Air pollution and development: advice for local authorities
Source: gov.uk (2025-10-16)

How to assess sector-specific planning applications that could affect air quality on a protected site.

This is Natural England’s ‘standing advice’ on the impacts of air pollution on protected sites. It is general advice that Natural England, as a statutory consultee, gives to local planning authorities. It avoids the need for you to consult Natural England on every application.

In England, this advice is a ‘material consideration’ when making decisions on planning applications. This means you must take this advice into account.

You should also consider any relevant case law that could affect how you carry out any air quality assessments.

This advice relates to the protection of protected sites under the Conservation of Habitats and Species Regulations 2017 (the Habitats Regulations) and the Wildlife and Countryside Act 1981.

Protected sites are ‘sites of special scientific interest’ (SSSIs) and ‘habitats sites’ (also called ‘European sites’). In this advice, habitats sites are:
- special protection areas (SPAs) and potential SPAs
- special areas of conservation (SACs) and possible SACs
- Wetlands of International Importance (Ramsar sites)
- sites providing compensatory measures for adverse effects on habitats sites
When you can use this advice

You can use this advice to assess planning applications for certain types of development that will emit the following air pollutants:
- ammonia (NH3)
- nitrogen oxides (NO, NO2 or NOx)
- nitrogen deposition
- acid deposition
- sulphur dioxide (SO2)
You cannot use this standing advice to assess Nationally Significant Infrastructure Projects (NSIPs) or local plans.

Types of development

Agricultural proposals

You can use this advice to assess agricultural proposals that are:
- first-time planning applications for agricultural structures, such as slurry stores and animal housing
- changing how slurry, nutrients or existing animal housing are used
- increasing herd or flock size
You can only use this advice for assessing applications for slurry infrastructure grant proposals if you consult Natural England and they advise you to. Read more advice on slurry infrastructure grant planning applications (https://www.gov.uk/government/publications/slurry-infrastructure-grant-information-for-local-planning-authorities).

Industrial proposals

Industrial proposals could include:
- anaerobic digesters
- data centres
- combined heat and power plants
- factories
- biomass plants
- combustion plants
- energy-from-waste facilities
You can use this advice for industrial proposals that produce aerial emissions as long as they do not involve:
- carbon capture
- generation or use of hydrogen fuel
- industrial development within Hynet North West (https://hynet.co.uk/), Net zero Teesside onshore (https://www.netzeroteesside.co.uk/), Northern Endurance partnership (https://northernendurancepartnership.co.uk/) or East Cost Cluster (https://eastcoastcluster.co.uk/)
- low-carbon energy technologies
Examples of low-carbon energy technology include:
- bioenergy with carbon capture and storage (BECCS)
- electric arc furnace steelworks
- blue or green hydrogen plants
- retrofitting carbon capture and storage (CCS)
- sustainable aviation fuel (SAF), green fuels or syngas plants
- small modular nuclear reactors (SMRs)
- lithium refineries
- battery manufacturing plants
Proposals creating road traffic

You can use this advice to assess:
- new developments that will create road traffic, such as residential, mixed-use, and industrial or commercial developments
- transport-related applications or new road schemes, including expansion of existing roads
Other proposals

If you’re assessing a proposal that’s not covered by the criteria listed, you should consult Natural England for environmental advice (https://www.gov.uk/guidance/local-planning-authorities-get-environmental-advice).

Steps to assess a proposal

When assessing a proposal, you will need to first complete screening steps. These help you to decide if a development is likely to have an effect on the air quality at a protected site.

For proposals with a likely significant effect (on a habitats site) or likely to have an adverse effect (on an SSSI), you will need to complete a detailed air quality assessment.

This advice explains how to:

Check if emissions will reach a protected site.

Check relevant ‘critical loads’ and ‘critical levels’.

Check if agricultural developments can use an emissions reduction approach.

Consider the proposal in combination with other projects.

Complete a detailed air quality assessment.

Steps 1 to 4 are the screening steps.

Step 1: check if emissions will reach a protected site

This step is part of screening a proposal.

You first need to check if the proposal’s emissions will reach a protected site. You should consider emissions from the construction, operational and decommissioning stages of the development.

Checking industrial and agricultural proposals

You need to check if industrial and agricultural proposals are within a certain distance of a protected site. Emissions from proposals within these distances could reach the protected site.

