A wood-burning stove
Dr Tom Smith is a wildfires scientist. His career has focused on tracking down wildland fires in savannahs and tropical peatlands around the globe, but his latest investigation was closer to home.
It took place on a weekend in early December. “I noticed the familiar smell of wood smoke inside my flat,” Smith said. “I’m well aware of its harmful health effects from my research, so I went outside with my portable pollution sensor in search of the source.”
Air pollution in the street was even worse than indoors. “As soon as I got outside, the readings on my sensor jumped. A short walk upwind confirmed my suspicions: the pub opposite my estate had smoke billowing from its chimney.
“Concentrations in front of the houses near the pub were even higher than outside my flat. Exposure like this over long periods of time will aggravate the heart and lungs of anyone in the smoke plume. Children, asthmatics and pregnant women are particularly vulnerable.”
Smith’s experience is not an isolated example. Last winter, researchers from Imperial College London surveyed wood and coal smoke in gardens and streets. There is further evidence from citizen scientists, including a group of friends who track the smoke that drifts across the gardens and into houses in Chorley, Lancashire.
Last month I visited one of the UK’s most advanced air pollution measurement sites, located in the south of Manchester, where researchers from the University of Manchester make detailed measurements of the gases and particles in the air. The roof is a forest of sample pipes sucking air into the instruments below. A laser scans the sky to search for pollution above and another set of lasers create a light curtain to measure rain and fog.
Dr James Allan sat down at a computer screen and looked at data streams from the past 24 hours. It was clear that the particle pollution in the city had changed around sunset. During the day there were clear signs of traffic emissions, but in the evening the air contained smoke from home fires.
Allan said: “At night in the winter we see high concentrations of particle pollution. The particles are smaller than 1 micron [a thousandth of a millimetre]. There is a lot of organic particles and black carbon, which we’d associate with soot.”
He explained how his instruments detected wood burning using light of different wavelengths. “Soot from wood burning absorbs more ultraviolet light compared with fossil fuel emissions, and when we compare the daytime to nighttime readings we see this signature. It indicates wood burning is having a stronger influence at night.”
Regular exposure has a health impact. A recent study estimated that 284 Londoners a year are dying earlydue to outdoor air pollution from solid fuel heating. It also estimated that about 90 new cases of asthma in children, 60 new cases of stroke and 30 new lung cancer cases a year were linked to this pollution. This is a health burden of almost £800 a year created by the average person in London who uses a fireplace or stove.
Research commissioned by the charities Global Action Plan and Impact on Urban Health used a computer simulation of two mid-terrace houses to investigate the costs of different heating choices. The houses had simulated occupants. One housed a family with two children and the other a retired couple.
The neighbourhood health cost from heating the homes with fossil gas central heating was about £25 a year. Adding a wood stove for 20% of their heating took the cost to about £160 for one of the most modern stoves, or more than £1,000 for an older stove design. This does not include health harm to the stove owners.
Dr Gesche Huebner, of University College London, one of the researchers on the study, said: “Wood burning is not a solution for reaching net zero or avoiding high bills for individuals. It is not cheaper, not truly renewable, but it constitutes a major health risk.”