Unravelling the atmospheric and climate implications of hydrogen leakage

Abstract

In recent years, hydrogen is adopted as a clean source of energy to combat emissions and climate change resulting from fossil fuels. All along the value chain of hydrogen economy, leakage of hydrogen is possible which is expected to have profound impacts on air quality and climate. In the present study, quantum chemistry calculations are employed to understand the atmospheric oxidation mechanism of H2 by OH and O3. The results reveal that oxidation of H2 by both the OH and O3 are both possible and the reaction of H2 with O3 is thermodynamically favoured over its reaction with OH radical. The O3 initiated reaction of H2 is around 80 kcal/mol more exothermic than that of the OH initiated reaction. The O3 initiated reactions of H2 has longer lifetime in the atmosphere when compared to OH initiated reactions. This shows that in addition to undergoing OH radical initiated reaction, where ozone is formed as a product, the H2 can also undergo oxidation by O3 leading to the tropospheric ozone loss processes. Depending upon the background atmospheric concentration, either the OH radical generation is suppressed and methane is formed or the H2 can undergo oxidation with O3. The global warming potential (GWP) weighted emissions for hydrogen leakage incidents reported in the literature is obtained. The emissions are maximum from the hydrogen leakage in transportation and power sectors and minimum in the pipeline leakage. Taken together the atmospheric oxidation potential of H2 by OH radical and O3 oxidation and its GWP weighted emissions, it is clear from the study that the atmospheric and climate implications of H2 leakage is relatively less. The present study is based on molecular level and a rigorous model accounting the atmospheric composition is required for better understanding of the atmospheric and climate implications.