10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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BioAerosol Generation Methods
JAY D. EVERSOLE, Cathy S. Scotto, Naval Research Laboratory
Abstract Number: 556 Working Group: Infectious Bioaerosol
Abstract This presentation will review recent methods of bioaerosol generation and assess their advantages and disadvantages. The term bioaerosol is taken here to be aerosol particles that includes, but is not restricted to microorganisms, so that particles composed of any biogenic or biomolecular material would be included. Unfortunately, this is such a broad category, in which each organism or specific material has a multitude of somewhat unique specific characteristics that it is difficult to organize along general principles. Rather than simply attempt to summarize and catalog recent literature on bio-aerosol generation results, we approach this question in terms of available methods. In broad stroke, bioaerosol generation for experimental purposes falls into one of two methods: (a) producing droplets of liquid suspension, or (b) directly producing dry particles from powdered sample material. For both these approaches a number of specific devices or methods exist, each of which will affect the resulting aerosol in terms of its composition, aerodynamic diameter (Dae), and relevant biological function(s).
As with all aerosols, particle composition and Dae distribution are important aspects to either control or characterize, but bioaerosols have a large range of additional factors that characterize their biological state. Examples of biological characteristics include: enzymatic activity, toxicity, culturability, viability, and infectivity. Specific factors will depend on both the biological material being addressed as well as the purpose, or application, of the aerosol experiments. For most of the work referenced in this review, the materials considered are microorganisms and either viability or culturability are critical parameters for the resultant aerosol.
Far from a simply pedantic concern, the preparation and characterization of a bioaerosol material can have direct and significant consequences for the data analysis and interpretation of experimental measurements. Biodegradation can and generally does occur on a continuous basis even during sample storage, and the process of aerosolizing the sample will have its own degradation effect. Once the particles are airborne, then experimentally one has to account for mechanical loss of particles to surfaces and gravitational settling, which is referred to as aerosol decay, but additionally there will be bio-degradation effects due to the new physical condition of being a particle suspension in air, which generally will be greater than the decay rate as a bulk sample. Since these effects are measured in terms of populations of particles/organisms, it is important to characterize and engineer sample homogeneity. To illustrate, suppose one wants to determine the effect of an environmental parameter on viability of a specific organism as a bioaerosol. To establish a baseline, or control, consider that the rate of degradation may also depend on sample growth protocol, growth stage at harvesting, method of preparation for being aerosolized as well as aerosol generation method itself. In other words, the measured result is to some extent a package which includes the detailed sample history. Additionally, it is extremely rare for an organism to be aerosolized by itself, and to the extent that the organism is just one constituent in the presence of other material(s) adds more variable(s) that potentially can modify results.
This brief description should provide some appreciation for the extensive list of characteristics, initial conditions and experimental variables that can arise when attempting to quantify biological materials as aerosols. In light of this situation, one could argue the necessity of establishing some sorts of standards through which results from different experiments could be compared. We will illustrate our perspective using current popular methods and discuss the positive and negative features of each.