Thin water films on coniferous needles

During a laboratory measurement in a dew chamber in which the relative humidity was stabilized, constant conductance signals were achieved due to the strong coupling between relative humidity and electrical conductance along the needle surface. After several hours of constant conductance at 70%'relative humidity, the addition of ammonia to the chamber clearly led to an increase of the signal, thus indicating dissolution of NH, and the formation of ammonium ions in the films. This is taken as an indication for the general ability of thin water films to dissolve trace gases as well as for the migration of ions along the needle surface. The implications of these results on the exchange processes between vegetation and the atmosphere are discussed