Inter-comparison of ammonia fluxes obtained using the Relaxed Eddy Accumulation technique

Hensen, A.; Nemitz, Eiko; Flynn, Michael J.; Blatter, A.; Jones, S. K.; Sørensen, Lise Lotte; Hensen, B.; Pryor, Sara C.; Jensen, Bente Thoft; Otjes, R.P.; Cobussen, J.; Loubet, Benjamin; Erisman, J. W.; Gallagher, M. W.; Neftel, A.; Sutton, Mark A.

doi:10.5194/bg-6-2575-2009

Cited by 61 publications

(68 citation statements)

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“…It should be noted that several of the sonic anemometers formed part of relaxed eddy accumulation (REA) systems for NH 3 (CEH REA; ECN and FAL-IUL) (Hensen et al, 2008). Although attempts were made to minimise the impact of these sampling systems on the anemometer measurements, they may nevertheless influence the measurements to some extent, especially during calm conditions.…”

Section: Instrumentation Deploymentmentioning

confidence: 99%

Intercomparison and assessment of turbulent and physiological exchange parameters of grassland

et al. 2009

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Abstract. Commonly, the micrometeorological parameters that underline the calculations of surface atmosphere exchange fluxes (e.g. friction velocity and sensible heat flux) and parameters used to model exchange fluxes with SVATtype parameterisations (e.g. latent heat flux and canopy temperature) are measured with a single set of instrumentation and are analysed with a single methodology. This paper evaluates uncertainties in these measurements with a single instrument, by comparing the independent results from nine different institutes during the international GRAMINAE integrated field experiment over agricultural grassland near Braunschweig, Lower Saxony, Germany. The paper discusses uncertainties in measuring friction velocity, sensible and latent heat fluxes, canopy temperature and investigates the energy balance closure at this site. Although individual 15-min flux calculations show a large variability between the instruments, when averaged over the campaign, fluxes agree within 2% for momentum and 11% for sensible heat. However, the spread in estimates of latent heat flux (λE) is Correspondence to: E. Nemitz (en@ceh.ac.uk) larger, with standard deviations of averages of 18%. The dataset averaged over the different instruments fails to close the energy budget by 20%, significantly larger than the uncertainties in the individual flux corrections. However, if the largest individual turbulent flux estimates are considered, energy closure can be achieved, indicating that the closure gap is within the spread of the measurements. The uncertainty in λE feeds results in an uncertainty in the bulk stomatal resistance, which further adds to the uncertainties in the estimation of the canopy temperature that controls the exchange. The paper demonstrated how a consensus dataset was derived, which is used by the individual investigators to calculate fluxes and drive their models.

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Section: Instrumentation Deploymentmentioning

confidence: 99%

Intercomparison and assessment of turbulent and physiological exchange parameters of grassland

et al. 2009

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“…In particular, at the field scale, wet denuder systems with automated online detection Blatter et al, 1994;Erisman et al, 2001;Thomas et al, 2009) have helped produce many exchange flux datasets by aerodynamic gradient methods (AGM) or Bowen ratio techniques, both at remote background locations with low (sub-ppb) concentration levels (Flechard and Fowler, 1998b;Milford et al, 2001a), and over polluted semi-natural ecosystems and fertilized agricultural systems (Wyers and Erisman, 1998;Nemitz et al, 2000a, b;Neirynck and Ceulemans, 2008;Sutton et al, 2009b;Flechard et al, 2010;Wolff et al, 2010a;Loubet et al, 2012;Walker et al, 2013). Relaxed eddy accumulation systems have allowed NH 3 flux measurements at one single height Meyers et al, 2006;Hensen et al, 2009a). In parallel, a range of new generation, fast-response optical and mass spectrometry instruments have emerged over the last 15 yr (see von Bobrutzki et al, 2009, for a review and intercomparison), which have proved suitable for eddy covariance (EC) measurements of large (emission) fluxes such as those occurring after the land spreading of manures (Whitehead et al, 2008;Sintermann et al, 2011).…”

