Evaluation of the effects of PM2.5 due to domestic solid fuel burning on health outcomes in Scotland

Executive Summary

The detrimental impacts on health associated with exposure to air pollution are well documented. Fine particulate matter (or PM_2.5) can penetrate deep into the lungs and bloodstream, and are associated with a wide range of health issues, from severe respiratory and cardiovascular conditions to dementia and diabetes. Domestic solid fuel burning is a key source of PM_2.5: according to the UK’s National Atmospheric Emissions Inventory (NAEI), small combustion was the largest source of PM_2.5 emissions in 2024 accounting for 25% of total UK PM_2.5 emissions, with residential wood burning alone accounting for over 40% of this category. In terms of pollutant concentrations in air as a result of these emissions, modelling by UKCEH in 2025 estimated of population-weighted mean PM_2.5 concentration across all-sources in Scotland of 7.11 µg m^-3, with a contribution from Scottish solid fuel burning of 0.359 µg m^-3 (approximately 5%).

Data on patterns of domestic burning has limitations, however the latest survey evidence suggests that overall burning prevalence in Scotland has been increasing, rising from 14.9% in 2018–19 to 22.2% of households in 2022–23, in which indoor burning increased from 6.8% to 11.3%. Information on who is burning is also incomplete: although there is evidence to suggest high levels of burning amongst more affluent households, some evidence also suggests greater burning in more deprived areas in Scotland. The Cleaner Air for Scotland 2 (CAFS2) strategy defined a range of actions aimed at improving health through tackling this source. This study assesses the potential health benefits of further policy actions affecting domestic solid fuel burning in Scotland.

Current levels of burning were estimated to be associated each year with 160 deaths (with an associated life years lost of 1,814), 38 respiratory hospital admissions, and new cases of ischemic heart disease (23), stroke (27), lung cancer (13) and asthma in children (38). There are also ‘productivity’ impacts, with pollution linked to 18,400 working days lost through absenteeism, 5,000 care hours lost, 2,100 volunteering hours lost and a further 6,400 working days lost through presenteeism (known as minor restricted activity days, or mRADs). When expressed in monetary terms, the detrimental impacts of domestic solid fuel burning on health present a cost each year to Scottish society of around £117 million. Furthermore, the majority of health impacts are concentrated in a small number of areas: 68% of impacts are observed across 9 (out of total 32) Local Authority areas, with those most affected all lying in urban or peri-urban areas in the corridor between or in close proximity to Glasgow and Edinburgh. Between demographic groups, exposure appears to be higher for areas: with greater numbers of black and minority ethnic residents, with higher levels of young adult residents, and that are either the most or least deprived.

This study identified a long-list of potential measures to address emissions from domestic solid fuel use, divided between: operational measures, stock renewal, restricting use and public information. The measures can be defined according to two basic policy aims: (1) “burn better” by improving the emission performance of domestic burning; and (2) “burn less” by reducing the frequency of burning and/or numbers of households burning. Successful policy packages are likely to contain measures from both “burn better” and “burn less” categories, and allow the balance between to shift between the categories depending on location and the availability of alternative heating options. There will also need to be an integration across governance levels, i.e. from national to local, with clear policy aims for each. Based on a screening of the long-list against a set of criteria, three options were taken forward for more detailed modelling:

1) Burn less: The main component of this scenario is a nation-wide information campaign, aimed at both better use of appliances and the selection of correct fuels, and an increasing awareness of impacts on health.

2) Burn better: This scenario focusses on the regulation of fuels as well as an information campaign on the selection of correct fuels. It includes a campaign of mandatory chimney sweeping and appliance inspection, which has proved effective at eliminating “wet” wood burning in Germany.

3) Targeted stock upgrades: In this scenario, a program of upgrading older fireplaces and stoves is implemented in the six Local Authorities most impacted by solid fuel emissions. The precise upgrade mechanism has not been defined, but could include one or both of mandatory measures or means-tested financial support.