To do this:
- Find the distances for emission sources relevant to the proposal in table 1 (agricultural proposals) or table 2 (industrial proposals).
- Go to SCAIL Agriculture (https://www.scail.ceh.ac.uk/cgi-bin/agriculture/input.pl) (agricultural proposals) or SCAIL Combustion (https://www.scail.ceh.ac.uk/cgi-bin/combustion/input.pl) (industrial proposals).
- Fill out the project, location, installation, and source (agricultural proposals) or stack (combustion proposals) details.
- Under ‘Designated site details’, enter the relevant distance you found in table 1 or 2 in the ‘search radius’ field.
- Choose ‘Run receptor search’. The page should list all protected sites within this range.
Make a note of all protected sites listed and continue to step 2.

If no protected sites are listed:
- there is no likely significant effect (habitats sites) or no adverse effect (SSSIs) from air pollution
- you do not need to complete further air quality assessment
Table 1: Agricultural air pollution screening distances

Table 2: Industrial air pollution screening distances

Note 1: ‘General combustion processes’ includes developments that involve:
- incineration, including energy from waste incineration
- landfill gas generation plant
- pyrolysis or gasification
- anaerobic digestion
- sewage treatment works
Note 2: ‘Mechanical and biological waste treatment’ includes developments that involve:
- household civic amenity recycling facilities
- construction, demolition and excavation waste
- other waste management
Checking road and traffic proposals

For road and traffic proposals, you need to check how far any protected site is from the edge of any:
- new road proposed
- part of the existing road network where the proposal could create additional traffic
To do this:
- Open MAGIC Map (https://magic.defra.gov.uk/MagicMap.html) and go to the proposal’s location on the map.
- Choose the ‘Map layers’ icon in the left menu, then ‘Designations’, ‘Land-Based Designations’, and select all relevant types of designation (such as ‘Ramsar Sites (England)’). Protected sites will be highlighted on the map.
- Choose the ruler icon from the top navigation bar.
- In the pop-up that opens, choose the first icon (‘Measure distance between two or more points’).
- Select the edge of the road, at the point nearest to a protected site, then double-click on the boundary of the nearest protected site. The distance will be shown on screen.
- If the protected site is within 200m of the proposal, make a note of its name.
- Repeat for any other roads or nearby protected sites.
If all affected roads are further than 200m from a protected site:
- there is no likely significant effect (habitats sites) or no adverse effect (SSSIs) on the site from air pollution
- you do not need to complete further air quality assessment
Step 2: check relevant ‘critical loads’ and ‘critical levels’

This step is part of screening a proposal.

You need to check emissions from the proposal against the ‘critical loads’ or ‘critical levels’ for each type of:
- pollutant the proposal is emitting
- habitat or feature the proposal will affect on protected sites identified in step 1
Critical loads and levels are the points at which air pollutants could cause harm to a protected site. They are either a concentration in the air (levels) or a deposition on the ground (loads).

Finding relevant critical levels or loads

Use the Air Pollution Information System (APIS) (https://www.apis.ac.uk/) to check:
- which habitats and features are present on the protected sites the proposal will affect (identified in step 1)
- the critical levels and loads of each habitat and feature in relation to each air pollutant
Some habitats may not have a critical load because there is not enough data. In these cases, you should find the critical load for a similar habitat type or feature.

Calculate the proposal’s process contribution

You will need to check the ‘process contribution’ of each air pollutant the proposal will release. The process contribution is the additional pollution produced as a result of the proposed development.

You should include both:
- direct effects from the proposed development
- any indirect effects – for agricultural developments, this could include land spreading within the relevant pollution screening distance, including on third party land
You should not include any proposed mitigation measures in your calculations at this stage.

To calculate the process contribution from:
- agricultural proposals (except combustion plants and vehicles), use SCAIL Agriculture (https://www.scail.ceh.ac.uk/cgi-bin/agriculture/input.pl) – read the SCAIL Agriculture user guide (https://www.scail.ceh.ac.uk/agriculture/SCAIL-Agriculture%20USER%20GUIDE%20March%20-%202024.pdf)
- combustion plants, use SCAIL Combustion (https://www.scail.ceh.ac.uk/cgi-bin/combustion/input.pl) – read the SCAIL Combustion user guide (https://www.scail.ceh.ac.uk/combustion/SCAIL-Combustion%20USER%20GUIDE%20June-2023.pdf)
- road and traffic proposals, you will need to consider ammonia and nitrogen oxide emissions and nitrogen deposition – read guidance on assessing ammonia from road traffic (LAQM) (https://laqm.defra.gov.uk/faqs/faq143-assessment-of-ammonia/)
If the proposal affects a motorway, only include emissions from trips that will be generated by the development. The proposal’s traffic modelling should define which journeys are included.

