2 results
9 - Nitrogen processes in the atmosphere
- from Part II - Nitrogen processing in the biosphere
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- By Ole Hertel, University of Aarhus, Stefan Reis, Centre for Ecology and Hydrology, Carsten Ambelas Skjøth, Aarhus University, Albert Bleeker, Energy Research Centre of the Netherlands, Roy Harrison, University of Birmingham, John Neil Cape, Centre for Ecology and Hydrology, David Fowler, Food and Rural Affairs, Kingspool, Ute Skiba, Centre fro Ecology and Hydrology, David Simpson, Norwegian Meteorological Institute, Tim Jickells, University of East Anglia, Alex Baker, University of East Anglia, Markku Kulmala, University of Helsinki, Steen Gyldenkærne, Danmarks Miljøundersøgelser, Lise Lotte Sørensen, Risø National Laboratory for Sustainable Energy, Jan Willem Erisman, Energy Research Centre of the Netherlands
- Edited by Mark A. Sutton, NERC Centre for Ecology and Hydrology, UK, Clare M. Howard, NERC Centre for Ecology and Hydrology, UK, Jan Willem Erisman, Gilles Billen, Albert Bleeker, Peringe Grennfelt, Hans van Grinsven, Bruna Grizzetti
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- Book:
- The European Nitrogen Assessment
- Published online:
- 16 May 2011
- Print publication:
- 14 April 2011, pp 177-208
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Summary
Executive summary
Nature of the problem
The two main groups of atmospheric reactive nitrogen compounds (reduced and oxidized nitrogen) have different fates due to differences in governing processes.
Abatement strategies need to take into account these differences when assessing the impact on the sensitive ecosystems.
Approaches
The chapter outlines the governing physical and chemical processes for the two main groups of reactive nitrogen compounds.
The chapter is divided into sections concerning: emissions, transformation, aerosol processes, dry deposition and wet deposition.
Key findings/state of knowledge
Reactive nitrogen compounds consist of reduced nitrogen (ammonia and its reaction product ammonium), oxidized nitrogen (nitrogen oxides) and organic nitrogen compounds.
Nitrogen oxides have little impact close to the sources since they are emitted as nitrogen monoxide and nitrogen dioxide with low dry deposition rates. These compounds need to be converted into nitric acid (about 5% per hour) before deposition is efficient.
Ammonia has a high impact near the sources due to high dry deposition rates. Ammonia may therefore have significant impact on ecosystems in areas with intense agricultural activity leading to high emissions of ammonia.
Both ammonia and gaseous nitrogen oxides lead to formation of aerosol phase compounds (ammonium and nitrate) which are transported over long distances (up to more than 1000 km).
Very little is known either quantitatively or qualitatively about organic nitrogen compounds, other than that they can contribute a significant fraction of wet-deposited N, and are present in gaseous and particulate forms in the atmosphere.
The atmospheric budget of oxidized nitrogen and its role in ozone formation and deposition
- DAVID FOWLER, CHRIS FLECHARD, UTE SKIBA, MHAIRI COYLE, J. NEIL CAPE
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- Journal:
- The New Phytologist / Volume 139 / Issue 1 / May 1998
- Published online by Cambridge University Press:
- 01 May 1998, pp. 11-23
- Print publication:
- May 1998
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- Article
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Emissions of reactive oxidized nitrogen (NO and NO2), collectively known as NOx, from human activities are c. 21 Tg N annually, or 70% of global total emissions. They occur predominantly in industrialized regions, largely from fossil fuel combustion, but also from increased use of N fertilizers. Soil emissions of NO not only make an important contribution to global totals, but also play a part in regulating the dry deposition of NO and NO2 (NOx) to plant canopies. Soil microbial production of NO leads to a soil ‘compensation point’ for NO deposition or emission, which depends on soil temperature, N and water status. In warm conditions, the net emission of NOx from plant canopies contributes to the photochemical formation of ozone. Moreover, the effect of NOx emissions from soil is to reduce net rates of NO2 deposition to terrestrial surfaces over large areas.
Increasing anthropogenic emissions of NOx have led to an approximate doubling in surface O3 concentrations since the last century. NOx acts as a catalyst for the production of O3 from volatile organic compounds (VOCs). Paradoxically, emission controls on motor vehicles might lead to increases in O3 concentrations in urban areas.
Removal of NO and NO2 by dry deposition is regulated to some extent by soil production of NO; the major sink for NO2 is stomatal uptake. Long-term flux measurements over moorland in Scotland show very small deposition rates for NO2 at night and before mid-day of 1–4 ng NO2-N m−2 s−1, and similar emission rates during afternoon. The bi-directional flux gives 24-h average deposition velocities of only 1–2 mm s−1, and implies a long life-time for NOx due to removal by dry deposition.
Rates of removal of O3 at the ground are also influenced by stomatal uptake, but significant non-stomatal uptake occurs at night and in winter. Measurements above moorland showed 40% of total annual flux was stomatal, with 60% non-stomatal, giving nocturnal and winter deposition velocities of 2–3 mm s−1 and daytime summer values of 10 mm s−1. The stomatal uptake is responsible for adverse effects on vegetation. The critical level for O3 exposure (AOT40) is used to derive a threshold O3 stomatal flux for wheat of 0·5 μg m−2 s−1. Use of modelled stomatal fluxes rather than exposure might give more reliable estimates of yield loss; preliminary calculations suggest that the relative grain yield reduction (%) can be estimated as 38 times the stomatal ozone flux (g m−2) above the threshold, summed over the growing season.