Tuesday, October 19, 2021
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Modelling ammonia reduction strategies

Co-authors Dr Ulli Dragosits,

UK Centre for Ecology & Hydrology (UKCEH), AND Prof Tom Misselbrook,

Rothamsted Research

AMMONIA emissions from livestock present a major challenge for the Northern Ireland agricultural indust-

ry. Funded by the Depart-ment of Agriculture, Environment and Rural Affairs, the Agri-Food and Biosciences Institute (AFBI) is currently conducting a major programme of research and has 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-commission-ed scientific research programme on ammonia, AFBI, working in collaboration with Rothamsted Research and the UK Centre for Ecology and Hydrology (UKCEH), has 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.

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 per cent reduction in agricultural ammonia emissions across Northern Ireland (Figure 1).

This 25 per cent reduction in ammonia would allow Northern Ireland to fulfil its contribution to the UK reduction target of a 16 per cent decrease over 2005 levels by 2030, as set out in the Gothenburg Protocol and UK Air Quality Strategy.

In order to determine the effect of this 25 per cent reduction in agricultural ammonia emissions on atmospheric ammonia concent-rations 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 Figure 2) and subsequently total nitrogen deposition at a 1km2 grid resolution.

Whilst reductions in ammonia concentrations and nitrogen de-position were significant across Northern Ireland, with an eight per cent decrease in the exceeded area and average exceedance dropping by 2.5kg 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, two 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 thro-ugh longer-range dry deposition or through precipitation (“wet dep-osition”) rainfall.

Targeting of ammonia reduction strategies to

key sources of emis-sions 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 No-

rthern Ireland, in add-ition to the reductions achieved in the Northern Ireland-wide ammonia reduction scenario.

These targeted interventions took the form of enhanced ammonia reduction measures, ie, 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 (Figure 3).

The targeted measures resulted in several additional designated sites being brought out of critical ammonia levels exceedance, with

one additional SAC and five additional ASSIs returning to favourable status under the largest 5km buffer zone scenario.

The targeting of ammonia reduction strategies is on average four 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 strat-egies 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 effect-iveness of ammonia reduction measures will require an approach that combines country-wide mea-

sures to decrease ammonia con-centrations 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.

n 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 mea-sures modelled and identify those measures which are the most cost-effective at reducing ammonia emissions.



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