The expanding use of prescribed fire to achieve North American land management objectives has led, in recent years, to the increased use of helicopter-ignition, large-scale controlled burns. These mass-ignition convection burns often generate extremely intense and erratic fire behavior and towering convection columns. Environmental concerns over smoke management practices and air quality, in addition to questions about the impact of biomass burning on atmospheric chemistry on a global scale, are also being raised. Fire managers require a better understanding of interactive mass fire behavior, convection column dynamics, and smoke chemistry and dispersal in order to conduct future prescribed burns in a safe, effective, and environmentally sound manner. This problem is being addressed through a cooperative investigation involving fire research scientists from Canada and the United States, in which airborne and ground-based instrumentation is being used to document fire behavior characteristics and atmospheric environmental impact on large-scale operational prescribed fires. To date, three Ontario burns have been monitored (one in 1987 and two in 1988) and the study is continuing. The goal is the development of models to predict fire behavior and air quality impact relative to ignition techniques, surface weather, and atmospheric conditions.