RH is the major factor that determines droplet evaporation kinetics, as shown in Fig 6. The initial evaporation rate was much higher at 20% RH than at 50% and 80%. At 20% and 50% RH, droplets fully desiccated in 1 h. At both conditions, the evaporation rates were relatively steady at the beginning (the first ~10 min and ~15 min for 20% and 50% RH, respectively), but later gradually decreased. However, at 80% RH the evaporation rate was more consistent throughout the experiment, and droplets did not fully evaporate within 1 h.