Victoria Agranovski

Real-time measurement of bacterial aerosols with the UVAPS: performance evaluation

The Ultraviolet Aerodynamic Particle Sizer (UVAPS, Model 3312, TSI Inc., St. Paul, MN) spectrometer is the only commercially available aerosol counter for real-time monitoring of viable bioaerosols. Though the feasibility of this technique to monitor bioaerosols has been previously demonstrated by the instrument designers in a number of studies, the collection of meaningful data and their correct interpretation are still not possible without a thorough understanding of its capabilities and limitations. This paper presents the results of the first independent study aimed towards evaluating selectivity, sensitivity, counting efficiency, and the detection limits of the UVAPS. The study has demonstrated limitations in the capability of the instrument to measure bacterial spores that is explained by biochemical composition of the spores, which contain only minute amounts of the specific fluorophores that appeared to be below the instrument sensitivity level. The results were also indicative of strong sensitivity of the UVAPS to the physiological state of bacteria. Counting efficiency of the fluorescent particles was shown to depend on particle concentration with the upper limit of detection of the UVAPS around 6 x 107 particles/ m3.

Performance evaluation of the UVAPS: Influence of physiological age of airborne bacteria and bacterial stress

This study evaluated the effect of bacterial physiology, such as physiological age and stress, on the performance of the ultraviolet aerodynamic particle sizer (UV-APS, model 3312, TSI Inc., St. Paul, MN). Intensity of the fluorescent signals was measured for three bacteria having various sensitivities to environmental stresses, Bacillus subtilus (spores and vegetative cells), Pseudomonas fluorescens, and Micrococcus luteus. The performance of the UVAPS was found to depend on the type of airborne bacteria. In addition, the fluorescence signals for stationary-phase bacteria were generally stronger than for their log-phase counterparts. These results indicated that bacterial injury due to environmental stresses has a strong influence on the measured fluorescence signals. This hypothesis was confirmed by obtaining a linear relationship between the percentage of fluorescent particles and the proportion of injured bacteria in the total population of cultivable bacteria in samples simultaneously collected with the AGI-30 impingers. This indicates that the amount of fluorophors (specifically NADH) within injured bacteria is below the UVAPS sensitivity level. The practical implications of these findings are discussed in the paper. The reported results contribute to broadening our understanding of the method and may assist in developing sampling strategies for the application of the UVAPS to various bioaerosol studies.

Development and evaluation of a new personal sampler for culturable airborne microorganisms

The objective of this study was to develop a new personal sampler for viable airborne microorganisms and to evaluate its performance under controlled laboratory conditions and in a field. In the sampler, air is bubbled through a porous medium submerged in a liquid layer, as has earlier been demonstrated to be highly efficient for air purification. The prototype had the physical collection efficiency >95% for particles >0.32 μm in aerodynamic diameter during 8 h of continuous operation. The pressure drop across the sampler was below 1700 Pa, much lower than that of most conventional bioaerosol samplers. The collection liquid losses due to evaporation and aerosolization did not exceed 18% in 8 h and the culturability of sampled microorganisms remained high: the recovery rate of stress-sensitive gram-negative P. fluorescens bacteria was 61±20%; for stress-resistant B. subtilis bacteria and A. versicolor fungal spores it was 95±9% and 97±6%, respectively. Six identical personal samplers were tested simultaneously on a simplified human manikin in an office environment. The culturable microbial concentration data obtained during 2, 4 and 8-h sampling were not affected by the sampling time. Inter-sample variation did not exceed 30%. The laboratory and field evaluations have demonstrated that the new sampler is capable of long-term personal sampling of airborne culturable microorganisms. The estimation of the detection limits has indicated that the sampler is capable of monitoring microbial exposure in the environments with the bacterial concentrations above 15 CFU/m3 and fungal concentrations above 5 CFU/m3 when using a sampling time of 8 h.

