Project Lead
Challenges
Poor air quality continues to harm public health and the natural environment in Scotland. Progress in improving air quality is both uncertain (due to an inadequate evidence base) and slow (due partly to uncertainty about the efficacy, cost, and consequences of improvement measures). Studies suggest that biomass burning makes a very significant contribution to concentrations of particular matter (PM) in the air, which can lead to serious health problems. Particulates are classified according to size. The UK is currently focused on measuring the fractions of PM where particles are less than 10 micrometres in diameter (PM10) and less than 2.5 micrometres in diameter (PM2.5) based on the latest evidence on the effects of PM on health. Even in a smoke-controlled area like London, 10% of the winter PM10 has been attributed to wood smoke.
The contribution to PM2.5 is larger and can exceed that from tailpipe emissions. Air pollution, especially PM2.5, is highly correlated with various adverse health impacts. Particulates contribute to climate change, for example: a) emission savings due to the replacement of fossil fuels, b) the indirect effect of black carbon emitted from fossil fuels, and c) variable embodied carbon in imported biofuels used in Scotland.
Comparatively little is known for the Scottish context, where solid fuel combustion is used both as a traditional heat source, as well as increasingly as a renewable heat source, encouraged by policies such as the Renewable Heat Incentive, Feed-in Tariffs, and the Merton rule for on-site renewable heating for new builds. The only measurement evidence for the proportion of PM2.5 from biomass burning in Scotland comes from the UK’s black carbon network, from which a wood-burning proxy can be derived as brown carbon from aethalometer measurements. Winter contributions of wood smoke to total PM10 ranged between 3-6% at background sites (Auchencorth) to 6-8% at urban sites (Edinburgh and Glasgow). The relative contribution to PM2.5 could not be established using older data but is likely to be significantly larger. No information currently exists for populated regions outside of smoke-controlled areas (for example, rural village settings) where solid fuel use likely lies above the UK average. For example, Scotland, making up 8.2% of the UK population accounts for 30% of the UK’s domestic Renewable Heat Incentive biomass installations.
Questions
- What are the environmental, climate change, health and other effects of biomass burning taking place in Scottish urban settings? How does biomass burning contribute to the climate-carbon cycle?
- What is the impact of biomass burning in urban areas on local air quality, and how do we measure success, including co-benefits?
- What are the options for mitigating negative impacts on air quality, climate change and health?
Solutions
We are providing quantified evidence on domestic biomass burning and its contribution to fine particulate emissions (PM2.5) and understanding the impact of fine particulate emissions due to domestic biomass burning on human health across Scotland.
Biomass burning quantification
Biomass burning inventorying
We build on the work of others to improve the emissions inventory for Scotland. Emission factors are highly dependent on fuel type and burning conditions which in turn are dictated by fuel quality (incl. moisture), type of appliance, and operation. To capture this variability and tailor the information to Scottish conditions, we are reviewing the latest literature for emission factors and utilising spatial statistics. In addition, we are conducting targeted surveys on fuel use where required to supplement recent work by KANTAR.
Measurement quantification of the biomass burning contribution to PM2.5
We are exploiting existing and emerging data from the black carbon network and three English urban supersites that perform Aerosol Chemical Speciation Monitor measurements (London, Birmingham, Manchester) under the Clean Air Strategic Priority Fund. In addition, we conduct measurements of the biomass burning component at two contrasting sites for which data are lacking: a rural village/ and small town setting not subject to smoke control, and a larger smoke-controlled city where concentrations are expected to be elevated due to local topography and meteorology. We are comparing the contribution of Scottish and wider UK biomass burning emissions through modelling different scenarios.
Modelling quantification of the biomass burning contribution to PM2.5
We are estimating the contribution of domestic and institutional biomass burning to PM2.5 across Scotland. The contribution of Scottish and wider UK biomass burning emissions is being quantified through the comparison of different emission scenarios for different regions in our model. The results are being assessed against the new and existing measurements. We are comparing the biomass burning impact with the impact from other sources, including agriculture and from sources outside Scotland. This will inform the prioritisation of tackling domestic biomass burning compared with other short-term actions proposed in the Clean Air for Scotland 2 Strategy.
Quantification of the effect of PM2.5 concentration levels due to biomass burning on health outcomes
Particulate air pollution, especially PM2.5, is highly correlated with various adverse health impacts. The Cleaner Air for Scotland 2 Strategy indicates that there is a need for quantification of the spatial effect of biomass burning on air quality in urban and rural centres across Scotland as well as a need for the evaluation of the effect of PM2.5 concentrations due to biomass burning on health outcomes. This work focuses on quantifying the spatial distribution of PM2.5 levels that are generated by biomass burning and their effect on human health outcomes across Scotland.
