Air quality

Reducing air pollution is vital for both nature recovery and human health.

Nitrogen and other pollutants travel as gases and fine particles through the atmosphere, eventually settling on habitats and soils.  This deposition disrupts biodiversity, it can alter ecosystem processes and poses risks to people’s health.

Nature-based solutions alongside technical measures can help by cutting emissions at source and buffer their impacts on sensitive environments.

What we need to do and where
Wistman's Wood, Dartmoor. Credit: Emma Simmonds

Wistman’s Wood, Dartmoor – Emma Simmonds

1. About

Clean air is vital for both people and nature. Nitrogen pollution is one of the leading causes of biodiversity loss in the UK and could impact the Government’s ambition to protect 30% of land by 2030.

While many air pollutants exist, those containing reactive nitrogen are among the most widespread and damaging. Nitrogen pollution includes nitrogen oxides (NOx), mainly from combustion in transport and industry, and ammonia (NH₃), largely from livestock manure and fertiliser use. These pollutants travel as gases and particles through the air and can settle on habitats affecting biodiversity and ecosystem function, and when inhaled, impact human health. These pollutants contribute to respiratory illness, soil acidification, and nutrient enrichment of sensitive habitats, putting species such as lichens, mosses, and heathland plants at risk.

Habitats like peatlands and woodlands also play a crucial role in carbon storage and sequestration. Healthy, functioning ecosystems help people adapt to and mitigate climate change, yet nitrogen pollution could hinder progress toward the UK’s 2050 ‘net zero’ target.

When considering human health, an Air Quality Management Area (AQMA) is a location where air pollution levels exceed national objectives. They are declared by local authorities under the Environment Act when monitoring shows legal limits are breached, mainly due to road traffic emissions. In Devon, several AQMAs have been declared. However, monitoring is also often limited, and the number of current monitoring stations may not be sufficient to fully understand exposure, meaning some pollution hotspots could go undetected. For more details and an interactive map of AQMAs, visit DEFRA’s AQMA map here.

Understanding Impacts of Nitrogen on Nature (Nitrogen Futures Summary) (jncc.gov.uk)

The ecological impacts of nitrogen pollution

Nitrogen deposition in terrestrial ecosystems causes major shifts in species composition, especially in nutrient-poor habitats. These areas often transition toward species that thrive under high nitrogen availability, such as tall grasses, brambles and nettles, leading to reduced species richness and increased plant growth. Sensitive lichens and bryophytes frequently decline or disappear, while nitrate leaching into soils becomes more pronounced. Soil acidification from nitrogen compounds further disrupts ecosystem balance. Indirect effects include altered species composition and greater vulnerability of plants to frost, drought, and pathogens.  All of which impacts the species which depend on these habitats.

Woodlands experience changes in the diversity and composition of lichens, fungi, and ground flora. Semi-natural grasslands, which depend on low nutrient levels, often lose characteristic species when nitrogen inputs rise. Sand dunes can undergo significant species shifts and habitat loss under increased nitrogen.

High concentrations of ammonia cause direct damage to sensitive species, such as mosses. Heathlands and peat bogs are particularly vulnerable to high levels of ammonia, with ammonia driving dramatic reductions in species diversity and altering flora, bryophyte, and lichen communities.

Nitrogen oxides can also cause visible leaf damage and pose risks to mosses, liverworts, and lichens that rely on atmospheric nutrients. Prolonged exposure leads to long-term shifts in species composition across affected ecosystems.

Critical levels and critical loads

Air quality standards for ecosystems are expressed as critical levels (concentrations in air) and critical loads (amount deposited to land).

Critical levels: The concentration of pollutants (ammonia and nitrogen oxides) in the air above which damage can occur to ecosystems.

Critical loads: The amount of pollution (nitrogen) an environment can handle without causing harm to sensitive plants or ecosystems.

For nitrogen pollutants:

Critical loads for nitrogen deposition can vary by habitat but generally fall within 5–15 kg of Nitrogen per hectare per year for sensitive ecosystems such as heathlands and bogs.

