Where, as a result of an air quality review, it appears that any air quality standards or objectives are not being achieved, or are not likely within the relevant period to be achieved, within the area of a local authority, the local authority shall by order designate as an air quality management area (in this Part referred to as a "designated area") any part of its area in which it appears that those standards or objectives are not being achieved, or are not likely to be achieved within the relevant period.
An order under this section may, as a result of a subsequent air quality review,—
be varied by a subsequent order; or
be revoked by such an order, if it appears on that subsequent air quality review that the air quality standards and objectives are being achieved, and are likely throughout the relevant period to be achieved, within the designated area.