# Error of the molecular weight for HGIIGAS **URL:** \ **Category:** CMAQ\ **Tags:** cmaq\ **Created:** [January 28, 2024, 11:36am UTC](https://forum.cmascenter.org/t/error-of-the-molecular-weight-for-hgiigas/4673 "2024-01-28T11:36:23Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Shengpo](https://avatars.discourse-cdn.com/v4/letter/s/77aa72/32.png) [@Shengpo](https://forum.cmascenter.org/u/Shengpo)\ **Post date:** [January 28, 2024, 11:36am UTC](https://forum.cmascenter.org/t/error-of-the-molecular-weight-for-hgiigas/4673/1 "2024-01-28T11:36:23Z")
I check mercury species in CCTM/src/cb6r5\_ae7\_aq and cb6r5hap\_ae7\_aq, and it appears that the molecular weight of HGIIGAS is wrong! For mercury species (HG, HGIIGAS, HGIIAER) in cb6r5, from GitHub they also share the same molecular weight (200.6 g/mol): [https://github.com/USEPA/CMAQ/blob/main/CCTM/src/MECHS/mechanism\_information/cb6r5\_ae7\_aq/cb6r5\_ae7\_aq\_species\_table.md](https://github.com/USEPA/CMAQ/blob/main/CCTM/src/MECHS/mechanism_information/cb6r5_ae7_aq/cb6r5_ae7_aq_species_table.md) I don’t know why in GC\_cb6r5hap\_ae7\_aq.nml or GC\_cb6r5\_ae7\_aq.nml, the molecular weight of HGIIGAS is 271.5 g/mol. ---
**Author:** ![foley.kristen](https://avatars.discourse-cdn.com/v4/letter/f/d9b06d/32.png) [@foley.kristen](https://forum.cmascenter.org/u/foley.kristen)\ **Post date:** [February 3, 2024, 12:37am UTC](https://forum.cmascenter.org/t/error-of-the-molecular-weight-for-hgiigas/4673/2 "2024-02-03T00:37:55Z")
Thank you for alerting us to this inconsistency. The molecular weight of 271.5 g/mol used in the GC namelist files for HGIIGAS is correct. The species table documentation has now been updated to also say 271.5. @bhutzell and @jbash provided this reference: Deanna L. Donohoue, Dieter Bauer, and Anthony J. Hynes. The Journal of Physical Chemistry A 2005 109 (34), 7732-7741. DOI: 10.1021/jp051354l