Inactivation of Viruses in Bubbling Processes Utilized for Personal Bioaerosol Monitoring

ABSTRACT A new personal bioaerosol sampler has recently been developed and evaluated for sampling of viable airborne bacteria and fungi under controlled laboratory conditions and in the field. The operational principle of the device is based on the passage of air through porous medium immersed in liquid. This process leads to the formation of bubbles within the filter as the carrier gas passes through and thus provides effective mechanisms for aerosol removal. As demonstrated in previous studies, the culturability of sampled bacterium and fungi remained high for the entire 8-h sampling period. The present study is the first step of the evaluation of the new sampler for monitoring of viable airborne viruses. It focuses on the investigation of the inactivation rate of viruses in the bubbling process during 4 h of continuous operation. Four microbes were used in this study, influenza, measles, mumps, and vaccinia viruses. It was found that the use of distilled water as the collection fluid was associated with a relatively high decay rate. A significant improvement was achieved by utilizing virus maintenance fluid prepared by using Hanks solution with appropriate additives. The survival rates of the influenza, measles, and mumps viruses were increased by 1.4 log, 0.83 log, and 0.82 log, respectively, after the first hour of operation compared to bubbling through the sterile water. The same trend was observed throughout the entire 4-h experiment. There was no significant difference observed only for the robust vaccinia virus.

Performance evaluation of the UVAPS in measuring biological aerosols: fluorescence spectra from NAD(P)H coenzymes and riboflavin

This article presents the results of the performance evaluation of the Ultraviolet Aerodynamic Particle Sizer (UVAPS, model 3312, TSI Inc., St. Paul, MN, USA), the novel instrument for real-time monitoring of biological aerosols. The main objective of the study was to compare the UVAPS response in measuring aerosols containing NADH, NADPH, or riboflavin particles. At the excitation and emission wavelengths at which the UVAPS operates, these compounds are the primary intrinsic fluorophores specific to biological particles. In addition, the study was focused on determining the detection limits of the UVAPS for these fluorophores. This information is important for the interpretation of UVAPS data while measuring bacterial aerosols. Fluorescence measurements were initially taken with a Varian Cary Eclipse Fluorescence Spectrophotometer for all three fluorophores. The samples were then aerosolized with the 6-jet Collison nebulizer. Riboflavin was found to be a stronger fluorophore than both NAD(P)H coenzymes. The fluorescence signals were considerably weaker for the NADPH samples compared to the NADH samples. The sensitivity of the UVAPS was found to be sufficiently high to detect the NADH and riboflavin at the concentrations characteristic of bacterial cells. The results of this study are discussed in a context of the results previously reported for the bacterial aerosols. It can be concluded that the amount of fluorophores detectable in uniformly mixed particles is equal to or less than the fluorophores expected to be present in the individual bacterial particles.

Collection of Airborne Microorganisms into Liquid by Bubbling Through Porous Medium.

A new method for the removal of airborne particles by air bubbling through fibrous filters immersed into a liquid has recently been developed (Agranovski et al. 1999) and shown to be very efficient for cleaning air environments with ultra-fine aerosol particles. The principal objective of the present study was to evaluate the new bubbling technique for the collection of airborne bacteria into a liquid for subsequent physical and microbiological analysis. It was found that the technique is capable of achieving a physical collection efficiency of 98.5% or higher for particles larger than 0.3 w m in aerodynamic diameter. The physical collection efficiency of the prototype bubbler remained at that high level for 8 h of continuous operation with negligible variation of the pressure drop across the device. Evaporation of the collection fluid did not exceed 20% during 8 h, and the reaerosolization effect on the physical collection efficiency of the bubbler prototype was <8%. The recovery rate of gram-negative Pseudomonas fluorescens bacteria collected for 20 min was shown to be as high as 74% - 10%. Its decrease with time was not statistically significant: the recovery rate reached 63% - 15% and 58% - 16% after 4 and 8 h of continuous operation, respectively. Thus the bubbling technique was demonstrated to be suitable for collecting viable airborne bacteria even if they are sensitive to the stress.

