Appendix F to Part 50 - Measurement Principle and Calibration Procedure for the Measurement of Nitrogen Dioxide in the Atmosphere (Gas Phase Chemiluminescence)
40:2.0.1.1.1.0.1.20.7 : Appendix F
Appendix F to Part 50 - Measurement Principle and Calibration
Procedure for the Measurement of Nitrogen Dioxide in the Atmosphere
(Gas Phase Chemiluminescence) Principle and Applicability
1. Atmospheric concentrations of nitrogen dioxide (NO2) are
measured indirectly by photometrically measuring the light
intensity, at wavelengths greater than 600 nanometers, resulting
from the chemiluminescent reaction of nitric oxide (NO) with ozone
(O3). (1,2,3) NO2 is first quantitatively reduced to
NO(4,5,6) by means of a converter. NO, which commonly exists
in ambient air together with NO2, passes through the converter
unchanged causing a resultant total NOX concentration equal to NO +
NO2. A sample of the input air is also measured without having
passed through the converted. This latter NO measurement is
subtracted from the former measurement (NO + NO2) to yield the
final NO2 measurement. The NO and NO + NO2 measurements may be made
concurrently with dual systems, or cyclically with the same system
provided the cycle time does not exceed 1 minute.
2. Sampling considerations.
2.1 Chemiluminescence NO/NOX/NO2 analyzers will respond to other
nitrogen containing compounds, such as peroxyacetyl nitrate (PAN),
which might be reduced to NO in the thermal converter. (7)
Atmospheric concentrations of these potential interferences are
generally low relative to NO2 and valid NO2 measurements may be
obtained. In certain geographical areas, where the concentration of
these potential interferences is known or suspected to be high
relative to NO2, the use of an equivalent method for the
measurement of NO2 is recommended.
2.2 The use of integrating flasks on the sample inlet line of
chemiluminescence NO/NOX/NO2 analyzers is optional and left to
couraged. The sample residence time between the sampling point and
the analyzer should be kept to a minimum to avoid erroneous NO2
measurements resulting from the reaction of ambient levels of NO
and O3 in the sampling system.
2.3 The use of particulate filters on the sample inlet line of
chemiluminescence NO/NOX/NO2 analyzers is optional and left to the
discretion of the user or the manufacturer.
Use of the filter should depend on the analyzer's susceptibility to
interference, malfunction, or damage due to particulates. Users are
cautioned that particulate matter concentrated on a filter may
cause erroneous NO2 measurements and therefore filters should be
changed frequently.
3. An analyzer based on this principle will be considered a
reference method only if it has been designated as a reference
method in accordance with part 53 of this chapter.
Calibration
1. Alternative A - Gas phase titration (GPT) of an NO
standard with O3.
Major equipment required: Stable O3 generator.
Chemiluminescence NO/NOX/NO2 analyzer with strip chart recorder(s).
NO concentration standard.
1.1 Principle. This calibration technique is based upon
the rapid gas phase reaction between NO and O3 to produce
stoichiometric quantities of NO2 in accordance with the following
equation: (8)
The quantitative nature of this reaction is
such that when the NO concentration is known, the concentration of
NO2 can be determined. Ozone is added to excess NO in a dynamic
calibration system, and the NO channel of the chemiluminescence
NO/NOX/NO2 analyzer is used as an indicator of changes in NO
concentration. Upon the addition of O3, the decrease in NO
concentration observed on the calibrated NO channel is equivalent
to the concentration of NO2 produced. The amount of NO2 generated
may be varied by adding variable amounts of O3 from a stable
uncalibrated O3 generator. (
9)
1.2 Apparatus. Figure 1, a schematic of a typical GPT
apparatus, shows the suggested configuration of the components
listed below. All connections between components in the calibration
system downstream from the O3 generator should be of glass, Teflon
®, or other non-reactive material.
1.2.1 Air flow controllers. Devices capable of
maintaining constant air flows within ±2% of the required
flowrate.
1.2.2 NO flow controller. A device capable of maintaining
constant NO flows within ±2% of the required flowrate. Component
parts in contact with the NO should be of a non-reactive
material.
1.2.3 Air flowmeters. Calibrated flowmeters capable of
measuring and monitoring air flowrates with an accuracy of ±2% of
the measured flowrate.
