Effect of deposited polydispersed particles on respirable cyclone penetration

Transcription

1 University of Iowa Iowa Research Online Theses and Dissertations Spring 2013 Effect of deposited polydispersed particles on respirable cyclone penetration William Andrew Leach University of Iowa Copyright 2013 William Leach This thesis is available at Iowa Research Online: Recommended Citation Leach, William Andrew. "Effect of deposited polydispersed particles on respirable cyclone penetration." MS (Master of Science) thesis, University of Iowa, Follow this and additional works at: Part of the Occupational Health and Industrial Hygiene Commons

2 EFFECT OF DEPOSITED POLYDISPERSED PARTICLES ON RESPIRABLE CYCLONE PENETRATION by William Andrew Leach A thesis submitted in partial fulfillment of the requirements for the Master of Science degree in Occupational and Environmental Health in the Graduate College of The University of Iowa May 2013 Thesis Supervisor: Professor Patrick O'Shaughnessy

3 Copyright by WILLIAM ANDREW LEACH 2013 All Rights Reserved

4 Graduate College The University of Iowa Iowa City, Iowa CERTIFICATE OF APPROVAL MASTER'S THESIS This is to certify that the Master's thesis of William Andrew Leach has been approved by the Examining Committee for the thesis requirement for the Master of Science degree in Occupational and Environmental Health at the May 2013 graduation. Thesis Committee: Patrick O'Shaughnessy, Thesis Supervisor T. Renée Anthony Thomas M. Peters

5 ABSTRACT Workplace aerosol sampling has been used to assess exposure to airborne materials that are known to cause adverse health effects in the respiratory system. Respirable cyclones are a common instrument used to monitor occupational exposures to respirable particles and are designed to have a penetration similar to the definition for the respirable fraction. However, deposited particles inside the walls of the cyclone may influence the penetration of cyclones. The aim of this study was to determine if there is a difference in collection efficiencies of a clean SKC 37-mm aluminum cyclone compared to a SKC 37- mm aluminum cyclone deposited with polydispersed dust. Glass beads (Count Median Diameter CMD 3.3 µm, Geometric Standard Deviation GSD 1.7) were used to test a clean cyclone. The cyclone was then loaded by sampling with one of three dust types individually for three hours at concentrations of at least 3 mg/m 3 : Arizona Road Dust (CMD 1.04 µm, GSD 1.57), organic dust (CMD 2.90 µm, GSD 1.77), and titanium oxide (CMD 0.85 µm, GSD 1.28). After the cyclone was deposited with dust without cleaning, glass beads were used to retest the penetration. Particle penetration was measured using the Aerosol Particle Sizer (APS, TSI 3321). Particles depositing on the walls of the cyclone caused a shift in the penetration compared to clean samplers. When the cyclone was loaded with Arizona Road Dust, the penetration of particles increased as much as 5% at 3.5 µm. Depositing with Organic Dust increased particle penetration as much as 4% at 3.5 µm. Depositing did not occur with Titanium Oxide and did not significantly particle penetration. Sampling with cyclones deposited with polydispersed particles can cause sampling errors by oversampling, and therefore overestimate the respirable concentration relative to a clean sampler. To counteract sampling errors from deposited particles would require the cyclone to be thoroughly dried and clean before sampling. ii

6 TABLE OF CONTENTS LIST OF TABLES...v LIST OF FIGURES... vii CHAPTER I. LITERATURE REVIEW...1 Respirable Aerosols...1 Particle Deposition...4 Particle Clearance...4 Toxicology of Respirable Particles...4 Prevalence of Pulmonary Diseases from Occupational Exposures...5 Regulations Concerning Respirable Particles...7 Respirable Samplers...8 Factors Affecting Collection Efficiency...10 Shortcoming in Literature...13 Study Aim...13 II. EFFECT OF DEPOSITED POLYDISPERSED PARTICLES ON RESPIRABLE CYCLONE PENETRATION...15 Introduction...15 Materials and Methods...18 Experimental Apparatus...18 Cleaning the Cyclone...19 Aerosol Tests...19 Depositing Particles on the Cyclone...21 Masses of the Cyclone and Grit Pot...21 Calculating Cut Points...22 Sampler Bias Calculation...22 Statistical Analysis...23 Results...23 Cyclone Penetration...23 Arizona Road Dust...24 Organic Dust...24 Titanium Oxide...25 High Humidity Organic Dust...26 SKC Cyclone Bias Map...27 Discussion...27 Shift in Penetration between New and Cleaned Cyclone...27 Particle Depositing on Walls...28 Effect of Deposited Particles on Penetration...29 Total Mass Measured and Deposited Mass on Cyclone...31 SKC Cyclone Cut Point Bias Comparision...32 Study Limitations...33 Conclusion...34 III. CONCLUSION...55 iii

7 APPENDIX: CHAMBER LOADING CONDITIONS...57 REFERENCES...59 iv

8 LIST OF TABLES Table 1. Numbers of runs and samples for each loading aerosol Size distribution of loading and challenge aerosols Aerosol concentrations during loading with Arizona Road Dust Weights of cyclone and grit pot through each step of sampling with Arizona road dust. Bold data indicate reject H o : α = Average penetration percentage of particles by bin size for Arizona Road Dust over all Runs (n=6). Bold data indicate reject H o : α = Values of cyclone cut points, obtained via linear interpolation for Arizona Road Dust. Bold data indicate reject H o : α = Aerosol concentrations of chamber while loading with organic dust when humidity was less than 50% Weights of cyclone and grit pot through each step of sampling with organic dust. Bold data indicate reject H o : α = Average penetration percentage of particles by bin size for organic dust over each Run (n=3). Bold data indicate reject H o : α = Values of cyclone cut points, obtained via linear interpolation for organic dust. Bold data indicate reject H o : α = Aerosol concentrations while loading with titanium oxide Weights of cyclone and grit pot for each step of sampling with titanium oxide. Bold data indicate reject H o : α = Penetration percentage of particles by bin size for clean and deposited cyclone for titanium oxide (n=3). Bold data indicate reject H o : α = Values of cyclone cut points, obtained via linear interpolation for titanium oxide. Bold data indicate reject H o : α = Aerosol concentrations while loading with organic dust when humidity was 95% Weight of cyclone and grit pot through each step of sampling with high humidity organic dust Penetration of percentage by bin size of clean and deposited cyclone with high humidity organic dust (n=1)...54 v

9 18. Penetration cut point of clean and deposited cyclone with high humidity organic dust...54 A-1. Chamber conditions while loading with Arizona Road Dust...57 A-2. Chamber conditions while loading with organic dust when humidity was less than 50%...57 A-3. Chamber conditions while loading with titanium oxide...58 A-4. Chamber conditions while loading with organic dust when humidity was 95%...58 vi

10 LIST OF FIGURES Figure 1. Experimental apparatus mm cassette with drilled hole and tubing to minimize cassette wall losses Particle penetration for glass beads in new SKC 37-mm aluminum cyclone, shifted particle penetration of clean used SKC 37-mm aluminum cyclone, and respirable criterion Penetration curves of clean and deposited cyclones from Arizona road dust. Error bars are one standard deviation and are only represented in one direction for each curve at each bine size Penetration curves of clean and deposited cyclones from organic dust. Error bars are one standard deviation and are only represented in one direction for each curve at each bine size Penetration curves of clean and deposited cyclone from titanium oxide. Error bars are one standard deviation and are only represented in one direction for each curve at each bine size Penetration curves of clean and deposited cyclone from high humidity organic dust Mass bias of clean SKC 37-mm aluminum cyclone when cut point was at 3.7 µm operated at 2.5 lpm Mass bias of SKC 37-mm aluminum cyclone when particles deposited inside cyclone and cut point was 3.8 µm operated at 2.5 lpm Bias map of SKC 37-mm aluminum cyclone at factory specifications when cut point is at 4 µm operated at 2.5 lpm vii

11 1 CHAPTER I Literature Review Respirable Aerosols Since toxicity of aerosols is affected by where they deposit in the airways, the ACGIH recommended the use of three particulate size-selective sampling criteria for workplace sampling. The three particulate size selective sampling criteria are: inhalable, thoracic, and respirable particulate matter criterion (ACGIH, 1985). The American Conference of Governmental Industrial Hygienist (ACGIH) has defined respirable particles as materials that are hazardous when deposited in the gas-exchange (alveolar) region of the lung (ACGIH, 2011). Respirable particles that can reach the alveolar region range from to 10 µm (James et al., 1991). Adverse health effects have been caused by the inhalation of hazardous substances found in occupational atmospheres. Personal samplers are often used to measure occupational exposure to hazardous substances. The respirable particulate matter deposition (RPM) criterion was developed to determine what size of particles that are hazardous when deposited in the gas-exchange region of the lung (ACGIH, 2011; Hinds, 1999). There have been historical accounts of Miners Black Lung also known as Coal Worker s Pneumoniosis (CWP) that date back to CWP has been studies by numerous epidemiological studies on miners since then and in 1959 the Johannesburg Penumoconiosis Conference met to address the issue (Merchant et al., 1986). To monitor exposures to respirable dust, respirable criterions definitions were developed for sample for it. In the 1980 s there were two main definitions for the respirable criterion: The British Medical Research Council (BMRC), which had a d 50, or cut point, of 5 µm and an earlier ACGIH curve with a d 50 of 3.5 µm. A d 50, or cut point, is when 50% of particles of that size are collected by the sampler. It was difficult to distinguish the respirable particle matter with estimates of deposition between the two curves since the BMRC definition excluded particles larger than 7.07 µm. A major issue with the BMRC was that most samplers do not have such an exclusion of the

