Abstract
Abstract. At present, anthropogenic halogens and oceanic emissions of very short-lived substances (VSLSs) both contribute to the observed stratospheric ozone depletion. Emissions of the long-lived anthropogenic halogens have been reduced and are currently declining, whereas emissions of the biogenic VSLSs are expected to increase in future climate due to anthropogenic activities affecting oceanic production and emissions. Here, we introduce a new approach for assessing the impact of oceanic halocarbons on stratospheric ozone by calculating their ozone depletion potential (ODP)-weighted emissions. Seasonally and spatially dependent, global distributions are derived within a case-study framework for CHBr3 for the period 1999–2006. At present, ODP-weighted emissions of CHBr3 amount up to 50 % of ODP-weighted anthropogenic emissions of CFC-11 and to 9 % of all long-lived ozone depleting halogens. The ODP-weighted emissions are large where strong oceanic emissions coincide with high-reaching convective activity and show pronounced peaks at the Equator and the coasts with largest contributions from the Maritime Continent and western Pacific Ocean. Variations of tropical convective activity lead to seasonal shifts in the spatial distribution of the trajectory-derived ODP with the updraught mass flux, used as a proxy for trajectory-derived ODP, explaining 71 % of the variance of the ODP distribution. Future climate projections based on the RCP 8.5 scenario suggest a 31 % increase of the ODP-weighted CHBr3 emissions by 2100 compared to present values. This increase is related to a larger convective updraught mass flux in the upper troposphere and increasing emissions in a future climate. However, at the same time, it is reduced by less effective bromine-related ozone depletion due to declining stratospheric chlorine concentrations. The comparison of the ODP-weighted emissions of short- and long-lived halocarbons provides a new concept for assessing the overall impact of oceanic halocarbon emissions on stratospheric ozone depletion for current conditions and future projections.
Highlights
The overall abundance of ozone-depleting substances in the atmosphere has been decreasing since the beginning of the 21st century as a result of the successful implementation of the 1987 Montreal Protocol and its later adjustments and amendments (Carpenter and Reimann, 2014)
The method and application are introduced for CHBr3 within a case-study framework and can be applied to all very shortlived substances (VSLSs) where emissions and ozone depletion potential (ODP) are available at a spatial resolution necessary to describe their variability
Since currently no information is available on the strength of anthropogenic CHBr3 emissions, the ODP concept is applied to the complete emission budget including the natural oceanic contribution
Summary
The overall abundance of ozone-depleting substances in the atmosphere has been decreasing since the beginning of the 21st century as a result of the successful implementation of the 1987 Montreal Protocol and its later adjustments and amendments (Carpenter and Reimann, 2014). Among the brominated VSLSs, the calculation of CHBr3 ODP-weighted emissions is possible, since global emission inventories (Ziska et al, 2013) and global ODP maps (Pisso et al, 2010) has become available. In a globally averaged framework, the ODP-weighted emissions allow comparisons of the impact of past, present and future long- and short-lived halocarbon emissions. Can be estimated based on the convective mass flux from meteorological reanalysis data and develop a proxy for the ODP of CHBr3 We use this method to derive long-term time series of ODP-weighted CHBr3 emissions for 1979–2013 based on ERA-Interim data in Sect. This approach provides a new tool for an assessment of future growing biogenic VSLSs and declining chlorine emissions in the form of a direct comparison of the global-averaged ODP-weighted emissions of short- and long-lived halocarbons
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