Article 2

Definitions For the purposes of this Directive: 1. "ambient air" shall mean outdoor air in the troposphere, excluding work places; 2. "pollutant" shall mean any substance introduced directly or indirectly by man into the ambient air and likely to have harmful effects on human health and/or the environment as a whole; 3. "level" shall mean the concentration of a pollutant in ambient air or the deposition thereof on surfaces in a given time; 4. "assessment" shall mean any method used to measure, calculate, predict or estimate the level of a pollutant in the ambient air; 5. "limit value" shall mean a level fixed on the basis of scientific knowledge, with the aim of avoiding, preventing or reducing harmful effects on human health and/or the environment as a whole, to be attained within a given period and not to be exceeded once attained; 6. "alert threshold" shall mean a level beyond which there is a risk to human health from brief exposure and at which immediate steps shall be taken by the Member States as laid down in Directive 96/62/EC; 7. "margin of tolerance" shall mean the percentage of the limit value by which this value may be exceeded subject to the conditions laid down in Directive 96/62/EC; 8. "zone" shall mean part of their territory delimited by the Member States; 9. "agglomeration" shall mean a zone with a population concentration in excess of 250000 inhabitants or, where the population concentration is 250000 inhabitants or less, a population density per km2 which for the Member States justifies the need for ambient air quality to be assessed and managed. 10. "oxides of nitrogen" shall mean the sum of nitric oxide and nitrogen dioxide added as parts per billion and expressed as nitrogen dioxide in micrograms per cubic meter; 11. "PM10" shall mean particulate matter which passes through a size-selective inlet with a 50 % efficiency cut-off at 10 μm aerodynamic diameter; 12. "PM2,5" shall mean particulate matter which passes through a size-selective inlet with a 50 % efficiency cut-off at 2,5μm aerodynamic diameter; 13. "upper assessment threshold" shall mean a level specified in Annex V, below which a combination of measurements and modelling techniques may be used to assess ambient-air quality, in accordance with Article 6(3) of Directive 96/62/EC; 14. "lower assessment threshold" shall mean a level specified in Annex V, below which modelling or objective-estimation techniques alone may be used to assess ambient-air quality in accordance with Article 6(4) of Directive 96/62/EC; 15. "natural events" shall mean volcanic eruptions, seismic activities, geothermal activities, wild-land fires, high-wind events or the atmospheric resuspension or transport of natural particles from dry regions; 16. "fixed measurements" shall mean measurements taken in accordance with Article 6(5) of Directive 96/62/EC.

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Source: EUR-Lex (Cellar) · retrieved 2026-10-12 · Text as adopted (Official Journal); later amendments are not incorporated in this text.