A lumped parameter model for the atmosphere-to-snow transfer function for hydrogen peroxide

Abstract

Of the main atmospheric oxidants, only hydrogen peroxide (H2O2) is preserved in polar ice cores. To make use of the peroxide record, however, requires a quantitative understanding of the transfer function or relation between atmospheric concentrations of H2O2 and those preserved in the ice core. Snow-pit H2O2 profiles adjacent to three automatic snow-depth gages from Summit, Greenland were used to estimate parameters and evaluate the performance of a lumped parameter model to relate concentrations in the atmosphere with those in surface snow and shallow firn. Three of the model parameters define an equilibrium partitioning coefficient between snow and atmosphere as a nonlinear function of depositional temperature. Model parameters yielded a function that closely matched previous laboratory estimates [Conklin et al., 1993]. A fourth parameter reflects the disequilibrium that may be preserved during periods of rapid accumulation. The final model parameter describes the exchange of H2O2 between near-surface snow and the atmosphere, allowing already buried snow to either take up or release H2O2 as conditions in and above the snowpack change. We simulated snow pit profiles by combining this transfer function model with a finite-difference model of gas-phase diffusion in the snowpack. Two applications for this transfer function are (1) to estimate the local seasonal or annual atmospheric H2O2 concentration in the past from snow-pit and ice-core records and (2) to invert snow-pit and ice-core H2O2 profiles to obtain estimates of the seasonal or annual accumulation time series. In the first case, an independent estimate of snow accumulation is needed, and in the second application, an independent estimate of the annual H2O2 atmospheric cycle is needed.