Once pathogens are in the air, one of the few things we can do to minimise the health risk is to source control (reduce/eliminate the source and its strength and the aerosolisation factors, as well as potential dispersal interception near the source) [15] . Modelling the movement of bioaerosols in order to advise people to prepare or even evacuate is another option for reducing the health risk [10] . Although the physical properties and transport of aerosols can be predicted in most environments, it is not always known how biological properties change in the aerosol dynamics pathway and during outdoor transport (e.g. aggregation, scavenging and deposition). Source control is not always possible, for instance, if the sources of pathogens are unknown. The longer it takes to identify the source, the higher the risk it poses to people.