Secondary organic aerosol (SOA) particles, formed from gas-phase biogenic volatile organic compounds (BVOCs), contribute large uncertainties to the radiative forcing that is associated with aerosols in the climate system. Reactive uptake of surface-active organic oxidation products of BVOCs at the gas–aerosol interface can potentially decrease the overall aerosol surface tension and therefore influence their propensity to act as cloud condensation nuclei (CCN). Here, we synthesize and measure some climaterelevant physical properties of SOA particle constituents consisting of the isoprene oxidation products α-, δ-, and cisand trans-β-IEPOX (isoprene epoxide), as well as synand anti-2-methyltetraol. Following viscosity measurements, we use octanol–water partition coefficients to quantify the relative hydrophobicity of the oxidation products while dynamic surface tension measurements indicate that aqueous solutions of αand trans-β-IEPOX exhibit significant surface tension depression. We hypothesize that the surface activity of these compounds may enhance aerosol CCN activity, and that trans-β-IEPOX may be highly relevant for surface chemistry of aerosol particles relative to other IEPOX isomers.