An aerosol delivery apparatus is used to deliver an aerosol into a reaction chamber for chemical reaction to produce reaction products such as nanoparticles. A variety of improved aerosol delivery approaches provide for the production of more uniform reaction products. In preferred embodiments, a reaction chamber is used that has a cross section perpendicular to the flow of reactant having a dimension along a major axis greater than a dimension along a minor axis. The aerosol preferably is elongated along the major axis of the reaction chamber.