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Abstract Molecular hydrogen (H2) is an abundant and reactive constituent of Earth's atmosphere, with links to climate and air quality. Anthropogenic emissions of H2are expected to rise as the use of H2as an energy source increases. Documenting past variations in atmospheric H2will help to validate current understanding of the global H2budget. The modern instrumental record begins in the 1980s; there is little information about atmospheric H2prior to that time. Here, we use firn air measurements from a 2001 South Pole campaign to reconstruct atmospheric H2levels over the 20th century. Inversion of the measurements indicates that H2over South Pole has increased from 350–540 ppb from 1910–2000. A biogeochemical box model indicates that the atmospheric burden of H2increased by 37% over that time. The rise in H2is consistent with increasing H2emissions from fossil fuel combustion and increasing atmospheric production from methane oxidation.
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Diffusivity and Solubility of H 2 in Ice Ih: Implications for the Behavior of H 2 in Polar Ice
Abstract Reconstructions of paleoatmospheric H2using polar firn air and ice cores would lead to a better understanding of the H2biogeochemical cycle and how it is influenced by climate change and human activity. In this study, the permeability, diffusivity, and solubility of H2are determined experimentally in ice Ih at temperatures relevant to polar ice sheets (199–253 K). The experimental data are used in conjunction with simplified diffusion models to assess the implications for: (a) Diffusion of H2from pressurized closed bubbles to open pores in polar firn, (b) diffusive smoothing of H2gradients in the ice sheet, and (c) post‐coring diffusive losses of H2from ice core samples. The results indicate that diffusive equilibrium between open and closed pores is likely achieved in the firn lock‐in zone. Diffusive smoothing of atmospheric variations is significant and should be accounted for in atmospheric reconstructions on millennial time scales. Diffusive losses from a bubbly ice sample are sufficiently slow that samples may be meaningfully analyzed for H2after storage on the order of a year. These results suggest that the mobility of H2in ice should not preclude the reconstruction of paleoatmospheric H2from firn air and ice cores.
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- Award ID(s):
- 1907974
- PAR ID:
- 10414183
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 126
- Issue:
- 10
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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