Drying of droplets containing nanoscaled particles is investigated for the first drying stage by means of a population balance model. The novelty of the model consists in the consideration of not only gas-side heat and mass transfer, and liquid-side diffusion, but also aggregation as a particulate process. Size-dependency of particle mobility links liquid-side mass transport and aggregation, leading to different particle concentration profiles in the droplet depending on the thermal conditions and aggregation kinetics. The main focus of this work lies on the influence of the aggregation kinetics on the profiles, the time of crust formation and the resulting droplet porosity at the end of the first drying stage. Model validation and justification is performed by use of experimental data from literature. (c) 2012 American Institute of Chemical Engineers AIChE J, 2012