Methane and nitrous oxide emissions in The Netherlands: ambient measurements support the national inventories

We present net emission estimates of CH4 and N2O of The Netherlands based on measurements conducted during the period of May 2006 to April 2009 at station Lutjewad, The Netherlands (6 degrees 21' E, 53 degrees 24' N, 1 m a.s.l.). (222)Radon mixing ratios were applied as an indicator for vertical mixing and long-range air mass transport and used to calculate the net surface fluxes from atmospheric mixing ratios of CH4 and N2O. Our study shows that our measurement site Lutjewad is well-suited to measure emissions from The Netherlands and validation of the national inventories using the (222)Radon flux method. Since this study is purely observation-based it is independent from inventories or atmospheric models. Our results are compared to the national inventories as reported to the UNFCCC. We found net emissions of: (15.2 +/- 5.3) t km(-2) a(-1) for CH4 and (0.9 +/- 0.3) t km(-2) a(-1) for N2O. These values are lower than the inventory-based emissions (2006-2008 averages) of (18.3 +/- 3.3) t km(-2) a(-1) for CH4, and (1.3 +/- 0.6) t km(-2) a(-1) for N2O, but the differences are insignificant.