Comparing the proposal’s emissions to the critical load or level

Take the process contribution of each pollutant and calculate it as a percentage of each relevant critical load or level. For critical loads, use the lowest point of the range for this calculation.

You do not need to calculate the percentage for a feature if the applicant has given sufficient and appropriate evidence to prove it will not be affected.

If the proposal’s process contribution is 1% or more of any critical level or load, you will need to continue to:
- step 3 if you’re assessing an agricultural development
- step 5 for all other developments
If the process contribution is under 1% of all critical levels or loads, continue to step 4.

Step 3: check if agricultural developments can use an emissions reduction approach

This step is part of screening a proposal.

To support their application, applicants might show their agricultural proposal will result in a reduction in air pollution emissions at the site. You need to check these proposals meet emissions reduction requirements.

If the applicant is not proposing any emissions reduction, continue to step 4.

Check which emissions reduction guidance to follow

You can use Natural England’s emissions reduction approach (in this standing advice) to assess the proposal if the:
- proposal does not need an Environment Agency permit
- current activity on the site causing pollution would continue even if the proposal was not approved
You should follow the Environment Agency’s emissions reduction advice if the proposal needs both:
- an Environment Agency permit
- planning permission
If the Environment Agency permit is:
- awaiting a decision, check with the Environment Agency to see what emissions reduction they will require
- already granted, check that the proposal meets the emissions reduction requirements in the permit
You should also consider if the proposal needs additional measures to cover pollution sources or mitigate impacts not included or assessed as part of the Environment Agency permit. To do this, follow step 5 in this standing advice.

Identify relevant protected sites

If you have not already gathered this information in previous steps, you will need to identify any protected sites the proposal could affect.

Use SCAIL Agriculture (https://www.scail.ceh.ac.uk/cgi-bin/agriculture/input.pl) to search for any protected sites within 5km of the proposal. SCAIL will show the distance between the proposal site’s boundary and the boundary of the protected site.

For each of the affected protected sites, use the Air Pollution Information System (APIS) (https://www.apis.ac.uk/) to check the:
- description of protected features at the site
- critical levels and load relevant to each protected feature
Check the baseline emissions on the proposal site

You need to check the applicant has accurately calculated the current annual emissions of each air pollutant at the site of the proposal, to use as a baseline. This figure should be in kilograms per year.

To calculate the emissions, you can use:
- SCAIL Agriculture (https://www.scail.ceh.ac.uk/cgi-bin/agriculture/input.pl) for livestock housing, slurry and manure storage, and spreading
- SCAIL Combustion (https://www.scail.ceh.ac.uk/cgi-bin/combustion/input.pl) for combustion plants
- Calculator for Road Emissions of Ammonia (CREAM) (https://www.aqconsultants.co.uk/resources/calculator-for-road-emissions-of-ammonia) for road emissions of ammonia
Screen out dominant sources

You need to check if the proposal’s site is currently a ‘dominant source’ of air pollution on any protected site.

A dominant source means it will emit 25% or more of any relevant critical level or load. An example could be an uncovered slurry lagoon with a surface area over 4,000m2 located very close to a protected site.

Take the baseline emission of each pollutant (in kilograms per year) and calculate it as a percentage of each protected site’s critical loads and levels.

If the baseline emissions are under 25% of all critical loads and levels, you should move on to review emissions reduction measures.

If the baseline emissions meet or exceed 25% of any relevant critical load or level, it is a dominant source for that air pollutant. You will not be able to consider emissions reductions for this proposal.

Check the proposal’s process contribution, calculated at step 2. You should move to:
- step 4 if the proposal’s process contribution is below 1%
- step 5 if the proposal’s process contribution is 1% or above
Reviewing emissions reduction measures

If the applicant is proposing emissions reductions, they should have included measures to achieve a net reduction in emissions compared to the baseline. These measures must be embedded in the proposal. For example, the applicant could include scrubbers as part of the building fabric.

