Morphological classification of bioaerosols from composting using scanning electron microscopy

•Bioaerosols were captured using the filter method.•Bioaerosols were analysed using scanning electron microscope.•Bioaerosols were classified on the basis of morphology.•Single small cells were found more frequently than aggregates and larger cells.•Smaller cells may disperse further than heavier aggregate structures. This research classifies the physical morphology (form and structure) of bioaerosols emitted from open windrow composting. Aggregation state, shape and size of the particles captured are reported alongside the implications for bioaerosol dispersal after release. Bioaerosol sampling took place at a composting facility using personal air filter samplers. Samples were analysed using scanning electron microscopy. Particles were released mainly as small (1μm) single cells, with aggregates occurring in smaller proportions. Most aggregates consisted of clusters of 2–3 particles as opposed to chains, and were