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While all bioaerosols are biological in origin by definition, an important attribute is whether the bioaerosol is living. Based on this attribute, bioaerosols are categorized into two very important classifications: viable and non-viable. Non-viable bioaerosols are not currently alive and, therefore, cannot multiply; aerosolized pollen, animal dander and saliva, and insect excreta are all forms of non-viable bioaerosols. In contrast, viable bioaerosols are living organisms that demonstrate microbiological activity and have the potential to multiply. These include airborne bacteria, fungi, and viruses, of which bacteria and fungal spores are the two most prevalent bioaerosols present.
Individual bioaerosol particles can range in size from approximately 0.02 to 100 micrometers in diameter, depending on the type and source. However, they also frequently agglomerate in clusters, thereby forming larger particles.
Figure 3: Individual particle sizes for some common bioaerosols.
Important properties characterizing bioaerosols are size, viability, infectivity, allergenicity, toxicity, and pharmacological activity. For a bioaerosol to be infectious or pathogenic (cause disease), it must be viable. However, non-viable bioaersols can still cause allergies or toxic reactions. Note that an innate characteristic of bioaerosols is that these properties may change with time, which can play an important role in sampling, especially for the viable organisms.
The following sections will cover the different types of bioaerosols, including a quick review of microbiology, to aid in your understanding of viable bioaerosols and concepts related to them.