INDUSTRIAL HYGIENE -INDUSTRIAL HYGIENE - SAMPLING AND SIZING OF SAMPLING AND SIZING OF

AIRBORNE PARTICLES AIRBORNE PARTICLES

UNIVERSITY OF HOUSTON - CLEAR LAKEUNIVERSITY OF HOUSTON - CLEAR LAKE

INTRODUCTIONINTRODUCTIONIntroduce the techniques available for Industrial Introduce the techniques available for Industrial Hygienists to evaluate exposures to particulates in Hygienists to evaluate exposures to particulates in occupational settings. occupational settings.

Inhaled particles may react with or be absorbed Inhaled particles may react with or be absorbed through tissues to cause adverse health effects. through tissues to cause adverse health effects. Variables include:Variables include:

-- size, shape, and density;size, shape, and density;

-- chemical properties;chemical properties;

-- airborne concentration and time of airborne concentration and time of exposure, and other factors, etc.; so, exposure, and other factors, etc.; so,

-- health effects – irritation, illness, disease. health effects – irritation, illness, disease.

AEROSOLS AEROSOLS Aerosol – described as solid and/or liquid particles Aerosol – described as solid and/or liquid particles dispersed in a gaseous medium. Range of > 50 dispersed in a gaseous medium. Range of > 50 um to microscopic particles invisible to naked eye.um to microscopic particles invisible to naked eye.For IH, gaseous medium is usually For IH, gaseous medium is usually AIRAIR. . Occupational aerosol hazards recognized by: Occupational aerosol hazards recognized by:

-- PlinyPliny-- AgricolaAgricola-- RamazziniRamazzini

Advances in aerosol science and inhalation Advances in aerosol science and inhalation toxicology have extended understanding and also toxicology have extended understanding and also promoted development of refined techniques for promoted development of refined techniques for aerosol exposure characterization. aerosol exposure characterization.

ASSESSMENT TECHNIQUESASSESSMENT TECHNIQUES

Techniques for sampling and analysis Techniques for sampling and analysis continue to evolve for characterization of continue to evolve for characterization of aerosols. A single technique is not aerosols. A single technique is not appropriate; IH must be familiar with appropriate; IH must be familiar with properties and assessment techniques. properties and assessment techniques.

Evolving ultrafine and nano-sized aerosols.Evolving ultrafine and nano-sized aerosols.

Incidentally addresses bioaerosols or Incidentally addresses bioaerosols or aerosols of biological origin. aerosols of biological origin.

DEFINITIONSDEFINITIONS

Forms of Aerosols:Forms of Aerosols:

Dust (also crystalline materials)Dust (also crystalline materials) FumesFumes Mists Mists FogsFogs SmokesSmokes Fibers (length exceeds diameter)Fibers (length exceeds diameter)

DUSTSDUSTS

Particulate aerosols produced by mechanical Particulate aerosols produced by mechanical processes such as breaking, grinding, and processes such as breaking, grinding, and pulverizing. Examples: mining; material handing; pulverizing. Examples: mining; material handing; dry material prep and packaging. Chemically dry material prep and packaging. Chemically unchanged; smaller size and higher specific unchanged; smaller size and higher specific surface area may enhance ability to be airborne, surface area may enhance ability to be airborne, inhaled, penetration, toxicity, solubility or inhaled, penetration, toxicity, solubility or explosion. Less than 1 um up to 1 mm; regular in explosion. Less than 1 um up to 1 mm; regular in shape; some crystalline materials; length to width shape; some crystalline materials; length to width ratio less than 3:1 with some notable exceptions.ratio less than 3:1 with some notable exceptions.

FUMESFUMES

Fine solid aerosol particles produced from Fine solid aerosol particles produced from the re-condensation of vaporized material the re-condensation of vaporized material that is normally solid at standard conditions that is normally solid at standard conditions is melted and vaporized; condensation (0.01 is melted and vaporized; condensation (0.01 um) occurs during cooling of vapor – um) occurs during cooling of vapor – nucleation; coagulation – agglomerates at 1 nucleation; coagulation – agglomerates at 1 um in diameter are nearly spherical. Small um in diameter are nearly spherical. Small enough to penetrate to deep lung areas; enough to penetrate to deep lung areas; chemically quite reactive. Examples: chemically quite reactive. Examples: welding/smelting – “metal fume fever”. welding/smelting – “metal fume fever”.

