Source and airborne measurements were made in October 1979, at the TVA Widows Creek Steam Plant in northeastern Alabama. Primary emissions from the flue gas stacks were determined including total mass, particle size distribution, SO2, NOx, and SO3/H2SO4. An instrumented fixed wing airplane was used to acquire plume data at various altitudes and downwind distances. This data was used to establish secondary pollutant formation rates. Sulfate transformation rates were measured between 4.3 percent/hr and 0.6 percent/hr for a well-defined plume at 1.1 hr and 2.2 hr plume ages respectively. A chemical element balance around the scrubber indicates that as much as 40% of the total mass exiting the scrubber was generated from entrained liquor. This accounts for 90% of the unit's sulfate emissions. These primary emissions account for between 4 and 17% of the total sulfates measured downwind in the plume.