Critical levels of ammonia (NH₃) are typically, 3 µg/m³ (as an annual mean) for some vegetation (higher plants), with a lower threshold of 1 µg/m³ for sensitive species and habitats such as lichens and bryophytes.Nitrogen Oxides (NOₓ) Critical level is 30 µg/m³ for most vegetation types.

Health check

Across Devon you will find nitrogen-sensitive habitats above critical levels and loads for nitrogen deposition.

Ammonia emissions largely come from intensive livestock farming and fertiliser use, while nitrogen oxides are released through road traffic and fossil fuel combustion. Many sensitive habitats in Devon already exceed critical nitrogen thresholds.

Although nitrogen oxide emissions have fallen significantly in recent decades, ammonia levels have remained stubbornly high. Agriculture is responsible for around 88% of UK ammonia emissions, 48% from cattle, 27% from other livestock, and 25% from non-manure fertilisers. Large livestock housing and heavily trafficked roads can create local “hotspots” of atmospheric nitrogen.

The UK has legally binding targets to cut ammonia emissions by 16% and nitrogen oxides by 73% by 2030.  Whilst this will bring improvements for nature, this will not be enough for nature restoration, and many sites will still exceed their environmental thresholds.

Ammonia emissions are projected to increase as the climate warms, which is a concerning trend.

Interactive map guidance

On our interactive map, you’ll find a layer called “Select a Pollutant”. Using this layer, you can view current levels of nitrogen deposition, ammonia concentrations, and NOx concentrations across Devon. The data shows that many areas are already exceeding critical loads and critical levels for these pollutants, highlighting the urgent need to address this issue at scale.

Alternative if we can’t integrate APIS mapping

To help you view the current air quality situation across Devon, you can access detailed information via the Air Pollution Information System (APIS) at the link below. The site offers a comprehensive mapping tool with a wealth of data. Using the map controls, you can select specific pollutant layers, which will allow you to view information such as current ammonia concentrations for any area in Devon. The data shows that many areas are already exceeding critical loads and critical levels for pollutants, highlighting the urgent need to address this issue at scale.

APIS – Air Pollution Information System | APIS

Why this matters for habitat restoration

High nitrogen deposition and elevated ammonia and NOx concentrations can make it challenging to restore habitats or create new ones. Excess nitrogen alters soil chemistry, favouring fast-growing species and reducing biodiversity. This nutrient imbalance can prevent the successful establishment of sensitive habitats such as heathlands, bogs, and species-rich grasslands. Such effects of nitrogen on plant communities in turn affects wildlife species dependent on these plant communities. Addressing nitrogen pollution is therefore essential to achieve long-term habitat and species recovery and meet nature recovery targets.

Key pressures and opportunities

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Emissions

Nitrogen pollution in Devon arises from multiple sources, with agriculture being the dominant contributor. Emissions stem from practices such as intensive livestock housing, uncovered slurry stores, slurry and fertiliser spreading, and high-input land management.

Road traffic and fossil fuel combustion add further pressure with emissions creating localised hotspots near busy routes and urban areas.

Tackling these sources requires a mix of technical and land management solutions: covering slurry stores, adopting low-emission slurry spreading techniques, installing low-emission flooring in livestock housing, and shifting from high-input fertiliser systems to low- or no-input land uses.

For transport-related emissions, measures include reducing traffic volumes, promoting cleaner vehicle technologies, and incorporating green infrastructure along roadsides to intercept pollutants.

2. What we need to do and where

Priority

Better, bigger and more wildlife-rich habitats across Devon to improve air quality.   

Improving air quality in Devon requires a focus on reducing nitrogen emissions and protecting sensitive habitats. Areas close to heathlands, bogs, and other nitrogen-sensitive sites should be prioritised for emission reduction measures and/or land use change and habitat restoration and creation. In some areas, habitats such as woodlands, that act as natural filters capturing airborne pollutants and reducing nitrogen deposition could be created (if suitable in that location), also providing benefits for wildlife and carbon storage.

Farmers play a vital role in tackling nitrogen pollution. Supporting the adoption of low-emission practices, such as improved manure management and precision low emission fertiliser and slurry spreading techniques, can significantly cut ammonia emissions. Creating buffer zones with species-rich grasslands or hedgerows around farmland helps intercept nutrients before they reach vulnerable ecosystems. These measures not only protect biodiversity but also improve soil health and water quality.

