Bioaerosol concentrations

Table 1.7-2. Problems with Assessment of Bioaerosol Concentrations Indoors.

In sampling for bioaerosols, the objective is to determine the presence or the number concentration of specific species or the total bioaerosol concentration. Sampling... 

The most common collection methods rely on impaction, the same process as described in Section 5.5 for nonbioaerosols. Slit impactors impact particles directly onto a culture medium. For bacteria and fungal spores, the culture medium, called agar, is a semisolid material containing water and nutrients that foster the growth of the viable particles that are collected. For viruses, cell or tissue culture media are used. Typically, the agar fills a 100-mm or 150-mm disposable petri dish, called a culture plate, that is slowly rotated under the slit to provide a history of bioaerosol concentration. Rotating slit impactors have flow rates of 28-50 L/min and cutoff diameters of about 0.5 pm. 

An adjustable-speed, rotating slit impactor has a total deposition area of 50 cm for one full rotation. For how long should a sample be taken to get the desired colony surface density if bioaerosol concentration is 1000 cfii/m Assume the sample flow rate is 28 L/min, and that sampling takes place for one full rotation. 

Naik, D. V., C. J. Weschler, and H. C. Shields, Indoor and Outdoor Concentrations of Organic Compounds Associated with Airborne Particles Results Using a Novel Solvent System, in Indoor Air Pollution—Radon, Bioaerosols, VOC s (J. G. Kay, G. E. Keller, and J. F. Miller, Eds.), Chap. 6, pp. 59-70, Lewis Publishers, Chelsea, MI, 1991. 

Natural outdoor bioaerosol backgrounds come from a wide range of sources such as viruses, bacteria, fungi, and plants (Merill et al 2006). Pollens from plants vary seasonally and diumally and can sometimes result in visible clouds with more than 10,000 particles per liter of air. Weather patterns such as rain and wind also impact outdoor bioaerosol particle concentration. 

A laser ablation TOF mass spectrometer has been developed to iderrtily individual airborne micrometer-sized particles, comprising a single cell or a small mrmber of clumped cells (Tobias et al. 2005). This approach is reagerrt-less, and it relies on laser ablation and detection of lower mass (less than m/z 200) positive and negative ions. MS signatrrres for aerosolized Mycobacterium tuberculosis particles are distinct fromM smegmatis. Bacillus atrophaeus, and B. cereus particles. This technique is tested as a stand-alone airborne M. tuberculosis detector in bioaerosols from an infected patient at airborne concentrations of 1 particle/liter. 

Another common measure of concentration is number concentration, the ntim-ber of particles per unit volume of aerosol, commonly expressed as number/cm or number/m. An older unit is mppcf (million particles per cubic foot). Concentrations of bioaerosols and fibers are expressed in terms of number concentration. 

TABLE 19.1 Particle Size and Natural Background Concentration of Bioaerosols ... 

Bioaerosols can be sampled by allowing them to settle directly onto culture plates, a simple, inexpensive method that allows one to determine the presence of a specific microorganism. The technique, however, is not useful for quantifying airborne concentrations because, after culturing, the size of the initial particle cannot be determined, so TS and the flux are not known. 

A 400-jet impactor samples a bioaerosol at 28 L/min for 20 minutes. If 344 colonies are counted, what is the average airborne number concentration of viable particles. Assume no loss of viability during sampling. 

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