Dynamic Surface Tension Measurements. Dynamic surface tension measurements taken over 10-minute time periods using pendant drop tensiometry were carried out following procedures previously outlined by this group. The dimers were suspended in both deionized water and 1.0 M ammonium sulfate solution, the latter employed to replicate the high concentrations of inorganic species in the atmospheric SOA particle bulk phase. The surface tension of the 1.0 M ammonium sulfate solution-1.0 M being chosen based on our previous estimate of the upper limit of salts in SOA particles -is approximately 75 mN m -1 , compared to that of pure water (72.8 mN m -1 ). As atmospheric aerosols and their proxies are most typically studied with some inorganic content, 2 herein we highlight the data collected in ammonium sulfate solution (1.0 M ammonium sulfate solution = pH 5.6); measurements taken in pure water (fresh Millipore water = pH 8.8) can be found in the Supporting Information. The concentration of the dimers in the 1.0 M ammonium sulfate solution ranged from 0.01 mM to 0.1 mM, above which they were found to be insoluble.