We characterized the reversibility of aqSOA formed from isoprene at a location in the eastern United States. WSOCp evaporation with drying was observed systematically throughout the late spring and summer, indicating reversible aqSOA formation. The absolute reversible aqSOA concentrations, as well as the relative amount of reversible aqSOA, increased with decreasing NO_x / isoprene ratios, suggesting that IEPOX or other low-NO_x oxidation products were responsible for these effects.