Bernard A. Olson

Development and evaluation of a low cutpoint virtual impactor

Designing an impactor with a submicrometer cutpoint is a technical challenge, since high jet velocities (resulting in low pressures downstream of the jet nozzle) or small orifices are required. This paper presents the development of a low cutpoint virtual impactor that operates at a small pressure drop. A parametric study was performed to determine the conditions that affect the performance of the virtual impactor. In addition, a detailed measurement of the particle losses through the system is presented. By developing a better understanding of the particle collection and losses as a function of geometric and flow parameters, the design of low cut-point virtual impactors can be optimized. The results show that the virtual impactor has a cutpoint of 0.12 μm at a pressure drop of 0.08 atm, with low particle losses, averaging about 7% with a maximum of 14% at the 50% cutpoint. The separation characteristics of the virtual impactor are similar to those predicted by the theory. Reducing the minor flow ratio fr...

Assessing Potential Nanoparticle Release During Nanocomposite Shredding Using Direct-Reading Instruments

This study was conducted to determine if engineered nanoparticles are released into the air when nanocomposite parts are shredded for recycling. Test plaques made from polypropylene resin reinforced with either montmorillonite nanoclay or talc and from the same resin with no reinforcing material were shredded by a granulator inside a test apparatus. As the plaques were shredded, an ultrafine condensation particle counter; a diffusion charger; a photometer; an electrical mobility analyzer; and an optical particle counter measured number, lung-deposited surface area, and mass concentrations and size distributions by number in real-time. Overall, the particle levels produced were both stable and lower than found in some occupational environments. Although the lowest particle concentrations were observed when the talc-filled plaques were shredded, fewer nanoparticles were generated from the nanocomposite plaques than when the plain resin plaques were shredded. For example, the average particle number concentrations measured using the ultrafine condensation particle counter were 1300 particles/cm3 for the talc-reinforced resin, 4280 particles/cm3 for the nanoclay-reinforced resin, and 12,600 particles/cm3 for the plain resin. Similarly, the average alveolar-deposited particle surface area concentrations measured using the diffusion charger were 4.0 μm2/cm3 for the talc-reinforced resin, 8.5 μm2/cm3 for the nanoclay-reinforced resin, and 26 μm2/cm3 for the plain resin. For all three materials, count median diameters were near 10 nm during tests, which is smaller than should be found from the reinforcing materials. These findings suggest that recycling of nanoclay-reinforced plastics does not have a strong potential to generate more airborne nanoparticles than recycling of conventional plastics.

A Low-Loss Cascade Impactor with Stage Collection Cups: Calibration and Pharmaceutical Inhaler Applications

A new cascade impactor design having low interstage losses is described. A novel feature is the use of external stage collection cups, to simplify applications requiring chemical determination of the mass collected on each stage. The design has been executed in versions to operate at two flow rates: 30 and 60 L/min. Calibration data are presented for these flow rates, and, in addition, for the latter version at 90 L/min. Size results using the new impactor on a typical pharmaceutical inhalation product are shown to be equivalent to those obtained using a current cascade impactor. An example is presented to indicate the utility of gathering size data at more than one flow rate.

Calibration of Sharp Cut Impactors for Indoor and Outdoor Particle Sampling

ABSTRACT A low-flow rate, sharp cut point inertial impaction sampler was developed in 1986 that has been widely used in PM exposure studies in the United States and several other countries. Although sold commercially as the MS&T Area Sampler, this sampler is widely referred to as the Harvard Impactor, since the initial use was at the Harvard School of Public Health. Impactor nozzles for this sampler have been designed and characterized for flows of 4,10, 20, and 23 L/min and cut points of 1, 2, 5, and 10 |im. An improved method for determining the actual collecting efficiency curve was developed and used for the recent impactor calibrations reported here. It consists of placing a multiplet reduction impactor inline just downstream of the vibrating orifice aerosol generator to remove the multiplets, thus allowing only the singlet particle s to penetrate through to the impactor being calibrated. This paper documents the techniques and results of recent nozzle calibrations for this sampler and compares it with other size-selective inertial impactors. In general, the impactors were found to have sharp cutoff characteristics. Particle interstage losses for all of the impactors were very low, with the exception of the 10-|im cut size 20 L/ min impactor, which had greater losses due to the higher flow rate. All of the cut nozzle laboratory calibrations compare favorably to the U.S. Environmental Protection Agency (EPA) WINS-96 fine particle mass (PM2 5) impactor calibration data.

