Calibration,Intersampler Comparison,and Field Application of a New PM-10 Personal Air-Sampling Impactor

The MS&T personal impactor is designed to provide a particle size cut (d _50%) of 10 μm in aerodynamic diameter (PM-10) at a flow rate of 4 L/min. Data are presented that verify the designed particulate mass cut specifications of this impactor for personal sampling. These data are derived from three different analyses', laboratory calibration, intersampler comparison, and field application. Laboratory calibration using monodispersed liquid aerosol shows a sharp 10-μm particle cut size.

The performance of the personal impactor was tested using ambient and combustion-generated aerosols. Established PM-10 samplers (the Sierra/Andersen dichotomous and the MS&T indoor air sampler impactor) were run side by side with the personal impactor. The intra- and intersampler vari-abilities in PM-10 measurements were evaluated. Results showed good precision among personal impactors (CV = 3.2%). The PM-10 sampled by the personal impactor was found to be highly correlated with measurements made with the indoor air sampler impactor (r ² = 0.99) and the dichotomous sampler (r¹ = 0.97).

The impactor was subsequently employed for personal air sampling in the Total Human Environmental Exposure Study (THEES). The THEES sampling protocol entailed 24-hour sampling during a 14-day study interval. THEES field measurements included indoor, outdoor, and personal PM-10 samples. The personal impactor measurements for 13 participants were predicted by a time-weighted exposure model using indoor and outdoor PM-10 and specific activity variables (p < 0.01).     

Effects of Dilution Sampling on Fine Particle Emissions from Pulverized Coal Combustion

A dilution sampler was used to examine the effects of dilution ratio and residence time on fine-particle emissions from a pilot-scale pulverized coal combustor. Measurements include the particle size distribution from 0.003 to 2.5 μm, PM_2.5 mass, and PM_2.5 composition (OC/EC, major ions, and elemental). Heated filter samples were also collected simultaneously at stack temperatures in order to compare the dilution sampler measurements with standard stack sampling methodologies. Measurements were made both before and after the bag house, the particle control device used on the coal combustor, and while firing three different coal types and one coal–biomass blend. The PM_2.5 mass emission rates measured using the dilution sampler agreed to within experimental uncertainty with those measured with the hot-filter sampler. Relative to the heated filter sample, dilution did increase the PM_2.5 mass fraction of selenium for all fuels tested, as well as ammonium and sulfate for selected fuels. However, the additional particulate mass created by gas-to-particle conversion of these species is within the uncertainty of the gravimetric analysis used to determine the overall mass emission rate. The enrichment of PM_2.5 selenium caused by dilution did not vary with dilution ratio and residence time. The enrichment of PM_2.5 sulfate and ammonium varied with fuel composition and dilution ratio but not residence time. For example, ammonium was only enriched in diluted acidic aerosol samples. A comparison of the PM_2.5 emission profiles for each of the fuels tested underscores how differences in PM_2.5 composition are related to the fuel ash composition. When sampling after the bag house, the particle size distribution and total particle number emission rate did not depend on residence time and dilution ratio because of the much lower particle number concentrations in diluted sample and the absence of nucleation. These results provide new insight into the effects of dilution sampling on measurements of fine particle emissions, providing important data for the ongoing effort of the EPA and ASTM to define a standardized dilution sampling methodology for characterizing emissions from stationary combustion sources.     

Characteristics of traffic-induced fugitive dust from unpaved roads

The characteristics of fugitive dust emitted from vehicles traveling on unpaved dirt roads were measured using a suite of instruments including a real-time fugitive dust sampler. The fugitive dust sampler is formed from a combination of a large particle inlet and an optical particle spectrometer that reports particle sizes from 6 to 75 µm. The large particle inlet permits the sampling of particles up to 75 µm with only a moderate dependence of sampling efficiency on wind-speed. Measurements made with the sampler showed that particles as large as ～50 µm were suspended from vehicular movement on the dirt roads, with the mode of the fugitive dust particle number size distribution ～2 µm, while the mass distribution mode was ～7 µm. A comparison of the fugitive dust sampler measurements with those made using standard PM instruments showed that the conventional instruments have a wind-direction bias that can result in under-sampling of large particles. The current measurements suggest that particles suspended from dirt roadways are of importance for local air quality within the near-road environment.

