# A confusion about change Aerosol Refractive Indices **URL:** \ **Category:** CMAQ\ **Created:** [June 14, 2023, 2:31am UTC](https://forum.cmascenter.org/t/a-confusion-about-change-aerosol-refractive-indices/4172 "2023-06-14T02:31:32Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![bandaoshutiao](https://avatars.discourse-cdn.com/v4/letter/b/9fc348/32.png) [@bandaoshutiao](https://forum.cmascenter.org/u/bandaoshutiao)\ **Post date:** [June 14, 2023, 2:31am UTC](https://forum.cmascenter.org/t/a-confusion-about-change-aerosol-refractive-indices/4172/1 "2023-06-14T02:31:32Z")
Hi There seems two way to change **Aerosol Refractive Indices** , when I search in `/CMAQ/UTIL/inline_phot_preproc/readne.md`. One is use enviroment vars in `AE_REFRAC_LIST` , another is change the _OPTICS_ entries in the aerosol species name list. Is this two way as a same thing? If I change all _OPTICS_ in zero, is this means all **Aerosol Refractive Indices** is zero? Looking forward your reply !! ---
**Author:** ![bhutzell](https://avatars.discourse-cdn.com/v4/letter/b/dfb087/32.png) [@bhutzell](https://forum.cmascenter.org/u/bhutzell)\ **Post date:** [June 28, 2023, 7:17pm UTC](https://forum.cmascenter.org/t/a-confusion-about-change-aerosol-refractive-indices/4172/2 "2023-06-28T19:17:08Z")
Both ways deal with the aerosol refractive indices used by the CMAQ model but they do not accomplish the same function. - `AE_REFRAC_LIST` defines what raw data files to process for refractive indices in PHOT\_OPTICS, _an input file for the CMAQ model_. The processing converts the raw data to the wave bands used by the inline calculation of CMAQ photolysis frequencies. A CMAQ aerosol species or component can use any of these refractive indices. The defaults are assigned in the AERO\_DATA.F file. - **OPTICS** allows overriding the default assignments to different refractive indices available in the PHOT\_OPTICS files. The value should be a character string **not** a real number used as a scaling factor. As a side note, I recommend against setting refractive indices to zero. Such materials have weird properties affecting light’s phase and probably do not exist naturally. Researchers are trying create them for applications such as quantum computing computer chips. Also, the CMAQ code will encounter floating point errors (_division by zero_) if all aerosol refractive indices equal zero. ---
**Author:** ![bandaoshutiao](https://avatars.discourse-cdn.com/v4/letter/b/9fc348/32.png) [@bandaoshutiao](https://forum.cmascenter.org/u/bandaoshutiao)\ **Post date:** [June 30, 2023, 7:01am UTC](https://forum.cmascenter.org/t/a-confusion-about-change-aerosol-refractive-indices/4172/3 "2023-06-30T07:01:06Z")
I want to conduct a sensitivity experiment where the refractive indices of all aerosols is set to zero to test the impact of aerosols on other substances. Does this imply that there is currently no straightforward method to achieve this in CMAQ? ---
**Author:** ![bhutzell](https://avatars.discourse-cdn.com/v4/letter/b/dfb087/32.png) [@bhutzell](https://forum.cmascenter.org/u/bhutzell)\ **Post date:** [June 30, 2023, 11:25pm UTC](https://forum.cmascenter.org/t/a-confusion-about-change-aerosol-refractive-indices/4172/4 "2023-06-30T23:25:18Z")
I believe that a method exists. Try commenting out the line `CALL GET_AERO_DATA` in phot.F and recompile the model. ---
**Author:** ![bandaoshutiao](https://avatars.discourse-cdn.com/v4/letter/b/9fc348/32.png) [@bandaoshutiao](https://forum.cmascenter.org/u/bandaoshutiao)\ **Post date:** [July 27, 2023, 1:51am UTC](https://forum.cmascenter.org/t/a-confusion-about-change-aerosol-refractive-indices/4172/5 "2023-07-27T01:51:26Z")
Thank you very much. I will do a test.