OBSERVATIONS OF THE CHEMICAL-PROPERTIES OF DEW ON VEGETATION THAT AFFECT THE DRY DEPOSITION OF SO2

For 2-3 hours after sunrise, liquid samples were extracted directly from the upper 1/3 of the plant canopies and from surrogate surfaces, concurrently with selected atmospheric observations. Chemical analyses showed that aqueous concentrations of S(IV), SO4 2-, and several other ions in the leaf wetness were often high compared to values typically found in rain, while NH+ 4 was not very abundant. Guttation produced substantial amounts of liquid, which mainly contributed Cl- to the leaf wetness. The dry deposition of S(IV) to leaf wetness was not always apparently limited by aqueous oxidation by O3, especially when aerodynamic resistances limited the maximum potential deposition velocity to less than 0.5 cm/s at a height of 8 m. A more effective oxidant than atmospheric O3 or NO2 could have been present. Foliar uptake of NO- 3 and SO4 2- was significant after sunrise. -from Authors