Articles | Volume 17, issue 6
Research article
20 Mar 2017
Research article |  | 20 Mar 2017

A new time-independent formulation of fractional release

Jennifer Ostermöller, Harald Bönisch, Patrick Jöckel, and Andreas Engel

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.

Please read the corrigendum first before accessing the article.


The requested paper has a corresponding corrigendum published. Please read the corrigendum first before downloading the article.

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.
Final-revised paper