MISTSMISTS

Spherical droplet aerosols produced from Spherical droplet aerosols produced from bulk liquid by mechanical processes such as bulk liquid by mechanical processes such as splashing, bubbling, or spraying. Droplets splashing, bubbling, or spraying. Droplets are chemically unchanged from the parent are chemically unchanged from the parent liquid and range in size from a few microns liquid and range in size from a few microns to over 100 um. Mist aerosol from spray to over 100 um. Mist aerosol from spray painting. Examples: mist aerosol from spray painting. Examples: mist aerosol from spray painting; crop spraying operations designed painting; crop spraying operations designed to produce mists; mist droplet aerosols by to produce mists; mist droplet aerosols by coughing or treatment of infected patients in coughing or treatment of infected patients in health care settings. health care settings.

FOGSFOGS

Droplet aerosols produced by physical Droplet aerosols produced by physical condensation from the vapor phase. Fog condensation from the vapor phase. Fog droplets are typically smaller than droplets are typically smaller than mechanically generated mist droplets, and mechanically generated mist droplets, and are of the order of 1 to 10 um. Whereas are of the order of 1 to 10 um. Whereas mists may visibly settle toward the ground, mists may visibly settle toward the ground, fogs appear to remain suspended in the air. fogs appear to remain suspended in the air.

SMOKESSMOKES Complex mixtures of solid and liquid aerosol Complex mixtures of solid and liquid aerosol

particles, gases, and vapors resulting from particles, gases, and vapors resulting from incomplete combustion of carbonaceous materials incomplete combustion of carbonaceous materials and are formed by complex combinations of and are formed by complex combinations of physical nucleation-type mechanisms and physical nucleation-type mechanisms and chemical reactions. Examples: tobacco smokes; chemical reactions. Examples: tobacco smokes; smokes from other combustion (i.e. plastics, smokes from other combustion (i.e. plastics, synthetic fabrics, and petrochemical products – synthetic fabrics, and petrochemical products – toxic). Primary smoke particles are on the order of toxic). Primary smoke particles are on the order of 0.01 to 1 um in diameters; but like fumes, 0.01 to 1 um in diameters; but like fumes, agglomerates containing many particles may be agglomerates containing many particles may be much larger. much larger.

FIBERSFIBERS

Elongated particles with length much greater than Elongated particles with length much greater than width. May be naturally occurring or synthetic. width. May be naturally occurring or synthetic. Examples: asbestos with convention to define a Examples: asbestos with convention to define a “fiber” as a particle with a ratio of length or width “fiber” as a particle with a ratio of length or width greater than 3:1; specific asbestos-related greater than 3:1; specific asbestos-related diseases; synthetic fibers, etc. Fibrous aerosols diseases; synthetic fibers, etc. Fibrous aerosols display aerodynamic and health effects behaviors display aerodynamic and health effects behaviors that differ in many respects from spherical or near-that differ in many respects from spherical or near-spherical particles of the same material and mass, spherical particles of the same material and mass, so aerosol characterization is more complex for so aerosol characterization is more complex for fibers than other aerosols. fibers than other aerosols.

AEROSOLS AEROSOLS Aerosol concentrations in air are often Aerosol concentrations in air are often assessed by mass per unit volume (mg/M3); assessed by mass per unit volume (mg/M3); when using mass, large particles have the when using mass, large particles have the most significant impact on total mass. most significant impact on total mass. mass = volume x densitymass = volume x densityOther methods to assess aerosols include Other methods to assess aerosols include particle counting (mppcf) and total surface particle counting (mppcf) and total surface area. Can account for contribution of area. Can account for contribution of reactive surfaces and give consideration to reactive surfaces and give consideration to smaller particles; good evaluation tools to smaller particles; good evaluation tools to assess risk of ultrafine and nano-materials. assess risk of ultrafine and nano-materials.