You should check that the applicant has given evidence that each measure is:
- achievable – realistic and based on established good practice, such as the best available techniques (BAT) reference documents (https://www.gov.uk/guidance/best-available-techniques-environmental-permits)
- proportionate – causing a net reduction in emissions that will positively affect pollutant levels on protected sites
- verifiable – modelling and calculations should demonstrate the reductions and clearly link them to the applicant’s measure
Checking measures result in an emissions reduction

You then need to confirm if the measures will result in an emissions reduction. To do this:
- Use the baseline emissions figure previously calculated in kilograms per year. As an example, this could be 5,500kg per year of ammonia.
- Calculate the emissions for the proposed new activity, using the tools you used to calculate the baseline. This should include emissions from the baseline and the new activity. For example, 7,500kg per year.
- Calculate the value of emissions saved by any proposed measures, using the tools used to calculate the baseline. As an example, the measures will save 3,000kg per year.
- Subtract the total value of the proposed measures from the new activity emissions. For example, 7,500kg minus 3,000kg. This example would give you a saving of 4,500kg.
- Repeat the steps for all pollutants. If the total savings are greater than total baseline values, you’ve achieved an emission reduction.
You should consider if any emissions reduction will benefit the protected sites. You could ask the applicant to include further measures.

If you’re content with the measures, you should next secure the applicant’s commitment to the emissions reduction.

If there is not an emissions reduction or you are not content with the measures, applicants cannot use emissions reduction to support their application. You should continue to step 4.

Secure commitment to emissions reduction

You will need to make sure emissions reduction measures are secured as part of any approval. For example, they could be secured by a planning condition.

Once the measures are secured, you do not need to complete any further air quality assessment.

Step 4: consider the proposal in combination with other projects

This step is part of screening a proposal.

If a proposal does not exceed 1% of the critical levels and loads alone, you will need to consider it in combination with other projects. This is an in-combination assessment.

It is a legal requirement for habitats sites. For SSSIs, the assessment will help you understand any adverse effect to the SSSI and decide if the proposal needs further assessment.

Decide if the proposal needs an in-combination assessment

Applicants might use the Joint Nature Conservation Committee (JNCC) ‘decision-making thresholds’ as a reason for not completing an in-combination assessment.

If so, you should check they have correctly followed the JNCC guidance on decision-making thresholds (https://hub.jncc.gov.uk/assets/6cce4f2e-e481-4ec2-b369-2b4026c88447). If this guidance shows they do not need to complete an in-combination assessment, you do not need to complete further air quality assessment.

If applicants have not used the decision-making thresholds, or have not followed them correctly, they will need to provide an in-combination assessment.

Review the in-combination assessment

You will need to review the applicant’s in-combination assessment.

You should check that the assessment contains:
- all relevant pollutants – for example, road proposals should cover NOx, ammonia and nitrogen deposition
- direct effects from the proposed development, as well as any indirect effects
- other projects or activities that could affect the same protected sites – this includes proposals being dealt with by other authorities
- accurate calculations of the combined effects of all projects on relevant critical levels and loads on the site
Finding projects

To find projects, you can use:
- local authorities’ planning portals, which cover proposals that need planning permission
- Public Registers Online (https://environment.data.gov.uk/public-register/view/index), which covers proposals that need an Environment Agency permit
The Air Pollution Information System (APIS) (https://www.apis.ac.uk/) includes all background pollutants and is updated every 3 years. You should only include projects that are not part of the background pollution on APIS.

Types of projects could include:
- applications for a new permission
- applications to change an existing permission
- granted permissions that have not begun or been completed
- granted permissions that need renewing
- plans that have been drafted but not yet adopted
- allocations for development in local plans
- existing environmental permits
Calculating combined emissions

The assessment should calculate the effects of all proposals combined on relevant critical loads and levels on the protected site. You should use the details in planning portals and the permitting register to check that these calculations are accurate.

If the air pollution caused by all proposals at the protected site combined is above 1% of any critical load or level, continue to step 5.

If it is below 1% in combination with other proposals, you do not need to complete any further air pollution assessment.