12 2 larger particles, particles larger than 7.07 µm, which would underestimate hazards with larger aerodynamic diameters (Soderholm, 1989). To help solve this issue, Soderholm (1989) proposed a new definition of respirable fraction which slightly differed from the previous conventions with a 50% cut off at 4 µm. The respirable fraction that Soderholm proposed has been agreed upon by the Comité Européen de Normalisation (CEN), American Conference of Governmental Industrial Hygienist (ACGIH), and the International Standards Organization (ISO) (CEN 1993, Phalen et al., 1995). The ACGIH Respirable Particle Matter (RPM) was calculated using the Inhalable Particle Matter (IPM) Particle Size-Selective threshold limit value (TLV). aerodynamic diameter in µm, 100 µm Particle Deposition Adverse health effects can be caused by inhaled particles depending on their site of deposition in the respiratory system. Regional deposition has been found to be largely dependent on their aerodynamic size (James et al., 1991). The internal dose of inhaled particles and their site of deposition within the respiratory system vary widely and are mainly determined by their aerodynamic size and shape, breathing patterns and structures of the lung (Fleming et al., 1996). Particle deposition follows physical laws that take place during inspiration and expiration. The three primary mechanisms of deposition are inertial impaction, sedimentation and diffusion (Stuart, 1984). Mechanisms of deposition models are typically based on the aerodynamic diameter of a given particle. The aerodynamic diameter of a given particle, as defined by Hinds

13 3 (1999), is the diameter of a spherical particle with a standard density of 1000 kg/m 3 that has the same settling velocity as the particle of interest. The principle mechanism for deposition of large particles is inertial impaction in the upper airways (Stuart, 1984). Inertial impaction acts on particles ranging from 2 to 3 µm up to larger than 20 µm in diameter. Large airborne particles will follow their initial path when the airstream path diverts due to the branching of airways (Stuart, 1984). Deposition by impaction is characterized by the particle s Stokes number. A Stokes number is the ratio of the particle s stopping distance to the width of the airway, characteristic dimension, of an obstacle (Hinds, 1999). As the Stokes number increases so does the deposition efficiency due to inertial impaction (Kim et al., 1994). In the alveolar region particles larger than 0.1 µm can be deposited by sedimentation, and deposition will increase with particle size, particle density, and respiratory cycle time (Heyder, 2004). Sedimentation is the most important mechanism of deposition in trachea, bronchi airways and the alveolar region. The maximum sedimentation deposition is found in the horizontally orientated airways. Sedimentation deposition depends highly on the particles terminal settling velocity. Large particles, greater than 0.1 µm, that make their way to the alveolar, gas exchange, regions of the lungs are likely to deposit due to long residence times and high terminal settling velocity (Stuart, 1984). Deposition by diffusion or Brownian motion is the primary mechanism for particles less than 0.1 µm (Heyder, 2004). Brownian motion is the random irregular wiggling motion of an aerosol particle caused by random and relentless bombardment by gas particles, as particles get smaller their Brownian motion increases. Deposition by diffusion happens in all regions of the respiratory tract (Stuart, 1984). Particle deposition by electrostatic charges can be of secondary importance unless very highly charged particles are generated (Chan and Yu, 1982). Chan and Yu (1982) provided an example of the effect of electrostatics charges. Inhaled particles with a mass median diameter of 2 µm and a charge of 200 elementary charges/particle will have a deposition of 39% in the

14 4 tracheobronchial region compared to 3% of uncharged particles of the same size. At very low levels particle deposition by electrostatic charge can be considered negligible. Particle deposition increases with electrostatic charges through all regions of the respiratory system (Prodi and Mularoni, 1985). Particle Clearance Insoluble particles that have been deposited in the upper airways and tracheobronchial regions of the respiratory tract can be cleared by mucociliary transport as either intact particles or following phagocytosis by pulmonary alveolar macrophages (Stuart, 1984). The respiratory epithelium is lined with cilia, and a thin film of mucus surrounds the cilia and particles will stick to that mucus. Mucociliary clearance works by the movement of mucus covered cilia making rapid forward moving stroke and slow return strokes. The quick and slow movement of the cilia pushes mucus up to the pharynx. When the mucus is transported up to the mouth, it is then swallowed or expelled by coughing (Wanner et al., 1996). The body has different techniques in removing particles that reach the pulmonary region. Several methods are available to remove particles in this region, including engulfment by macrophages towards the bronchioles which are dissolved in the blood (Lidén, 1994). The alveolar macrophage is the primary phagocyte of the innate immune system. The innate immune system is responsible for the removal of the infectious, toxic, or allergic particles that have made their way to the alveolar region of the lung (Rubins, 2003). Toxicology of Respirable Particles Chemical aerosols that are present in the air can be suspended as solids, gases or liquid droplets and their chemical composition can cause adverse health effects (ACGIH, 2011). There are a wide range of adverse health effects caused by respirable particles including depressed phagocytic activity of alveolar macrophages, lung inflammation, fibrosis and chronic obstructive lung disease.

15 5 Animal studies have been conducted to determine the effects of chemical aerosols on alveolar macrophages. Waters et al. (1975) exposed rabbits to chlorides of Cd 2+, Ni 2+, Mn 2+, and Cr 3+ and saw these chlorides caused cell lysis (breaking down of a cell) and a decrease in cell viability in alveolar macrophages. When diesel exhaust was exposed to rats Castranova and Vallyathan (1985) found that diesel emissions depressed the phagocytic activity of alveolar macrophages. Scarring of the lung has been associated with decreased lung function and fibrosis (Shi- Wen et al., 2008). Asbestos is a naturally occurring fiber that causes fibrotic diseases of the lung. Injuries to epithelial and mesothelial cells are initiated by the formation of reactive oxygen intermediates (Craighead and Mossman, 1982). Silica dust particles that penetrate the respiratory system and deposit in the alveolar region of the lung and can cause scarring of the lung tissue. The scarring of the lung impairs the exchange of oxygen and carbon dioxide in the blood (Mossman and Churg, 1998). Silicon based radicals can react with aqueous media to produce oxygen radicals (Vallyathan et al., 1988). The scarring of the lung by silica is known as silicosis and is one of the oldest occupational lung diseases in the world (Mossman and Churg, 1998). Silicosis has been a recognize pulmonary disease process for over 400 years. Bernardino Ramazzini, Father of Occupational Medicine, identified Silicosis in his De Morbis Artificum Diatriba (Disease of Workers) in 1713 (Willis, 2013). Inflammation of the lung has been identified as a cause of particle-induced lung disease. A Chronic inflammatory response can occur from both toxic and nuisance particles such as carbon black, titanium oxide, diesel exhaust, and ultrafine particles. The increases in inflammatory response paralleled the number of HPRT gene mutations in rat lung epithelial cells (Borm and Driscoll, 1996). Prevalence of Pulmonary Diseases from Occupational Exposures The prevalence of pulmonary diseases from occupational exposures has been studied. Pulmonary diseases occur in several occupations such as mining, stone quarrying, construction,

