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

Anotations

Scope note:

Extremely small particles and droplets suspended in air. They may include organic chemicals, acids, metals, and dust or soil particles. Also known as particle pollution, particulate matter is used as a measure of air pollution. The EPA groups inhalable pollutants which pass through the throat and nose and enter the lungs into two categories: “inhalable coarse particles” (between 2.5 micrometers and 10 micrometers in diameter); and “fine particles” (2.5 micrometers in diameter and smaller).