Characterization of the δ13C signatures of anthropogenic CO2 emissions in the Greater Toronto Area, Canada

In urban environments, carbon dioxide (CO₂) is emitted from a variety of anthropogenic and biogenic sources. The isotopic ratio δ¹³CO₂ has been widely used to source apportion CO₂ as different sources have distinct isotopic fingerprints; the disadvantage of this technique is that δ¹³CO₂ signatures are often spatially and temporally specific. We present a study characterizing the δ¹³CO₂ signatures of the dominant anthropogenic sources of CO₂ in the Greater Toronto Area (GTA). Refined gasoline and diesel fuel were sampled from various stations around the GTA in three separate campaigns (April, July and November 2015) to assess the variability of their δ13CO2 signatures. Mean winter δ¹³CO₂ signatures for refined gasoline were measured to be −27.58 ± 0.52 ‰ and −28.12 ± 0.43 ‰ (uncertainties represent the standard deviation in sample signatures) in April and November respectively while the mean summer signature was measured to be −28.09 ± 0.34 ‰. Diesel fuel samples δ¹³CO₂ signatures from the same campaign periods were measured to be −29.09 ± 0.34 ‰, −29.47 ± 0.29 ‰, and −29.28 ± 0.21 ‰, respectively. We hypothesize that inter-seasonal variability in signatures is likely a result of the use of different parent crude petroleum. We found no significant impacts from octane grade, fuel distributor or municipality the fuel was purchased from on the measured δ¹³CO₂ signatures. Other transportation fuels that were measured include dyed-diesel (δ¹³CO₂ signature = −29.3 ± 0.20 ‰) and jet fuel (δ¹³CO₂ signature = −29.5 ± 0.20 ‰), which were both different than measurements made for the same fuels in other locations globally. To account for emissions from residential and commercial heating and electricity production, a variety of fuels were characterized in this study. The primary heating fuel used in the GTA, natural gas, was measured to have a δ¹³CH₄ signature of −44.2 ± 0.20 ‰. Anthracite coal (a fuel that was used prior to 2014 for electricity) was measured to have a δ¹³CO₂ signature of −23.8 ± 0.20 ‰, which is fairly consistent with coal samples measured elsewhere. With the transition in Ontario from coal to biomass-fueled power generation, softwood, hardwood and mixed wood pellets were sampled from two distributors in the GTA and measured δ¹³CO₂ signatures were −25.0 ± 0.20 ‰, −26.8 ± 0.20 ‰, and −25.8 ± 0.20 ‰, respectively. Using these measured signatures, we performed a sensitivity analysis to quantify the precision required for continuous ambient measurements to separately identify fuel type using δ¹³CO₂ as the sole tracer. The local signatures were also used in a mass balance calculation to quantify the relative contribution of two end-members (with the signatures of −44 ‰ and −28 ‰) to total measured CO₂ in the GTA in 2014.