Encyclopaedia of the Anthropocene: Magnetic particulates as markers of fossil fuel burning

Particulate matter derived from various sources of fuel combustion contains minor to trace amounts of Fe-oxides that can be detected by magnetic measurements. These magnetic particulates can be used as proxies for particulate pollution, since oxide contents are often larger in amounts and may have distinctive magnetic properties, compared to most types of natural dusts. Magnetic particulates range in size from a few nanometres to 100s of microns. Magnetic measurements of sediment cores and soils therefore provide evidence for historical particulate pollution loads, both in time since ca. AD 1800, and the spatial expression of pollution loads. {97 words} Main text Inorganic particulate matter from fossil fuel burning Particles in the atmosphere are derived from several sources, which include sea salt, biogenic aerosol particles, inorganic dusts (from soils, rocks, volcanic ash and anthropogenic activities) and combustion-derived particles (Gieré and Querol, 2010). Our use and burning of fossil fuels generates both carbonaceous particles and various kinds of inorganic dusts, emitted into the atmosphere, with a wide range of particle sizes from a few nanometres (nm) to several hundred microns (μm) (Fig. 1). This large range of particle size is a reflection of the diverse modes of formation of these aerosols. Inorganic Particulate Matter (PM), can comprise both crystalline and amorphous particulate matter. Here a specific focus is on the crystalline PM, and its characterisation using magnetic methods (Petrovsky & Ellwood, 1999; Snowball et al., 2014). These magnetic properties are largely carried by magnetite (Fe3O4) and like aerosol formation processes, magnetic behaviour is in part particle size dependent (Fig. 1). Prior to the major utilisation of coal during the early parts of the industrial revolution, wood and charcoal burning would have been the major source of anthropogenic generated PM. This was added to during the 17 th and 18 th century, when coal (and oil shale) combustion, and the fly ash emitted by its burning, took over as the major source of inorganic PM dispersed in the environment from fuel combustion. As happening now and into the future, sources of anthropogenically-derived PM will change, as dominant fuel use changes away from coal. Magnetic methods of PM characterisation are receiving wider use, because of the non-destructive, simple and rapid