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Calculation of
Particulate Mass
on Filter Tape
Thermo Fisher Scientific
The SHARP optical assembly senses the light scattered by the aerosol
passing through an 880 nm illumination beam. The nephelometry response
is linear with aerosol concentration; independent of sample flow rate; and a
running one-minute average and dynamic average are continuously
calculated. Within the base of the optical assembly, a relative humidity
(RH) sensor is located immediately upstream of the sample filter-tape
assuring a representative measurement of the aerosol conditioning prior to
real-time mass determination.
Thereafter, the aerosol is deposited onto a glass fiber filter tape. The filter
tape will accumulate an aerosol sample towards a threshold value,
whereupon the filter tape will automatically advance prior to reaching
saturation. During the collection of aerosol onto the filter tape the SHARP
Monitor uses the radiometric principle of beta attenuation through a
known sample area to continuously collect and detect the deposited mass.
Additionally, the beta-attenuation chamber measures alpha emissions from
the accumulated aerosol and excludes negative mass artifacts due to the
presence of daughter nuclides from radon gas decay to achieve a "refined
mass" measurement. Simultaneous refined mass measurements of sampled
aerosol on the filter tape and sample volume measurement through a
calibrated orifice provide a continuous concentration measurement of the
ambient mass concentration. The collected sample temperature is measured
within the attenuation chamber.
The beta detector of the 5030 SHARP delivers a count rate, which is
proportional to the intensity of the beta beam. The mass is calculated from
this count rate according to the following equation :
∑
=
m
F
cal
n
where;
Σ
m
= mass loading in micrograms [μg],
n
β
= background β count rate with an unloaded filter [1/s],
0
β
= the gross count rate with a loaded filter [1/s],
n
F
= mass foil calibration factor in micrograms [μg],
cal
= global natural β : α count rate ratio ≈ 3.5
Fβ
/α
n
n
α
= the gross α count rate of natural aerosol radioactivity [1/s], and
n
α
= background α count rate [1/s]
o
Calculation of Particulate Mass on Filter Tape
⎛
β
⎜
∗
0
ln
⎜
β
−
F
*
⎝
β
α
n
/
n
n
Model 5030 SHARP Monitor Instruction Manual
Introduction
⎞
⎟
⎟
α
α
−
(
)
⎠
n
0
1-3
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