16 6 pottery making, textile industry, and in agriculture (Becklake et al., 1989; Castranova and Vallyathan, 2000; Viegi et al., 2001). Many pulmonary diseases can be caused by occupational exposure to respirable aerosols including silicosis, asbestosis, coal workers pneumoconiosis (CWP), and chronic obstructive pulmonary disease (COPD). From 1970 to 2000 the prevalence of pneumoconiosis in coal workers has been decreasing in the United States due to federal respirable dust restrictions in coal mines since being enacted in 1969 (Castranova and Vallyathan, 2000). However, since 2000 the prevalence of pneumoconiosis has increased in miners of 15 or more years of experience (NIOSH, 2013A). The largest increase in prevalence of pneumoconiosis has been observed among miners in Kentucky Virginia, and West Virginia (Laney et al., 2010). In the 1970s, 32% of miners who had 25 or more years of coal mining had evidence of CWP. By the 1990s the prevalence of CWP had dropped to about 4%. In the 2000s the prevalence of CWP has increased back up to 9% in miners (NIOSH, 2013B). Crystalline silica near coal seams have been theorized to be why the prevalence of pneumoconiosis is on the rise in the US (Laney et al., 2010). Chronic exposures to welding fumes, heavy metals, mineral dusts, isocyanates and grains are known to cause COPD. Occupations that have a high risk of developing COPD are miners, quarry, construction, textile, and agricultural workers (Becklake et al., 1989, Viegi et al., 2001). In 2003 the US had roughly 10.7 million people diagnosed with COPD. Of those diagnosed with COPD 15% (about 1.6 million) were estimated to have the disease as a result of occupational exposures such as from coal mine dust and silica (NIOSH, 2013B). In 1997 COPD was the fourth leading cause of death in the US. The prevalence, incidence, and mortality rates for COPD have increased with age. The prevalence and mortality rates of COPD tend to be higher in Caucasians, blue-collar workers, and lesser educated people (Viegi et al., 2001). In 2000 the prevalence rate of COPD for Caucasians was 63.6 per 1000 and 50.4 per 1000 for African Americans. Women had a higher prevalence of COPD at 73.2 per 1000 compared to men at 45.5 per 1000 (CDC, 2013). The number of people with COPD is increasing worldwide from

17 7 increase of smoking prevalence in developing countries and reduction in mortality from infectious disease (Viegi et al., 2001). Regulations Concerning Respirable Particles Regulations have been developed on a number of hazardous substances that can cause adverse health effects in the lung. Respirable particles are regulated when particles of their chemical composition and size are hazardous in the alveolar region of the lung (Soderholm, 1989). The Occupational Safety and Health Administration (OSHA) and the ACGIH have developed enforceable regulations and health based recommendations to limit exposures to hazardous substances. OSHA has established enforceable permissible exposure limits (PEL) that are meant to protect workers from adverse health effects to hazardous substances. For respirable particles that do not have a PEL, they are covered under Particles Not Otherwise Regulated with an eight-hour time-weighted average(twa) of 5 mg/m 3 (OSHA, 2013). When exposure limits and guidelines for PNOR were initially established, the justification for the limits were based on reduction of visibility in the workplace and irritant effects to the skin, eyes, ears and nasal passages (Hearl, 1998). Over time, studies of respirable particles found that a pulmonary overload phenomenon can occur at sufficiently high concentrations and cause damage to the airways beyond irritation effects (Soutar et al., 1997). For regulatory monitoring of respirable PELs, OSHA requires the use of the 10-mm Dorr-Oliver nylon cyclone operating at a d 50 cut point of 3.5 µm. In 2013 OSHA had 39 established PELs to sample for using the respirable criterion (OSHA, 2013). The recommendations established by the ACGIH Threshold Limit Values (TLV) are typically more stringent than the OSHA PELs. In 2012 there were 20 adopted respirable TLVs. A TLV is created when the Threshold Limit Value for Chemical Substance Committee determines that there is sufficient evidence of adverse health effects to airborne concentrations of a material encountered in the workplace. For respirable aerosols that do not have a TLV, ACGIH also recommends sampling for Particles Not Otherwise Specified (PNOS), which covers

18 8 substances that can be biologically inert, insoluble, or poorly soluble, and have a low toxicity. The rationale of the ACGIH PNOS was based off of the OSHA equivalent PNOR. PNOS are believed by the ACGIH that even biologically inert and insoluble, or poorly soluble, particles may have adverse health effects. The airborne concentrations for these PNOS substances should be kept below 3 mg/m 3 for respirable particles unless a TLV is established for a particular substance (ACGIH, 2011). Respirable Samplers A variety of personal respirable samplers can be used to sample for the RPM. Personal respirable samplers fall under two types of samples: size-selective sampling and size-segregated collection of aerosol particles. Size-selective sampling refers to the use of a specific particle deposition curve, such as the respirable curve which collects particles less than 10 µm with a d 50 cut point of 4 µm, as adopted by the ACGIH (Hering, 1995). The respirable samplers being employed are inertial and gravitational collectors, which include cyclones, impactors, and elutriators. These samplers are designed to collect particles in characteristic size ranges instead of all sizes as an open face cassette would do. Airborne particles are size-selected by these samplers. A horizontal elutriator is a type of respirable sampler that is currently being used. A common horizontal elutriator was the MRE 113A gravimetric sampler. Horizontal elutriators work by the principle that particles up to a certain size will deposit before reaching the end of a horizontal duct. The elutriator s collection efficiencies depend on the particles terminal settling velocity. Particles with lower terminal settling velocities will generally pass through the duct, while those closer to the floor may be captured and those particles higher up pass through. Elutriators can be designed so as to collect 100% of particles up to designated size and with a d 50 cut point (Wright, 1954). The BMRC respirable fraction was based on the horizontal elutriator. Horizontal elutriators were used as the basis for the British and US coal-mine respirable dust regulations (Ogden et al., 1978).

19 9 Cyclones are currently the most widely used technique for respirable sampling. Some very common cyclones are the British Safety in Mines Personal Equipment for Dust Sampling (SIMPEDS), British Cast Iron Association (BCIRA), Dorr-Oliver 10-mm nylon, and the SKC 37-mm aluminum cyclone. Cyclones are favored for their low bounce and re-entrainment characteristics. A low bounce and re-entrainment means that as particles contact the wall of the cyclone, they are less likely to bounce off the sampler wall and re-enter the sampling airstream. The cyclone works by pulling dusty air through an inlet that is tangential to the cylindrical center of the cyclone. The geometry of the inlet causes the sampled air to rotate around the inside of the cyclone, as air moves to the bottom of the device. As the air is being sampled, larger particles are deposited on the wall due to centrifugal motion and fall into the grit pot at the bottom of the cyclone. The sampling airstream goes around the edges and then up through the middle. Particles that make it through the middle of the cyclone are collected in a filter found at the top of the cyclone (Hinds, 1999). When the SKC, Inc. 37-mm aluminum cyclone was originally designed it followed the BMRC criteria (Harper et al., 1998). The BMRC critera had a higher penetration of particles compared to the ACGIH criteria until you reach the BMRC cut-off of 7.07 µm. At sizes 1, 2, 3, 4, and 5 µm the BMRC criteria had penetrations of particles at 98, 92, 82, 68, and 50 percent. In contrast the ACGIH criteria had penetration of particles at 97, 91, 74, 50, and 30 percent at the same sizes (Belle, 2004). The penetration curve for medium sized particles, 2 to 5 µm, was much sharper than that BRMC curve (Lidén, 1993). After the ACGIH adopted the Soderholm (1989) Convention in 1991, which used the d 50 cut point of 4 µm, SKC was able to adjust the cut point of the SKC aluminum cyclone by altering the flow rate to 2.5 liters per minute (lpm) from 1.7 lpm (Harper et al., 1998). The penetration curve shape of the SKC 37-mm aluminum cyclone was similar to the BCIRA and SIMPEDS cyclones except for large particles. Larger particles had an increase in penetration, in the SKC 37-mm aluminum cyclone, compared to the other cyclones. One major drawback of the SKC 37-mm aluminum cyclone is that it is

20 10 manufactured from aluminum and is prohibited from certain environments because it is not intrinsically safe, such as in coal mines (Lidén 1993). Factors Affecting Penetration Tsai and Shih (1995) investigated the penetration of solid and liquid monodispersed aerosols on the 10-mm nylon and SKC 37-mm aluminum cyclones. They observed that the 10- mm nylon cyclone had a higher penetration of larger solid particles, greater than 4 µm, than that of liquid particles of the same size. The higher collection efficiency of larger solid particles was attributed to particle bounce since they had the potential to re-enter the sampling airstream compared to particles that did not bounce and stayed near the wall surface. Solid particles larger than 4 µm accumulated less on the inner wall opposite the inlet than smaller particles. In the case of the SKC 37-mm aluminum cyclone the difference in particle penetration between solid and liguid particles was not nearly as significant as the 10-mm nylon cyclone. The lower difference between solid and liquid particle penetration has been attributed to a longer vortex finder tube in the SKC 37-mm aluminum cyclone that helps recapture bouncing solid particles. The problem of particle bounce is a common problem for impactors and could exist to a lesser extent in small cyclones such as the 10-mm nylon and SKC 37-mm aluminum cyclone (Tsai and Shih, 1995). The effect of particles depositing and accumulating on the internal wall has been investigated with regards to aerosol penetration. A study conducted by Chen and Huang (1999) investigated how the penetration of four different cyclone samplers (10-mm nylon, SKC 37-mm aluminum, big body, and multi-inlet) changed as dust deposited. After loading the 10-mm nylon cyclone for three hours at 10% relative humidity with potassium sodium tartrate PST (CMD 3.5 µm, GSD 1.3) at 4.6 mg/m 3, there was no observed accumulation of particles seen inside the 10- mm nylon cyclone. When the loading particle size of PST was increased to a CMD of 7.4 µm and a GSD of 1.5 at a concentration of 15.1 mg/m 3, a noticeable amount of particles deposited on the walls of the cyclone. Chen and Huang recorded that after three hours of loading, a layer

