Regional non-CO2 greenhouse gas fluxes inferred from atmospheric measurements in Ontario, Canada

Independent verification of bottom-up greenhouse gas (GHG) emission inventories is crucial for a reliable reporting of Kyoto gases to the United Nations Framework Convention on Climate Change. Here, we use a pseudo-data experiment to test if our improved version of the well-known Radon tracer method (RTM) is able to quantitatively retrieve regional GHG fluxes. Using in-situ observations in Egbert, Canada, from 2006 to 2009 for the RTM, we derive night-time fluxes of CH₄ and N₂O in southern Ontario. The N₂O fluxes found have a inter-quartile range of 7.6–31.2 μgN₂O/(m²h) with an overall mean of 24.4 ± 5.6 μgN₂O/(m²h). Comparison with the EDGAR4.1 inventory revealed an underestimation by a factor of 1.7 ± 0.4 in the inventory, which is explainable by missing natural sources and a missing seasonal cycle in the inventory. Our RTM-based fluxes of CH₄ with a inter-quartiles range of 0.19–0.49 mgCH₄/(m²h) and a mean of 0.36 ± 0.08 mgCH₄/(m²h) lie significantly below the inventory-based estimates of 0.79 ± 0.06 mgCH₄/(m²h). Using a Stochastic Time-Inverted Lagrangian Transport (STILT) model this difference can be attributed to an overestimation of CH₄ emissions in a specific region, the highly urbanized Greater Toronto Area. This study displays how the application of the RTM in future monitoring networks could help to assess high-resolution emission inventories.