Abstract FTIR-ATR technology is used to study the efflorescence kinetic of Na2SO4 and mixed Na2SO4/CTAB aerosols. As the RH decreased linearly, the ν3 SO42− band shifts from 1094 cm−1 to 1132 cm−1, suggesting the phase transition of Na2SO4 from solution to crystal phase (III). For pure Na2SO4 aerosols, the ERH is 75.1% RH, whereas the efflorescence point of mixed Na2SO4/CTAB aerosols (74.2%) is lower. By further analysis of IR differential spectra, the ratio of Na2SO4 crystals in mixed aerosols is only 62.7% and the heterogeneous nucleation rate of Na2SO4 in Na2SO4/CTAB mixed aerosols is lower than that in pure Na2SO4 aerosols. They showed that CTAB assembled into reversed micelle and part Na2SO4 droplets are in the core to form core-shell structure, and CTAB shell prevents core Na2SO4 solutions from crystallizing. However, the counter ion Br− for CTAB reversed micelle can interact with Na+ ions, which decreases the crystallization rate of free Na2SO4 droplets and ERH is delayed.