We are using the Scottish Health Survey and the National Records of Scotland to identify the spatial-temporal distribution of life expectancy and respiratory or coronary diseases in Scotland. This information is being employed to identify the spatial sources of air pollution and produce a spatial distribution of risk associated with air pollution across Scotland. This spatial distribution is being developed for different stratification approaches to determine the effect of spatial stratification on the concentration of emissions across Scotland. We are using these insights to investigate the effect of PM2.5 concentration levels due to biomass burning on health outcomes across Scotland.
Low Emission Zones (LEZ) will be introduced in larger Scottish cities in 2022. We are evaluating the effect of LEZ on health outcomes in Scotland. This includes establishing the actual health outcomes within each LEZ versus non-LEZs and identifying opportunities to utilise and expand the available data to ensure maximum social equity in terms of health outcomes for Scotland’s populations. We also identify zones across Scotland suitable to become LEZ based on their PM2.5 concentration and health outcomes.
Project Partners
Progress
Results are still emerging and solidifying, as the measurements still require full quality control assessment. First indications are however that domestic burning of solid fuels makes a significant contribution to the PM concentrations in smoke-controlled cities like Edinburgh. These results still need to be put into the context of total PM2.5 concentrations encountered during this period. First indications are that the measurements are broadly consistent with the emissions represented in the recently revised National Atmospheric Emissions Inventory (NAEI). The measurements highlight cooking (presumably dominated by deep frying in restaurants and take-aways) as a contributor that is potentially larger at the annual average for city centre locations than domestic fuel burning. This source is currently also poorly controlled and policed. Both sources appear to be larger than primary tailpipe emissions during winter.
Objective 1. Improve the emission inventory for biomass burning for Scotland
Recent UK projects provide revised activity figures for the NAEI 2021 inventory (National Atmospheric Emissions Inventory, 2023 release) and revised emission factors. We accessed these data and processed emission fields for various solid fuel types for input to our Atmospheric Chemistry and Transport Model (Objective 3 below). We are awaiting updated data from DEFRA's current survey of fuel use across the UK, to update information for Scotland.
Objective 2. Quantify the contribution of biomass-burning aerosol to PM2.5 (PM - Particulate Matter) in understudied settings (database to inform emission inventory work and for model assessment)
We completed the analysis of the winter PM measurement campaign 2022/23 targeting a smoke controlled area (Edinburgh University Drummond St Campus) and are nearing completion of measurements in a rural village setting (winter 2023/24; Charlestown, Fife). We compared two quantifications of biomass burning aerosol (black/brown carbon using a three-wavelength aethalometer and positive matrix factorisation of aerosol mass spectrometer data), finding large inconsistencies of the former, more commonly applied approach. Results show clear presence of biomass burning emissions with a diurnal cycle, lasting later in the day than other sources such as traffic and cooking. Analysis suggests average wintertime concentrations of burning-related PM of 0.2 µg/m3, peaking at 0.4 µg/m3 around 8-9pm (exceeding the organic aerosol contribution from tailpipe emissions). Measurements highlight cooking-derived PM (assumed dominated by deep-frying) at this city location: a poorly controlled source offering opportunities for further reduction. Because cooking occurs throughout the year, it likely makes a larger annual contribution than domestic biomass burning. Comparison of modelled and measured contributions are reasonably consistent.
Objective 3. Assess the contribution of biomass burning to PM2.5 concentrations through high resolution modelling. Coupling the 2020 NAEl with 2019 meteorology at area of 3 km x 3 km, we have explored the contribution of domestic solid fuel burning. We used a state-of-the-art atmospheric chemistry and transport model (EMEP4UK) to simulate the PM concentration before and after removal of emissions from domestic burning of wood and smokeless fuels from the inventory. The difference quantifies the PM due to these sources. At an annual average, this modelling suggested maximum contributions of about 0.2 to 0.3 µg/m3, peaking at about 5% of the total PM. For January (representative winter month) the average contribution increases to about 0.7 µg/m3, peaking east of Glasgow and locally exceeding 10% of the PM. We have now calculated meteorology at area of 1 km x 1 km and are preparing the NAEI 2021 (2023 release) for the final calculations, now also including the impact of house coal. Following comments from NatureScot, we have started to investigate the contribution of wild fires (in Scotland mainly representative of muirburn) through an improved satellite-derived dataset on fire counts to quantify its contribution.
Results are continuing to emerge and solidify and have not yet been communicated in written form to ScotGov. With the village campaign still ongoing and the final model runs awaiting input from a DEFRA-funded study, first indications are that domestic burning of solid fuels makes a significant contribution to the PM concentrations both in smoke controlled cities like Edinburgh and rural settings. We still need to put these results into context of total PM2.5 concentrations encountered during this period. Measurements are broadly consistent with the emissions represented in the recently revised NAEI. The measurements highlight cooking (presumably dominated by deep frying in restaurants and takeaways) as a contributor that, in city centre locations, is potentially larger (on the basis of the annual average) than domestic fuel burning. This source is currently also poorly controlled and policed. In the urban setting both sources appear to be larger than primary tailpipe emissions during winter.