Wasserstoff-Emissionen und ihre Auswirkungen auf den arktischen Ozonverlust-Risikoanalyse einer globalen Wasserstoffwirtschaft

Hydrogen (H$_{2}$) could be used as one of the major components in our future energy supply in an effort to avoid greenhouse gas emissions. ”Green” hydrogen in particular, which is produced from renewable energy sources, should significantly reduce emissions that damage the climate. Despite this basically environmentally-friendly property, however, the complex chain of interactions of hydrogen with other compounds means that the implications for the atmosphere must be analysed in detail. For example, H$_{2}$ emissions, which could increase the tropospheric H$_{2}$ inventory, can be released throughout the complete hydrogen process chain. H$_{2}$ enters the stratosphere via the tropical tropopause and is oxidised there to form water vapour (H$_{2}$O). This extra water vapour causes increased radiation in the infrared region of the electromagnetic spectrum and thus causes the stratosphere to cool down. Both the increase in H$_{2}$O and the resulting cooling down of the stratosphere encourage the formation of polar stratospheric clouds (PSC) and liquid sulphate aerosols, which facilitate the production of reactive chlorine, which in turn currently leads to dramatic ozone depletion in the polar stratosphere. In the future, H$_{2}$ emissions from a global hydrogen economy could therefore encourage stratospheric ozone depletion in the polar regions and thus inhibit the ozone layer in recovering from the damage caused by chlorofluorocarbons (CFCs). In addition to estimating possible influences on the trace gas composition of the stratosphere, one of the main aims of this thesis is to evaluate the risk associated with increased polar ozone depletion caused by additional H$_{2}$ emissions. Studies reported on here have shown that even if around 90% of today’s fossil primary energy input was to be replaced by hydrogen and if around 9.5% of the gas was to escape in a ”worst-case” scenario, the additional ozone loss for unchanged CFC loading in the stratosphere would amount to a maximum of between around 4 and 7% (15 - 26 Dobson Units [DU]). A consistency check of the applied approximation technique with the chemistry-transport model, CLaMS, shows that this estimate is more than likely the upper limit. If more realistic estimates are made of future hydrogen emission rates, then additional ozone depletion is rather low (≤ 2.5% ≈ 10 DU). Furthermore, the adverse effects only fully come into play, if CFC quantities remain static. Due to the CFC phase-out in the Montreal Protocol, current forecasts predict a decrease of about 50% in CFC loading by 2050, whereby the added effect would amount to less than 1% (≤ 4 DU). When compared to the positive effect on the climate, if greenhouse gas emissions are avoided, the damage potential of H2 emissions caused by a global hydrogen economy for stratospheric ozone depletion is therefore very low