Derbyniodd y Gweinidogion gynllun Cyngor Caerdydd ar 31 Gorffennaf gyda nifer o amodau. Mae'n rhaid i'r Awdurdod fireinio'r achos ar gyfer eu hopsiwn a ffefrir, ac mae'n rhaid canolbwyntio ar sicrhau'r gofyniad cyfreithiol gan ddangos pam bod mesurau ategol ychwanegol yn hanfodol i sicrhau cydymffurfio â'r terfynau cyfreithiol ar hyd Stryd y Castell. Mae'n rhaid i'r Awdurdod gynnal gwaith modelu pellach hefyd i asesu y posibilrwydd o gynnal Parth Aer Glân er mwyn cadw at y terfynau. Mae Cyngor Caerdydd wedi cymryd 3 mis i wneud gwaith ychwanegol i wella eu cynllun terfynol a chyflwyno tystiolaeth gadarn mai y pecyn o fesurau a nodwyd ganddynt yw'r ffordd fwyaf tebygol o sicrhau eu bod yn cydymffurfio cyn gynted â phosibl.
Ministers accepted Cardiff Council’s plan on 31 July with a number of caveats. The Authority must refine the case for their preferred option which must be focused on achieving the legal requirement and must demonstrate why any additional complementary measures are essential to ensure compliance with the legal limits along Castle Street. The Authority must also undertake further modelling to better assess the potential of a charging Clean Air Zone to achieve limit values. Cardiff Council have up to 3 months to undertake additional work to improve their final plan and present robust evidence their identified package of measures is the route most likely to achieve compliance in the soonest time possible.