You can conclude there is no likely significant effect for habitats sites and no adverse effect for SSSIs. You should record this conclusion and how it has informed your decision on the proposal.

Step 5: completing a detailed air quality assessment

If screening shows you cannot rule out a likely significant effect on a habitats site or adverse effect on a SSSI, you will need to complete a detailed air quality assessment. This is an ‘appropriate assessment’ for habitats sites.

This standing advice explains how to consider air quality in your assessment.

You should read it alongside the guidance on carrying out appropriate assessments (part of a habitats regulations assessment (https://www.gov.uk/guidance/habitats-regulations-assessments-protecting-a-european-site)) and detailed air quality assessments (https://iaqm.co.uk/text/guidance/air-quality-impacts-on-nature-sites-2020.pdf).

How to complete your assessment

Your assessment needs to be a more precise review of the ecological impacts of emissions on any protected sites. It should take into account the best available evidence, including any available detailed modelling.

At the end of the assessment, you should be able to conclude whether there will be:
- an adverse effect on the integrity of a habitats site
- an adverse effect on an SSSI
To make your conclusion, you’ll need to:
- collect more detail on the affected protected sites and how the proposal’s emissions will affect them
- consider other factors that could affect the proposal’s impact – trends in background air quality, the scale and duration of the impact, and direct and indirect effects
- consider effects of the proposal in combination with other plans or projects
If there could be an adverse effect, you’ll need to consider measures that could mitigate this.

The applicant should provide their own assessment containing the information and detailed modelling you need. You need to review this and make your own conclusion.

Check protected site details

You should use Designated Sites View (https://designatedsites.naturalengland.org.uk/SiteSearch.aspx) to check the applicant has provided accurate information on:
- any interest features sensitive to air pollution on all protected sites the proposal will affect
- conservation objectives for habitats sites
If you have not gathered this information in previous steps, use the Air Pollution Information System (APIS) (https://www.apis.ac.uk/) to check the applicant has provided accurate information on:
- background (current) concentrations of NOx, SO2 and NH3, and background nitrogen deposition levels on the protected site
- critical loads, critical levels and nitrogen sensitivity of all features the proposal will affect – these vary by habitat type
When checking nitrogen deposition, choose the most appropriate habitat:
- moorland for short vegetation (up to knee height)
- forest for taller vegetation (over knee height)
If you do not know the vegetation type or there is a mix, you should use the vegetation with the highest deposition values.

Check if the emissions from the proposal will cause interest features to be above their critical levels or loads.

Make sure the applicant has used the correct emissions factor for transport emissions, using the Emissions Factor Toolkit (https://laqm.defra.gov.uk/wp-content/uploads/2025/03/EFTv13.0-user-guide-v1.0.pdf).

Calculate the predicted environmental contribution

Check the applicant has accurately calculated the proposal’s ‘predicted environmental contribution’ (PEC) for each pollutant. To calculate PEC, add the process contribution (calculated at step 2) to the background level.

If any PEC exceeds the relevant critical level or load, there could be an adverse effect. You should continue to consider other factors that could affect the proposal’s impact.

If no PEC exceeds the relevant critical level or load, you can conclude there is no adverse effect. You do not need to complete further air quality assessment.

Consider trends in background air quality

You should check for any trends in background air pollution that could affect the protected sites. You can review:
- national trends in air quality over time – use the ‘Site Relevant Critical Loads’ tool and background concentrations displayed under the ‘Site Detailed Grid Information’ tab in Air Pollution Information System (APIS) (https://www.apis.ac.uk/)
- any available modelling, monitoring and ecological survey data on air quality in the area local to the proposal
- strategies published by public bodies that could affect air quality on the protected sites
Strategies could include:
- measures in place to reduce nitrogen emissions, such as an air quality strategy
- clean air zones or ultra-low emission zones
- evidence of uptake of emission-reduction measures in local agri-environment schemes
Assess the impact of trends

Assess the impact of each pollutant on interest features on the protected sites, considering conservation objectives and trends. You need to determine if there’s an adverse effect.

For example, a downward trend in background pollution levels might indicate an improvement over the longer term, which could negate the immediate impact from the proposal. You need to have a high degree of certainty that background levels of pollution would reduce.

Applicants cannot use a habitat developing tolerance to high nitrogen levels as the only justification for further increasing nitrogen deposition. This is likely to undermine the site conservation objectives and could significantly harm the interest features of a habitats site.