Copyright © 2017 American Association for Aerosol Research     

Physical and Chemical Characteristics and Volatility of PM in the Proximity of a Light-Duty Vehicle Freeway

Abstract

Volatility properties of ultrafine particles were analyzed next to State Route 110 (Pasadena freeway CA), a light-duty vehicle freeway where heavy-duty traffic is prohibited. In addition, mass concentration and chemical composition of particulate matter (PM) were measured in coarse, accumulation, and ultrafine modes. On weekdays from 17 May to 4 June 2004, measurements were performed in two locations, one very close to the freeway (within 2.5 m from the curb) and one at a distance of about 50 m from the freeway. For measurement of mass and chemical composition, the study employed in each location a micro-orifice uniform deposit impactor (MOUDI) and a modified high-volume sampler. Both instruments sampled with the same size cutpoints: a coarse mode from 2.5 to 10 μm, an accumulation mode from 0.18 to 2.5 μm, and an ultrafine mode of particles less than 0.18 μm in aerodynamic diameter. Alternately, a tandem differential mobility analyzer (TDMA) was used at the two sites. A heater between the two DMAs evaporated volatile material from the monodisperse aerosol, size selected by the first DMA. The second DMA analyzed the losses of volatile components. The ultrafine number concentrations next to the freeway were 46,000 cm^?3 on average during the sampling period. The MOUDI ultrafine mass concentration, nitrate, and EC were higher next to the freeway than at the background site farther from the freeway. The other components analyzed in the ultrafine mode had similar concentrations next to the freeway and at the background site. Volatility ranged from about 65% volume losses of 120 nm particles heated to 110°C to 95% of 20 nm particles. The 20 nm aerosol was only internally mixed, whereas increasing nonvolatile fractions were found for 40 nm (6% next to the freeway), 80 nm (20%), and 120 nm (28%) aerosols.     

Evaluation of a High Volume Aerosol Concentrator

A virtual impactor sampler, which is designed to concentrate aerosols from a 1000 L/min ambient air sample into a 1 L/min exhaust airflow stream, was tested with near monodisperse aerosols in aerosol wind tunnels to characterize sampling performance. New methodology is introduced to correct results for the presence of doublet and satellite aerosol particles that can be present in the particle size distribution from a vibrating jet atomizer. Aerosol penetration from the free stream near the sampler inlet to the outlet of the device has a peak value of 78% at a particle size of 3.9 w m AD. Sampling effectiveness, which is the mean penetration over the size range of 2.5 to 10 w m AD, is 48%. There are 4 virtual impaction stages in the sampler, and examination of the regional losses shows that most of the aerosol deposition occurs on surfaces of the last 2 stages. The ideal power expenditure of the sampler (excluding electrical and frictional losses in the motor and bearing losses in the blower) is 58 watts as compared to the actual power consumption of 320 watts.     

Size Characterization of Carbonaceous Particles Using a Lovelace Multijet Cascade Impactor / Parallel-Flow Diffusion Battery Serial Sampling Train

A serial sampling train consisting of a Lovelace multijet cascade impactor (LMJI) and a seven cell parallel-flow diffusion battery (PFDB) has been used to provide a comprehensive method for sizing aerosols with a wide size distribution ranging from less than 0.01 μm to over 10 μm. The fraction of the aerosol greater than 0.7 μm is collected by the impactor. The remaining fraction of the aerosol is sampled by the PFDB. Design of the PFDB is based on the theory of a screen-type diffusion battery. The concept of parallel flow is employed to provide a method for sampling aerosols that fluctuate too rapidly in concentration and size distribution to be measured by conventional methods. The LMJI/PFDB sampling system is useful for characterizing multimodel size distributions such as those that occur in ambient aerosols. It can also be used to determine the chemical composition of collected samples as a function of particle size. This sampling system has been used to size classify diesel and diesel-oil shale exposure atmospheres, and benzo(a)-pyrene-coated carbon black aerosols. The diffusion equivalent diameter (D _de) of the diesel exhaust was 0.07–0.08 μm, and the oil-shale dust had a mass median aerodynamic diameter (MMAD) of 2.6–2.9 μm. The size distribution of the carbon black aerosol was bimodal, with the fine fraction having a D _de of 0.2 μm, and the coarse fraction having a MMAD of 2.0 μm.     

