The Meteorological Synthesizing Centre-West (MSC-W) of the European Monitoring and Evaluation Programme (EMEP) has been performing model calculations in support of the Convention on Long Range ...Transboundary Air Pollution (CLRTAP) for more than 30 years. The EMEP MSC-W chemical transport model is still one of the key tools within European air pollution policy assessments. Traditionally, the model has covered all of Europe with a resolution of about 50 km × 50 km, and extending vertically from ground level to the tropopause (100 hPa). The model has changed extensively over the last ten years, however, with flexible processing of chemical schemes, meteorological inputs, and with nesting capability: the code is now applied on scales ranging from local (ca. 5 km grid size) to global (with 1 degree resolution). The model is used to simulate photo-oxidants and both inorganic and organic aerosols. In 2008 the EMEP model was released for the first time as public domain code, along with all required input data for model runs for one year. The second release of the EMEP MSC-W model became available in mid 2011, and a new release is targeted for summer 2012. This publication is intended to document this third release of the EMEP MSC-W model. The model formulations are given, along with details of input data-sets which are used, and a brief background on some of the choices made in the formulation is presented. The model code itself is available at www.emep.int, along with the data required to run for a full year over Europe.
The carbon exchange of managed temperate grassland, previously converted from arable rotation, was quantified for two levels of management intensities over a period of 3 years. The original field on ...the Swiss Central Plateau had been separated into two plots of equal size, one plot was subjected to intensive management with nitrogen inputs of 200
kg
ha
−1
year
−1 and frequent cutting, and the other to extensive management with no fertilization and less frequent cutting. For both plots, net CO
2 exchange (NEE) was monitored by the eddy covariance technique, and the flux data were submitted to extensive quality control and gap filling procedures. Cumulative NEE was combined with values for carbon export through biomass harvests and carbon import through application of liquid manure (intensive field only) to yield the annual net carbon balance of the grassland ecosystems. The intensive management was associated with an average net carbon sequestration of 147 (±130)
g
C
m
−2
year
−1, whereas the extensive management caused a non-significant net carbon loss of 57 (+130/−110)
g
C
m
−2
year
−1. Despite the large uncertainty ranges for the two individual systems, the special design of the paired experiment led to a reduced error of the differential effect, because very similar systematic errors for both parallel fields could be assumed. The mean difference in the carbon budget over the 3-year study period was determined to be significant with a value of 204 (±110)
g
C
m
−2
year
−1. The difference occurred in spite of similar aboveground productivities and root biomass. Additional measurements of soil respiration under standardized laboratory conditions indicated higher rates of soil organic carbon loss through mineralization under the extensive management. These data suggest that conversion of arable land to managed grassland has a positive effect on the carbon balance during the initial 3 years, but only if the system receives extra nitrogen inputs to avoid carbon losses through increased mineralization of soil organic matter.
