ATMOSPHERE-SNOW TRANSFER-FUNCTION FOR H2O2 - MICROPHYSICAL CONSIDERATIONS

H2O2 analyses of polar ice cores show an increase in concentration from 200 years to the present. In order to quantitatively relate the observed trend in the ice to atmospheric levels, the atmosphere-snow transfer behavior and postdepositional changes must be known. Atmosphere-snow transfer was studied by investigating uptake and release of H2O2 in a series of laboratory column experiments in the temperature range -3-degrees-C to -45-degrees-C. Experiments consisted of passing H2O2-containing air through a column packed with 200-mum diameter ice spheres and measuring the change in gas phase H2O2 concentration with time. The uptake of H2O2 was a slow process requiring several hours to reach equilibrium. Uptake involved incorporation of H2O2 into the bulk ice as well as surface accumulation. The amount of H2O2 taken up by the ice was greater at the lower temperatures. The sticking coefficient for H2O2 on ice in the same experiments was estimated to be of the order of 0.02 to 0.5. Release of H2O2 from the ice occurred upon passing H2O2-free air through the packed columns, with the time scale for degassing similar to that for uptake. These results suggest that systematic losses of H2O2 from polar snow could occur under similar conditions, when atmospheric concentrations of H2O2 are low, that is, in the winter.