Measurement and modeling of fluxes of chemical species to the Greenland ice sheet at Summit

This work focuses on the deposition of atmospheric chemical species to the Greenland ice sheet at Summit. The experiments focused on the characterization of aerosol and gas-phase chemical species in the atmosphere, as well as the chemical composition of surface snow, and the deposition pathways of chemical species. The objectives of this research are to develop a better understanding of the air/snow transfer processes of gases and aerosols, and to create models that can eventually be used to estimate the past atmospheric chemical composition based on the 250,000 year chemical record contained in the ice cores recently retrieved from Summit, Greenland.; The most detailed sets of experiments were performed during May-July of 1993 at Summit, Greenland. Aerosol mass size distributions as well as daily average concentrations of several anionic and cationic species were measured. Dry deposition velocities for SO{dollar}sbsp{lcub}4{rcub}{lcub}2-{rcub}{dollar} were estimated using surrogate surfaces (symmetric airfoils), as well as impactor data. Real time concentrations of particles greater than 0.5 um and greater than 0.01 um were measured. Filter sampler results indicate that SO{dollar}sbsp{lcub}4{rcub}{lcub}2-{rcub}{dollar} is the dominant aerosol anion species, with Na{dollar}sp*{dollar}, NH{dollar}sbsp{lcub}4{rcub}{lcub}+{rcub}{dollar}, and Ca{dollar}sp{lcub}2+{rcub}{dollar} being the dominant cations. The rough agreement between the airfoil and impactor estimated dry deposition velocities suggests that the airfoils may be used to approximate the dry deposition to the snow surface. Snow deposition is the dominant mechanism transporting chemicals to the ice sheet. For NO{dollar}sbsp{lcub}3{rcub}{lcub}-{rcub}{dollar}, a species that apparently exists primarily in the gas phase as HNO{dollar}sb3{dollar}(g), 93% of the seasonal inventory (mass of a deposited chemical species per unit area during the season) is due to snow deposition, which suggests efficient scavenging of HNO{dollar}sb3{dollar}(g) by snowflakes. A simple fog model is developed and used to provide an independent theoretical estimate of the seasonal fog inventories of MSA, SO{dollar}sbsp{lcub}4{rcub}{lcub}2-{rcub}{dollar}, Na{dollar}sp+{dollar}, NH{dollar}sbsp{lcub}4{rcub}{lcub}+{rcub}{dollar}, K{dollar}sp+{dollar}, and Ca{dollar}sp{lcub}2+{rcub}{dollar}. These values are in general agreement with measured seasonal fog inventories, although the model underestimates the inventories of the aerosol species that reside mainly in the accumulation mode.; A Lagrangian radiation fog model is applied to a fog event at Summit, Greenland. Model results suggest that in addition to the aqueous-phase partitioning of the initial HNO{dollar}sb3{dollar} present in the air mass, the gas phase decomposition of PAN and subsequent reactions of NO{dollar}sb2{dollar} with OH as well as nighttime nitrate chemistry may play significant roles in depositing N(V) with fog.; A simple model is presented to estimate atmospheric concentrations of irreversibly deposited aerosol chemical species based on snow core/ice core chemistry at Summit, Greenland. The results estimate the seasonal mean atmospheric SO{dollar}sbsp{lcub}4{rcub}{lcub}2-{rcub}{dollar} and Ca{dollar}sp{lcub}2+{rcub}{dollar} concentrations to within 10% and 40%, respectively. The application of the model to ice core chemical signals is briefly discussed. (Abstract shortened by UMI.)...