OPTIONAL INDICATORS FOR MONITORING AIR POLLUTION IMPACTS REFERRED TO IN ARTICLE 9

for freshwater ecosystems: establishing the extent of biological damage, including sensitive receptors (microphytes, macrophytes and diatoms), and loss of fish stock or invertebrates: the key indicator acid neutralising capacity (ANC) and the supporting indicators acidity (pH), dissolved sulphate (SO_(4)), nitrate (NO_(3)) and dissolved organic carbon: frequency of sampling: from yearly (in lake autumn turnover) to monthly (streams). for terrestrial ecosystems: assessing the soil acidity, soil nutrients loss, nitrogen status and balance as well as biodiversity loss: the key indicator soil acidity: exchangeable fractions of base cations (base saturation) and exchangeable aluminium in soils: frequency of sampling: every 10 years; supporting indicators: pH, sulphate, nitrate, base cations, aluminium concentrations in soil solution: frequency of sampling: every year (where relevant); the key indicator soil nitrate leaching (NO_(3,leach)): frequency of sampling: every year; the key indicator carbon-nitrogen ratio (C/N) and the supporting indicator of total nitrogen in soil (N_(tot)): frequency of sampling: every 10 years; the key indicator nutrient balance in foliage (N/P,N/K, N/Mg): frequency of sampling: every four years. for terrestrial ecosystems: assessing ozone damage to vegetation growth and biodiversity: the key indicator vegetation growth and foliar damage and the supporting indicator carbon flux (C_(flux)): frequency of sampling: every year; the key indicator exceedance of flux-based critical levels: frequency of sampling: every year during the growing season.

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Source: EUR-Lex (Cellar) · retrieved 2026-10-29 · Text as adopted (Official Journal); later amendments are not incorporated in this text.