On ozone dry deposition—with emphasis on non-stomatal uptake and wet canopies

Measurements of O3 fluxes and concentrations over five different sites were used to study O3 dry deposition. It was found that high humidity, dew and rain increase O3 uptake by canopy cuticles. However, the increase by cuticle uptake maybe offset by a decrease in stomatal uptake due to weak solar radiation or stomatal blocking under wet conditions. Thus, during nighttime the overall canopy resistances (Rc) for O3 uptake under wet conditions was usually smaller than under dry conditions, while in the daytime, Rc for wet canopies could be either larger or smaller compared to dry canopies. This will depend on the relative contributions of the decrease in cuticle resistance and the increase in stomatal resistance. The non-stomatal uptake of O3 was found to be affected by friction velocity, relative humidity, canopy wetness, leaf area index, etc. Parameterizations for non-stomatal resistance for dry and wet canopies were developed based on the five site O3 flux data. These equations were found to provide reasonable predictions of non-stomatal canopy resistance based upon comparisons with the nighttime and daytime measurements.