Wind Tunnel Evaluation of PM10 Samplers

The U.S. Environmental Protection Agency (EPA) has promulgated new national ambient air quality standards for PM₁₀ (particles smaller than 10 μm aerodynamic diameter). Samplers used to collect PM₁₀ must be subjected to wind tunnel tests before they can be approved as part of a designated reference or equivalent method. Monodisperse liquid and solid particles are used over a range of particle sizes and windspeeds to characterize the sampling effectiveness and 50 percent cutpoint of candidate samplers. This paper describes an EPA wind tunnel test facility, sampler test procedures, and the results of selected sampler tests with liquid and solid test particles. The agreement between wind tunnel results and observations from field measurements of ambient particulate matter is also discussed.     

High-Volume Dichotomous Virtual Impactor for the Fractionation and Collection of Particles According to Aerodynamic Size

A prototype dichotomous virtual impactor (DVI) using a single acceleration nozzle, operating at approximately 500 1/min, and having an aerodynamic particle outpoint diameter of about 2–3 μm has been constructed and tested. Under these conditions the flow through the acceleration nozzle is calculated to be turbulent. This sampler was calibrated with a monodisperse aerosol, and the measured particle size-dependent collection efficiencies demonstrate that the sampler size fractionates atmospheric particulate matter as efficiently as the low-volume dichotomous virtual impactors. Analysis of test data indicates that the high-volume sampler can be described by classical impaction theory. These data also indicate that over the range of Reynolds numbers from 24,000 to 81,000 there is little, if any, dependence of inferred acceleration nozzle turbulence on the performance characteristics of the sampling system. A comparison of the concentration of atmospheric particulate matter, sulfate, and calcium on the fine filter samples collected with colocated high- and low-volume virtual impactors also shows that the two samplers are operating with similar performance characteristics. Additionally, the high-volume DVI collects at least 10–30 times the mass of particulate matter that the presently available virtual impactors collect and thus allows one to obtain improved precision in the measurement of those airborne species that are near the minimum detectable level of current analytical methods.     

Development of an Automatic Beta Gauge Particulate Sampler with Filter Cassette Mechanism

A beta gauge particulate sampler for measuring the aerosol mass concentration in the ambient air is described. The instrument is automatically calibrated with two self-calibration mass standards during each sampling period, while it samples particles continuously with minimum sampling dead-time loss. Key design features of the instrument based on the attenuation of beta radiation include filter cassette mechanism, auto-calibration system, low sampling dead-time, high sensitivity, and straightforward audit procedures. The instrument consists of three main components: PM 10 inlet, mechanical filter movement system, and control and data processing system. The mechanical filter movement system includes particle collection system with filter cassette magazine, g -ray measuring module and particle sampling module, auto-calibration system, and flow control system. The control and data processing system performs filter cassette movement control, sampling pump control, and data analysis. The instrument has been tested in the field to compare the measurement results with those by gravimetric mass measurement. The developed beta gauge instrument has been proved to be an efficient measuring guage for the ambient particulate mass determination.     

Instrument Busy Time and Mass Measurement using Aerosol Time-of-Flight Mass Spectrometry

Aerosol Time-of-Flight Mass Spectrometry (ATOFMS) instruments have been used widely to measure the size and composition of single ambient aerosol particles. ATOFMS data do not directly and quantitatively represent aerosol composition because the instruments exhibit non-linear response to particle concentration, size, and composition. Our approach is to analyze separately the components of non-linear ATOFMS response using field sampling data in order to understand ATOFMS response to ambient aerosols so that ATOFMS data can be scaled to more closely represent ambient aerosols. In this work we examine the effect of instrument busy time, mainly the time to process and save data, on ATOFMS response to ambient aerosols sampled during the 1999 Bakersfield Instrument Intercomparison Study (BIIS). During this study an ATOFMS instrument was operated alternately in normal and fast scatter data acquisition modes. In fast scatter mode, the instrument does not record mass spectra, minimizing instrument busy time; these data were used to determine particle arrival rates. Busy time in normal mode was found by a comparison of the number of particles detected to that expected for a Poisson process modified to include busy time. During the BIIS experiment, the ATOFMS instrument was busy between 5 and 95% of the nominal sampling time; thus busy time cannot be ignored for accurate quantitative analysis of ATOFMS data. ATOFMS data were scaled for on-line time and transmission efficiency, found by comparison with reference aerosol measurements, in order to estimate fine particle mass concentrations. Fine aerosol mass concentrations from scaled ATOFMS data demonstate semi-quantitative agreement with independent measurements using Beta Attenuation Monitors. We recommend that ATOFMS instruments be modified to measure busy time directly.     

