NATE TOPHAM

1
High Concentration and High Temperature Aerosol
Sampling

• NATE TOPHAM
• AEROSOL MECHANICS

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Topics to be Discussed

• Sources
• Formation Mechanisms
• Challenges with Sampling
• Sampling Methods
• Summary

Anthropogenic aerosol formation
http//stopsmokingwithbanjojones.blogspot.com/2007
/01/shocking-disregard-for-law.html
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High Concentration/Temperature Aerosols

• Some are desirable
• Carbon black, pigments, ceramic powders
• Some are undesirable
• MSW Incinerators, welding, automobile engines,
  aircraft engines, hazardous waste incinerators

http//www.twi.co.uk/content/c1478.html
http//sites.google.com/site/leedsfoe/Home/no-to-i
ncineration
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High Concentration Aerosol Generation

• Characteristics of aerosols are dependent on
  industry in which theyre produced
• Beneficial Aerosols
• Monodisperse distribution is often desired
• Process parameters must be modified to achieve
  desired size size distribution
• Sampling analysis required for quality control
  measures
• Harmful Aerosols
• Desired size range is based on control technology
  used
• Combustion aerosols are often very difficult to
  collect due to their size

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Characteristics of High Temperature Aerosols

• What mechanisms discussed in this class are
  evident in these images?

Welding Agglomerate Particle
Welding Primary Particle
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Issues with Sampling

• Potential interference with sampling devices
• Coagulation
• Decrease in number concentration
• Increase in particle size
• Condensation
• Increase in mass concentration
• Increase in particle size
• Big problem with organic aerosols
• Thermophoresis
• Loss of particles in sampling system
• Results from high temperature aerosols gas
  passing through cool sampling system

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Thermophoresis
is very large when the gas flow containing the
aerosols is from a combustion source and a cold
probe is inserted

• How will thermophoresis impact data on aerosols
  from a combustion source?
• Particle number concentration will be lower than
  actual value
• Particle number concentration could be higher
  than the actual value
• How?
• Impact on regulatory control
• PM concentration might seem lower than actual
  value, violator could get away with excessive
  emission

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Sampling Issues (continued)

• Potential interference with sampling devices
• Overloading
• Damage to filters or instrumentation from high
  temperature
• Time dependent changes in aerosols
• Temperature changes yield changes in aerosol
  properties and distribution

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Sampling Methods

• Sampling techniques vary based on analytical
  techinques
• Destructive vs. non-destructive analytical
  techniques
• Destructive Inductively-coupled Plasma
• If the aerosols are deformed or agglomerate
  during sampling, its OK!
• We digest aerosols for this technique, theyre
  destroyed in the end anyway
• Non-destructive Transmission Electron
  Microscopy
• If the aerosols are deformed/destroyed, the TEM
  images will not represent the true aerosol
  properties

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• Different filters have different operable
  temperature ranges
• Some filters would actually melt when attempting
  to sample high temperature aerosols

Chow, J. Air Waste Manage. Assoc. 45 320-382.
1995
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Sampling Methods

• Dilution
• Goal Quench all changes in aerosol
  characteristics as quickly as possible
• Primary
• Addresses a number of challenges this type of
  sampling presents
• Overloading
• Reduces number concentration to operable range
  for analytical instruments
• Coagulation
• Reduces collisions
• Thermophoresis
• Aerosols and gas are cooled, lowering the
  temperature difference between aerosols and
  surfaces of sampling equipment

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Sampling Methods

• Dilution
• Secondary
• Lowers number concentration to a level that is
  within operable range for instrumentation
• Optional, process is similar to that of primary
  dilution
• Long mixing times are desirable to ensure
  homogeneity of sample

http//www.dekati.com/cms/dekati_diluter/accessori
es
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In-Situ Sampling Methods