Section: Ammonia Measurement and Modelling Approachesmentioning

confidence: 99%

Advances in understanding, models and parameterizations of biosphere-atmosphere ammonia exchange

et al. 2013

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Atmospheric ammonia (NH₃) dominates global emissions of total reactive nitrogen (N_r), while emissions from agricultural production systems contribute about two-thirds of global NH₃ emissions; the remaining third emanates from oceans, natural vegetation, humans, wild animals and biomass burning. On land, NH₃ emitted from the various sources eventually returns to the biosphere by dry deposition to sink areas, predominantly semi-natural vegetation, and by wet and dry deposition as ammonium (NH₄⁺) to all surfaces. However, the land/atmosphere exchange of gaseous NH₃ is in fact bi-directional over unfertilized as well as fertilized ecosystems, with periods and areas of emission and deposition alternating in time (diurnal, seasonal) and space (patchwork landscapes). The exchange is controlled by a range of environmental factors, including meteorology, surface layer turbulence, thermodynamics, air and surface heterogeneous-phase chemistry, canopy geometry, plant development stage, leaf age, organic matter decomposition, soil microbial turnover, and, in agricultural systems, by fertilizer application rate, fertilizer type, soil type, crop type, and agricultural management practices. We review the range of processes controlling NH₃ emission and uptake in the different parts of the soil-canopy-atmosphere continuum, with NH₃ emission potentials defined at the substrate and leaf levels by different [NH₄⁺] / [H⁺] ratios (Γ). Surface/atmosphere exchange models for NH₃ are necessary to compute the temporal and spatial patterns of emissions and deposition at the soil, plant, field, landscape, regional and global scales, in order to assess the multiple environmental impacts of airborne and deposited NH₃ and NH₄⁺. Models of soil/vegetation/atmosphere NH₃ exchange are reviewed from the substrate and leaf scales to the global scale. They range from simple steady-state, "big leaf" canopy resistance models, to dynamic, multi-layer, multi-process, multi-chemical species schemes. Their level of complexity depends on their purpose, the spatial scale at which they are applied, the current level of parameterization, and the availability of the input data they require. State-of-the-art solutions for determining the emission/sink Γ potentials through the soil/canopy system include coupled, interactive chemical transport models (CTM) and soil/ecosystem modelling at the regional scale. However, it remains a matter for debate to what extent realistic options for future regional and global models should be based on process-based mechanistic versus empirical and regression-type models. Further discussion is needed on the extent and timescale by which new approaches can be used, such as integration with ecosystem models and satellite observations

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“…Above-canopy NH 3 fluxes can be estimated using micrometeorological techniques, flux gradient approaches (6,14), relaxed eddy accumulation (15,16), or directly measured via eddy covariance methods (17). Such measurements are a net soil-canopy-atmosphere flux and do not distinguish between soil and vegetation contributions needed to advance model development (2).…”

Section: Introductionmentioning

confidence: 99%

Estimation of In-Canopy Ammonia Sources and Sinks in a Fertilized Zea mays Field

Bash

Walker

Katul

et al. 2010

Environ. Sci. Technol.

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An analytical model was developed to describe in-canopy vertical distribution of ammonia (NH 3 ) sources and sinks and vertical fluxes in a fertilized agricultural setting using measured in-canopy mean NH 3 concentration and wind speed profiles. This model was applied to quantify in-canopy air-surface exchange rates and above-canopy NH 3 fluxes in a fertilized corn (Zea mays) field. Modeled air-canopy NH 3 fluxes agreed well with independent above-canopy flux estimates. Based on the model results, the urea fertilized soil surface was a consistent source of NH 3 one month following the fertilizer application, whereas the vegetation canopy was typically a net NH 3 sink with the lower portion of the canopy being a constant sink. The model results suggested that the canopy was a sink for some 70% of the estimated soil NH 3 emissions. A logical conclusion is that parametrization of within-canopy processes in air quality models are necessary to explore the impact of agricultural field level management practices on regional air quality. Moreover, there are agronomic and environmental benefits to timing liquid fertilizer applications as close to canopy closure as possible. Finally, given the large withincanopy mean NH 3 concentration gradients in such agricultural settings, a discussion about the suitability of the proposed model is also presented.

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Inter-comparison of ammonia fluxes obtained using the Relaxed Eddy Accumulation technique

Cited by 61 publications

References 44 publications

Intercomparison and assessment of turbulent and physiological exchange parameters of grassland

Intercomparison and assessment of turbulent and physiological exchange parameters of grassland

Advances in understanding, models and parameterizations of biosphere-atmosphere ammonia exchange

Estimation of In-Canopy Ammonia Sources and Sinks in a Fertilized Zea mays Field

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