Reducing ammonia emissions across Northern Ireland - Second article in a series of seven being released by AFBI to address Ammonia Emissions in NI

Date published: 12 February 2021

Area of Expertise:

Ammonia emissions from livestock present a major challenge for the Northern Ireland agricultural industry.

Funded by the Department of Agriculture, Environment and Rural Affairs, the Agri-Food and Biosciences Institute (AFBI) is currently conducting a major programme of research and have released this series of articles to help stakeholders understand the issue and adopt the solutions which will reduce emissions.

In December 2017, the Sustainable Agriculture Land Management Strategy (SALMS) Expert Working Group (EWG) published an annex to the SALMS ‘Delivering Our Future, Valuing Our Soils’ report entitled ‘Making Ammonia Visible’. This report outlined a suite of potential ammonia (NH3) reduction strategies of relevance to the Northern Ireland agricultural sector which, if adopted, should achieve significant reductions in agricultural ammonia emissions and consequent reductions in atmospheric ammonia concentrations and total nitrogen deposition on nitrogen-sensitive designated sites (SACs and ASSIs) across the province.

As part of the DAERA-commissioned scientific research programme on ammonia, AFBI, working in collaboration with Rothamsted Research and the UK Centre for Ecology and Hydrology (UKCEH), have now accurately quantified the impact of these reduction strategies on ammonia emissions from Northern Ireland agriculture, and the resultant atmospheric ammonia concentrations and total nitrogen deposition.  The ammonia reduction strategies that were modelled, together with the assumed rate of uptake that may be possible across NI, are shown in Table 1.

Strategy Rationale Assumed
uptake rates
Lower crude protein
diet for dairy, beef, finishing
pigs, broilers and layers.
Lowering the crude protein
of diets to meet, but not 
exceed requirement,
results in a reduction in
nitrogen excretion
Genetic improvement
in pigs and poultry
Improving feed
efficiency in pigs and
poultry can result
in a 5% reduction
in nitrogen excretion
Extended grazing season
(+2 weeks)
Ammonia emissions
from grazing beef and
dairy animals are
significantly lower
at pasture than
in housing
Low-emission livestock 
housing - cattle
Novel flooring systems
such as grooved floors
or slat mats and increased
scraping frequencies can
significantly reduce
housing emissions

25% beef

35% dairy

Improved structure of
dairy cow collecting yards
If collecting yards are
covered with roofs
and are scraped more
frequently ammonia
emmissions can be 
Low emission livestock
housing - pigs and poultry
A range of options are
available to reduce
emissions from pig and
poultry housing such as
flooring solutions for 
pigs, frequent belt
removal of manure for
layers and alum addition
to litter for broilers
25% pigs

60% layers

15% broilers
Covering above-ground
slurry stores
Covering outdoor
slurry stores using a
combination of flexible/
floating and rigid

The modelled Northern Ireland-wide scenario was developed around what were considered to be realistic uptake rates (outlined in Table 1) for the individual reduction measures in a 5-10 year period. The application of the reduction strategies, at the uptake levels noted in Table 1 resulted in a 25% reduction in agricultural ammonia emissions across Northern Ireland (Fig. 1).  This 25% reduction in ammonia would allow Northern Ireland to fulfil its contribution to the UK reduction target of a 16% decrease over 2005 levels by 2030, as set out in the Gothenburg Protocol and UK Air Quality Strategy.

Figure 1. Reduction in ammonia emissions from agriculture in NI under the modelled scenario
Figure 1. Reduction in ammonia emissions from agriculture in NI under the modelled scenario
In order to determine the effect of this 25% reduction in agricultural ammonia emissions on atmospheric ammonia concentrations and total nitrogen deposition at NI’s designated sites, the results were incorporated by UKCEH into a series of geographical emission models, which determine atmospheric concentrations of ammonia (incorporating both agri and non-agri sources) (see Fig. 2) and subsequently total nitrogen deposition at a 1km2 grid resolution.

