Assessment criteria
11.—(1) The Scottish Ministers must assess concentrations of arsenic, cadmium, nickel and benzo(a)pyrene in ambient air in all zones.
(2) In zones where the level of any pollutant mentioned in paragraph (1) is above the upper assessment threshold for that pollutant, fixed measurements must be used in relation to that pollutant but may be supplemented by modelling techniques to provide an adequate level of information on ambient air quality.
(3) In zones where the level of any pollutant mentioned in paragraph (1) is above the lower assessment threshold but below the upper assessment threshold for that pollutant, fixed measurements must be used in relation to that pollutant but may be supplemented by indicative measurements as referred to in Section I of Annex IV to Directive 2004/107/EC or modelling, or both, to assess the level of these pollutants in ambient air.
(4) In zones where the level of any pollutant mentioned in paragraph (1) is below the lower assessment threshold for that pollutant, modelling or objective estimation techniques may be used instead of measurement in relation to that pollutant.