The accumulation and reactivity of polycyclic aromatic hydrocarbons on wildfire-influenced environmental surfaces

Abstract

Wildfires emit large amounts of pollutants into the atmosphere, including polycyclic aromatic hydrocarbons (PAHs). In my thesis, I investigate the accumulation and persistence of wildfire PAHs on two surfaces, urban grime and wildfire ash, and discuss the potential implications of their presence on the environment. In the first part, I investigate the potential accumulation of PAHs in wildfire smoke-influenced urban grime collected in Calgary and Kamloops, Canada. The potential influence of wildfire emissions on urban population centers is likely to grow, and grime can act as a pollutant reservoir in urban areas. I show that the influx of wildfire smoke into urban areas is reflected in changes in the grime PAH composition, providing evidence that the pollutants in passing wildfire plumes are retained in the urban environment long after the conclusion of a wildfire smoke event. In the second part, I further probe the persistence of wildfire and anthropogenic PAHs in the urban environment by collecting urban grime samples in seven Canadian and US cities. I show that grime PAHs continue to accumulate over a six-month period, confirming that grime can be a long-term PAH reservoir in urban areas. I demonstrate that wildfires can be the dominant source of grime PAHs and provide field evidence that the grime uptake of wildfire PAHs cannot occur without preexisting grime present, suggesting that more polluted urban areas are more susceptible to wildfire smoke influence. In the third part, I explore the effect of ozonation on wildfire ash PAH degradation, which is currently unknown. I show that changes in ozone concentration, ozone exposure time, and relative humidity does little to reduce the PAH mass loadings in wildfire ash, suggesting that PAHs in aged wildfire ash is recalcitrant. The recalcitrance is found to stem from PAH sequestration deep within the particle matrix, making the PAHs inaccessible to oxidants. This means that these ash PAHs will likely be persistent for long periods of time in the environment but may not necessarily be a hazard. Wildfire emissions are a current and ongoing concern, and there are still knowledge gaps regarding their persistence and fate in the environment. This thesis presents new insights into wildfire PAHs, which enhances our understanding of their impact in wildfire-affected areas.