An Intensive Study of the Size and Composition of Submicron Atmospheric Aerosols at a Rural Site in Ontario,Canada

Atmospheric sampling was conducted at a rural site near Egbert, about 70 km north of Toronto, Ontario, Canada from March 27 to May 8, 2003 to characterize the physical and chemical properties of the ambient aerosol in near real-time. The instrumentation included a tapered element oscillating microbalance (TEOM), an ultrafine condensation particle counter (UCPC), a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), an aerosol mass spectrometer (AMS), and a particulate nitrate monitor (R&P 8400N) for aerosol measurements. Gas-phase non-methane hydrocarbon compounds (NMHCs) were measured by gas chromatograph-flame ionization detection (GC-FID). Filter samples were also collected for analysis of inorganic ions by ion chromatography (IC). Aerosol properties varied considerably depending upon meteorological conditions and airmass histories. For example, urban and industrial emissions advected from the south strongly influenced the site occasionally, resulting in higher particulate mass with the higher fractions of nitrate and organics. Cleaner northwesterly winds carried aerosols with relatively higher fractions of organics and sulfate. The AMS derived mass size distributions showed that the inorganic species in the particles with vacuum aerodynamic diameters between about 60 nm and 600 nm had mass modal vacuum aerodynamic diameters around 400–500 nm. The particulate organics often exhibited two modes at about 100 nm and 425 nm, more noticeable during fresh pollution events. The small organic mode was well correlated with gas-phase nonmethane hydrocarbons such as ethylbenzene, toluene, and propene, suggesting that the likely sources of small organic particles were combustion related emissions. The particulate nitrate exhibited a diurnal variation with higher concentrations during dark hours and minima in the afternoon. Particulate sulfate and organics showed evidence of photochemical processing with higher levels of sulfate and oxygenated organics in the afternoon. Reasonable agreement among all of the co-located measurements is found, provided the upper size limit of the AMS is considered.     

High-Volume Diffusion Denuder Sampler for the Routine Monitoring of Fine Particulate Matter: II. Field Evaluation of the PC-BOSS

The high-volume Brigham Young University organic sampling system with a particle concentrator (PC-BOSS) has been field evaluated for the determination of airborne fine particulate matter including semivolatile chemical species during 3 intensive sampling programs in 1997: Tennessee Valley Authority (TVA), Lawrence County, TN; Riverside, CA; and Provo, UT. The PC-BOSS precision was tested using 2 collocated PC-BOSS samplers. In addition, the PC-BOSS results were compared with results from a prototype PM 2.5 U.S. EPA federal reference method (FRM sampler), a filter pack sampler (quartz and charcoal sorbent filters), the BIG BOSS, an annular denuder sampler, and the ChemSpec sampler for the determination of major fine particulate species. Fine particulate mass, sulfate, nitrate, and organic carbonaceous material (OC) determined by 2 PC-BOSS samplers agreed within - 10%. Possibly due to absorption of SO 2 by a quartz filter, the sulfate concentrations determined by the filter pack sampler and the BIG BOSS were higher (by 10 - 3%) than concentrations obtained with the other samplers. No absorption of SO 2 (g) by the quartz filters of the PC-BOSS occurred due to the high efficiency (>99%) of its denuder. The PC-BOSS, annular denuder, and ChemSpec samplers agreed with each other (to within - 0.5 w g/m 3 , - 17%, with no bias) for the determination of fine particulate nitrate concentrations, including volatilization losses. The prototype PM 2.5 FRM sampler collected only particle-retained nonvolatile mass. The mass concentrations determined by the PM 2.5 FRM agreed with those collected by the post-denuder Teflon filters of the PC-BOSS (to within - 1.1 w g/m 3 , - 10%, with no bias). The overall loss of material from particles and the resultant underestimation of the particulate mass concentrations by the PM 2.5 FRM depended on the fine particle composition and the ambient temperature.     

