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| Titel: |
Advection of NH3 over a pasture field, and its effect on gradient flux measurements |
| Auteur: |
B. Loubet C. Milford A. Hensen U. Daemmgen J.-W. Erisman P. Cellier M. A. Sutton |
| Verschenen in: |
Biogeosciences discussions |
| Paginering: | Jaargang 6 (2009) nr. 1 pagina's 163-196 |
| Jaar: |
2009 |
| Inhoud: |
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 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 (Δ Fz,adv) were estimated over a 14 ha grassland field, which was successively cut and fertilised, as part of the GRAMINAE integrated Braunschweig experiment. The magnitude of Δ Fz,adv was determined up to 810 m 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 Δ Fz,adv: (1) based on direct measurements of horizontal concentration gradients, and (2) based on inverse dispersion modelling. Two sources of local advection were clearly identified: the farm NH3 emissions leading to positive Δ Fz,adv, and field NH3 emissions, after cutting and fertilisation, which led to a negative Δ Fz,adv. The local advection flux from the farm was in the range 0 to 27 ng m−2 s−1 NH3 at 610 m from the farm, whereas Δ Fz,adv due to field emission was proportional to the local flux, and ranged between −209 and 13 ng m−2 s−1 NH3. The local advection flux Δ Fz,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 Δ Fz,adv was estimated at 2 m 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 1 m height, were 121% on average, before the field was cut (when downwind of the farm), and less than 7% when the field was fertilised. |
| Uitgever: |
Copernicus Publications (provided by DOAJ) |
| Bronbestand: |
Elektronische Wetenschappelijke Tijdschriften |
Details van artikel 2 van 75 gevonden artikelen
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