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Volume 17, issue 6
Atmos. Chem. Phys., 17, 3785-3797, 2017
https://doi.org/10.5194/acp-17-3785-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: The Modular Earth Submodel System (MESSy) (ACP/GMD inter-journal...

Atmos. Chem. Phys., 17, 3785-3797, 2017
https://doi.org/10.5194/acp-17-3785-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 20 Mar 2017

Research article | 20 Mar 2017

A new time-independent formulation of fractional release

Jennifer Ostermöller1, Harald Bönisch2, Patrick Jöckel3, and Andreas Engel1 Jennifer Ostermöller et al.
  • 1Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, Frankfurt, Germany
  • 2Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 3Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany

Abstract. The fractional release factor (FRF) gives information on the amount of a halocarbon that is released at some point into the stratosphere from its source form to the inorganic form, which can harm the ozone layer through catalytic reactions. The quantity is of major importance because it directly affects the calculation of the ozone depletion potential (ODP). In this context time-independent values are needed which, in particular, should be independent of the trends in the tropospheric mixing ratios (tropospheric trends) of the respective halogenated trace gases. For a given atmospheric situation, such FRF values would represent a molecular property.

We analysed the temporal evolution of FRF from ECHAM/MESSy Atmospheric Chemistry (EMAC) model simulations for several halocarbons and nitrous oxide between 1965 and 2011 on different mean age levels and found that the widely used formulation of FRF yields highly time-dependent values. We show that this is caused by the way that the tropospheric trend is handled in the widely used calculation method of FRF.

Taking into account chemical loss in the calculation of stratospheric mixing ratios reduces the time dependence in FRFs. Therefore we implemented a loss term in the formulation of the FRF and applied the parameterization of a mean arrival time to our data set.

We find that the time dependence in the FRF can almost be compensated for by applying a new trend correction in the calculation of the FRF. We suggest that this new method should be used to calculate time-independent FRFs, which can then be used e.g. for the calculation of ODP.

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Short summary
We analysed the temporal evolution of fractional release factors (FRFs) from EMAC model simulations for several halocarbons and nitrous oxide. The current formulation of FRFs yields values that depend on the tropospheric trend of the species. This is a problematic issue for the application of FRF in the calculation of steady-state quantities (e.g. ODP). Including a loss term in the calculation, we develop a new formulation of FRF and find that the time dependence can almost be compensated.
We analysed the temporal evolution of fractional release factors (FRFs) from EMAC model...
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