Effect of relative humidity on passive spore release from substrate surfaces

Fungal spores are abundant in ambient air and exposure to this type of bioaerosols are found to cause significant health and climatic effects. In this study, we investigated the influence of air relative humidity (RH) on the passive release of spores from solid substrates. Preliminary investigations into the effect of RH on fungal spore release indicated an increase in spore flux with reduced air RH. The change in spore emission flux occurred very quickly in response to a change in ambient RH. To verify the hypothesis of extremely rapid drying under lower RH, experiments were conducted using a quartz crystal microbalance with dissipation (QCM-D) to understand the timescales of spore moisture uptake and drying. The analysis of mass transfer of water to and from the spores indicated that the bulk of the transfer occurred within a minute of exposure to any RH. The effect of the ambient RH was explained using a mathematical model with the spotlight on the parameter, E, that represented the energy required to aerosolise one spore. This study demonstrates the application of QCM-D to study interaction between ambient aerosol particles and various vapor phase and gas phase environments. The study enhances the overall understanding and capability to characterise passive fungal spore release under varying humidity conditions in the natural environment.