Estimation of diffusion losses when sampling diesel aerosol: A quality assurance measure

Under the sponsorship of the Coordinating Research Council (CRC), the University of Minnesota (UMN) formed an international research team to investigate the physical and chemical nature of diesel emissions from heavy-duty vehicles while operating on highways (CRC Project E-43). These ambient measurements of vehicle emissions following their release into and dilution by the atmosphere guided the development of dilution and sampling procedures for laboratory test cells to simulate on-highway conditions. The importance, visibility, and potential implications of the project prompted the adoption of a quality assurance (QA) plan by an independent implementation team. Because exhaust aerosol characterization for mobile sources lacks prescribed sampling methodologies, standard operating procedures were developed as part of the QA effort to ensure the consistency and validity of the data collected. To verify the daily protocols used, the QA team made surveillance visits to observe UMN team performance on project tasks. Evaluation of instrument performance using aerosols of known size was also done as part of QA system audits conducted to assess the accuracy of particle size measurements. QA for particle concentration measurement was hampered by the lack of a concentration standard, which is a problem common to aerosol science investigations today. Thus, the standard practice in aerosol work is to verify particle concentration by comparing results from two identical condensation particle counters (CPC) and rely on instrument manufacturer calibrations. A fundamental component of QA for assessment of instruments and sampling system performance was investigation of particle losses. Along an aerosol sample pathway from source to collection media or measuring instrument, some particles are lost to surfaces. The magnitude of these losses as a function of particle size was determined experimentally by challenging the sampling trains with mono-disperse particles in the sub-50 nm aerodynamic diameter size range (nm=10 - 9 meters). Since the most probable loss mechanism was diffusion for sub-50 nm sized particles, theoretical calculations of diffusion loss for 100 nm particles and smaller were also made. Results indicated average sampling train total losses of approximately 50% and 20% for 10 nm and 17 nm size particles, respectively.

Diesel Exhaust/Mine Dust Virtual Impactor Personal Aerosol Sampler: Design, Calibration and Field Evaluation

A virtual impactor personal aerosol sampler (VIPAS) has been developed for use in diesel-equipped mines to collect size-separated samples of diesel exhaust and mine dust particles in the respirable size range. This sampler consists of three stages: a 10-mm cyclone, a 0.8-[mu]m outpoint virtual impactor and two filter cassettes. The large nonrespirable particles are removed in a 10-mm cyclone. The respirable particles from the cyclone pass through a 0.8-[mu]m cutpoint virtual impactor with the particles larger than and smaller than 0.8 [mu]m (mine dust and diesel exhaust particles, respectively) collected on two 37-mm filter cassettes. The sampling flow rate is 2 L/min so as to be compatible with the standard respirable dust sampler and personal sampling pumps. 22 refs., 10 figs.

Development and Calibration of a Low-Flow Version of the Marple-Miller Impactor (MMI™)

ABSTRACT Cascade impactor analysis of drugs for inhalation in aerosol form is regarded by both European and U.S. pharmacopoeias as an important method to determine particle size-related information concerning dose that might be delivered to various parts of the respiratory tract. Existing measurements usually are made at flow rates in excess of 25 1/min, which are more representative of peak inspiratory flow rates achieved by adults. There is therefore a need for a low-flow impactor that can be used to evaluate drug delivery devices intended for use by infants or small children, or by those whose disease status prevents the achievement of higher inspiratory flow rates. A new version of the Marple-Miller impactor™ (MMI™) is described that meets this need, operating at either 4.9 or 12 1/min by the substitution of a different uppermost stage jet. A novel feature is the use of external stage collection cups instead of plates, enabling quantitative transfer of drug collecting on each stage for subsequent chem...

