Temporally and spatially resolved investigations of the efflorescence of equimolar mixtures of ammonium sulfate (AS) and ammonium nitrate (AN) aerosol droplets were performed by confocal Raman spectroscopy combined with high-speed photography. Information was obtained on the dynamic process of morphological changes and the heterogeneous distribution of efflorescence products. The supersaturated AS/AN mixed droplet was found to first precipitate as the double salt 3AN·AS when the relative humidity was 50%. The excess AS was irregularly distributed on the surface of the double salt as an inclusion structure. No formation of 2AN·AS was observed throughout the efflorescence process.
