Associations of Fungal Aerosols,Air Pollutants,and Meteorological Factors

The relationships between fungal aerosols and air pollutants meteorological factors were investigated in the Taipei urban area. In summer, it was observed that geometric mean (GM) concentrations of airborne fungal aerosols were 2,835 CFU m^-3 and 2,651 CFU m^-3 at Kuting and Hsichih stations, respectively. In winter, GM levels of airborne fungi were 1,107 CFU m I 3 and 2,248 CFU m^-3 at Kuting and Hsichih stations, respectively. Moreover, fungal aerosol concentrations were observed to highly depend on weather conditions, and the highest concentration of total colony counts appeared when the temperature was 25-30 C, the RH was 60-70% , and the wind speed was > 1 m s^-1 and from the S-SE wind direction. In addition, total fungal concentrations were negatively correlated with ozone concentrations, and concentration of Cladosporium spp. was positively correlated with hydrocarbons. PM₁₀ were positively correlated with Penicillium and the yeasts in Hsichih station. Our results demonstrated that airborne fungal aerosols are definitely correlated with air pollutants and meteoro logical factors. The complex dynamic interactions were indicated to occur among bioaerosols, air pollutants, and meteorological factors.     

Effects of single-walled carbon nanotube filter on culturability and diversity of environmental bioaerosols

In this study, single-walled carbon nanotube (SWNT) filters were prepared using mixed cellulose ester (MCE) filters and carbon nanotubes with three levels of loading: 0.02, 0.16 and 0.64 mg/cm². Both MCE and SWNT filters were used to collect bacterial and fungal aerosols with a total volume of 200 L air sampled in indoor and outdoor environments. After sampling, the filters were directly placed on agar plates at 26 °C for culturing. The culturable aerosol counts were manually obtained both for MCE and SWNT filters, and the resulting bacterial colony forming units (CFUs) were washed off and subjected to the culturable bioaerosol diversity analysis using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). For fungal CFUs, microscopy method was used to study the diversity obtained using different filter types.The results showed that use of SWNT filters with medium and high CNT loadings resulted in significant reduction (up to 2 logs) of culturable bacterial and fungal aerosol counts compared to MCE filters in both environments. For low CNT loading (0.02 mg/cm²), very limited inactivation effects were observed for fungal aerosols, while more bacterial counts were obtained possibly due to increased sampling efficiency. PCR-DGGE analysis revealed that SWNT filters at high CNT loading (0.64 mg/cm²) resulted in lowest culturable bioaerosol diversity, especially pronounced for outdoor bacterial aerosols. For low and medium CNT loading, the culturable bacterial aerosol diversity remained similar. Fungal aerosol analysis showed that the use of SWNT filters with medium to high CNT loading also resulted in significant reduction of fungal species diversity. The results here demonstrated great promise of the SWNT hybrid filter in controlling biological aerosols, and suggested its potential to impact current air conditioning system.     

Profile and Morphology of Fungal Aerosols Characterized by Field Emission Scanning Electron Microscopy (FESEM)

Fungal aerosols consist of spores and fragments with diverse array of morphologies; however, the size, shape, and origin of the constituents require further characterization. In this study, we characterize the profile of aerosols generated from Aspergillus fumigatus, A. versicolor, and Penicillium chrysogenum grown for 8 weeks on gypsum boards. Fungal particles were aerosolized at 12 and 20 L min^?1 using the Fungal Spore Source Strength Tester (FSSST) and the Stami particle generator (SPG). Collected particles were analyzed with field emission scanning electron microscopy (FESEM). We observed spore particle fraction consisting of single spores and spore aggregates in four size categories, and a fragment fraction that contained submicronic fragments and three size categories of larger fragments. Single spores dominated the aerosols from A. fumigatus (median: 53%), while the submicronic fragment fraction was the highest in the aerosols collected from A. versicolor (median: 34%) and P. chrysogenum (median: 31%). Morphological characteristics showed near spherical particles that were only single spores, oblong particles that comprise some spore aggregates and fragments (<3.5 μm), and fiber-like particles that regroup chained spore aggregates and fragments (>3.5 μm). Further, the near spherical particles dominated the aerosols from A. fumigatus (median: 53%), while oblong particles were dominant in the aerosols from A. versicolor (68%) and P. chrysogenum (55%). Fiber-like particles represented 21% and 24% of the aerosols from A. versicolor and P. chrysogenum, respectively. This study shows that fungal particles of various size, shape, and origin are aerosolized, and supports the need to include a broader range of particle types in fungal exposure assessment.     

