New research has found that burning “smokeless” or low-smoke fuels may be causing new air pollution hazards on streets and in homes.
These fuels are sold as alternatives to burning coal, wood and peat at home, but tests reveal their smoke contains large quantities of tiny ultrafine particles, smaller than the wavelength of light, that can deposit themselves deep in our lungs.
The findings were an accidental discovery while researchers were testing fuels in traditional and modern eco design stoves.
As expected, burning alternative fuels, both smokeless coal ovoids and briquettes made from olive stones, produced less particle pollution compared with wood or coal.
Prof Jurgita Ovadnevaite, from the University of Galway, said: “No one had taken the next step to consider that less smoke could simultaneously lead to an increase in ultrafine particles. We hadn’t anticipated such a pronounced effect either until we saw the data.”
Dr Chunshui Lin, also at Galway, said: “It took us nearly two months with sample burning almost every single day to ensure data quality and consistency.”
For each kilogram burned, the low-smoke fuels produced between two and three times more ultrafine particles than wood or coal.
Lin continued: “The unexpected finding on ultrafine particles encouraged us to go back and re-analyse our outdoor measurements to trace how these particles contribute to local air pollution.”
The researchers turned to their past measurements in Dublin and the small town of Birr, in the Irish Midlands.
They found ultrafine particles in winter evenings, consistent with home fires but at concentrations far greater than expected. Sometimes these exceeded those in Beijing and Shanghai. In Dublin, these ultrafine particles increased from 2021, as homes shifted towards low-smoke fuels, consistent with the laboratory findings.
Ovadnevaite added: “Without sustained measurements, it would have been impossible to evaluate these consequences.”
The size of the ultrafine particles means that they are deposited deep in the lungs, multiplying the health impact. In Dublin, the low smoke fuels accounted for more than half of ultrafine particles that can deposit in people’s lungs. This includes particles of poly-aromatic hydrocarbons, some of which are known carcinogens.
The sale of house coal was phased out in England from 2020 and in Ireland in 2022, but low-smoke fuels continue to be sold. In the UK, these are the only fuels that can be legally used on open fires in the smoke control areas that cover most large cities.
Measurements from Imperial College London’s research supersite show that the greatest concentrations of ultrafine particles in south London happen during the evenings, warranting further investigation.
The banning of smoky coals in Dublin in 1990 saved lives. It was followed by a 17% decrease in people dying from breathing problems during the following winter, but the new results on smokeless and low-smoke fuels show that substituting one solid fuel for another may not be the best solution for air pollution problems.
Ovadnevaite said: “We need a more holistic approach to air pollution – one that accounts for the full range of effects. So before lighting a fire, it’s worth pausing to think. Are we prepared to accept those health costs for our children, our older relatives, and our neighbours? Every fire adds to that burden.”