21 11 inside of the cyclones can reach a maximum height of 1 to 2 mm. When challenging all four cyclones at 10% relative humidity with the PST (CMD 3.5 µm) for three hours, the penetration of particles decreased as particles deposited on the walls of the cyclones. At 4 µm the 10-mm nylon cyclone was underestimating by 20% after 1 hour of sampling using PST (CMD 3.5). After three hours of sampling the collection efficiencies would stabilize and there was no significant change. When the four cyclones were challenged at 10% relative humidity with PST (7.4 µm) the shift in penetration was not as significant as with the PST (3.5 µm) loading aerosol. They did observe that the SKC 37-mm Aluminum, Big Body, and Multi-Inlet Cyclones showed an increase in particle penetration after 3 hours with the PST (7.4 µm), although the increases in penetration may not be statistically significant. The notable increase was seen with the SKC 37- mm aluminum cyclone which displayed an increase in aerosol penetration in aerosols from 4 to 7 µm (Chen and Huang, 1999). When the loading conditions increased to a relative humidity of 60% with PST (3.5 µm) a change in size was observed in the loading aerosol. The CMD of PST at 10% was 3.5 µm. When the humidity surpassed 60%, the aerosol size grew to a size of 3.85 µm at 90% humidity. The saturation of water helped grow the PST particles and also may have caused changes in the particles elasticity. At higher humidity, over 60%, the penetration curves for the cyclones had sharper separation efficiency curves than when the humidity was 10% (Chen and Huang, 1999). The use of monodispersed aerosols, solid ammonium fluorescein particles, has been used to investigate the change in aerodynamic cutoff diameters when particles are deposited in the cyclone. The aerodynamic diameter of the ammonium fluorescein particles ranged from 1 to 10 µm. Tsai et al. (1999) investigated the cutoff aerodynamic diameters of cyclones with regards to mass deposited on a 10-mm nylon cyclone and an 18-mm aluminum cyclone with monodispersed aerosol particles. As the mass deposited on the cyclone sampler increased, the penetration of particles at that size decreased. Penetration of 3.06, 3.53, 4.04, and 4.7 µm particles decreased from 97.1 to 71.1%, 75.9 to 31.1%, 62.3 to 25.2% and 31.4 to 8.7% as deposited particle mass increased from 0 to mg, 0.3 mg, 0.27 mg, and 0.40 mg

22 12 respectively. The cut point decrease in the 10-mm nylon cyclone was more pronounced than in the 18-mm aluminum cyclone (Tsai et al., 1999). The effects of particle buildup by polydispersed dusts in high flow rate cyclone samplers, 10 liters per minute, have been investigated. A study was conducted by Lee et al. (2010) on the sampling efficiencies of three high flow rate respirable dust cyclone samplers (GK2.69, and FSP10) at varying concentrations, at about 2 mg/m 3, 3 mg/m 3, and 8 mg/m 3. This study had sampling efficiency increase for some tests and decrease in others at 4 µm. At 4 µm the GK2.69 had a clean sampling efficiency of 27.2% (4.4) and it increased to 29.7% (4.3) after 3 hours at a loading dust concentration of 1.9 mg/m 3. When the loading concentration was increased to 3.1 mg/m 3 the clean sampling efficiency was 36.7% (0.1) and 28.3% (0.6) after loading. The FSP10 cyclone had a clean sampling efficiency of 75.3%(1.0) and it decreased to 67.6%(1.7) after 3 hours of loading at 2.3 mg/m 3. When the loading concentration was increased to 3.3 mg/m3, the clean sampling efficiency was 70.8% (4.8) and increased to 71.7% (5.2) at 4 µm. The inconsistent changes in sampling efficiency were concluded as experimental random error rather than a sign of changes in sampling efficiency (Lee et al., 2010). Thorpe et al. (2009) investigated the investigated the performance of the VSCC (Very Sharp Cut Cyclone), developed by BGI Inc., to verify its performance after 90 days of sampling with Arizona road dust. The VSCC is used to monitor for Environmental Protection Agency (EPA) PM2.5 aerosol sampling criterion. EPA PM2.5 is similar to the ACGIH respirable criterion except with a d 50 cut point of 2.5 µm instead of the 4 µm. The VSCC sampled for the equivalent of 150 µg/m 3 for 90 days and found no significant change in the cyclone s cut point. The bias of observed mass concentration was 1% for fine particles, less than 2.5 µm, and 4% for coarse particles, larger than 2.5 µm. The VSCC did not exceed the EPA 5% criteria established by the EPA in the equivalent of 90 days of sampling (Thorpe et al., 2009). The effect of particle electrostatic charge has been investigated as a contribution to penetration on respirable sampling efficiencies for cyclones (Tsai et al., 1999). Tsai et al. (1999) tested the change on penetration of particles carrying several hundred elementary units of charge

23 13 on the 10-mm nylon cyclone and an 18-mm aluminum cyclone. An effect on particle penetration becomes noticeable on the 10-mm nylon cyclone and negligible on the 18-mm aluminum cyclone as particle charge increased beyond several hundred elementary units of charge. The 10- mm nylon cyclone had the most significant influence occur near the cut-off aerodynamic diameter and negligible on particles much larger and smaller than the cutoff. For the 10-mm nylon cyclone the penetration of 3.06 µm particles shifted to the left from 92.4 to 69.4% as the charge increased from 4 to 1300 (Tsai et al., 1999). Shortcomings in Literature The effect of deposited polydispersed particles has not been thoroughly investigated with regards to their influence on the cyclone s particle penetration. The majority of tests conducted on cyclones have been performed by depositing with one size of monodispersed particles and challenging with a different sized monodispersed particle. Results of these studies have concluded that as particle deposition increases, particle penetration decreases. A major issue with testing with monodispersed aerosols is that typical personal occupational monitoring situations consist of polydispersed aerosols. The effects of deposited polydispersed particles may be different than the effects of deposited monodispersed particles. The cyclones used in the monodispersed aerosol testing were not the same as the cyclones used in the polydispersed aerosol testing. Since different different samplers were used between the two aerosol types, a sampler from the monodispersed aerosol testing should be selected and used to identify if desposited polydispersed aerosols have the same or different effect as deposited monodispersed aerosols. The SKC 37-mm aluminum cyclone was chosen for this experiment because it has been previously observed to deposit particles in its internal wall from previous studies and have an effect on particle penetration (Tsai and Shih, 1995; Chen and Huang, 1999). Study Aim Two goals were established for this study:

24 14 1) Investigate whether the cut point and penetration curve of the SKC 37-mm aluminum cyclone changes after it has been deposited with a polydispersed dust. 2) Compare the SKC 37-mm aluminum cyclone penetration to the RPM criterion.

25 15 CHAPTER II EFFECT OF DEPOSITED POLYDISPERSED PARTICLES ON RESPIRABLE CYCLONE PENETRATION Introduction Workplace aerosol sampling is required to assess occupational airborne exposures in order to determine worker risks of developing adverse health effects. Since toxicity of aerosols is dependent upon both the chemical composition of the aerosol and where they deposit in the airways, the American Conference of Governmental Industrial Hygienists (ACGIH) recommended three particulate matter fractions for assessing workplace exposures. The particulate matter fractions for size-selective aerosol sampling are: inhalable, thoracic, and respirable particle matter (ACGIH, 1985). Particles that have been defined as respirable are materials that are hazardous when in the gas-exchange (alveolar) region of the lung (ACGIH, 2011). Respirable particles that can reach the alveolar region of the lung generally range from to 10 µm (James et al., 1999). Cyclones are some of the most used respirable samplers (Tsai et al., 1999B). Cyclone samplers have a low particle bounce and low re-entrainment characteristics when compared to conventional impactors (John et al., 1980). Respirable cyclones are designed to operate at a designated flow rate to achieve a d 50, cut point, of 4 µm (Chen and Huang, 1999) which corresponds to the Respirable Particle Matter (RPM) cut point (ACGIH, 2012). A d 50 cut point is when 50% particles of that size penetrate the sampler. The penetration curves for most cyclones have much sharper slopes than the defined respirable curve. Due to the sharper slope, cyclones collect more particles that are smaller than the 4 µm cut point and fewer particles larger than the cut point, between 4 and 10 µm (Lidén, 1993). Cyclones work by allowing air containing an aerosol to enter tangentially into the sampler. The incoming aerosol stream moves in a spinning motion around the inside of the sampler and creates a centrifugal force on the particles. As the particles are forced to move to the outward walls, the larger particles will

