Sulphur dioxide, nitrogen dioxide, particulate matter and lead are indicated as the first priorities for action. Scottish Ministers have been designated as the competent authority for implementation of the Directive and subsequent daughter directives, as required under Article 3 of the Framework Directive. The First Daughter Directive relating to limit values for sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter and lead was adopted on 22 April 1999. It is concerned with the first group of pollutants identified by the Air Quality Framework Directive for daughter legislation. The table below lists the First Daughter Directive's limit values, the dates for their attainment, and the maximum number of exceedances permitted each calendar year.
MOTs are pollutant levels set a fixed percentage above the limit value.
The margins decrease by a constant percentage year by year until the date for attainment of the limit value. From that date onwards, no MOTs are permitted. This provision gives a guide for the rate at which pollutant levels may need to fall in order to reach the limit value successfully. If the margin is surpassed in a zone or agglomeration in any particular year, it acts as a trigger, indicating that a plan or programme needs to be implemented there in order to attain the limit value and address the pollution problem. The following table summarises the margins of tolerance set by the First Daughter Directive.