Seasonal variation of N₂O emissions in France inferred from atmospheric N₂O and²²²Rn measurements

Abstract

Nitrous oxide (N 2 O) concentrations and 222 Rn 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‐Dôme (a mountain site). From 2002 to 2011, we have found a mean rate of N 2 O increase of 0.7 pbb a −1 . The analysis of the mean diurnal N 2 O and 222 Rn cycles shows maximum variabilities at the semi‐urban site of Gif‐sur‐Yvette (0.96 ppb for N 2 O and 2 Bq m −3 for 222 Rn) compared to the rural site of Trainou tower (0.32 ppb for N 2 O and 1.3 Bq m −3 for 222 Rn). The use of 222 Rn as a tracer for vertical mixing and atmospheric transport, combined with the semi‐continuous N 2 O measurements, allows estimation of N 2 O emissions by applying the Radon‐Tracer‐Method. Mean N 2 O emissions values between 0.34 ± 0.12 and 0.51 ± 0.18 g(N 2 O) m −2 a −1 and 0.52 ± 0.18 g(N 2 O) m −2 a −1 were estimated in the catchment area of Gif‐sur‐Yvette and Trainou, respectively. The mean annual N 2 O fluxes at Gif‐sur‐Yvette station correlate well with annual precipitation. A 25% increase in precipitation corresponds to a 32% increase in N 2 O flux. The N 2 O 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 N 2 O 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.