Identifying fly ash at a distance from fossil fuel power stations

A method has been developed to identify fly ash originating at fossil fuel power stations, even at a distance where the ash level is lower by a factor of 1000 from that close to a source. Until now such detection has been difficult and uncertain. The technique combines collection of particles, measurement of magnetization and coercive field, and microscopy. The analysis depends on the fact that ash from iron sulfide in fossil fuels is in the form of spherical magnetite. These particles have a relatively high coercive field H-c, near 135 Oe, compared with airborne particulates from soil erosion which have an H-c of similar to 35 Oe. The coercive field of any sample therefore gives an indication for the percentage of fly ash relative to the total amount of magnetic material that is airborne. The concentration of ash from a large, isolated coal burning power station is found to fall off with the distance from the source, approximately as D-1. As D increases there is a drop in H-c, associated with the reduced amount of fly ash relative to the airborne particulates from soil erosion.