Cleaner Air for Scotland 2 - Towards a Better Place for Everyone

A new air quality strategy to replace Cleaner Air for Scotland - The Road to a Healthier Future, setting out the Scottish Government's air quality policy framework for the next five years and a series of actions to deliver further air quality improvements.

7. Tackling Non-Transport Emissions Sources

110. Although the contribution of all the major emissions sources to overall air pollution levels was highlighted in CAFS, the focus in terms of actions was very much on transport emissions. Whilst road transport in urban areas remains the issue of most concern in relation to air quality and its impact on human health, the CAFS review emphasised the need for a greater focus on other sectors, notably domestic (household) combustion and agriculture.

Domestic (household) combustion

111. The main pollutants of concern arising from domestic combustion are PM10, PM2.5, nitrogen dioxide and sulphur dioxide. A summary of domestic combustion emission sources, pollutants and trends in Scotland can be found in the CAFS review emissions working group report.

Figure 7: Relative emissions from different types of domestic appliance
Burning solid fuel in an open fire produces the most emissions, with electric heating systems producing the least emissions.

(Source: Defra)

112. The continuing uncertainty over emissions levels from domestic burning means that setting precise reduction targets is difficult. Further research into the proportion of emissions attributable to domestic burning, as well as assessment of type and source of emissions, is required. Further targeted monitoring of PM2.5 levels particularly in urban areas is desirable, subject to finding an agreed method of measurement. A further complicating factor is that around 50% of local ambient PM2.5 concentrations can relate to long-range transboundary transport from outwith Scotland.[83] This suggests that a consistent national, as opposed to local, approach will have a large impact on reducing domestic combustion emissions.

113. Actions to tackle domestic sources of air pollution need to be coordinated with related policies and actions, especially those included in the updated Climate Change Plan and those targeted at building standards and energy efficiency. The upcoming Heat Decarbonisation Policy Statement and updated Energy Efficient Scotland Routemap will set out our policy proposals and actions to drive down emissions from heating our homes and buildings. This is central to meeting the ambitious climate change targets set out in the Climate Change (Emissions Reduction Targets) (Scotland) Act 2019 (CAA). As well as delivering reductions in CO2 emissions, these actions will also contribute to reduced air pollution by reducing the need for supplementary domestic heating. The Committee on Climate Change (CCC), which is the Scottish Government's statutory advisor on climate change, produced a report in 2018, Biomass in a Low Carbon Economy,[84] which explored how biomass could be prioritised for the most valuable end use. The CCC recommended a transition on the use of biomass towards construction and Bioenergy Carbon Capture and Storage (BECCS), with government support moving away from biomass boilers to heat buildings where there are other low carbon alternatives.

114. We know that 79% of households using solid mineral fuel in Scotland as their primary fuel type are in rural areas[85] and that around half of households (46%) using solid mineral fuels in Scotland are fuel poor compared to the national average of 25%. Emissions from burning wood depend on the type of appliance and the dryness of the wood. Other factors include the way the householder burns the wood and uses any appliance. Maintenance of the appliance and the chimney also have an impact, as do burning practices. For solid fuel, the amount of sulphur released depends on the sulphur content of the fuel.

115. Current legislation for controlling domestic combustion emissions derives from the Clean Air Act 1993 and associated regulations. This is based around the establishment of Smoke Control Areas (SCAs). Only appliances which have passed tests to demonstrate that they emit a minimal level of smoke are permitted for use in SCAs. Similar tests apply for fuels; only exempted fuels can be used in non permitted appliances. However the Clean Air Act provisions are becoming increasingly outdated and have little relevance to modern air quality legislation. This results in the anomaly that appliances and fuels may pass the SCA tests without necessarily being compliant with LAQM air quality objectives.

116. In addition, the provisions are difficult for local authorities to enforce and are poorly understood by members of the public. They also do nothing to address the impact of domestic combustion emissions outwith SCAs, nor the recent trend to install woodburning stoves in urban areas as a secondary or amenity heating source. The SCA approach is therefore, to a large extent, ineffective in ensuring that air pollution from domestic combustion is properly controlled.

117. At present flues, where they might constitute a material change, which form part of a domestic biomass system have permitted development rights (PDR). PDR means that for many/most such flues an application for planning permission is not required for their installation. PDR do not apply to flues located within an Air Quality Management Area, where they are attached to the principal elevation of a building in a conservation area or World Heritage Site, or if the flue projects more than one metre from the wall or roof. As the flue height to ensure dispersal of pollutants is likely to be unique to each installation, those flues that need to be taller than one metre from the wall or roof may require planning permission.

