Summary of ozone dry deposition velocity measurements and model estimates over vineyard, cotton, grass and deciduous forest in summer

Measurements of dry deposition velocity (Vd) of O3 (using the eddy correlation technique) and related air quality parameters were made during the Summer of 1991 in Fresno, California over a vineyard, a cotton field and senescent grass. Similar measurements were made over a mixed deciduous forest in Ontario, Canada during the Summer of 1988. A comparison of measured Vd reveals that over the vineyard, the cotton, the grass and the forest, the approximate values are 0.5, 0.8, 0.2 and 1.0 cm s−1 respectively, during the early afternoon hours and 0.2 cm s−1 at night, except for the senescent grass which had a value of about 0.05 cm s−1 at night. Using a variety of dry deposition velocity models, which include different surface and aerodynamic resistance formulations, an analysis is presented of the possible causes for the differences among these Vd values. Among the factors that were considered, the surface resistance, which is primarily dependent upon the stomatal resistance and the Leaf Area Index (LAI), appears to have a major influence. The LAI values were estimated to be about 3.0, 2.0 to 3.0, 1.0 and 5.0 for the vineyard, cotton, senescent grass and forest, respectively. The corresponding measurements for the leaf stomatal resissances were 1.3, 0.7, large and 1.3 scm−1 respectively.