Why are there large differences between models in global budgets of tropospheric ozone?

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Read Full Article (file size: 1215130 bytes) Cited by JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D05302, doi:10.1029/2006JD007801, 2007 Why are there large differences between models in global budgets of tropospheric ozone? Shiliang Wu Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA Loretta J. Mickley Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA Daniel J. Jacob Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA Jennifer A. Logan Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA Robert M. Yantosca Division of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA David Rind NASA Goddard Institute for Space Studies, New York, New York, USA Abstract Global 3-D tropospheric chemistry models in the literature show large differences in global budget terms for tropospheric ozone. The ozone production rate in the troposphere, P(O _x), varies from 2300 to 5300 Tg yr⁻¹ across models describing the present-day atmosphere. The ensemble mean of P(O _x) in models from the post-2000 literature is 35% higher than that compiled in the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR). Simulations conducted with the GEOS-Chem model using two different assimilated meteorological data sets for 2001 (GEOS-3 and GEOS-4), as well as 3 years of GISS GCM meteorology, show P(O _x) values in the range 4250–4700 Tg yr⁻¹; the differences appear mostly because of clouds. Examination of the evolution of P(O _x) over the GEOS-Chem model history shows major effects from changes in heterogeneous chemistry, the lightning NO_x source, and the yield of organic nitrates from isoprene oxidation. Multivariate statistical analysis of model budgets in the literature indicates that 74% of the variance in P(O _x) across models can be explained by differences in NO_x emissions, inclusion of nonmethane volatile organic compounds (NMVOCs, mostly biogenic isoprene), and ozone influx from stratosphere-troposphere exchange (STE). Higher NO_x emissions, more widespread inclusion of NMVOC chemistry, and weaker STE in the more recent models increase ozone production; however, the effect of NMVOCs does not appear generally sensitive to the magnitude of emissions within the range typically used in models (500–900 Tg C yr⁻¹). We find in GEOS-Chem that P(O _x) saturates when NMVOC emissions exceed 200 Tg C yr⁻¹ because of formation of organic nitrates from isoprene oxidation, providing an important sink for NO_x. Received 17 July 2006; accepted 6 November 2006; published 3 March 2007. Keywords: global model; tropospheric chemistry; ozone production; nonmethane hydrocarbons; NO_x emissions; stratosphere-troposphere exchange. Index Terms: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry; 3324 Atmospheric Processes: Lightning; 3362 Atmospheric Processes: Stratosphere/troposphere interactions. Read Full Article (file size: 1215130 bytes) Cited by Citation: Wu, S., L. J. Mickley, D. J. Jacob, J. A. Logan, R. M. Yantosca, and D. Rind (2007), Why are there large differences between models in global budgets of tropospheric ozone?, J. Geophys. Res., 112, D05302, doi:10.1029/2006JD007801. Copyright 2007 by the American Geophysical Union.

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