The viability of MS2, a non-enveloped virus, and Φ6, an enveloped virus, was examined in droplets of different compositions at RHs of 20%, 50%, and 80% by plaque assay. As shown in Fig 2A and 2C, the effect of sodium chloride on MS2 viability was RH-dependent. MS2 decayed more in 35 g/L NaCl droplets than in 0 and 1 g/L NaCl droplets at 20% RH, while the pattern was opposite at 80% RH. At 80% RH, the viability of MS2 was significantly higher in droplets containing NaCl than in those without it, suggesting that NaCl had a protective effect at this RH condition. At 50% RH, the relative viability of MS2 was lower than at the other RHs and was similar across all NaCl levels.