# Lower simulation concentration **URL:** \ **Category:** CMAQ\ **Created:** [January 20, 2025, 8:08am UTC](https://forum.cmascenter.org/t/lower-simulation-concentration/5532 "2025-01-20T08:08:25Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![LMZ](https://avatars.discourse-cdn.com/v4/letter/l/a587f6/32.png) [@LMZ](https://forum.cmascenter.org/u/LMZ)\ **Post date:** [January 20, 2025, 8:08am UTC](https://forum.cmascenter.org/t/lower-simulation-concentration/5532/1 "2025-01-20T08:08:25Z")
Dear Professors, I would like to ask you a question. At present, the ozone concentration NMB simulated by me is only negative 46%, and the PM2.5 concentration simulated is even lower. In this case, how do you think my simulation is correct？ ---
**Author:** ![Ryan](https://avatars.discourse-cdn.com/v4/letter/r/a8b319/32.png) [@Ryan](https://forum.cmascenter.org/u/Ryan)\ **Post date:** [January 21, 2025, 7:04am UTC](https://forum.cmascenter.org/t/lower-simulation-concentration/5532/2 "2025-01-21T07:04:01Z")
Please post more information about your CMAQ outputs. Time series of observation vs simulation would be helpful. ---
**Author:** ![LMZ](https://avatars.discourse-cdn.com/v4/letter/l/a587f6/32.png) [@LMZ](https://forum.cmascenter.org/u/LMZ)\ **Post date:** [January 21, 2025, 7:15am UTC](https://forum.cmascenter.org/t/lower-simulation-concentration/5532/3 "2025-01-21T07:15:39Z")
Hello, professor. Now I have checked the error in the picture after opening CTM\_EMISCHK, and I input two emissions. What should I do to solve the error in the BVOC emission report txt file generated by MEGAN? Thank you very much for reading the letter [CCTM.txt](https://forum.cmascenter.org/uploads/short-url/th0MWsr1qss46tcSEyykDrCggqK.txt) (85.5 KB) ![模拟报错](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/c/c8b136c970aefea95e12d4b52f5dd5a84f41acd1.png) ---
**Author:** ![cgnolte](https://yyz1.discourse-cdn.com/flex027/user_avatar/forum.cmascenter.org/cgnolte/32/53_2.png) [@cgnolte](https://forum.cmascenter.org/u/cgnolte)\ **Post date:** [January 21, 2025, 2:54pm UTC](https://forum.cmascenter.org/t/lower-simulation-concentration/5532/4 "2025-01-21T14:54:58Z")
Thanks for making a new post for this question. The error message in your screenshot says you are looking for emissions of AACD, which is not found in any of the provided emissions input files. You need to either make sure that AACD exists on one of the emissions inputs or set CTM\_EMISCHK to F. Please also see the “Please read before posting” [page](https://forum.cmascenter.org/t/please-read-before-posting/1321) for tips on how to debug your simulation and the information needed to include in your post. ---
**Author:** ![LMZ](https://avatars.discourse-cdn.com/v4/letter/l/a587f6/32.png) [@LMZ](https://forum.cmascenter.org/u/LMZ)\ **Post date:** [January 22, 2025, 2:14am UTC](https://forum.cmascenter.org/t/lower-simulation-concentration/5532/5 "2025-01-22T02:14:14Z")
Dear Professor, Hello, and thank you so much for your reply. I truly appreciate your guidance. I still have a couple of issues that I would like to ask you about. Following your advice, I have turned off the modules you mentioned. However, I now have two types of emission inputs. One is anthropogenic emissions, EMIS\_001 and EMS\_002, and EMS\_002 is generated by MEGAN. However, after adding EMS\_002, I encountered the error shown in the attached image. I am unsure how to resolve this issue. Once again, thank you for your help. Best regards, ![图片3](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/2/2b7233d79089c97a81ef79ae0736043825a51952.png) ![图片2](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/d/d8bf2bf1403a247f204f64a949025e032d1d5656.png) ![图片1](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/f/f00033058509cc4793924726092f256154ad2858.png) ---
**Author:** ![hogrefe.christian](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@hogrefe.christian](https://forum.cmascenter.org/u/hogrefe.christian)\ **Post date:** [January 22, 2025, 2:24am UTC](https://forum.cmascenter.org/t/lower-simulation-concentration/5532/6 "2025-01-22T02:24:11Z")
You likely have some missing or bad values (e.g. very large positive or negative values) in your MEGAN emissions file which then cause the reported NaN values when the CCTM reads in these emissions. You will need to examine the fields in that emissions file to identify these bad values and then trace your way back to why such values were generated by MEGAN. ---
**Author:** ![LMZ](https://avatars.discourse-cdn.com/v4/letter/l/a587f6/32.png) [@LMZ](https://forum.cmascenter.org/u/LMZ)\ **Post date:** [January 22, 2025, 2:38am UTC](https://forum.cmascenter.org/t/lower-simulation-concentration/5532/7 "2025-01-22T02:38:11Z")
Dear professor, hello and thank you very much for receiving your reply. There is still a small question, that is, do we need to open setenv CTM\_BIOGEMIS\_MG N and when inputing EMI2 emission setenv BDSNP\_MEGAN N These two modules ---
**Author:** ![hogrefe.christian](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@hogrefe.christian](https://forum.cmascenter.org/u/hogrefe.christian)\ **Post date:** [January 22, 2025, 2:58am UTC](https://forum.cmascenter.org/t/lower-simulation-concentration/5532/8 "2025-01-22T02:58:17Z")
You would only set these variable to TRUE if you wanted to use inline MEGAN rather than providing an emissions file prepared by MEGAN offline. The issue you are encountering may be similar to the one discussed in this [previous thread](https://forum.cmascenter.org/t/how-to-replace-very-small-value-with-0-in-meganv3-2-result-with-ioapi-library/4922/).