New research finds almost half of PM2.5 emissions from domestic burning come from outdoor sources

The full report can be downloaded here.

A summary sheet is available here.

A new peer reviewed research report has found that the previously accepted contribution of indoor domestic burning to the UK’s PM2.5 emissions has been dramatically overestimated, with almost half the emissions coming from outdoor burning.

Among the key findings of The Contribution of Outdoor Burning to UK PM Emissions by Dr Josh Cottam and Dr Edward Mitchell is the following:

• 46% (21,951 tonnes) of PM2.5 originate from outdoor burning.
• Significant quantities of fuel were found to be burnt outdoors, many sources of which are unregulated and highly polluting, such as bonfires.
• The largest single contributor to domestic outdoor burning emissions is green waste. This accounts for 90% of all outdoor burning emissions when combined with waste wood and rubbish.
• The estimate for indoor wood fuel use is significantly lower than the estimate used in the NAEI.
• Modern Ecodesign stoves contribute just 2.7% of PM2.5 emissions from the burning of wood logs.

The study analysed the data from a wide range of sources including the Defra commissioned Kantar Survey (2020), the EMEP/EEA Inventory Guidebook, NAEI, industry surveys and sales data, and a range of peer-reviewed journal articles, enabling the authors to establish new model estimates of domestic PM2.5 emissions from solid fuel combustion both indoors and outdoors.

The research shows that between 46% and 51% of domestic PM2.5 originates from outdoor burning. This is a significantly higher figure than the 5% currently estimated in the NAEI and accounts for a very large proportion of the emissions previously regarding as coming from indoor burning alone. The findings suggest that bonfires are a major source of PM2.5 emissions, possibly contributing as much as all wood burnt indoors.

Commenting on the findings, Andy Hill, chair of the Stove Industry Alliance (SIA), said: “For far too long now the finger of blame for poor air quality has been pointed at burning wood for heat inside the home. What this analysis shows is that half of the PM2.5 emissions that the Clean Air Strategy links to indoor domestic burning are coming from outdoor burning. The problem with these outdoors burning emissions is that they are almost entirely unregulated and produce no useable heat.”

The study also highlighted that stoves meeting Ecodesign requirements contribute just 2.7% of emissions from indoor burning, while open fires contribute 39%. The authors noted that: “These results therefore highlight the substantial improvements in emissions that can be made by switching to modern Ecodesign stoves.”

Andy added: “Indoor wood burning stoves are subject to a range of regulations to ensure that emissions are minimised, and efficiency is maximised. This new research shows that appliances that meet Ecodesign regulations account for a very small percentage of PM2.5 emissions, just 2.7%, whereas open fires contribute over 14 times as much. This provides clear evidence of the benefits of switching to modern Ecodesign stoves and shows that calls for all wood burning stoves to be banned are misguided and based on flawed data.”

The authors of the study note in their conclusions that: “PM2.5 emissions in the 1A4bi (residential stationary combustion sector of the NAEI) are at present largely attributed to indoor burning due to a lack of distinction between indoor and outdoor burning sources. This has led to regulations focusing purely on indoor burning whilst outdoor burning sources have been largely ignored.”

Andy concluded: “The time has now come for policy makers to look again at the data within the NAEI and correctly apportion all sources of particulate matter so that the appropriate action to improve air quality and meet our low carbon objectives can be taken.”

The research findings have been shared with all key government departments in the UK and the SIA is calling for an urgent review of the NAEI quantification of domestic burning PM2.5 emissions.

A modern Ecodesign stove that is correctly installed and well maintained (including annual chimney sweeping), using correctly seasoned wood fuel, produces up to 90% less emissions than an open fire and up to 80% less than many older, basic stove models. As well as being inherently low carbon and low emission, they offer homeowners protection against rapidly rising gas and electricity prices, peace of mind in the event of grid outages brought on by severe weather and offset our use of fossil fuel for heating.