It looks like the secondary emissions from wood smoke are far more dangerous than we previously thought. A recent study from the University of Eastern Finland has demonstrated that the formation of secondary aerosols is much higher then was estimated.
When wood smoke ages in the ambient air, aerosols are created rapidly. In just three hours the aerosols that are formed increase significantly, so it looks like we need to have a hard look at our campfires.
The studies were undertaken at the ILMARI research laboratory at the University of Eastern Finland, with the assistance of the Finnish Meteorological Institute. These studies are considered to be a part of the European HICE Helmholtz Virtual Institute network’s area of research, and the experiments clearly demonstrated that many organic gaseous compounds are released when wood is burned.
After the initial formation on these organic compounds, secondary aerosols are created by reacting with the atmosphere. Interestingly, the way a campfire is burned makes a big difference when ti comes to emissions. Slower burning fires create more organic compounds, while a faster burning fire will create less.
The study found that the time of day also plays a role, with daytime emissions creating far more secondary aerosols than a fire at night would. But it appears that a large percentage of the secondary aerosols that were formed during nighttime aging were organonitrates. This class of chemical aren’t well understood, so we are left to hope that further research is forthcoming.
So the takeaway from this study is that a green fire is one that burns hot and fast, after the sun goes down. It looks like a bonfire is as green as it gets after all. As long as there isn’t something sinister lurking in the organonitrates.