Aerosols I

Aerosols I

Tuesday, June 2, 2015, 10:30 AM - 1:00 PM

SR-117-01 Deposition of Graphene Aerosol in Human Airways

W. Su, Lovelace Respiratory Research Institute, Albuquerque, NM

Objective: Graphene has been widely applied in today’s nanotechnology for manufacturing carbon nanotubes. However, the graphene material might become airborne during application processes, ​​which could then be inhaled by related workers causing possible adverse health effects. Therefore, studying the deposition of graphene aerosol in human respiratory tract is essential from the viewpoint of occupational health. This study tried to use a special experimental approach to obtain some original data for graphene aerosol human airway deposition.

Methods: The test graphene material was aerosolized by an electrospray. A differential mobility analyzer (DMA) was employed to size classify the generated graphene aerosols into three designated classification diameters (50, 100, and 200 nm). The airway deposition experiments were conducted by delivering the size classified graphene aerosol into well-defined human nasal and oral-lung airway replicas (down to the 4th lung generation). The deposition fraction of the graphene aerosol in the human airway was determined by measuring the concentration of the graphene aerosol at the inlet and outlet(s) of the airway replica using a sequential mobility particle sizer (SMPS). 

Results: The experimental results obtained showed that very few graphene aerosols were deposited in the airway replicas. The deposition fractions in different airway sections were generally less than 4%, and the deposition efficiencies were comparable to that acquired from spherical particles. 

Conclusions: The result obtained implies that most of the graphene aerosols inhaled into the human airway can easily transit down to the lower lung airways where adverse health effects might be induced. The experimental method used in this study can be a useful approach for investigating nanoparticle human airway deposition, which can greatly facilitate the health risk assessment for worker exposure to various nanomaterials.

SR-117-02 Development and Characterization of PM2.5 Samplers

H. Hung, C. Hsu, S. Huang, J. Lai, C. Chen, National Taiwan University, Taipei, Taiwan; Y. Kuo, Chung Hwa University of Medical Technology, Tainan, Taiwan

Objective: Cyclones are relatively free of operational problems such as clogging and re-entrainment. That makes them ideal for aerosol size-selective sampling. This study aimed to develop a series of sampling cyclones designed for different flow rates, but all fit to the PM2.5 sampling convention. 

Methods: To investigate the performance of sampling cyclones, an ultrasonic atomizing nozzle was used to generate micrometer-sized potassium sodium tartrate particles. An Am-241 radioactive source was employed to neutralize the particles to the Boltzmann charge equilibrium. Aerosol size distributions and number concentrations upstream and downstream of the cyclones were measured using an aerodynamic particle sizer. Each aerosol penetration measurement was repeated five times to assure data quality. The pressure drop across the cyclone was measured using an inclined manometer. The cyclone body diameter was used as the reference of other dimensions - including cyclone body height, cyclone height without cone, cone height, cone angle, cone bottom diameter, vortex finder diameter, and vortex finder length. All cyclones were variations on the design of the Very Sharp Cut Cyclone (VSCC). 

Results: The tested VSCC sampler had a design flow of 16.7 L/min and fit quite well to the PM2.5 sampling convention, except a slight over-estimation for aerosol size larger than 3 mm. The cyclone efficiency increased with the increasing flow rate because of increasing centrifugal force. The cyclone efficiency surprisingly decreased with increasing cyclone length. This phenomenon was particularly apparent for the no-cone design. The cone played an important role affecting not only the cutoff size but also the shape of the separation curves. The empirical equations derived and reported in previous studies could only provide rough dimensions of the cyclones designed for different sampling flow rates. Further fine-tune was needed to better match the PM2.5 sampling convention.

Conclusions: The cyclone structure is simple. Yet the alterations of configurations in the cyclone affect one another, which make it complicated to fully understand the impact of every configuration on the particle collection efficiency as a function of particle size, pressure drop, and the combined cyclone quality factor.

