Local ammonia emissions from agricultural activities are often associated with high nitrogen deposition in the close vicinity of the sources. High nitrogen (N) inputs may significantly affect the local ecosystems. Over a longer term, high loads may change the composition of the ecosystems, leading to a general decrease in local biodiversity. In Europe there is currently a significant focus on the impact of atmospheric N load on local ecosystems among environmental managers and policy makers. Model tools designed for application in N deposition assessment and aimed for use in the regulation of anthropogenic nitrogen emissions are, therefore, under development in many European countries. The aim of this paper is to present a review of the current understanding and modelling parameterizations of atmospheric N deposition. A special focus is on the development of operational tools for use in environmental assessment and regulation related to agricultural ammonia emissions. For the often large number of environmental impact assessments needed to be carried out by local environmental managers there is, furthermore, a need for simple and fast model systems. These systems must capture the most important aspects of dispersion and deposition of N in the nearby environment of farms with animal production. The paper includes a discussion on the demands on the models applied in environmental assessment and regulation and how these demands are fulfilled in current state-of-the-art models.

Abstract.A local-scale Gaussian dispersion-deposition model (OML-DEP) has been coupled to a regional chemistry-transport model (DEHM with a resolution of approximately 6 km × 6 km over Denmark) in the Danish Ammonia Modelling System, DAMOS. Thereby, it has been possible to model the distribution of ammonia concentrations and depositions on a spatial resolution down to 400 m × 400 m for selected areas in Denmark. DAMOS has been validated against measured concentrations from the dense measuring network covering Denmark. Here measured data from 21 sites are included and the validation period covers 2-5 years within the period [2005][2006][2007][2008][2009]. A standard time series analysis (using statistic parameters like correlation and bias) shows that the coupled model system captures the measured time series better than the regional-scale model alone. However, our study also shows that about 50 % of the modelled concentration level at a given location originates from non-local emission sources. The local-scale model covers a domain of 16 km × 16 km, and of the locally released ammonia (NH 3 ) within this domain, our simulations at five sites show that 14-27 % of the locally (within 16 km × 16 km) emitted NH 3 also deposits locally. These results underline the importance of including both high-resolution local-scale modelling of NH 3 as well as the regional-scale component described by the regional model. The DAMOS system can be used as a tool in environmental management in relation to assessments of total nitrogen load of sensitive nature areas in intense agricultural regions. However, high spatio-temporal resolution in input parameters like NH 3 emissions and landuse data is required.

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