Air quality

High nitrogen levels are a significant problem for habitats such as peat bogs, heaths and wildlife-rich grasslands.

Wildlife habitats such as woodlands can be used to help absorb pollution and so help to improve air quality.

Some rare lichens and mosses are particularly sensitive to high nitrogen levels.

What we need to do and where

Wistman's Wood, Dartmoor. Credit: Emma Simmonds — Wistman’s Wood on Dartmoor, Emma Simmonds

Covered slurry store big black panels. — Covered slurry store, Natural England

Motorway as seen from on top of a bridge. Heavy traffic is visible on one side and lighter traffic on the other. — Motorway traffic, Henry Burrows

1. About

Clean air is vital for both people and nature.

Nitrogen

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 through soil acidification, and nutrient enrichment of sensitive habitats.

Nitrogen pollution in Devon comes from many different sources. Agriculture produces the most emissions (ammonia) from practices such as intensive livestock housing, uncovered slurry stores, slurry and fertiliser spreading and high-input land management. Emissions (nitrogen oxides) from road traffic and burning fossil fuels add further pressure, creating localised hotspots near busy routes and in urban areas.

The environmental impacts of ammonia pollution. Image credit: Defra

Impacts on wildlife

Nitrogen pollution is a major driver of biodiversity loss in the UK and could impact the Government’s ambition to restore nature, as set out in the Environmental Improvement Plan 2025.

Many plant species in our wildlife habitats are unable to survive in these conditions leading to significant changes in vegetation and impacts on wildlife (especially invertebrates) which rely on these plants. Some species of mosses and lichens are especially vulnerable to nitrogen pollution and in turn so are habitats such as peat bogs (composed largely of bog mosses) and temperate rainforests (with rich lichen and moss communities). Read more in the drop downs below.

Impacts on human health

When inhaled, air pollution can also impact human health, contributing to respiratory illness, heart disease and other health problems. See the Air Quality Management Area drop down below.

Improving 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, land use change and habitat restoration and creation.

Habitats such as trees and woodlands act as natural filters, capturing airborne pollutants and reducing nitrogen deposition. Creating buffer zones by planting species-rich grasslands or hedgerows around farmland helps to intercept nutrients before they reach vulnerable ecosystems.

Farmers have a vital role in tackling nitrogen pollution. Adopting low-emission practices, such as improved manure management and precision fertiliser and slurry spreading techniques, can significantly cut ammonia emissions.

The ecological impacts of nitrogen pollution – sensitive habitats

Nitrogen deposition in terrestrial ecosystems causes major changes in species composition, especially in nutrient-poor habitats. These areas often transition to species that thrive under high nitrogen availability, such as tall grasses, brambles and nettles, leading to less species richness and more 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 the ecosystem’s balance. Indirect effects include greater vulnerability of plants to frost, drought and pathogens, all of which impacts the species that depend on these habitats.

Under increased nitrogen, 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.

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, where it causes dramatic reductions in species diversity and changes 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 changes in species composition across affected ecosystems.

Many of these species and habitats, along with others that are sensitive to nitrogen pollution, form the features of our important protected sites. Maintaining their integrity is essential for meeting conservation objectives and legal obligations. Public bodies have a statutory duty to ensure that activities within their remit do not compromise the condition of these protected sites. This includes considering air quality impacts in planning decisions and working collaboratively to reduce nitrogen emissions.

Habitat restoration

High nitrogen deposition and raised ammonia and nitrogen oxide concentrations can make it hard to restore habitats or create new ones. Excess nitrogen changes 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. These effects on plant communities in turn affect the wildlife species that depend on them. Therefore, it’s vital to address nitrogen pollution if we are to achieve long-term habitat and species recovery and meet nature recovery targets.

Critical levels and critical loads for wildlife habitats

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 are typically 3 micrograms of pollutant per cubic metre (3 µg/m³) as an annual average for some vegetation (higher plants), with a lower threshold of 1 µg/m³ for sensitive species and habitats such as lichens and bryophytes. The critical level for nitrogen oxides is 30 µg/m³ for most vegetation types.

Many sensitive habitats in Devon already exceed critical nitrogen levels and loads.

Air Pollution Information System (APIS)

To see a map of critical levels and loads see the Air Pollution Information System (APIS). 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 in Devon are already exceeding critical loads and critical levels for pollutants, highlighting the urgent need to address this issue at scale.

The EA coordinates the UK Air Pollution Monitoring Network for Defra. As part of this the National Ammonia Monitoring Network (NAMN) provides gaseous ammonia concentrations (NH₃) monthly at 113 sites. There are limited monitoring sites in Devon.

Air Quality Management Areas (human health)

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 including parts of Crediton, Newton Abbot and Cullompton. However the number of current monitoring stations is limited. For more details and an interactive map see Defra’s AQMA map.

Emissions

Although nitrogen oxide emissions have fallen significantly in recent decades, ammonia levels in the UK 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, as detailed within the Environmental Improvement Plan, 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 expected to rise as the climate warms because higher temperatures increase the release of ammonia from manure and fertilisers. Longer growing seasons and changing agricultural practices further amplify this concerning trend.

2. What we need to do and where

Priority

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

Actions

Create and restore wildlife habitats to capture airborne pollutants (ammonia and nitrogen oxides). This can include:

Tree shelterbelts around emission sources. Plant trees near livestock housing, slurry stores, manure application areas and roads. See Find out more for a guidance note on shelterbelts.
Vegetation buffers around sensitive habitats. Establish woodland or shrub buffers around nitrogen-sensitive habitats to shield them from atmospheric ammonia and nitrogen deposition. Ensure that these buffers do not negatively impact on or lead to the loss of wildlife habitats.
Agroforestry systems. Integrate trees within farmland – see Trees outside Woodlands.
Habitat restoration. Restore and manage habitats to increase their resilience to nitrogen pollution. In some cases, excess nitrogen may need to be removed before habitat can be restored.

