In-Line Impactor Inlet for Bioaerosol Sampling

The proof of concept of a novel in-line real impactor (IRI) for preseparation of large particles in ambient inlets was demonstrated with a 1,250 L/min design. Numerical simulations predicted a cutpoint Stokes number 0.3 for a ratio of jet-to-plate spacing to jet width (S/W) of 2.0 and 0.5 for a ratio of 4.0. This variation in cutpoint Stokes number allows minor adjustments in cutpoint for a given device size. Experimental benchmark tests support the prediction of a shift in cutpoint with S/W. Inlet systems with flow rates of 100 and 400 L/min were designed by Stokes scaling of the 1,250 L/min IRI and integrating the lower flow devices with an existing inlet aspiration section and an insect screen. Experiments with the inlet system were conducted in a wind tunnel with particles from 3 to 20 μm aerodynamic diameter (AD) and wind speeds of 2, 8, and 24 km/h. A nominal cutpoint of approximately 11 μm AD was selected to accommodate bioaerosol sampling needs, and the wind tunnel results showed the average cutpoints of the 100 and 400 L/min inlet systems at the three wind speeds were 11.2 and 11.6 μm AD, respectively. Stand-alone tests with the 100 and 400 L/min IRIs were conducted where dry dusts (Arizona road dust/fine and coarse) were impacted on three types of collection surfaces (dry, grease-coated, and oil-soaked porous surfaces) to characterize solid particle carryover. The oil-soaked porous media allowed the least carryover of large solid particles.     

Design and Test of 2.5 μ m Cutoff Size Inlet Based on a Particle Cup Impactor Configuration

Based on the particle cup impactor configuration, an inlet for sampling fine particles smaller than 2.5 w m in diameter was designed for operation at a flow rate of 25 l/min. To determine the optimal dimensions of the particle cup impactor applicable to the PM 2.5 inlet, calibration experiments were carried out at wind velocities of 2 and 24 km/h in a wind tunnel. It was noted that the particle cup impactor having an impaction nozzle diameter of 3.2 mm and the nozzle-to-cup spacing of 3.6 mm yielded a sharp size cutoff. Supplementary experiments were conducted on sampling performance with the inlet having the optimally selected configuration at a near-zero wind speed in the test chamber. Results of the tests showed the inlet had a cutoff size of 2.43 w m in aerodynamic diameter, at 25 l/min, and that particles larger than 2.5 w m were trapped in the cup. Additional experiments covering a flow rate between 10 and 40 l/min with particle sizes between 0.8 and 4.3 w m were conducted in the test chamber. A field test was performed to examine the PM 2.5 inlet in real situations. The performance indicated that the inlet design met the basic requirements of fine-particle sampling.     

Large Particle Penetration During PM10 Sampling

The objective of the present study was to characterize the performance of a federal reference method (FRM) PM₁₀ size-selective inlet using analysis methods designed to minimize uncertainty in measured sampling efficiencies for large particles such as those most often emitted from agricultural operations. The performance of an FRM PM₁₀ inlet was characterized in a wind tunnel at a wind speed of 8 km/h. Data were also collected for 20 and 25 μm particles at wind speeds of 2 and 24 km/h. Results of the present sampler evaluation compared well with those of previous studies for a similar inlet near the cutpoint, and the sampler passed the criteria required for certification as a FRM sampler when tested at 8 km/h. Sampling effectiveness values for particles with nominal diameters of 20 and 25 μm exceeded 3% for 8 and 24 km/h wind speeds in the present study and were statistically higher than both the “ideal” PM₁₀ sampler (as defined in 40 CFR 53) and the ISO (1995) standard definition of thoracic particles (p < 0.05) for 25 μm particles leading to the potential for significant sampling bias relative to the “ideal” PM₁₀ sampler when measuring large aerosols.

