Atmosphere‐snow transfer function for H₂O₂: Microphysical considerations

Abstract

H 2 O 2 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 H 2 O 2 in a series of laboratory column experiments in the temperature range −3°C to −45°C. Experiments consisted of passing H 2 O 2 ‐containing air through a column packed with 200‐μm diameter ice spheres and measuring the change in gas phase H 2 O 2 concentration with time. The uptake of H 2 O 2 was a slow process requiring several hours to reach equilibrium. Uptake involved incorporation of H 2 O 2 into the bulk ice as well as surface accumulation. The amount of H 2 O 2 taken up by the ice was greater at the lower temperatures. The sticking coefficient for H 2 O 2 on ice in the same experiments was estimated to be of the order of 0.02 to 0.5. Release of H 2 O 2 from the ice occurred upon passing H 2 O 2 ‐free air through the packed columns, with the time scale for degassing similar to that for uptake. These results suggest that systematic losses of H 2 O 2 from polar snow could occur under similar conditions, when atmospheric concentrations of H 2 O 2 are low, that is, in the winter.