Performance of Two Fluorescence-Based Real-Time Bioaerosol Detectors: BioScout vs. UVAPS

A 405 nm diode laser-based on-line bioaerosol detector, BioScout, was tested and compared with the Ultraviolet Aerodynamic Particle Sizer (UVAPS). Both instruments are based on laser-induced fluorescence of particles. Only a fraction of microbial particles produce enough fluorescence light to be detected by the instruments. This fluorescent particle fraction (FPF) is aerosol and instrument specific. The FPF values for common bacterial and fungal spores and biochemical particles were experimentally determined for both instruments. The BioScout exhibited higher FPF values for all the test aerosols except coenzyme NADH. The difference was higher for smaller particles. The FPF values of fungal spores and bacteria varied between 0.34 to 0.77 and 0.13 to 0.54 for the BioScout and the UVAPS, respectively. The results indicate that the 405 nm diode laser is a useful excitation source for fluorescence-based real-time detection of microbial aerosols. The FPF results of this study can be utilized to estimate the actual concentrations of bacterial and fungal spores in fluorescence-based ambient measurements.

Copyright 2014 American Association for Aerosol Research     

Identification of single microbial particles using electro-dynamic balance assisted laser-induced breakdown and fluorescence spectroscopy

Online characterization of fungal and bacterial spores is important in various applications due to their health and climatic relevance. The aim of this study was to demonstrate the capability of the combination of electro-dynamic balance assisted laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) techniques for the online detection of single fungal spores (Aspergillus versicolor and Penicillium brevicompactum) and bacteria (Bacillus aureus). The method enabled sensitive and repeatable LIBS analysis of common elemental components (Ca, Na, and K) from single microbial particles for the first time. Significant differences in the concentrations of these elements were observed between the species, e.g., bacterial spores had over three orders of magnitude higher Ca concentration (2 × 10^?12 g/particle) compared to fungal spores (3–5 × 10^?16 g/particle). The LIF analysis has previously been used to distinguish bioaerosols from other aerosols due to their fluorescence ability. This study showed that combination of LIF and LIBS analysis is a promising tool for identification of different bioaerosol particle types.

Copyright © 2016 American Association for Aerosol Research     

Aerosolbildung durch spontane Phasenübergänge bei Absorptions- und Kondensationsprozessen

Formation of aerosols by spontaneous condensation or desublimation in condensers or absorbers often causes serious problems in industrial processes. The fine aerosol particles, formed under special operating conditions, remain suspended in gases and are carried over into downstream stages or lead to high pollutant concentrations in the exhaust gas. The present paper describe under what conditions aerosols are formed. The characteristic behaviour of aerosols is discussed with the aid of experiments and computer simulation.     

Aerosole und ihre technische Bedeutung

Aerosols and Their Technical Significance Aerosols occur in many technical processes. For example, aerosols are formed to generate products of highly disperse solids in gas phase processes. Particle formation and growth in the aerosol state decisively determine the product properties by the size, shape, and structure of the particles. Undesired aerosol formation can also occur in technical processes. These undesired aerosols pollut process gases or products or increase the pollutant content of exhaust gases. If undesired aerosol formation cannot be avoided, efficient separation techniques have to be used. Efficient separators are also required to recover fine product particles from the gas phase. Moreover, aerosols, whether desired or undesired, have to be measured and characterized. This requires high performing measuring techniques. The paper outlines the technical significance of aerosols.     

Differences in Detected Fluorescence Among Several Bacterial Species Measured with a Direct-Reading Particle Sizer and Fluorescence Detector

