Recent Field Studies of Dry Deposition to Surfaces in Plant Canopies

A variety of field techniques were used to assess the dry deposition of sulfur. In a deciduous forest canopy in eastern Tennessee, inert petri plates and adjacent chestnut oak leaves showed similar SO/sub 4//sup -2/ deposition velocities of about 0.1 cm s/sup -1/. In the same forest, statistical analysis of throughfall yielded a deposition velocity of 0.48 cm s/sup -1/ for total sulfur (SO/sub 4//sup -2/ plus SO/sub 2/). The throughfall technique appears useful for scaling individual surface measurements to larger spatial and temporal scales. On a grassy field in Illinois, flat Teflon plates, petri dishes, and dustfall buckets were exposed side by side. Measured sulfate deposition increased with increasing rim height on the collection surface, and deposition velocities ranged from 0.14 to 0.70 cm s/sup -1/. Much of the deposition to these surfaces can be attributed to large-particle SO/sub 4//sup -2/. Dry season (summer) deposition velocities of /sup 7/Be in California were found to be similar to dry deposition velocities of /sup 212/Pb in Tennessee, ranging from 0.18 to 0.35 cm s/sup -1/. These natural radionuclides attach to submicron aerosols in the atmosphere and may be useful tracers of submicron SO/sub 4//sup -2/ deposition. 9 references, 5 figures, 4 tables