Airborne Particle Size Distribution Research Articles

Fate of Atmospheric Particles within the Buddhist Cave Temples at Yungang, China

The Yungang Grottoes are a collection of man-made cave temples dating from the 5th century A.D. that now are situated in the middle of one of China's largest coal mining regions. Air pollutant particles enter these caves and deposit onto the more than 50 000 stone carvings contained within the caves, leading to rapid soiling of the sculptures. In order to study this problem, computer-based models have been combined that simulate the air flow into the caves and particle deposition within the caves. The evolution of the airborne particle concentration and size distribution is tracked as outdoor air is drawn into the caves by a natural convection flow that is driven by the temperature difference between the outdoor air and the interior walls of the caves. Particle deposition rates are computed from the boundary layer flows along the surfaces within the caves. Predicted coarse airborne particle (diameter > 2.3 μm) size distribution and coarse particle deposition fluxes to horizontal surfaces within caves 6 and 9 at Yungang compare closely to experimental observations made during the period April 15−16, 1991. It is found that horizontal surfaces within caves 6 and 9 at Yungang would become completely covered by a full monolayer of particles in only 0.3−0.5 yr under the April conditions studied here and will be soiled even more rapidly under annual average conditions. The model developed here can be used in the future to compute the effects of particle filtration systems and/or altered ventilation rates on soiling within the grottoes.

Optical methods for measurement of concentration, size distribution and refractive index of airborne particles

Optical methods for measurement of concentration, size distribution and refractive index of airborne particles

Formation of respirable particles during ski waxing

The formation processes and the final size distributions of airborne particles produced by ski waxing with fluor-powder were investigated. For the present study the flow system for controlled production of inhalable particles from ski wax was constructed. The particle formation was studied as a function of time and temperature. The particle size distributions were obtained using both electrical (DMA) and optical method (OPC). The mean diameter of particles was some hundred nanometers and the mass concentration was found to be tens of milligrams per m 3 in maximum.

Effect of Environmental Variables in Turkey Confinement Houses on Airborne Aspergillus and Mycoflora Composition

Environmental conditions and airborne mycoflora were measured concurrently in 10 turkey confinement houses during warm and cold weather. The following variables in the environment were measured: numbers of feed- and litter-associated yeast and mold fungi, temperature, relative humidity, airspeed, carbon dioxide and ammonia concentration, airborne bacteria, and airborne particulate mass, particle number, and particle size distribution. Winter air in turkey confinement houses contained significantly higher concentrations of Aspergillus, Scopulariopsis, and Mucor sp. and significantly lower concentrations of Cladosporium, Fusarium, and Alternaria sp. when compared with summer air. Significantly greater numbers of Mucor sp. were recovered per cubic meter of air where the current turkey flock was present less than 100 d when compared to houses where the current flock resided 100 d or more. Management decisions regarding control of the internal environment of turkey confinement houses apparently influence airborne mycoflora composition.

A field experiment on contrast reduction law

Abstract Atmospheric opacity monitoring employs visibility meters based on various physical principles. All the meters currently in use suffer from systematic errors typical of photometric measurements as well as systematic effects due to airborne particle size distribution. Ruhle's luminance contrast meter, which avoids all these sources of error, is not considered a wholly reliable comparison instrument for the other meters because the restrictive conditions on atmosphere and illumination required by the visibility theory on which it relies would not be verifiable during measurements. A re-examination of contrast reduction by the atmosphere in both ideal and non-ideal visibility conditions, and a re-interpretation of Ruhle's hypotheses on errors in apparent luminance measurements, show that Ruhle's instrumental apparatus itself makes it possible to verify the presence of ideal conditions a posteriori of a prolonged measurement period in as broad an opacity range as possible. Field experiment results confirming this fact are reported and discussed.

The effectiveness of the Duo-Flo BioClean unit for controlling airborne antigen levels.

The Duo-Flo BioClean unit, consisting of a chamber unit with an animal rack, a HEPA filtration system, an air plenum, and a blower, was evaluated as a control unit for airborne rat antigen levels in the room housing the unit. The unit was evaluated in negative and positive pressure operating modes. In the negative mode, room air is drawn into the unit, passes over the animal cages, and is then exhausted into the room through the filters. In the positive mode, air passes through the filters, traverses the animals, and then is discharged into the room. Airborne antigen concentrations (ng/m3) and particle size distributions associated with antigen were measured during the two operating modes and prior to operation (background mode). Airborne antigen concentrations during the positive pressure operating mode were higher than during the negative pressure mode or background. Approximately 70% of airborne antigen was associated with respirable particles during background and positive pressure operating modes. A total of 36% of airborne antigen mass was associated with respirable particles during negative pressure operation. The unit is usually operated in the positive mode to protect experimental animals. This study clearly indicates that negative pressure operation would reduce the dispersion of dust-containing antigen, the exposure of room occupants to airborne antigen, and the risk to many workers of contracting animal allergy.