Copyright 2014 American Association for Aerosol Research     

Development of a PM 10/PM 2.5 Cascade Impactor and In-Stack Measurements

Combustion and industrial processes are an important source of particles. Due to the new PM 10 and PM 2.5 standards for ambient air quality, a sampling system for PM 10/PM 2.5 in-stack measurements was designed and calibrated. In this new system, the exhaust gas is isokinetically sucked into a two stage impactor through the inlet of a plane filter device and the aerosol is fractionated in the particle size classes >10 w m, 10-2.5 w m, and <2.5 w m. Due to a relatively high volume flow (ca. 3.2 m 3 /h, depending on exhaust gas conditions), sampling times are kept short, e.g., 30 min for dust concentrations of 10 mg/m 3 . The impactor was calibrated in the laboratory and then operated at various industrial plants. Parallel measurements with identical devices showed average standard deviations of 3.1% (PM 10) and 3.4% (PM 2.5). Measurements of the cascade impactor together with the plane filter device gave plausible results and average PMx/TSP ratios of 0.49 (PM 2.5/TSP) and 0.78 (PM 10/TSP), showing a large variability for different processes. Elemental analysis using total-reflection X-ray fluorescence spectrometry, together with the size-fractionated sampling, proved to give characteristic patterns of the emitted aerosols, which can be used for a subsequent fingerprint modelling for source apportionment of ambient air pollution.     

A Circumferential Slot In-Line Virtual Impactor

An In-line Virtual Impactor is presented, which has an application as a pre-separator for sampling inlets, where the device scalps large particles from the aerosol size distribution. Numerical simulation was the principal tool employed in the design process, with physical experiments used to verify computational predictions. Performance investigations were primarily carried out for a configuration that provides a nominal cutpoint particle size of 10 μ m aerodynamic diameter at an inlet flow of 111 L/min and a major flow exhaust of 100 L/min; however, the concept is scalable in terms of both flow rates and cutpoint sizes. An inverted dual cone configuration contained within a tube provides a characteristic circumferential slot of width 2.54 mm (0.100 inches) and a slot length of 239 mm (9.42 inches) at the critical zone. The upper cone causes the flow to accelerate to an average throat velocity of 3.15 m/s, while the lower cone directs the major flow toward the exit port and minimizes recirculation zones that could cause flow instabilities in the major flow region. The cutpoint Stokes number is 0.73; however, the cutpoint can be adjusted by changing the geometrical spacing between the acceleration nozzle exit plane and a flow divider. When the system is operated at the major exhaust flow rate of 100 L/min, the pressure drop is 45 Pa. Good agreement is obtained between numerically predicted and experimentally observed performance.     

Development and field evaluation of an online monitor for near-continuous measurement of iron,manganese, and chromium in coarse airborne particulate matter (PM)

A novel air sampling monitor was developed for near-continuous (i.e., 2-h time resolution) measurement of iron (Fe), manganese (Mn), and chromium (Cr) concentrations in ambient coarse particulate matter (PM) (i.e., PM_10–2.5). The developed monitor consists of two modules: (1) the coarse PM collection module, utilizing two virtual impactors (VIs) connected to a modified BioSampler to collect ambient coarse PM into aqueous slurry samples; (2) the metal concentration measurement module, which quantifies the light absorption of colored complexes formed through the reactions between the soluble and solubilized target metals and pertinent analytical reagents in the collected slurries using a micro volume flow cell (MVFC) coupled with UV/VIS spectrophotometry. The developed monitor was deployed in the field for continuous ambient PM collection and measurements from January to April 2016 to evaluate its performance and reliability. Overall, the developed monitor could achieve accurate and reliable measurements of the trace metals Fe, Mn, and Cr over long sampling periods, based on the agreement between the metal concentrations measured via this online monitor and off-line parallel measurements obtained using filter samplers. Based on our results, it can be concluded that the developed monitor is a promising technology for near-continuous measurements of metal concentrations in ambient coarse PM. Moreover, this monitor can be readily configured to measure the speciation (i.e., water-soluble portion as well as specific oxidation states) of these metal species. These unique abilities are essential tools in investigations of sources and atmospheric processes influencing the concentrations of these redox-active metals in coarse PM.

Copyright © 2016 American Association for Aerosol Research     

Numerical,wind-tunnel,and atmospheric evaluation of a turbulent ground-based inlet sampling system

The use of inlets for transferring aerosols from the environment to instrumentation can introduce uncertainty in the measurement of aerosol properties. Aerosol loss during this process is a non-negligible issue that may bias the subsequent measurements. These loss mechanisms include aspiration at the inlet head and deposition/evaporation/condensation during transport through the sampling lines. Coarse-mode aerosol is significantly impacted by the aspiration and inertial loss mechanisms within an inlet system. This work uses wind tunnel experiments to investigate aerosol losses through the Storm Peak Laboratory’s (SPL) new aerosol inlet system. The inlet is used extensively for both intensive field campaigns and long-term aerosol monitoring. The results of numerical simulations of the SPL aerosol inlet sampling efficiency are provided at several wind speeds, and experimental results demonstrate the system has a 50% cut off for the coarse-mode at an aerodynamic diameter of approximately 13?μm and wind speed of 0.5?m s^?1. This investigation will lead to improved accuracy of in situ aerosol measurements at SPL and this system can be replicated at other atmospheric stations.

