Preprints
https://doi.org/10.5194/egusphere-2024-470
https://doi.org/10.5194/egusphere-2024-470
21 Feb 2024
 | 21 Feb 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Intercomparison of GEOS-Chem and CAM-chem tropospheric oxidant chemistry within the Community Earth System Model version 2 (CESM2)

Haipeng Lin, Louisa K. Emmons, Elizabeth W. Lundgren, Laura Hyesung Yang, Xu Feng, Ruijun Dang, Shixian Zhai, Yunxiao Tang, Makoto M. Kelp, Nadia K. Colombi, Sebastian D. Eastham, Thibaud M. Fritz, and Daniel J. Jacob

Abstract. Tropospheric ozone is a major air pollutant and greenhouse gas. It is also the primary precursor of OH, the main tropospheric oxidant. Global atmospheric chemistry models show large differences in their simulations of tropospheric ozone budgets. Here we implement the widely used GEOS-Chem atmospheric chemistry module as an alternative to CAM-chem within the Community Earth System Model version 2 (CESM2). We compare the resulting simulations of tropospheric ozone and related species to observations from ozonesondes, the ATom-1 aircraft campaign over the Pacific and Atlantic, and the KORUS-AQ aircraft campaign over the Seoul Metropolitan Area. We find that GEOS-Chem and CAM-chem within CESM2 have similar tropospheric ozone budgets and concentrations usually within 5 ppb but important differences in the underlying processes including (1) photolysis scheme (no aerosol effects in CAM-chem), (2) aerosol nitrate photolysis, (3) N2O5 cloud uptake, (4) tropospheric halogen chemistry, and (5) ozone deposition to the oceans. Global tropospheric OH concentrations are the same in both models but there are large regional differences reflecting the above processes. Carbon monoxide is lower in CAM-chem (and lower than observations) because of higher OH concentrations in the northern hemisphere and insufficient production from isoprene oxidation in the southern hemisphere. CESM2 does not scavenge water-soluble gases in convective updrafts leading to some upper tropospheric biases. Comparison to KORUS-AQ observations shows successful simulation of oxidants under polluted conditions in both models but suggests insufficient boundary layer mixing in CESM2. The implementation and evaluation of GEOS-Chem in CESM2 contributes to the MUSICA vision of modularizing tropospheric chemistry in Earth system models.

Haipeng Lin, Louisa K. Emmons, Elizabeth W. Lundgren, Laura Hyesung Yang, Xu Feng, Ruijun Dang, Shixian Zhai, Yunxiao Tang, Makoto M. Kelp, Nadia K. Colombi, Sebastian D. Eastham, Thibaud M. Fritz, and Daniel J. Jacob

Status: open (until 03 May 2024)

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  • RC1: 'Comment on egusphere-2024-470', Anonymous Referee #1, 08 Apr 2024 reply
Haipeng Lin, Louisa K. Emmons, Elizabeth W. Lundgren, Laura Hyesung Yang, Xu Feng, Ruijun Dang, Shixian Zhai, Yunxiao Tang, Makoto M. Kelp, Nadia K. Colombi, Sebastian D. Eastham, Thibaud M. Fritz, and Daniel J. Jacob
Haipeng Lin, Louisa K. Emmons, Elizabeth W. Lundgren, Laura Hyesung Yang, Xu Feng, Ruijun Dang, Shixian Zhai, Yunxiao Tang, Makoto M. Kelp, Nadia K. Colombi, Sebastian D. Eastham, Thibaud M. Fritz, and Daniel J. Jacob

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Short summary
Tropospheric ozone is a major air pollutant, greenhouse gas, and a major indicator of model skill. Global atmospheric chemistry models show large differences in simulations of tropospheric ozone but isolating sources of differences is complicated by different model environments. By implementing the GEOS-Chem model side-by-side to CAM-chem within a common Earth system model, we identify and evaluate specific differences between the two models and their impacts on key chemical species.