Je Hanssen

Temporal and spatial variations of airborne Mg, Cl, Na, Ca and K in rural areas of Norway

The Norwegian air chemistry monitoring network includes measurements of gaseous and particulate compounds in air at 12 rural sites. The sampling method is designed to determine concentration levels of sulphur and nitrogen compounds and uses a three-stage filter pack sampler. Concentration levels of base-cations and sea salts may also be determined from the chemical analysis of the filter extracts. In this study, concentration levels of water soluble Mg, Cl, Na, Ca and K in air have been investigated in terms of temporal, seasonal and spatial trends during the period 1986-1996. The results have been combined with precipitation chemistry data to estimate total deposition, and to evaluate the relative importance of dry deposition. While Na, Cl and Mg are of marine origin, which is clearly reflected in concentration ratios and spatial gradients, Ca and K are of a mixed origin. Air trajectory analyses indicate that air masses originating in Eastern Europe result in significantly higher airborne concentrations of non-sea salt Ca and K, than air from other sectors. Major sources of airborne Ca and K in Norway are expected to be of anthropogenic origin from combustion plants and industrial processes in Eastern Europe, while aeolian dust from agricultural areas within Europe or from Sahara is of limited importance. Concentration levels of non-sea salt base-cations in air were 20-30% lower during the 1990s, compared to 1986-1989. Precipitation chemistry data available since the early 1980s indicate even larger reductions, and in the order of 50%. Total deposition of non-sea salt base-cations during 1993-1996 was generally below 10 mmol(c) m-2 year-1, whereas in coastal areas with large precipitation amounts, inputs exceeding 15 mmol(c) m-2 year-1 occurred. Deposition of base-cations may thus counteract up to 25% of the strong acid anion input, but more typically in the order of 5-10%. Dry deposition of non-sea salt base-cations of southern Norway is comparatively small, typically contributing 10-30% to the total deposition in the inland areas, and relatively less in other regions.

Mass size distributions for atmospheric trace elements at the Zeppelin background station in Ny Ålesund, Spitsbergen

Measurements of the multielemental composition of size-fractionated aerosols provide information on the source processes of the various elements and they allow one to examine the physico-chemical transformation processes that take place during the atmospheric transport or as a result of local meteorology and atmospheric conditions. Furthermore, such measurements provide the necessary input data for estimating the scavenging probabilities and dry deposition velocities of the elements. Several studies on elemental mass size distributions have already been performed in the Arctic, e.g., by Pacyna et al. [1984], Li and Winchester [1990], Hillamo et al. [1993] and Barrie et al. [1994], but virtually all former studies were done in the winter and were limited to time periods of a few months. To investigate changes in sources, source processes and/or particle size modification processes over the course of the year, in late 1990 we started long-term (and still ongoing) samplings with a cascade impactor at the Zeppelin mountain station in Spitsbergen. Selected preliminary results of these samplings are presented and briefly discussed.