Cenospheres, Tire Wear, and Natural Minerals

Transmitted Off Crossed Polarized light and Oblique Top Light Illumination

Definition/Function:

Road Dust is an assemblage rather than a single particle type. An assemblage is characterized by a set of particles of different types, in this case, tire wear, engine emissions, and natural minerals. Each of these particles have multiple sources but when found together indicate relative proximity of roads.

Significance in the Environment:

Road Dust indicates proximity to roads and the size, shape, and blend of assemblage members helps indicate the type of road, the type of traffic on the road, relative distance to the road, and volume of traffic.

Characteristic Features:

The most characteristic particle of this assemblage is tire wear. Occationally an asphalt coated mineral grain will be present. The cenospheres tend to be small because mobile diesel engines are much smaller than the large fixed boilers of power plants or large ship. Wear metals, nitrate aerosols, and exhaust corrosion products can also be part of this assemblage.

Associated Particles:

The mix of Road Dust with pollens, spores, insect parts, plant parts, and other "exterior" particle types helps to characterized the nature of the exterior environment and entry path of the particles. Garages under a building, open windows, and door access directly from the street all have different mixes of particle types. Though these mixes overlap, multiple samples from the same site can often help differentiate these conditions.

References:

1. http://en.wikipedia.org/wiki/Cenosphere (see Fuel or Oil Cenospheres heading)