A New Threat to the Stratospheric Ozone Layer from Anthropogenic Very Short-lived Halocarbons

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The stratospheric ozone layer protects the Earth from most of the sun's harmful ultraviolet radiation. The depletion of ozone in response to anthropogenic emissions of long-lived chlorofluorocarbons (CFCs) has been one of the major environmental issues of the last decades. Emissions of CFCs have been strongly reduced following the Montreal Protocol of 1987 and as a consequence a gradual recovery of the ozone layer over the next decades is expected. Marine Very Short-Lived Halocarbons (VSLH), which also have the potential to destroy ozone, are, on the other hand, expected to increase due to new technologies. In particular, oxidative water treatment of ship ballast water and increasing macro algae farming impact the marine biogeochemical systems and are suspected to drastically enhance the production and emissions of VSLH. In addition to their damaging effect on the ozone layer, anthropogenic VSLH from the oceans will also impact the radiative forcing and the oxidizing capacity of the atmosphere, i.e. the capacity of the atmosphere to ultimately remove many trace gases, including pollutants. There is only an emerging awareness of the impending increase of VSLH which represents a new, human-made threat to radiative forcing and ozone recovery and it is of high priority to properly assess planed anthropogenic activities regarding the release of such substances. This proposal aims to assess current and future emissions of anthropogenic VSLH, their multisided impact on atmospheric chemistry and physics, and in particular their potential to prolong stratospheric ozone depletion. In a first step, a global inventory of oceanic emissions of anthropogenic VSLH will be developed. In a second step, the fate of anthropogenic VSLH in the atmosphere after their emissions from the ocean will be quantified based on high resolution atmospheric chemistry-transport modelling. This requires the development of coast line-resolving modelling systems which can eventually be used to parameterize the key processes in global climate models. In a third step, the overall role of anthropogenic VSLH for ozone chemistry, global oxidizing capacities and the radiation budget will be assessed and possible climate feedback mechanisms will be identified. The research will be undertaken in a multifaceted way comprising the synthesis of existing data, in-situ measurements, ocean circulation-, biogeochemical-, atmospheric chemistry transport- and global climate modelling. The interdisciplinary research proposal will enable the answer to the emerging question if anthropogenic activities in marine and oceanic environments will pose a new threat to the stratospheric ozone layer recovery. Such an atmospheric risk assessment is of large societal relevance and will provide information that is essential for decision makers to plan future human activities.