We are evaluating a range of commercially available liquid aerosol generators to produce chemical aerosols of controlled characteristics such as aerosol size, mass, and concentration that can be implemented at our Ambient Air Test Facility (AATF). For our current program of interest, we generate simulant aerosols representing classes of chemicals of interest. Various types of generators are characterized in the laboratory, including atomizing nozzles and vibrating mesh-based devices. Studies are conducted to quantify the range of aerosol size, mass, and number concertation achievable for the different types of aerosol generators. Some of the analysis and the laboratory results are presented here.
One of the uses of the Ambient Aerosol Test Facility (AATF) at the U.S. Naval Research Laboratory is to operate as a test facility for developmental chemical aerosol sensors. The facility draws ambient air from outside the building, with or without HEPA filtration, then introduces aerosols by various means within a 30 cm diameter, 14 m long wind tunnel at flow velocities ranging from 2 to 20 m/s. The turbulent flow generated provides a uniform distribution to a few percent across 90% of the tube diameter to sampling ports in a 3 m long test section at the end. The test section allows sampling and analysis by various sensors to determine aerosol size, concentration, and chemical composition. For the current program of interest, we generate simulant aerosols representing various classes of chemicals of interest. A range of referee instruments to characterize the aerosol in terms of size, number and composition is planned. Commercially available particle sizers and counters, a gas analyzer and an aerosol mass spectrometer are part of the suite of referee instruments. We use a high-resolution, time-of-flight aerosol mass spectrometer (HR-ToF-AMS) from Aerodyne, Inc., which is configured with an aerosol focusing lens to transmit between 50 nm and 3.5 μm diameter particles, and provides size, mass loading and chemical composition information. A calibration system consisting of a scanning mobility particle sizer and a water-based condensation particle counter is used to validate the operation of the AMS instrument. We describe the AMS instrument and its use at the AATF for the assessment of other instruments.
The most accurate insight to how aerosolized material responds to UV radiation is obtained by performing experiments on freely suspended particles, absent from the shadowing that deposition on a surface may impose. For this purpose we have developed a linear electrodynamic particle trap to confine suspended particles using a contact-free technique. The trap allows us to challenge and study aerosols under controlled environmental parameters such as temperature, humidity and radiation exposure. We present the results of a quantitative study on the changes in viability of Bacillus anthracis Sterne strain spores confined within this trap and illuminated by either simulated sunlight or a UV light source at 253.7 nm. Up to 500 same-size particles, (that is, consisting of approximately the same number of spores), were created from a droplet-on-demand injector, trapped and irradiated with varying time scales. Illumination times ranged from 5 to 300 seconds with a maximum fluence of 500 J/m2 using the UV source, and particle clusters containing as little as 1 up to as many as 55 spores were used. As will be discussed, the viability of spores decreased as total fluence increased as expected, and for the same fluence, viability improved as the number of spores in each particle increased.
We examine how aggregation affects the light-scattering signatures, especially the polarization in the near-backward-scattering direction. We use the discrete dipole approximation (DDA) to study the backscatter of agglomerate particles consisting of oblong monomers. We examine the effects of monomer number and packing structure on the resulting negative polarization branch at small phase angle. We find large a dependence on the orientation of the monomers within the agglomerate and a smaller dependence on the number of monomers, suggesting that the mechanism producing the negative polarization minimum depends strongly on the interactions between the individual monomers. We also examine experimental measurements of substrates composed of biological cells. We find that the light-scattering signatures in the backward direction are not only different for different spore species, but for spores that have been prepared using different methodologies. These signatures are reproducible in different substrates composed of the spores from the same batches.
A partnership that includes the Naval Research Laboratory (NRL), MIT Lincoln Laboratories and the Edgewood Chemical and Biological Command is engaged in an effort to develop optical techniques for the rapid detection and classification of biological aerosols. This paper will describe two efforts at NRL: development of an improved UV fluorescence front-end trigger and the use of infrared absorption spectroscopy to classify biological aerosol particles. UV Laser-induced fluorescence (UVLIF) has been demonstrated to provide very high sensitivity for differentiating between biological and inorganic aerosol particles. Unfortunately, current UVLIF systems have unacceptably high false alarm rates due to interferences from man made and naturally occurring organic and biological particulates. We have developed a two-wavelength, UVLIF technique that offers a higher level of discrimination than is possible using single wavelength UVLIF. Infrared absorption spectroscopy coupled with multivariate analysis demonstrates a high potential for differentiation among members of biological and chemical sample classes. Two-wavelength UVLIF in combination with the IR interrogation of collected bioaerosols could provide a rapid, reagentless approach to specific classification of biological particles according to an operational level of discrimination - the degree of particle characterization required in order to signal the presence of pathogenic material.
A two-wavelength excitation bioaerosol sensor has been developed and characterized for classifying various types of aerosols, including biological organisms and non-biological interferents. Single aerosols, smaller than 10 μm, are interrogated with 266 nm and 355 nm laser pulses separated in time by 400 ns. Fluorescence signals excited by these pulses are detected in three broad spectral bands centered at 350 nm, 450 nm and 550 nm. The results indicate that bacterial spores, vegetative bacterial cells and proteins can be differentiated based on the two wavelength excitation approach.
We describe an instrument developed to monitor the biological fraction of ambient aerosol. This device simultaneously sizes individual particles in an air stream, and measures their total fluorescence following excitation at 266 nm. Recent results of single blind outdoor tests carried out in Alberta, Canada are described. In these, aerosols were generated containing four different types of biological material: ova albumin, MS-2 phage, Erwinia herbicola vegetative cells and Bacillus subtilis spores. Results indicate a probability of detection of 87% was achieved for target aerosol concentrations as low as a few (1-5) P particles/liter. Absolute quantitative detection efficiencies for individual bioaerosols were at least 70%. During the tests, nonbiological aerosols were also released and found not to generate any significant fluorescent signals.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.