Hierarchy classification:

1. top of the aat hierarchies
2. Materials Facet
3. Materials (hierarchy name)
4. materials (substances)
5. [materials by origin]
6. residue materials
7. ash (residue)

Anotations

Scope note:

Finely divided particulate matter resulting from the burning of pulverized coal or wood, often emitted as an airborne pollutant at power and manufacturing plants. Current practice in the United States is to trap and recover fly ash; used as a filler in brick and concrete.