Ammonia screening for poultry and livestock units

Ammonia screening decides whether an intensive poultry or livestock proposal can be granted planning permission, and it is assessed by the planning authority as well as by the Environment Agency. The trigger is distance. Once a proposed unit sits within the screening distances of a European site, an SSSI or an ancient woodland, the authority needs evidence on ammonia concentration and nitrogen deposition before it can lawfully decide the application.

That evidence is separate from odour work and separate from the permit application, even though all three use the same emissions data. Getting the sequence right saves months.

Why planning assesses ammonia at all when the permit covers it

Intensive installations above the thresholds in Schedule 1 to the Environmental Permitting (England and Wales) Regulations 2016 need a permit from the Environment Agency. The usual triggers are 40,000 poultry places, 2,000 places for production pigs over 30 kg, or 750 places for sows.

Planning practice guidance tells authorities to assume that the pollution control regime will operate effectively and not to duplicate it. That principle does not displace the council's own duty under the Conservation of Habitats and Species Regulations 2017. Where a proposal is likely to have a significant effect on a European site, the council is the competent authority for the planning permission and must carry out its own screening, and an appropriate assessment where screening cannot rule the effect out. It cannot hand that duty to the Environment Agency.

So two regulators look at the same plume for different reasons. Natural England is a statutory consultee to both and will usually comment in near-identical terms.

The screening distances that set the scope

The Environment Agency's risk assessment guidance for intensive farming sets the distances at which habitats must be brought into the assessment. In practice the numbers most often applied are 5 kilometres to a European site such as a Special Area of Conservation, Special Protection Area or Ramsar site, and 2 kilometres to an SSSI, with shorter distances for local wildlife sites, ancient woodland and veteran trees. Confirm the current figures in the guidance before scoping, because they have been revised.

Screening then compares the predicted process contribution against a standard. Two apply to ammonia. The critical level is 3 micrograms per cubic metre as an annual mean for higher plants and 1 microgram per cubic metre where lichens and bryophytes are part of what makes the site special. Nitrogen deposition is compared against habitat-specific critical loads, which you take from the national air pollution information system for the exact habitat feature, not the site as a whole.

An effect is normally screened out where the process contribution is below 1 per cent of the long-term critical level or critical load at a designated site. Above that, the assessment continues.

In-combination effects, and why neighbours matter

A single shed rarely fails on its own. The failure comes in combination.

Natural England expects the assessment to add the contributions of other intensive units already permitted or consented within the screening distance, together with the background deposition, which in much of Shropshire, Herefordshire, Norfolk and Lincolnshire is already at or above critical load for sensitive habitats. Where background alone exceeds the critical load, even a small process contribution can be hard to screen out, and the argument shifts to whether the increase is imperceptible.

Build the in-combination list from the council's planning register and the Environment Agency public register, and state the search radius and date in the report. An assessment that ignores a consented unit 1.5 kilometres upwind will be sent back.

When screening fails and detailed modelling starts

Screening tools such as the free agricultural screening model give a conservative first pass. They are deliberately cautious, so failing them is common and not fatal.

Detailed dispersion modelling follows, using a recognised model with site-specific meteorological data from a representative station, actual stack or fan heights and discharge velocities, terrain, and building downwash. The output is a contour map of ammonia concentration and nitrogen and acid deposition at each designated feature, with the process contribution, the predicted environmental concentration and the percentage of the relevant standard set out receptor by receptor.

Modelling of this kind is specialist work. Councils expect a suitably qualified author and professional review is strongly advised, and the same applies to the Air Quality Assessment that carries the ammonia chapter in most submissions.

Mitigation that regulators accept

Mitigation is assessed in a hierarchy, and reductions have to be secured by condition or by the permit rather than promised in the covering letter.

• Diet. Reducing crude protein and using phase feeding cuts nitrogen excretion at source, and is the change with the best evidence behind it.
• Housing and ventilation. Fully slatted or partly slatted floors, frequent manure removal, and the position and height of ridge or gable fans all change the emission rate and the dispersion pattern.
• Manure and slurry storage. Covered stores, rapid incorporation after spreading and bandspreading or injection rather than splash plate.
• Abatement. Acid scrubbers and bio-scrubbers achieve high removal rates on pig housing, though capital and running costs are heavy and they suit mechanically ventilated buildings.
• Shelterbelts. Tree planting downwind captures a share of deposition near the source. Regulators treat it as a supplement, never as the main measure, and the planting has to be secured and maintained.

Illustrative example. A proposed 60,000 bird broiler unit sits 1.2 kilometres from a lowland heath SSSI with a lichen interest. Screening against the 1 microgram per cubic metre critical level fails at the nearest boundary. Detailed modelling with a raised ridge discharge and a 20 per cent crude protein reduction brings the process contribution below 1 per cent of the critical load at the qualifying feature, and the shortfall at the boundary is addressed by a 30 metre planted buffer inside the applicant's own land. The figures here are for illustration only.

Where this sits against the permit and the rest of the application

Run the permit and the planning application in parallel rather than in series. The emissions inventory, the modelling and the habitats work are shared, and the Environment Agency's pre-application service will tell you early whether the unit is permittable at that location.

The planning submission itself usually needs more than air quality. Expect an Odour Assessment on the same emissions data, an ecology appraisal, landscape and visual work, highways evidence on feed and catch traffic, and a manure management plan. Where the unit exceeds 85,000 broiler places, 60,000 laying hen places, 3,000 places for pigs over 30 kg or 900 sows, it falls within Schedule 1 to the Town and Country Planning (Environmental Impact Assessment) Regulations 2017 and an Environmental Impact Assessment is mandatory. Those regulations require the Environmental Statement to be prepared by competent experts, so an AI-assisted draft is a starting point for that team and never a substitute. Below those figures, a new intensive livestock installation with more than 500 m² of new floorspace is Schedule 2 development and needs a screening opinion.

What to put in front of the case officer

1. A constraints plan showing every designated site within 5 kilometres, with the qualifying features named.
2. An emissions inventory: bird or animal numbers, housing type, ventilation arrangement, fan or ridge heights and discharge velocities, and the manure regime.
3. Screening results against the critical level and the habitat-specific critical loads, with the source of each critical load stated.
4. An in-combination list naming every other unit counted, with the search radius and the date of the search.
5. Detailed modelling where screening is failed, with meteorological years, the model used and a sensitivity run.
6. Mitigation expressed as conditions the council can impose, with monitoring.
7. A short note on the permit position and its timetable.

Scale, odour and screening interact throughout, and the wider poultry unit question is worth reading alongside this before you fix the shed size.

This is general guidance, not legal advice. Check the position with your local planning authority, the Environment Agency or a qualified professional before relying on it.

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