Definitions

2.  In these Regulations—

• “agglomeration” (“crynhoad”) means a zone with a population concentration in excess of 250,000 inhabitants or, where the population concentration is 250,000 inhabitants or less, a population density per km² for which the National Assembly considers that the need for ambient air to be assessed or managed is justified;

• “alert threshold” (“trothwy rhybuddio”) has the meaning given by regulation 9(2);

• “ambient air” (“aer amgylchynol”) means outdoor air in the troposphere, excluding work places;

• “assessment” (“asesu”) means any method used to measure, calculate, predict or estimate the level of a relevant pollutant in the ambient air;

• “fixed measurements” (“mesuriadau sefydlog”) means measurements taken at fixed sites either continuously or by random sampling, the number of measurements being sufficiently large to enable the levels observed to be determined;

• “level” (“lefel”) means the concentration of a relevant pollutant in ambient air;

• “limit value” (“gwerth terfyn”) has the meaning given in regulation 4(1);

• “lower assessment threshold” (“trothwy asesu isaf”) has the meaning given in regulation 6(5);

• “National Assembly” (“Cynulliad Cenedlaethol”) means the National Assembly for Wales;

• “natural events” (“digwyddiadau naturiol”) means volcanic eruptions, seismic activities, geothermal activities, wild-land fires, high-wind events or the atmospheric resuspension or transport of natural particles from dry regions;

• “oxides of nitrogen” (“ocsidau nitrogen”) means the sum of nitric oxide and nitrogen dioxide added as parts per billion and expressed as nitrogen dioxide in microgrammes per cubic metre;

• “PM_2.5” means particulate matter which passes through a size-selective inlet with a 50% efficiency cut-off at 2.5 mm aerodynamic diameter;

• “PM₁₀” means particulate matter which passes through a size-selective inlet with a 50% efficiency cut-off at 10 mm aerodynamic diameter;

• “relevant pollutants” (“llygrynnau perthnasol”) means sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter, lead, benzene and carbon monoxide;

• “upper assessment threshold” (“trothwy asesu uchaf”) has the meaning given in regulation 6(5); and

• “zone” (“parth”) means a part of Wales shown on a map published by the National Assembly on 3 December 2002, deposited at the offices of the National Assembly, Environmental Protection Division, Cathays Park, Cardiff CF10 3NQ.