Actions

Habitat creation and restoration for ammonia and nitrogen mitigation

  • Tree shelterbelts around emission sources
    Planting trees near livestock housing, slurry stores, manure application areas, and roads can intercept ammonia and reduce its impact. Species selection and density matter for effectiveness.
  • Vegetation buffers around sensitive habitats
    Establishing woodland or shrub buffers around nitrogen-sensitive habitats can help shield them from atmospheric ammonia and nitrogen deposition. Dense hedgerows around fields and livestock areas also reduce wind speed, trapping ammonia, and these measures also provide wider habitat benefits.  However, it is essential to ensure these buffers do not negatively impact the sensitive habitats you are trying to protect. This type of intervention should only be implemented where it is suitable for the specific habitat and location, following careful assessment to confirm it is the right measure in the right place.
  • Agroforestry systems
    Integrating trees within farmland enhances nitrogen uptake, reducing volatilization, and improving soil health.
  • Habitat restoration
    Restoring habitats such as moss-dominated habitats helps maintain nitrogen-sensitive ecosystems and carbon storage, reducing vulnerability to nitrogen enrichment.
  • Soil remediation
    Techniques such as phytoremediation using deep-rooted plants, grasses, or cover crops absorb excess nitrogen in the soil. These plants also capture nitrates and ammonium, reducing leaching and improving soil health.

Reducing emissions from agriculture

  • Cover slurry and manure stores – Use impermeable covers or floating lids to prevent ammonia volatilization.
  • Low-emission spreading techniques – Apply slurry using trailing shoe, injection, or dribble bar instead of splash plate to reduce emissions.
  • Apply under cool, moist conditions and incorporate quickly – Timing and rapid incorporation into soil minimise ammonia losses.
  • Improve livestock housing systems – Use floor scrapers to reduce emissions inside housing.
  • Adjust livestock diets – Lower crude protein and balance feed to reduce nitrogen excretion.
  • Use fertiliser additives (urease or nitrification inhibitors) – Slows conversion of nitrogen compounds, reducing ammonia and nitrous oxide emissions.
  • Optimise fertiliser use – Apply only what crops need, avoid excess, and consider controlled-release products.
  • Precision farming techniques – Use GPS-guided application and soil testing to match nutrient supply to crop demand.
  • Replace ammonium-based fertilisers – Switch to nitrate-based alternatives where appropriate to reduce ammonia volatilization.
  • Establish vegetation buffers and cover crops – Captures residual nitrogen and prevent runoff or leaching.
  • Improve soil health and drainage – Enhances nitrogen efficiency and reduces denitrification losses.

Reducing emissions from road traffic

  • Promote cultural change in travel habits
    Promote public transport, cycling, and walking to reduce overall vehicle emissions.
  • Improve driving behaviour
    Eco-driving techniques (steady speeds, reduced idling) lower fuel consumption and emissions.
  • Promote low-emission vehicles
    Transition to electric or hybrid vehicles eliminates ammonia emissions from combustion.
  • Reduce traffic congestion
    Smoother traffic flow reduces stop-start conditions that increase ammonia formation.
  • Implement low-emission zones
    Restrict high-emission vehicles in urban areas to cut emissions.

Where to focus action

Air quality goals should be embedded in local planning and transport strategies. Reducing traffic emissions through sustainable transport options and green infrastructure can limit nitrogen oxides from vehicles. Planting trees along roadsides and in urban areas provides an additional barrier against pollutants and enhances community wellbeing.

Understanding where nitrogen pollution comes from is essential for effective action. Agricultural activities, major roads, and industrial sources are the main contributors. Tools such as the Air Pollution Information System (APIS) can help identify sources and sensitive habitats and assess likely impacts. On-site indicators, like nitrogen-tolerant lichens, can also reveal areas under pressure. In some cases, habitat restoration may require removing excess nitrogen before recovery can begin.

Raising awareness among local communities and authorities is key to success. By highlighting the links between air quality, biodiversity, and human health, we can encourage collective action. Measures such as tree planting, habitat buffers, and improved farming practices not only reduce nitrogen emissions but also deliver wider benefits for climate resilience and nature recovery.

