Bioaerosol release from composting sites is a known health risk, with the structure of bacterial and fungal bioaerosol communities varying both temporally and spatially. However, little is known about how the the bioaerosol community varies by size fraction. Additionally focused studies using specific qPCR or media potentially overlook pathogens. Here, Andersen six stage impactors were used to collect size segregated bioaerosol samples at a composting site (0.65-1.1 μm, 1.1-2.1 μm, 2.1-3.3 μm, 3.3-4.7 μm, 4.7-70 μm, and > 7 μm). qPCR and next-generation sequencing (NGS) were used to give a comprehensive picture of the bacterial diversity. The highest bacterial abundances were found in the largest size fraction with a decrease from 4.2 (±0.3) to 3 (±0.4) log10 16S rRNA copies m-3 air between the largest and smallest fractions. There was also greater diversity and evenness of bacterial communities in the largest size fractions. The bacterial community with particle sizes > 3.3 μm was dominated by OTUs related to Bacilli and Clostridia, whereas Actinobacteria dominated the < 3.3 μm community. In addition, sequences related to bacterial pathogens Bordetella (whooping cough), Corynebacterium (diphtheria), Legionella (legionnaires), Mycobacterium (tuberculosis and leprosy), Streptococcus (pneumonia), and Turicella (otitis media) were detected. Further research with NGS is required to understand the drivers of these patterns of diversity as smaller particles are a greater heath risk as they can penetrate the respiratory system more deeply. Furthermore, screening with NGS could be used to identify pathogens (even if present in low abundances) as part of a bioaerosol monitoring network.