Monitoring of viable airborne SARS virus in ambient air

Abstract Due to recent SARS related issues (Science 300 (5624) 1394; Nature 423 (2003) 240; Science 300 (5627) 1966), the development of reliable airborne virus monitoring procedures has become galvanized by an exceptional sense of urgency and is presently in a high demand (In: Cox, C.S., Wathers, C.M. (Eds.), Bioaerosols Handbook, Lewis Publishers, Boca Raton, FL, 1995, pp. 247–267). Based on engineering control method (Aerosol Science and Technology 31 (1999) 249; 35 (2001) 852), which was previously applied to the removal of particles from gas carriers, a new personal bioaerosol sampler has been developed. Contaminated air is bubbled through porous medium submerged into liquid and subsequently split into multitude of very small bubbles. The particulates are scavenged by these bubbles, and, thus, effectively removed. The current study explores its feasibility for monitoring of viable airborne SARS virus. It was found that the natural decay of such virus in the collection fluid was around 0.75 and 1.76lg during 2 and 4h of continuous operation, respectively. Theoretical microbial recovery rates of higher than 55 and 19% were calculated for 1 and 2h of operation, respectively. Thus, the new sampling method of direct non-violent collection of viable airborne SARS virus into the appropriate liquid environment was found suitable for monitoring of such stress sensitive virus.

Elemental composition of combustion emissions from spark ignition vehicles

In petrol engines, solid particle phases are formed as a result of incomplete combustion. In emissions from combustion processes such as petrol, natural gas or diesel, concentration of particles smaller than 1 µm could be several orders of magnitude higher than those which are larger than 1 µm. Due to their physical properties, submicrometer particles have a high probability of deposition in the deeper parts of the respiratory tract. It is known that petrol particles are mutagenic and carriers of hydrocarbons (and other compounds) adsorbed on the particulate and as a result represent a serious health hazard if inhaled. The present paper reports on some measurements of particle size distribution and composition of the bulk aerosol, as well as on morphological and elemental information from individual particles. The study was performed on non-diluted petrol exhaust obtained under different engine operation conditions. The bulk aerosol chemistry study has been performed. The concentrations of the following trace elements were measured: Boron, Calcium, Titanium, Chromium, Manganese, Iron, Cobalt, Nickel, Copper, Zinc, Cadmium, Barium, and Lead. The petrol particles have been found to be spherical. The most abandon elements were Fe, Ca, and Zn that have their origin from the additives in lubricating oil. It is interesting to note that although particle concentrations increased for 3 orders of magnitude from 40 to 120 km/h, emissions of metals did not significantly increase. This would indicate that most of the particle emission at higher loads comes from the unburned fuel and consists mainly of carbon either in elemental or organic form.

Dust emissions from a tunnel-ventilated broiler poultry shed with fresh and partially reused litter.

Dust emissions from large-scale, tunnel-ventilated poultry sheds could have negative health and environmental impacts. Despite this fact, the literature concerning dust emissions from tunnel-ventilated poultry sheds in Australia and overseas is relatively scarce. Dust measurements were conducted during two consecutive production cycles at a single broiler shed on a poultry farm near Ipswich, Queensland. Fresh litter was employed during the first cycle and partially reused litter was employed during the second cycle. This provided an opportunity to study the effect that partial litter reuse has on dust emissions. Dust levels were characterised by the number concentration of suspended particles having a diameter between 0.5 and 20 μm and by the mass concentration of dust particles of less than 10 μm diameter (PM10) and 2.5 μm diameter (PM2.5). In addition, we measured the number size distributions of dust particles. The average concentration and emission rate of dust was higher when partially reused litter was used in the shed than when fresh litter was used. In addition, we found that dust particles emitted from the shed with partially reused litter were finer than the particles emitted with fresh litter. Although the change in litter properties is certainly contributing to this observed variability, other factors such as ventilation rate and litter moisture content are also likely to be involved.

Continuum regime motion of a growing droplet in opposing thermo-diffusiophoretic and gravitational fields of a thermal diffusion cloud chamber

A model for the motion of aerosol particles by Stefan flow, thermo-diffusiophoresis and gravity in a continuum regime is described, which considers a phase change on the particle surface. It is tested in a thermal diffusion cloud chamber where a droplet formed by nucleation quickly grows and simultaneously moves upwards due to vertical temperature and concentration gradients. Kinetic coefficients are assumed to be constant. Model predictions of the height where the droplet reverses its motion are in satisfactory agreement with the experimental results of Ždimal et al. ((1996). Colloids Surfaces A, 106, 119). The droplet motion seems to be predicted well at higher gradients and vapor fluxes, but model underestimates droplet motion at lower ones. For those cases also the free-molecule and transition regimes need to be included.