The global nitrogen (N) cycle at the beginning of the 21st century has been shown to be strongly influenced by the inputs of reactive nitrogen (Nr) from human activities, including combustion-related ...NOx, industrial and agricultural N fixation, estimated to be 220 Tg N yr−1 in 2010, which is approximately equal to the sum of biological N fixation in unmanaged terrestrial and marine ecosystems. According to current projections, changes in climate and land use during the 21st century will increase both biological and anthropogenic fixation, bringing the total to approximately 600 Tg N yr−1 by around 2100. The fraction contributed directly by human activities is unlikely to increase substantially if increases in nitrogen use efficiency in agriculture are achieved and control measures on combustion-related emissions implemented. Some N-cycling processes emerge as particularly sensitive to climate change. One of the largest responses to climate in the processing of Nr is the emission to the atmosphere of NH3, which is estimated to increase from 65 Tg N yr−1 in 2008 to 93 Tg N yr−1 in 2100 assuming a change in global surface temperature of 5 °C in the absence of increased anthropogenic activity. With changes in emissions in response to increased demand for animal products the combined effect would be to increase NH3 emissions to 135 Tg N yr−1. Another major change is the effect of climate changes on aerosol composition and specifically the increased sublimation of NH4NO3 close to the ground to form HNO3 and NH3 in a warmer climate, which deposit more rapidly to terrestrial surfaces than aerosols. Inorganic aerosols over the polluted regions especially in Europe and North America were dominated by (NH4)2SO4 in the 1970s to 1980s, and large reductions in emissions of SO2 have removed most of the SO42− from the atmosphere in these regions. Inorganic aerosols from anthropogenic emissions are now dominated by NH4NO3, a volatile aerosol which contributes substantially to PM10 and human health effects globally as well as eutrophication and climate effects. The volatility of NH4NO3 and rapid dry deposition of the vapour phase dissociation products, HNO3 and NH3, is estimated to be reducing the transport distances, deposition footprints and inter-country exchange of Nr in these regions. There have been important policy initiatives on components of the global N cycle. These have been regional or country-based and have delivered substantial reductions of inputs of Nr to sensitive soils, waters and the atmosphere. To date there have been no attempts to develop a global strategy to regulate human inputs to the nitrogen cycle. However, considering the magnitude of global Nr use, potential future increases, and the very large leakage of Nr in many forms to soils, waters and the atmosphere, international action is required. Current legislation will not deliver the scale of reductions globally for recovery from the effects of Nr deposition on sensitive ecosystems, or a decline in N2O emissions to the global atmosphere. Such changes would require substantial improvements in nitrogen use efficiency across the global economy combined with optimization of transport and food consumption patterns. This would allow reductions in Nr use, inputs to the atmosphere and deposition to sensitive ecosystems. Such changes would offer substantial economic and environmental co-benefits which could help motivate the necessary actions.
Inferential models have long been used to determine pollutant dry deposition to ecosystems from measurements of air concentrations and as part of national and regional atmospheric chemistry and ...transport models, and yet models still suffer very large uncertainties. An inferential network of 55 sites throughout Europe for atmospheric reactive nitrogen (Nr) was established in 2007, providing ambient concentrations of gaseous NH3, NO2, HNO3 and HONO and aerosol NH4+ and NO3− as part of the NitroEurope Integrated Project. Network results providing modelled inorganic Nr dry deposition to the 55 monitoring sites are presented, using four existing dry deposition routines, revealing inter-model differences and providing ensemble average deposition estimates. Dry deposition is generally largest over forests in regions with large ambient NH3 concentrations, exceeding 30–40 kg N ha−1 yr−1 over parts of the Netherlands and Belgium, while some remote forests in Scandinavia receive less than 2 kg N ha−1 yr−1. Turbulent Nr deposition to short vegetation ecosystems is generally smaller than to forests due to reduced turbulent exchange, but also because NH3 inputs to fertilised, agricultural systems are limited by the presence of a substantial NH3 source in the vegetation, leading to periods of emission as well as deposition. Differences between models reach a factor 2–3 and are often greater than differences between monitoring sites. For soluble Nr gases such as NH3 and HNO3, the non-stomatal pathways are responsible for most of the annual uptake over many surfaces, especially the non-agricultural land uses, but parameterisations of the sink strength vary considerably among models. For aerosol NH4+ and NO3− discrepancies between theoretical models and field flux measurements lead to much uncertainty in dry deposition rates for fine particles (0.1–0.5 μm). The validation of inferential models at the ecosystem scale is best achieved by comparison with direct long-term micrometeorological Nr flux measurements, but too few such datasets are available, especially for HNO3 and aerosol NH4+ and NO3−.
