Indoor bioaerosol dynamics

Nazaroff, William W

The largest published survey of indoor bioaerosol levels involved more than 12 000 fungi samples measured indoors and outdoors in~1700 buildings in the United States (Shelton et al., 2002) . The analysis was culture based, so the results reflect number concentrations of viable airborne spores. Little information was reported on the sampling protocol; however, it seems likely that the measurements were based on short-term sample collection. Also, little information was reported about the buildings in which these measurements were taken. The cumulative probability distribution functions ( Figure 1) show that the data are well fit by lognormal distributions. The geometric mean outdoor concentration (493 CFU/m 3 ) is about 6 9 higher than the geometric mean indoor concentration (79 CFU/ m 3 ). The indoor levels show considerably broader range of concentration than do the outdoor levels (GSD of 5.5 compared to 3.3). These data support an important general finding that 'in the majority of cases, indoor fungal aerosols are controlled by outdoor concentrations' (Burge, 2002) . Note that the ratio of geometric mean concentrations, 0.16, lies well within the range 0.04-0.46 predicted by Riley et al. (2002) to apply as the fraction of coarse-mode (2.5-10 lm) particles that would be found in indoor air when outdoor air was the sole source.