SIZE DISTRIBUTIONS AND CONCENTRATIONS OF SPHEROIDAL CARBONACEOUS FLY-ASH PARTICLES (SCPs) IN LAKE SEDIMENTS AS AN AID TO DETECTING LOCALLY DEPOSITED ATMOSPHERIC POLLUTIONJORUNN LARSEN Department of Botany, University of Bergen, Allgaten 41, N-5007 Bergen, Norway (e-mail: Jorunn.Larsenbot.uib.no; Fax: (+47) 55 58 96 67)(Received 5 March 2002; accepted 20 May 2003)Abstract. Size distributions and concentrations of spheroidal carbonaceous fly-ash particles (SCPs) 5 m have been counted in surface sediments from 20 lakes along a 62 km west-east transect in the Bergen area, Norway. Increased concentrations of SCPs are found in lakes immediately downwind, closest to the city. These lakes also have a dominance of larger particles ( 10 m) than further downwind where smaller particles (510 m) dominate. The pattern of SCPs 5 m is compared with a previous study of anthropogenic Pb and SCPs 3 m in the same sediments. Along the transect there isadifference inpatternbetween the concentrations of SCPs5m and thepatternsof anthropogenic Pb and SCPs 3 m. The result indicates that increased altitude and rainfall probably explain the increased concentrations of anthropogenic Pb and SCPs 3m in the eastern part of the transect. Metals are in the size range for which atmospheric residence times are greatest, whereas particles 5 m in diameter are of the size thought to be effectively removed from the atmosphere by sedimentation. This may explain, at least partially, why there is a difference between the pattern of SCPs 5 m concentrations and anthropogenic Pb and SCPs 3 m concentrations. This study shows that SCPs 5 m in lake sediments can potentially provide a better signal of locally-deposited atmospheric pollution than trace elements from the same source. A SCP distribution dominated by large particles ( 10 m) is found up to 20 km downwind of the city. Within this area, temporal SCP size distribution patterns can help detect local-deposited atmospheric pollution.Keywords: lake sediments, lead, local air pollution, seeder-feeder effect, sizedistribution, spheroidal carbonaceous particles1. IntroductionCoal and oil combustion produces three major types of insoluble fly-ash spheres (Wik and Renberg, 1996; Rose, 2001). These include two types of micrometer size organic and inorganic ash spheres. The inorganic ash spheres (IASs) are composed of mineral inclusions present within the fuel (McLean, 1991; Rose, 1996). They have surface appearances ranging from clear and glassy to black and metallic (seeFisher et al., 1978; Griffin and Goldberg, 1981). The source of IASs includes nat- ural sources such as volcanic ash, and the burning of fossil fuels. The organic ashspheres, named spheroidal carbonaceous fly-ash particles (SCPs), are produced by the incomplete combustion of fossil fuels and their appearance ranges from per-Water, Air, and Soil Pollution 149: 163175, 2003. 2003 Kluwer Academic Publishers. Printed in the Netherlands.164J. LARSENforated spheres to sponge-like spheres with very little surface area (see Goldbergand Griffin, 1979; Rose et al., 1994). Bacci et al. (1983) also describe particles 10 m in diameters after the refinery started in 1975. Particles 5 m in dia- meter are thought to be effectively removed from the atmosphere by sedimentation (Ogren et al., 1984). The sedimentation of different sizes seems to be dependent on the distance from the emission source, changing from long-range transported air pollution with small diameter (510 m) particles dominant, to also include a local source giving a dominance of particles 10 m diameter (Larsen, 2000). The SCP diameter distribution in a reference lake, assumed to be receiving only long- range transported air pollution, was dominated by small diameter particles (510 m) both before and after 1975 implying that the SCPs there have continued to be only from long-range transport. In the present investigation, the concentrations of SCPs in surface sediment samples from twenty lakes (Figure 1) along a west- east transect in the Bergen area, Norways second largest city, are presented. The dominant wind direction is from the sea, west of the lakes. This is an exploratoryinvestigation to find out whether the SCP concentrations and diameter distributions can give more information about long-range versus locally-deposited atmospheric pollution in the area. The study includes SCPs 5 m as described in Rose et al. (1994), and as counted in the previous study of Larsen (2000), so that the size distributions of the SCPs could be compared. The twenty investigated lakes are a subsample of twenty nine investigated lakes in Larsen et al. (1996) but also include the reference lake from Larsen (2000) situated inthe western part ofthetransect. TheSCPscounted in the twenty nine lakes along the original transect in Larsen et al. (1996) were black and larger than 3 m. These included the least perforated SCPs described by Bacci et al. (1983), but