MRI conducted an airborne plume monitoring program as part of the Chalk Point Cooling Tower Project. Plume measurement included: temperature, dew point, visibility, turbulence, droplet size distribution and concentration, liquid water content, sodium chloride concentration (NaCl), sulfuric acid concentration (H2SO4), sulfur dioxide concentration (SO2). Vertical cross sections of the plume were mapped at several downwind distances. Data were recorded every half second to provide the short response times required for accurate plume profile measurements. The presence of stable visible plumes was observed during cold high humidity conditions. Even under these conditions, the decrease in visibility is not considered to be a hazard to aircraft because of the limited distance over which it extends. Interactions between the cooling tower plume and the boiler plume are limited. The boiler plume is saturated with water from combustion products and from a venturi wet scrubber. Therefore, chemical reactions that require moisture have occurred prior to mixing with the cooling tower plume, and the additional water supplied by the cooling tower plume has little effect.