Size Distributions and Concentrations of Spheroidal Carbonaceous Fly-Ash Particles (SCPs) in Lake Sediments as an Aid to Detecting Locally Deposited Atmospheric Pollution

Abstract

Size distributions and concentrations of spheroidal carbonaceous fly-ash particles (SCPs) > 5 μm 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 μm) than further downwind where smaller particles (5–10 μm) dominate. The pattern of SCPs > 5 μm is compared with a previous study of anthropogenic Pb and SCPs > 3 μm in the same sediments. Along the transect there is a difference in pattern between the concentrations of SCPs > 5 μm and the patterns of anthropogenic Pb and SCPs > 3 μm. The result indicates that increased altitude and rainfall probably explain the increased concentrations of anthropogenic Pb and SCPs > 3μm in the eastern part of the transect. Metals are in the size range for which atmospheric residence times are greatest, whereas particles > 5 μm 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 μm concentrations and anthropogenic Pb and SCPs > 3 μm concentrations. This study shows that SCPs > 5 μm 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 μm) 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.