Development and evaluation of the simplified tropospheric chemistry mechanism T4 in the Community Earth System Model (CESM) for climate simulations
Zhang, J., Emmons, L. K., Orlando, J. J., Buchholz, R., Gaubert, B., et al. (2026). Development and evaluation of the simplified tropospheric chemistry mechanism T4 in the Community Earth System Model (CESM) for climate simulations. Journal of Advances in Modeling Earth Systems, doi:https://doi.org/10.1029/2025ms005640
| Title | Development and evaluation of the simplified tropospheric chemistry mechanism T4 in the Community Earth System Model (CESM) for climate simulations |
|---|---|
| Genre | Article |
| Author(s) | Jun Zhang, Louisa K. Emmons, John J. Orlando, Rebecca Buchholz, Benjamin Gaubert, Shawn B. Honomichl, Danny M. Leung, Simone Tilmes, Kyle Shores, Francis M. Vitt |
| Abstract | Simulating atmospheric chemistry in Earth system models is critical for climate projections but remains computationally intensive. Comprehensive mechanisms, such as the MOZART-T1 scheme in the Community Earth System Model (CESM), often limit the feasibility of long-term or large-ensemble simulations. We introduce and evaluate T4, a new simplified tropospheric chemistry mechanism (63 species, 135 reactions) designed as a high-performance alternative to the standard T1 mechanism (151 species, 287 reactions). Using nudged (MERRA-2) CESM simulations for the period 2003-2008, we performed a cross-evaluation of both schemes against observational data sets, focusing on key climate-relevant species: ozone (O3), the hydroxyl radical (OH), and aerosols. The global mean tropospheric ozone column shows good agreement between the simulations, differing by less than 2%, while comparisons with ozonesonde data confirm that T4 robustly captures O3 seasonal cycles and spatial distributions. Global tropospheric O3 budgets and large-scale distributions of aerosols and OH remain highly consistent between the two schemes. Furthermore, independent process-level evaluations via box modeling confirm that T4 preserves the nonlinear sensitivities of the parent mechanism across diverse chemical regimes. While shared model biases exist, such as an underestimation of aerosol optical depth and a high-OH bias, these are present in both simulations and are not artifacts of the T4 simplification. Ultimately, the T4 scheme achieves a similar to 30% reduction in total computational cost while maintaining the scientific integrity of the complex T1 mechanism, providing a robust and efficient tool for multi-century climate simulations and ensemble studies with CESM. |
| Publication Title | Journal of Advances in Modeling Earth Systems |
| Publication Date | Sep 1, 2026 |
| Publisher's Version of Record | https://doi.org/10.1029/2025ms005640 |
| OpenSky Citable URL | https://n2t.net/ark:/85065/d75t3r23 |
| OpenSky Listing | View on OpenSky |
| ACOM Affiliations | MODELING, ACRESP, ESS |