How does cmaq deal with stratospheric chemistry?

Hi all, I’m currently trying to use CMAQ to simulate SO2 and sulfate at the bottom of the stratosphere, at an altitude of about 16-20km (50-100hPa).
I would like to find out how CMAQ handles stratospheric chemistry, in particular the chemical mechanisms associated with sulfates, and stratospheric tropospheric exchange (STE)?
I’m using cmaq 5.0.2 and I’ve searched the tutorials and scientific documents but haven’t found a detailed description of stratospheric chemistry for the moment. Where can I find the appropriate code or documentation? Should I update the version of CMAQ?
Thank you all.

Yes, you should update to use the latest release of CMAQv5.4 to benefit from the latest code improvements.

Regarding stratospheric chemistry, it is my understanding that CMAQ does not handle this.

There is a paper about stratospheric intrusion. Hopefully one of the authors of that study will be able to follow up with a more detailed explanation.

The S(IV) to S(VI) chemical conversions between 50-100hPa are represented the same way as in the lower troposphere. Currently, the model top for majority of CMAQ applications is 50hPa and the model does not include any explicit stratospheric chemistry reactions. Nevertheless, the effects of stratosphere-troposphere exchange (STE) on O3 mixing ratios in the UTLS can be represented by invoking the potential vorticity (PV) scaling option in newer versions of CMAQ (see section 6.13 of the CMAQ User’s Guide). You can find more information on the formulation of the PV-based parameterization for O3 and its performance relative to measurements in: (ACP - Representing the effects of stratosphere–troposphere exchange on 3-D O3 distributions in chemistry transport models using a potential vorticity-based parameterization; ACP - Extending the Community Multiscale Air Quality (CMAQ) modeling system to hemispheric scales: overview of process considerations and initial applications) and comparisons of predicted 3D O3 distributions with other global models (ACP - Impacts of different characterizations of large-scale background on simulated regional-scale ozone over the continental United States). Other studies assessing STE impacts that may be of interest:

Yes, we do recommend updating to CMAQv5.4.

Thanks for the reply, I will try to use the latest CMAQ version.

Thank you for your reply.
I still have some questions about the hemispherical CMAQ. Is this a publicly downloadable version of CMAQ? I didn’t find it in the CMAQ github.
Or does hemispheric CMAQ just use different input files? (I found the corresponding script run_cctm_2015_HEMI.csh within CCTM/scripts)
Best wishes.

Yes, updating to CMAQv5.4 will enable you to use all the relevant process updates for running CMAQ on hemispheric scales.