26 16 contact onto the outer wall of the cyclone and move down the cone, which eventually leads to a grit pot at the bottom of the sampler (Tsai et al., 1999B). After particles are separated by the cyclone stage, the sample respirable mass is collected on the filter (Tsai and Shih, 1995). A respirable sampler that is used to collect the RPM is the SKC 37-mm aluminum cyclone. When the SKC 37-mm aluminum cyclone was originally created, it was calibrated for the British Medical Research Council respirable sampling criteria with a d 50 cut point of 5 µm. When the ACGIH adopted the Soderholm (1989) respirable sampling criteria, SKC Inc. adjusted the recommended flow rate of the 37-mm aluminum cyclone to 2.5 lpm to achieve the newly established d 50 cut point of 4 µm from the originally recommended 1.9 lpm flow rate (Harper et al., 1998). Respirable cyclones are known to have a sampler bias compared to the RPM criteria. Sampler bias can be identified for an aerosol sampler. Sampling bias is the deviation in mass sampled by a specific sampler from the mass sampled by a true respirable sampler which matches the ACGIH respirable criterion (Lidén 1991 and 1992). The collection efficiency of the SKC 37-mm aluminum cyclone has been characterized by Harper et al. (1998) and Lidén (1993). The efficiency of the cyclone changes when particles accumulate on the internal walls of the cyclone during sampling. Tsai and Shih (1995) investigated how monodispersed particles collected inside of the 10-mm nylon cyclone and SKC 37-mm aluminum cyclones, and found that solid particles, especially ones over 4 µm in diameter, had a tendency to deposit across from the opening of the cyclone. Chen and Huang (1999) investigated the effect of how the penetration curve shifts as particles accumulate on the cyclone walls of the 10-mm nylon, SKC 37-mm aluminum, big body, and multi-inlet cyclone, and they observed a decrease in particle penetration over time. After one hour of sampling the 10-mm nylon cyclone had decreased in collection of 4 µm particles by 20%. The decreases in penetration had would stabilize after 3 hours of sampling. When the humidity was increased over 60% Chen noticed the size of their loading aerosols increased in size. As the particles increased from 3.74 µm to 3.83 µm at 90% humidity the

27 17 particle penetration curves through the cyclone had a sharper slope than under dry conditions, humidity of 10% (Chen and Huang, 1999). Tsai et al. (1999) used monodispersed particles on the 10-mm nylon and a newly developed 18-mm aluminum cyclone to detect if there was a change in the cut points of the cyclones before and after material was deposited inside. Tsai et al. (1999A) found that as particle loading increased, the penetration of particles decreased. The penetration of 3.06, 3.53, 4.04, and 4.7 µm particles decreased from 97.1 to 71.1%, 75.9 to 31.1%, 62.3 to 25.2% and 31.4 to 8.7% as deposited particle mass increased from 0 to mg, 0.3 mg, 0.27 mg, and 0.40 mg respectively (Tsai et al., 1999). Lee et al. (2010) attempted to incorporate an examination of a cut point shift when sampling with polydispersed particles with high-flow, 4.2 and 10 lpm, respirable cyclones (GK2.69 and FSP10). When using polydispersed aerosols, Lee et al. (2010) observed both an increase and decrease, over several samples, in particle penetration of 4 µm particles over the course of several trials. At 4 µm the GK2.69 had a mean clean sampling efficiency of 27.2% standard deviation (4.4) and it increased to 29.7% (4.3) after 3 hours with a loading dust concentration of 1.9 mg/m 3. When the loading concentration was increased to 3.1 mg/m 3 the clean sampling efficiency was 36.7% (0.1) and 28.3% (0.6) after loading. The FSP10 cyclone had a clean sampling efficiency of 75.3% (1.0) and it decreased to 67.6% (1.7) after 3 hours of loading at 2.3 mg/m 3. When the loading concentration was increased to 3.3 mg/m3, the clean sampling efficiency was 70.8% (4.8) and increased to 71.7% (5.2) at 4 µm. The reasoning for the variations in sampling efficiency was never fully identified and was eventually accredited to experimental error (Lee et al., 2010). Thorpe et al. (2001) performed an experimental evaluation on the BGI very sharp cut cyclone (VSCC) and its effect on sampling bias of the cyclone from prolonged sampling. The VSCC was exposed to the equivalent concentration of 150 µg/m 3 at 1, 2, 3, 7, 14, 30, and 90 days of sampling. After 90 days of sampling the sampler bias was 1% for fine particles, less than 2.5 µm in size, and 4% for coarse particles, larger than 2.5 µm in size. (Thorpe et al., 2001).

28 18 The goal of this study was to investigate whether the cut point and penetration curve of the SKC 37-mm aluminum cyclone changes after it has been loaded with a polydispersed aerosol. This study will also investigate the penetration curve of the SKC 37-mm aluminum cyclone and compare it to the RPM criterion. The SKC 37-mm aluminum cyclone was chosen for this experiment because it has been previously observed to deposit particles in its internal wall (Tsai and Shih, 1995; Chen and Huang, 1999). Materials and Methods Experimental Apparatus As shown in Figure 1, the experimental setup consisted of a vertical calm-air chamber, an aerosol generation system, a SKC 37-mm aluminum cyclone sampler ( , SKC Inc., Eighty Four, PA), and an Aerosol Particle Sizer (APS, 3321, TSI, Shoreview, MN). One new SKC 37-mm aluminum cyclone was used throughout the experiment. Aerosols were created by one of two aerosol generation systems: a Wright Dust Feeder (WDF II, BGI Inc., Waltham, MA) or a sonic generator, designed after the aerosol generator used by Weyel (1984). The aerosol generation systems were fed into the vertical chamber at the top. Airflow in the chamber was kept to less than 0.25 m/s throughout the whole experiment to simulate calm air conditions as measured by a velocicalc anemometer (9565-X Velocicalc, TSI, Shoreview, MN). To increase the count concentration of aerosols in the experiment, the mixed aerosol was guided to the cyclone sampler by 203-mm round metal ducts. Below the 203-mm duct, a moveable flap was included to keep the area around the cyclone sampler confined during sampling, which decreased aerosol dilution. A personal/data RAM (Model pdr-1200, Thermo Electron Corporation, Waltham, MA) was used to measure the chamber s respirable concentration. To measure through the cyclone a 9.5-mm hole was drilled into the 37-mm cassette on top of the cyclone (Figure 2). The filter and back-up back were not used with the 37-mm cassette. Drilling a hole on top of the cyclone cassette allowed for sampling to occur directly after running through the cyclone and minimize particle accumulation on cassette walls. A brass tube was fed through the drilled hole

29 19 up to the outlet of the cyclone. Rubber O-rings and were secured above the below the drilled hole by nuts. The cyclone was operated at the manufacturer specifications of 2.5 liters per minute (lpm) to achieve a d 50 cut point of 4 µm and the flow rate was calibrated with a soap bubble meter (Gilibrator 2, Sensidyne, St. Petersburg, FL). To achieve the cyclone s 2.5 lpm flow rate, a make-up air tube with a HEPA filter was used on the APS to achieve the appropriate sampler flow rate. The cyclone was set-up in the sampler collection area on the end of 9.5-mm copper tubing bent into a half circle. The copper tubing was connected to the APS and cyclone by conductive tubing to reduce losses due to charge. The challenge aerosol was used to measure the cyclone penetration when the chamber s relative humidity was below 50%, as monitored by a humidity temperature meter (HH134A, Omega Engineering Inc., Stamford, CT). Cleaning the Cyclone Before each test, the deposited, dirty, cyclone and grit pot were separated and cleaned thoroughly. The loaded cyclone and grit pot were flushed out under running water for 30 seconds. During this process, the cyclone was rotated under the running water and holes were randomly plugged shut to increase internal pressure. After the cyclone was flushed under running water, the cyclone and grit pot were set in a sonic resonator bath (Model B200, Branson, Danbury, CT) for at least five minutes. Once the sonic resonator bath was complete, the cyclone and grit pot were allowed to air dry for at least 12 hours inside of the chamber with a humidity of less than 50%. Aerosol Tests The SKC 37-mm aluminum cyclone s penetration was measured with a challenge aerosol, glass beads (GB, count median aerodynamic diameter CMAD 3.3 µm, geometric standard deviation GSD 1.7). Glass beads were chosen because their CMAD was close to the SKC 37-mm aluminum cyclone s d 50 cut point of 4 µm. The same challenge aerosol was used so we could have a reference aerosol with the desired cut point since not all loading aerosols effectively spanned the cyclone s d 50 cut point with high particle counts at the 4 µm cut point.

