Middle Atmosphere Processes and Lifetime Evaluation for ODSs and GHGs (MAPLE)
Lead Research Organisation:
University of Leeds
Department Name: School of Earth and Environment
Abstract
Gases emitted into the atmosphere can persist for many years or even centuries. The rate at which a gas is removed is determined by its so-called lifetime. Therefore, to understand the impact of, for example, pollutant gases emitted by human activity, it is essential to have an accurate knowledge of their atmospheric lifetimes. However, there is currently large uncertainty in the known lifetime of many key pollutant gases.
Ozone-depleting substances (ODS), such as chlorofluorocarbons (CFCs), are long-lived source gases which decompose in the stratosphere to release chlorine and bromine. Under the Montreal Protocol the emissions of these species have been phased out and the ozone layer is expected to recover over the next 50-100 years. However, the rate of this recovery will depend on the atmospheric lifetime of the these gases and their replacements which are still being emitted. In fact, there is currently significant uncertainty in these atmospheric lifetimes, which are used in all model predictions of future halogen loadings (via predicted surface mixing ratio model boundary conditions). For example, a major chlorofluorocarbon CFC-11 has a quoted atmospheric lifetime of 45 years in WMO and IPCC assessments, although other studies suggest a lifetime of up to 60 years.
This key uncertainty has been recognised by the recent establishment of a World Climate Research Program (WCRP) Stratospheric Processes and their Role in Climate (SPARC) project to re-evaluate the lifetimes of these ODS and their replacements (such as hydrofluorocarbons, HFCs) using up-to-date laboratory data in state-of-the-art 3-D chemistry-climate models (CCMs). These species are also efficient greenhouse gases (GHGs) and changes to their known atmospheric lifetime will change estimates of how they will affect climate change (as measured by their global warming/temperature potential (GWP/GTP)). This project will ensure full participation of the UK's chemistry-climate model (UKCA) in the WCRP/SPARC re-evaluation.
Lifetime estimates directly affect model predictions of future ozone recovery. Previous CCM studies of the recovery of the ozone layer have used projected future surface ODS concentrations based on old lifetime estimates and a simple box model. Therefore, the major driver of future ozone change, the stratospheric chlorine and bromine loading, has been constrained with crude time-dependent boundary conditions. A more realistic representation of the rate of ozone recovery can be obtained by removing this constraint and running the CCMs with emission flux surface boundary conditions for major ODSs, and allow the model itself to predict the future decadal removal of chlorine and bromine. We will perform these simulations within this project.
Source gases with very long lifetimes (many hundreds to thousands of years) are too stable to affect stratospheric ozone by decomposition but they are invariably potent GHGs. For these gases loss processes in the upper atmosphere (mesosphere), which are usually ignored or treated very crudely, could significantly reduce their atmospheric lifetime, thereby decreasing their estimated climate impact. Three examples of such gases are NF3, CFC-115, and SF6. We have identified that the reactions of these gases with metallic atoms (Fe, Na and Mg) which are present in the upper mesosphere could be an important additional sink and compete with Lyman-alpha photolysis and other reactions. We will evaluate the rates of these sinks in the laboratory.
For all of the gases studied, we will produce new, improved estimates of their climate impact by recalculating their GWP/GTP values.
This project will use the UK's core tropospheric-stratospheric chemistry-climate model (UKCA). The testing and development work performed will lead to an improved, and more thoroughly tested, model for the UK community of researchers
Ozone-depleting substances (ODS), such as chlorofluorocarbons (CFCs), are long-lived source gases which decompose in the stratosphere to release chlorine and bromine. Under the Montreal Protocol the emissions of these species have been phased out and the ozone layer is expected to recover over the next 50-100 years. However, the rate of this recovery will depend on the atmospheric lifetime of the these gases and their replacements which are still being emitted. In fact, there is currently significant uncertainty in these atmospheric lifetimes, which are used in all model predictions of future halogen loadings (via predicted surface mixing ratio model boundary conditions). For example, a major chlorofluorocarbon CFC-11 has a quoted atmospheric lifetime of 45 years in WMO and IPCC assessments, although other studies suggest a lifetime of up to 60 years.
This key uncertainty has been recognised by the recent establishment of a World Climate Research Program (WCRP) Stratospheric Processes and their Role in Climate (SPARC) project to re-evaluate the lifetimes of these ODS and their replacements (such as hydrofluorocarbons, HFCs) using up-to-date laboratory data in state-of-the-art 3-D chemistry-climate models (CCMs). These species are also efficient greenhouse gases (GHGs) and changes to their known atmospheric lifetime will change estimates of how they will affect climate change (as measured by their global warming/temperature potential (GWP/GTP)). This project will ensure full participation of the UK's chemistry-climate model (UKCA) in the WCRP/SPARC re-evaluation.