Reduce emissions from agriculture

Cover slurry and manure stores: Use impermeable covers or floating lids to prevent ammonia volatilization.
Follow best practice for slurry spreading (apply slurry using trailing shoe, injection or dribble bar instead of splash plate to reduce emissions and apply quickly under cool, moist conditions to minimise ammonia losses).
Improve livestock housing systems and adjust livestock diets: Use floor scrapers to reduce emissions inside housing. Feed less crude protein and balance diets to reduce nitrogen excretion.
Reduce emissions from fertilisers: Use fertiliser additives to slow conversion of nitrogen compounds and reduce ammonia and nitrous oxide emissions. Optimise fertiliser use using precision farming techniques. Use GPS-guided application and soil testing to match nutrient supply to crop demand. Switch to nitrate-based alternatives where appropriate to reduce ammonia volatilization.
Establish vegetation buffers and cover crops: Plant vegetation buffers and cover crops to capture residual nitrogen and prevent runoff or leaching.
Improve soil health and drainage: Improve soil health to increase nitrogen efficiency and reduce denitrification losses. See Rocks and Soils.
Soil remediation. Adopt techniques such as using deep-rooted plants, grasses or cover crops to absorb excess nitrogen into the soil.
Shift towards more plant-based diets. This would reduce demand for livestock products, leading to lower agricultural emissions from manure and fertiliser use.

Reduce emissions from road traffic

Fund/promote/use public transport, cycling and walking to reduce overall vehicle emissions.
Promote eco-driving techniques (such as steady speeds and reduced idling) to lower fuel consumption and emissions.
Encourage and be part of the transition to electric or hybrid vehicles.
Improve traffic flow to reduce the stop-start conditions that create more ammonia emissions and restrict high-emission vehicles in urban areas to cut emissions.

Embed air quality targets into relevant strategies such as local plans, green infrastructure and transport strategies.

Monitoring and awareness

Support and promote citizen science programmes to better monitor and understand air quality, such as the LicheN app. See case study below.
Increase monitoring and modelling of air quality across Devon to ensure accurate data on ammonia and nitrogen levels, identify hotspots and inform targeted mitigation measures.
Coverage of the National Ammonia Monitoring Network (NAMN) is sparse and there are 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.
Raise awareness of air quality issues amongst all sectors (local authorities, farming, communities etc). By highlighting the links between air quality, biodiversity and human health, we can encourage collective action.

Where to focus action

The actions listed above are needed across Devon but can be prioritised to the following areas:

At emission sources (farms, roads and urban areas)
In and around sensitive habitats including designated sites (SACs, SPAs, SSSIs)
Prioritise mitigation where critical loads and levels are high or exceeded. Focus emissions reduction and shielding on holdings that are closest to and sit immediately upwind of protected areas, whether, for example, a farm unit, an industrial yard or a busy stretch of road.
Cities, towns and villages to most benefit public health.

No Opportunity Areas have been mapped in the LNRS for air quality as actions are widespread. Use tools such as the Air Pollution Information System (APIS), mapping such as the Air Quality Management Areas and citizen science such as the LichenApp to help identify where action is most needed.

3. Inspiration

Case studies

Collaborative plans and action

Shared Nitrogen Action Plans (SNAPs) were produced by Natural England for designated sites and are being replaced by Air Quality Protected Site Strategies. A few examples include:

Fenn’s & Whixall Mosses Shared Nitrogen Action Plan (SNAP): Shropshire/Wales: A collaborative SNAP was 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 were held to identify emission sources and mitigation options. Measures included covering slurry stores, hard standing at feeding stations and slurry injection. The measures will help protect rare bog habitats, improve water quality and support carbon storage

Braunton Burrows Shared Nitrogen Action Plan (SNAP): North Devon -The site was identified as a priority 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 was applied to engage farmers and reduce ammonia emissions near the site. Webinar: Introduction to SNAPs at Braunton Burrows

Nitrogen Futures Project: UK-Wide

This was a Defra-funded initiative led by UKCEH and partners to model nitrogen reduction scenarios and spatial targeting. It produced evidence to prioritise mitigation near sensitive habitats and inform SNAP development.

Ammonia Reduction by Trees (ART Project): Cumbria

This was a Natural England-funded project led by UK Centre for Ecology & Hydrology. The project aimed to provide new scientific evidence on how tree planting can reduce the impact of ammonia emissions from farming to inform better advice, guidance and incentives and encourage farmers to plant tree shelterbelts. It tested tree shelterbelts around poultry and dairy farms and found that they significantly reduced ammonia plumes from livestock housing, improved air quality and reduced nitrogen deposition on nearby sensitive habitats. Other benefits include carbon sequestration, improved biodiversity and shelter for livestock.

LicheN app

A mobile app that uses lichens to assess atmospheric nitrogen pollution effects has been developed by the Centre for Ecology & Hydrology (CEH). The app includes:
– Lichen identification key guide for nitrogen sensitive and tolerant species;
– Simple Recording system for surveying lichens on tree trunks and branches;
– Field guide with instructions on carrying out the survey;
– Auto-calculated and robust method to determine nitrogen pollution levels using a standardised nitrogen air quality index (NAQI);
– Informs the public of their local nitrogen air quality based on four pollutant zones – ‘Clean’, ‘At risk’, ‘Nitrogen Polluted’ or ‘Very Nitrogen Polluted’