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 impact of dry deposition and fog deposition on surface snow chemical inventories. The fluxes of SO2-4, NO-3, Cl-, MSA, Na, Ca, and Al were measured by collecting deposited fog on flat polyethylene plates. Dry deposition fluxes of SO2-4 were measured using aerodynamic surfaces. Real-time concentrations of atmospheric particles greater than 0.5 um and greater than 0.01 um were measured using continuous monitors. Filter samplers were used to determine daily average atmospheric SO2-4 and MSA concentrations. Also, daily surface snow samples were taken and analyzed for SO2-4, NO-3, Cl-, Na+, Ca2+, and NHJ+4. The real-time concentration data indicate that aerosol particles greater than 0.5 urn are efficiently incorporated into fog droplets. Results also show that condensation nuclei (CN) are not as greatly affected by fog as the larger particles. Fog fluxes of SO2-4 and NO-3 have similar values and are approximately 4 times greater than those of Cl-, an order of magnitude greater than those of MSA, Na, and Ca, and two orders of magnitude greater than those of Al. The fog deposition flux of SO2-4 appears to be much greater than the dry deposition flux, based on experimental data. This indicates that dry deposition has a negligible effect on surface snow SO2-4 concentrations on days when there is fog. Such a finding is consistent with significant increases in surface snow SO2-4, NO-3, and NH+4 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 daily chemical fluxes. Surface snow Ca2+ and Na+ are relatively unaffected by post snowfall processes due to low atmospheric concentrations relative to the amount of material in fresh snow. Model results suggest that the fog fluxes have been underestimated by the current sampling technique. © 1994.