Submicrometer Aerosol Mass Distributions of Emissions from Boilers,Fireplaces, Automobiles,Diesel Trucks,and Meat-Cooking Operations

The predominant peak in the mass distribution emitted from each source measured in this study occurs at or below about 0.2 μm in particle diameter, whereas the Los Angeles atmospheric aerosol contains peaks at a variety of sizes in the range between 0.1 and 1.0 μm in particle diameter, including peaks at sizes larger than 0.2 μm. This suggests that considerable modification of the primary aerosol size distribution occurs because of subsequent processes in the atmosphere. The data presented here are intended for use in defining the size distribution of the primary combustion source effluent for use with mathematical models of the evolution of the atmospheric aerosol size distribution.     

Characterization of an Ambient Coarse Particle Concentrator Used for Human Exposure Studies: Aerosol Size Distributions,Chemical Composition,and Concentration Enrichment

The goals of the experiments described herein involve determining in real time the size, concentration enrichment, and chemical composition of coarse-mode (<2.5 μm) and fine-mode (>2.5 μm) particles within the nonconcentrated and concentrated flows of a coarse particle concentrator used for human exposure studies. The coarse particle concentrator was intended to concentrate ambient particles in the PM_10–2.5 size range before sending them into a human exposure chamber. The aerodynamic size and chemical composition of particles in the upstream and downstream flows of the concentrator were monitored with an aerosol time-of-f1ight mass spectrometer (ATOFMS) for fixed time intervals over the course of three days. Based on the ATOFMS results, it was found that there was no change in the composition of the ten major particle types observed in the upstream and downstream flows of the concentrator under normal operating conditions. Furthermore, no new particle types were detected downstream that were not detected upstream of the concentrator. A characterization of the aerosol chemical composition and its dependence on sampling conditions is also discussed. Aerosol size distributions were measured with three aerodynamic particle-sizing (APS) instruments sampling simultaneously from different regions of the concentrator. The APS size distributions were used to scale ATOFMS data and measure the ambient concentration factors for the coarse particle concentrator and the exposure chamber. The average concentration factor (ratio of inlet number concentration to the outlet number concentration) for the particle concentrator was 60 + 17 for the 2.5–7.2 μm size range before dilution and transport to the exposure chamber. It was observed that not only were coarse particles being concentrated but fine (<2.5 μm) particles were being concentrated as well, with concentration factors ranging from 2–46 for aerodynamic particle sizes from 0.54–2.5 μm.     

A Preliminary Apportionment of the Sources of Fine Particulates Impacting on the Israeli Coast

The Chemical Mass Balance (CMB) receptor model was used to apportion the sources of PM_2.5 aerosol (particulate matter with aerodynamic diameter <2.5 μm) sampled during a limited period at Caesarea, a site located in northern Israel along the Mediterranean coast, from late May to early June, 1993, a period corresponding to the time of year when air mass transport from Europe is frequent. Observed PM_2.5 concentrations averaged 25.5 μg/m³ during the sampling period, with sulfate accounting for the majority (>50%) of the total observed mass. Source contribution estimates predicted by the CMB receptor model were similar for all periods, with predicted ammonium sulfate, mobile source, coal-fired power plants, marine aerosol, and residual oil combustion contributions of 74, 14, 9, 3, and 0.3%, respectively. Transport (coupled with transformation) sources accounted for almost 97% of the ambient particulate loadings observed in this preliminary study.     

