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A two-wavelength laser-induced fluorescence technique is described for detecting and classifying biological aerosols. Single aerosols, smaller than 10 mm, 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. Estimates of the fluorescence cross sections for 16 bioaerosol simulants and interferents are presented.

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This report describes procedures and results of recent outdoor tests in evaluating a prototype single particle fluorescence analyzer (SPFA), an instrument that is being developed to simultaneously monitor ambient concentrations of both biological and nonbiological aerosols using optical techniques. Recent modifications to the SPFA are also noted and discussed. During recent outdoor tests, aerosols were generated containing four different types of biological material: ova albumin, MS-2 phage, Erwinia herbicola vegetative cells and Bacillus subtilis spores. Analysis of the SPFA results indicates that a probability of detection of at least 87% was achieved for target aerosol concentrations as low as a few (1-5) particles/liter. Moreover, comparison with different reference instruments indicate that the SPFA can achieve absolute quantitative detection efficiencies for individual biological aerosols of at least 70% (assuming appropriate alignment and threshold settings are made). During some of the outdoor tests different nonbiological aerosols were also released that generally did not generate any significant fluorescent signals. Although official test scores have not yet been distributed, we provide here the SPFA results for each of the aerosol releases made during the test. Analysis of the relative fluorescent intensities in the visible and UV spectral bands suggests that these data can be used in the future to provide an indication of the type of biological aerosol being released as well. C