1.2.4 NO flowmeter. A calibrated flowmeter capable of
measuring and monitoring NO flowrates with an accuracy of ±2% of
the measured flowrate. (Rotameters have been reported to operate
unreliably when measuring low NO flows and are not
recommended.)
1.2.5 Pressure regulator for standard NO cylinder. This
regulator must have a nonreactive diaphragm and internal parts and
a suitable delivery pressure.
1.2.6 Ozone generator. The generator must be capable of
generating sufficient and stable levels of O3 for reaction with NO
to generate NO2 concentrations in the range required. Ozone
generators of the electric discharge type may produce NO and NO2
and are not recommended.
1.2.7 Valve. A valve may be used as shown in Figure 1 to
divert the NO flow when zero air is required at the manifold. The
valve should be constructed of glass, Teflon ®, or other
nonreactive material.
1.2.8 Reaction chamber. A chamber, constructed of glass,
Teflon ®, or other nonreactive material, for the quantitative
reaction of O3 with excess NO. The chamber should be of sufficient
volume (VRC) such that the residence time (tR) meets
the requirements specified in 1.4. For practical reasons, tR should
be less than 2 minutes.
1.2.9 Mixing chamber. A chamber constructed of glass,
Teflon ®, or other nonreactive material and designed to provide
thorough mixing of reaction products and diluent air. The residence
time is not critical when the dynamic parameter specification given
in 1.4 is met.
1.2.10 Output manifold. The output manifold should be
constructed of glass, Teflon ®, or other non-reactive material and
should be of sufficient diameter to insure an insignificant
pressure drop at the analyzer connection. The system must have a
vent designed to insure atmospheric pressure at the manifold and to
prevent ambient air from entering the manifold.
1.3 Reagents.
1.3.1 NO concentration standard. Gas cylinder standard
containing 50 to 100 ppm NO in N2 with less than 1 ppm NO2. This
standard must be traceable to a National Bureau of Standards (NBS)
NO in N2 Standard Reference Material (SRM 1683 or SRM 1684), an NBS
NO2 Standard Reference Material (SRM 1629), or an NBS/EPA-approved
commercially available Certified Reference Material (CRM). CRM's
are described in Reference 14, and a list of CRM sources is
available from the address shown for Reference 14. A recommended
protocol for certifying NO gas cylinders against either an NO SRM
or CRM is given in section 2.0.7 of Reference 15. Reference 13
gives procedures for certifying an NO gas cylinder against an NBS
NO2 SRM and for determining the amount of NO2 impurity in an NO
cylinder.
1.3.2 Zero air. Air, free of contaminants which will
cause a detectable response on the NO/NOX/NO2 analyzer or which
might react with either NO, O3, or NO2 in the gas phase titration.
A procedure for generating zero air is given in reference 13.
1.4 Dynamic parameter specification.
1.4.1 The O3 generator air flowrate (F0) and NO flowrate (FNO)
(see Figure 1) must be adjusted such that the following
relationship holds:
where:
PR = dynamic parameter specification, determined
empirically, to insure complete reaction of the available O3,
ppm-minute [NO]RC = NO concentration in the reaction chamber, ppm R
= residence time of the reactant gases in the reaction chamber,
minute [NO]STD = concentration of the undiluted NO standard, ppm
FNO = NO flowrate, scm 3/min
FO = O3 generator air
flowrate, scm 3/min
VRC = volume of the reaction chamber,
scm 3
1.4.2 The flow conditions to be used in the GPT system are
determined by the following procedure:
(a) Determine FT, the total flow required at the output
manifold (FT = analyzer demand plus 10 to 50% excess).
(b) Establish [NO]OUT as the highest NO concentration (ppm)
which will be required at the output manifold. [NO]OUT should be
approximately equivalent to 90% of the upper range limit
(URL) of the NO2 concentration range to be covered.
(c) Determine FNO as
(d) Select a convenient or available reaction chamber volume.
Initially, a trial VRC may be selected to be in the range of
approximately 200 to 500 scm 3.
(e) Compute FO as
(f) Compute tR as
Verify that
tR <2 minutes. If not,
select a reaction chamber with a smaller
VRC.
(g) Compute the diluent air flowrate as
where:
FD = diluent air flowrate, scm
3/min
(h) If FO turns out to be impractical for the desired
system, select a reaction chamber having a different VRC and
recompute FO and FD.
