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The City of Toronto (Ontario) is Canada’s largest urban area in population and areal extent. As a result, elevated activity from urban, industrial, and transportation sectors has increased atmospheric carbon-12 ( 12 C) and carbon-13 ( 13 C) from fossil fuel combustion. Excess 12 C and 13 C mask natural levels of atmospheric carbon-14 ( 14 C), a phenomenon known as the Suess Effect. Consequently, measurements of atmospheric 14 C can be used to quantify anthropogenic fossil fuel contributions. With southern Ontario having an air sampler run by Environment and Climate Change Canada (ECCC) in northern Toronto, there is opportunity to expand our understanding of the atmospheric carbon inventory. Using dendrochronological methods, tree-ring 14 C measurements were obtained and compared with background 14 C levels to assess urban 14 C-depletion across Toronto via six trees representing different urban microclimates. One tree located near the ECCC air sampler closely tracked measured atmospheric 14 C levels (Spearman’s ρ=0.93). While most samples analyzed were 14 C-depleted, some years also experienced 14 C-enrichment due to elevated 14 C emissions from the Pickering Nuclear Generating Station. Trees located in urban parks recorded 14 C levels closer to background levels. In general, tree rings effectively record 14 C variations, reflecting both fossil fuel and nuclear contributions. Meteorological analysis indicates that proximity to the Pickering Nuclear Generating Station and lake-influenced air masses affects 14 C uptake, suggesting that Toronto’s atmospheric carbon inventory is spatially complex and that urban sampling sites must be evaluated individually. • Tree-ring and air sampler radiocarbon measurements track one another closely. • Most tree-ring radiocarbon measurements in the City of Toronto are depleted in radiocarbon. • Tree rings enriched in radiocarbon align with nuclear emission peaks/maintenance.