Second generation micro-orifice uniform deposit impactor, 120 MOUDI-II: Design, Evaluation, and application to long-term ambient sampling

The original MOUDI (Micro-Orifice Uniform Deposit Impactor) cascade impactor, reported in the literature in 1991, used an external gear system to achieve a uniform deposit and was intended for industrial hygiene studies with sample times in the range of minutes to a few hours. To facilitate much longer run times, a second generation MOUDI, MOUDI-II, which uses internal electric motors to rotate the impaction plates, was developed. Three model 120 MOUDI-IIs were used in a 32-month program to sample ambient atmospheric aerosols at several industrial and urban locations in Minnesota. For these sampling locations, each 120 MOUDI-II operated continuously for a minimum of five, and optimally 7 days, to collect a sample at a site. During these community sampling events, the three 120 MOUDI-IIs logged 4007, 2637, and 3230 h of operating time, respectively. A laboratory side-by-side comparison of the three 120 MOUDI-IIs showed good agreement amongst the three 120 MOUDI-IIs and, thus, the particle size distributions were independent of the 120 MOUDI-II used. Application of the 120 MOUDI-IIs for long-term ambient sampling was demonstrated by comparing size distributions from the background locations: Minneapolis, Duluth and Ely, Minnesota, representing urban, light industrial, and pristine area type of aerosols, respectively. PM2.5 averages from Minneapolis and Duluth compare well with three-year averages from state regulatory sampling. Copyright 2014 American Association for Aerosol Research

Inertial Impactors to Measure Aerodynamic Diameters of Man-Made Organic Fibers

It is widely accepted that the aerodynamic diameter of a particle is one of the main factors that determines particle deposition into the human respiratory system. The determination of aerodynamic diameter of spheres or near spherical objects is routinely accomplished using impactors. The aerodynamic diameter of man made organic fibers (MMOF), on the other hand, has not traditionally been measured using impactors, because fibers of the same cross section may have different lengths and a variety of shapes (straight, curved, etc.) for each length. The aerodynamic size of the fibers is thus a function of fiber orientation. Single and multiple stage impactors have been developed, calibrated, and validated specifically for the determination of the aerodynamic diameter of large fibers with circumscribed diameters between 20 and 35 w m and an aspect ratio ranging from subfiber lengths (aspect ratio < 3) up to 40. The impactor allows measurements of the aerodynamic diameter of cellulose acetate fibers released during mechanical smoking of cigarettes. The performance characteristics were evaluated by spherical particles of known diameters, fibers of known length and diameter, and computational fluid dynamic calculations. Our methodology has shown that inertial impactors can be used to determine the aerodynamic diameter of large cellulose acetate fibers.

Assessment of air sampling methods and size distribution of virus-laden aerosols in outbreaks in swine and poultry farms:

Swine and poultry viruses, such as porcine reproductive and respiratory syndrome virus (PRRSV), porcine epidemic diarrhea virus (PEDV), and highly pathogenic avian influenza virus (HPAIV), are economically important pathogens that can spread via aerosols. The reliability of methods for quantifying particle-associated viruses as well as the size distribution of aerosolized particles bearing these viruses under field conditions are not well documented. We compared the performance of 2 size-differentiating air samplers in disease outbreaks that occurred in swine and poultry facilities. Both air samplers allowed quantification of particles by size, and measured concentrations of PRRSV, PEDV, and HPAIV stratified by particle size both within and outside swine and poultry facilities. All 3 viruses were detectable in association with aerosolized particles. Proportions of positive sampling events were 69% for PEDV, 61% for HPAIV, and 8% for PRRSV. The highest virus concentrations were found with PEDV, followed by HPAIV and PRRSV. Both air collectors performed equally for the detection of total virus concentration. For all 3 viruses, higher numbers of RNA copies were associated with larger particles; however, a bimodal distribution of particles was observed in the case of PEDV and HPAIV.