Satellite Observations of Halogen-Containing Molecules

Ozone depletion in the upper atmosphere is caused mainly by the anthropogenic release of chlorinated molecules such as chlorofluorocarbons (CFCs). This damage to the ozone layer increases the amount of deleterious ultraviolet radiation that reaches the ground. As a result of the Montreal Protocol long-lived CFCs are being replaced by shorter-lived species that contain hydrogen (hydrochlorofluorocarbons, HCFCs) and molecules without chlorine (hydrofluorocarbons, HFCs). It is anticipated that the success of the Montreal Protocol will end ozone destruction by the middle of this century. In order to verify compliance and monitor progress, the concentrations of these species need to be measured as function of time, location and altitude. Ozone destruction takes place in the upper atmosphere so measurements of chlorine and fluorine budgets are needed there. We propose to measure the global distributions of the main fluorine- and chlorine-containing gases (both organic source gases and inorganic product gases) with the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). The ACE satellite has been providing high quality data from 2004 to the present so trends can be derived as a function of altitude and latitude.
Organic fluorine- and chlorine-containing species are powerful greenhouse gases. In fact, after carbon dioxide and methane, this group of gases are the third most important drivers of climate change. The success of the Montreal Protocol has lead to an inadvertent climate benefit, although the rapid increase in replacement HFCs is cause for concern. We propose to determine improved lifetimes for many of these species, and our global distributions will lead to improved estimates of global warming potentials and radiative forcings that quantify their effectiveness in causing climate change.
Climate change and ozone depletion in the upper atmosphere are two of the most important problems in atmospheric science. Our proposal will make important contributions to the World Meteorological Organization's 2014 Scientific Assessment of Ozone Depletion and the Fifth Assessment Report of the Intergovernmental Panel on Climate Change that is now under way for 2013/2014.

Apart from other academics (outlined in the 'academic beneficiaries' section), this work will benefit policy makers and the general public because of its relevance to the ozone layer and climate change. In general this work will lead to a greater awareness of the potential of satellite observations for such research.
This work will benefit policy makers, who are best able to enforce reductions in anthropogenic emissions, and various environmental agencies around the world, such as the European Environment Agency. In the UK, DEFRA (Department for Environment, Food and Rural Affairs) is responsible for ozone monitoring and DECC (Department of Energy and Climate Change) is responsible for tackling global climate change on behalf of the UK. The Global Atmospheres Division of DEFRA also supports the in situ measurement of halogenated gases at the Mace Head AGAGE station in Ireland. DEFRA is responsible for ensuring UK compliance with the Montreal Protocol and, for example, paid the travel expenses of Bernath so he could participate in the November 2009 meeting, near Washington DC, of the WMO Scientific Ozone Assessment Panel.
This research will provide atmospheric profiles/abundances of important chlorine- and fluorine-containing molecules. These are important minor constituents of the Earth's atmosphere and very strong greenhouse gases since they absorb infrared radiation very effectively. A number of these molecules contribute to the depletion of the stratospheric ozone layer, which prevents harmful ultraviolet radiation from passing through the Earth's atmosphere, and are regulated by the Montreal Protocol.
The concentrations of ozone-depleting substances in the atmosphere need to be monitored to ensure that the Montreal Protocol is working and that emissions reflect those reported by the signatories of the Protocol. Additionally, monitoring the temporal speciation of chlorine and fluorine via their stratospheric budgets will lead to a better understanding of the chemistry involved. Such satellite observations are crucial for validating the models used to predict ozone layer recovery, which should occur in the second half of this century.
Fluorine- and chlorine-containing molecules are very strong greenhouse gases, meaning that even small amounts of these gases contribute significantly to the radiative forcing of climate. However, not all of these molecules are regulated by the Montreal Protocol. In particular, HFCs are increasing at a very fast rate. HFCs were introduced as replacements for the ozone-depleting CFCs and HCFCs. HFCs do not deplete the ozone layer but are strong greenhouse gases. The success of the Montreal Protocol has led to a number of proposals calling for its revision to also phase out HFCs. It is uncertain when agreement on this will be reached. Satellite observations of HFCs are important in quantifying how rapidly they are accumulating in the atmosphere.
This project will provide more accurate calculations of radiative forcings and global warming potentials (in collaboration with Prof. Piers Forster, Leeds). These are particularly important as inputs for chemistry-climate models (in addition to abundances and temporal trends), which will lead to more precise calculations of future temperature changes. Additionally, GWPs of these gases are used in the Kyoto Protocol and emission trading schemes to compare the radiative impact of their emissions to that of carbon dioxide. GWPs are assessed in both IPCC and WMO reports.
This work will contribute to two international assessments: the 2014 World Meteorological Association (WMO) ozone assessment report and the Intergovernmental Panel on Climate Change (IPCC) Fifth assessment report (AR5) due in 2013/2014. These international reports are the primary documents used to form the scientific basis for policy on ozone depletion and climate change. This is expanded upon in "Pathways to Impact."