Copyright © 2019 American Association for Aerosol Research     

Characterizing Indoor and Outdoor 15 Minute Average PM 2.5 Concentrations in Urban Neighborhoods

While a number of studies have looked at the relationship between outdoor and indoor particulate levels based on daily (24 h) average concentrations, little is known about the within-day variability of indoor and outdoor PM levels. It has been hypothesized that brief airborne particle excursions on a time scale of a few minutes to several hours might be of health significance. This article reports variability in measurements of daily (24 h) average PM 2.5 concentrations and short-term (15 min average) PM 2.5 concentrations in outdoor and indoor microenvironments. Daily average PM 2.5 concentrations were measured using gravimetry, while measurements of 15 min average PM 2.5 mass concentrations were made using a light scattering photometer whose readings were normalized using the gravimetric measurements. The measurements were made in 3 urban residential neighborhoods in the Minneapolis-St. Paul metropolitan area over 3 seasons: spring, summer, and fall of 1999. Outdoor measurements were made at a central monitoring site in each of the 3 communities, and indoor measurements were made in 9-10 residences (with nonsmoking occupants) in each community. Residential participants completed a baseline questionnaire to determine smoking status, sociodemographics, and housing characteristics. Outdoor PM 2.5 concentrations across the Minneapolis-St. Paul metropolitan area appear to be spatially homogeneous on a 24 h time scale as well as on a 15 min time scale. Short-term average outdoor PM 2.5 concentrations can vary by as much as an order of magnitude within a day. The frequency distribution of outdoor 15 min averages can be described by a trimodal lognormal distribution, with the 3 modes having geometric means of 1.1 w g/m 3 (GSD = 2.1), 6.7 w g/m 3 (GSD = 1.6), and 20.8 w g/m 3 (GSD = 1.3). There is much greater variability in the within-day 15 min indoor concentrations than outdoor concentrations (as much as ～40-fold). This is most likely due to the influence of indoor sources and activities that cause high short-term peaks in concentrations. The indoor 15 min averages have a bimodal lognormal frequency distribution, with the 2 modes having geometric means of 8.3 w g/m 3 (GSD = 1.66) and 35.9 w g/m 3 (GSD = 1.8), respectively. The correlation between the matched outdoor and indoor 15 min average PM 2.5 concentrations showed a strong seasonal effect, with higher values observed in the spring and summer ( R 2 adj = 0.49 - 0.33) and lower values in the fall ( R 2 adj = 0.13 - 0.13).     

A Computational Fluid Dynamics Study of Particle Penetration through an Omni-Directional Aerosol Inlet

Computational fluid dynamics (CFD) was used to study aerosol penetration through the entrance section of a bell-shaped omni-directional ambient aerosol sampling inlet. The entrance section did not include either an insect screen or a large-particle pre-separator. Simulations of the flow field were carried out for wind speeds of 2, 8, and 24 km/h and a fixed exhaust flow rate of 100 L/min; and, particle tracking was performed for 2 to 20 μ m aerodynamic diameter particles. Penetration calculated from CFD simulations was in excellent agreement with experimental results from previous studies with the root mean square relative error between simulation and experimental data being 3.8%. CFD results showed that the most significant regional particle deposition occurred on the upwind side of a curved flow passage between two concentric axisymmetric shells of the inlet housing and that deposition at the leading edges of the shells and within the exhaust tube was far less significant. At a wind speed of 2 km/h, penetration was affected by gravitational settling, e.g., penetration of 20 μ m particles was 71.9% when gravity was included and 80.4% without gravity. At higher wind speeds gravity had little effect. An empirical equation was developed to relate aerosol penetration to a Stokes number, a gravitational settling parameter, and a velocity ratio. Good fits of the correlation curves to experimental data and numerical results were obtained.     

