Kitchener is a city located next to the city of Waterloo, so close together that it’s hard to tell where one city stops and the other starts. They are two separate legal entities however, and in Kitchener there is a raging debate about limiting or banning backyard fires (Waterloo banned them some years ago). The debate boils down to the rights of individuals to use their property as they see fit, versus the rights of their neighbours to clean air. On technical grounds, I would side with the people who are seeking a ban, based on what we already know about wood fires and air quality.
In my course on Air Pollution Control we briefly look at pollutant sources as quantified by Environment Canada. Most people are surprised to learn that residential wood combustion is one of the single largest sources of several Criteria Air Contaminants, for example particulate matter (PM) and volatile organic contaminants (VOCs). PM is clearly linked to respiratory and heart disease, and possibly linked to other health effects such as some cancers and diabetes. VOCs add to the formation of smog in the summer, through a complex set of reactions in the atmosphere.
Let’s focus on PM. Data from Environment Canada shows residential wood combustion emits around 34% of the total fine particulate (called PM2.5) emitted by human activity. PM2.5 is of particular concern, as it tends to penetrate most deeply into the lungs. The next largest amount (at 11%) is off-road diesels, such as construction equipment. So the wood burning is 3 times the amount, and a huge impact versus any other single industrial sector. The difference of course, is that industrial activity is regulated and uses pollution control equipment to minimize PM emissions. A fire in your backyard has poor combustion control and no emission control system, so lots of PM gets sent into the air.
Over the past few decades, North Americans have been highly resistant and organized against solid waste incineration, in part because of the perceived impact on air quality. And so, rather than burning our non-recyclable waste and recovering energy from it, we end up burying it in landfills for future generations to deal with. But it’s easy to show that the concern about air quality is directed at the wrong target. Using published emission factors, we can find that one backyard fire using a few kilograms of wood puts out the same quantity of PM as a modern waste incinerator processing 5 to 10 tonnes of municipal solid waste. Burning wood in a firepit or fireplace is not as “green” as you might think. It would be better for air quality if we burned our wood in a large scale incinerator with pollution controls, made electricity, and used an electric fireplace. Admittedly not as romantic however.