The Effectiveness of the Duo-Flo BioClean Unit for Controlling Airborne Antigen Levels

The Duo-Flo BioClean unit, consisting of a chamber unit with an animal rack, a HEP A filtration system, an air plenum, and a blower, was evaluated as a control unit for airborne rat antigen levels in the room housing the unit. The unit was evaluated in negative and positive pressure operating modes. In the negative mode, room air is drawn into the unit, passes over the animal cages, and is then exhausted into the room through the filters. In the positive mode, air passes through the filters, traverses the animals, and then is discharged into the room. Airborne antigen concentrations (ng/m3) and particle size distributions associated with antigen were measured during the two operating modes and prior to operation (background mode). Airborne antigen concentrations during the positive pressure operating mode were higher than during the negative pressure mode or background. Approximately 70% of airborne antigen was associated with respirable particles during background and positive pressure operating modes. A total of 36% of airborne antigen mass was associated with respirable particles during negative pressure operation. The unit is usually operated in the positive mode to protect experimental animals. This study clearly indicates that negative pressure operation would reduce the dispersion of dust-containing antigen, the exposure of room occupants to airborne antigen, and the risk to many workers of contracting animal allergy.

Particle Suspension in a Rotating Drum Chamber When the Influence of Gravity and Rotation are Both Significant

In recent years, rotating chambers have been found to be an effective method of retaining particles suspended in the air for an extended period of time. Rotating drum chambers have the potential of providing a stable atmosphere of well-characterized inhalable particles for periods lasting from hours to days for use in inhalation toxicology studies. To aid in planning for the use of rotating drum chambers in inhalation studies, we created a model that describes (a) the concentration of particles in the chamber under various conditions and (b) the particle sizes for which gravity and rotation influence particle dynamics. Previous publications describe the suspension / deposition of particles when the rotational effect is dominant, but do not describe particle suspension / deposition when gravitational settling is significant as occurs when such drum chambers are operated at optimal conditions for retaining the highest fraction of particles over time. By using the limiting trajectory of particles, the fraction of particles that remain suspended in a 1-m diameter rotating drum chamber was derived for forces of gravity only, rotation only, and gravity plus rotation. For particles between 0.5 and 1 μm in diameter and for suspension times of < 96 h, there was no loss of the suspended particles for drum rotation rates from 0.1 to 10 rpm. For 2- and 5-μm diameter particles, > 98% and 91%, respectively, remain suspended after 96 h under optimal rotation of the drum chamber. Optimal rotation rates were independent of particle size for particles < 10 μm in diameter (agreeing with Gruel et al. [1987] even though we predicted suspended fractions higher by > 30% for 10-μm particles after 96 h). For 20-μm diameter particles and suspension times < 96 h, the maximum suspended fraction occurred for drum rotation rates between 0.3 and 0.5 rpm. The particles > 2 μm can be selectively removed from an airborne particle size distribution in time periods of < 15 h when the rotational rate is > 5 rpm.

Evaluation of aerosol deconvolution algorithms for determining submicron particle size distributions with diffusion battery and condensation nucleus counter

Determining the particle size distribution of airborne particles is important in many contexts, including understanding and thus reducing the deposition of particles on micro-electronic components during their manufacture. Sizing of particles smaller than 0.1 μm is usually done with a diffusion battery, which requires use of a deconvolution algorithm to obtain particle size distributions. The following algorithms were evaluated: CINVERSE (Crump and Seinfeld, Aerosol Sci. Technol. 1, 363, 1982). Twomey's iterative procedure (Twomey, J. Comput. Phys. 18, 188, 1975), expectation maximization (Maher and Laird, J. Aerosol Sci. 16, 557, 1985), constrained least-squares fit (Nelder and Mead, Comput. J. 7, 308, 1965; Cooper and Spielman, Atoms. Envir. 10, 1976). Expectation maximization and constrained least-squares fit are more suited to this use than are the other two. The non-monotonic response of the diffusion battery with respect to particle size cannot be corrected for by any such algorithm. One could modify the diffusion battery to prevent entrance of the larger particles or one could use an independent measurement of the larger particles to correct the diffusion battery data. Using the latter approach provided an improved estimate of the particle size distribution in a clean room.

