Rates of conversion of sulfur dioxide to sulfate in a scrubbed power plantplume

The rate of conversion of SO2 to SO42- was re-estimated from measurements m ade in the plume of the Cumberland power plant, located on the Cumberland R iver in north-central Tennessee, after installation of flue gas desulfuriza tion (FGD) scrubbers for SO, removal in 1994. The ratio of SO2 to NOy emiss ions into the plume has been reduced to similar to0.1, compared with a pres crubber value of similar to2. To determine whether the SO2 emissions reduct ion has correspondingly reduced plume-generated particulate SO42- productio n, we have compared the rates of conversion before and after scrubber insta llation. The prescrubber estimates were developed from measurements made du ring the Tennessee Plume Study conducted in the late 1970s. The postscrubbe r estimates are based upon two series of research flights in the summers of 1998 and 1999. During two of these flights, the Cumberland plume did not m ix with adjacent power plant plumes, enabling rate constants for conversion to be estimated from samples taken in the plume at three downwind distance s. Dry deposition losses and the fact the fact that SO2 is no longer in lar ge excess compared with SO42- have been taken into account, and an upper li mit for the conversion rate constant was re-estimated based on plume excess aerosol volume. The estimated upper limit values are 0.069 hr(-1) and 0.03 4 hr(-1) for the 1998 and 1999 data, respectively. The 1999 rate is compara ble with earlier values for nonscrubbed plumes, and although the 1998 upper limit value is higher than expected, these estimates do not provide strong evidence for deviation from a linear relationship between SO2 emissions an d SO42- formation.