The air–water interface plays a crucial role in microdroplet reactions. In this study, we investigated the oxidation of two thiol molecules on water microdroplets: 2‐mercaptosuccinic acid (MSH) and 3‐phenyl‐2‐sulfanylpropanoic acid (PSH), with PSH being much more amphiphilic than MSH. Mass spectrometric experiments showed much higher oxidation yields of PSH compared to MSH. Theoretical results indicated that PSH anions preferentially partitioned to the air–water interface, but MSH anions showed no enrichment trend, which is consistent with the experimental results. This study highlights the central importance of the air–water interface in microdroplet reactions.
Chen et al. (2026) studied this question.