DISPERSION AND WET DEPOSITION OF SULFUR FROM A POWER-PLANT PLUME

In an experimental study at an oil fired 1000 M W power plant in Sweden the wet fallout of sulfate and the SO2 to sulfate transformation rate has been studied. The project comprised 7 wet fallout tests, with 100 sampling points up to 60 km from the source and 6 dispersion experiments. In the analysis of the wet deposition tests an objective method of analysis is employed for the quantitative identification of the contribution from the studied source. The result of this analysis is that 2/3 of the emitted amount is deposited within 80-120 km in 5 tests and within ca. 190 km in one test. In the seventh test the wind blew the plume out of the sampling network. In the dispersion experiments SO2, sulfate and an inert tracer, SF6, were measured in ground based cross plume traverses and in flights. This program was severely hampered by technical problems, but two tests give clear indication of SO2 to sulfate transformation rates in conditions of widely different relative humidity. On a day with close to 100% relative humidity 70% of the sulfur from the power plant occurs as sulfate at a distance of 30 km from the source. On the much drier next day, the corresponding figure was only ca. 10% at 30km. Analysis of ammonium deposition in two tests and of back trajectories give indication that the rapid SO2 to sulfate transformation rate observed and the corresponding rapid wet fallout are caused by ammonia. It is shown that with expected NH3 background concentration levels the rate of turbulent flux into the plume is sufficient to account for the observed NH4+ fallout rate. © 1979.