The Andersen impactor: Calibration, wall losses and numerical simulation

Andersen cascade impactors are widely used to assess airborne particle size distributions. Two forms (MkI and MkII) have been calibrated using solid and liquid aerosols, measured by microscopy, fluorimetry, and aerodynamic particle sizer. A fluorescent tracer was used to examine qualitatively the details of the wall loss deposition patterns when using greased and ungreased plates, and to quantify their magnitude at different particle sizes. The resultant calibrations differ in some respects from the manufacturer's, but are broadly consistent with theory. Suggestions are made for improvements to the design. The results of these investigations were used to produce size-dependent curves for deposition on each plate, and between stages. An entry efficiency curve was assumed. A computer simulation was then performed of the sampling of various log-normal size distributions, so that measured distribution parameters can be corrected for the inevitable imperfections of the impactors. The assumption about entry efficiency is important, but there is little information on this variable, which remains to be determined for the various versions of the Andersen impactor.

Concentration and size distribution of airborne particles in a broiler house

Airborne dust particles were sampled in a broiler house using the quartz crystal microbalance cascade impactor designed for the measurement of mass concentration and size distribution from 0.05 to 25 gm. No significant difference was noticed in the dust concentration from morning to evening or at different sampling sites in the broiler house. The concentration of airborne dust particles decreased as the age of the chickens increased. Ratio of dust particles smaller than 0.8 pm to the total dust ranged from 10 to 50%. The highest concentration of dust was in the particle size range of 3.2 μm. The fogging system in use reduced the concentration of larger particles but not that of the smaller particles.

Respirable Dust Control in Grinding Gray Iron Castings

High speed grinding of gray iron castings long has been associated with excessive exposure to crystalline silica. Not all workers engaged in these operations are protected by conventional ventilation techniques. Dust in the air that has been entrained by the spinning grinding wheel and not captured in the grinder hood has been postulated to be a major exposure source. A pilot grinding operation was constructed, and the size distribution and concentration of airborne particles were measured with the aerodynamic particle sizer (APS). Various control measures proved effective in reducing the respirable dust concentration: increased exhaust ventilation, and installation of baffles and/or the use of an air jet to deflect the entrained air stream. The concentration of respirable dust is the breathing zone was reduced approximately 20-fold through the combined use of increased ventilation, interior baffles, and an air jet. The air jet and baffle utilized at the base ventilation rate reduced the respirable dust concentration by a factor of three to four, whereas the baffle alone halved the concentration.

Respirable Dust Control in Grinding Gray Iron Castings

High speed grinding of gray iron castings long has been associated with excessive exposure to crystalline silica. Not all workers engaged in these operations are protected by conventional ventilation techniques. Dust in the air that has been entrained by the spinning grinding wheel and not captured in the grinder hood has been postulated to be a major exposure source. A pilot grinding operation was constructed, and the size distribution and concentration of airborne particles were measured with the aerodynamic particle sizer (APS). Various control measures proved effective in reducing the respirable dust concentration: increased exhaust ventilation, and installation of baffles and/or the use of an air jet to deflect the entrained air stream. The concentration of respirable dust is the breathing zone was reduced approximately 20-fold through the combined use of increased ventilation, interior baffles, and an air jet. The air jet and baffle utilized at the base ventilation rate reduced the respirable dust concentration by a factor of three to four, whereas the baffle alone halved the concentration.

Particulate Contamination and Microelectronics Manufacturing: An Introduction

The manufacture of integrated circuits for computers and various microprocessors is of increasing importance. Higher speeds of operation and lower costs require higher circuit densities, thus further miniaturization. Circuit elements have features in the submicron size domain and are quite sensitive to contaminant particles of comparable sizes. People, equipment, chemicals, and piping generate particles which are transported to the vicinity of the product and some of which are deposited. The deposition rate depends upon the airborne particle size distribution and the concentration and the deposition velocities caused by various deposition mechanisms. Methods for measuring submicron particles in gases and on surfaces are widely used and are being further developed, along with improved methods for data analysis. Cleaning submicron particles from surfaces is difficult; those particles that remain can have major impacts on process yield, to which process economic viability is strongly related. Research is needed in: source determination, transport modeling, aerosol characterization, deposition mechanisms, surface particle characterization, cleaning, defect analysis, and the design of processes and products that are robust.

Deduction of aerosol size distribution from particle sampling by whisker collectors

A method of deducing airborne particle size distributions from the deposition on a collector is described. The method basically consists in collecting submicron-sized particles on whisker filters for subsequent electron-microscopic examination. The empirical size distributions on the collectors can be approximated by log-normal functions. Moreover, it has been found that the variation in particle distribution across a four-stage whisker filter can be interpreted on the basis of a simple model of the collection process. The effective absorption coefficient derived from this modeling is used to correct the empirical data for the effect of a selective collection characteristic.