Note:
A dynamic parameter lower than 2.75 ppm-minutes may be used if
it can be determined empirically that quantitative reaction of O3
with NO occurs. A procedure for making this determination as well
as a more detailed discussion of the above requirements and other
related considerations is given in reference 13.
1.5 Procedure.
1.5.1 Assemble a dynamic calibration system such as the one
shown in Figure 1.
1.5.2 Insure that all flowmeters are calibrated under the
conditions of use against a reliable standard such as a soap-bubble
meter or wet-test meter. All volumetric flowrates should be
corrected to 25 °C and 760 mm Hg. A discussion on the calibration
of flowmeters is given in reference 13.
1.5.3 Precautions must be taken to remove O2 and other
contaminants from the NO pressure regulator and delivery system
prior to the start of calibration to avoid any conversion of the
standard NO to NO2. Failure to do so can cause significant errors
in calibration. This problem may be minimized by (1) carefully
evacuating the regulator, when possible, after the regulator has
been connected to the cylinder and before opening the cylinder
valve; (2) thoroughly flushing the regulator and delivery system
with NO after opening the cylinder valve; (3) not removing the
regulator from the cylinder between calibrations unless absolutely
necessary. Further discussion of these procedures is given in
reference 13.
1.5.4 Select the operating range of the NO/NOX/NO2 analyzer to
be calibrated. In order to obtain maximum precision and accuracy
for NO2 calibration, all three channels of the analyzer should be
set to the same range. If operation of the NO and NOX channels on
higher ranges is desired, subsequent recalibration of the NO and
NOX channels on the higher ranges is recommended.
Note:
Some analyzer designs may require identical ranges for NO, NOX,
and NO2 during operation of the analyzer.
1.5.5 Connect the recorder output cable(s) of the NO/NOX/NO2
analyzer to the input terminals of the strip chart recorder(s). All
adjustments to the analyzer should be performed based on the
appropriate strip chart readings. References to analyzer responses
in the procedures given below refer to recorder responses.
1.5.6 Determine the GPT flow conditions required to meet the
dynamic parameter specification as indicated in 1.4.
1.5.7 Adjust the diluent air and O3 generator air flows to
obtain the flows determined in section 1.4.2. The total air flow
must exceed the total demand of the analyzer(s) connected to the
output manifold to insure that no ambient air is pulled into the
manifold vent. Allow the analyzer to sample zero air until stable
NO, NOX, and NO2 responses are obtained. After the responses have
stabilized, adjust the analyzer zero control(s).
Note:
Some analyzers may have separate zero controls for NO, NOX, and
NO2. Other analyzers may have separate zero controls only for NO
and NOX, while still others may have only one zero control common
to all three channels.
Offsetting the analyzer zero adjustments to + 5 percent of scale
is recommended to facilitate observing negative zero drift. Record
the stable zero air responses as ZNO, Znox, and Zno2.
1.5.8 Preparation of NO and NOX calibration
curves.
1.5.8.1 Adjustment of NO span control. Adjust the NO flow
from the standard NO cylinder to generate an NO concentration of
approximately 80 percent of the upper range limit (URL) of
the NO range. This exact NO concentration is calculated from:
where: [NO]OUT = diluted NO concentration at
the output manifold, ppm Sample this NO concentration until the NO
and NOX responses have stabilized. Adjust the NO span control to
obtain a recorder response as indicated below: recorder response
(percent scale) =
where:
URL = nominal
upper range limit of the NO channel, ppm Note:
Some analyzers may have separate span controls for NO, NOX, and
NO2. Other analyzers may have separate span controls only for NO
and NOX, while still others may have only one span control common
to all three channels. When only one span control is available, the
span adjustment is made on the NO channel of the analyzer.
If substantial adjustment of the NO span control is necessary, it
may be necessary to recheck the zero and span adjustments by
repeating steps 1.5.7 and 1.5.8.1. Record the NO concentration and
the analyzer's NO response.
1.5.8.2 Adjustment of NOX span control. When
adjusting the analyzer's NOX span control, the presence of any NO2
impurity in the standard NO cylinder must be taken into account.
Procedures for determining the amount of NO2 impurity in the
standard NO cylinder are given in reference 13. The exact NOX
concentration is calculated from:
where: [NOX]OUT = diluted NOX concentration at
the output manifold, ppm [NO2]IMP = concentration of NO2 impurity
in the standard NO cylinder, ppm Adjust the NOX span control to
obtain a recorder response as indicated below: recorder response (%
scale) =
Note:
If the analyzer has only one span control, the span adjustment
is made on the NO channel and no further adjustment is made here
for NOX.