118. Whilst planning controls are wide-ranging, they cannot necessarily control specific aspects of technology and do not generally extend to works to the interior of buildings. The internal elements of the biomass system (including the furnace) do not require planning permission.[86] Planning permission is required for development, including material changes to the exterior of a building.

119. In the absence of appropriate control mechanisms it is difficult for local authorities to accurately assess the amount and location of appliances in their areas. In urban areas, it is often the cumulative effect of a number of appliances in a relatively small geographic area which makes a notable contribution to overall emissions, rather than emissions from an individual stove or fireplace, although locally it may be a single installation and its use which causes immediate concern for some residents.

120. Defra's Clean Air Strategy for England[87] sets out several proposals for addressing domestic combustion emissions that would also be of relevance in Scotland. The proposals cover both appliances and fuels, and focus on three key areas: the right appliance burning the right fuel, consumer education and proper installation/maintenance.

121. For appliances, the focus is on implementing and promoting Ecodesign,[88] the EU-wide programme to lower emissions and improve efficiency. The Ecodesign legislation forms part of retained EU law and will therefore continue to have effect after the UK's exit from the EU. Although the Ecodesign standards do not have legal effect until 2022, the stove industry has commenced initiatives to promote early uptake. The Stove Industry Alliance (SIA) is marketing Ecodesign Ready stoves, of which there are already over 400 models available, accounting for around 40% of current sales UK-wide. The SIA is also currently developing a scheme that will encourage appliance manufactures to produce appliances with even lower emissions than the Ecodesign requirements. Consumers will be able to clearly identify stoves with lower emissions than Ecodesign from the accreditation label. The PM limit in Ecodesign is 55% lower than in the current UK testing regime for exempting appliances for use in SCAs.

122. Ecodesign standards only apply to new appliances. Therefore a concerted effort is needed to encourage householders to replace their open fires and upgrade their existing stoves, given the significant emissions reductions that this will achieve (90% for open fires and, depending on the age of the appliance, up to 80% for stoves).

123. For fuels, additional support for local authorities can be provided by enforcing standards at point of sale rather than at point of use. Enforcement through trading standards in this way would mean retailers facing significantly greater scrutiny and detection of infringements. This approach can be further enhanced by restricting or banning the sale of the most polluting fuels, and ensuring that remaining fuels are produced and used in such a way that emissions are minimised. Setting a mandatory minimum renewables content for manufactured smokeless fuels could also have a positive impact on emissions.

124. Reducing the moisture content of wood for burning is especially important in this context, with dried wood (less than 20% moisture content) having around 80% lower emissions than wet wood. Woodsure, the UK's woodfuel accreditation scheme, launched the Ready to Burn[89] scheme in 2017 which provides a certification mark to woodfuel suppliers who can demonstrate that the moisture content of their product is below 20%. Besides potential controls on the sale of wet wood, it will also be necessary to consider complementary approaches such as promoting locally produced and sustainable wood sources, alongside the benefits of seasoning by air drying. Such an approach could have wide-reaching positive impacts on Scotland's rural economy.

125. Regulatory control on its own will be insufficient to effect the necessary changes. Education for consumers is also important, both in terms of correct operation of appliances and using the right fuel for the appliance. Burnright[90] is an educational campaign which provides a range of materials and resources for stove users. Advice and support is also available to households looking to switch to a low-carbon heating solution via Home Energy Scotland.[91] Chimney sweeps are potentially well placed to play a key role in the educational process. A register of installers, engineers and sweeps who could report back on installations and advice given may be useful in this context, as could official recognition for trained and approved sweeps.

126. It is also important to consider the impact of non-domestic biomass emissions. In 2017 the Scottish Government published its energy strategy[92] which sets out a vision for energy production and use in Scotland to 2050. Meeting the ambitious targets set out in that strategy will require a range of energy sources to be utilised, including biomass.

127. In general, the larger the biomass unit, the easier it is to control the combustion conditions and therefore the easier it is to reduce the level of air pollution emissions. A single large boiler will tend to produce lower emissions than a series of smaller units using the same fuel and for the same energy output. It is more difficult to fit additional pollution abatement equipment to smaller units, and so emission reductions must rely on good boiler design, operation and maintenance. This lower size range includes most small-scale domestic wood burning stoves and boilers. Encouraging the use of plant scaled to make best use of available heat and biomass resource, for example in conjunction with the development of heat networks, will result in a system where air quality emissions are easier to control than from a larger number of small plant.

