FLUXES OF CHEMICAL-SPECIES TO THE GREENLAND ICE-SHEET AT SUMMIT BY FOG AND DRY DEPOSITION

Experiments were performed during June-July 1992 to determine the impa ct of dry deposition and fog deposition on surface snow chemical inven tories. The fluxes of SO42-, NO3-, Cl-, MSA, Na, Ca, and Al were measu red by collecting deposited fog on flat polyethylene plates. Dry depos ition fluxes of SO42- were measured using aerodynamic surfaces. Real-t ime concentrations of atmospheric particles greater than 0.5 um and gr eater than 0.01 um were measured using continuous monitors. Filter sam plers were used to determine daily average atmospheric SO42- and MSA c oncentrations. Also, daily surface snow samples were taken and analyze d for SO42-, NO3-, Cl-, Na+, Ca2+, and NH4+. The real-time concentrati on data indicate that aerosol particles greater than 0.5 um are effici ently incorporated into fog droplets. Results also show that condensat ion nuclei (CN) are not as greatly affected by fog as the larger parti cles. Fog fluxes of SO42- and NO3- have similar values and are approxi mately 4 times greater than those of Cl-, an order of magnitude greate r than those of MSA, Na, and Ca, and two orders of magnitude greater t han those of Al. The fog deposition flux of SO42- appears to be much g reater than the dry deposition flux, based on experimental data. This indicates that dry deposition has a negligible effect on surface snow SO42- concentrations on days when there is fog. Such a finding is cons istent with significant increases in surface snow SO42-, NO3-, and NH4 + inventories seen after fog events. Cl- surface snow inventories are affected by fog but not as greatly. Variation in surface snow chemical inventories makes it difficult to obtain quantitative estimates of da ily chemical fluxes. Surface snow Ca2+ and Na+ are relatively unaffect ed by post snowfall processes due to low atmospheric concentrations re lative to the amount of material in fresh snow. Model results suggest that the fog fluxes have been underestimated by the current sampling t echnique.