30 20 The size distribution of the aerosol dusts were measured with the APS. A sonic generator, similar to the generator created by Weyel (1984), was used to generate the challenge aerosol. The sonic generator ran for 30 minutes to allow for concentrations to stabilize. A personal/data RAM (Model pdr-1200, Thermo Electron Corporation, Waltham, MA) was used to confirm stable chamber concentrations (five second data logging interval). Samples were collected in groups referred to as Runs. The experimental steps of each Run were: 1) test the clean cyclone s penetration with the APS 2) run the cyclone for three hours while generating a loading dust to deposit dust on cyclone walls 3) re-test the deposited cyclone s penetration with the APS. Each Run of this experiment consisted of collecting 10 clean sampler penetration curves and 10 deposited sampler penetration curves which were averaged for each Run. Each penetration curve sample was accomplished with two samples using the APS, one with the cyclone inline (cyclone penetration) and one without the cyclone (ambient concentration). The penetration curves of the cyclone were then calculated by taking the ratio of the sample with the cyclone inline against a sample without the cyclone inline. The APS counts particles according to their bin size. Each sample used to calculate the penetration curve, inline cyclone (cyclone penetration) and without the inline cyclone (ambient concentration), was the average of 12, five-second samples taken over the course of a minute by the APS. Samples were taken at alternating intervals (i.e. with cyclone, without cyclone, without cyclone, with cyclone, with cyclone, without cyclone ) to decrease the chance of a systematic error from opening the sample area flap and putting on and taking off the cyclone for each sample. The same sampling tube was used for each set of samples, with and without the cyclone, so the losses to tubing between the samples were assumed to cancel each other out. Due to the possibility of fluctuations of glass bead concentration over time, the samples were allowed to fluctuate within 10%, as monitored by the PDR, of each other without repeating the with and without cyclone sample set. Individual penetration samples were re-sampled when chamber concentrations exceeded the 10% value.

31 21 Depositing Particles on the Cyclone After the penetration of the clean cyclone was determined, the cyclone was operated with one of three polydispersed aerosols by sampling for three-hours at concentrations of at least 3 mg/m 3 as measured by the PDR. The three hour loading was chosen because Chen and Huang (1999) identified that after three hours of loading at a concentration of 4.6 mg/m 3 the penetration curve would not change significantly during loading. Three different loading aerosols were chosen to identify what dust characteristics may cause particles to deposit inside the cyclone and their effects on cyclone penetration. The polydispersed aerosols used were Arizona Road Dust (ARD), organic dust (OD), and titanium oxide (TiO 2 ). These three were selected because they were known to be sticky dusts and were assumed to be most likely to accumulate, deposit, inside the cyclone. The ARD and TiO 2 were generated by the Wright Dust Feeder, and the OD was generated by the sonic generator. A separate sampling tube and pump was used during the loading of the cyclone to prevent buildup in the APS sampling lines. The number of Runs conducted is displayed in Table 1. A total of six runs were conducted while loading with the ARD at a humidity of less than 50%. Three runs were completed on both the loading of OD and TiO 2 at a humidity of less than 50%. One run was conducted while loading the OD at a humidity of 95%. After the cyclone was operated for three hours, the penetration of the cyclone with deposited particles was tested with glass beads and the penetration was compared to the clean sampler penetration. Masses of the Cyclone and Grit Pot Weights of the cyclone and grit pot were taken separately at each stage of the experiment. The weights were taken at the following stages: when the cyclone was clean and before any sampling, after the clean penetration was tested with the challenge aerosol, after loading the cyclone for three hours, and at the end of the run after challenging a deposited cyclone to test its penetration.

32 22 Calculating Cut Points The cut points for the penetration curves were calculated using linear interpolation from the APS bin data for clean and deposited penetration curve. When looking at the penetration curves, the penetration curve around the cut point is observed to be a straight line at the d 50 cut point. The linear interpolation calculation used ratios of the bins to calculate the d 50 cut point for the penetration curve. The d 50 cut point linear interpolation calculation is as follows: where Bin 1 at this size has a Penetration 1 of a certain percent and Bin 2 at that size has a Penetration 2 of a certain percent. Sampler Bias Calculations Sampler bias was determined from penetration curves sampled in the experiment. The cyclone s bias was the examined bias of the SKC 37-mm aluminum cyclone when the cyclone was operated at 2.5 lpm with a presumed d 50 cut point of 4 µm and when the cut point was 3.7 µm. The respirable criterion was modified to create the cyclone sampling fraction (CSF) under both cut points of 3.7, 3.8 and 4 µm. ( )

33 23 C and D were determined from a process to minimize the SEE of the fractions produced by the experimental data relative to the modeled values. Bias was calculated from the mass median aerodynamic diameter MMAD and the geometric standard deviation GSD of sampled materials. The sampler bias was calculated for the cut points were 3.7 and 3.8 µm and were compared to a true sampler with a defined cut point of 4 µm. Calculations of fractional mass sampled (FMS) were carried out with MMAD between 1 and 15 µm with GSD s between 1.5 and 4. Bias was calculated following the Lidén et al., (1991) equation. ( ) Statistical Analysis For the changes in collection efficiency, cut points, and changes in mass, t-tests were used. Two sample t tests assuming unequal variances and were performed on all measurements. The statistical tests were performed at a 95% Confidence Interval, α = Results Cyclone Penetration The sampler fractions of the new and shifted cyclone are displayed in Figure 3 as well as the respirable criterion for comparison. The cut point of the new SKC 37-mm aluminum cyclone was found to be at 4 µm. After the preliminary testing with the new sampler, the cut point of the same SKC 37-mm aluminum cyclone shifted to the left to 3.7 µm.

34 24 Arizona Road Dust Six Runs were conducted with ARD (count median aerodynamic diameter CMAD 1.04 µm, geometric standard deviation GSD 1.57) at a relative humidity less than 50%. Table 3 displays the chamber concentrations of ARD during the loading phase as measured by the pdr and filter, the total mass at measured concentrations for three hours, and how much deposited in the cyclone for each Run. The target concentration of the loading aerosol was at least 3 mg/m 3 as measured by the pdr. Average measured loading concentration by the pdr was 4.23 (0.98) mg/m 3. The total chamber concentration was also collected by a filter after going through the pdr and the average loading concentration was 5.06 (1.65) mg/m 3. Average weights of the cyclone and grit pot were weighed among each step in the sampling process and are displayed in Table 4. There was an average increase of 4 (1) mg in cyclone weight after three hours of loading with ARD. The increased difference in weight during the loading sampling step was statistically significant from the challenging with glass beads sampling step (p < 0.01). The grit pot mass did not have a statistically significant difference in mass until the challenging of the deposited sampler step, average increase of 7 (2) mg (p < 0.01). The average penetration curves over all six Runs taken after loading with ARD is shown in Figure 4. The sampled penetration percentage of all particles increased after the cyclone was loaded with ARD. Particle penetration between clean and deposited penetration in bin size µm, differences were statistically significant as shown in Table 5 (p = 0.04). The clean penetration curve had a 32.3% (0.86) penetration and the deposited cyclone had a 36.1% (0.99) penetration at µm. Table 6 gives the cut points calculated for each Run. Over all the Runs, the average cut point for the clean cyclone was 3.7 (0.1) µm while the average cut point increased to an average of 3.8 (0.1) µm, difference were statically significant (p = 0.04). Organic Dust Three Runs were conducted with OD (CMAD 2.90, GSD 1.77) at a relative humidity less than 50%. Table 7 displays the chamber concentrations of OD during the loading phase as

35 25 measured by the pdr and filter, the total mass at measured concentrations for three hours, and how much deposited in the cyclone for each run. The average chamber concentration during loading was measured by the pdr at 3.76 (0.20) mg/m 3. Filters were also used to determine the average chamber concentration during loading, and they determined the average chamber concentration was 5.28 (0.53) mg/m 3. The average weights of the cyclone and grit pot through each sampling step are displayed in Table 8. During the three-hours of loading with Organic Dust, the cyclone mass increased an average of 6 (2) mg, while the mass of the grit pot increased an average of 9 mg, during the same three-hour loading phase (p = < 0.01 to 0.04). The mass of the cyclone decreased by an average of 4 (1) mg (p = 0.07) and the grit pot increased by an average of 6 (2) mg (p = 0.02) when the loaded cyclone was being challenged with GB. The average clean and loaded penetration curves are displayed in Figure 5. The overall penetration of particles increased while the SKC 37-mm aluminum cyclone was deposited with OD (Table 9). The differences in penetration were statistically significantly for particles up to the APS bins size of µm (P = < 0.01 to 0.04). The cut points, as shown in Table 10, found that the average clean cyclone was 3.8 (0.0) µm while the cut point increased to 3.8 (0.0) µm after being loaded with Organic Dust after 3-hours. The difference in the cut point after loading was not found to be statistically significant (p = 0.13). Titanium Oxide Three Runs of TiO 2 (CMAD 0.85 µm, GSD 1.28) were conducted at a relative humidity below 50%. Table 11 displays the chamber concentrations of TiO 2 during the loading phase as measured by the pdr and filter, the total mass at measured concentrations for three hours, and how much deposited in the cyclone for each run. The average chamber concentration while loading titanium oxide was 9.06 (0.82) mg/m 3 when measured with the pdr. Using gravimetric analysis of the filter following the pdr, the average chamber concentration while loading was 1.97 (0.46) mg/m 3. The weights of the cyclone and grit pot were collected during each step in the sampling with TiO2. The average weights of all three runs and changes in each step are