Lifetime estimates directly affect model predictions of future ozone recovery. Previous CCM studies of the recovery of the ozone layer have used projected future surface ODS concentrations based on old lifetime estimates and a simple box model. Therefore, the major driver of future ozone change, the stratospheric chlorine and bromine loading, has been constrained with crude time-dependent boundary conditions. A more realistic representation of the rate of ozone recovery can be obtained by removing this constraint and running the CCMs with emission flux surface boundary conditions for major ODSs, and allow the model itself to predict the future decadal removal of chlorine and bromine. We will perform these simulations within this project.
Source gases with very long lifetimes (many hundreds to thousands of years) are too stable to affect stratospheric ozone by decomposition but they are invariably potent GHGs. For these gases loss processes in the upper atmosphere (mesosphere), which are usually ignored or treated very crudely, could significantly reduce their atmospheric lifetime, thereby decreasing their estimated climate impact. Three examples of such gases are NF3, CFC-115, and SF6. We have identified that the reactions of these gases with metallic atoms (Fe, Na and Mg) which are present in the upper mesosphere could be an important additional sink and compete with Lyman-alpha photolysis and other reactions. We will evaluate the rates of these sinks in the laboratory.
For all of the gases studied, we will produce new, improved estimates of their climate impact by recalculating their GWP/GTP values.
This project will use the UK's core tropospheric-stratospheric chemistry-climate model (UKCA). The testing and development work performed will lead to an improved, and more thoroughly tested, model for the UK community of researchers
Planned Impact
Policy makers, atmospheric scientists and the general public will be among the long-term beneficiaries of this research. The work relates to two major policy questions; the control of halogenated substances, regulated under the Montreal Protocol, and climate change, the topic of the Kyoto Protocol. MAPLE address the atmospheric lifetime of major ozone-depleting substances and greenhouse gases. Our science will inform the international assessment processes and will be of direct interest to government departments, chiefly DECC and DEFRA.
MAPLE will further develop modelling tools for chemistry-climate studies and the wider research community will be beneficiaries. In particular, the community of users of the UKCA model is growing and these enhancements will make the model an even more suitable tool for a wider range of studies. UKCA for a major part of the QESM model, and the model development and testing performed in MAPLE will benefit the wider Earth System Science community.
The general public has a keen interest in global change, in general, and ozone depletion, in particular. It remains extremely important to engage with the public, to provide latest scientific evidence related to these issues, to counter the increasing levels of misinformation being propagated.
We will engage with these various groups in a number if ways: through formal and informal meetings, through the peer-reviewed literature and through our web pages. All of the PIs/Co-Is give popular lectures on environmental change issues at e.g. schools and will continue to do so. We also often speak to the media.
Results from MAPLE will feed into future IPCC and WMO/UNEP (ozone) assessments. We have been heavily engaged with these in the past. The PIs/Co-Is have served as convening lead authors for WMO/UNEP, or chapter authors/reviewers. Braesicke works in the same group as Prof. John Pyle who is currently an International Co-Chair of the assessment.
We will organise a focussed workshop towards the end of the project in which we will attempt to provide a key interface between scientists, media, government civil servants and key industries.
MAPLE will further develop modelling tools for chemistry-climate studies and the wider research community will be beneficiaries. In particular, the community of users of the UKCA model is growing and these enhancements will make the model an even more suitable tool for a wider range of studies. UKCA for a major part of the QESM model, and the model development and testing performed in MAPLE will benefit the wider Earth System Science community.
The general public has a keen interest in global change, in general, and ozone depletion, in particular. It remains extremely important to engage with the public, to provide latest scientific evidence related to these issues, to counter the increasing levels of misinformation being propagated.
We will engage with these various groups in a number if ways: through formal and informal meetings, through the peer-reviewed literature and through our web pages. All of the PIs/Co-Is give popular lectures on environmental change issues at e.g. schools and will continue to do so. We also often speak to the media.
Results from MAPLE will feed into future IPCC and WMO/UNEP (ozone) assessments. We have been heavily engaged with these in the past. The PIs/Co-Is have served as convening lead authors for WMO/UNEP, or chapter authors/reviewers. Braesicke works in the same group as Prof. John Pyle who is currently an International Co-Chair of the assessment.
We will organise a focussed workshop towards the end of the project in which we will attempt to provide a key interface between scientists, media, government civil servants and key industries.
