The burning question of Bonfire Night pollution

Bonfire Night celebrations contaminate our air with hugely elevated amounts of soot, scientists have discovered.

Researchers from the University of Leeds tested air quality during Guy Fawkes Night events in the city – and found soot in the atmosphere was around 100 times its normal level. 

Soot, or black carbon, is produced by incomplete combustion. Black carbon particles are so small, they can penetrate deep into the lungs and cause irritation. Long term exposure can cause harmful effects on the heart and lungs and contributes to millions of deaths worldwide each year. 

Our measurements showed that the elevated concentrations of soot and other pollutants in the atmosphere should be a warning to those with pre-existing health conditions.

The team took hourly air quality samples on the university campus during Bonfire Night celebrations in 2016 and 2017. 

Equipment was set up on the School of Earth and Environment balcony, 15m from ground level and more than 0.5 km from any individual bonfires or firework displays, to give a representative view of the air quality across the city. 

The researchers did not expect to see such high levels of the polluting matter in the atmosphere. 

Lead author Michael Adams, Research Fellow in Atmospheric Ice Nucleation and PhD student in the School of Earth and Environment, said: “Our measurements showed that the elevated concentrations of soot and other pollutants in the atmosphere should be a warning to those with pre-existing health conditions, as the aerosol particles are in the size range where they can enter the lungs and cause problems.” 

An air filter before and after the experiment, showing the amount of polluting materials collected on Bonfire Night 2017. Credit: Michael Adams

Research supervisor Benjamin Murray, Professor of Atmospheric Science in Leeds’ School of Earth and Environment, said: “Bonfire Night is a massive pollution event across the UK. People with existing health problems, such as heart and lung conditions, are at increased risk.  

 “I was surprised to see levels of black carbon so persistently high for so long on multiple nights. It was striking how poor air quality was on Bonfire Night.” 

Weather conditions can affect how long the particles remain in the air. The team found the pollution was flushed out of the city within a few hours during the 2016 experiment, due to a brisk wind from the north. 

But in 2017 the air was relatively still and the pollution lingered into the next day. 

While providing insight into the levels of black carbon emitted on Bonfire Night, the team’s discoveries have also contributed to the understanding of different sources of ice nucleating particles – a key research area in climate science. 

Ice occurs naturally in clouds, but tiny particles of desert dust, soil dust, fungus and bacteria swept high into the air can cause supercooled water droplets in clouds to freeze around them. High concentrations of these ice-nucleating particles can cause clouds to freeze, potentially impacting the earth’s climate. 

Clouds containing supercooled water and ice are first order importance for climate.

Black carbon is known to cause climate warming, but its impact on clouds was not clear. The researchers discovered black carbon produced on Bonfire Night did not act as ice nucleating particles. 

Professor Murray said: “Clouds containing supercooled water and ice are first order importance for climate. Vast cloud systems made of a mixture of ice and water over the world’s oceans buffer the warming effect of CO2.   

“But the buffering capacity depends on how much ice is in them, which in turn depends on the concentration and distribution of ice nucleating particles. 

“We found that aerosol particles emitted during the celebration are not as effective at nucleating ice as aerosol particle already present in the atmosphere.  

“We conclude that aerosol particles emitted from combustion processes such as those observed on Bonfire Night are not an important source of ice nucleating particles.” 

For further information, please visit the University website.