The Welsh Ministers must assess the level of ozone in ambient air in each zone.

The Welsh Ministers must ensure, for the purposes of paragraph (1), that fixed measurements are taken in any zone where the level of ozone has exceeded the long-term objectives specified in Schedule 3 during any of the five years preceding those measurements.

In any zone where fixed measurements are supplemented by modelling or indicative measurements or both, the Welsh Ministers must take account of the results of those supplementary methods for the purposes of paragraph (1).

The data quality objectives and requirements set out in Sections A and C of Annex I to Directive 2008/50/EC must be applied in carrying out the assessment referred to in paragraph (1).

Save as provided in paragraph (6), measurements for the purposes of paragraph (1) must be taken in accordance with the reference measurement methods specified in point 8 of Section A of Annex VI to Directive 2008/50/EC.

Alternative methods to those referred to in paragraph (5) may be used provided the conditions set out in Section B of Annex VI to Directive 2008/50/EC are complied with.