Organisations
Publications
Dhomse S
(2018)
Estimates of ozone return dates from Chemistry-Climate Model Initiative simulations
in Atmospheric Chemistry and Physics
Kovács T
(2017)
Determination of the atmospheric lifetime and global warming potential of sulfur hexafluoride using a three-dimensional model
in Atmospheric Chemistry and Physics
Morgenstern O
(2017)
Review of the global models used within phase 1 of the Chemistry-Climate Model Initiative (CCMI)
in Geoscientific Model Development
Liang Q
(2017)
Deriving Global OH Abundance and Atmospheric Lifetimes for Long-Lived Gases: A Search for CH3CCl3 Alternatives.
in Journal of geophysical research. Atmospheres : JGR
Sukhodolov T
(2016)
Evaluation of simulated photolysis rates and their response to solar irradiance variability
in Journal of Geophysical Research: Atmospheres
Kovács T
(2016)
<i>D</i>-region ion-neutral coupled chemistry (Sodankylä Ion Chemistry, SIC) within the Whole Atmosphere Community Climate Model (WACCM 4) - WACCM-SIC and WACCM-rSIC
in Geoscientific Model Development
Chipperfield M
(2016)
Model Sensitivity Studies of the Decrease in Atmospheric Carbon Tetrachloride
Poulain V
(2016)
Evaluation of the inter-annual variability of stratospheric chemical composition in chemistry-climate models using ground-based multi species time series
in Journal of Atmospheric and Solar-Terrestrial Physics
Totterdill A
(2016)
Atmospheric lifetimes, infrared absorption spectra, radiative forcings and global warming potentials of NF<sub>3</sub> and CF<sub>3</sub>CF<sub>2</sub>Cl (CFC-115)
in Atmospheric Chemistry and Physics
Dhomse S
(2016)
On the ambiguous nature of the 11 year solar cycle signal in upper stratospheric ozone
in Geophysical Research Letters
Totterdill A
(2016)
Correction to "Experimental Study of the Mesospheric Removal of NF3 by Neutral Meteoric Metals and Lyman-a Radiation".
in The journal of physical chemistry. A
Dhomse SS
(2015)
Revisiting the hemispheric asymmetry in midlatitude ozone changes following the Mount Pinatubo eruption: A 3-D model study.
in Geophysical research letters
Totterdill A
(2015)
Mesospheric removal of very long-lived greenhouse gases SF6 and CFC-115 by metal reactions, Lyman-a photolysis, and electron attachment.
in The journal of physical chemistry. A
Chipperfield MP
(2015)
Quantifying the ozone and ultraviolet benefits already achieved by the Montreal Protocol.
in Nature communications
Chipperfield M
(2014)
Multimodel estimates of atmospheric lifetimes of long-lived ozone-depleting substances: Present and future
in Journal of Geophysical Research: Atmospheres
Totterdill A
(2014)
Experimental study of the mesospheric removal of NF3 by neutral meteoric metals and Lyman-a radiation.
in The journal of physical chemistry. A
Description | - Some previous estimates of lifetimes of atmospheric gases were in error by a considerable amount. We have derived updated estimates of these lifetimes. - We have derived a new best estimate for the long-lived greenhouse gas sulphur hexafluoride. - We have diagnosed the main factors which control the lifetimes of atmospheric gases in the troposphere and stratosphere. |
Exploitation Route | The following sectors need accurate estimates of atmospheric lifetimes: - Policy makers - Chemical Manufacturing Industries - Atmospheric Scientists |
Sectors | Chemicals Environment |
URL | http://www.see.leeds.ac.uk/research/icas/research-themes/atmospheric-chemistry-and-aerosols/groups/atmospheric-chemistry/projects/maple-middle-atmosphere-processes-and-lifetime-estimates/ |
Description | - Used in the WMO/UNEP Assessment of Stratospheric Ozone to update future predictions of the recovery of the ozone layer. - Results will also likely be used in the forthcoming 2018 WMO/UNEP Assessment |
First Year Of Impact | 2013 |
Sector | Environment |
Impact Types | Societal |
Description | Montreal Protocol Scientific Assessment Steering Committee |
Geographic Reach | Multiple continents/international |
Policy Influence Type | Membership of a guideline committee |
Impact | Reduction in stratospheric ozone depletion and in surface climate change |
Description | WMO/UNEP |
Geographic Reach | Multiple continents/international |
Policy Influence Type | Citation in other policy documents |
Impact | Improved understanding of past ozone depletion and reduced risk of future depletion. |