Relationship between chemistry of air, fresh snow and firn cores for aerosol species in coastal Antarctica

Abstract

Abstract. Aerosol and fresh snow concentrations have been determined at three coastal Antarctic stations, Dumont d'Urville, Halley, and Neumayer. Model estimates suggest that dry deposition, including that caused by wind pumping, is only a minor contributor (of order 1%) to chemical fluxes at these sites with relatively high snow accumulation. Larger dry deposition fluxes are possible for very large aerosol particles, including sea-salt aerosol. Measurements of surface snow on successive days provide experimental data that constrain the contribution of dry deposition to probably less than 10% of annual fluxes for all ions, although very high episodic fluxes of giant sea-salt aerosol cannot be ruled out. Spatial variability, and frequent snow, fog and drift events, make it difficult to improve this quantification. Both theory and measurement suggest that fog deposition is also a minor contributor to the annual flux (probably <1%). Sublimation of surface snow and of blowing snow may increase snow concentrations by a few percent, with a larger role in summer, but should not affect fluxes. Wet deposition in falling snow appears to be by far the major contributor. However, the relationship between concentrations in snow and in simultaneously sampled aerosol at ground level was poor for most species. Scavenging ratios derived from these data are higher than those from the limited data previously available, but have huge uncertainties associated with them. Particularly at sites with frequent drifting snow, groundlevel aerosol measurements may be inappropriate for deriving scavenging ratios. Despite this, there is a general seasonal coincidence of high aerosol concentrations and high snow concentrations. We are also able to trace the chemistry of fresh snowfall to an ice core collected up to 2 years later. Although some major snowfall events may be missing, it seems that, as expected, there is no significant postdepositional modification of chemistry for aerosol species in the top meter of firn.

Surface Snow, Firn and Ice Core Composition in Polar Areas in Relation to Atmospheric Aerosol and Gas Concentrations: Critical Aspects

“…The contribution of dry deposition in Antarctica is higher during winter (due to the lower precipitation rate and decreased scavenging efficiency of unrimed snow in winter), and on sites in central Antarctica, which have very low snow accumulation rates with respect to coastal regions [90] [91]. According to Gjessing [92], dry deposition is the dominant sink on the Antarctic Plateau, whereas snow scavenging predominates in the coastal areas of Antarctica [16].…”

“…concentrations in snow and in air are sometimes related and sometimes not [7] [9] [16] [17] [19] [20]. Published papers frequently compared ion concentration (soluble and/or insoluble) in snow and aerosol, neglecting to discuss the fact that snow could also scavenge chemical compounds in the gas phase.…”

Past atmospheric composition and chemistry from ice cores - progress and prospects

“…[18] Because the snow accumulation rate is so low at this site, dry deposition is expected to dominate, and in this case it is expected that fluxes rather than ice concentrations represent atmospheric composition. [19] Models of atmospheric transport have suggested that neither transport nor residence time should have altered appreciably between the glacial and interglacial periods, [e.g. 20] although this assumption certainly requires further study.…”

Aerosol and snow transfer processes: An investigation on the behavior of water-soluble organic compounds and ionic species

“…So far, only the relationship between ionic compounds and carboxylic acids has been investigated since they are the most easily detectable in most matrices. Wolff et al (1998) determined the most abundant ionic compounds in the aerosol, fresh snow and firn cores from three coastal Antarctic stations and highlighted the difficulties in studying processes in an area where environmental conditions change frequently. Investigations on the depositional fluxes of non-sea salt sulfate and methanesulfonic acid allowed an assessment of the spatial variation of marine biogenic sulfur (Minikin et al, 1998) to be made.…”