At the University of Colorado, I have helped pioneer a new technique to probe depositional ice nucleation onto internally mixed ammonium sulfate/palmitic acid particles, namely optical microscopy coupled with Raman microscopy. The deliquescence and efflorescence phase transitions of the mixed particles were first studied to gain insight into whether the particles are likely to be liquid or solid in the tropical tropopause region. The ice nucleating ability of the particles was then measured under typical upper tropospheric conditions. It was found that coating the particles with insoluble palmitic acid had little effect on the deliquescence, efflorescence or ice nucleating ability of ammonium sulfate. Additional experiments involving Raman mapping provided new insights into how the composition and morphology of mixed particles impact their ability to nucleate ice. Future research will be devoted to studying other types of particles using the Raman system.
aerosols, ice nucleation, cloud formation, water uptake