An advanced rotating aerosol chamber was developed to study the changes of fluorescence spectral profile and intensity, the viability and the quantitative polymerase chain reaction (qPCR) signal of ...Escherichia coli aerosol particles as they are exposed to simulated atmospheric conditions over time. These conditions included relative humidity (RH) below 30% or ∼75%, ozone ∼100 ppb, volatile organic compounds (VOCs) α-pinene (∼5 ppb) or toluene (∼45 ppb), and simulated solar (SS) irradiation. Individual experiments examined the effects of these conditions applied individually and in combination. Experimental results demonstrate that the 263 nm laser excited UV fluorescence band (280-400 nm) showed the greatest rate of decrease, and the visible band (400-580 nm) generally had a smaller change rate which followed the change in the UV band. The 351 nm excited visible band (380-650 nm) had the smallest decay rates, and sometimes increased, when exposed to ozone, high RH, and VOCs. Generally, the viability, qPCR signal intensity, and the fluorescence intensity decayed faster when more variables were applied in combination. Simulated solar irradiation was the most dominant factor in the aging process, followed by the combination of high RH and ozone. Interestingly, the decay of fluorescence and qPCR signal do not appear to correlate directly with loss in viability. Therefore, additional studies are expected to further understand the mechanisms by which atmospheric chemical processes impact viability, qPCR signal intensity, and the fluorescence of biological aerosols.
A variety of methods have been used to study atmospheric bioaerosols. A common technique employed for the detection and measurement of bioaerosols is the measurement of the autofluorescence of ...biological particles when excited by ultraviolet light. We examined the changes in the fluorescence spectra of bioaerosols when exposed to ambient outdoor conditions for periods of several hours. The bioaerosols in this study were contained in a Captive Aerosol Growth and Evolution (CAGE) chamber that employed two rotating drums constructed with an exterior FEP Teflon film to allow sunlight to penetrate and an inner ePTFE membrane to allow ambient trace gasses to permeate the drums. The bioaerosols were periodically measured with a TSI UV-APS (excited at 355 nm) and a single-particle fluorescence spectrometer (excited at 351 and 263 nm). The data indicate changes in both fluorescence spectral profile and intensity from Bacillus thuringiensis var. kurstaki spores and MS2 bacteriophage particles during the experiments. The changes observed in these particles appear to be due to a combination of the environmental conditions rather than attributable to any single factor. The results of this study indicate that bioaerosols are significantly altered by atmospheric aging processes and that these changes may affect measurements by ultra-violet light induced fluorescence (UV-LIF) or other spectroscopic techniques.
Boundary layer wind data observed by a Doppler lidar and sonic anemometers during the mornings of three intensive observational periods (IOP2, IOP3, and IOP7) of the Joint Urban 2003 (JU2003) field ...experiment are analyzed to extract the mean and turbulent characteristics of airflow over Oklahoma City, Oklahoma. A strong nocturnal low-level jet (LLJ) dominated the flow in the boundary layer over the measurement domain from midnight to the morning hours. Lidar scans through the LLJ taken after sunrise indicate that the LLJ elevation shows a gradual increase of 25–100 m over the urban area relative to that over the upstream suburban area. The mean wind speed beneath the jet over the urban area is about 10%–15% slower than that over the suburban area. Sonic anemometer observations combined with Doppler lidar observations in the urban and suburban areas are also analyzed to investigate the boundary layer turbulence production in the LLJ-dominated atmospheric boundary layer. The turbulence kinetic energy was higher over the urban domain mainly because of the shear production of building surfaces and building wakes. Direct transport of turbulent momentum flux from the LLJ to the urban street level was very small because of the relatively high elevation of the jet. However, since the LLJ dominated the mean wind in the boundary layer, the turbulence kinetic energy in the urban domain is correlated directly with the LLJ maximum speed and inversely with its height. The results indicate that the jet Richardson number is a reasonably good indicator for turbulent kinetic energy over the urban domain in the LLJ-dominated atmospheric boundary layer.
This paper uses a mathematical model of fluorescent biological particles composed of bacteria and/or proteins (mostly as in Hill et al., 2013 23) to investigate the size-dependence of the total ...fluorescence emitted in all directions. The model applies to particles which have negligible reabsorption of fluorescence within the particle. The specific particles modeled here are composed of ovalbumin and of a generic Bacillus. The particles need not be spherical, and in some cases need not be homogeneous. However, the results calculated in this paper are for spherical homogeneous particles. Light absorbing and fluorescing molecules included in the model are amino acids, nucleic acids, and several coenzymes. Here the excitation wavelength is 266 nm. The emission range, 300 to 370 nm, encompasses the fluorescence of tryptophan. The fluorescence cross section (CF) is calculated and compared with one set of published measured values. We investigate power law (Ady) approximations to CF, where d is diameter, and A and y are parameters adjusted to fit the data, and examine how y varies with d and composition, including the fraction as water. The particle's fluorescence efficiency (QF=CF/geometric-cross-section) can be written for homogeneous particles as QabsRF, where Qabs is the absorption efficiency, and RF, the fraction of the absorbed light emitted as fluorescence, is independent of size and shape. When QF is plotted vs. mid or mi(mr-1)d, where m=mr+imi is the complex refractive index, the plots for different fractions of water in the particle tend to overlap.