CHARACTER/MORPHOLOPYCHARACTER/MORPHOLOPY Aerosol distribution – Figure 14.1Aerosol distribution – Figure 14.1 Monodisperse vs. Polydisperse Monodisperse vs. Polydisperse Particle size distribution: Particle size distribution: log normal log normal !!!!!! Isometric – length dimension independent of Isometric – length dimension independent of

particle orientation (e.g. dusts)particle orientation (e.g. dusts) Spherical – based on diameterSpherical – based on diameter Singlet – single discrete particles and remainSinglet – single discrete particles and remain Aggregate – coagulate or flocculate (i.e. Aggregate – coagulate or flocculate (i.e.

soot); large surface are per unit masssoot); large surface are per unit mass Morphology – optical or electron microscopy Morphology – optical or electron microscopy

AIRBORNE PARTICLE MOTIONAIRBORNE PARTICLE MOTIONDoseDose – drives biological response; result of – drives biological response; result of exposure history; deposition efficiency; exposure history; deposition efficiency; target organs; depends on exposure history; target organs; depends on exposure history; pharmacokinetics of clearance process and pharmacokinetics of clearance process and intrinsic toxicity. Bioaccumulation.intrinsic toxicity. Bioaccumulation.

Dose rateDose rate – rate at which substance arrives – rate at which substance arrives (inhaled or deposited) and exposure may be (inhaled or deposited) and exposure may be measured by IH. Influenced by physical measured by IH. Influenced by physical properties of aerosol (size, shape, density, properties of aerosol (size, shape, density, and hygroscopicity [take up water].and hygroscopicity [take up water].

TRANSPORT MECHANISMSTRANSPORT MECHANISMS-- SedimentationSedimentation

-- Inertial Motion and DepositionInertial Motion and Deposition

-- DiffusionDiffusion

-- InterceptionInterception

-- Others: Others:

++ Centrifugation (large); Centrifugation (large);

++ Electrical (large); and,Electrical (large); and,

++ Thermophoretic motions – (small); Thermophoretic motions – (small); temperature gradient. temperature gradient.

SEDIMENTATIONSEDIMENTATIONRefers to movement of an aerosol particle through Refers to movement of an aerosol particle through a gaseous medium under the influence of gravity. a gaseous medium under the influence of gravity. The rate of settling depends on particle size, The rate of settling depends on particle size, shape, mass, and orientation (for non-spherical shape, mass, and orientation (for non-spherical particles) and on the air density and viscosity. particles) and on the air density and viscosity.

Gravitational force opposed by gas viscosity. Gravitational force opposed by gas viscosity. Stokes’ Law and Diameter (Equations 14-2/14-4).Stokes’ Law and Diameter (Equations 14-2/14-4).

Aerodynamic equivalent diameter – “normalizes” Aerodynamic equivalent diameter – “normalizes” different aerosols to common basis for different aerosols to common basis for comparison. comparison.

STOKES AND AERODYNAMIC STOKES AND AERODYNAMIC DIAMETERDIAMETER

Discuss particle size in terms of the diameter of a Discuss particle size in terms of the diameter of a spherical particle of the same density that would spherical particle of the same density that would exhibit the same behavior as the particle in exhibit the same behavior as the particle in question = Stokes diameter (dquestion = Stokes diameter (dSTST). ). Aerodynamic equivalent diameter, dAerodynamic equivalent diameter, daeae, which is the , which is the diameter of a unit density sphere (density = 1 diameter of a unit density sphere (density = 1 g/cmg/cm33) that would exhibit the same settling velocity ) that would exhibit the same settling velocity as the particle in question. as the particle in question. Aerodynamic equivalent diameter “normalizes” Aerodynamic equivalent diameter “normalizes” different aerosols to a common basis so that different aerosols to a common basis so that behaviors may be directly compared. Particle behaviors may be directly compared. Particle Stokes and aerodynamic diameters are important Stokes and aerodynamic diameters are important for inertial and gravitational deposition, collector for inertial and gravitational deposition, collector design, and data interpretation. design, and data interpretation.

INERTIAL MOTION/DEPOSITIONINERTIAL MOTION/DEPOSITION

Inertia - defined as tendency to resist a Inertia - defined as tendency to resist a change in motion; important for human change in motion; important for human inhalation/deposition as well as aerosol inhalation/deposition as well as aerosol sampling. sampling. Impaction on surface within distance Impaction on surface within distance traveled; likelihood increased with the mass traveled; likelihood increased with the mass and velocity of particle and the sharpness of and velocity of particle and the sharpness of change in direction. change in direction. Stokes Number = St. (Equation 14-7)Stokes Number = St. (Equation 14-7)Inefficiency of impaction increases with Inefficiency of impaction increases with increasing St.increasing St.

