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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, D14302, doi:10.1029/2007JD009617, 2008

Evaluation of emissions and transport of CFCs using surface observations and their seasonal cycles and the GEOS CCM simulation with emissions-based forcing

Qing Liang

NASA Goddard Space Flight Center, Atmospheric Chemistry and Dynamics Branch, Greenbelt, Maryland, USA
Oak Ridge Associated Universities, NASA Postdoctoral Program, Oak Ridge, Tennessee, USA

Richard S. Stolarski

NASA Goddard Space Flight Center, Atmospheric Chemistry and Dynamics Branch, Greenbelt, Maryland, USA

Anne R. Douglass

NASA Goddard Space Flight Center, Atmospheric Chemistry and Dynamics Branch, Greenbelt, Maryland, USA

Paul A. Newman

NASA Goddard Space Flight Center, Atmospheric Chemistry and Dynamics Branch, Greenbelt, Maryland, USA

J. Eric Nielsen

NASA Goddard Space Flight Center, Global Modeling and Assimilation Office, Greenbelt, Maryland, USA
Science Systems and Applications Inc., Lanham, Maryland, USA

Abstract

Levels of ozone depleting substances (ODSs) in our atmosphere are determined by production, emission, and loss processes. However, atmospheric models are forced by the specified mixing ratios of these ODSs rather than the more fundamental emissions-based forcing. To more accurately represent the physics and chemistry of climate change on atmospheric circulation and ODSs, and therefore future ozone recovery, it is desirable to switch from the current highly constrained mixing-ratio-based forcing to emissions-based forcing in general circulation models (GCMs). As a first step of this model transition, we have conducted a 45-year (1960–2005) emissions-based simulation of the three primary chlorofluorocarbons (CFC-11, -12, -113) using the GEOS coupled chemistry-climate model (CCM). The simulated CFC concentrations and their seasonal cycles are compared with AGAGE and NOAA-GMD observations to evaluate emissions and atmospheric transport. The simulated CFC-12 agrees well with the observations, indicating a good estimate of emission and atmospheric loss. The simulated CFC-11 and CFC-113 shows high biases due to overestimate of emissions. Using tagged CFC tracers to track recent surface emissions and aged air masses transported downward from the stratosphere separately, we quantify the relative contribution of stratosphere-troposphere exchange (STE) and tropospheric transport to the seasonal cycles of CFCs in the lower troposphere. The seasonal cycles of CFCs in the lower troposphere are dominated by tropospheric transport of recent emissions during 1985–1994. The 1995–1999 period marks the transition period when variations due to fresh emissions and STE become equally important. Seasonal cycles of CFCs at most surface sites in the 2000–2004 period are dominated by STE. Seasonal cycles of CFCs due to STE show a late winter/early spring maximum and a summer/fall minimum. Seasonality of the tropospheric transport component at individual stations is governed by seasonal transport variations of fresh emissions from the polluted regions.

Received 15 November 2007; accepted 13 March 2008; published 17 July 2008.

Keywords: CFC; chemistry climate model; ODS.

Index Terms: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0341 Atmospheric Composition and Structure: Middle atmosphere: constituent transport and chemistry (3334); 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry.

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Citation: Liang, Q., R. S. Stolarski, A. R. Douglass, P. A. Newman, and J. E. Nielsen (2008), Evaluation of emissions and transport of CFCs using surface observations and their seasonal cycles and the GEOS CCM simulation with emissions-based forcing, J. Geophys. Res., 113, D14302, doi:10.1029/2007JD009617.

Copyright 2008 by the American Geophysical Union.