Agricultural atmospheric ammonia: identification & assessment of potential impacts

Reactive nitrogen pollution, particularly ammonia (NH3), when above critical limits adversely impacts biodiversity through eutrophication, acidification or direct toxic effect. Though total nitrogen deposition is a primary driver for species community changes and impacts, the concentration of ammonia should also be considered. Both total nitrogen deposition and ambient ammonia concentrations are above levels that can result in harm to biodiversity at many Natura 2000 sites across Europe and in Ireland. Reactive nitrogen is principally composed of both chemically reduced ammonia and ammonium (NH4+), alongside oxides of nitrogen (NOx). While traffic is the primary source of oxides of nitrogen, agriculture accounts for virtually all ammonia emissions in Ireland.


Although there is substantial evidence that reactive nitrogen causes negative impacts on biodiversity, the relationship between exposure to reactive nitrogen (dose) and negative ecological indicators (effect) is not always straightforward. The complexity of understanding dose-effect relationships increases if multiple factors with negative effects occur concurrently (e.g. adverse effects of air quality occurring at the same time as adverse effects of climate change). Additionally, adverse impacts of reactive nitrogen are likely to occur over long periods of time and may not be immediately visible during a site survey. It is recommended that, although indicators of negative effects may be observed during field visits, these indicators should be used alongside other evidence (such as monitored or modelled concentration or deposition, local sources, local knowledge) to build evidence of adverse impacts on a site. Essentially, ecological indicators alone should not be used as evidence of adverse impacts but rather considered as part of a suite of indicators. Survey indicators could include algal proliferation, presence of nitrogen tolerant species, absence of nitrogen sensitive species, presence of pink or decaying Reindeer Lichen (Cladonia portentosa) or of decaying Sphagnum spp.


A guidance document describing a framework for the assessment of impacts of ammonia emissions from intensive agricultural installations has recently been published in the Republic of Ireland by the Environmental Protection Agency (EPA). Similar guidance has also been published in Northern Ireland, England, Scotland and Wales as well as other European Member States on how reactive nitrogen should be assessed in the context of Environmental Impact Assessment (EIA), Appropriate Assessment (AA) and AA screening. Recent court rulings in the Netherlands support the need to implement science-based and defensible approaches to the assessment and management of agricultural emissions of nitrogen to the atmosphere. There have been two broad approaches applied within Europe to the assessment of potential reactive nitrogen and ammonia impacts on Natura 2000 sites, namely the Critical Criteria Approach and the Integrated Approach.


The Critical Criteria Approach prevents the development of new sources that have a significant potential to adversely affect Natura 2000 Sites but allows the development of sources that do not have significant adverse effects. The Critical Criteria Approach is currently adopted by the majority of Member States who have a policy of dealing with such emissions. The Integrated Approach provides a framework for reducing emissions from existing sources to create room for new activities such as infrastructure, housing or intensive agricultural installations. The Integrated Approach was adopted by the Netherlands in 2015. However, because it allowed credits for reductions to be gained prior to the gains being realised, it was deemed illegal by the Dutch Council of State in 2019. As a consequence, modifications to the integrated approach are currently being investigated in the Netherlands. However, the European Commission commended the integrated approach highlighting it as the most appropriate method to deal with the issue of adverse impacts of reactive nitrogen from agriculture.


The assessment of emissions of ammonia from agricultural developments, required for planning or licence consent, is predominantly undertaken using air dispersion modelling techniques. A range of dispersion modelling approaches are available for the assessment of impacts from agricultural development. These dispersion modelling approaches vary in complexity and accuracy with simple approaches generally overestimating impacts to provide a highly conservative indication of potential

impacts and more advanced modelling approaches generally providing a more representative, yet conservative indication of potential impacts. This Irish Wildlife Manual aims to summarise:
– The effects of emissions of ammonia from intensive agricultural sources and its deposition on biodiversity.
– The regulatory requirements for the assessment of these effects and the indicators of adverse effects including physical observations and theoretical limits used in modelling assessment.
– The approach recommended by the Irish EPA and approaches used in various European Countries that are currently used to assess and report on the potential effects of emissions of ammonia from agricultural development.
– A framework for high-level review of dispersion modelling assessment intended for non-expert users of dispersion models that details a non-technical basis to consider whether the critical components of a dispersion modelling study meet the requirements of dispersion modelling guidance issued by the Irish EPA.

There is no single publicly available database in Ireland that quantifies and locates ammonia emitting activities

Emissions from individual projects that are determined to be insignificant in isolation can be approved using a critical criteria approach. The use of the same approach for multiple projects, either concurrently or consecutively can result in baseline creep, where over time the combined impacts of individually insignificant projects result in a significant adverse impact, that may not be identified using a critical criteria approach.

The predominant source of ammonia in Ireland is cattle farming, which is well dispersed throughout the country. Intensive farming of pigs and poultry contributes a far lower proportion of total emissions of ammonia, but these activities are concentrated in a small number of high production areas, where the effects on biodiversity can be significant.

The border counties of Cavan and Monaghan have the highest concentrations of IED licensed and sub-threshold intensive agricultural facilities. Both Cavan and Monaghan also have high densities of cattle (cattle/kmĀ²) compared to the average cattle density in Ireland.