Wood burning accounts for between 23 and 31% of fine particulate (PM2.5) emissions in London and Birmingham, although emissions have not risen in recent years, a major study has suggested.
Findings of the research by King’s College London’s Environmental Research Group and the National Physical Laboratory (NPL) – which were compiled on behalf of the Department for Environment, Food and Rural Affairs (Defra) – were published last week.
Research will likely inform policy developments at Defra, which is seeking to draw up plans to improve air quality from sources including domestic solid fuel burning. A consultation was launched last week calling for information on the use of solid fuels in homes (see airqualitynews.com story).
The study, from which initial results were presented in the summer (see airqualitynews.com story), looked at the long term trends in PM emissions from wood smoke in UK cities using aethalometer data from Defra’s black carbon network from 2009 to 2016.
According to the research, air pollution from wood burning was greatest in winter and “almost absent” in summer. It suggested that mean wintertime PM from wood burning varied between cities, ranging between 0.2 and 2.7μg m3.
On annual basis wood burning in PM2.5 ranged between 4 to 6% as an average across rural areas; and between 6 to 9% averaged across urban areas.
It was estimated that wood burning was between 23 and 31% of the urban derived PM2.5 in London and Birmingham, “making control of wood burning an important urban issue”, the researchers claimed.
Interestingly, the study noted that a long term downward trend in PM from wood burning – 0.03 (-0.05, -0.01) μg/m3 year had been recorded between 2009 and 2015.
This was met with surprise by the researchers, due to a reported growth in the number of householders burning wood in the home for heat.
The report notes: “This was unexpected given anticipated growth in biomass combustion due to policy initiatives aimed at increasing production of heating and electricity from renewable and low-carbon energy sources. UK Industry data also suggests stove sales are running at between 150,000 and 200,000 units per year with over one million stoves sold between in 2010 and 2015.
“One possible explanation for the observed trend is the replacement of high emission fireplaces with newer, and lower emission wood stoves, balancing an increase in total wood heating.”
Stove manufacturers have welcomed the findings of the study, which they claim supports the theory that the replacement of older stoves with newer, more efficient models, is helping to reduce emissions.
However, the organisation warned that there is evidence to suggest that a large volume of wood being burnt in homes – particularly in London – is thought to be on open fires, which will potentially prevent further reductions in emissions.
In a statement, the Stove Industry Alliance said: “The outcome of the study reflects the fact that only Defra Exempt stoves, with emissions that meet strict Defra limits on emissions can be installed in smoke control areas.
“The reduction may not have been as great as we would all have liked but the decrease in emissions is partly offset by the continued use of open fires to burn wood. Although burning wood in an open fire is not permitted under the Clean Air Act, 70% of the wood burnt in London is on an open fire.”
Looking ahead, the study suggests that increases in PM emissions are likely based on an expected rise in biomass burning for energy over the next two decades. Additional coverage for the aethalometer network will be needed to track changes in trends the report suggests.