Indoor bioaerosol dynamics

Nazaroff, William W

Across the aerodynamic diameter range of 0.1-10 lm, particle deposition onto room surfaces is an important fate. In equations (1) and (2), the deposition loss rate is parameterized by a size-dependent rate constant, b. The importance of deposition as a removal mechanism for airborne bioaerosol particles can be explored by comparing b to the air exchange rate. Figure 9 presents some data on size-dependent particle loss rates by means of deposition to room surfaces. These data show that, for particles in the size range 0.5-1 lm, the deposition loss rate coefficient is~0.2-0.3 per hour, a value that is comparable to the lower end of range of air exchange rates discussed in the previous subsection. Under low air exchange conditions, deposition of these submicron particles is competitive with air exchange as a removal process, but in indoor For each house, one or two measurements of air exchange rate were taken over a few-day period using perfluorocarbon tracers. Analysis is based on treating each house as a single unit; in cases where two AER measurements were taken, the results were averaged. Yamamoto et al. (2010) have also published an analysis of these data. Fig. 9 Particle deposition loss rate coefficient (b) measured in a 14-m 3 room as a function of particle diameter. Three of four experiments were conducted with four small fans operating to induce different degrees of air motion. As noted in the key, the mean measured speed in the room with the fans on ranged between 5.4 and 19.1 cm/s. The room was furnished with carpeting, chairs, table, bookcase, and curtains. Source: Thatcher et al. (2002) spaces with high air exchange rates, deposition of these smaller particles is less important than air exchange. For larger particles, in the range 3-10 lm in diameter, the deposition loss rate coefficient is much higher, in the range 2-10 per hour. For these larger particles, deposition is an important mechanism influencing the fate of bioaerosols even for buildings with relatively high air exchange rates.