PELTI: Measuring the Passing Efficiency of an Airborne Low Turbulence Aerosol Inlet

In an effort to improve the accuracy of airborne aerosol studies, we compared a new porous-diffuser low-turbulence inlet (LTI) with three other inlets on the NSF/NCAR C-130, using both dust and sea salt as test aerosols. Analysis of bulk filters behind the LTI and an external reference total aerosol sampler (TAS) found no significant differences, while both the NASA shrouded solid diffuser inlet (SD) and NCAR community aerosol inlet (CAI) passed smaller amounts. However, scanning electron microscopic analyses of particles behind the LTI and TAS confirmed the model prediction that the LTI porous diffuser (PD) enhanced 7 μm particle concentrations by about 60%. Aerodynamic particle size distributions behind the other inlets began to diverge from enhancement-corrected LTI values above 2 μm, with mass concentrations of larger particles lower by as much as a factor of ten behind the CAI and a factor of 2 behind the SD. We conclude that the corrected LTI distributions were closer to ambient values than those from either the CAI or the SD. Since tubing losses contributed the most uncertainty when deducing ambient supermicron size distributions from LTI data, minimizing them should be a high priority for future experiments. Measured transfer tubing losses were larger than model estimates, in part because of some complex pieces for which no suitable model exists. The LTI represents a significant advance in our ability to sample populations of large particles from aircraft. A necessary part of using an LTI is the calculation of and correction for large-particle enhancement using a computational fluid dynamics (CFD) program. Although the solid diffuser inlet performed well under some conditions, its large-particle efficiency cannot be modeled, varies with humidity and particle morphology, and involves wall contact that has the potential to modify some particles.     

Development of a Personal Sampler for Collecting Fungal Spores

Exposure to fungal aerosols is of concern in indoor environments. However, sampling limitations have previously made it difficult to assess exposures accurately, especially long-term exposures. A prototype personal aerosol sampler, based on cyclone principles and using a 1.5 ml microcentrifuge tube as a particle collection receptacle has been designed and fabricated. Collection efficiency for aerosol particles in the size range of fungal spores has been evaluated for different types of microcentrifuge tubes, together with the effect of a polyethylene glycol coating on the inside of the tube and the effect of adding water to the tube. Monodisperse, fluorescently tagged polymer microspheres with median diameters of 0.5, 1, 2, 3, 6, 11, and 16 μm were used to evaluate sampler performance with particle diameter. The microcentrifuge-tube sampler was tested at flow rates of 2 and 4 liters per minute (l/min). Experimental results indicate that the microcentrifuge-tube sampler has an aspiration efficiency of 100% in calm air for particles up to 16 μm. At 4 l/min, the microcentrifuge-tube sampler is able to collect nearly 100% of particles greater than 3 μm and > 90% of particles between 2.5 and 3 μm. The 50% cutoff size is 1.5 μm. The performance of the sampler did not vary with the different brands of tubes tested or with the presence or absence of a coating on the tube surface. Furthermore, the addition of water to the tube resulted in a slight increase in collection efficiency. A sampling time of 5 h was feasible at 45–50% relative humidity before evaporation led to significant water loss.

The cutoff size of 1.5 μm is comparable to many commercially available bioaerosol samplers. Besides being easy to use, simple to fabricate, and inexpensive, this novel sampler has several advantages over conventional samplers: long-term samples are possible (the limitation of impaction methods); there is no sample transfer loss since the transfer step has been eliminated (the limitation of filter cassettes); laboratory analyses are not dependent solely upon a single analysis method (the limitation of impaction methods), and there is no sampler adherence loss (the limitation of trying to wash microorganisms from filters). In addition, use of the sampler would be applicable in a variety of occupational settings from low bioaerosol concentrations (i.e., indoor environments) to high bioaerosol concentrations (i.e., agricultural setting) by varying sampling time periods and using sensitive analytical methods.     

Inverting High Spectral Resolution Aerosol Optical Depth to Determine the Size Distribution of Atmospheric Aerosol

Measurements of aerosol optical depth are presented in the spectral interval 0.40–1.10 μm, which includes the most transparent region of the solar spectrum and the near infrared. The measurements were obtained by a grating spectrometer with a resolution ≈ 0.5 nm during the 1994 summer season at a mountain site (about 850 m above sea level) in the South of Italy. Spectral regions free from gas absorption features have been singled out and used to retrieve the aerosol columnar size distribution. Inversions have been performed by using the Phillips-Twomey inversion method along with a χ² criterion which allows one to choose a suitable value for the regularization parameter. The result of the inversions are presented in the particle radius range 0.1 ÷ 3 μm and indicate the presence of a bimodal aerosol with the second mode radius at about 1.0 μm undergoing transformations which are well correlated with relative humidity.     