If substantial adjustment of the NOX span control is necessary, it
may be necessary to recheck the zero and span adjustments by
repeating steps 1.5.7 and 1.5.8.2. Record the NOX concentration and
the analyzer's NOX response.
1.5.8.3 Generate several additional concentrations (at least
five evenly spaced points across the remaining scale are suggested
to verify linearity) by decreasing FNO or increasing FD. For each
concentration generated, calculate the exact NO and NOX
concentrations using equations (9) and (11) respectively. Record
the analyzer's NO and NOX responses for each concentration. Plot
the analyzer responses versus the respective calculated NO and NOX
concentrations and draw or calculate the NO and NOX calibration
curves. For subsequent calibrations where linearity can be assumed,
these curves may be checked with a two-point calibration consisting
of a zero air point and NO and NOX concentrations of approximately
80% of the URL.
1.5.9 Preparation of NO2 calibration curve.
1.5.9.1 Assuming the NO2 zero has been properly adjusted while
sampling zero air in step 1.5.7, adjust FO and FD as determined in
section 1.4.2. Adjust FNO to generate an NO concentration near 90%
of the URL of the NO range. Sample this NO concentration
until the NO and NOX responses have stabilized. Using the NO
calibration curve obtained in section 1.5.8, measure and record the
NO concentration as [NO]orig. Using the NOX calibration curve
obtained in section 1.5.8, measure and record the NOX concentration
as [NOX]orig.
1.5.9.2 Adjust the O3 generator to generate sufficient O3 to
produce a decrease in the NO concentration equivalent to
approximately 80% of the URL of the NO2 range. The decrease must
not exceed 90% of the NO concentration determined in step 1.5.9.1.
After the analyzer responses have stabilized, record the resultant
NO and NOX concentrations as [NO]rem and [NOX]rem.
1.5.9.3 Calculate the resulting NO2 concentration from:
where: [NO2]OUT = diluted NO2 concentration at
the output manifold, ppm [NO]orig = original NO concentration,
prior to addition of O3, ppm [NO]rem = NO concentration remaining
after addition of O3, ppm Adjust the NO2 span control to obtain a
recorder response as indicated below: recorder response (% scale) =
Note:
If the analyzer has only one or two span controls, the span
adjustments are made on the NO channel or NO and NOX channels and
no further adjustment is made here for NO2.
If substantial adjustment of the NO2 span control is necessary, it
may be necessary to recheck the zero and span adjustments by
repeating steps 1.5.7 and 1.5.9.3. Record the NO2 concentration and
the corresponding analyzer NO2 and NOX responses.
1.5.9.4 Maintaining the same FNO, FO, and FD as in section
1.5.9.1, adjust the ozone generator to obtain several other
concentrations of NO2 over the NO2 range (at least five evenly
spaced points across the remaining scale are suggested). Calculate
each NO2 concentration using equation (13) and record the
corresponding analyzer NO2 and NOX responses. Plot the analyzer's
NO2 responses versus the corresponding calculated NO2
concentrations and draw or calculate the NO2 calibration curve.
1.5.10 Determination of converter efficiency.
1.5.10.1 For each NO2 concentration generated during the
preparation of the NO2 calibration curve (see section 1.5.9)
calculate the concentration of NO2 converted from:
where: [NO2]CONV = concentration of NO2
converted, ppm [NOX]orig = original NOX concentration prior to
addition of O3, ppm [NOX]rem = NOX concentration remaining after
addition of O3, ppm Note:
Supplemental information on calibration and other procedures in
this method are given in reference 13.
Plot [NO2]CONV (y-axis) versus [NO2]OUT (x-axis) and draw or
calculate the converter efficiency curve. The slope of the curve
times 100 is the average converter efficiency, EC The average
converter efficiency must be greater than 96%; if it is less than
96%, replace or service the converter.
2. Alternative B - NO2 permeation device.
Major equipment required:
Stable O3 generator.
Chemiluminescence NO/NOX/NO2 analyzer with strip chart
recorder(s).
NO concentration standard.
NO2 concentration standard.
