# Adjust the HNO₃ dry deposition

**URL:** <https://forum.cmascenter.org/t/adjust-the-hno-dry-deposition/6148>\
**Category:** CMAQ\
**Created:** [February 8, 2026, 3:20pm UTC](https://forum.cmascenter.org/t/adjust-the-hno-dry-deposition/6148 "2026-02-08T15:20:01Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![XIAO](https://avatars.discourse-cdn.com/v4/letter/x/2acd7d/32.png) [@XIAO](https://forum.cmascenter.org/u/XIAO)\
**Post date:** [February 8, 2026, 3:20pm UTC](https://forum.cmascenter.org/t/adjust-the-hno-dry-deposition/6148/1 "2026-02-08T15:20:01Z")

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I am using CMAQ v5.3.1 with the M3Dry dry deposition scheme. I would like to modify the dry deposition velocity of gaseous HNO₃ for a sensitivity experiment. May I ask which part of the CCTM source code controls HNO₃ dry deposition and how this can be adjusted?

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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:** [February 9, 2026, 8:08pm UTC](https://forum.cmascenter.org/t/adjust-the-hno-dry-deposition/6148/2 "2026-02-09T20:08:31Z")

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We recommend upgrading to the latest version of CMAQ v5.5.

Please also search the forum for previous posts about HNO3 dry deposition as they may provide the answer that you need.

> [@About HNO3 dry deposition velocity](https://forum.cmascenter.org/t/about-hno3-dry-deposition-velocity/4032/3):
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> How you approach this depends on what processes you are considering and the CMAQ model options. If you are using the M3Dry deposition option: Constants related to cuticular and soil resistances by deposition species are found in: AS\_DATA\_MOD.F All other surface resistances are estimated in: m3dry.F The aerodynamic and stomatal resistances are passed down from the meteorological model All modifications will require a recompile of the code. Documentation can be found in Pleim and Ran 2011 ([A…](https://doi.org/10.3390/atmos2030271)