Mostbigcitiesaredeclaredtobesuchzones.Ifair‑qualitystandardsareexceededinazone,theMemberStatehastoreporttotheEuropeanCommissionandexplainthereasons.

Please segment the words.
Most big cities are declared to be such zones. If air‑quality standards are exceeded in a zone, the Member State has to report to the European Commission and explain the reasons.