Naturally-contained fluorescing chemicals (such as riboflavin or NADPH) can be used to detect the presence of biological organisms. A new instrument from TSI Incorporated measures fluorescence of particles using an ultraviolet laser operating at an excitation wavelength of 355 nm. We have employed this instrument (Model 3312 Ultraviolet Aerodynamic Particle Sizer (tm) Spectrometer) to assess the degree of fluoresence associated with a variety of biological aerosols. Nonfluorescent and fluorescent latex sphere and sodium chloride aerosols were first used to assure proper operation of the instrument and to obtain correct instrument settings. Biological aerosols were then generated by combining organisms with double distilled and filtered water in a Collison nebulizer operated at low pressure. After passage through a charge neutralizer and dilution with humidified air (45%RH), the aerosol was measured downstream for both particle size and fluorescence distributions. Bacterial aerosols generated include Bacillus subtilis subsp. niger (spores and vegetative cells), Staphylococcus epidermidis, Eschericia coli, and Mycobacterium abscessus (a surrogate for M. tuberculosis). Cladosporium spp. fungal spores were also evaluated, and the effect of heat treatment on fluorescence was tested using B. subtilis spores. For each test the percentage of organisms that produced a fluorescence signal above a threshold was recorded. The organisms demonstrated considerable differences in percent fluorescence, ranging from means of 11% for S. epidermidis to 44% for B. subtilis spores. Vegetative cells of B. subtilis were generally less fluorescent (mean of 33%) than the spores, while the highest level of fluorescence was associated with heat-treated spores (averaging about 75%). This instrument has some potential for use in settings where immediate detection of biological organisms is important. Work remains to be done on understanding the effect on fluorescence of organism viability, presence of nonbiological particles, and interferences from mixtures.     

Use of Electric Image Forces for Collection of Aerosols by Arrays of Drops

The use of electric image forces for collection of uncharged aerosols by two- and three-dimensional arrays of charged drops is considered. Trajectories of aerosols are simulated using an algorithm for transformation of electric image forces and flow field from spherical coordinate systems of the drops to the central system, where the equation of motion is solved. Radius and efficiency of collection of aerosols, as a function of the number of rows of drops, are presented for different geometries and charge levels. The nature of the weak image force dictates the need to use a charge level closer to the Rayleigh limit and optimized array geometries. Inertial effects that enhance dispersive modes, of otherwise convergent trajectories, become significant for aerosols as small as 20 w m. In this case, multiple values of radius of collection and collection efficiency can be obtained for the same number of rows. Geometries with no shifts between rows of drops are shown to be inferior to those involving a larger shift. The former geometries require a substantially larger number of rows for a prescribed level of collection and may not facilitate complete collection. Systems of uncharged drops and charged aerosols behave similarly to those with charged drops and uncharged aerosols. Three-dimensional arrays can be more efficient than two-dimensional ones, provided that weakness planes, where aerosols show deep penetration, are eliminated by appropriate shifts of rows. A decrease of the drop size at a fixed volume fraction with the charge set at its Rayleigh limit enhances the collection efficiency. Finally, the random model of collection, using the exponential distribution, is recast in order to accommodate for the effect of the order of the array and the deterministic nature of the aerosol trajectories.     

Electrically Produced Standard Aerosols in a Wide Size Range

Non-uniformly charged particles cause a major problem in electrical methods for producing standard aerosols, imposing strict limitations on the usability of the obtained standard aerosols. This article gives a quick overview of this problem, examining the ways how differently charged particles affect the generation of standard aerosols, and presenting a new method for producing standard aerosols and avoiding the effects of multiply charged particles, with the key idea that the probability for small particles to have more than one charge is very low. A two-stage aerosol generator is used. Small silver particles (d< 40 nm) generated by homogeneous nucleation of silver vapors obtain in bipolar charger not more than one elementary charge. These condensation nuclei are enlarged by a condensational growth device. Big particles are now also not more than singly charged, and narrow size distribution can be obtained by electrical separation. Properties of standard aerosols produced experimentally by both the conventional and the new method, are compared and the validity of the new idea behind the new method is confirmed.     

Characterization of Multicomponent Aerosols by Raman Spectroscopy

In this work the feasibility of Raman spectroscopy, especially the detection limit of this technique for the chemical characterization of multicomponent aerosols, which appear in technical processes has been investigated. In such kind of aerosols high number concentrations (>10⁶ cm^?3) can be observed whereas the range of the pollutant loading varies from 10–1000 mg/m³. For these purposes different type of aerosols have been investigated. Aerosols in which the pollutant can be found in the dispersed phase as well as in the gas phase (aqueous solutions of NH₃ aerosols), those where the pollutant appears only in the dispersed phase (aqueous solutions containing SO₄ ^2?/ NO₃ ^? salts) and aerosols where there is no Raman shift between the signals of the gas and the dispersed phase (toluene/ dodecane aerosols). Furthermore aerosols generated by the reaction between NH₃ and HCl in nitrogen containing different amounts of vapor are also investigated.