SR-117-03 Direct-reading Instrument Correlation for Dry Aerosol Personal Decontamination Method Evaluation

C. Lieb, J. Slagley, J. Engler, Indiana University of Pennsylvania, Indiana, PA

Objective: The objective of the test was to compare respirable dust concentrations from two direct-reading instruments for use in a research method to evaluate dry aerosol personal decontamination.

Methods: Two direct-reading instruments were used side-by-side to estimate respirable dust exposure within an aerosol chamber immediately after doffing coveralls from a manikin torso for different dry aerosol decontamination protocols. A manikin torso was dosed with 75 g of sodium bicarbonate on all surfaces of its coveralls. One of three decontamination methods (none, vacuum, or blower) was applied for three randomized trials each (n=9). The high efficiency particulate arresting (HEPA) vacuum method followed a set protocol which took 1.5 minutes. For the air shower simulation, a blower was secured at 30 cm (12 in) from the manikin to deliver an air velocity of 1351 cm/sec (2660 feet per min) while the manikin was rotated on a turn table for a 30 second duration. Exposure to respirable dust was measured with a six-channel optical particle counter (OPC), and a nepholometer. The OPC results were used to calculate a respirable dust concentration, while the nepholometer directly reported respirable dust concentration. Background-corrected readings ranged from 0.008–0.392 mg/m3. While both instruments use light scattering for measuring aerosols, they are different in their operation and assumptions. The instruments were compared for correlation to each other. 

Results: The nepholometer consistently measured 18% of the OPC response, with a linear correlation coefficient of 0.94. 

Conclusions: This study was one in a series to compare decontamination method effectiveness. The airborne exposure of concern is dry aerosols after applying a decontamination protocol. As such, direct-reading instruments are essential for the short period of exposure and high variability in concentrations. Two instruments were compared in the laboratory-based evaluation phase because the nepholometer is best-suited for field use, while the OPC gives more particle size information and is therefore more useful in the laboratory studies. The investigators wanted to confirm that the two different instruments would be highly correlated so that what was discovered in the laboratory could be seen in the field settings. 

SR-117-04 Development of a Low-Cost Integrated Sampler and Sample Pump

C. L’Orange, C. Quinn, D. Miller-Lionberg, J. Volckens, Colorado State University, Fort Collins, CO

Objective: Personal exposure assessments for aerosol hazards are often constrained by available resources: personnel, sampling, analytic. The sampling devices available for assessing aerosol exposure are either too costly and complex or non-representative in their ability to estimate dose; these limitations have reduced their use. A critical step needed to increase the affordability and throughput of personal exposure assessment is the development of simple and economical measurement devices.

Methods: A new integrated aerosol sampler and sample pump have been designed to address this need. The sampler system incorporates swappable sampler inlets directly into a small, light-weight personal sampling pump. The sampler body has been configured to handle multiple sampler inlets to meet a diverse range of study needs including the ability to directly incorporate size selective inlets. The sampler inlets were evaluated through a combination of calm air chambers, wind tunnels, and trial field studies for a range of particle sizes. Pump performance was characterized by generating a detailed pump curves using a calibrated flow bench.

Results: The new sampler inlets were found to be within ±13% of the proposed low velocity inhalability criterion for all particle sizes tested and with low limits of detection (<15 mg). The new sampler inlets tested were found to have comparable or superior performance to currently available designs while having a reduced complexity and minimal maintenance requirements. The lightweight sampler (<300g) was capable of maintaining precise flow control for flow rates ranging from 0.5L/min to >15L/min with moderate backpressure.

Conclusions: The process of collecting personal exposure measurements has been streamlined by incorporating two of the major physical elements into a single package. The availability of robust, simple, versatile, and economic sampling systems should reduce barrier to entry for organizations seeking to incorporate personal exposure measurements into their health and safety programs.

SR-117-05 A Sampling and Measurement System for Motorcycle Exhaust PM2.5

J. Lai, S. Huang, C. Hsu, C. Cheng, National Taiwan University, Taipei, TaiwanH. Cheng, The Environmental Analysis Laboratory, Taoyuan, Taiwan

Objective: The objective of this work was to develop a sampling and measurement system for PM2.5 emission from motorcycle engines.

