Laboratory simulation of gas hydrate formation at ice surfaces in Earth atmosphere

For fourteen days in November the world’s attention turned to the rise in atmospheric GHG levels, on this occasion with a special focus on methane (Nature 25 August 2021).  Methane had previously been the subject of a study on gas hydrate formation and, while noting the relevance of this property to climate change modelling, the authors in that case wrote: `Curiously, gas hydrates seem to defy intuition about hydrophobic compounds, as the concentration of a nonpolar gas in the solid hydrate lattice is more than two orders of magnitude higher than the solubility of such a gas in liquid water’ (Walsh et al 2008 `Microsecond Simulations of Spontaneous Methane Hydrate Nucleation and Growth' ). 

The term `non-polar’ applies to the gases of Earth’s atmosphere - so does the same concentration paradox apply to the inclusion of each of these species in atmospheric ice? For CO<sub>2</sub>, curves published by the University of Lille quantify hydrate formation across a range of partial pressures, and are projected to a zero pressure origin, thereby embracing the partial pressure of the gas in Earth atmosphere (Chazallon and Pirim (2018) `Selectivity and CO2 capture efficiency in CO2-N2 clathrate hydrates investigated by in-situ Raman spectroscopy', Figs 4A and 4B).  Moreover, in the presence of ice phase at -12°C our own results have shown that, from a CO₂+N₂ mixture, more than 90% of CO₂ goes into the ice/hydrate phase, which is three times higher that at 10°C (Hassanpouryouzband et al 2019 `Geological CO₂ capture and storage with flue gas hydrate formation in frozen and unfrozen sediments').

We simulate hydrate formation in the Earth's atmosphere using laboratory apparatus designed to quantify the depletion of GHGs (including water vapour) from a chilled airstream at atmospheric pressure across a range of temperatures, followed by analysis of the condensate.