The effects of ozone and relative humidity (RH) at common atmospheric levels on the properties of single octapeptide bioaerosol particles were studied using an improved rotating reaction chamber, an ...aerosol generator, an ultraviolet aerodynamic particle sizer (UVAPS), an improved single particle fluorescence spectrometer (SPFS), and equipments to generate, monitor and control the ozone and RH. Aerosol particles (mean diameter ~2μm) were generated from a slurry of octapeptide in phosphate buffered saline, injected into the rotating chamber, and kept airborne for hours. Bioaerosols were sampled from the chamber hourly for the measurements of particle-size distribution, concentration, total fluorescence excited at 355-nm, and single particle fluorescence spectra excited at 266-nm and 351-nm under different controlled RH (20%, 50%, or 80%) and ozone concentration (0 or 150ppb). The results show that: (1) Particle size, concentration, and the 263-nm-excited fluorescence intensity decrease at different rates under different combinations of the RH and ozone concentrations used. (2) The 263-nm-excited UV fluorescence (280–400nm) decreased more rapidly than the 263-nm-excited visible fluorescence (400–560nm), and decreased most rapidly when ozone is present and RH is high. (3) The UV fluorescence peak near 340nm slightly shifts to the shorter wavelength (blue-shift), consistent with a more rapid oxidation of tryptophan than tyrosine. (4) The 351/355-nm-excited fluorescence (430–580nm/380–700nm) increases when ozone is present, especially when the RH is high. (5) The 351/355-nm-excited fluorescence increase that occurs as the tryptophan emission in the UV decreases, and the observation that these changes occur more rapidly at higher RH with the present of ozone, are consistent with the oxidation of tryptophan by ozone and the conversion of the resulting ozonides to N-formyl kynurenine and kynurenine.
•Changes of fluorescence spectra and intensity of single octapeptide bioerosol particles•Bioaerosol aging and processing at common atmospheric ozone and relative humidity levels.•Time evolution of bioaerosol size, concentration, and fluorescence in rotating reaction chamber.•Oxidation of tryptophan by ozone and conversion to N-formyl kynurenine and kynurenine.
This paper describes a mathematical model of fluorescent biological particles composed of bacteria, viruses, or proteins. The fluorescent and/or light absorbing molecules included in the model are ...amino acids (tryptophan, etc.); nucleic acids (DNA, RNA, etc.); coenzymes (nicotinamide adenine dinucleotides, flavins, and vitamins B₆ and K and variants of these); and dipicolinates. The concentrations, absorptivities, and fluorescence quantum yields are estimated from the literature, often with large uncertainties. The bioparticles in the model are spherical and homogeneous. Calculated fluorescence cross sections for particles excited at 266, 280, and 355 nm are compared with measured values from the literature for several bacteria, bacterial spores and albumins. The calculated 266- and 280-nm excited fluorescence is within a factor of 3.2 of the measurements for the vegetative cells and proteins, but overestimates the fluorescence of spores by a factor of 10 or more. This is the first reported modeling of the fluorescence of bioaerosols in which the primary fluorophores and absorbing molecules are included.
A system for measuring spectrally-resolved fluorescence cross sections of single bioaerosol particles has been developed and employed in a biological safety level 3 (BSL-3) facility at Edgewood ...Chemical and Biological Center (ECBC). It is used to aerosolize the slurry or solution of live agents and surrogates into dried micron-size particles, and to measure the fluorescence spectra and sizes of the particles one at a time. Spectrally-resolved fluorescence cross sections were measured for (1) bacterial spores: Bacillus anthracis Ames (BaA), B. atrophaeus var. globigii (BG) (formerly known as Bacillus globigii), B. thuringiensis israelensis (Bti), B. thuringiensis kurstaki (Btk), B. anthracis Sterne (BaS); (2) vegetative bacteria: Escherichia coli (E. coli), Pantoea agglomerans (Eh) (formerly known as Erwinia herbicola), Yersinia rohdei (Yr), Yersinia pestis CO92 (Yp); and (3) virus preparations: Venezuelan equine encephalitis TC83 (VEE) and the bacteriophage MS2. The excitation wavelengths were 266 nm, 273 nm, 280 nm, 365 nm and 405 nm.
A multigrid numerical method has been applied to a three-dimensional, high-resolution diagnostic model for flow over complex terrain using a mass-consistent approach. The theoretical background for ...the model is based on a variational analysis using mass conservation as a constraint. The model was designed for diagnostic wind simulation at the microscale in complex terrain and in urban areas. The numerical implementation takes advantage of a multigrid method that greatly improves the computation speed. Three preliminary test cases for the model’s numerical efficiency and its accuracy are given. The model results are compared with an analytical solution for flow over a hemisphere. Flow over a bell-shaped hill is computed to demonstrate that the numerical method is applicable in the case of parameterized lee vortices. A simulation of the mean wind field in an urban domain has also been carried out and compared with observational data. The comparison indicated that the multigrid method takes only 3%–5% of the time that is required by the traditional Gauss–Seidel method.
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