Size-selective sampling performance of six low-volume “total” suspended particulate (TSP) inlets

Several low-volume inlets (flow rates ≤ 16.7 liters per minute (Lpm)) are commercially available as components of low-cost, portable ambient particulate matter samplers. Because the inlets themselves do not contain internal fractionators, they are often assumed to representatively sample “total” mass concentrations from the ambient air, independent of aerodynamic particle size and wind speed. To date, none of these so-called “TSP” inlets have been rigorously tested under controlled conditions. To determine their actual size-selective performance under conditions of expected use, wind tunnel tests of six commonly used omnidirectional, low-volume inlets were conducted using solid, polydisperse aerosols at wind speeds of 2, 8, and 24 km/h. With the exception of axially-oriented, isokinetic sharp-edge nozzles operating at 5 and 10 Lpm, all low-volume inlets showed some degree of nonideal sampling performance as a function of aerodynamic particle size and wind speed. Depending upon wind speed and assumed ambient particle size distribution, total mass concentration measurements were estimated to be negatively biased by as much as 66%. As expected from particle inertial considerations, inlet efficiency tended to degrade with increasing wind speed and particle size, although some exceptions were noted. The implications of each inlet's non-ideal behavior are discussed with regards to expected total mass concentration measurement during ambient sampling and the ability to obtain representative sampling for size ranges of interest, such as PM_2.5 and PM₁₀. Overall test results will aid in low-volume inlet selection and with proper interpretation of results obtained with their ambient field use.

Copyright © 2018 American Association for Aerosol Research     

Design,Calibration, and Field Test of a Cyclone for PM 1 Ambient Air Sampling

Ambient air sampling at a flow rate of 16.7 Lpm (1 m 3 /h) has been well established with the adoption, within the USA, of the EPA regulations governing PM 2.5 sampling. Subsequent to the adoption of the new regulation, problems were encountered with the impactor technique utilized for establishing a PM 2.5 cut ( D 50 = 2.5 w m aerodynamic equivalent diameter, A.E.D.). In order to avoid the depression in the cut point engendered by a buildup of collected material on the impactor stage and to extend the operating interval between cleanings, a cyclone was developed to replace the impactor. Although not an adopted standard, PM 1 has a practical appeal in that it represents the smallest cut point that can practically be assessed for long periods of time at high flow rates utilizing inertial techniques. Further relevance is attributed to this cut by interest in particulate matter related to diesel engine emissions. A new version of the sharp cut cyclone (SCC) was constructed with the aim of obtaining a cut point at D 50 = 1 w m at a flow rate of 16.7 Lpm. The dimensions of the cyclone were calculated using the SCC design model by Kenny and Gussman. Field studies were conducted to validate the PM 1 cyclone and to compare the results to colocated PM 10 and PM 2.5 concentration measurements.     

Automated Measurement of the Size and Concentration of Airborne Particulate Nitrate

A three-stage, cascaded integrated collection and vaporization system has been developed to provide automated, 10 min resolution monitoring of the size and concentration of fine particulate nitrate in the atmosphere. Particles are collected (7 min) by a humidified impaction process, and analyzed in place (3 min) by flash vaporization and chemiluminescent detection of the evolved nitrogen oxides. The three size fractions, < 0.45 w m, 0.45-1.0 w m, and 1.0-2.5 w m, are chosen to distinguish the condensation, droplet, and coarse components of PM 2.5 . The size precut at 2.5 w m is done at ambient conditions, while the size fractionation at 1.0 w m and 0.45 w m is done at a constant relative humidity of 65%. The system is calibrated with laboratory aerosols, including comparison of sizing for hygroscopic salt and hydrophobic organic aerosols. The complete system is tested with monodisperse ammonium nitrate aerosol generated with a high-flow differential mobility analyzer coupled with an impactor precut and yields results consistent with the calibration of the individual stages.     

DEVELOPMENT OF A DICHOTOMOUS SLIT NOZZLE VIRTUAL IMPACTOR

A high-volume slit nozzle virtual impactor has been developed to collect fine and coarse particles. The size cut-off and particle loss characteristics of the developed slit virtual impactor agree well with those of the 16.7 lmin⁻¹ commercially available dichotomous sampler. The effects of various flow and physical design parameters on the collection of both fine and coarse particles have been investigated. The results of these tests indicated that many of the theoretical principles established for round nozzle virtual impactors can be successfully applied to slit nozzle virtual impactors. However, the effects of the flow volume and Reynolds number (Re) on the cut-off behavior and particle losses are more pronounced for slit virtual impactors. The impactor's particle size cutpoint decreased as the total inlet flow and Re increased. For Re<about 7000, particle losses increased with particle size. For Re of about 7000, particle losses exhibited a maximum near the 50% cutpoint, which is typical in round nozzle virtual impactors. For Re>7000, losses of fine particles were significant, while coarse particle losses were low. Changes in the minor-to-total flow ratio and collection slit width also affected particle losses.     

