Ostwald ripening in evaporating respiratory breath figures

Understanding collective evaporation of micron-sized breath droplets can enhance modeling of clouds and inform strategies to limit virus transmission. In this work, we analyze thousands of micron-sized droplets within human and pure water breath figures, identifying two regimes. First, during coarsening, whilst the entire array is evaporating, larger droplets grow at the expense of smaller ones, driven by differences in equilibrium vapor concentration as low as 0.02%, arising from varying interfacial curvature. In this regime, the temporal distribution of droplet radii behaves according to classic Ostwald ripening theory, a mechanism which is usually considered only for submicron droplets. We then use a mean field model to connect droplet evaporation theory with Ostwald ripening, and predict individual droplet dynamics, showing how the accuracy depends on droplet coverage fraction. Finally, we show how the Coarsening regime is terminated by an edge regime, in which all remaining droplets evaporate rapidly.