# CH4 simulation in CMAQ

**URL:** <https://forum.cmascenter.org/t/ch4-simulation-in-cmaq/5041>\
**Category:** CMAQ\
**Tags:** cmaq\
**Created:** [June 29, 2024, 2:13pm UTC](https://forum.cmascenter.org/t/ch4-simulation-in-cmaq/5041 "2024-06-29T14:13:11Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![fengsz](https://avatars.discourse-cdn.com/v4/letter/f/53a042/32.png) [@fengsz](https://forum.cmascenter.org/u/fengsz)\
**Post date:** [June 29, 2024, 2:13pm UTC](https://forum.cmascenter.org/t/ch4-simulation-in-cmaq/5041/1 "2024-06-29T14:13:11Z")

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Hi all,

I want to activate CH4 simulation in CMAQ with ready emissions and ICBC files. I found there are CH4 species in the `mech.def` file, but not in the `GC_cb05tucl_ae6_aq.nml` file. What should I do? Do I need to use the CHEMMECH tool?

Additionally, does anyone know how significant the differences in concentrations are with or without OH/CH+CH4 reactions in regional simulations when the boundary conditions come from a global model?

Thank you in advance.

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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:** [July 2, 2024, 12:30pm UTC](https://forum.cmascenter.org/t/ch4-simulation-in-cmaq/5041/3 "2024-07-02T12:30:19Z")

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Please review this previous post about CH4 in CMAQ. [How are background methane and emissions methane handled in CMAQ?](https://forum.cmascenter.org/t/how-are-background-methane-and-emissions-methane-handled-in-cmaq/2329)

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**Author:** ![fengsz](https://avatars.discourse-cdn.com/v4/letter/f/53a042/32.png) [@fengsz](https://forum.cmascenter.org/u/fengsz)\
**Post date:** [July 2, 2024, 2:07pm UTC](https://forum.cmascenter.org/t/ch4-simulation-in-cmaq/5041/4 "2024-07-02T14:07:46Z")

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I have resolved by modifing F code. Thanks all.