Biomedical Engineering Reference
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Positive electrode
Needle tip
Flow
Field lines
TEM grid substrate
Negative electrode
FIGURE 2.11
Principle of a handheld electrostatic precipitator to collect airborne (nano-)
particles. (From Miller, A. et al. 2010. A handheld electrostatic precipitator for sampling
airborne particles and nanoparticles,
Aerosol Sci Technol
,
4 4: 417- 427.)
ions near a tip electrode. When a positive high voltage is applied to the tip, a corona
is formed that ionizes the air. The tip electrode faces the sampling electrode.
Consequently, the generated ions follow the electric field lines into the perpendicular
aerosol flow, where they collide with the particles to charge them. The charged par-
ticles are then deposited onto the collection substrate within the same electric field
that is used to generate the ions and charge the particles. A TEM grid is used as a
sampling electrode and is available for analysis of the particle size and morphology
by TEM and chemical composition by EDX.
2.6 SUMMARY
A large variety of methods exist to characterize airborne particles. The choice of
instruments for a specific task depends strongly on the aerosol and particle charac-
teristics (sizes, concentrations, etc.) and the specific requirements, that is, need for
particle size-, time-, or spatial resolution. In general, all highly accurate instruments
are rather bulky and heavy (especially for the characterization of nanoparticles).
Smaller, portable, or personal instruments are available, but the wealth of informa-
tion from these as well as the accuracy is limited. Chemical speciation and morpho-
logical characterization of the airborne particles require sampling for subsequent
analyses, which is hence rather time consuming. In conclusion, there is not a single
instrument that can fulfill all requirements of exposure assessment in workplaces.
Instead, the choice of an instrument is always a compromise concerning instrument
mobility, particle size and concentration range, measured metric, and accuracy.
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