The Welsh Ministers must classify each zone according to whether or not the upper or lower assessment thresholds specified in Section I of Annex II to Directive 2004/107/EC are exceeded in relation to arsenic, cadmium, nickel and benzo(a)pyrene.

The Welsh Ministers must review the classification of zones in paragraph (1) at least every five years, and must do so more frequently than every five years if there are significant changes in the activities which may affect levels of the pollutants referred to in paragraph (1) in ambient air.

When reviewing the classification of zones in accordance with assessment thresholds, the Welsh Ministers must comply with Section II of Annex II to Directive 2004/107/EC.

The Welsh Ministers must assess the level of arsenic, cadmium, nickel and benzo(a)pyrene in ambient air in each zone in accordance with paragraphs (2) to (4).

In zones where the level of any pollutant mentioned in paragraph (1) exceeds the upper assessment threshold for that pollutant referred to in regulation 10, fixed measurements must be used in relation to that pollutant, but may be supplemented by modelling in order to provide an adequate level of information on ambient air quality.

In zones where the level of any pollutant mentioned in paragraph (1) is between the upper and lower assessment thresholds for that pollutant referred to in regulation 10 over a representative period, fixed measurements must be used in relation to that pollutant but may be combined with indicative measurements as referred to in Section I of Annex IV to Directive 2004/107/EC or modelling, or both.

In zones where the level of any pollutant mentioned in paragraph (1) is below the lower assessment threshold for that pollutant referred to in regulation 10, modelling or objective estimation techniques or both may be used instead of measurement in relation to that pollutant.

Measurements for the purposes of paragraph (6) must be coordinated with the monitoring strategy and measurement programme of the Cooperative Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe (EMEP), where appropriate.

The data quality objectives and requirements set out in Annex IV to Directive 2004/107/EC must be applied in carrying out the assessments referred to in paragraphs (1), (5) and (6).

Measurements in this regulation must be taken in accordance with the reference measurement methods specified in Annex V to Directive 2004/107/EC.

In this regulation, “total gaseous mercury” (“mercwri nwyol llwyr”) means elemental mercury vapour (Hg0) and reactive gaseous mercury, being water-soluble mercury species with sufficiently high vapour pressure to exist in the gas phase.

The Welsh Ministers must install sampling points in accordance with the criteria set out in Sections I, II and IV of Annex III to Directive 2004/107/EC for the assessment of arsenic, cadmium, nickel and benzo(a)pyrene.