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.     

Wind Tunnel Evaluation of an Aircraft-Borne Sampling System

The U.S. Environmental Protection Agency (EPA), the Florida Department of Environmental Protection (FLDEP), and Texas A&M University collaborated in the design, construction, and testing of a unique, highly crosslinked, Teflon-coated inlet and manifold gas and aerosol sampling system that is being used in EPA aircraft atmospheric pollution characterization studies. The aircraft-borne ambient sampling system, which consists of a Teflon-coated shrouded probe coupled to a Teflon-coated aluminum manifold, is designed to collect reactive gases (e.g., mercury and halide species) and aerosols for subsequent analysis and characterization. The shrouded inlet probe was tested for particle transmission ratios in a high-speed aerosol wind tunnel. An existing wind tunnel was upgraded from a maximum wind speed of 13.4 m/s (48 km/h or 30 miles/h) to 50.5 m/s (182 km/h or 113 miles/h) to test this probe. The wind tunnel was evaluated for compliance with the criteria of ANSI 13.1 to establish the acceptability of its use in testing probes. The results demonstrated that the velocity and tracer gas concentration profiles were within the specified limits. A wellcharacterized ThermoAndersen Shrouded Probe (Model RF-2-112) was also tested to check tunnel performance and test methodology. The results obtained from these tests are in close agreement with earlier published data.

When operated at a sampling flow rate of 90 L/min, the aircraft-borne shrouded probe showed a transmission ratio of about 0.76 at 45 m/s (162 km/h or 100 miles/h) for 10 μ m aerodynamic diameter particles. To improve the transmission ratio of the sampling probe, the sampling flow rate was reduced to 80 L/min and the air speed increased to 50.5 m/s, which increased the transmission ratio to about 0.9 for 10 μ m particles. Further reduction of the flow rate to 60 L/min increased the transmission to 1.2. The Teflon-coated manifold, which is located downstream of the shrouded probe, was statically tested for transmission ratio at flow rates of 90 L/min and 30 L/min. The results were a transmission ratio of about 0.80 for 10 μ m aerodynamic diameter particles. The combination of the shrouded probe operated at 60 L/min with a transmission ratio of 1.2 and the manifold with its transmission of 0.8 will give an overall transmission of about unity for 10 μ m aerodynamic diameter particles at a flight speed of 50.5 m/s.

These findings suggest that shrouded probes can be used for low speed (～ 100 miles/h) aircraft applications. The transmission ratio of these probes is a significant improvement over the conventional aircraft-mounted, sharp-edged isokinetic diffuser-type inlets.     

DESIGN AND EXPERIMENTAL CHARACTERIZATION OF A PM1 AND A PM2.5 PERSONAL SAMPLER

This paper presents the development, laboratory and field evaluation of two personal particle samplers (PPS). Both samplers operate at a flow rate of 4 l min^-1, and collect particles smaller than 1.0 and 2.5 μm in aerodynamic diameter, respectively, on 3.7 cm Teflon filters. In each sampler, particles larger than 2.5 or 1.0 μm are retained by impaction onto a coated porous metal disk, which minimizes particle bounce. Using the substrates without any coating results in a substantial reduction of the collection efficiency for particles larger than the 50% cutpoint of the sampler. Particle losses in each sampler are quite low (e.g., on the order of 10% or less) and do not depend significantly on aerodynamic particle diameter. Both samplers display sharp particle cut characteristics, with the ratio of the aerodynamic particle diameter corresponding to 84% collection efficiency to the 50% cutpoint being approximately 1.18 and 1.27 for the PM₁ and the PM_2.5 samplers, respectively. Field tests showed that the mass, sulfate and nitrate concentrations measured by the PM_2.5 PPS and a collocated PM_2.5 Personal Exposure Monitor (PEM) agreed within 10% or less. Such agreement, however, was not observed between the PM_2.5 PPS and the Harvard/EPA Annular Denuder System (HEADS), with the HEADS nitrate concentrations being on the average higher by a factor of 2.1. The particle mass, sulfate and nitrate concentrations obtained with a modified MOUDI sampler collecting all particles smaller than 1 μm in aerodynamic diameter on a filter and the PM₁ PPS were also in very good agreement (e.g., within 7% or less). The two personal particle samplers will be used in field studies in different locations of the U.S. to provide better estimates of human exposures to exclusively particles of the accumulation mode. (e.g., without incorporating the contribution of the coarse mode).     

