Fly-ash particles in lake sediments: Extraction, characterisation and distribution

Fly-ash particles produced from the high temperature combustion of fossil-fuels are found in high concentrations in the lake sediments of regions of high acid deposition. The sediment record of these particles showing the onset of industrialisation correlates well with the record of acidification as indicated by diatom analysis. There are two types of fly-ash particle; spheroidal carbonaceous particles produced from the incomplete combustion of the fossil-fuel and inorganic ash spheres formed by the fusing of mineral inclusions present within the fuel. Procedures were developed to extract both types of particle from lake sediments. These involved selective chemical attack to remove unwanted sediment fractions thus enabling quick and accurate particle enumeration. A reference data-set of carbonaceous particle surface chemistries was produced using EDS measurements and a fuel-type characterisation developed using multivariate statistics. This characterisation allocated over 97% of the particles to the correct fuel-type. These methods were then applied to a series of sediment cores to study temporal changes in particle deposition and spatial trends over Scotland. The concentrations of both particle types in sediment cores correlate well to fossil- fuel combustion histories, and the characterisation of the carbonaceous particles from a 210Pb-dated core from a north London lake showed good agreement with the change in coal and oil use through time in the area. Spatial trends were studied using surface sediments from 94 lakes in Scotland and the north of England. These showed higher concentrations near industrial areas and generally good agreement with sulphur deposition data. Characterisation revealed two areas where above average concentrations of oil particles occurred, indicating source areas outside the country to the east and the south-west. There is potential to extend this characterisation to other fossil-fuel types such as peat, lignite and brown coal and to apply the techniques to a range of environmental questions in Britain, Europe and on a global scale