Although the model has its limitations, indicative calculations of changing fraction of the original aerosols and droplets remaining elevated from expiratory activity at varying distance can be made and, thus, the potential degree of exposure. It should be recognised that the model makes no attempt to represent: the intricacies of the dynamics of particle impaction on surfaces (in this case, the face of a susceptible individual) and the change in deposition efficiency with particle size and Stokes number; the actual area of exposed mucous membranes (i.e. the eyes, nose and mouth); the thermal flows generated by individuals; the inhalation dynamics on inspiration; and the dose required for infection. It also only considers which are initially emitted along the centre of the respiratory jet (i.e. those which are anticipated to travel the furthest) and ignores any of the complexities associated with an ensemble droplet plume, such as droplet/droplet interactions. However, the model does make it possible to integrate the fraction of the droplet size distribution passing through a chosen window transverse to the exhalation jet (Fig ). We have explored the dependence of this fraction remaining airborne on RH, temperature and distance, considering travel distances of 1, 1.5, 2, 2.5, 3, 3.5 and 4m.