Figure 2. Reductions in atmospheric ammonia concentrations achieved by the 25% reduction in agricultural ammonia in NI as modelled by FRAME
Figure 2. Reductions in atmospheric ammonia concentrations achieved by the 25% reduction in agricultural ammonia in NI as modelled by FRAME
Whilst reductions in ammonia concentrations and nitrogen deposition were significant across Northern Ireland, with an 8% decrease in the exceeded area and average exceedance dropping by 2.5 kg nitrogen per hectare per year, the majority of Northern Ireland’s nitrogen-sensitive designated sites remained in exceedance of their site-specific critical levels of ammonia. Specifically, 2 out of 53 Special Areas of Conservation (SAC) and 14 out of 188 Areas of Special Scientific Interest (ASSI) no longer exceeded their critical levels of ammonia and were returned to favourable status under this scenario.

Targeting of Ammonia Reduction Strategies to Specific Areas

Ammonia is a highly reactive gas and a large proportion of emitted ammonia will be deposited to ground rapidly and relatively close to the emission source. The remaining proportion of emitted ammonia will interact with other atmospheric components forming ammonium aerosols. These more stable compounds can travel much larger distances and be deposited through longer-range dry deposition or through precipitation (“wet deposition”) rainfall. Targeting of ammonia reduction strategies to key sources of emissions which are in the vicinity of nitrogen-sensitive designated sites has been shown to be more cost-effective per unit of emission reduction than country-wide measures.

With this rationale, a series of geographically targeted interventions were modelled for Northern Ireland, in addition to the reductions achieved in the Northern Ireland-wide ammonia reduction scenario. These targeted interventions took the form of enhanced ammonia reduction measures, i.e. measures similar to those applied nationally from Table 1, but with more ambitious uptake rates, applied within circular zones of 1, 2 and 5km from the boundary of each nitrogen-sensitive designated site (Fig. 3).

Figure 3. An example of circular buffers of 1, 2 and 5km applied around Main Valley Bogs SAC and within which the enhanced ammonia reduction measures were applied
Figure 3. An example of circular buffers of 1, 2 and 5km applied around Main Valley Bogs SAC and within which the enhanced ammonia reduction measures were applied

The targeted measures resulted in several additional designated sites being brought out of critical ammonia levels exceedance, with 1 additional SAC and 5 additional ASSIs returning to favourable status under the largest 5km buffer zone scenario.

The targeting of ammonia reduction strategies is on average 4 times more effective than non-targeted strategies at reducing ammonia concentrations for SACs. However, different sites respond differently to ammonia reduction measures because the make-up of their local emission sources is different.

In general, nitrogen-sensitive designated sites located near intensive agricultural land use, such as lowland bogs, respond well to geographical targeting, as dry deposited ammonia from local sources will be the predominate form of atmospheric nitrogen input to these sites. The targeting of reduction strategies in the vicinity of these types of sites will significantly reduce these local ammonia sources.

For nitrogen-sensitive designated sites further away from intensive agricultural land use such as upland moor / mountain sites, geographical targeting of reduction strategies is less effective, as nitrogen deposition at these sites is generally dominated by longer range or background nitrogen sources including wet deposited ammonium. Significantly reducing these longer range inputs requires a regional approach to tackle regionally elevated concentrations and for some sites will require the addressing of transboundary long-range nitrogen inputs.

Therefore, maximising the effectiveness of ammonia reduction measures will require an approach that combines country-wide measures to decrease ammonia concentrations region-wide from a high baseline, and selective local targeting of measures to decrease ammonia concentrations and local nitrogen deposition at nitrogen-sensitive sites where there are high emission densities in close proximity.

Overall this work provides an insight to the effectiveness of reduction strategies applied at NI scale and has been used to inform DAERA’s forthcoming Ammonia Strategy.

Over the coming weeks, this series of articles focusing on the AFBI research programme to address ammonia emissions in NI will outline the work being undertaken in more detail and the key findings to date.

Next week’s article will focus on the economics of the ammonia reduction measures modelled and identify those measures which are the most cost-effective at reducing ammonia emissions.

You can view previous articles in the series below:

Notes to editors: 

AFBI is an arms-length body of DAERA delivering research and development, diagnostic and analytical testing, emergency response capability and expert scientific advice for DAERA and other government departments, public bodies and commercial companies in Northern Ireland, and further afield.


AFBI’s Vision is “Advancing the Local and Global Agri-Food Sectors Through Scientific Excellence”.

AFBI’s core areas:

  • Leading improvements in the agri-food industry;
  • Protecting animal, plant and human health;
  • Enhancing the natural and marine environment.

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