Seasonal variation of N2O emissions in France inferred from atmospheric N2O and 222Rn measurements

Nitrous oxide (N2O) concentrations and Rn-222 activities are measured semi-continuously at three stations in France: Gif-sur-Yvette (a semi-urban station near Paris), Trainou tower (a rural station) and Puy-de-Dome (a mountain site). From 2002 to 2011, we have found a mean rate of N2O increase of 0.7 pbb a(-1). The analysis of the mean diurnal N2O and Rn-222 cycles shows maximum variabilities at the semi-urban site of Gif-sur-Yvette (0.96 ppb for N2O and 2 Bq m(-3) for Rn-222) compared to the rural site of Trainou tower (0.32 ppb for N2O and 1.3 Bq m(-3) for Rn-222). The use of Rn-222 as a tracer for vertical mixing and atmospheric transport, combined with the semi-continuous N2O measurements, allows estimation of N2O emissions by applying the Radon-Tracer-Method. Mean N2O emissions values between 0.34 +/- 0.12 and 0.51 +/- 0.18 g(N2O) m(-2) a(-1) and 0.52 +/- 0.18 g(N2O) m(-2) a(-1) were estimated in the catchment area of Gif-sur-Yvette and Trainou, respectively. The mean annual N2O fluxes at Gif-sur-Yvette station correlate well with annual precipitation. A 25% increase in precipitation corresponds to a 32% increase in N2O flux. The N2O fluxes calculated with the Radon-Tracer-Method show a seasonal cycle, which indicates a strong contribution from the agricultural source, with the application of fertilizers in the early spring inducing a strong increase in N2O emissions. Finally, the results of the Radon-Tracer-Method agree well with the national and global emission inventories, accounting for the uncertainties of both methods.