THE EXCHANGE OF NITRIC-OXIDE, NITROGEN-DIOXIDE AND OZONE BETWEEN PASTURE AND THE ATMOSPHERE

Fluxes of NO, NO2 and O3 were determined over a drained marshland pasture in south-east England by using flux-gradient techniques. Nitric oxide was found to be emitted at rates of up to 40 ng m-2 s-1, the rate of emission being related to the magnitude of the eddy diffusivity. Nitrogen dioxide deposited at rates of up to 90 ng m-2 s-1 under the control of stomatal resistance, a clear diurnal cycle being observed. Minimum canopy resistance was of the order of 80 s m-1. Ozone deposition was also controlled by stomatal resistance, the minimum canopy resistance being around 100 s m-1 and fluxes reaching a maximum of 220 ng m-2 s-1. Corrections made to NO and NO2 fluxes to compensate for chemical reactions showed flux divergences of the order of 30% for NO and NO2, but these were not statistically significantly different from the measured fluxes. The pasture was found to be a net sink for nitrogen in the form of NO(x).