Fig 1.
Puffball fungus Lycoperdon pyriforme sprays its spores.
The fruiting body serves to generate an aerosol. In this figure, the puffball is dried-up as it has been stored for 2 years before the experiment, but this does not affect the aerosol characteristics, as shown by the data given hereafter.
Fig 2.
Morphological comparison of the particles of the three test samples.
The left-hand images were taken at 400x zoom (grid size is 30 μm) with the optical microscope, and the right-hand images were taken with the SEM microscope and show the particles’ morphologies. (A) Spores of L. pyriforme. The image shows that the spores have a spherical shape and are almost identical in size. The SEM image shows a complex surface morphology of the spores. (B) Polystyrene latex (PSL) microspheres. Both images show that the all PSL spheres have a spherical shape and the same size. They are very stable in a water suspension, i.e. they do not form agglomerates therein (left-hand image) but coagulate quickly, once the solution dries up (see the “Long-term storage” section hereafter). (C) Al2O3 particles. The images show particles’ complex morphology and diverse sizes. Overall, their sizes are comparable to the PSL spheres and spores studied herein.
Fig 3.
The time course of the mean Sauter diameter (D32) of the fungal bioaerosol particles (orange diamonds) compared to Al2O3 (green triangles) and PSL (blue circles).
The trends of changes in the particle sizes are indicated by solid line (spores) and dashed line (alumina and PSL).
Fig 4.
The particle size distribution immediately after atomization (blue) and after 14 min (pink) in the air.
(A) Al2O3 particles. Distribution has shifted towards larger particle sizes, indicating that coagulation has occurred. (B) PSL microspheres. The size distribution narrowed and the mean Sauter diameter decreased because the water covering the spheres had evaporated. (C) Fungal spores. The size distribution showed no considerable change, suggesting that nor coagulation, nor settling had occur.
Fig 5.
Storage-related changes in morphology of the fungal spores and PSL microspheres.
(A) Spores after long-term storage (3.5 years). Some spores (about 20%) collected in 2014 had germinated, which, however, had no considerable effect on the size distribution (see Fig 6A). (B) PSL spheres after evaporation of the water solution aggregated into long chains.
Fig 6.
Size distributions of the particles collected/purchased at different times.
(A) The size distribution of the spores of L. pyriforme collected in different seasons (2014, 2016, 2017). Spores from 2014 (green) had germinated and, therefore, the size distribution slightly shifted towards larger sizes. (B) The comparison of alumina powders purchased in 2016 and 2017. The particles that were stored 1 year longer had more stable aggregates and the size distribution shifted towards larger values.
Table 1.
Characteristics of different particles commonly used as standard aerosol samples compared to the spores of Lycoperdon pyriforme.