A habitats site can have a conservation objective to ‘maintain or restore’ air pollutants to within certain thresholds. If background pollution is already exceeding critical levels or loads, any proposal adding further emissions could undermine the objective.

Consider the scale of the impact

Consider the duration and size of the air pollution impact on the ecological functionality of the affected area or feature.

For example, it could be temporary and reversible, returning to below critical loads and levels within an appropriate timeframe. An example of this would be increased road traffic during a housing development construction, which would reduce once complete.

Where a proposal would delay achievement of air quality conservation objectives, it’s harder to conclude there is no adverse effect. An example of this would be increased road traffic generated by a housing development after completion.

You should consider the risk to site integrity proportionally. The proposal could impact a small amount of a rare habitat or species, which could have a disproportional negative effect. Consider the interest features in the affected area in terms of their:
- rarity
- location and distribution across the site
- vulnerability to change
- ecological structure
Consider direct and indirect effects

You should consider any direct and indirect effects of pollutants on the relevant interest features of a protected site. For example, if a proposal increases ammonia levels:
- a direct effect could be harm caused to lichens (an interest feature), which are sensitive to even very small increases in ammonia pollution
- an indirect effect could be increased nitrogen deposition, causing nitrogen-loving plants to grow at the expense of rarer or nitrogen-sensitive plants that are interest features
Confirm there will be no adverse effect alone or in combination

For habitat sites, you should confirm beyond reasonable scientific doubt that there will be no adverse effect, either alone or in combination with other plans or projects.

Air pollution could lead to an adverse effect if it:
- destroys, damages or changes all or part of an interest feature
- harms a site’s ability to survive damage and reduces its ability to support interest features
- changes the site’s physical environment, for example, by changing the chemical makeup of its soil
- has any other effect that could undermine the site’s conservation objectives
You should follow the same principles for SSSIs to confirm if there is an adverse effect.

You may have identified the other relevant plans or projects at step 4. You need to review the applicant’s in-combination assessment again in the same way, taking into account the information gathered for this detailed assessment.

If you cannot conclude there is no adverse effect, alone or in combination, you will need to consider mitigation measures.

Considering mitigation measures

If there could be an adverse effect on the protected site, the applicant should have proposed mitigation measures.

You should have sufficient certainty that the mitigation measures are:
- achievable, proportionate and verifiable, as explained in step 3
- supported by evidence showing they will reduce emissions on the protected site below harmful levels
- quantifiable – you should be able to quantify the effectiveness of the mitigation measures in avoiding adverse effects over the lifetime of the project
You must secure any mitigation or monitoring measures through formal conditions or restrictions in any permission or authorisation.

If the applicant has not proposed adequate mitigation, you should either:
- ask the applicant for further mitigation measures
- impose mitigation measures – these may be different or stricter measures than ones proposed by the applicant
Examples of mitigation measures could include:
- traffic management that will measurably reduce emissions from road proposals
- adding wooded shelterbelts, trees, green walls and hedges to limit dispersal of emissions, as long as these would not negatively impact the protected site
- relocating or redesigning developments to avoid impacts on protected sites
- reducing other sources of the same pollutants that have an overlapping pollution footprint on the affected protected site
Reaching a conclusion

You need to be able to conclude that the proposal will have:
- no adverse effect on the integrity of a habitats site, alone or in combination
- no adverse effect on an SSSI
This should be based on the evidence on air quality you have gathered and any mitigation measures.

If the applicant has made a conclusion in the evidence they provided to you, you will need to make your own assessment of this.

If you cannot conclude there will be no adverse effect

If you cannot conclude there will be no adverse effect on an SSSI and mitigation measures will not fully address the impacts, you can refuse the application.

If you cannot conclude there will be no adverse effect on the integrity of a habitats site and mitigation measures will not fully address the impacts, you can:
- refuse the application
- consider if ‘derogation’ (allowing a proposal that could have an adverse effect to go ahead) (https://www.gov.uk/guidance/habitats-regulations-assessments-protecting-a-european-site#derogation) would be justifiable
If you can conclude there will be no adverse effect

If you have followed this advice and concluded there will be no adverse effect on any protected site from air pollution, Natural England would be able to agree with your decision.