128. Where certain conditions are met, the impacts of biomass deployment for heat production can be managed to minimise impacts on local air quality. These conditions are:

  • all new biomass plant are of high quality, corresponding to the best performing units currently on the market;
  • the majority of biomass heat uptake replaces or displaces existing coal- and oil-fired heating;
  • the majority of uptake is located off the gas grid and therefore generally away from densely populated urban areas; and
  • levels of uptake where a local authority has declared an AQMA are substantially lower than other areas.

129. As conditions move away from this scenario, the adverse/negative impacts on air quality and public health increase significantly.


We will:

  • Encourage uptake of Ecodesign stoves through Ecodesign Ready and other initiatives, along with consideration of how best to address widespread replacement of pre-Ecodesign appliances.
  • Work with business and industry to support and further develop educational schemes such as Woodsure and Ready to Burn, including manufacturers, suppliers and users of both fuels and appliances.
  • Take forward, working with businesses that may be affected and other interested parties, potential measures to control the supply of the most polluting domestic fuels – including a ban on house coal, restricting the sulphur content of smokeless fuels to 2%, prohibiting the sale of certain types of wet wood and introduction of a minimum renewables content for manufactured smokeless fuels. In taking forward this work, we are mindful that any new measures would require to be implemented over a period of time, such as a transitional period during which businesses could adapt to the new requirements without disproportionate costs.
  • In developing policies and programmes to support households and businesses in transitioning to low-carbon heating solutions, we will consider the needs of those affected by any controls on the supply of the most polluting domestic fuels.
  • Consider with local government what changes are needed to the current permitted development rights for flues for woodburning stoves and biomass boilers.
  • Work with local government and SEPA to consider revision of the Clean Air Act 1993.
  • Commission work to provide further evidence on the proportion of PM emissions and other key pollutants attributable to domestic burning in Scotland, together with geographic and demographic distribution of domestic burning.


130. Agricultural emissions related to air quality are dominated by ammonia (NH3) and agriculture accounts for around 90% of total ammonia emissions in Scotland. Unlike emissions of the other main air pollutants, which have declined significantly over the last 30 years, ammonia levels have decreased by only around 12% in this period. Even this modest reduction has started to reverse slightly since 2012. Sources such as large intensive pig and poultry units above certain capacities are classed as industrial installations, and are regulated under the Industrial Emissions Directive and the Pollution Prevention and Control (Scotland) Regulations 2012.[93] However, there are currently no regulatory mechanisms in place in the UK for other agricultural ammonia emission sources, which make up the bulk of emissions. Further background on ammonia can be found in the report by the CAFS review emissions working group.

Figure 8: Changes in ammonia emissions in Scotland since 1990
Ammonia emissions have declined by 16% since 1990. Agriculture sources have dominated the inventory throughout the time-series, with cattle manure management accounting for at least 30% of the emissions from this sector across the entire time-series.

(Source: National Atmospheric Emissions Inventory)

131. Ammonia is a nitrogen-based gas which is released when slurries, manures and nitrogen fertilisers come into contact with the air. It is very reactive and combines readily with acids and particulates. These chemical reaction products have a longer atmospheric lifetime, are harmful to human health and result in regional and long-range transport of nitrogen compounds. As air pollution does not stop at country boundaries, pollutants emitted both within Scotland and elsewhere can contribute to impacts a long distance away. The resulting pollution through ammonia and reaction products therefore occurs both close to sources and at greater distances (including remote areas of Scotland) through atmospheric dispersion and deposition onto sensitive vegetation. Nitrogen deposition (from both ammonia emissions and nitrogen oxides) effectively provides fertiliser from the air, leading to the eutrophication of our naturally nutrient-poor ecosystems and related damage to plant and animal species through eutrophication and acidification. Ammonia also produces odours and related nuisance effects, thereby impacting on both human and ecosystem health.

Figure 9: Ammonia sources and impacts

Sources of ammonia

Agriculture (including anaerobic digestion)

Impacts of ammonia emissions

Ammonia reacts in the atmosphere to produce particulate matter which has significant health impacts, including cardiovascular and respiratory disease.

Ammonia emissions can travel long distances and combine with urban NOx contributing to smog

Effects of ammonium deposition

Acidification of habitats

Excessive nitrogen in habitats

Reduction in biodiversity

(Source: Defra)

132. The most effective measures to reduce these impacts are those which directly reduce emissions of ammonia to the atmosphere, as opposed to attempting to introduce post-emission mitigation. Other emission mitigation strategies can also be useful and include physical separation of sensitive receptors from local sources through planning interventions (pre-emission) and the use of shelterbelts to enhance both dispersion through increasing turbulence and recapture of ammonia close to source (post-emission, secondary mitigation).

