A GAS-EXCHANGE SYSTEM TO STUDY THE EFFECTS OF LEAF SURFACE WETNESS ON THE DEPOSITION OF OZONE

A leaf chamber system has been developed for measuring the uptake of ozone (O3) by whole plant leaves artificially wetted with dew or raindrops. Tests showed negligible amounts of O3 being lost on internal walls of the chamber, and good heat and mass transfer characteristics without the use of internal mixing fans. The system enables easy and accurate determination of pollutant uptake by wet and dry foliage. Measurements of O3 fluxes to individual leaves indicate that leaf surface wetness, either in the form of a dew layer or raindrops, on the adaxial surface of hypostomatous red maple leaves, enhances the deposition of O3. The increased O3 deposition is ascribed mainly to the presence of compounds in aqueous form that readily scavenge O3, with a lesser additional contribution from decreased stomatal resistance to O3 diffusion.