Size Considerations for Establishing a Standard for Inhalable Particles

The U. S. Environmental Protection Agency (EPA) is required, under the amended Clean Air Act of 1977, to review the scientific basis for the total suspended par-ticulate (TSP) ambient air quality standard and determine whether a revised particulate standard can be promulgated by December, 1980. It is recommended that research to develop information for a size-specific standard should focus on inhalable particulate (IP) matter defined as airborne particles ≤15 jum aerodynamic equivalent diameter. This particle size range relates to that fraction of particulate matter which can primarily deposit in the conducting airways and the gas-exchange areas of the human respiratory system during mouth breathing. It is also recommended that a second particle size cut-point of ≤2.5 yum diameter be incorporated in the air sampling devices, based upon considerations of the chemical composition and the size distribution of airborne particles, and on the predominant penetration of particles ≤2.5 /im diameter into the gas-e...

CHARACTERISTICS OF AIRBORNE PARTICLES PRODUCED BY WIND EROSION OF SANDY SOIL, HIGH PLAINS OF WEST TEXAS

Mass size distributions of airborne particles generated by wind erosion of two soils, one coarse-grained and one fine-grained, show two distinct modes in each. The coarser mode, between 10 and 100 μm equivalent radius, is due to the presence in the parent soil of loose erodible particles which x-ray analyses indicate are almost exclusively quartz grains. The finer mode is between 1 and 10 μm equivalent radius which x-ray analyses show to be clay minerals consisting predominantly of illite and mixed layer clays. The proportion of fine particles to large ones increases relative to wind speed for the finer soil but not for the coarse soil; hence, we ascribed the fineparticle mode as due to sandblasting of the soil, which gives rise to fine particles by disaggregation. Scanning electron microscope (SEM) photographs of airborne fine and large particles give supporting evidence in that the fine particles are similar to clay platelets which adhere to the surfaces of the larger particles and which almost certainly are removed from the grains by the wind erosion sandblasting mechanism. In addition, when coupled with wind velocity data, the SEM photographs indicate that with increased wind speed a higher percentage of the large particles eroded from both soils consists of aggregates of clay. These aggregates are very fragile and they should be readily disaggregated by sandblasting. It is concluded, therefore, that the fine airborne particles (1–10 μm equivalent radius) consist predominantly of clay minerals which are derived from the exposed soils by sandblasting during wind erosion. The clay is removed from the soil as individual platelets, as coatings of platelets on quartz grains, and as coarse aggregates of platelets. Continued sandblasting during wind transport removes the clay platelets from the exposed surfaces of quartz grains and separates the aggregates. As should be expected, the finer-grained soil contains the highest percentage of clay and, upon erosion, yields the highest percentage of fine airborne particles.

The size-distribution and protease content of airborne particles in textile mill cardrooms

The concentration of 1.-4 mum airborne particles and the protease content of the airborne dust measured in the cardrooms of ten cotton mills were found to correlate with byssinosis prevalence. Airborne proteases were found in abundance also in wool mills where byssinosis does not occur.

Determination of airborne particle size distributions: Calculation of cross-sensitivity and discreteness effects in cascade impaction

A theory is developed which permits numerical evaluation of errors associated with the determination of aerosol size distributions using cascade impactors. Account is taken of errors due to the overlap of a given particle size between adjacent impaction stages and to the discrete nature of cascade impaction. The theory is applied to both log-normal and polynomial functional approximations to an aerosol size distribution. Numerical determination of errors considered shows that the mass of large and small particles present in the wings of a log-normal aerosol distribution is over-estimated manyfold by most cascade impactors but that the mass of particles having aerodynamic diameters close to the aerosol mass median diameter is generally subject to quite small (<20%) negative errors. Even under extremely unfavorable conditions the mass median diameter of an aerosol can be determined to well within 25% of the true value.

Detection of Airborne Particles Using Optical Extinction Measurements

A method for obtaining real-time size distributions of airborne particles is discussed, and experimental sensitivity measurements are presented. By detecting the transmitted power of a low noise He-Ne laser, the optical extinction cross sections of individual particles are measured as they flow through the focused beam. Calculations for various absorbing materials show the extinction cross sections are from one to more than two orders of magnitude larger than their scattering cross sections for particle diameters in the 0.02-0.2-microm range. Sensitivity calculations and measurements indicate extinction cross sections down to 2 x 10(-12) cm (2) can be detected. This suggests absorbing particles as small as 0.04-microm diam can be measured using this technique.