36 26 displayed in Table 12. The only change in weight in the cyclone was observed was after the initial testing of the clean cyclone with glass beads, at an increase of 2 mg (p = 0.05). The mass of the cyclone remained the same throughout the rest of the sampling with TiO 2. The average mass in the grit pot showed a steady increase through each of the steps in the procedure, 3 mg after initial testing, 2 mg while loading with Titanium Oxide, and 1 mg during the loaded cyclone testing. None of the increases in the grit point were found to be statistically significant. The average of the penetration curves for clean and deposited samplers are shown in Figure 6 for the TiO 2 samples. Table 13 displays the APS bin sizes and the penetration percentage of the clean and deposited cyclones. Small increases in penetration can be observed over the particles up to bin size µm but the difference were not statistically significant. The average cut points were obtained via linear interpolation, shown in Table 14, and the average clean cyclone penetration was 3.8 (0.1) µm while the loaded cyclone was 3.8 (0.1) µm. The difference in cut point between the clean and loaded cyclone was not statistically significant (p = 0.73). High Humidity Organic Dust One Run was conducted with OD at a relative humidity of 95%. Table 15 displays the chamber concentrations of OD during the loading phase as measured by the pdr and filter, the total mass at measured concentrations for three hours, and how much deposited in the cyclone for each run. The average chamber concentration of OD was 2.11 mg/m 3 when measured with the pdr during loading. Gravimetric analysis of the filter determined that the average chamber concentration was 0.16 mg/m 3 during loading. Weights of the cyclone and grit pot were measured through each step of sampling with the high humidity OD, which is displayed in Table 16. The weight of the cyclone initially increased by 4 mg after the 3-hour loading of high humidity OD but decreased to only 2 mg after allowing to dry overnight. A similar trend was observed to happen in the grit pot as mass of the grit pot increased by 2 mg after loading but only ended up being an increase of 1 mg after drying overnight. The cyclone weight decreased by 1

37 27 mg during the deposited cyclone challenging phase and the grit pot increased by 1 mg during the same time. The average penetration curves of the clean and loaded samples are shown in Figure 7. Table 17 shows the penetration percentage of particles through the clean anddeposited cyclone. Particles up to bin size µm were found to be higher in the loaded cyclone than the clean cyclone. At bin size µm the clean cyclone penetration was 101% and the deposited cyclone penetration was 107%. From bin size µm and up the clean cyclone was found to have higher penetration of particles compared to the loaded cyclone. The clean cyclone had a penetration of 36.2% and the deposited cyclone had a penetration of 30.9 at bin size µm. The d 50 cut point was calculated via linear interpolation which identified the clean cyclone cut point at 3.8 µm and a deposited cyclone cut point of 3.7, as shown in Table 18. SKC Cyclone Bias Map Mass bias sampling maps were created for the SKC 37-mm aluminum cyclone comparing the clean and deposited SKC 37-mm aluminum cyclone sampling fraction to the respirable criterion. Figure 8 shows the mass bias of clean SKC 37-mm aluminum cyclone when cut point was at 3.7 µm operated at 2.5 lpm compared to the respirable criterion. Figure 9 shows the mass bias of the SKC 37-mm aluminum cyclone after Arizona road dust deposited inside the cyclone and challenged with GB with a cut point of 3.8 µm compared to the respirable criterion. Figure 10 shows the mass bias of the SKC 37-mm aluminum cyclone when operating at factory specification with a cut point of 4 µm compared to the respirable criterion. Discussion Shift in Penetration between New and Cleaned Cyclone The first collection efficiencies with a brand new SKC 37-mm aluminum cyclone closely matched the results obtained by Harper et al. (1998). When the new cyclone was first tested in the preliminary tests the cut point was found to be very close to the defined ACGIH (2011) cut

38 28 point of 4 µm. After the initial testing, that only consisted of testing the penetration of the sampler with GB, the cut point of the sampler shifted to 3.7 µm. The cause of this shift, in the cut point, was thoroughly investigated and could not be identified. The new cut point was found to be systematic and was used as the sampler s clean cut point throughout the rest of this experiment. Particle Depositing on Walls Even though respirable cyclones are known for their low particle bounce and low reentrainment characteristics, circumstances do exist that allow particles to deposit and accumulate onto the internal wall of the cyclone, which may alter the SKC 37-mm aluminum cyclone s particle penetration. Respirable cyclones are designed so that as particles increase in size, they end up in collected in the grit pot and smaller particles following the respirable criterion are collected in the filter. Particle depositing on the walls of the cyclone was observed to happen with dusts when the dust size distribution spanned across the cyclone s cut point, such as the case with ARD (CMAD 1.04 µm, GSD 1.57) and OD (CMAD 2.90 µm, GSD 1.77). The larger particles would contact the surface of the sampler wall and collect there, as well as in the grit pot, over the 3-hours of loading. Although both the ARD and OD collected in the cyclone and the grit pot, a noticeable difference was observed where the majority of particles ended up. The majority of particles deposited from the ARD collected inside of the cyclone rather than in the grit pot. Alternatively, a larger amount of OD ended up in the grit pot than accumulated on the cyclone walls. The dust size distributions were larger with the OD, than with the ARD, with a CMD closer to the cut point and a larger mass of particles may have collected in the grit pot because of it. Depositing particles were not observed on the cyclone walls when the loading dust had a much smaller size distribution, such as with the TiO 2 (CMAD 0.85 µm, GSD 1.28). Since the majority of particles TiO 2 were below the cut point, most particles penetrated the cyclone and did not collect on the walls.

39 29 Effect of Deposited Particles on Penetration An effect was observed on sampler penetration after particles collected on the walls. When the relative humidity was under 50%, deposited ARD and OD increased the cyclone penetration, as shown in Figures 4 and 5. The d 50 cut point increased from 3.7 to 3.8 µm after depositing with ARD. The penetration of particles after the cyclone was deposited with ARD increased as much as 4.8% at bin size µm when compared to the clean cyclone penetration. The increases in particle penetration can cause a shift of the curve to the right and an oversampling of concentration. The deposited polydispersed particles on the SKC 37-mm aluminum cyclone effected the penetration of particles differently than studies that deposited particles on cyclone with monodispersed particles. Tsai et al. (1999A) loaded and challenged cyclone samplers with monodispersed particles and observed a decrease in measured cut points. At 4.04 µm Tsai et al. (1999) observed a decrease in particle penetration from 62.3 to 25.2% when monodispersed particles were deposited on the cyclone wall. In contrast this study observed, at µm, an increase in particle penetration from 32.3 to 36.1% after polydispersed ARD was deposited on the cyclone wall (Table 5). OD dust also saw a slight increase in particle penetration after deposited on the wall from 34.1 to 36.6% at µm (Table 9). Thorpe et al. (2001) also saw biases mass sampled after running a VSCC cyclone for 90 days, 1% for fine (less than 2.5 µm) particles and an increase of 4% over coarse (greater than 2.5 µm) particles (Thorpe et al., 2001). From looking at the change in penetration from deposited polydispersed and monodispersed aerosols it can be theorized that the effect of the two dust distributions differ on their effect on particle penetration of the SKC 37-mm aluminum cyclone. Under the TiO 2 loading, very little collected on the walls of the sampler. The amount of penetration change between the clean and loaded TiO 2 had minor variations, within 4% up to µm TiO 2. The variations between the clean and deposited cyclone penetrations continued to decrease significantly to much less than 1% as particles increased in size, refer to Table 13. The cut point of the cyclone deposited with TiO 2 was found to be unaffected between clean and