  • At emission sources (farms and roads/urban areas)
    Apply measures where pollutants originate, e.g., livestock housing and slurry stores and along major roads/junctions, to prevent emissions before dispersion.
  • Around sensitive habitats
    Use carefully designed vegetation buffers or other shielding interventions near nitrogen‑sensitive habitats. Ensure the intervention suits the habitat so it protects without altering site conditions.
  • Within and around designated sites (SACs, SPAs, SSSIs)
    Prioritise mitigation where critical loads/levels are high, both from nearby agricultural sources and transport corridors, while verifying that any planting or engineered measures do not harm qualifying features.
  • Landholdings adjacent to designated sites (farms, estates, roads)
    Focus emission reduction and shielding on holdings that are closest to and sit immediately upwind of protected areas, whether that’s a farm unit, an industrial yard, or a busy stretch of road.
  • Areas with documented exceedance or high vulnerability
    Deploy measures across whole areas where monitoring/modelling shows exceedance of nitrogen critical loads/levels, integrating actions on transport, land use, and agriculture.
  • Urban greenspaces and roadside greens infrastructure
    Introduce green barriers (suited species and designs) in towns and along roads to intercept pollutants, combined with traffic measures.

Monitoring and Awareness:

  • While the UK has the National Ammonia Monitoring Network (NAMN), coverage is sparse, with limited monitoring sites in Devon. This means localised hotspots may go undetected, and the true scale of nitrogen deposition on sensitive habitats could be underestimated. Therefore, there is a need for increased air quality monitoring/modelling across Devon to ensure accurate data on ammonia and nitrogen levels, identifying hotspots, and informing targeted mitigation measures.
  • We need to raise awareness of air quality issues across Devon. Improving air quality is vital for creating a healthier environment for people and protecting nature for future generations.

3. Inspiration

Case studies

Fenn’s & Whixall Mosses Shared Nitrogen Action Plan (SNAP) – Shropshire/Wales

A collaborative SNAP developed for the Marches Mosses SAC, one of the UK’s largest lowland raised bogs. The site was suffering from excess nitrogen deposition from nearby poultry farms and other sources. Stakeholder workshops to identify emission sources and mitigation options. Measures included covering slurry stores, hard standing at feeding stations, and slurry injection. This helps protect rare bog habitats, improves water quality, and supports carbon storage.

Braunton Burrows Shared Nitrogen Action Plan SNAP – North Devon

Identified as a priority site under Natural England’s Catchment Sensitive Farming Air Quality Priority Areas. Braunton Burrows is a Special Area of Conservation with nitrogen-sensitive dune habitats. SNAP methodology applied to engage farmers and reduce ammonia emissions near the site.

YouTube – Webinar: Introduction to SNAPs at Braunton Burrows

Nitrogen Futures Project (UK-Wide)

A Defra-funded initiative led by UKCEH and partners to model nitrogen reduction scenarios and spatial targeting. Evidence for prioritising mitigation near sensitive habitats and informing SNAP development.

Ammonia Reduction by Trees (ART Project) – Cumbria

A Natural England-funded project led by UK Centre for Ecology & Hydrology tested tree shelterbelts around poultry and dairy farms to capture ammonia emissions. Tree belts significantly reduced ammonia plumes from livestock housing, improving air quality and reducing nitrogen deposition on nearby sensitive habitats. Carbon sequestration, improved biodiversity, and shelter for livestock. Demonstrates how agroforestry and targeted planting can mitigate agricultural emissions.

4. Find out more

Environmental Improvement Plan (EIP) 2025 – GOV.UK

Clean Air Strategy 2019 – GOV.UK

APIS – Air Pollution Information System | APIS

Natural England Strategy

Understanding Impacts of Nitrogen on Nature (Nitrogen Futures Summary)

2407301154_UK_Agriculture_Ammonia_Emission_Report_1990-2022_23072024.pdf

Code of Good Agricultural Practice (COGAP) for Reducing Ammonia Emissions – GOV.UK (www.gov.uk)

Tree Shelter Belts for Ammonia Mitigation | Tree Shelter Belts for Ammonia Mitigation (ceh.ac.uk)

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