (ANO3K           )  -6.645E-08
  2021182:002100   23   74   32  190 (ANO3K           )  -6.923E-08
  2021182:002100   24   74   32  190 (ANO3K           )  -7.221E-08
  2021182:002100   25   74   32  190 (ANO3K           )  -7.507E-08
  2021182:002100   26   74   32  190 (ANO3K           )  -7.778E-08
  2021182:002100   27   74   32  190 (ANO3K           )  -9.430E-08
  2021182:002100   28   74   32  190 (ANO3K           )  -9.758E-08
  2021182:002100   29   74   32  190 (ANO3K           )  -1.004E-07
  2021182:002100   30   74   32  190 (ANO3K           )  -1.029E-07
  2021182:002100   14   74   32  195 (ACLK            )  -1.388E-06
  2021182:002100   15   74   32  195 (ACLK            )  -1.482E-06
  2021182:002100   16   74   32  195 (ACLK            )  -1.570E-06
  2021182:002100   17   74   32  195 (ACLK            )  -1.643E-06
  2021182:002100   18   74   32  195 (ACLK            )  -1.705E-06
  2021182:002100   19   74   32  195 (ACLK            )  -1.762E-06

I searched for similar problems on the CMAS forum and it seems if it is ok if it happens rarely. But i have the FLOOR files generated every days of the simulation with a lot of lines in each FLOOR file. I tried to use a shorter timestep but the preoblem is still there. Does anyone know how to solve this issue? Any suggestions are appreciated.

Thanks,
Lin

2

Hello Lin,

we suspect that the issue is caused by incompatibilities between the aerosol mechanism used in the model generating these 2021 12US1 boundary conditions (GEOS-Chem) and the CMAQ aerosol mechanism. Such inconsistencies might cause instabilities at low concentrations in upper layers near the boundaries that then result in FLOOR files. You probably are ok ignoring this issue if your main focus is on Hg chemistry, but I cannot say for sure.

3

Thanks Christian,

Yes i focused on mercury. I will keep the model running for a while and see if the results make sense.

Best,
Lin

4

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