# AQCHEM maximum iterations exceeded

**URL:** <https://forum.cmascenter.org/t/aqchem-maximum-iterations-exceeded/757>\
**Category:** Chemistry and Aerosols\
**Created:** [June 14, 2019, 5:00pm UTC](https://forum.cmascenter.org/t/aqchem-maximum-iterations-exceeded/757 "2019-06-14T17:00:43Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![jzhang](https://avatars.discourse-cdn.com/v4/letter/j/df788c/32.png) [@jzhang](https://forum.cmascenter.org/u/jzhang)\
**Post date:** [June 14, 2019, 5:00pm UTC](https://forum.cmascenter.org/t/aqchem-maximum-iterations-exceeded/757/1 "2019-06-14T17:00:43Z")

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Hello!

I am running CMAQv5.2.1 for nest simulation. But it crashed for certain days with the AQCHEM error: maximum iterations exceeded. There is no NaN or Infinity showing up in my log files.

I know this is caused by MCIP generated METCRO2D file. Because when I run that day with a fake METCRO2D file (copied from other days), it ran well. However, I checked the RC and RN values in the METCRO2D file. There is no negative or unreasonable large value. I don’t know what else in the METCRO2D could cause this error.

Any help is appreciate on how to solve this issue.

Thank you so much  
Jay

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**Author:** ![lizadams](https://avatars.discourse-cdn.com/v4/letter/l/49beb7/32.png) [@lizadams](https://forum.cmascenter.org/u/lizadams)\
**Post date:** [September 12, 2019, 2:35pm UTC](https://forum.cmascenter.org/t/aqchem-maximum-iterations-exceeded/757/2 "2019-09-12T14:35:01Z")

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Jay - have you been able to resolve this issue?  
@tlspero do you have an idea of how to diagnose this problem?

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**Author:** ![jzhang](https://avatars.discourse-cdn.com/v4/letter/j/df788c/32.png) [@jzhang](https://forum.cmascenter.org/u/jzhang)\
**Post date:** [September 12, 2019, 4:39pm UTC](https://forum.cmascenter.org/t/aqchem-maximum-iterations-exceeded/757/3 "2019-09-12T16:39:35Z")

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It was caused by my mistake on GRIDDESC file. I set the cell thickness wrong. After I changed it to 1, it runs fine. Your error may be caused by other reasons. But I found my mistakes by turning on debug option while running CMAQ.

Good luck to you.  
Jay

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**Author:** ![nkwyn](https://avatars.discourse-cdn.com/v4/letter/n/b5ac83/32.png) [@nkwyn](https://forum.cmascenter.org/u/nkwyn)\
**Post date:** [July 18, 2020, 1:59pm UTC](https://forum.cmascenter.org/t/aqchem-maximum-iterations-exceeded/757/4 "2020-07-18T13:59:46Z")

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would you tell me how to turn no debug option while running CMAQ ? thanks

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**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:** [July 18, 2020, 8:23pm UTC](https://forum.cmascenter.org/t/aqchem-maximum-iterations-exceeded/757/5 "2020-07-18T20:23:41Z")

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In the bldit\_cctm.csh script, uncomment the line ‘#set Debug\_CCTM’

Alternatively, if you already have an existing BLD directory and want to recompile in debug mode, do the following (from [Chapter 5 of the User Guide](https://github.com/USEPA/CMAQ/blob/master/DOCS/Users_Guide/CMAQ_UG_ch05_running_a_simulation.md#56-compiling-cmaq-chemistry-transport-model-cctm)):

```auto
cd BLD_CCTM_v53_[compiler][version]
make clean
make DEBUG=TRUE

```

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**Author:** ![Aurora](https://avatars.discourse-cdn.com/v4/letter/a/b9e5f3/32.png) [@Aurora](https://forum.cmascenter.org/u/Aurora)\
**Post date:** [December 7, 2021, 2:47am UTC](https://forum.cmascenter.org/t/aqchem-maximum-iterations-exceeded/757/6 "2021-12-07T02:47:14Z")

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Which parameter in the MCIP script is the cell thickness you set? I didn’t find this parameter. In addition, I don’t seem to have the CMAQ debugging option you mentioned