• EPA Methods
• Method 5
• External filtration
• Widely used for stationary sources, such as
  utility plants, incinerators, other stacks
• Sampling probe is placed directly in gas flow
  carrying aerosols
• Method 17
• In-stack filtration
• Allows isokinetic sampling, however, it is more
  difficult in high temperature flows

http//www.cleanair.com/Equipment/Express/catm5tr.
htm
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EPA Method 5
Example sampling train from gas-fired boiler
http//www.epa.gov/ttn/emc/ftir/reports/r04.html
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High Temperature Impactor

• Isokinetic Sampling
• Some use ceramic fibers as substrate
• Some use virtual impactors
• Difficult to employ multistage impactors because
  secondary flow must be closely controlled in each
  stage

http//www.photometer.com/en/abc/show.html?qIsoki
netic20sample
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Optical Methods

• Elastic Light Scattering
• Scattering/Extinction
• Mean particle size, number concentration for
  absorbing aerosols
• No size limitation
• Angular Dissymetry
• Mean size, number concentration, spread in
  distribution
• Polarization Ratio
• Measurable particle size greater than 0.1?
• Good for non-absorbing aerosols with known
  refractive index
• Non-Elastic Light Scattering
• Dynamic Light Scattering (Photon Correlation
  Spectroscopy)
• Diffusion Coefficient
• Requires system temperature to compute particle
  size, no size limitation, refractive index not
  needed

From Aerosol Measurement-Principles, Techniques,
and Applications 2nd Edition. (2001).
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Challenges in Sampling

• Different sampling probes can yield different
  aerosol size distributions
• Thermophoresis is an important factor in final
  measured distribution due to thermophoresis at
  probe inlet
• Jiménez, Santiago Ballester, Javier (2005). A
  Comparative Study of Different Methods for the
  Sampling of High Temperature Combustion Aerosols.
  Aerosol Science and Technology, 39 (9), 811-821.

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Reactions Between Vapor and Particles

• Vapor phase species can impact aerosol
  characteristics
• Laser-Induced Fluorescence
• In-Situ measurement technique that measures
  gaseous species that are precursors for gas to
  particle conversion
• In some systems, reaction between aerosols and
  particles is desired
• Owens, T.M. and Biswas, P. (1996). Vapor phase
  sorbent precursors for toxic metal emissions
  control from combustors. Ind. Eng. Chem. Res.,
  35. 792-798.
• Lee, M.H., Cho, K., Shah, A.P. and Biswas, P.
  (2005). Nanostructured sorbents for capture of
  cadmium species in combustion environments.
  Environ. Sci. Technol., 39. 8481-8489.
• Biswas, P. and Zachariah, M.R. (1997). In situ
  immobilization of lead species in combustion
  environments by injection of gas phase silica
  sorbent precursors. Environ. Sci. Technol.,
  31(9). 2455-2463.
• Liu, Z.S., Wey, M.Y. and Lin, C.L. (2001). The
  capture of heavy metals from incineration using a
  spray dryer integrated with a fabric filter using
  various additives. J. Air Waste Manage. Assoc.,
  51. 983-991.
• Whats the take-home message from these research
  studies?
• Reactions between aerosols and vapor phase
  chemicals are important, and can be controlled to
  achieve desirable physical and chemical traits
  in aerosols

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Combustion Aerosols
Transmission electron microscopy image of
combustion aerosols

• Electron Microscopy
• X-Ray Diffraction
• Raman Spectroscopy
• Ex-Situ
• Chemical analysis of particles
• Mössbauer Spectroscopy
• Measures resonant absorption in a solid as a
  result of resonant emission from another solid

From Aerosol Measurement-Principles, Techniques,
and Applications 2nd Edition. (2001).
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Summary

• High concentration high temperature aerosols
  come from a variety of sources
• Many mechanisms influence their formation
• These mechanisms present challenges for accurate
  sampling and analysis
• Many in-situ and ex-situ sampling techniques
  exist
• Combustion aerosols present unique sampling
  challenges