133. Ammonia, and therefore nitrogen content of fertiliser, can be lost whenever slurry or manure is exposed to the atmosphere; practices that reduce exposure in housing, storage or during application can therefore reduce losses and result in more efficient use. Retaining as much nitrogen as possible by reducing losses to the atmosphere or leaching into, for example, ground or surface water bodies will maximise nitrogen use efficiency and thus optimise returns on farm. However, care must be taken and measures will need to be carefully assessed for any potential pollution swapping, e.g. when reducing emissions to air may lead to increased leaching into ground water and eutrophication of water bodies.

134. The Gothenburg Protocol requires countries to produce a national advisory code of good agricultural practice to control ammonia emissions. Guidance was provided in the UNECE Framework Code for Good Agricultural Practice for Reducing Ammonia Emissions[94] and in Options for Ammonia Mitigation from the Task Force on Reactive Nitrogen.[95] Therefore the development of such a code of practice within Scotland has been identified as requiring consideration. Although similar codes have either been or are being produced in other parts of the UK, Scotland's climate, soils, topography and agricultural practices will need to be considered to inform the development of any such Scottish guidance.

135. Recent work done on the health and environment impacts, and on the costs and benefits of ammonia reduction measures, by the Air Quality Expert Group[96] and others[97], [98] is a useful basis for considering the range of issues which needs to be covered. There is already good awareness on many farms of measures to improve nitrogen and wider nutrient use efficiency through good soil, fertiliser, manure and slurry management practices. However, increasing awareness and implementation of these measures can help to further reduce ammonia emissions. Given that the effects on human health and ecosystems/biodiversity of agricultural ammonia emissions and other pollutants have not received significant attention in air quality policy to date, there is a need to ensure that there is a strong focus on education, engagement and awareness raising around good practice.

136. While there are opportunities to deliver both emission reductions and improved business performance and sustainability through guidance, mitigation practices may require investment in infrastructure and new equipment, such as low emission slurry spreading equipment or covers for slurry storage. The Scottish Government has already taken action to support farmers to make such investments through the pilot Sustainable Agriculture Capital Grant Scheme.[99] The Scottish Government established five farmer-led groups to provide advice and proposals on action key agricultural sectors should take to cut emissions and tackle climate change, including considering how the agricultural industry can be strategically supported in the investments needed to transition to a sustainable low emission future, both in terms of ammonia and greenhouse gases. Their reports were made available in March 2021[100] and the detailed proposals and ideas within these reports are now being considered by government as it begins its work to create a new rural support scheme as required to do by statute by 2026.

137. Given the synergies between the practices that can mitigate ammonia emissions and greenhouse gases, it is clear that action must be considered as part of the wider work of the Climate Change Plan and its update in light of Scotland's new net zero greenhouse gas emissions targets. This strategy provides the framework for involving the agriculture and wider land management sectors in considering how to target these complex messages to farmers and agricultural contractors.

138. Related to the lack of direct policy focus, in Scotland until recently there has been little coverage of ammonia in the agricultural press. A productive approach to initial engagement with the sector could be to ensure that ammonia emissions feature prominently within farmer-focused messages on nutrient management and related good practice. The concept of retaining the nutrient value of manures and fertilisers coupled with messaging related to increased productivity and lower costs has helped to promote positive engagement and this should continue to be the case. It will also be important to recognise that, in addition to the direct gains that farmers achieve through reduced ammonia emissions, there is also a positive impact on human and environmental health.

139. The creation of a Scottish Nitrogen Balance Sheet (SNBS) will provide a baseline on Scotland's current nitrogen use efficiency, i.e. the proportion of nitrogen used for its intended purpose vs. losses to the environment, at the national scale. This baseline creates a new type of cross-sectoral evidence base that quantifies the uses and losses of nitrogen and enables identification of more and less nitrogen use-efficient processes, and will inform future decision making across a range of policy areas. These include agriculture, as well as transport, waste management and others. A national-scale SNBS will enable tracking of progress over time and dialogue to focus on policies that provide win-win outcomes rather than shifting nitrogen losses (with air quality and/or climate change impacts) within or between sectors. From the CAFS 2 perspective, the SNBS will be an important tool for assessing progress with ammonia reduction approaches to be included in the code of good practice for agriculture (as well as for progress with nitrogen emissions from combustion).