The global nitrogen (N) cycle at the beginning of the 21st century has been shown to be strongly influenced by the inputs of reactive nitrogen (Nr) from human activities, including combustion-related ...NOx, industrial and agricultural N fixation, estimated to be 220 Tg N yr-1 in 2010, which is approximately equal to the sum of biological N fixation in unmanaged terrestrial and marine ecosystems. According to current projections, changes in climate and land use during the 21st century will increase both biological and anthropogenic fixation, bringing the total to approximately 600 Tg N yr-1 by around 2100. The fraction contributed directly by human activities is unlikely to increase substantially if increases in nitrogen use efficiency in agriculture are achieved and control measures on combustion-related emissions implemented. Some N-cycling processes emerge as particularly sensitive to climate change. One of the largest responses to climate in the processing of Nr is the emission to the atmosphere of NH3, which is estimated to increase from 65 Tg N yr-1 in 2008 to 93 Tg N yr-1 in 2100 assuming a change in global surface temperature of 5 degree C in the absence of increased anthropogenic activity. With changes in emissions in response to increased demand for animal products the combined effect would be to increase NH3 emissions to 135 Tg N yr-1. Another major change is the effect of climate changes on aerosol composition and specifically the increased sublimation of NH4NO3 close to the ground to form HNO3 and NH3 in a warmer climate, which deposit more rapidly to terrestrial surfaces than aerosols. Inorganic aerosols over the polluted regions especially in Europe and North America were dominated by (NH4)2SO4 in the 1970s to 1980s, and large reductions in emissions of SO2 have removed most of the SO42- from the atmosphere in these regions. Inorganic aerosols from anthropogenic emissions are now dominated by NH4NO3, a volatile aerosol which contributes substantially to PM10 and human health effects globally as well as eutrophication and climate effects. The volatility of NH4NO3 and rapid dry deposition of the vapour phase dissociation products, HNO3 and NH3, is estimated to be reducing the transport distances, deposition footprints and inter-country exchange of Nr in these regions. There have been important policy initiatives on components of the global N cycle. These have been regional or country-based and have delivered substantial reductions of inputs of Nr to sensitive soils, waters and the atmosphere. To date there have been no attempts to develop a global strategy to regulate human inputs to the nitrogen cycle. However, considering the magnitude of global Nr use, potential future increases, and the very large leakage of Nr in many forms to soils, waters and the atmosphere, international action is required. Current legislation will not deliver the scale of reductions globally for recovery from the effects of Nr deposition on sensitive ecosystems, or a decline in N2O emissions to the global atmosphere. Such changes would require substantial improvements in nitrogen use efficiency across the global economy combined with optimization of transport and food consumption patterns. This would allow reductions in Nr use, inputs to the atmosphere and deposition to sensitive ecosystems. Such changes would offer substantial economic and environmental co-benefits which could help motivate the necessary actions.
Atmospheric ammonia (NH3) dominates global emissions of total reactive nitrogen (Nr), 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.
The loss of N2 from intensively managed agro-ecosystems is an important part of the N budget. Flux monitoring of N2 emissions at the field scale, e.g., by eddy correlation or aerodynamic gradient ...method, is impossible due to the large atmospheric N2 background (78%). The acetylene (C2H2) inhibition technique (AIT) is a rather simple and frequently used, albeit imperfect, method to determine N2 losses from intact soil cores. In principle, AIT allows an estimation of total denitrification at high temporal resolution and on small spatial scales, with limited workload and costs involved. To investigate its potential and limitations, a laboratory system with two different detection systems (photoacoustic IR spectroscopy and gas chromatography) is presented, which allowed simultaneous measurements of up to 7 intact soil cores in air-tight glass tubes in a temperature controlled cabinet (adjusted to field conditions) with automated C2H2 injection. A survey of total denitrification losses (N2 + N2O) over 1.5 yr in soil cores from an intensively managed, cut grassland system in central Switzerland supports previous reports on severe limitations of the AIT, which precluded reliable estimates of total denitrification losses. Further, the unavoidable sampling and transfer of soil samples to the laboratory causes unpredictable deviations from the denitrification activity in the field.
