“Remember, remember the fifth of November....” It’s that time of year again, when eager Brits celebrate Guy Fawkes Night with extravagant fireworks displays and bonfires to burn the traitorous Fawkes in effigy. But a new study says that all that extra smoke and debris in the air wreak havoc with visibility.

The idea for the study — just published in the journal Weather — grew out of an informal chat over coffee and biscuits in Birmingham, according to Francis Pope, one of the co-authors. His graduate student, Ajit Singh, was keen to test his idea for using historic visibility measurements — which stretch back hundreds of years — as an indication of historic levels of air pollution. In contrast, pollution monitoring is a relatively recent innovation.

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“We realized that the UK has a ready-made yearly test every fifth of November,” Pope told Gizmodo via email — Guy Fawkes Night, marking the foiling of the infamous Gunpowder Plot of 1605 to assassinate King James I by blowing up the House of Lords. The combination of lots of fireworks and bonfires across the country pours a lot of extra particulates into the air, albeit temporarily.

Pope and his colleagues wondered how much this would impact visibility, building on numerous prior studies providing evidence for such a connection. The Birmingham group chose Nottingham for their specific case study because it had the nearby monitoring stations they needed: one to monitor visibility and the other to monitor air pollutants. They used datasets tracking weather and air pollution over a 13-year period (2000-2012) and looked for any marked decreases in visibility coinciding with Guy Fawkes Night.

Pope said they were all surprised at just how pronounced the impact proved to be: on average, there was 25% reduction in visibility associated with Guy Fawkes Night. And in urban locations like Nottingham, where the denser population translates into more bonfires per capita than in a more rural area, they found as much as 60% reduction in visibility.

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While fireworks do have some nasty compounds, and particulate matter isn’t necessarily good for you, either, brief annual exposure shouldn’t have too many adverse health effects, according to Pope. The biggest concern is the impact on driving conditions, since there are likely to be a lot of cars on the road on Guy Fawkes Night, and lots of revelers partying late into the night. If it’s a relatively clear night, Pope said a 25% reduction in visibility wouldn’t make much difference to driving conditions. But if the visibility were already poor — particularly with high levels of humidity — an extra 25% decrease could prove pretty hazardous.

In fact, their paper cites a tragic car accident in 2011 on the M5 motorway in Somerset that killed seven people and injured 57 other revelers. “The resulting investigation found that a local fireworks display near the road might have contributed to the poor visibility on an already foggy night,” the authors write, although they note that “no blame was assigned to the organizer of the fireworks event.”

Keeping the fuel for the bonfires dry before the big night would result in less smoke, and fewer particles released into the air. So would having fewer bonfires in general. That said, “I do enjoy a good bonfire,” Pope admitted. You don’t want to mess too much with tradition.

References:

Singh, Ajit; Bloss, William J.; and Pope, Francis D. (2015) “Remember, remember the 5th of November: gunpowder, particles and smog,” Weather 70(11): 320-324.

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Godri, K.J. et al. (2010) “Particulate oxidative burden associated with firework activity,” Environ. Sci. Technol. 44(21): 8295-82301.

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[Via Improbable Research]

Top image: Nick Dale/Shutterstock. Bottom image: Singh et al./Weather.