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Electrostatic Charge/Discharge Processes in Biological Aerosols


OBJECTIVE: To develop a bioaerosol trigger based on electrostatic charge/discharge rates. DESCRIPTION: The current generation of UV fluorescence based triggers for bioweapon detection systems are not able to detect the complete spectrum of anticipated bioweapon attacks. Current biological warfare agent detection systems within the chem/bio defense community depend on UV fluorescence to trigger a detection event. Most biological agents possess a strong fluorescence signature that can be utilized both as a trigger and as a detection mechanism. Once the BW agent aerosol enters a sensor and triggers the device with an appropriate fluorescence signature, a series of confirming tests are performed to determine the presence or absence of a BW threat. Non-fluorescent BW threats, however, pose a problem. Without an appropriate trigger, confirming tests are not performed. Thus false negative responses can occur and may place personnel at risk. For non-fluorescent threats other properties must be utilized to develop a working trigger. A trigger technology that can better detect non-fluorescent threats is urgently needed. A promising solution to this important problem is a trigger based on the electronic charging physics of aerosol particles. Previous work has shown that aerosol particles exposed to an ionization source gain charge based on its material properties. Evidence of charging events or changes in aerosol charge could be used as a trigger in a bioaerosol detection system. Charging methods could potentially include corona discharge, charged air ions, UV, X-rays, gamma rays, electron beams, and beta particles. To facilitate the development of a bioaerosol trigger, aerosol charge signatures must be determined and the characteristic signatures of bioweapons identified. Previous experiments on the charging of smoke and soot particles have shown that aerosol particles can be charged by ionizing UV light. The UV photons were found to knock electrons off the surface of the aerosol particles in a manifestation of the photoelectric effect. The amount of charge developed was found to be a function of the material properties. Additionally, many charging process rates depend on a material"s electric permittivity. These and other charging effects could be combined or isolated to detect the presence of spores. Little is known about the charging and discharging process for biological spores. However, preliminary experiments have shown that the charge/discharge rates for airborne microorganisms could be significantly different than the charge/discharge rates of common airborne aerosols such as dust and smoke. An accurate experimental technique is required to catalogue the charge/discharge characteristics of spores and common interferants, as well as to anchor models. Physics based models are needed to support the experiment by predicting charge/discharge rates as well as to extrapolate experimental results to the design of a trigger system. PHASE I: Develop concepts for a diagnostic system to accurately measure the charging/discharging process of biological spores and common atmospheric aerosols. Develop a model that simulates the expected rate of particle charge and discharge for the same set of aerosols. Demonstrate the system"s feasibility through experiments or detailed analysis. Estimate the error level of the data collected with the system. PHASE II: Build a charge/discharge diagnostic system, and verify its operation. Build a database of charge/discharge rates for common atmospheric aerosols, as well as aerosolized bacterial spores. Determine rates for particles alone and in mixtures with other particle types. Confirm model predictions for charge/discharge rates with the experimental data. Analyze the database of charge/discharge rates and enumerate patterns that could be used to detect aerosolized bacterial spores. Determine the ability of the system to detect aerosolized bacterial spores in the presence of common airborne contaminants such as dust and smoke. PHASE III DUAL USE APPLICATIONS: Further research and development during Phase III efforts will be directed towards refining a final deployable design, incorporating design modifications based on results from tests conducted during Phase II, and improving engineering/form-factors, equipment hardening, and manufacturability designs to meet U.S. Army CONOPS and end-user requirements. An inexpensive system that can monitor for bioaerosols suspended in air has numerous commercial applications. REFERENCES: 1. K.R.S. Prier, B. Lighthart, and J. J. 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