ABSTRACT
AIMS: Generally it is more economical to first characterize a concentrator system with nonbiological particles followed by more rigorous bioaerosol testing. This study compares sampling system performance for various particle types and sizes. METHODS AND RESULTS: Performances of five concentrators were characterized with five nonviable and viable laboratory aerosols, although not every concentrator was tested with all aerosol types. For particle sizes less than c. 6 microm aerodynamic diameter, similar efficiencies are obtained for all test particles; however, for larger sizes there is a significant difference between liquid and dry particles. CONCLUSIONS: Aluminium oxide particles provide results over a broad range of sizes with a single test, but the method is less reproducible than other methods. A combination of monodisperse polystyrene spheres and oleic acid droplets provides an accurate representation of the system performance, but ultimately biological particle tests are needed. SIGNIFICANCE AND IMPACT OF THE STUDY: Devices are being developed for concentrating bioaerosol particles in the size range of 1-10 microm aerodynamic diameter and this study provides insight into data quality for different test methodologies. Also, the results show some current concentrators perform quite poorly.
Subject(s)
Aerosols , Air Pollution/analysis , Environmental Monitoring/instrumentation , Air Movements , Bacillus/isolation & purification , Environmental Monitoring/methods , Equipment Design , Humans , Materials Testing , Microscopy, Electron , Occupational Exposure , Particle SizeABSTRACT
We measured fluorescence from spherical water droplets containing tryptophan and from aggregates of bacterial cells and compared these measurements with calculations of fluorescence of dielectric spheres. The measured dependence of fluorescence on size, from both droplets and dry-particle aggregates of bacteria, is proportional to the absorption cross section calculated for homogeneous spheres containing the appropriate percentage of tryptophan. However, as the tryptophan concentration of the water droplets is increased, the measured fluorescence from droplets increases less than predicted, probably because of concentration quenching. We model the dependence of the fluorescence on input intensity by assuming that the average time between fluorescence emission events is the sum of the fluorescence lifetime and the excitation lifetime (the average time it takes for an illuminated molecule to be excited), which we calculated assuming that the intensity inside the particle is uniform. Even though the intensity inside the particles spatially varies, this assumption of uniform intensity still leads to results consistent with the measured intensity dependence.
ABSTRACT
Two-dimensional angular optical scattering (TAOS) patterns from clusters of polystyrene latex spheres are measured in the near-forward and near-backward directions. In both cases, the scattering pattern contains a rich and complicated structure that is the result of the interaction and interference of light among the primary particles. Calculations are made for aggregates that are similar to those generated experimentally and also demonstrate the rich structure in the scattering pattern. A comparison of the experimental and theoretical TAOS patterns gives good qualitative agreement.
ABSTRACT
Reproducible fluorescence spectra of individual 2- to 5-microm -diameter biological aerosol particles excited with a single shot from a Q -switched laser (266 or 351 nm) have been obtained with highly improved signal-to-noise ratios. Critical to the advance are crossed diode-laser trigger beams, which precisely define the sample volume, and a reflecting objective, which minimizes chromatic aberration and has a large N.A. for collecting fluorescence. Several allergens (red oak, meadow oat pollen, paper mulberry pollen, and puffball spores) have different fluorescence spectra. Bacillus subtilis fluorescence spectrum deteriorates at high 266-nm incident intensity. Dry riboflavin particles illuminated with a 351-nm light exhibit a new 420-nm fluorescence peak that grows nonlinearly with laser pulse energy.
ABSTRACT
Two-dimensional angular optical scattering (TAOS) is recorded for several particle shapes and configurations. A lens is used to collect a large solid angle of the light and transform the angular profile into a planar distribution according to the Abbé sine condition. Qualitative agreement is found between experiment and theory for the TAOS from spheroids having the same aspect ratio but different sizes. A distinctive irregular island structure is observed in the TAOS from clusters of Bacillus subtilis spores and polystyrene latex spheres. The density per solid angle of these islands is found to increase with cluster diameter.
ABSTRACT
The complete 16-element Mueller matrices for backscattering from amino acids, sugars, and other enantiomorphic compounds pressed into wafer form were measured at infrared wavelengths. For each compound a pair of CO(2) laser lines was selected from the 9.1-11.6-mum region such that one line excited an absorption band in the compound, whereas the other did not. It was observed that at least some of the matrix elements differed significantly depending on which of the two wavelengths was used in the measurement. We propose that a neural network pattern recognition system can be trained to detect the presence of specific compounds based on multiwavelength backscatter Mueller matrix measurements.
ABSTRACT
A new multiangle light scattering instrument is described for the classification of single aerosol particles in a flowing gas stream. Simultaneous measurement at sixteen scattering angles over the surface of a spherical chamber permits determination of a variety of optical observables useful for the subsequent characterization of each measured particle. Particles of 0.2 - 4.0-microm diameter have been measured and data collected at rates exceeding 200 particles/s. Data from polystyrene latex particles, liquid droplets, and irregular particles are shown. Spherical particle data are compared to theoretical calculations and used to confirm the validity of the measurement as well as a powerful calibration procedure.
ABSTRACT
A new instrument for rapid and accurate measurement of the Mueller matrix is described. Distinct measurements of all sixteen elements are made simultaneously and with an absolute accuracy of 1-5%. The instrument employs electrooptic modulators. Results are presented for several simple optical devices and systems.