DIFFUSIONDIFFUSIONDiffusion - aerosol particles in a gaseous Diffusion - aerosol particles in a gaseous medium collide with individual gas medium collide with individual gas molecules that are in random Brownian molecules that are in random Brownian motion associated with their fundamental motion associated with their fundamental microscopic thermal behavior. microscopic thermal behavior. Diffusion coefficient is inversely proportional Diffusion coefficient is inversely proportional to particle geometric size and is to particle geometric size and is independent of particle density. independent of particle density. Favored by small particle diameter, large Favored by small particle diameter, large concentration differences, and short concentration differences, and short distances for diffusion. distances for diffusion.

INTERCEPTIONINTERCEPTIONInterception – flow of an aerosol past a Interception – flow of an aerosol past a surface may produce particle deposition. surface may produce particle deposition.

Deposition process does not depend on Deposition process does not depend on particle motion across fluid stream lines, as particle motion across fluid stream lines, as for inertial impaction. Depends on particle for inertial impaction. Depends on particle coming close enough to a flow boundary (by coming close enough to a flow boundary (by any means) that it may be collected by any means) that it may be collected by virtue of its own physical size. virtue of its own physical size.

Significant to elongated particles (i.e. fibers) Significant to elongated particles (i.e. fibers)

OTHER PARTICLE TRANSPORT OTHER PARTICLE TRANSPORT MECHANISMS MECHANISMS

Other mechanisms are relevant to aerosols Other mechanisms are relevant to aerosols either in terms of deposition in the either in terms of deposition in the respiratory tract or sampling: respiratory tract or sampling:

- - Centrifugal motion; Centrifugal motion;

-- Electrical motion;Electrical motion;

-- Thermophoretic particle motion. Thermophoretic particle motion.

Centrifugal and electrical forces are more Centrifugal and electrical forces are more effective for larger particles. effective for larger particles.

SURFACE PARTICLE RETENTION SURFACE PARTICLE RETENTION

Action of various forces: Action of various forces: - - London-van der Waals (by molecular London-van der Waals (by molecular

interactions between particle and interactions between particle and surfaces); surfaces);

-- electrostatic attraction (charge electrostatic attraction (charge differences between particle and differences between particle and

surface);surface);-- capillary forces (adsorption of water capillary forces (adsorption of water

{or other liquid} film between the {or other liquid} film between the particle particle and the surface). and the surface). Smaller particles are more difficult to dislodge than Smaller particles are more difficult to dislodge than larger ones. larger ones.

DEPOSITIONDEPOSITIONFor a given exposure situation, the amount For a given exposure situation, the amount of aerosolized material actually inhaled; the of aerosolized material actually inhaled; the fraction of inhaled aerosol depositing in the fraction of inhaled aerosol depositing in the different regions of the respiratory tract, and different regions of the respiratory tract, and the fate of the deposited material are the fate of the deposited material are functions of: functions of:

-- Physical and chemical nature; Physical and chemical nature;

-- Exposure conditions;Exposure conditions;

-- Individual characteristics.Individual characteristics.

DEPOSITION BY INHALATIONDEPOSITION BY INHALATIONDefinition of “Breathing zone”:Definition of “Breathing zone”: NasopharyngealNasopharyngeal (NP): hygroscopic; absorb water; (NP): hygroscopic; absorb water;

humid; inertial impaction is most significant. humid; inertial impaction is most significant. TracheobronchialTracheobronchial (TB): conducting airways (TB): conducting airways

distribute the inhaled air quickly and evenly to distribute the inhaled air quickly and evenly to deeper portions of lung; therefore, lower velocities deeper portions of lung; therefore, lower velocities and higher residence times favor sedimentation and higher residence times favor sedimentation and diffusion. Thoracic fraction of < 10 um.and diffusion. Thoracic fraction of < 10 um.

PulmonaryPulmonary (P): depending on particle size, either (P): depending on particle size, either sedimentation or diffusion is the dominant sedimentation or diffusion is the dominant deposition mechanism. Respirable fraction. deposition mechanism. Respirable fraction.

SAMPLING THEORYSAMPLING THEORYSampling objective is to obtain information Sampling objective is to obtain information about aerosol properties at a given location about aerosol properties at a given location over a specified length of time. Therefore, over a specified length of time. Therefore, nature of air flow and particle motion both nature of air flow and particle motion both inside and outside of sampling device is a inside and outside of sampling device is a critical issue regarding performance. critical issue regarding performance.

