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Context: Ystyr “asesu” ac “asesiad” (“assessment”) yw asesu a wneir drwy gyfrwng mesuriadau sefydlog, mesuriadau dangosol, modelu neu dechnegau amcangyfrif gwrthrychol.
Notes: Term o faes mesur ansawdd aer. Daw'r frawddeg gyd-destunol o Reoliadau Safonau Ansawdd Aer (Cymru) 2010.