Hi there. I am running an ISAM simulation and I find that the concentration of SO2 simulated by CMAQ5.4 is much higher than by CMAQ5.3.3. The emission files for the two model versions were basically the same, so I tried to change the Meteorological field, but nothing changed. I extracted the SO2 contribution sources using ISAM, but the sum of all the concentration contributions (mean around 30μg/m3) was roughly equivalent to the actual observed surface concentration mean, but much lower than the extracted SO2 concentration (mean 100+μg/m3, whether extracted from AELMO or CONC files). I also checked the process of my emission files in the SMOKE model, but could not find the problem. So I wonder who also use CMAQ5.4, have similar problems? How did it happen? How to solve it?
Best
pbwang
Hello pbwang,
when we compared CMAQv5.4 to CMAQv5.3.3 in our CMAQv5.4 release testing, we saw only very minor differences in simulated SO2. These tests used CB6 and were performed for both the M3DRY and STAGE dry deposition options, using the same meteorological and emission inputs for all simulations. Your finding of a significant increase in SO2 between the two CMAQ versions is not something we would expect.
You also mention that the sum of your SO2 ISAM tags was much smaller than the bulk SO2 mixing ratio in the ACONC or AELMO files. This is also unexpected. In our experience, the sum of all ISAM tags (the user-defined tags plus the ICO, BCO, and OTH tags) for gaseous pollutants like SO2, O3, CO, or NO2 is very close to the bulk mixing ratios for these pollutants in the ACONC/AELMO files.
I would suggest a careful comparison of your emissions as well as the portions of the log files related to DESID that document how the emissions are read into CMAQ and are mapped to CMAQ model species to make sure that no unintended behavior occurred at that stage. It might also be a good idea to enable output of the diagnostic emission files supported by DESID. Be aware that the run script and namelist configuration options for doing so are slightly different between the two model versions so you would want to consult the documentation and run scripts associated with each version when enabling this.
Could you please also clarify whether you are running CMAQ offline or are using the two-way coupled WRF/CMAQ model, and whether all of your emission inputs are gridded files or a mixture of gridded and inline point source files?
In March 2023, this bug affecting plume rise for inline point sources was made to the CMAQv5.4+ branch, so if you are using the twoway coupled model, have inline point sources, and are using CMAQv5.4 code pulled from the CMAQv5.4+ branch after March 2023, this would affect your comparisons to earlier versions of the code.
Thank you for your replies.
I used CMAQ, not the two-way coupled WRF/CMAQ model. There are 2 mixture of gridded and inline point source files(merge form area and point souces), 1 inline point sources and 5 gridded files. In my simulation, the sum of the contribution values of PM2.5 form ISAM_CONC is basically equivalent to that from the AELMO files. So do I have to install CMAQ5.5 to get rid of this bug?
Best
pbwang
No, this bug only affected the two-way coupled WRF/CMAQ model, not the offline CMAQ model. While in general it’s always a good idea to consider upgrading to the latest CMAQ version, for the CB6 framework there were no changes from CMAQv5.4 to CMAQv5.5 that would have any substantial impact on SO2. CMAQv5.5 does include the bug fix for the two-way coupled model mentioned above, but if you’re not using that coupled model, the bug doesn’t affect you.
The sum of the tag values from ISAM_CONC should be even closer to the corresponding bulk AELMO values for gases than for aerosols. If that is not the case, something isn’t right.
OK，I see. But that’s really strange that the sum of all the concentration contributions (mean around 30μg/m3) were much lower than the extracted SO2 concentration (mean 100+μg/m3, whether extracted from AELMO or CONC files).
Thank you for your suggestion. I’ll keep trying to figure out why.
Best
pbwang
One additional thought on this: in your posts, you mention units of μg/m3 while all CMAQ output files (AELMO, ACONC, SA_ACONC) report SO2 in ppm. Prior to comparing the sum of the ISAM tags to the values you extracted from the ACONC or AELMO files, do you apply any unit conversions in your post-processing?
The reason for this question is that if during the post-processing the ACONC/AELMO output was converted to μg/m3 and the ISAM tag output was converted to ppb, the difference between the post-processed ACONC/AELMO and the sum of the post-processed ISAM tags would be roughly a factor of 3.
Thank you for your reply.
I checked my extraction script and there were no errors in the unit conversion.
I tried to run CMAQv5.3.3 and v5.4 with the same emission source file at the same time, and found that the concentrations of SO2 were both high between 8 and 13 am. it seems that it is not a problem with the CMAQ version. In the past two days, I recalled a simulation severl months ago. In terms of point sources, I used meteorological files to form off-line sources for key Industries, Residential and Power. The concentrations of SO2 and NO2 in my simulation results would be lower than the actual observed concentrations.Therefore, I would like to ask you whether there is a big difference between the simulation results from off-line point source formed by meteorological documents and in-line point source? Are pollutants dispersed according to meteorological documents in off-line point emission. Is the chemical transformation of the pollutants not considered during the diffusion process? In addition, when I did the Process Analysis, I found that the off-line point source would lead to "EMIS in the layer very high above the surface. In my reference, I found that the pollution process caused by point sources is mainly in the three layers near the ground. Looking forward to your reply.
Best
pbwang
I’m glad that you were able to confirm that the discrepancy in your simulated SO2 you described in your first post is caused by a difference in your emissions processing and not any significant changes due to the CMAQ version and/or issues during post-processing.
CMAQ’s inline plume rise algorithm is contained in file PT3D_DEFN.F, specifically in function CALC_PLUME_HEIGHT. It generally follows the plume rise calculations implemented in SMOKE, taking into account stack parameters and meteorological conditions.
To investigate your issue further, you will have to compare the plume rise from the CMAQ inline approach with what you call your “off-line point source formed by meteorological documents”. The plume rise you calculate for SO2 emissions sources certainly can affect modeled near-surface SO2 mixing ratios.