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Frequently
Asked Questions
If you can't
find the answer you require, please email your query to info@wrastechnology.com.
How does particle shape affect distribution?
- Particle size: For spherical particles particle size is the
diameter of the particle. Real particles in the air often have complicated
shapes. For non-spherical particles, the term "diameter" does not strictly
applicable. For example, a flake or a fibre has different dimensions
in different directions. Particles of identical shape can be composed
of different chemical substances and have different densities. The differences
in shape and density cause considerable confusion in defining particle
size.
- Aerodynamic diameter: The term "aerodynamic diameter" has been
introduced in order to provide a single parameter of describing real
non-spherical particles having of arbitrary shapes and densities. The
aerodynamic diameter is the diameter of a spherical particle having
a density of 1 g/cm3 that has the same inertial property (terminal settling
velocity) in the air (at standard temperature and pressure) as the particle
of interest. Inertial sampling instruments like cascade impactors enable
the aerodynamic diameter to be determined. The term "aerodynamic diameter"
is convenient for all particles including clusters and aggregates of
any forms and density. It is not a true geometric size because non-spherical
particles usually have lesser terminal settling velocity than the spherical
ones.
What is a 'nanoparticle'?
- 1 nanometre
(nm) is 1 millionth of a millimetre
- Nanoparticles are particles of less than 0.1 Micrometer (µm)
in diameter
What is Brownian Diffusion of particles?
- Brownian diffusion is erratic random movements of particles in a gas
medium. Brownian diffusion is the dominant collection mechanism for
particles less than 0.3 micrometer. It is especially significant for
nanoparticles. Nanoparticles in a gas medium deflect slightly when gas
molecules strike them. It causes the diffusion.
- Diffusivity is a measure to which molecular collisions influence small
particles. The diffusion coefficient is influenced by the particle size
and gas medium conditions.
What is Particle Size terminology?
-
Since
the range of particle sizes for air quality evaluation is quite broad
it is convenient to divide this range into smaller sections. Defining
different size sections is useful since particles of different sizes
behave differently and are deposited in different parts of the respiratory
system. Four size sections historically have been defined.
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The table
below shows these sections of particle sizes.
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Term
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Aerodynamic
Particle Size Range
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Dust
|
D
› 10 µm
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Coarse
particles
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2.5
µm
‹ D
‹ 10 µm
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Fine
particles
|
0.1
µm
‹ D
‹ 2.5 µm
|
|
Nanoparticles
or Ultrafine particles
|
1
nm ‹
D ‹ 0.1
µm
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What
is Total Suspended Particulate Matter?
What
is PM10?
- PM10 is particulate matter collected with
a sampling collection device having a cut off aerodynamic diameter
of 10 micrometers (with 50% collection efficiency at 10 micrometers
aerodynamic diameter).
What
is the benefit of size distribution?
-
The particle
size distribution can be very broad. It is influenced by the creation
of particles during the industrial process and its evolution.
-
Here
are some benefits of particle size distributions:
- The efficiency of the particle collection depends on the particle
size.
- The particle size distribution determines the operating conditions
necessary to collect the particles.
- Particle size distributions are important in determining the
behaviour of particles in the respiratory tract and they affect
the exposure to the particulate matter.
What
is the particle size distribution?
-
Particle
size distribution is a particle frequency distribution that shows
the fraction or number or mass of particles found in each size range.
Frequency can be plotted (on the Y-axis) by percentage, in addition,
number count, surface area, or mass can be plotted. A histogram is
one way to display a particle size distribution.
Is
the total mass measurement sufficient to evaluate the health risk associated
with exposure to airborne particle pollution?
Who
is responsible for providing safe environment at your company working
places?
Are
nanoparticles toxic?
-
Yes,
some particles that are harmless in bulk or micro-size form become
considerably more toxic in the nano-form. The toxicity of insoluble
materials increases with decreasing particle size, on a mass for mass
basis.
-
A few
facts:
- Nano-particles can cross the blood-brain barrier in humans and
gold nano-particles can move across the placenta from mother to
foetus
- Early studies with PTFE (polytetrafluoroethylene) particles
around 20 nm in diameter showed that airborne concentrations of
a supposedly inert insoluble material lower than 50 µg/m3 could
be fatal to rats
- Nano-tubes produce a more toxic response in rats than quartz
dust
- Engineered carbon molecules known as "buckyballs" cause brain
damage in fish.
Can
one extrapolate manufactured nanoparticle toxicity using existing micro-particle
and bulk toxicological databases?
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No, ability
to extrapolate manufactured nanoparticle toxicity using existing particle
and fibre toxicological databases are very limited. The toxicity of
nanoparticles is influenced by the size and increases with decreasing
particle size, on a mass for mass basis.
What
is the most cost-effective way of improving air quality at working places
and avoiding health related litigation?
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