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 7.631.2gN2O/(m2h) with an overall mean of 24.4 +/- 5.6gN2O/(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 0.190.49mgCH4/(m2h) and a mean of 0.36 +/- 0.08mgCH4/(m2h) lie significantly below the inventory-based estimates of 0.79 +/- 0.06mgCH4/(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.