Aerosol-cloud interactions, including the ice nucleation of supercooled liquid water droplets caused by ice nucleating particles (INPs), are a source of  uncertainty in predicting future climate. Because of INP’s spatial and temporal heterogeneity in source, number, and composition, predicting their concentration and distribution is a challenge. In our group, we developed new instrumentation (Freezing Ice Nucleation Counter, FINC) and methodologies (high speed camera, tensiometer) to study the mechanisms of freezing in mixed-phase clouds. We are interested in why and how organic aerosols nucleate ice to reduce the uncertainty in projected global warming estimates.