140. The fact that, almost uniquely amongst the main air pollutants, ammonia levels have not fallen significantly suggests that additional interventions are now required to address issues in the agriculture sector, through awareness raising and supporting farmers and crofters to take up best practice measures. This includes the need to ensure better management of fertiliser application and management in relation to dairy and beef as well as pig and poultry units, both in general terms and specifically where there is proximity to urban areas and sensitive ecosystems. Tackling these should also help to address odour complaints. Large intensive pig and poultry units are already regulated (see paragraph 118). These are sites which have a capacity of more than 40,000 poultry, 2,000 fattening pigs or 700 sows. Further consideration with the sector is required on options to reduce emissions from large scale units, including whether currently unregulated activities be brought into consideration in existing legal frameworks, alongside an improved understanding of the implications of these options.

141. In a wider agricultural context, the Muirburn Code[101] advises land managers and others on best practice and legislation regarding the use of fire as a land management tool. The Code, which was most recently updated in 2017, does not consider in detail the health and amenity impacts of visible smokes. This is an issue requiring further consideration.


We will:

  • Continue to share best practice and raise awareness of air pollutants and greenhouse gases, along with actions that farmers and crofters can take to minimise their environmental impact while improving efficiency.
  • Work directly with farmers, supported by scientific and economic expertise to co-develop new ways of working to better contribute towards delivering Scotland's climate change and environmental outcomes.
  • Consider options to reduce emissions from large scale units in consultation with the agricultural sector, aligning with broader policy development around future rural support.
  • Work together with SEPA and the agricultural industry to develop a voluntary code of good agricultural practice for improving air quality in Scotland.
  • Undertake a specific assessment of visible smokes and their health and amenity impacts arising from Muirburn. The assessment will consider pollution characteristics and downwind impacts into populated areas, along with appropriate management responses and interventions.

Atmospheric nitrogen and environmental impacts

142. Compared with human health effects, the damage caused by air pollution on ecosystems may be less obvious and more difficult to identify on the ground (due to the specialist knowledge needed to identify symptoms and effects), and it remains important to disseminate knowledge on how to spot signs and raise awareness. Poor air quality and direct deposition of pollutants can cause damage to plants and animals, and to aquatic and terrestrial ecosystems, impacting on biodiversity through its contribution to eutrophication, acidification and otherwise damaging sensitive habitats. This can result in species loss, habitat composition changes and increased sensitivity of organisms to environmental stresses.

143. Eutrophication is caused by deposition of nitrogen oxides and ammonia. Nitrogen oxides can travel long distances in the atmosphere before being deposited, affecting upland and montane areas, while ammonia is shorter-lived and deposited closer to its source, more often affecting Scotland's lowland areas. Emissions of nitrogen oxides have decreased considerably since peaking in the period 1970-1990, and this has led to considerable decreases in nitrogen deposition across the UK. The far more modest emission reductions of ammonia since the 1980s have also contributed to deposition reductions, but to a lesser extent due to changes in atmospheric chemistry. These changes, largely due to the very successful mitigation of sulphur dioxide emissions from combustion processes, mean that the main result has been reduced exports of emissions to mainland Europe and decreased risk of acidification. Decreases in nitrogen deposition in the UK are mainly due to mitigation of emissions of nitrogen oxides both in the UK and Europe. Currently, critical loads for nitrogen (habitat-specific damage thresholds for atmospheric nitrogen deposition) are exceeded in 34% of habitats sensitive to eutrophication and 76% of Special Areas of Conservation in Scotland (SACS).[102]

144. The Nitrogen Futures project, which was published in autumn 2020 by the JNCC in partnership with the UK administrations and conservation agencies,[103] is bringing together available data on nitrogen emissions and estimating the environmental benefits of different possible policy options and ambition levels to reduce pollution. As part of this project, the research consortium tested possible local measures to reduce and mitigate nitrogen pollution, in the context of a 2030-2040+ time scale, for example:

  • predict future atmospheric nitrogen emissions, concentrations, deposition and environmental impacts from the implementation of the NAPCP, including reduction in emissions from power generation and industry, and the use of catalytic reduction technology;
  • introducing low emission 'buffer zones' for agricultural emissions around protected nature conservation sites;
  • planting trees to recapture airborne nitrogen; and
  • initiatives to target pollution from transport and combustion sources.


We will:

  • Use available data and other information to set a Scottish contribution for overall UK ammonia emissions reduction targets required under the National Emission Ceilings Directive.
  • Support investigation into the method of assessing risk of significant harmful ecological effects from atmospheric nitrogen (nitrogen deposition and elevated concentrations of ammonia and NOx), comparing critical loads/levels with dose-response or other options.
  • Assess the potential costs of implementing identified improvements to the current site condition monitoring of designated conservation sites, to improve on current methods which don't detect air pollution effects.
  • Review current monitoring of terrestrial ecosystems (and air pollution effects) in Scotland.



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