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| Particle Particle Size Parts Per Million (Ppm) Pathogen Peat Pectine Peptide Permeability Pesticides Pext Ph Phagocyte Polymer Prebiotic Probiotic Protein (Protid) Protein-Prion |
| The diameter of a particle, which is assumed to be spherical. (While we assume particles are spherical, this is rarely the case.) Size is usually defined in microns (q.v.). |