Ers i Lywodraeth Cymru wneud y penderfyniad i gyflwyno terfynau cyflymder amgylcheddol i wella lefelau ansawdd aer mewn pum lleoliad gwahanol ledled Cymru, y cyntaf o’i fath yn y DU, mae'r lefelau nitrogen deuocsid wedi cael eu gostwng yn llwyddiannus yn yr ardaloedd hyn.
Since the Welsh Government took the decision to introduce environmental speed limits to improve air quality levels at five different locations across Wales, the first of its kind in the UK, there has been a successful lowering of nitrogen dioxide levels in these areas.