Geert Ducastel

Sources and physico-chemical characteristics of the atmospheric aerosol in southern Norway.

Abstract An intensive aerosol sampling campaign was carried out simultaneously at Birkenes and Nordmoen, southern Norway, from 11 April to 4 May 1988. Two different size segregative sampling instruments were used at each site. Parallel analysis was performed using several methods which allowed the determination of up to 45 components. The atmospheric concentrations were mostly found to be similar at the two sampling sites, which are separated by a distance of about 250 km. During long-range transport episodes, the pollutant concentrations were 20–50 times higher than during background periods. At the Birkenes site detailed information about the elemental and particle mass size distributions was obtained from Berner low-pressure impactor samples. The aerosol fine particle mode clearly shifted to larger particle sizes when the average relative humidity was higher than 80% during sampling. The average fine to total elemental concentration ratios of most elements were found to be similar for the different samplers and for the two sites, although differences between the sites occurred depending on the origin of the air masses sampled. A new approach based on the size distributions measured, the relative size distributions (RSD) method, was developed for the assessment of local and regional aerosol sources. The RSD method and conventional methods revealed local/regional sources of Mn, Zn, Pb, Bi, Br, I, Si and K. The interelemental concentration ratios in air masses of different geographical origin were studied and found to be similar in this study and in southern Sweden (Swietlicki et al., 1989) for air masses originating from the U.K.

Atmospheric aerosol studies in southern Norway using size-fractonating smapling devices and nuclear analytical techniques

Atmospheric aerosol samples were collected during spring sampling campaigns in 1988 and 1989 at Birkenes and Nordmoen in southern Norway. The aerosol collectors used included stacked filter units (SFUs), a low volume sampler (referred to as ILVS), which consists of a filter preceded by three impaction stages, and an 11-stage Berner low-pressure impactor (LPI). All samples were analyzed for up to about 40 elements by INAA and PIXE. The resuls obtained from parallel samplings were intercompared in terms of ratios ILVS/SFU and LPI/SFU, whereby these ratios were calculated separately for the coarse and fine size fractions. For the ILVS/SFU parallel samplings, excellent agreement was observed between the results for the fine fraction, with the overall mean average ratio (based on 21 samples and 22 elements) being 0.99±0.10. For the coarse fraction, the overall mean ILVS/SFU ratio (based on 21 elements) was 0.75±0.13. This low result is explained by different upper-particle-size cut-offs of the two samplers. For the parallel samplings with LPI and SFU, the agreement was poorer, but still reasonable. The atmospheric concentrations observed at the two sites in the two campaigns and also the LPI size distributions for the various elements are discussed briefly.

Evaluation of the applicability of the MOUDI impactor for aerosol collections with subsequent multielement analysis by PIXE

Abstract The micro-orifice uniform deposit impactor (MOUDI) is an 8-stage impactor with cut-sizes down to 0.056 μm and which allegedly provides uniform aerosol deposits for the various stages. In the present study it was examined how uniform the aerosol deposits really are for each impaction plate and whether the uniformity is sufficient for a straightforward PIXE analysis. This was done by collecting several samples of ambient aerosol with the MOUDI and by determining the deposition pattern of various elements on the foils through a linear PIXE scan across each impaction foil. It was found that the deposits are far from uniform at the millimeter level for the stage numbers up to 6. Despite this, concentration data can easily be obtained by PIXE from such samples, provided that the analyzed area is carefully selected and appropriate correction factors for the nonuniformity are employed. Some size distribution data are presented. A comparison is also made of the size distribution data and detection limits that result from employing the MOUDI in combination with PIXE with those obtainable by PIXE analysis of some other types of cascade impactors.

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.