Abstract. 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.

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International audienceExisting descriptions of bi-directional ammonia (NH3) land-atmosphere exchange incorporate temperature and moisture controls, and are beginning to be used in regional chemical transport models. However, such models have typically applied simpler emission factors to upscale the main NH3 emission terms. While this approach has successfully simulated the main spatial patterns on local to global scales, it fails to address the environment- and climate-dependence of emissions. To handle these issues, we outline the basis for a new modelling paradigm where both NH3 emissions and deposition are calculated online according to diurnal, seasonal and spatial differences in meteorology. We show how measurements reveal a strong, but complex pattern of climatic dependence, which is increasingly being characterized using ground-based NH3 monitoring and satellite observations, while advances in process-based modelling are illustrated for agricultural and natural sources, including a global application for seabird colonies. A future architecture for NH3 emission-deposition modelling is proposed that integrates the spatio-temporal interactions, and provides the necessary foundation to assess the consequences of climate change. Based on available measurements, a first empirical estimate suggests that 5°C warming would increase emissions by 42 per cent (28-67%). Together with increased anthropogenic activity, global NH3 emissions may increase from 65 (45-85) Tg N in 2008 to reach 132 (89-179) Tg by 2100

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 (N_r) was established in 2007, providing ambient concentrations of gaseous NH₃, NO₂, HNO₃ and HONO and aerosol NH₄⁺ and NO₃^&minus; as part of the NitroEurope Integrated Project. <br><br> Network results providing modelled inorganic N_r 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 N_r 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. <br><br> Differences between models reach a factor 2–3 and are often greater than differences between monitoring sites. For soluble N_r 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^&minus; 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 N_r flux measurements, but too few such datasets are available, especially for HNO₃ and aerosol NH₄⁺ and NO₃^&minus;

.[1] Any change in the ability of northern peatlands to act as a sink for atmospheric CO 2 will play a crucial part in the response of the Earth system to global warming. We argue that a true assessment of the sink-source relationships of peatland ecosystems requires that losses of C in drainage waters be included when determining annual net C uptake, thus connecting measurements of stream C fluxes with those made at the land surfaceatmosphere interface. This was done by combining estimates of net ecosystem exchange (NEE) with stream water measurements of TOC, DIC, and gaseous C loss, in a 335-ha lowland temperate peatland catchment (55°48.80 0 N, 03°14.40 0 W) in central Scotland over a 2-year period (1996)(1997)(1998). Mean annual downstream C flux was 304 (±62) kg C ha À1 yr À1 , of which total organic carbon (TOC) contributed 93%, the remainder being dissolved inorganic carbon (DIC) and free CO 2 . At the catchment outlet evasion loss of CO 2 from the stream surface was estimated to be an additional 46 kg C ha À1 yr À1 . Over the study period, NEE of CO 2 -C resulted in a flux from the atmosphere to the land surface of 278 (±25) kg C ha À1 yr À1 . Net C loss in drainage water, including both the downstream flux and CO 2 evasion from the stream surface to the atmosphere, was therefore greater or equal to the net annual C uptake as a result of photosynthesis/respiration at the land surface. By combining these and other flux terms, the overall C mass balance suggests that this system was either acting as a terrestrial C source or was C neutral.

Soil respiration constitutes the second largest flux of carbon (C) between terrestrial ecosystems and the atmosphere. This study provides a synthesis of soil respiration (R s ) in 20 European grasslands across a climatic transect, including ten meadows, eight pastures and two unmanaged grasslands. Maximum rates of R s (R s max ), R s at a reference soil temperature (10°C; R s 10 ) and annual R s (estimated for 13 sites) ranged from 1.9 to 15.9 μmol CO 2 m −2 s −1 , 0.3 to 5.5 μmol CO 2 m −2 s −1 and 58 to 1988 g C m −2 y −1 , respectively. Values obtained for Central European mountain meadows are amongst the highest so far reported for any type of ecosystem. Across all sites R s max was closely related to R s 10 .Assimilate supply affected R s at timescales from daily (but not necessarily diurnal) to annual.Reductions of assimilate supply by removal of aboveground biomass through grazing and cutting resulted in a rapid and a significant decrease of R s . Temperature-independent seasonal fluctuations of R s of an intensively managed pasture were closely related to changes in leaf area index (LAI). Across sites R s 10 increased with mean annual soil temperature (MAT), LAI and gross primary productivity (GPP), indicating that assimilate supply overrides potential acclimation to prevailing temperatures. Also annual R s was closely related to LAI and GPP. Because the latter two parameters were coupled to MAT, temperature was a suitable surrogate for deriving estimates of annual R s across the grasslands studied. These findings contribute to our understanding of regional patterns of soil C fluxes and highlight the importance of assimilate supply for soil CO 2 emissions at various timescales.

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