Low-smoke and smokeless fuels do not lower the risk to human health from air pollution, scientists in Galway have found.
Their study found that burning smokeless coals and biomass briquettes produces much more tiny toxic particles of burned materials and chemicals than expected.
These ultrafine particles, PM0.1, are invisible to the naked eye so even when there are many of them, they are emitted without appearing as smoke.
Larger particles, PM10 and PM2.5, that come mainly from burning traditional coal, peat and wood, are more visible, which makes the pollution they cause more obvious.
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PM10 and PM2.5 are linked to a range of respiratory and cardiovascular illnesses and smoky fuels are banned for sale in the Republic, although air-quality monitoring shows there are wide-scale breaches of the regulations.
However, PM0.1 can penetrate deeper into human lungs, travel to other organs “and even pass the blood-brain barrier”, a layer of cells that blocks dangerous substances reaching the brain.
The health impacts can be even wider and more severe because the particles can travel so much further throughout the body and lodge for longer.
“These low-smoke fuels, designed to lower particulate mass emissions, have unexpectedly led to a two-to-threefold increase in the emissions of ultrafine particle numbers, resulting in a higher contribution to lung-deposition particles than all their smoky counterparts combined,” the study, published in Nature Geosciences on Monday, says.
Prof Jurgita Ovadnevaite, director of the Centre for Climate and Air Pollution Studies at the University of Galway, led the joint Irish-Chinese study and said the findings were a surprise.
“We did not even have a suspicion. We just wanted to quantify the emissions from different fuels,” she said.
Around 1,600 people die prematurely from air pollution in Ireland each year and Ovadnevaite said she worried about how the findings would be interpreted.
“We were hesitant. We didn’t want people to think that there is no point in stopping burning coal and wood.
“The answer [for clean air] is not to burn anything but unfortunately that is not the answer people want to hear.”
The researchers analysed smoke from a range of fuels with advanced instruments that track how many particles are produced, how big they are, and what they are made of.
They also collected real‑world air measurements in Dublin and Birr, Co Offaly over several years, allowing them to compare laboratory results with what people actually breathe during winter pollution episodes.
“Our results indicate that switching from raw solid fuels to those marketed as ‘smokeless’ may not yield the anticipated health benefits,” their study states.
“Due to the unexpectedly high emission factor for particle numbers, even a modest increase in the consumption of these solid fuels will disproportionately increase the exposure risk of ultrafine particles.”
Ovadnevaite said Ireland’s network of air-quality monitors did not detect ultrafine particles but the World Health Organisation and European Union had recently said they must be measured.
There are no limits set for them yet – unlike for PM10 and PM2.5 – but the move to require measuring was a step in the right direction, she said.
She said the findings had been shared with the Environmental Protection Agency, which oversees air quality monitoring in Ireland, and further research with new instruments was planned.
“It’s a very harsh message to deliver – to tell people that what you thought was better for health is not,” Ovadnevaite said.
“But at least if you understand how burning fuels affects your own health, you can make that conscious decision to burn or not. Many people do not understand so they are not making an informed choice.”
