Droplets undergoing evaporation and settling while transported in a turbulent buoyant jet is a complicated multiphase flow problem. And never as in the past few months was it appreciated how strong this problem can impact our daily life. COVID-19 is just a tiny proteinic chain, which requires multiphase flow to exist and spread. We, as the editors of International Journal of Multiphase Flow, felt compelled to communicate to the broader community what multiphase flow has to offer in way of solution to the present global pandemic problem. We consulted several esteemed colleagues in our community asking the question, "how can multiphase flow community help the broader community of scientists, doctors, engineers and policy makers in addressing the present problem?". The decision was to form a team of world-class expertise in every aspect of the problem and write a paper that presents simple theoretical framework that encapsulates the current understanding of the community.

The object of the paper is to write about the state-of-the-art in modelling the evolution of a swarm of expectorated droplets, starting from their initial size distribution ejected and arriving at the potential contagion concentration at the breathing zone of a susceptible individual. Clear understanding of these phenomenon and our current prediction capabilities and limitations will help us identify the much needed fundamental and applied research to be conducted, so that the full commitment of our multiphase flow community can be properly directed. It is also our aim to stimulate and involve the multiphase flow community to advance the current knowledge further, working synchronously with virologists, biologists and policy makers so to establish a firm scientific basis for the prediction of airborne diseases, so that effective technologies for limiting the spread of contagion can be developed, and sound policies for protecting the public can be formulated.

[^1]: Editors in Chief International Journal of Multiphase Flow
