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. 'target value` shall mean a level fixed with the aim of avoiding more long-term harmful effects on human health and/or the environment as a whole, to be attained where possible over a given period; 7. '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 this Directive; 8. '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 this Directive; 9. 'zone` shall mean part of their territory delimited by the Member States; 10. 'agglomeration` shall mean 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 which for the Member States justifies the need for ambient air quality to be assessed and managed.

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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.