Turbulent transfer of sulphur dioxide to a wheat crop

Fluxes of sulphur dioxide to wheat were measured over two growing seasons. The deposition velocity, vup, depended primarily on affinities of surfaces for SO2 and varied from less than 0.1 to about 1.5cms-'. Stomata were an important sink, and diurnal changes in stomata1 resistance accounted for most of the variation in v, when leaves were green and dry. When leaves were wet with dew, v, was generally large, irrespective of the physiological state of vegetation. A resistance analogue of transfer to the canopy agrees well with published work and is used to estimate seasonal uptake of SOz by the crop, showing that 30% of the sulphur content of the crop at harvest was probably supplied by absorption of SO2 through stomata.