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Advection of NH3 over a pasture field, and its effect on gradient flux measurements

Loubet, B.; Milford, C.; Henson, A.; Daemmgen, U.; Erisman, J.-W.; Cellier, P.; Sutton, M.A.. 2009 Advection of NH3 over a pasture field, and its effect on gradient flux measurements. Biogeosciences Discussions, 6 (1). 163-196.

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Abstract/Summary

Deposition of atmospheric ammonia (NH3) to semi-natural ecosystems leads to serious adverse effects, such as acidification and eutrophication. A step in this quantification is the measurement of NH3 fluxes over semi-natural and agricultural land. However, measurement 5 of NH3 fluxes over vegetation in the vicinity of strong NH3 sources is difficult, since NH3 emissions are highly heterogeneous. Indeed, under such conditions, local advection errors may alter the measured fluxes. In this study, local advection errors (ÉFz,adv) were estimated over a 14 ha grassland field, which was successively cut and fertilised, as part of the GRAMINAE integrated Braunschweig experiment. The 10 magnitude of ÉFz,adv was determined up to 810m downwind from farm buildings emitting between 6 and 12 kg NH3 day−1. The GRAMINAE experiment provided a unique opportunity to compare two methods of estimating ÉFz,adv: (1) based on direct measurements of horizontal concentration gradients, and (2) based on inverse dispersion modelling. 15 Two sources of local advection were clearly identified: the farm NH3 emissions leading to positive ÉFz,adv, and field NH3 emissions, after cutting and fertilisation, which led to a negative ÉFz,adv. The local advection flux from the farm was in the range 0 to 27 ngm−2 s−1 NH3 at 610m from the farm, whereas ÉFz,adv due to field emission was proportional to the local flux, and ranged between −209 and 13 ngm−2 s−1 NH3. The 20 local advection flux ÉFz,adv was either positive or negative depending on the magnitude of these two contributions. The modelled and measured advection errors agreed well, provided the modelled ÉFz,adv was estimated at 2m height. This study constitutes the first attempt to validate the inverse modelling approach to determine advection errors for NH3. The measured advection errors, relative to the vertical flux at 1m height, were 25 121% on average, before the field was cut (when downwind of the farm), and less than 7% when the field was fertilised. 164

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 30 Nov 2013)
Additional Information. Not used in RCUK Gateway to Research.: Open Access Journal. The full text of this paper is available from the journal website. http://www.biogeosciences-discuss.net/6/163/2009/bgd-6-163-2009.html
NORA Subject Terms: Atmospheric Sciences
Date made live: 01 Jun 2009 09:38
URI: http://nora.nerc.ac.uk/id/eprint/5532

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