Aerosol mass per unit air volume (mass Aerosol mass per unit air volume (mass concentration) based on size fractions and concentration) based on size fractions and respiratory system penetration by inhalation. respiratory system penetration by inhalation.

SAMPLING THEORYSAMPLING THEORYThe intention of “total dust” sampling is that The intention of “total dust” sampling is that all particles in the air should be collected all particles in the air should be collected with equal efficiency without respect to any with equal efficiency without respect to any particular particle size fraction. By contrast, particular particle size fraction. By contrast, particle size-selective sampling is intended particle size-selective sampling is intended to separate the aerosol into size fractions to separate the aerosol into size fractions based on health rationale. based on health rationale.

Exercise caution regarding sampler choice Exercise caution regarding sampler choice and insure that the particle size fraction of and insure that the particle size fraction of interest is properly collected. interest is properly collected.

PARTICLE SIZE SELECTIONPARTICLE SIZE SELECTION Size selective aerosol sampling. Size selective aerosol sampling. External and internal sampling losses. External and internal sampling losses. Sampler efficiency is a complex function of: Sampler efficiency is a complex function of:

sampler geometry; sampling rate; flow sampler geometry; sampling rate; flow external to sampler; and sampler orientation external to sampler; and sampler orientation with respect to direction of air flow.with respect to direction of air flow.

Rudimentary sampler theory, but useful for Rudimentary sampler theory, but useful for IH related to sampler selection for IH related to sampler selection for application and assess losses and apply application and assess losses and apply correction factors. correction factors.

PARTICLE SIZE-SELECTIVE PARTICLE SIZE-SELECTIVE SAMPLINGSAMPLING

Aerosol particle size greatly influences Aerosol particle size greatly influences where deposition occurs in the respiratory where deposition occurs in the respiratory tract, and the site of deposition often tract, and the site of deposition often determines the degree of hazard determines the degree of hazard represented by the exposure. Sampling represented by the exposure. Sampling techniques to measure aerosol as:techniques to measure aerosol as:

-- inhalable,inhalable,-- thoracic, or thoracic, or -- respirable fractions. respirable fractions.

FILTRATION TECHNIQUESFILTRATION TECHNIQUES

- - Study aerosol mass concentration; number Study aerosol mass concentration; number concentration; particle morphology; concentration; particle morphology; radioactivity; radioactivity; chemical content; and biohazard chemical content; and biohazard potential. potential. - - Choice of media depends on the aerosol Choice of media depends on the aerosol characteristics and the analytical technique to characteristics and the analytical technique to be be used. used. - - Gravimetric analysis: mass/volume; mg/M3.Gravimetric analysis: mass/volume; mg/M3.- - Open–face vs. Closed-face filter cassettes. Open–face vs. Closed-face filter cassettes. -- “Total” particulates; under-sample inhalable “Total” particulates; under-sample inhalable fraction of larger particle sizes. fraction of larger particle sizes. -- Best is IOM sampler for inhalable fraction. Best is IOM sampler for inhalable fraction.

FILTRATION MEDIAFILTRATION MEDIA

- - Fiber filters: cellulose, glass, or quartz.Fiber filters: cellulose, glass, or quartz.- - Porous membrane: gels of cellulose Porous membrane: gels of cellulose

ester, PVC; high porous mesh ester, PVC; high porous mesh microstructure leaving convoluted flow microstructure leaving convoluted flow paths. Efficiency by pore size (i.e. 0.1 to paths. Efficiency by pore size (i.e. 0.1 to

10 um) but can be misleading.10 um) but can be misleading.- - Capillary membrane: PC or polyester Capillary membrane: PC or polyester film film with straight-through pores of nearly with straight-through pores of nearly

uniform size and distribution. uniform size and distribution. -- Polyester foam mediaPolyester foam media-- Also treated filters; sorbent/filter comboAlso treated filters; sorbent/filter combo

FILTER CHARACTERISTICSFILTER CHARACTERISTICS

- - Fiber: low pressure drop at high flow rates; Fiber: low pressure drop at high flow rates; high loading capacity; inexpensive; not high loading capacity; inexpensive; not adequate adequate for submicron size; water!for submicron size; water!

