Teledyne 9110E - Nitrogen Oxides Analyzer - Manual (Page 178)

Theory of Operation Model 9110E Instruction Manual
164 M9110E Rev B
in ambient air measurements, hence provide a constant amount of quenching and the
interference of varying CO
2
amounts is negligible at low concentrations.
Table 10-1: List of Interferents
Gas Interference Type Rejection Method
Dilution: Viscosity of CO
2
molecules causes
them to collect in aperture of Critical Flow
Orifice altering flow rate of NO.
CO
2 3 rd Body Quenching: CO
2
molecules collide
with NO
2
* molecules absorbing excess energy
kinetically and preventing emission of
photons.
If high concentrations of CO
2
are suspected,
special calibration methods must be
performed to account for the affects of the
CO
2
.
Contact TAI Customer Service department
for details.
Some SO
X
variants can also initiate a
chemiluminescence reaction upon exposure to
O
3
producing excess light.
Wavelengths of light produced by
chemiluminescence of SO
X
are screened out
by the Optical Filter.
Chemically reacts with NH
3
, O
2
and H
2
O in O
3
generator to create (NH
3
)
2
SO
4
(ammonium
sulfate) and NH
3
NO
2
(ammonium nitrate)
which form opaque white deposits on optical
filter window. Also forms highly corrosive
HNO
3
(Nitric Acid)
Most of the ammonium sulfate and
ammonium nitrate produced is removed
from the sample gas by an air purifier
located between the O
3
Generator and the
reaction cell. SO
X
3 rd Body quenching: SO
X
molecules collide
with NO
2
* molecules absorbing excess energy
kinetically and preventing emission of
photons.
If high concentrations of SO
X
are suspected,
special calibration methods must be
performed to account for the affects of the
SO
2
.
Contact TAI Customer Service department
for details.
3 rd Body quenching: H
2
O molecules collide
with NO
2
* molecules absorbing excess energy
kinetically and preventing emission of light.
Analyzer’s operating in high humidity areas
must have some drying applied to the
sample gas (Section 5.8 for more details).
H
2
0
Water also reacts with NH
3
and SO
X
in the O
3
generator to create (NH
3
)
2
SO
4
(ammonium
sulfate) and NH
3
NO
2
(ammonium nitrate)
which form opaque white deposits on the
optical filter window. This also forms highly
corrosive HNO
3
(nitric acid)
Water is effectively removed from the O
3
gas stream by the Perma Pure ® Dryer
(Section 10.2.6 for more details). We offer
several Perma Pure dryers for the sample
stream, see Section 5.9.
Direct Interference: NH
3
is converted to H
2
O
and NO by the NO
2
converter. Excess NO
reacts with O
3
in the reaction cell creating a
chemiluminescence artifact.
If a high concentration of NH
3
is suspected,
steps must be taken to remove the NH
3
from the sample gas prior to its entry into
the NO
2
converter, see Section 5.9.
NH
3
NH
3
also reacts with H
2
O, O
2
and SO
X
in the O
3
generator to create (NH
3
)
2
SO
4
(ammonium
sulfate) and NH
3
NO
2
(ammonium nitrate)
which form opaque white deposits on optical
filter window. Also forms highly corrosive
HNO
3
(nitric acid).
The Perma Pure ® dryer built into the
M9110E is sufficient for removing typical
ambient concentration levels of NH
3
.
In cases with excessively high CO
2
concentrations (larger than 0.5%), the effect can be
calibrated out by using calibration gases with a CO
2
content equal to the measured air. Only
very high and highly variable CO
2
concentrations will then be cause of measurable interfer-
ence. For those applications, we recommend to use other analyzer models. Please consult
sales or our website.