Evidence for changing the Critical Level for ammonia

Cape, J N.; van der Eerden, L. J.; Sheppard, L. J.; Leith, I. D.; Sutton, M. A.. 2009 Evidence for changing the Critical Level for ammonia. Environmental Pollution, 157 (3). 1033-1037.

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The current Critical Level for ammonia (CLENH3) in Europe is set at 8 µg NH3 m-3 as an annual average concentration. Recent evidence has shown specific effects of ammonia (NH3) on plant community composition (a true ecological effect) at much smaller concentrations. The methods used in setting a CLENH3 are reviewed, and the available evidence collated, in proposing a new CLENH3 for different types of vegetation. For lichens and bryophytes, we propose a new CLENH3 of 1 µg NH3 m-3 as a long-term (several year) average concentration; for higher plants, there is less evidence, but we propose a CLENH3 of 3 ± 1 µg NH3 m-3 for herbaceous species. There is insufficient evidence to provide a separate CLENH3 for forest trees, but the value of 3 ± 1 µg NH3 m-3 is likely to exceed the empirical Critical Load for N deposition for most forest ecosystems.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: CEH Programmes pre-2009 publications > Biogeochemistry > BG02 Recovery from acidification and eutrophication
UKCEH and CEH Sections/Science Areas: Billett (to November 2013)
ISSN: 0269-7491
Additional Information. Not used in RCUK Gateway to Research.: The definitive version of this paper is available at
Additional Keywords: air pollution; effects; ammonia; NH3; bryophytes; lichens; fumigation
NORA Subject Terms: Agriculture and Soil Science
Ecology and Environment
Atmospheric Sciences
Date made live: 13 Mar 2009 15:24 +0 (UTC)

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