CONTINUOUS MEASUREMENTS OF SURFACE EXCHANGE OF SO(2) AND NH(3) - IMPLICATIONS FOR THEIR POSSIBLE INTERACTION IN THE DEPOSITION PROCESS

Simultaneous measurements of SO2 and NH3 dry deposition using the micrometeorological gradient method were performed continuously at two heathlands. It is concluded that dry deposition of both SO2 and NH3 at the two locations in general is limited by aerodynamic resistance during conditions with wet surfaces. The results of the measurements are used to investigate the influence of pollution climates on the dry deposition of SO2 and NH3. It is demonstrated that low surface resistances of SO2 and NH3 will occur in humid regions, as surface wetness is found to be the most important parameter. A high flux of one gas relative to the other can increase its surface resistance through saturation of the surface and lower the resistance for the other gas. During dry conditions, SO2 and NH3 uptake is controlled by stomatal behaviour of the heather plants. Upward fluxes of NH3 have been observed during these periods. It is furthermore suggested that fog composition has a large influence on R(c) values, resulting in both high and low values. Frost was demonstrated to increase R(c) values of both gases.