- - Porous: also “depth” filters as above due to Porous: also “depth” filters as above due to deposition in matrix; higher flow resistance and deposition in matrix; higher flow resistance and lower loading capacity than fiber filters.lower loading capacity than fiber filters.

- - Capillary: high pressure drop and low loading Capillary: high pressure drop and low loading capacity; susceptible to static charge build-up capacity; susceptible to static charge build-up that that can affect particle capture and retention; can affect particle capture and retention; microscopy advantage [particles > pores are microscopy advantage [particles > pores are captured at smooth and flat surface to view]. captured at smooth and flat surface to view].

SEDIMENTATION TECHNIQUESSEDIMENTATION TECHNIQUESCyclones use centrifugal forces to effect particle Cyclones use centrifugal forces to effect particle capture. capture.

Cut size indicates aerodynamic diameter of Cut size indicates aerodynamic diameter of particle for which penetration through the cyclone particle for which penetration through the cyclone is 50% (d50 at 4 um for respirable fraction). is 50% (d50 at 4 um for respirable fraction).

Efficient for large particle sizes and IH use as pre-Efficient for large particle sizes and IH use as pre-separators in respirable aerosol samplers: separators in respirable aerosol samplers:

-- Dorr-Oliver nylon – 1.7 lpmDorr-Oliver nylon – 1.7 lpm

-- Casella and SKC cyclones – 1.9 lpm.Casella and SKC cyclones – 1.9 lpm.

Others: electrostatic or thermal precipitators.Others: electrostatic or thermal precipitators.

IMPACTION TECHNIQUESIMPACTION TECHNIQUESAmong most widely used in aerosol Among most widely used in aerosol characterization in relation to particle size. characterization in relation to particle size. Impactor performance by 50% cut point size as Impactor performance by 50% cut point size as d50, which is the particle size captured by the d50, which is the particle size captured by the impactor with 50% efficiency. impactor with 50% efficiency. Single stage – DPM or PEM.Single stage – DPM or PEM.Multi-stage – used in cascade configuration – Multi-stage – used in cascade configuration – cumulative mass distribution; Andersen or Marple. cumulative mass distribution; Andersen or Marple. Different analysis – gravimetric; chemical, etc..Different analysis – gravimetric; chemical, etc..Airborne Particulate Matter fractions – PM 2.5 / 10.Airborne Particulate Matter fractions – PM 2.5 / 10.Liquid impingers for mists; particle counting. Liquid impingers for mists; particle counting.

OPTICAL TECHNIQUESOPTICAL TECHNIQUESMeasurement employ scattered light to Measurement employ scattered light to characterize the concentration and/or particle size characterize the concentration and/or particle size distribution of aerosols. distribution of aerosols. Examples: count concentration; count particles Examples: count concentration; count particles and individually measure size; estimate aerosol and individually measure size; estimate aerosol mass concentration of a cloud of aerosol particles. mass concentration of a cloud of aerosol particles. Miniaturized personal samplers vs. real-time Miniaturized personal samplers vs. real-time aerosol measurements; datalogging, etc.. aerosol measurements; datalogging, etc.. IH application of single-particle optical counters is IH application of single-particle optical counters is the condensation nucleus counter (CNC) – range the condensation nucleus counter (CNC) – range of 0.005 to 1 um; component of respirator of 0.005 to 1 um; component of respirator quantitative fit-test systems (i.e. TSI Porta-Count).quantitative fit-test systems (i.e. TSI Porta-Count).Nephelometer Nephelometer

MICROSCOPY TECHNIQUESMICROSCOPY TECHNIQUESExamination of the aerosol particles after deposition on a Examination of the aerosol particles after deposition on a suitable substrate by microscopy:suitable substrate by microscopy:

-- Phase Contrast Microscopy (PCM) – fibers; look at Phase Contrast Microscopy (PCM) – fibers; look at count regarding concentration or size distribution;count regarding concentration or size distribution;

-- Polarized Light Microscopy (PLM) – fiber ID;Polarized Light Microscopy (PLM) – fiber ID;

-- Scanning Electron Microscopy (SEM); and,Scanning Electron Microscopy (SEM); and,

-- Transmission Electron Microscopy (TEM). Transmission Electron Microscopy (TEM).

