The impacts of forest fires on oxidative potential of air across Canada

A key pathway for air pollution health effects follows oxidative stress, resulting from increased human exposure to oxidants and decreased antioxidant defence. This involves the formation of reactive oxygen species (ROS) in the body, for which oxidative potential (OP) serves as a proxy.
Forest fires emit significant amounts of carbonaceous aerosol, primarily during the summer months. In 2023, wildfires globally emitted over 2,000 Mt of carbon; Canadian fires accounted for nearly a quarter of this total, with plumes reaching the United States and Europe. Recent studies have shown that the OP of urban air increases significantly during the Canadian summer, with indications that forest fire emissions contribute to this trend. The frequencies and magnitudes of wildfires are expected to increase worldwide in the coming years, and there is a growing interest in understanding their effects on air pollution, human exposure, and health outcomes.
We investigated the impacts of the 2023 forest fires on the OP of ambient air across Canada, with the aim to identify the molecular carriers of OP from this emission source. The study encompassed seven sites in Ontario, Quebec, Alberta, and British Columbia. The production of ROS in the lung was modelled using the KM-SUB-ELF and the concentrations of fine particulate matter (PM2.5), soluble copper and iron, secondary organic matter, ozone, and nitrogen dioxide. Aerosol chemical speciation was used to characterize the seasonal emission source profiles and aerosol acidity.
The arrival of forest fire smoke significantly elevated the concentrations of PM2.5, biomass burning markers, reactive gaseous and particulate species, organic ligands, and soluble metals. Consequently, this increased the modelled production of ROS - particularly the hydroxyl radical. The study demonstrates how forest fires contribute to atmospheric oxidative capacity both directly, through the emission of reactive species, and indirectly, via atmospheric transformation processes.