A Novel Multifilter PM10–PM2.5 Sampler (MFPPS)

A novel multifilter PM₁₀–PM_2.5 sampler (MFPPS) that enables the collection of four PM₁₀ and four PM_2.5 samples simultaneously has been developed and tested. The MFPPS uses a PM₁₀ impactor as the inlet and operates at 33.4 L/min. After the inlet, the aerosol flow is divided half by a Y-type fitting. Half of the flow is directed into four PM₁₀ filter cassettes, while the other half is directed into four PM_2.5 filter cassettes after the aerosols are further classified by a PM_2.5 impactor. An active flow control system consisting of two mass flow controllers (MFCs), one for PM₁₀ and the other for PM_2.5, is used to fix the total flow rate of 16.7 L/min for four PM₁₀ or four PM_2.5 channels based on the ambient pressure and temperature. To ensure flow rate uniformity through each of the four PM₁₀ or four PM_2.5 filter cassettes, an orifice is assembled behind each of the filter cassettes to increase the pressure drop, such that the flow rates of eight sampling lines are nearly equal using just two MFCs. The MFPPS was calibrated in the laboratory for particle collection efficiency curves first. Then, the ambient PM concentrations were compared with those of other two collocated FRM samplers, the dichotomous PM₁₀ and the EPA WINS PM_2.5 sampler in the field study. Calibration results showed the cutoff aerodynamic diameters of the PM₁₀ and PM_2.5 impactors were 9.8 ± 0.1 and 2.5 ± 0.05 μm, respectively. Field comparison results indicated PM₁₀ and PM_2.5 concentrations agreed well with the other two PM samplers.     

The tunnel impactor. A multiple inertial impactor for coarse aerosol

The Tunnel Impactor is a new sampling instrument which was developed to enable the determination of the mass concentration and mass size distribution of coarse aerosol from the ambient atmosphere. The instrument consists of a large wind-directed tube functioning as an aerosol inlet. Further down the tube four impactors are mounted, each with different dimensions (2, 5, 15 and 50 mm wide ribbons), thus offering different cut-off characteristics. A constant air flow through the tube is accomplished by four ventilators, mounted at the rear end, in order to keep impaction conditions constant and well defined. The calibration of the instrument was carried out under atmospheric conditions and involved liquid DEHS aerosol and solid copper sulphate aerosol. The data showed considerable scatter, inherent to atmospheric calibration. Nevertheless the S-shaped mass collection efficiency curves could be established. The results show that the cut-off diameters are in the range from 10 to 60 μm roughly. The instrument was found to perform properly at windspeeds above 1 m s⁻¹, and is expected to function satisfactorily up to wind speeds well above 7.5 m s⁻¹. Experiments during handling of coal in the yard of a steel factory showed good performance of the instrument in practice.     

Physical Characterization of the University of Toronto Coarse,Fine, and Ultrafine High-Volume Particle Concentrator Systems

Particle concentrators allow exposure to controlled levels of concentrated ambient particulate matter (PM) over a broad range of concentrations. The performance of these systems can be influenced by the physicochemical characteristics of PM and so it is vital to characterize the concentrators at a given site. The quasi-ultrafine PM (<0.2 μm), fine PM (0.15–2.5 μm), and coarse PM (2.5–10 μm) concentrators at the Southern Ontario Center for Atmospheric Aerosol Research (SOCAAR), University of Toronto, were characterized as a part of the “Health Effects of Aerosols in Toronto (HEAT)” campaign held during February–March, 2010. The full size distributions of ambient and concentrated particles were simultaneously measured in terms of number, surface area, and volume using high time-resolution instruments. Examination of the complete size distribution, including the unconcentrated particles beyond the cutpoints of the concentrator systems, revealed that particles in the unconcentrated size ranges made significant contributions to the particle number and surface area present in the concentrated airstreams of fine and coarse concentrators. Further transients in the ambient ultrafine particle concentrations were evident as dampened signals in these concentrated airstreams. The ultrafine concentrator exhibited a significant size shift when the ambient particle size distribution had a mode ≤30 nm. Overall the fine and coarse concentrators provided a reasonable concentrated reproduction of the ambient PM mass while questions remain regarding the representativeness of the ultrafine concentrator.

Copyright 2012 American Association for Aerosol Research     

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.