A LUMPED-PARAMETER MODEL FOR THE ATMOSPHERE-TO-SNOW TRANSFER-FUNCTIONFOR HYDROGEN-PEROXIDE

Of the main atmospheric oxidants, only hydrogen peroxide (H2O2) is pre served in polar ice cores. To make use of the peroxide record, however , requires a quantitative understanding of the ''transfer function'' o r relation between atmospheric concentrations of H2O2 and those preser ved in the ice core. Snow-pit H2O2 profiles adjacent to three automati c snow-depth gages from Summit, Greenland were used to estimate parame ters and evaluate the performance of a lumped parameter model to relat e concentrations in the atmosphere with those in surface snow and shal low firn. Three of the model parameters define an equilibrium partitio ning coefficient between snow and atmosphere as a nonlinear function o f depositional temperature. Model parameters yielded a function that c losely matched previous laboratory estimates [Conklin et al., 1993]. A fourth parameter reflects the disequilibrium that may be preserved du ring periods of rapid accumulation. The final model parameter describe s the exchange of H2O2 between near-surface snow and the atmosphere, a llowing already buried snow to either take up or release H2O2 as condi tions in and above the snowpack change. We simulated snow pit profiles by combining this transfer function model with a finite-difference mo del of gas-phase diffusion in the snowpack. Two applications for this transfer function are (1) to estimate the local seasonal or annual atm ospheric H2O2 concentration in the past from snow-pit and ice-core rec ords and (2) to invert snow-pit and ice-core H2O2 profiles to obtain e stimates of the seasonal or annual accumulation time series. In the fi rst 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.