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Inter-comparison of ammonia fluxes obtained using the relaxed eddy accumulation technique

Hensen, A.; Nemitz, E.; Flynn, M. J.; Blatter, A.; Jones, S. K.; Sorensen, L. L.; Henson, B.; Pryor, S.; Jensen, B.; Otjes, R. P.; Cobussen, J.; Loubet, B.; Erisman, J. W.; Gallagher, M. W.; Neftel, A.; Sutton, M. A.. 2008 Inter-comparison of ammonia fluxes obtained using the relaxed eddy accumulation technique. Biogeosciences Discussions, 5. 3965-4000.

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Abstract/Summary

The exchange of NH3 between grassland and the atmosphere was determined using Relaxed Eddy Accumulation (REA) measurements. The use of REA is of special interest for NH3, since the determination of fluxes at one height permits multiple systems to be deployed to quantify vertical flux divergence (either due to effects of chemical production or advection). During the Braunschweig integrated experiment four different continuous-sampling REA systems were operated during a period of about 10 days and were compared against a reference provided by independent application of the Aerodynamic Gradient Method (AGM). The experiment covered episodes before, after cutting and fertilising and provided a wide range of fluxes −60–3600 ng NH3 m−2 s−1 for testing the REA systems. The REA systems showed moderate to good correlation with the AGM estimates, with r2 values for the linear regressions between 0.3 and 0.82. For the period immediately after fertilization, the REA systems showed average fluxes 20% to 70% lower than the reference. At periods with low fluxes REA and AGM can agree within a few %. Overall, the results show that the continuous REA technique can now be used to measure NH3 surface exchange fluxes. While REA requires greater analytical precision in NH3 measurement than the AGM, a key advantage of REA is that auto-referencing periods can be introduced to remove bias between sampling inlets. However, while the data here indicate differences consistent with advection effects, further improvements in sampling precision are needed to allow measurement of flux divergence. Wet chemical techniques will be developed further since they use the sticky and reactive properties of NH3 that impedes development of cheaper optical systems.

Item Type: Publication - Article
Programmes: CEH Programmes pre-2009 publications > Biogeochemistry > BG01 Measuring and modelling trace gas, aerosol and carbon > BG01.1 UK nitrogen and sulphur compounds
CEH Programmes pre-2009 publications > Biogeochemistry > BG01 Measuring and modelling trace gas, aerosol and carbon > BG01.3 Nitroeurope NEU advanced flux network, fluxes pools and budgets
CEH Sections: Billett (to November 2013)
NORA Subject Terms: Atmospheric Sciences
Date made live: 18 Feb 2009 13:02
URI: http://nora.nerc.ac.uk/id/eprint/5522

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