Methods: The whole system could be divided into three parts: a diluter or a Nafion dryer, a PM2.5 pre-separator, and a prototype opacity meter. DEHS was used a surrogate agent whenever appropriate. A dynamometer was used to control a four-stroke motorcycle engine to generate stable exhaust aerosols. The hygroscopic property of motorcycle exhaust aerosols was investigated to provide the essential data for further design of diluter and/or dryer. A variety of sampling cyclones, based on the Very Sharp Cut Cyclone, were built and tested to check the fit to the PM2.5 sampling convention. A scanning mobility particle sizer and an aerodynamic particle size were used to measure aerosol number concentration and size distribution. Aerosol penetration tests were conducted for size-selective sampling cyclones, diluters, and dryers. A prototype opacity meter based on multi-reflection of laser light was built, tested and optimized for the PM measurement of motorcycle exhaust.

Results: The results showed that the aerosols, exhausted from a fuel-injection engine under the idle condition, had a count median diameter of 50 nm, with a GSD of 1.8. The aerosol number concentration was in the range from 104 to 105 #/cm3. The particle size was not affected as the relative humidity increased up to RH 95%. However, diluter and/or Nafion dryer were needed to remove water to prevent water vapor condensation. The diluter had the advantage of cooling the exhaust air effectively, but it led to lower aerosol concentration, a challenge to the opacity meter. The Nafion dryer could reduce the relatively humidity down to 25%. The VSCC with design flow of 16 L/min was used as PM2.5 pre-separator to work with the diluter. A smaller cyclone with a design flow of 3 L/min was developed to work with the Nafion dryer. The prototype opacity meter had a minimum detection limit of 0.5%, and could be used to monitor the aerosol concentration down to 104 #/cm3.

Conclusions: The sampling train and the opacity meter developed in this work performed satisfactorily. The whole measurement system was easier to operate, if Nafion dryer was adopted, because no additional flow control was needed. However, extra attention was needed to control the temperature to avoid water vapor condensation on the opacity meter.

CS-117-06 A Semi-Automated Scanning Electron Microscopy and Energy Dispersive X-ray (EDS) Method to Identify the Composition and Source(s) of Airborne and Surface Dust Complaints

D. Baxter, Environmental Analysis Associates, Inc., San Diego, CA

Situation/Problem: Although airborne and surface dust analysis is a powerful tool for solving air quality complaints, the absence of a systematic approach, skilled personnel, and time intensive analysis requirements, have limited the development of routine testing protocols. The time required to manually count and chemically analyze (2-3 hours) a sufficient number of particles is the main limitation. The absence of standards and industry guidelines for interpreting the data is also a factor. Although automated SEM/EDS is a standard analysis method for gunshot residue in criminal cases, a standardized approach to characterizing more generalized dust sources has remained undeveloped.

Resolution: This presentation, describes an automated SEM/EDS method for the quantification of indicator particles encountered in Indoor Air Quality investigations. The method employs commercially available EDS particle analysis software that can be retrofitted onto older Electron Microscopes. An entire “field of view” of up to 100 particles can be simultaneously analyzed for size, and chemistry at a rate of 10-50 particles/minute. Particle “classification” is then performed using a rule-based X-ray spectra library gathered by Environmental Analysis Associates, Inc. (EAA). The resulting data is presented in a format specifically designed to help the IH professional determine the potential sources and relative concentration of contaminant particles. The resulting microscopy data is reported by particle “classification” enabling the source of the particles to be determined.

Results: This presentation shows practical examples of automated dust analysis using an SEM/EDS system combined with a computer rule-based particle classification system. The “classification” categories are tailored to the likely source of the dust. The actual number of reported categories is based on the complexity of each sample. The applications discussed include the estimated size distribution and mass of quartz in coal dust samples, the quantification of fire residue, and locating the indoor source of corrosion particles.

Lessons Learned: When a semi-automated SEM/EDS system and a rule based particle characterization program are employed, large numbers of particles can be analyzed over a very short time frame. Significantly, implementation of this method brings the SEM analysis from a research mode to a commercial analytical tool for Industrial Hygiene investigations.​