EGU2020-6107
https://doi.org/10.5194/egusphere-egu2020-6107
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

CO2 hydrate equilibria at atmospheric partial pressures, and implications for atmospheric acidity

Brian Durham1 and Christian Pfrang2
Brian Durham and Christian Pfrang
  • 1University of Birmingham, United Kingdom of Great Britain and Northern Ireland (brian@oxpot.demon.co.uk)
  • 2University of Birmingham, United Kingdom of Great Britain and Northern Ireland (c.pfrang@bham.ac.uk

We take moist air (and artificial air) at +0.35 ⁰C, variously doped with CO2, and pass it through a chamber chilled to -3⁰C.  We record any depletion of CO2 in the gas stream using differential NDIR spectrometers, and we then de-gas the melt-water to measure the captured CO2, again with NDIR.  Preliminary results are consistent with published curves for the CO2/hydrate equilibrium at partial pressures relevant to the petrochemical industry and to industrial carbon capture as determined by Raman microscopy (Chazallon and Pirim 2018).

Extension of the CO2/ice curve to atmospheric partial pressures allows a review of a range of related issues in atmospheric water, one of the more accessible being its acidity. The dissociation of CO2 in water at equilibrium with 400ppm CO2 at Earth surface is quoted as pH5.6, but fresh rainwater (and snow-melt) can be significantly more acidic, decaying exponentially to equilibrium with a half life of around four hours. This observation is consistent with published analyses of [CO2] in rainwater that are significantly higher than the Henry equilibrium (Warneck 2000).  Both would be explained if convection was resulting in CO2/ice-formation in clouds within the boundary layer, in turn leading to deposition of supersaturated levels of CO2 together with enhanced acidity.

This paper speculates on the local [H3O+] delivered by the melting of an ice particle that had grown in an atmosphere of 400ppm CO2 at an altitude of 1km, and its dissipation through dilution by neighbouring unfrozen water drops and by slow release from the residue of hydrate caging in liquid water. For Earth surface it has potential implications for acid rain, for the solution and redeposition of carbonate rocks, and for ocean acidification.  

How to cite: Durham, B. and Pfrang, C.: CO2 hydrate equilibria at atmospheric partial pressures, and implications for atmospheric acidity , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6107, https://doi.org/10.5194/egusphere-egu2020-6107, 2020

Comments on the presentation

AC: Author Comment | CC: Community Comment | Report abuse

Presentation version 5 – uploaded on 31 May 2020 , no comments
Itemises assumptions made in Slide 7, and updates conclusions accordingly
Presentation version 4 – uploaded on 30 May 2020 , no comments
Removed ref to GEES
Presentation version 3 – uploaded on 30 May 2020 , no comments
Version description: We have added an Introduction (Slide 2) developed from conversations with Barbara Ervens (ICCF; CNRS); and a fourth[...]
Presentation version 2 – uploaded on 07 May 2020 , no comments
Version description: 1. Figure numbers corrected 2. Appendix 1 added: Poster presented to Royal Meteorological Society Atmospheric[...]
Presentation version 1 – uploaded on 04 May 2020 , no comments