Biomass burning aerosols have important global radiative effects that depend on particle size. However, model estimates of these effects do not explicitly account for the coagulation of particles in biomass burning plumes. In this work, we present the first use of a sub-grid coagulation scheme in a global aerosol model to account for in-plume coagulation. We find that this in-plume coagulation leads to important changes in the biomass burning aerosol radiative effects.