Concentration changes of N2O and 222Rn were monitored in the surface layer above a grass sward during the first half of two calm nights. N2O flux on a local or field scale was then estimated from the ratio of the concentration differences between 0.1m and 0.4m height and the directly measured 222Rn flux. This estimate (~7 g N2O-N ha-1d-1) was between the N2O flux on a larger scale (~4.5 g N2O-N ha-1d-1), as estimated from changes in the N2O/222Rn ratio over time, and the small scale flux on the grass plot (~50 g N2O-N ha-1d-1) as measured with closed chambers.