The characterization of the aerosols with Raman spectroscopy with respect to their gas phase is without any difficulty, whereas the analysis in the dispersed phase is partially marginal and in majority of cases almost not possible.

Especially for the reaction aerosols rejection of elastically scattered light is the principle limitation in collecting Raman scattered light from particles in the Mie-scattering regime.     

Experimental Study on Electrostatically Enhanced Granular Filters

Filtration of charged aerosols by granular bed filters enhanced by an externally applied electrostatic field was studied experimentally. The filtration efficiencies of latex aerosols by sand beds were measured for various aerosol and bed granule diameters. The results were compared with theoretical solutions. It was demonstrated that high filtration efficiencies of charged aerosols may be achieved when moderate electrostatic fields are applied to a filter.     

Simultaneous Use of Polystyrene Latex Particles of Different Sizes to Evaluate Performance of a Cyclone and Impactor

Monodisperse and polydisperse aerosols were produced to evaluate the effect of particle size on cyclone and impactor performance. Monodisperse aerosols were generated from polystyrene latex and divinylbenzene particles. Polystyrene aerosols were also generated by mixing several monodisperse aerosols of different sizes. The mixture ratio of monodisperse aerosols was found by trial and error to generate polydisperse aerosols. Generated polydisperse aerosols had multimodal aerosol size distribution, which had the same peak point as shown in the size distribution of monodisperse particles. The results show the collection efficiency curves of a cyclone and impactor, when generating monodisperse particles were coherent with those for polydisperse ones. Our findings show that the size distribution and the size range of test aerosols can be easily determined by mixing monodisperse particles of known particle sizes, using a time saving procedure.     

Optische Konzentrations- und Temperatur-Messung in Aerosolen und Sprays

Optical measurement of concentration and temperature in aerosols and sprays. This article surveyes progress in the development and application of optical methods, particullarly in Raman scattering and fluorescence for the analysis of aerosols and sprays. The main emphasis lies on examination of the particle phase. Fundamentals and state of the art in the determination of molecular composition of the particle phase with the aid of linear and simulated Raman scattering are described and the role of structural resonance discussed. Various models are presented for distinguishing between the contribution of the liquid and the gas phase to Raman scattering and fluorescence. Finally, new developments pertaining to the measurement of droplet temperature in aerosols and sprays are described.     

Automated Spore Measurements Using Microscopy,Image Analysis,and Peak Recognition of Near-Monodisperse Aerosols

Rapid detection of airborne fungal and bacterial spores would enable public agencies to respond quickly and appropriately to intentional releases of hazardous aerosols. Automated analysis of microscope images and automated detection of near-monodisperse peaks in aerosol size distribution data offer complementary approaches to traditional methods for the identification and counting of fungal and bacterial spores. First, spores of the fungus Scopulariopsis brevicaulis were aerosolized in a chamber and then collected with a slit impactor; later, digital microscope images were analyzed manually to determine spore cluster distributions. The images also were analyzed with ImageJ, a program that automatically outlined objects and measured Feret's diameter, area, perimeter, and circularity. These characteristics were used to identify spore clusters automatically using two data analysis methods. Second, a computer program was developed to discriminate near-monodisperse bioaerosol peaks from those for polydisperse ambient particulate matter (PM) and was successfully tested using simulated and real aerosol mixtures. The observed agreement between manual and automated spore counts and the ability to detect spore peaks suggest that it may be possible to develop a system to recognize intentional releases rapidly through examination of particle morphology and size distributions. The peak detection procedure is potentially the fastest technique when used with real-time instrument data, but assumes that intentional releases would consist of large numbers of uniformly sized particles in the respirable size range.

