Results from mathematical modeling of aerosol formation during combustion of woody biomass fuels were compared with results from particle size distribution (PSD) measurements at a pilotscale biomass combustion unit with moving grate and flame tube boiler. The mathematical model is a plug flow model considering coagulation, nucleation, condensation, and particle deposition mechanisms (thermophoresis, particle diffusion, turbophoresis: and gravitational settling) of spherical particles as well as condensation of vapors on cooled boiler walls and a changing flue gas composition determined by equilibrium calculations. Additionally, the influence of kinetically limited homogeneous and heterogeneous reactions was taken into account in the case of sulfation reactions. To check the modeling results, investigations regarding PSDs and total aerosol mass loadings of the flue gas resulting from biomass combustion (beech chips, waste wood) were performed by measurements at a fixed bed biomass combustion unit (nominal boiler capacity: 440 kW). Furthermore, the composition of the aerosols sampled was determined. The comparison of calculated and measured particle size distributions and aerosol compositions agreed well, which permits the conclusion to be drawn that the model is applicable to the estimation of amount, and chemical composition of aerosol emissions from fixed-bed biomass combustion.