Indoor bioaerosol dynamics

Nazaroff, William W

Culture-based analyses measure only a small portion of bioaerosols. Figure 2 presents data from a personal monitoring study of elementary school teachers in Finland (Toivola et al., 2004) . For each of the 81 subjects, air was sampled through filters throughout two 24-h periods using personal sampling pumps. Particles were extracted from the filters and analyzed for both fungi and bacteria, using culture-based methods and also using microscope-assisted visual counting. A key point is that the total number concentrations of fungal spores and bacterial cells determined microscopically were a few orders of magnitude higher than the corresponding number concentrations of colony forming units, as determined by culture-based assessment. If (Shelton et al., 2002) . In all, 9619 indoor and 2407 outdoor samples were collected during indoor air quality investigations Although it is common for fungi concentrations to be higher in outdoor air than indoors, in occupied spaces the reverse is commonly true for bacteria (Bartlett et al., 2004; Fox et al., 2005; Hospodsky et al., 2015) . Figure 3 (Chen and Hildemann, 2009a) illustrates this point. The plotted results are geometric mean concentrations based on filter samples of 9-12 h duration collected inside and outside of ten occupied residences in California. Summing across all particle sizes, the GM level of endotoxin (associated with Gramnegative bacteria) was about 50% higher indoors than outside, whereas the GM level of (1-3)-b-D-glucans (a marker of fungi) in outdoor air was almost twice the corresponding indoor level.