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A refined method for calculating equivalent effective stratospheric chlorine

Engel, Andreas and Bönisch, Harald and Ostermöller, Jennifer and Chipperfield, Martyn P. and Dhomse, Sandip and Jöckel, Patrick (2018) A refined method for calculating equivalent effective stratospheric chlorine. Atmospheric Chemistry and Physics (ACP), 18 (2), pp. 601-619. Copernicus Publications. DOI: 10.5194/acp-18-601-2018 ISSN 1680-7316

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Official URL: https://www.atmos-chem-phys.net/18/601/2018/

Abstract

Chlorine and bromine atoms lead to catalytic depletion of ozone in the stratosphere. Therefore the use and production of ozone-depleting substances (ODSs) containing chlorine and bromine is regulated by the Montreal Protocol to protect the ozone layer. Equivalent effective stratospheric chlorine (EESC) has been adopted as an appropriate metric to describe the combined effects of chlorine and bromine released from halocarbons on stratospheric ozone. Here we revisit the concept of calculating EESC. We derive a refined formulation of EESC based on an advanced concept of ODS propagation into the stratosphere and reactive halogen release. A new transit time distribution is introduced in which the age spectrum for an inert tracer is weighted with the release function for inorganic halogen from the source gases. This distribution is termed the "release time distribution". We show that a much better agreement with inorganic halogen loading from the chemistry transport model TOMCAT is achieved compared with using the current formulation. The refined formulation shows EESC levels in the year 1980 for the mid-latitude lower stratosphere, which are significantly lower than previously calculated. The year 1980 is commonly used as a benchmark to which EESC must return in order to reach significant progress towards halogen and ozone recovery. Assuming that - under otherwise unchanged conditions - the EESC value must return to the same level in order for ozone to fully recover, we show that it will take more than 10 years longer than estimated in this region of the stratosphere with the current method for calculation of EESC. We also present a range of sensitivity studies to investigate the effect of changes and uncertainties in the fractional release factors and in the assumptions on the shape of the release time distributions. We further discuss the value of EESC as a proxy for future evolution of inorganic halogen loading under changing atmospheric dynamics using simulations from the EMAC model. We show that while the expected changes in stratospheric transport lead to significant differences between EESC and modelled inorganic halogen loading at constant mean age, EESC is a reasonable proxy for modelled inorganic halogen on a constant pressure level.

Item URL in elib:https://elib.dlr.de/118415/
Document Type:Article
Title:A refined method for calculating equivalent effective stratospheric chlorine
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Engel, AndreasUniv. FrankfurtUNSPECIFIED
Bönisch, HaraldUniv. FrankfurtUNSPECIFIED
Ostermöller, JenniferUniv. FrankfurtUNSPECIFIED
Chipperfield, Martyn P.Univ. LeedsUNSPECIFIED
Dhomse, SandipUniv. LeedsUNSPECIFIED
Jöckel, PatrickDLR, IPAhttps://orcid.org/0000-0002-8964-1394
Date:19 January 2018
Journal or Publication Title:Atmospheric Chemistry and Physics (ACP)
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:18
DOI :10.5194/acp-18-601-2018
Page Range:pp. 601-619
Publisher:Copernicus Publications
ISSN:1680-7316
Status:Published
Keywords:stratospheric chlorine, ozone depleting substances, ODS, EMAC, ECHAM/MESSy Atmospheric Chemistry, Earth System Chemistry integrated Modelling (ESCiMo), ozone, stratosphere, EESC, TOMCAT
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Erdbeobachtung
DLR - Research theme (Project):R - Vorhaben Atmosphären- und Klimaforschung, R - Project Climatic relevance of atmospheric tracer gases, aerosols and clouds
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Earth System Modelling
Deposited By: Jöckel, Dr. Patrick
Deposited On:24 Jan 2018 14:20
Last Modified:02 May 2019 13:59

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