Copyright 2012 American Association for Aerosol Research     

Coagulation of highly concentrated aerosols

A number of material synthesis processes such as flame, plasma and laser ablation have been developed for production of films and powders at low pressure and high temperature. At these conditions particle growth typically takes place by coagulation in the free molecule and transition regimes. As economic manufacturing of these materials favors operation at high particle concentrations, classic coagulation theory may not be sufficient to describe the ensuing aerosol dynamics, especially if fractal-like particles are formed. The coagulation rate of highly concentrated, polydisperse aerosols is investigated here from the free molecule to the continuum regime by solving the corresponding Langevin dynamics (LD) equations. The LD simulations are validated by monitoring the attainment of the self-preserving size distribution (SPSD) for dilute particle volume fractions, φ_s, below 0.1%. High particle concentrations in the free molecule regime lead to deviations of the aerosol dynamics from the kinetic theory of gases especially during instantaneous coalescence (completely inelastic particle–particle collisions) resulting in slower coagulation rates and slightly narrower SPSDs than in conventional dilute aerosols. In the transition regime, the coagulation rate of highly concentrated aerosols is progressively higher than that for dilute aerosols as growing particles enter the continuum regime where coagulation rates are 2–30 times higher than that of classic Smoluchowski theory. At high particle concentrations (φ_s>1%), a SPSD is approached (σ_g,n=1.42) that does not exhibit the characteristic minimum at the transition regime of dilute aerosols. A relationship is developed for the aerosol coagulation rate of highly concentrated aerosols from the free molecule to continuum regime.     

气雾剂的检验检测要求和建议

研究了气雾剂相关国内外标准、法规及国际间条约，列出了气雾剂在物理危险、易燃性、健康和环境危害等方面的检验检测要求，并简述了相应的检验检测方法。对气雾剂实施检验检测有利于提升气雾剂的质量和安全。提前预防进口国对气雾剂出口使用技术壁垒，保障和促进气雾剂的生产和出口。     

The Filtration of Fibrous Aerosols

Fibrous particles constitute an important class of aerosols that are potential human health hazards. Filters can remove aerosols from the air. The capture of spherical and fibrous aerosols by fibrous filters was investigated in this study. The governing equations of motions for translation and rotation of fibrous particles are derived for airflow over a cylindrical object. Only impaction and interception losses were considered in this study. Transport and deposition of fibrous particles were found to depend on Stokes number, fibrous particle aspect ratio, and ratio of the fibrous particle diameter to the diameter of fibrous filters. Using the Kuwabara flow field, transport and single-fibrous filter capturing efficiency of spherical and fibrous particles were calculated numerically, and these calculations were compared with available data in the literature. The calculated results compared favorably with the results of Yeh and Liu (1974) for spherical particles. Good agreement for losses by interception for both spherical and fibrous particles was observed between our results and those of Lee and Liu (1982). Further experimental data are needed to verify the predicted losses of fibrous aerosols by impaction.     

Sampling of Carbon Fiber Aerosols

This paper describes theoretical and experimental studies undertaken in connection with the problem of sampling carbon fiber aerosols in an ambient environment. Calculations indicate that carbon fiber aerosols with an 8-μm fiber diameter and a density of 1.8 g/cm³ can be sampled by a sampler designed to collect particles in the 10–30–μm aerodynamic diameter range if fibers up to a few millimeters in length are to be collected. An approach is then described in which carbon fiber aerosols are collected in the impactor of the inlet of a dichotomous sampler. Experimental data are presented showing that the impaction characteristics of the carbon fiber aerosol can be predicted with a reasonable degree of accuracy by approximating the shape of the fibers by a prolate ellipsoid.     

Inactivation of Fungal Spores Collected on Fibrous Filters by Melaleuca alternifolia (Tea Tree Oil)

Microbial aerosols could cause various human and animal health problems and their control is becoming a significant scientific and technological topic for consideration. Filtration is considered to be one of the main processes of the removal of biological aerosols from the air carrier minimizing bioaerosol concentration in industrial and domestic dwellings. However, with regards to biologically active particles, their removal from the air carrier does not solely solve the problem of microbial contamination of the ambient air. Considering that in some situations bioaerosol particles collected on the filter could re-enter the air carrier, some disinfection is required to ensure that no biologically active particles could possibly be removed from the filter surface and reach human occupied areas. This article describes the results of laboratory investigations involving Melaleuca alternifolia (tea tree oil) as disinfecting media for inactivation of common environmental fungal spores on the filter surface. It was found that 50% and 40% of Aspergillus niger and Rhizopus stolonifer spores, respectively, were inactivated over a period of 60 minutes. A single factor ANOVA test confirmed that the reported rates of inactivation were statistically significant (> 95%). For Rhizopus statistically significant inactivation by 31% was also observed after 30 minutes with no inactivation occurring over shorter time periods. No statistically significant inactivation occurred for Aspergillus niger for any time shorter than 60 min.