Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 15, 11789-11805, 2015
http://www.atmos-chem-phys.net/15/11789/2015/
doi:10.5194/acp-15-11789-2015
© Author(s) 2015. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
23 Oct 2015
Implications of carbon monoxide bias for methane lifetime and atmospheric composition in chemistry climate models
S. A. Strode1,2, B. N. Duncan2, E. A. Yegorova2,3,a, J. Kouatchou2,4, J. R. Ziemke2,5, and A. R. Douglass2 1GESTAR, Universities Space Research Association, Columbia, MD, USA
2NASA Goddard Space Flight Center, Greenbelt, MD, USA
3Earth System Science Interdisciplinary Center, College Park, MD, USA
4Science Systems and Applications Inc., Lanham, MD, USA
5GESTAR, Morgan State University, Baltimore, MD, USA
anow at: Nuclear Regulatory Commission, Rockville, MD, USA
Abstract. A low bias in carbon monoxide (CO) at northern high and mid-latitudes is a common feature of chemistry climate models (CCMs) that may indicate or contribute to a high bias in simulated OH and corresponding low bias in methane lifetime. We use simulations with CO tagged by source type to investigate the sensitivity of the CO bias to CO emissions, transport, global mean OH, and the hemispheric asymmetry of OH. We also investigate how each of these possible contributors to the CO bias affects the methane lifetime. We find that the use of specified meteorology alters the distribution of CO compared to a free-running CCM simulation, improving the comparison with surface observations in summer. Our results also show that reducing the hemispheric asymmetry of OH improves the agreement of simulated CO with observations. We use simulations with parameterized OH to quantify the impact of known model biases on simulated OH. Removing biases in ozone and water vapor as well as reducing Northern Hemisphere NOx does not remove the hemispheric asymmetry in OH, but it reduces global mean OH by 18 %, bringing the simulated methane lifetime into agreement with observation-based estimates.

Citation: Strode, S. A., Duncan, B. N., Yegorova, E. A., Kouatchou, J., Ziemke, J. R., and Douglass, A. R.: Implications of carbon monoxide bias for methane lifetime and atmospheric composition in chemistry climate models, Atmos. Chem. Phys., 15, 11789-11805, doi:10.5194/acp-15-11789-2015, 2015.
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Short summary
A low bias in carbon monoxide (CO) at northern latitudes is a common feature of chemistry climate models. We find that increasing Northern Hemisphere (NH) CO emissions or reducing NH OH concentrations improves the agreement with CO surface observations, but reducing NH OH leads to a better comparison with MOPITT. Removing model biases in ozone and water vapor increases the simulated methane lifetime, but it does not give the 20% reduction in NH OH suggested by our analysis of the CO bias.
A low bias in carbon monoxide (CO) at northern latitudes is a common feature of chemistry...
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