The interdependence of aerosol processes and mixing in point source plumes

The basic aerosol phenomena, condensation, coagulation, nucleation and gravitational settling, were studied in plumes generated by industrial point sources. The investigation was concentrated on regions near the source, where the plume is still clearly distinguishable from the background and not vertically mixed. Initially vapors are depleted from the plume more by condensation than by mixing, while later these two processes are often comparable in magnitude. Explicit treatment of condensation is required during most stages of the plume development. Coagulation is normally suppressed by the more rapid dilution, and is probably significant only for nanometer sized nuclei. Gravitational settling depletes largest particles from the plume, but has no effect on other aerosol processes. Binary homogeneous nucleation of sulfuric acid and water is probably a commonplace phenomenon in power plant plumes, can take place only after the plume becomes rather diluted, and is favored by high SO2(g) to fine particulate mass ratio in the emissions, cool and humid ambient conditions, and strong solar radiation.