INTERCOMPARISON OF ELEMENTAL CONCENTRATIONS IN TOTAL AND SIZE-FRACTIONATED AEROSOL SAMPLES COLLECTED DURING THE MACE HEAD EXPERIMENT, APRIL1991

During an intercomparison field experiment, organized at the Atlantic coast station of Mace Head, Ireland, in April 1991, aerosol samples we re collected by four research groups. A variety of samplers was used, combining both high- and low-volume devices, with different types of c ollection substrates: Hi-Vol Whatman 41 filter holders, single Nuclepo re filters and stacked filter units, as well as PIXE cascade impactors . The samples were analyzed by each participating group, using in-hous e analytical techniques and procedures. The intercomparison of the dai ly concentrations for 15 elements, measured by two or more participant s, revealed a good agreement for the low-volume samplers for the major ity of the elements, but also indicated some specific analytical probl ems, owing to the very low concentrations of the non-sea-salt elements at the sampling site. With the Hi-Vol Whatman 41 filter sampler, on t he other hand, much higher results were obtained in particular for the sea-salt and crustal elements. The discrepancy was dependent upon the wind speed and was attributed to a higher collection efficiency of th e Hi-Vol sampler for the very coarse particles, as compared to the low -volume devices under high wind speed conditions. The elemental mass s ize distribution, as derived from parallel cascade impactor samplings by two groups, showed discrepancies in the submicrometer aerosol fract ion, which were tentatively attributed to differences in stage cut-off diameters and/or to bounce-off or splintering effects on the quartz i mpactor slides used by one of the groups. However, the atmospheric con centrations (sums over all stages) were rather similar in the parallel impactor samples and were only slightly lower than those derived from stacked filter unit samples taken in parallel.