40 30 deposited samplers. Since the TiO 2 had a negligible amount deposit on the sampler wall, it suggests that aerosols that are smaller than the cut-point, and do not span the cyclone s cut point, are unlikely to accumulate inside the sampler since they penetrate through. The results differ between the various polydispersed loading aerosols. The depositing of ARD and OD on the walls of the cyclone had a noticeable effect on the penetration of particles although none was statistically significant after µm. TiO 2 on the other hand had more of a negligible effect on particle penetration. ARD and OD showed a tendency to deposit on the cyclone walls compared to the TiO 2. A possible reason why the ARD and OD showed a tendency to deposit on the cyclone walls could be due to the fact that their size distribution spans the d 50 cut point of the SKC 37-mm aluminum cyclone, while the TiO2 does not span the d 50 cut point. Another observation that can be seen is that particle penetration is seen on particles larger and smaller than the d 50 cut point after polydispersed particles deposit on the cyclone wall. After noting the observation of particles that fall on the slope of the curve were depositing, it can be theorize that particles that were deposited deposited on the sampler wall cause penetration was being effected. These deposited particles were becoming dislodged and increased the penetration of particles through the cyclone. A similar effect of particle depositing can be observed from Chen and Huang s (1999) results. Chen and Huang (1999) investigated the effect of particle accumulation with regards to their effects on aerosol penetration and collection efficiency. Chen used polydispersed particles and observed a decrease in penetration for particles during the loading phase. A decrease in particles penetrated through the cyclone was because they were depositing on the walls of the sampler. Now when the cyclone deposited with polydispersed dusts is challenged with a different dust, particles over all sizes are being dislodged. The dislodging of the deposited dust may be what is increasing the cyclone penetration. When the OD was deposited under high humidity conditions, greater than 95%, the effect on particle penetration differed than under dryer conditions. The effect of depositing with high

41 31 humidity dust with its effect on penetration was unclear. The sampled penetration of particles increased for the smaller particles, and then decreased for particles around the cut point of the sampler. A possible explanation for the difference in curve would be that particles with high water saturation were more likely to impact the walls of the sampler and collect. The increased impaction of highly saturated particles allowed for the particles to form stronger adhesion with each other. After the particles were allowed to dry, they formed a stronger bond and had more cohesive clump. Chen and Huang (1999) also observed that the particles size and elasticity can be affected after the humidity increased past 60%. The increase in size and elasticity can cause a sharper cut in the cyclone s efficiency and decreased the penetration of particles. When the deposited cyclone was challenged again under dryer conditions the dusts impacted the deposited clump, smaller particles would break off and re-enter the airstream as the larger particle clumps were break off and collect in the grit pot. The challenge aerosol was thought of having a sandblasting effect on the deposited aerosol, slowly breaking off the loaded aerosol while being challenge and essentially cleaning the inside of the cyclone over time. This theory could not be validated with this form of sampler as it is impossible to visualize actual conditions inside the sampler without destroying the sampler by cutting it open. Total Mass Measured and Deposited Mass on Cyclone The total mass sampled for three hours at each concentration was less than the mass deposited inside the cyclone. The calculated total mass and deposited mass for each loading scenario were displayed in Tables 3, 7, 11, and 15. When looking at the concentrations measured, the concentrations from the pdr filter were considered to be more accurate than the pdr measurements themselves. The pdr filter is the collection of all particles that were read through the pdr. A pdr works by using a light scattering method to count and size particles (Chakrabarti et al., 2004). Since the pdr uses light scattering to measure concentration of aerosols, the concentrations measured may not be the same as the concentration measured by a filter depending upon the light scattering properties of a dust. For example the concentration

42 32 measured for the ARD corresponded to the measured filter concentration better than it did for the TiO 2. The reflective properties of TiO 2, due to it being a white dust, may have cause for additional light to be scattered and caused an oversampling of the measured concentration. Due to the discrepancies of concentration measured by the pdr, the filter measurements were considered a more accurate representation of the chamber concentration. The pdr did accomplish its role of being a reference to monitor if aerosol was being generated and if the concentration decided to spike or drop suddenly. When comparing the total mass measured in the chamber and the amount of mass deposited on the cyclone walls, it is easily observed that the mass loaded on the walls are higher than what the chamber generated. The measured concentrations are thought to be much lower than the actual chamber concentration measured by the pdr and pdr filter. SKC Cyclone Cut Point Mass Bias Comparison The SKC cyclone was designed to have a cut point of 4 µm, which was obtained during preliminary runs, but results from this study showed a decrease in the cut point to about 3.7 µm. A sampler bias map is the amount of mass a sampler is collecting compared to a reference that samples the defined criterion. Bias mapping shows that sampler bias of the SKC 37-mm aluminum cyclone decreased as the cut point decreased. The sampler cyclone sampler fraction (CSF) was compared to the respirable fraction (RF). As Lidén et al., (1992) identified in their study, respirable cyclones have a much sharper cut in penetration percentage than the respirable fraction. The sharper cut has a 50% penetration of particles at the cut point. Due to this sharper cut, there was a decrease in collection of particles larger than the cut point. As the median aerodynamic diameter of the particle size increased, the mass collected by the sampler was reduced when compared to a sampler that would have a collection curve equivalent to the respirable fraction. The amount of sampler bias is lower for particles with a distribution having a geometric standard deviation of one. A higher geometric standard deviation increases the size range and distribution of particles which decreases the sampler s bias at the same median

43 33 aerodynamic diameter. A negative sampler bias means that the sampler is collecting less mass than the respirable fraction would for the same particles. When the cut point was measured to be 3.7 µm, instead of the standard 4 µm for SKC 37-mm aluminum cyclones, the amount of sampler bias decreased. The lower cut point resulted in lower collections of particles larger than the cut point compared to the standard cut point. When the cut point shifted to 3.8 µm from 3.7 µm the amount of sampler bias increased a few percent. The increase in bias was due to a shift in penetration that better followed the standard 4 µm cut point. The bias maps obtained through this experiment did vary from the bias maps created by Harper (1998) and Lidén et al. (1993). Harper s (1998) and Lidén s et al. (1993) SKC cyclone sampler bias maps showed less sampler bias than the bias maps we created. The sampler bias created from this study displayed a positive bias up to a MMAD of 4 µm at 1.5 GSD. Harper (1998) identified a positive sampler bias up to a MMAD of 7 µm at 1.5 GSD. Lidén et al. (1993) had a positive sampler bias up to a MMAD of 6 µm at 1.5 GSD. The differences in the positive sampler bias in the bias maps are unclear. Study Limitations Although the study was able to identify a possible sampling error due to particle loading, it had some limitations. The study was limited to only three loading aerosols. There was a lack of a loading aerosol which was larger than cyclone s target d 50 that did not span it, and this effect on the penetration was not investigated. Only one run of the experiment was conducted under high humidity conditions which suggested a different effect on penetration. Observations were only obtained using one loading aerosol at a time and the effect should also be investigated using multiple loading aerosols, at the same time. The effect of multiple loading aerosols should be affected because in industry workers are likely to be exposed to multiple aerosols at the same time and this may affect penetration differently. Further studies should investigate with multiple cyclones of the same make and model as well as different manufacturers to determine if the effect of particle loading is limited to this respirable cyclone model. The process of using the

44 34 GB challenge aerosol upset the conditions inside of the cyclone and had a cleaning sand blasting effect. The GB was intended to be a reference aerosol to test penetration once particles deposited and was not intended to affect the deposited dust. Additional types of challenge aerosols should be investigated. This study did not investigate the collected concentration of a loaded sample compared to a clean sampler and determine if there could be a possible occupational sampling error. The experiment also lacked field study testing. A field study would have helped identify how much of an effect a loaded sampler would have on concentrations compared to a clean sampler. Some possible scenarios that would be great to explore would have been construction activities which included excavation, above or underground mining, or agricultural harvest season. Conclusion In this study, an investigation was performed to identify whether the penetration of a respirable cyclone was affected after sampling polydispersed particles due to particle deposited inside of the cyclone. In the cases when particles deposited onto the cyclone walls an effect was observed on the penetration. When the cyclone was loaded under dry conditions (humidity less than 50%) the overall penetration was increased, by up to 5% in some sizes, when challenged by a different aerosol. The increase in particle penetration indicated a shift in samplers penetration curve to the right, which means they are likely to oversample compared to the normal sampling efficiency. When there was no particle depositing the penetration was unaffected. Under high humidity loading conditions, humidity about 95%, the penetration increased with smaller particles and decreased for larger particles. The deposited particles under high humidity decreased particles at 3.5 µm by up to 8% and to a lesser amount thereafter. A decrease in particle penetration would indicate a shift in the sampler penetration curve to the left, which means that they are likely to under sample compared to the normal sampling efficiency. Results from this study suggest that there may be a sampler error associated with using unclean cyclones. The increase in penetration is theorized to be a loaded sampler error as

45 35 particle are thought to dislodge off of the walls of the cyclone and collect with the challenge aerosol. Additional studies would be required to further investigate the effects of high humidity loading and to verify the effects of particles loading under different varying conditions. Another study would also be recommended to compare the mass collected by a clean cyclone and the amount collected by a loaded cyclone to see if there s a possible occupational error. The only way to eliminate any possible loaded sampler error would be to thoroughly clean and dry cyclones after each use, especially after high concentration sampling. High concentration sampling can occur when sampling near the ACGIH Particles Not Otherwise Specified Threshold Limit Value of 3 mg/m 3.

46 Figure 1. Experimental apparatus 36

47 Figure mm cassette with drilled hole and tubing to minimize cassette wall losses 37