An Aerosol Wind Tunnel for Evaluation of Massive-Flow Air Samplers and Calibration of Snow White Sampler

Massive-flow air samplers are being deployed around the world to collect aerosol samples for analysis of radioactivity as a result of nuclear tests and nuclear accidents. An aerosol wind tunnel capable of an 1100 m³ min^?1 flow rate was built at Lovelace Respiratory Research Institute (LRRI) to test the sampling efficiency of these samplers. This aerosol wind tunnel uses a stationary air blender to enhance mixing, and therefore it achieves the required uniform distribution of wind speed and aerosol concentration in the test section. The test section of the wind tunnel has a cross section that is 4.3 m × 3.7 m. The aerosol wind tunnel was tested for performance in terms of distribution of wind speed, turbulent intensity, SF₆ tracer gas concentration, and aerosol concentration. Test criteria consistent with U.S. Environmental Protection Agency (EPA) and American National Standards Institute (ANSI) standards were adopted as the guidelines for the aerosol wind tunnel. Additional criteria for aerosol wind tunnel were also recommended. Initial test of the aerosol wind tunnel showed that the wind tunnel could be operated in a wind speed range of 2 to 24 km h^?1. Within this range, the distribution of wind speed SF⁶ trace gas concentration and aerosol concentration in two-thirds of the central area of the test section showed coefficient of variances (COVs) of less than 10% for the range of wind speeds. This met the stringent guidelines for aerosol wind tunnel performance set by EPA and ANSI standards.

The LRRI wind tunnel was used to evaluate the collection efficiency of the sampling head of massive-volume air samplers, including the Snow White sampler. The sampler was tested in this aerosol wind tunnel for particles between 2 and 20 μm. The sampling flow rates were 500 and 700 m³ h^?1 for the tested wind speeds of 2.2 and 6.6 m S^?1, respectively. The results showed that sampling efficiency was influenced by both sampling flow rate and wind speed. The sampling efficiency decreased with an increase in particle size of between 2 and 20 μm. The sampling efficiency also decreased as the wind speed was increased from 2.2 to 6.6 m S^?1.     

A Numerical Study of the Performance of an Aerosol Sampler with a Curved,Blunt, Multi-Orificed Inlet

The purpose of this study was to numerically simulate the performance of an aerosol sampler with a curved, blunt, multi-orificed inlet in order to understand the sampling characteristics of the first prototype of the button personal inhalable aerosol sampler ("button sampler"). Because the button sampler inlet design is too complicated to apply a three-dimensional model, an axisymmetric two-dimensional model was created to be similar in geometry and to simulate the major features of the airflow through the sampler when facing the wind. Particle trajectories were calculated in a variety of wind velocities and were categorized into 5 groups based on their interactions with the curved surface of the sampling plane. Empirical sampling efficiencies of the button sampler for 3 particle sizes were used to adjust the calculated sampling efficiencies in an attempt to improve the accuracy of the two-dimensional axisymmetric model in accounting for interactions between particles and the surface of the inlet of the button sampler. Sampling efficiencies for other particle sizes were then predicted. The results showed that sampling efficiency decreased with increasing particle size up to approximately 40 w m and then remained virtually unchanged at about 35% up to 100 w m. Although the efficiencies were lower than the American Conference of Governmental Industrial Hygienists' (ACGIH) inhalability curve for larger particles, the pattern of the predicted sampling efficiency was quite similar to the ACGIH inhalability curve. Sampling efficiencies for liquid aerosol particles larger than 15 w m were predicted to be noticeably lower than those for solid particles. The results also showed that the multi-orificed curved surface played an important role in establishing a pressure drop with desired flow alignment inside the sampler, thus greatly reducing the wind effect and significantly improving the uniformity of particle deposition on the filter. The less uniform deposition found at high wind velocity can be improved by increasing the sampling flow rate.