Particle size characteristics related to method; and also Particle size characteristics related to method; and also with respect to resolution power of microscope. Also a with respect to resolution power of microscope. Also a “representative” sample is necessary for analysis.“representative” sample is necessary for analysis.

OTHER SAMPLERSOTHER SAMPLERSSignificant interest in ultrafine and nanometer sized Significant interest in ultrafine and nanometer sized particulates. Engineered nano-particles (particles with at particulates. Engineered nano-particles (particles with at least one dimension less than 100 nm) may have designed least one dimension less than 100 nm) may have designed physical, chemical, or biological properties. physical, chemical, or biological properties.

-- Tapered-Element Oscillating Microbalance (TEOM) Tapered-Element Oscillating Microbalance (TEOM)

-- Electrical Aerosol Detectors (EAD) Electrical Aerosol Detectors (EAD)

-- Denuder systems and diffusion batteries – research Denuder systems and diffusion batteries – research tools used to collect ultrafine or nano-particles tools used to collect ultrafine or nano-particles

between between 1 m and 0.1 um. 1 m and 0.1 um.

AEROSOL SIZE DISTRIBUTION AEROSOL SIZE DISTRIBUTION ANALYSIS ANALYSIS

Particle sizes in an aerosol are often Particle sizes in an aerosol are often approximately lognormally distributed; that is , the approximately lognormally distributed; that is , the logarithms of the particles sizes follow a Gaussian, logarithms of the particles sizes follow a Gaussian, or normal, frequency distribution. or normal, frequency distribution. Therefore, “statistics” include geometric mean (or Therefore, “statistics” include geometric mean (or median) size and geometric standard deviation median) size and geometric standard deviation (GSD). Distribution expressed using either the (GSD). Distribution expressed using either the count median diameter (CMD) and GSD or the count median diameter (CMD) and GSD or the mass median aerodynamic diameter (MMAD) and mass median aerodynamic diameter (MMAD) and GSD, depending on how the measurement data GSD, depending on how the measurement data were obtained.were obtained.Graphical technique – Table 14.2; Figure 14.15Graphical technique – Table 14.2; Figure 14.15

AEROSOL SIZE DISTRIBUTION AEROSOL SIZE DISTRIBUTION ANALYSIS ANALYSIS

CMD is taken as the particle size corresponding CMD is taken as the particle size corresponding to the 50% probability of occurrence, and the GSD to the 50% probability of occurrence, and the GSD is calculated as either the ratio of CMD to the is calculated as either the ratio of CMD to the 15.75% particle size or the ratio of the 84.13% 15.75% particle size or the ratio of the 84.13% particle size to the CMD (both will give the same particle size to the CMD (both will give the same GSD value). If a single straight line cannot be GSD value). If a single straight line cannot be fitted to the data, then the distribution is not fitted to the data, then the distribution is not lognormal, as for mixtures of aerosols from lognormal, as for mixtures of aerosols from different sources (i.e. multimodal). different sources (i.e. multimodal). Cascade impactors are examples of mass-based Cascade impactors are examples of mass-based measurement instruments that characterize the measurement instruments that characterize the mass fraction rather than count fraction in mass fraction rather than count fraction in specified particle size intervals. MMAD>CMD.specified particle size intervals. MMAD>CMD.

CALCULATIONSCALCULATIONS

Airborne ConcentrationAirborne Concentration Air VolumeAir Volume Unit Conversions – mg/M3 to/from ppmUnit Conversions – mg/M3 to/from ppm Temperature/Pressure CorrectionsTemperature/Pressure Corrections Time-Weighted Averages Time-Weighted Averages Potential Work Shift Adjustments Potential Work Shift Adjustments

REMEMBERREMEMBERCALCULATIONSCALCULATIONS

A range of temperature and pressure changes can A range of temperature and pressure changes can be tolerated before corrections are applied to the be tolerated before corrections are applied to the volumevolume or or air sampledair sampled during an exposure during an exposure assessment. assessment.

All OELs and environmental exposure standards All OELs and environmental exposure standards and limits are expressed at 25 degrees C and 1 and limits are expressed at 25 degrees C and 1 atmosphere (760 mm Hg), defined as normal atmosphere (760 mm Hg), defined as normal temperature and pressure (NTP). temperature and pressure (NTP).

Therefore, corrections needed for meaningful Therefore, corrections needed for meaningful comparisons related to published exposure limits.comparisons related to published exposure limits.