SNOW-ATMOSPHERE CHEMICAL EXCHANGE

Recent Results

Work to date has involved: i) atmospheric and snow measurements at Summit, Greenland, ii) mathematical modeling, and iii) laboratory studies. Two general results are a conceptual understanding and mathematical model of processes affecting H₂O₂ in ice cores. H₂O₂ in surface snow equilibrates with atmospheric levels over a time scale of weeks to months. Once buried it is preserved, however redistribution continues throughout the firn. Firn gas H₂O₂ concentrations are in equilibrium with those at the surface of the ice grains, but not the bulk ice grain. Equilibration times in the firn are limited by grain-scale redistribution of H₂O₂ between grain interiors and surfaces rather than by diffusion in the open pore space. This equilibrium is temperature dependent, and influences the annual pattern of H₂O₂ in snow. Both seasonal and year-to-year H₂O₂ levels in snow (and thus ice) do respond to changes in atmospheric H₂O₂. However, degassing of H₂O₂ from surface snow also influences atmospheric concentrations.