A real time quantitative analytical approach, differential mobility analysis coupled to gas-phase Fourier-transform infrared spectroscopy (DMA/FTIR), is demonstrated for an aerosol spray-based synthesis of functional nanoparticles. Calcium oxide nanoparticle (CaO-NP) is chosen as the representative functional nanoparticle. The results show that a direct gas-phase characterization of the temperature-dependent transformation of aerosol spray to CaO-NP was achieved using DMA/FTIR. The changes in mobility size distributions and number and mass concentrations of the aerosol spray versus the precursor concentration were successfully quantified in the aerosol state. The synthesized CaO-NP demonstrated a remarkably high catalytic activity in colloidal form toward the transesterification of methyl hydroxyphenyl propionate (MHPP), the model catalytic application in the study. A maximum of approximate to 19 times of the MHPP conversion was achieved in comparison to the results without CaO-NP. Our work presents a proof of concept for aerosol spray-based controlled synthesis of functional nanoparticles with real-time monitoring using DMA/FTIR for applications in catalyst development.