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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Eutrophication events are frequent in Inner Danish waters and critical loads are exceeded for much of the Danish sensitive terrestrial ecosystems. The Danish air quality monitoring program combines measurements and model calculations to benefit from the complementarities in data from these two sources. Measurements describe actual status, seasonal variation, and temporal trends. Model calculations extrapolate the results to the entire country and determine depositions to specific ecosystems. Measurements in 2016 show annual depositions between 7.5 and 11 kg N/ha to terrestrial ecosystems, and a load to marine waters of 5.3 kg N/ha. The deposition on Danish marine waters in 2016 was calculated to be 73,000 tons N with an average deposition of 6.9 kg N/ha. For terrestrial areas, the deposition was calculated to be 57,000 tons N with an average deposition of 13 kg N/ha. This is above critical loads for sensitive ecosystems. Long-term trends show a 35% decrease since 1990 in measured annual nitrogen deposition. At two out of four stations in nature areas, measured ammonia levels exceeded critical levels for lichens and mosses. Conclusions: Nitrogen loads and levels to Danish nature is decreasing, but critical loads and levels are still exceeded for sensitive ecosystems. Combining measurements and model calculations is a strong tool in monitoring.

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Environmental context. Optimisation of allocated resources, improved quality, and better understanding of processes – these are the main advantages of applying integrated monitoring (IM). The paper describes IM as a combination of air pollution measuring and modelling, and describes how it is implemented in air-quality management in Denmark. However, the IM concept may also be applied to follow air-quality levels in other countries that currently do not have a corresponding system. It may also be applied to the environmental monitoring of other compartments. Abstract. Integrated air-quality monitoring (IM) is here defined as monitoring based on the combination of results of atmospheric measurements from usually fixed site stations, and results obtained from calculations with air-quality models. This paper outlines experience from the use of IM at the National Environmental Research Institute (NERI) within the two nationwide air-quality monitoring programmes for the Danish urban and rural environments, respectively. The measurements in these Danish monitoring programmes are used to determine actual levels and trends in pollutant concentrations and depositions of pollutants. The measurements are further used for process understanding, and for the development and validation of air-quality models. The results from the air-quality models are used in the interpretation of measurements, but they are also used to provide information about, for example, source apportionment. The model calculations are used to extend the geographical coverage of the monitoring, and to provide information about pollution loads at locations or regions that are not well covered by the limited number of measurement stations in the monitoring programmes. Finally, the air-quality models are applied to carry out scenario studies of future pollution loads, e.g. assessment of the effects of various emission reduction strategies. NERI operates and holds the overall responsibility for the Danish air-quality monitoring programmes. These monitoring programmes are designed to fulfil the Danish obligations in relation to the EU directives on air quality, as well as the Danish obligations in relation to the reporting of data to international organisations (EMEP, HELCOM, OSPARCOM, and WHO). The obtained results from the use of IM form the basis for the national assessment of the air pollution loads in relation to protection of the aquatic and terrestrial environment; in these assessments the use of IM plays a central role.