For each shortlisted option the anticipated change in annual average PM_2.5 concentrations, mapped across Scotland, has been quantified. For Policy 1 the impacts were assumed to be modest, but widespread, and a uniform 1% reduction of solid fuel burning across all fuels and areas in Scotland was applied (in line with previous impact studies by the Scottish Government and Defra). Policy 2 was assumed to result in a shift of solid fuel burning away from the most polluting fuels. Policy 3 was assumed to result in the upgrade of all open fireplaces and ‘old’ stoves to ‘modern’ stoves (at least Eco-Design standard) within the six targeted Local Authorities. The resulting magnitude of change in air pollution is estimated to be fairly small for all scenarios, but the largest change is found for Policy 2, driven by reductions from wood and MSF. The primary PM_2.5 emissions and SO₂ emissions from MSF are reduced by this scenario, but SO₂ emissions from wood and former coal burners increase, reflecting the relatively high emissions of SO₂ even from the ‘low sulphur’ MSF. The magnitude of changes for Policy 3 are limited by the initial proportions of old stoves and open fireplaces, along with the increase in gaseous emissions and thus secondary PM_2.5 from coal burning.

The scale of health benefits delivered by each policy option scale in line with the reductions in population weighted exposure estimated in the air quality modelling. Policy 2 delivers the most significant overall health benefits – it reduces attributable deaths per annum by 14.3, compared to a reduction of 4.9 deaths per annum under Policy 3 and 1.8 deaths per annum under Policy 1. Alongside impacts on attributable deaths, the scenarios also deliver benefits through reductions in hospital admissions, new cases of disease, and work days lost. Across Local Authorities, the effects of Policy 1 are strongest in the Local Authorities with higher concentrations associated with solid fuel burning, moving in proportion to the reduction in fuel use. Policy 2 has a varied impact on different Local Authorities, with the greatest effect being in those with a higher prevalence of MSF use as a fuel, which sees the greatest reduction in emissions under Policy 2. The effects of Policy 3 are strongest in the targeted Local Authorities but are also apparent in those which border the targeted Local Authorities within which stoves are upgraded.

Several key messages emerge from this analysis:

• Most of the existing health effects of domestic solid fuel burning are in urban areas: while the proportion of households using solid fuels tend to be higher in rural areas, the density of urban areas means that more people are exposed to air pollution from household burning. This also means that the greatest potential health benefits from reducing solid fuel emissions are also in urban areas, which is also where alternative, secure sources of heat are more readily available (both mains gas and electricity). In fact, 68% of the impacts observed across 9 (out of total 32) Local Authority areas which all lie in the corridor between or in close proximity to Glasgow and Edinburgh.
• The relatively modest improvement from Policy 3 (stock upgrades) could be related to very uncertain emission factors for both existing and new stock, for different stove and fuel types. More work is needed to improve emission factors, by both testing in the UK and reviewing testing done elsewhere, and also on the costs and availability of very low emission appliances (such as those meeting the Blue Angel standard).
• The modest improvement from Policy 3 could also be related to the fact that many stoves, especially in urban areas, will have been installed relatively recently. To drive significant reductions in emissions would require aligning with a much more ambitious emissions standard (compared to current ‘modern’ burners), and/or encouraging switching away from burning altogether (to, for example, electricity-based forms of heating).
• Policy 1 (Burn Less) was modelled as a uniform 1% reduction in emissions across Scotland. However, the impact of an information campaign of this nature is likely to be more nuanced and could potentially be more successful in urban areas, where the health impacts are greatest. A 1% reduction may be conservative and a larger reduction in fuel use might be achievable through more far-reaching action.
• The three scenarios are not mutually exclusive and there may be additive benefits from implementing a more comprehensive, mixed approach. Information campaigns, as well as having an effect in and of themselves, can help facilitate more interventionist measures.
• The outcomes emphasise the importance of considering spatial and demographic variations when developing policy, as the impact of interventions can potentially differ across Local Authorities, between urban and rural areas and on different demographic groups. Further work is needed in this area in order to identify specific groups which may be inequitably affected by the policy approaches analysed.
• Uncertainties in the modelling significantly influence the estimated health impacts, particularly regarding emission factors and overall fuel allocation to Scotland. These uncertainties need to be transparent, while ensuring clear public messaging on the reason for policy action on solid fuel burning.