Air Pollution and Protected Sites in Planning

 

Air pollution planning is not only about impacts on people. Development can also affect protected habitats through pollutants such as ammonia, nitrogen oxides, sulphur dioxide and nitrogen deposition.

This is particularly relevant to livestock buildings, slurry and manure storage, combustion plant, waste and industrial development, and proposals that generate additional road traffic. Where emissions could affect a Site of Special Scientific Interest or a habitats site, the planning authority may need a specific ecological air-quality assessment.

Natural England published detailed standing advice in October 2025, updated in December 2025, which gives local planning authorities a structured screening process for these proposals. The standing advice is for relevant planning applications; Natural England expressly says it should not be used to assess Nationally Significant Infrastructure Projects or local plans.

 

Why can air pollution be a planning constraint?

 

Some habitats are sensitive to changes in atmospheric pollution and nutrient deposition. A development that increases ammonia, nitrogen oxides or other pollutants can alter plant communities, encourage nutrient-loving species and damage the features for which a site is protected.

The issue can arise through direct emissions from a development or indirectly through associated traffic, manure spreading or other activities. For European sites and Ramsar sites this can engage the Habitats Regulations Assessment process. For SSSIs, the authority also needs to consider whether the proposal could adversely affect the designated interest features.

 

Which developments are most likely to be affected?

 

Natural England’s standing advice specifically covers:

• livestock and poultry buildings
• slurry lagoons, digestate stores and manure stores
• changes to livestock numbers or the way manure and slurry are managed
• industrial and commercial processes
• combustion plant, including energy-from-waste, anaerobic digestion and sewage treatment
• waste-management proposals
• airports and some other transport infrastructure
• residential, mixed-use, commercial and industrial development that creates additional road traffic

The fact that a development appears ordinary does not automatically remove the issue. A large housing scheme can be relevant if the additional traffic affects roads close to a sensitive protected site.

 

How does Natural England’s screening process work?

 

The standing advice uses a staged approach:

• check whether emissions could reach a protected site
• identify the relevant critical loads and critical levels
• for agricultural proposals, consider whether an emissions-reduction approach can be used
• consider the proposal in combination with other projects
• where necessary, complete a detailed air-quality assessment

The first four stages form the screening process. If a proposal cannot be screened out, a more detailed assessment is required.

 

What are the screening distances?

 

The screening distance depends on the type and scale of emission source. Natural England’s current advice gives different distances for agricultural and industrial development, ranging from hundreds of metres to several kilometres.

For example, livestock and poultry units over 500 square metres are screened for protected sites up to 5 kilometres for SSSIs and 10 kilometres for habitats sites. Large slurry or digestate stores can also trigger screening over several kilometres.

For road and traffic proposals, the initial check is different. If every affected road is more than 200 metres from the protected site, Natural England’s standing advice says there is no likely significant effect on a habitats site and no adverse effect on an SSSI from air pollution, so no further air-quality assessment is required on that pathway.

These are screening distances rather than automatic refusal zones.

 

What are critical loads and critical levels?

 

A critical level is the concentration of a pollutant in the air above which harm may occur. A critical load is the amount of pollutant deposited onto a habitat above which harmful ecological effects may occur.

The relevant figure depends on the habitat and pollutant. Natural England directs decision-makers to the Air Pollution Information System, commonly known as APIS, to identify the sensitivity of protected features.

The proposal’s additional contribution is then compared with those values.

 

What is the 1% screening threshold?

 

Under Natural England’s standing advice, if the proposal’s process contribution is 1% or more of a relevant critical load or critical level, further assessment is normally required. If it is below 1%, the authority must still consider the proposal in combination with other relevant projects.

If the combined effect is also below 1%, the proposal can normally be screened out on this air-pollution pathway. Where the threshold is exceeded, or the evidence does not provide the necessary certainty, a detailed assessment is needed.

This percentage is part of Natural England’s screening methodology; it should not be treated as a free-standing legal rule divorced from the protected-site assessment.

 

Agricultural development and ammonia

 

Ammonia is particularly important for agricultural proposals. Livestock housing, slurry storage, manure storage and spreading can all contribute to atmospheric ammonia and nitrogen deposition.

Natural England’s advice allows an emissions-reduction approach in some cases where the new development would reduce pollution compared with the existing lawful activity. The conditions are specific, and proposals that also require an Environment Agency permit need to be considered alongside the permitting regime.

This can make design details commercially important. Housing type, ventilation, slurry management, store covers, floor systems and other measures can materially change the emissions calculation.

 

Does an Environment Agency permit solve the planning issue?

 

Not automatically. Planning and environmental permitting are separate regimes. Where a proposal requires both, the planning authority can take the permit into account, but it may still need to consider effects that fall outside the permit assessment or require certainty under the Habitats Regulations.

The same general principle appears across environmental planning: another regulatory regime may be highly relevant, but it does not always remove the planning authority’s own legal duties.

 

Road traffic and housing development

 

Traffic-generated effects can arise from nitrogen oxides, ammonia and nitrogen deposition. For a housing or mixed-use proposal, the first practical question is whether the development changes traffic flows on roads within 200 metres of a sensitive protected site.

If it does, traffic modelling and ecological air-quality work may be needed. The relevant assessment should use the current emissions tools and consider background pollution as well as the development’s additional contribution.

 

What should an applicant check?

 

• Identify nearby SSSIs, SPAs, SACs and Ramsar sites at an early stage
• Check whether the proposal falls within Natural England’s screening distances
• For traffic-generating proposals, identify affected roads within 200 metres of a protected site
• Use APIS to identify the relevant habitat sensitivity, critical loads and critical levels
• Use the appropriate current screening model for agriculture, combustion or road traffic
• Consider in-combination effects with other projects
• Do not assume an Environment Agency permit removes the planning or HRA issue
• Where mitigation is relied upon, make sure it is specific, effective and capable of being secured

 

Useful related pages

 

For the legal assessment process see our Habitats Regulations Assessment guide. We also cover SSSIs, Special Protection Areas, Special Areas of Conservation and Ramsar sites.

 

Official guidance

 

Natural England – Air pollution and development: advice for local authorities

Conservation, Heritage & Protected Sites

 

Air Pollution Page Created: 27th August 2026