The EMEP/EEA guidebook 2009 for agricultural emission inventories reports an average ammonia (NH3) emission factor (EF) by volatilisation of 55% of the applied total ammoniacal nitrogen (TAN) content ...for cattle slurry, and 35% losses for pig slurry, irrespective of the type of surface or slurry characteristics such as dry matter content and pH. In this review article, we compiled over 350 measurements of EFs published between 1991 and 2011. The standard slurry application technique during the early years of this period, when a large number of measurements were made, was spreading by splash plate, and as a result reference EFs given in many European inventories are predominantly based on this technique. However, slurry application practices have evolved since then, while there has also been a shift in measurement techniques and investigated plot sizes. We therefore classified the available measurements according to the flux measurement technique or measurement plot size and year of measurement. Medium size plots (usually circles between 20 to 50 m radius) generally yielded the highest EFs. The most commonly used measurement setups at this scale were based on the Integrated Horizontal Flux method (IHF or the ZINST method (a simplified IHF method)). Several empirical models were published in the years 1993 to 2003 predicting NH3 EFs as a function of meteorology and slurry characteristics (Menzi et al., 1998; Søgaard et al., 2002). More recent measurements show substantially lower EFs which calls for new measurement series in order to validate the various measurement approaches against each other and to derive revised inputs for inclusion into emission inventories.
Carbon dioxide concentrations were measured semi-continuously in soil pore space under permanent grassland for a 3-year period, using gas-permeable membrane tubes buried at various depths in the ...soil, in an attempt to quantify temporal variations of soil CO2 storage. Diurnal wavelike variations in CO2 concentration were observed systematically through the soil profile down to 50cm, and the patterns and amplitude of mean diurnal waves depended on soil- and environmental conditions. For moderate to high soil water contents (SWC), soil CO2 concentrations were positively correlated with soil temperature on a diurnal basis, resulting from an exponential increase of soil respiration with temperature and a shift in thermodynamic gaseous/aqueous phase equilibria. In dry conditions, however, air-filled porosity CO2 concentrations tended to be lowest in the late afternoon and highest in the early morning, and thus negatively correlated with soil temperature. The storage of CO2 in soil was calculated in the air-filled and in the water-filled pore fractions using Henry's law and carbonate chemistry. Storage estimates were extremely sensitive to soil pH and a parametrisation of soil pH as a function of soil water content was derived from field measurements and used in the storage calculation scheme. Instantaneous rates of soil CO2 storage change with time were negatively correlated with atmospheric friction velocity in dry and moderately wet conditions, though in very wet conditions storage changes were dominated by vertical movements of soil water. The data suggest that CO2 can accumulate in the soil during the night when transport is restricted to molecular diffusion through soil layers, and that wind-induced pressure pumping results in a gradual daytime flushing out. These findings may help account for the oft-reported u*-dependence of night-time eddy covariance respiration fluxes.
A European scale network was established in 2006 as part of the NitroEurope Integrated Project to infer reactive nitrogen (Nr) dry deposition fluxes, based on low-cost sampling of gaseous and aerosol ...species and inferential modelling. The network provides monthly measurements of NH
3, NH
4
+, HNO
3 and NO
3
−, as well as SO
2, SO
4
2−, HCl, Cl
− and base cations at 58 sites. Measurements are made with an established low-cost denuder methodology (DELTA) as a basis to: (1) examine temporal trends and spatial patterns across Europe, (2) improve and calibrate inferential modelling techniques to estimate exchange of Nr species, (3) provide best estimates of atmospheric dry N deposition, and (4) permit an analysis of net GHG exchange in relation to atmospheric and agricultural N inputs at the European scale. Responsibility for measurements is shared among seven European laboratories. An inter-comparison of the DELTA implementation by 6 laboratories at 4 test sites (Montelibretti, Italy; Braunschweig, Germany; Paterna, Spain and Auchencorth, UK) from July to October 2006 provided training for the laboratories and showed that good agreement was achieved in different climatic conditions (87% of laboratory site-means within 20% of the inter-laboratory median). Results obtained from the first year of measurements show substantial spatial variability in atmospheric Nr concentrations, illustrating the major local (NH
3) and regional (HNO
3, NO
3
−, and NH
4
+) differences in Nr concentrations. These results provide the basis to develop future estimates of site-based Nr dry deposition fluxes across Europe, and highlight the role of NH
3, largely of agricultural origin, which was the largest single constituent and will dominate dry Nr fluxes at most sites.
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