Recent results are presented in the continuing investigation of SO2 washout by precipitation from plumes of large, coal-fired power plants. The research consisted of three phases: a washout modeling effort, a laboratory investigation of solubility and mass-transfer behavior in the SO2/water system, and an experimental field program. The modeling effort resulted in the creation of two washout models. The first of these is based on linear theory and provides a relationship that can be used for hand-calculated estimates of washout provided that the implicit assumption of vertical rainfall is not violated significantly. The second model can account for nonlinear behavior and is not restricted to vertical rainfall, but necessitates computer calculation to predict washout values. Solubility experiments were conducted. The field-study program was conducted on the Olympic Peninsula of Washington state to examine the washout of SO2 in an unpolluted atmosphere. Irreversible washout was shown to be untenable. Predictions from the nonlimiting washout models were found to agree well with experiments.

"To Environmental Protection Agency, Division of Meterology." "EPA 950-R-72-048." "BNW-389." "February 1972." Cover title.