Impacts of the sale of house coal and the most polluting manufactured solid fuels: report

2. Literature review

2.1 Identified Literature

The following data sources were established in the preliminary stages of the project. Exploring these data needs, in particular around their availability, accessibility, coverage and granularity, has been the focus of the first part of the project.

2.2 Reviewed data sets

2.2.1 Census data

A census has been conducted in Scotland in 2011^[3] and 2022, gathering information about households, including the central heating system used. The data for the 2022 Census were not available for use in this study due to being not yet available. The 2011 Census contained information on the numbers of households using various central heating types (e.g., solid fuels) by Council area or smaller Output Area (Table QS415SC). The Census had high spatial resolution of solid fuel use by OA. Limitations were that: only central heating is covered, as data on secondary heating fuels would be relevant to this study; there was a single solid fuels category, as detail around the split of solid fuels between wood and coal would be useful; and household data may have changed since 2011.

2.2.2 Scottish Household Survey

The Scottish Household Survey (SHS)^[4] is carried out annually and provides information about the composition, and characteristics of households in Scotland. Published data provided aggregated national information about travel, housing and demographics. The SHS contained recent data on household finances, e.g., income, but no information on heating or fuel use.

2.2.3 Scottish House Condition Survey

The Scottish House Condition Survey is the largest single housing research project in Scotland, and the only national survey to look at the physical condition of Scotland's homes as well as the experiences of householders.^[5] The survey is published annually, and the most recent dataset is from 2019.

The Scottish House Condition Survey contained limited information on solid fuel use. Like the Census, the statistics presented only pertained to primary heating (not secondary), and there was no detail on proportions of different types of solid fuel (i.e., wood or coal types) being used for heating. In addition, the only spatial information was a split between urban and rural fuel use, so there is insufficient spatial resolution available for our analysis.

2.2.4 Home Analytics

The Home Analytics database provides information about households in Scotland, including the primary and secondary heat sources in homes, total heat demand of the property, and fuel poverty indicators. The heating sources are categorised by fuel type, including solid fuel. Under an agreement with the Scottish Government, an extract of properties in Scotland from the Home Analytics v3.8 dataset was provided by the Energy Savings Trust.

As there was no detail about the specific type of solid fuel (e.g., house coal, wood logs, etc.) being used in each home, it was not possible to derive emissions calculations from the Home Analytics dataset. However, the data set offered the best spatial information of all data sets reviewed, as it contained the locations of houses using solid fuel as primary or secondary fuel types. This information was used for scaling PM_2.5 emissions spatially across Scotland. This data source was preferred for spatial information, as it was more recent and detailed than the 2011 Census, which only included data on fuel type for primary heating.

2.2.5 National Atmospheric Emissions Inventory (NAEI)

The NAEI publishes emission information for sectors in the UK including residential emissions.^[6] Mapped emissions for each sector were also available online to provide an estimate of spatial variation in emissions.^[7] The NAEI published emission factors for domestic combustion (Table 1A4bi) by fuel type and year.^[8] The NAEI have calculated relevant emission factors for the UK using EMEP/EEA emission factors (see below) with UK-specific data on domestic combustion technologies. NAEI emission factors for wood, coal and smokeless solid fuels were used in this study. Separate emission factors for wood based on moisture content are not available in the NAEI, so an emission factor for wet wood was derived from the literature. There were also no separate emission factors for solid fuels based on sulphur content, so it was not possible to calculate separate PM_2.5 emissions for high vs low manufactured solid fuels.

2.2.6 Defra Solid Fuel Burning and BEIS Residential Wood Survey

Defra and BEIS have conducted surveys on the use of wood in residential homes^[9],[10]. These surveys have provided information about the national and rural/urban disaggregation of fuel use (wood and coal/mineral fuels) from a national user survey.

The NAEI have reported that input activity data related to wood from the BEIS survey have been replaced with the updated 2020 Defra survey, as the methodology used in the 2016 BEIS survey led to the over-estimation of domestic fuel consumption.^[11] This update was reflected in the DUKES calculations of calorific values related to domestic fuel consumption of wood.^[12]

Thus, the 2020 Defra Solid Fuel Burning has been reviewed in greater detail. There were statistics available for Scotland, also split into urban and rural categories, of the amounts of wood and coal (kilotonnes) burned in one year (2019) as well as the number of households using each fuel type. It was also possible to calculate the percentage of wood burned wet and the percentage of house coal. As such, this dataset will be core in our analysis along with the Home Analytics database which provides spatial household data.

2.2.7 EMEP/EEA Air Pollutant Emission Inventory Guidebook

The EMEP emission guidebook provides technical guidance to prepare national emission inventories, including emission rates for different domestic burning sources.^[13] For more accurate emission factors, data related to domestic combustion technology types (e.g., stoves) were required. As the NAEI have already calculated appropriate emission factors based on UK technology, it was determined the NAEI emission factors were more suitable for this study.

2.2.8 DUKES calorific values

The Digest of UK Energy Statistics (DUKES)^[12] calorific values and density of fuels are produced annually. These calorific values were required for determining the amount of energy produced by burning quantities of wood or coal. The calorific values were available by domestic fuel type and year. Emission factor units for PM_2.5 are in the amount of PM_2.5 per amount of net energy.

2.2.9 2019 Defra Impact Assessment for the proposed regulation of the sales, distribution and marketing of Wet wood (>20% moisture) sold in units up to 2m³; Bituminous house coal; and Banning manufactured solid fuels with sulphur content over 2%

The Defra 2019 Impact Assessment^[14] provides a summary of the potential intervention and options under the proposed Regulation in England. The report assesses the costs and benefits of two options – a voluntary approach supported by a communications campaign and an enforced ban on the solid fuels – against the baseline do nothing scenario. Several useful data are acquired from this study, such as information on behavioural responses, information on costs of specific sub-fuel types and implementation costs.

2.2.10 Other Guidance and Relevant Documents

We will refer to other relevant guidance throughout the report, including:

• Defra Air quality appraisal: impact pathways approach guidance for methods to calculate damage costs and policy impacts on health, economy and the environment^[15]
• Green Book supplementary guidance for rules to evaluate greenhouse gas emissions^[16]
• The Air Quality (Domestic Solid Fuels Standards) (England) Regulations 2020.^[17]

2.3 Summary of Data sources used in the analysis

Having conducted our initial literature review, Table 2‑2 outlines the sources to be used in our analysis.