3D: CAM-chem developments and Community Support

The Community Atmosphere Model with Chemistry (CAM-chem), a component of CESM, continues to be improved through various developments and is widely used by the community.  CAM-chem is available as part of the new release of CESM2, with a number of configurations allowing community users to quickly set up simulations with the latest version of the model for chemistry-climate or air quality simulations.  A current focus of development in CAM-chem is the capability of running full tropospheric chemistry in the Spectral Element version of CAM with regional refinement, meaning the model is run at higher horizontal resolution (14 or 25 km) over a region of the globe (e.g., the continental U.S.) with the rest of the globe at the standard ~1 degree resolution.  Initial results (Figure 1) show that the finer resolution will allow a more accurate representation of the influence of fire emissions on air quality and tropospheric composition.

The tropospheric chemistry scheme in CAM-chem has been significantly expanded and updated over the MOZART-4 chemical mechanism and will be used in the CESM2 WACCM simulations for CMIP6 (Emmons et al., 2018).  Additional chemical mechanisms with increasing complexity are being developed, such as a more detailed representation of terpene oxidation chemistry, and speciated higher alkanes that have formerly been lumped as one compound in the model.  A new volatility bin set (VBS) approach is now fully tested and integrated in CESM2 (Tilmes et al., 2018). In collaboration with the University of Wyoming, the MOSAIC gas-to-aerosol exchange scheme is being included in CESM2, which will provide a more detailed representation of inorganic aerosols, including nitrate aerosols.

The addition of the representation of very short-lived (VSL) halogen compounds to CAM-chem has resulted in a number of recent studies including analysis of UT/LS field observations (Koenig et al., 2017; Navarro et al., 2017; Wales et al., 2018), analysis of observed increase in iodine in the North Atlantic since the mid-20th century (Cuevas et al., 2018), and the role of VSL bromine chemistry in the Antarctic ozone hole (Fernandez et al., 2017).  Another area of study with university collaborators has been to compare three chemical mechanisms of different complexity in CAM-chem to assess the accuracy of the simpler mechanisms in predicting tropospheric ozone, and the trade-off in computing costs (Brown-Steiner et al., 2018).

ACOM scientists support community use of CAM-chem through scientific collaborations (such as listed above) and participation in model intercomparisons (Section 1G), as well as direct support for community users who run CAM-chem (by the Chemistry-Climate Working Group liaison).  To assist new users of CAM-chem, ACOM scientists and postdocs have created a wiki page which serves as a quick-start guide to running CAM-chem with links to additional, detailed information (https://wiki.ucar.edu/display/camchem/Home).

Carbon monoxide (CO) mixing ratios.
Figure 1.  Carbon monoxide (CO) mixing ratios for July 2013 from the standard Finite Volume (FV) configuration of CAM-chem (left) and the Regionally Refined (RR) Spectral Element (SE) version of CAM-chem (right). Click for larger image.

References

Brown-Steiner, B., Selin, N. E., Prinn, R., Tilmes, S., Emmons, L., Lamarque, J.-F., and Cameron-Smith, P., Evaluating simplified chemical mechanisms within present-day simulations of the Community Earth System Model version 1.2 with CAM4 (CESM1.2 CAM-chem): MOZART-4 vs. Reduced Hydrocarbon vs. Super-Fast chemistry, Geosci. Model Dev., 11, 4155-4174, https://doi.org/10.5194/gmd-11-4155-2018, 2018.

Cuevas et al., Rapid increase in atmospheric iodine levels in the North Atlantic since the mid-20th century, Nature Geos. Sci., DOI: 10.1038/s41467-018-03756-1, 2018.

Emmons, L.K., et al., The MOZART chemical mechanism in CESM2, to be submitted to JAMES.

Fernandez, R. P., Kinnison, D. E., Lamarque, J.-F., Tilmes, S., and Saiz-Lopez, A., Impact of biogenic very short-lived bromine on the Antarctic ozone hole during the 21st century, Atmos. Chem. Phys., 17, 1673-1688, https://doi.org/10.5194/acp-17-1673-2017, 2017.

Koenig, T. K., Volkamer, R., Baidar, S., Dix, B., Wang, S., Anderson, D. C., Salawitch, R. J., Wales, P. A., Cuevas, C. A., Fernandez, R. P., Saiz-Lopez, A., Evans, M. J., Sherwen, T., Jacob, D. J., Schmidt, J., Kinnison, D., Lamarque, J.-F., Apel, E. C., Bresch, J. C., Campos, T., Flocke, F. M., Hall, S. R., Honomichl, S. B., Hornbrook, R., Jensen, J. B., Lueb, R., Montzka, D. D., Pan, L. L., Reeves, J. M., Schauffler, S. M., Ullmann, K., Weinheimer, A. J., Atlas, E. L., Donets, V., Navarro, M. A., Riemer, D., Blake, N. J., Chen, D., Huey, L. G., Tanner, D. J., Hanisco, T. F., and Wolfe, G. M., BrO and inferred Bry profiles over the western Pacific: relevance of inorganic bromine sources and a Bry minimum in the aged tropical tropopause layer, Atmos. Chem. Phys., 17, 15245-15270, https://doi.org/10.5194/acp-17-15245-2017, 2017.

Navarro, M. A., Saiz-Lopez, A., Cuevas, C. A., Fernandez, R. P., Atlas, E., Rodriguez-Lloveras, X., Kinnison, D., Lamarque, J.-F., Tilmes, S., Thornberry, T., Rollins, A., Elkins, J. W., Hintsa, E. J., and Moore, F. L., Modeling the inorganic bromine partitioning in the tropical tropopause layer over the eastern and western Pacific Ocean, Atmos. Chem. Phys., 17, 9917-9930, https://doi.org/10.5194/acp-17- 9917-2017, 2017.

Tilmes et al., Climate forcings and  trends of organic aerosols in the Community Earth System Model (CESM2), to be submitted to JAMES.

Wales et al., Stratospheric Injection of Brominated Very Short‐Lived Substances: Aircraft Observations in the Western Pacific and Representation in Global Models, J. of Geophys. Res., 123, 5690-5719, https://doi.org/10.1029/2017JD027978, 2018.