2.1 Principle. Atmospheres containing accurately known
concentrations of nitrogen dioxide are generated by means of a
permeation device. (10) The permeation device emits NO2 at a
known constant rate provided the temperature of the device is held
constant (±0.1 °C) and the device has been accurately calibrated at
the temperature of use. The NO2 emitted from the device is diluted
with zero air to produce NO2 concentrations suitable for
calibration of the NO2 channel of the NO/NOX/NO2 analyzer. An NO
concentration standard is used for calibration of the NO and NOX
channels of the analyzer.
2.2 Apparatus. A typical system suitable for generating
the required NO and NO2 concentrations is shown in Figure 2. All
connections between components downstream from the permeation
device should be of glass, Teflon ®, or other non-reactive
material.
2.2.1 Air flow controllers. Devices capable of
maintaining constant air flows within ±2% of the required
flowrate.
2.2.2 NO flow controller. A device capable of maintaining
constant NO flows within ±2% of the required flowrate. Component
parts in contact with the NO must be of a non-reactive
material.
2.2.3 Air flowmeters. Calibrated flowmeters capable of
measuring and monitoring air flowrates with an accuracy of ±2% of
the measured flowrate.
2.2.4 NO flowmeter. A calibrated flowmeter capable of
measuring and monitoring NO flowrates with an accuracy of ±2% of
the measured flowrate. (Rotameters have been reported to operate
unreliably when measuring low NO flows and are not
recommended.)
2.2.5 Pressure regulator for standard NO cylinder. This
regulator must have a non-reactive diaphragm and internal parts and
a suitable delivery pressure.
2.2.6 Drier. Scrubber to remove moisture from the
permeation device air system. The use of the drier is optional with
NO2 permeation devices not sensitive to moisture. (Refer to the
supplier's instructions for use of the permeation device.)
2.2.7 Constant temperature chamber. Chamber capable of
housing the NO2 permeation device and maintaining its temperature
to within ±0.1 °C.
2.2.8 Temperature measuring device. Device capable of
measuring and monitoring the temperature of the NO2 permeation
device with an accuracy of ±0.05 °C.
2.2.9 Valves. A valve may be used as shown in Figure 2 to
divert the NO2 from the permeation device when zero air or NO is
required at the manifold. A second valve may be used to divert the
NO flow when zero air or NO2 is required at the manifold.
The valves should be constructed of glass, Teflon ®, or other
nonreactive material.
2.2.10 Mixing chamber. A chamber constructed of glass,
Teflon ®, or other nonreactive material and designed to provide
thorough mixing of pollutant gas streams and diluent air.
2.2.11 Output manifold. The output manifold should be
constructed of glass, Teflon ®, or other non-reactive material and
should be of sufficient diameter to insure an insignificant
pressure drop at the analyzer connection. The system must have a
vent designed to insure atmospheric pressure at the manifold and to
prevent ambient air from entering the manifold.
2.3 Reagents.
2.3.1 Calibration standards. Calibration standards are
required for both NO and NO2. The reference standard for the
calibration may be either an NO or NO2 standard, and must be
traceable to a National Bureau of Standards (NBS) NO in N2 Standard
Reference Material (SRM 1683 or SRM 1684), and NBS NO2 Standard
Reference Material (SRM 1629), or an NBS/EPA-approved commercially
available Certified Reference Material (CRM). CRM's are described
in Reference 14, and a list of CRM sources is available from the
address shown for Reference 14. Reference 15 gives recommended
procedures for certifying an NO gas cylinder against an NO SRM or
CRM and for certifying an NO2 permeation device against an NO2 SRM.
Reference 13 contains procedures for certifying an NO gas cylinder
against an NO2 SRM and for certifying an NO2 permeation device
against an NO SRM or CRM. A procedure for determining the amount of
NO2 impurity in an NO cylinder is also contained in Reference 13.
The NO or NO2 standard selected as the reference standard must be
used to certify the other standard to ensure consistency between
the two standards.
2.3.1.1 NO2 Concentration standard. A permeation
device suitable for generating NO2 concentrations at the required
flow-rates over the required concentration range. If the permeation
device is used as the reference standard, it must be traceable to
an SRM or CRM as specified in 2.3.1. If an NO cylinder is used as
the reference standard, the NO2 permeation device must be certified
against the NO standard according to the procedure given in
Reference 13. The use of the permeation device should be in strict
accordance with the instructions supplied with the device.
Additional information regarding the use of permeation devices is
given by Scaringelli et al. (11) and Rook et al. (12).
2.3.1.2 NO Concentration standard. Gas cylinder
containing 50 to 100 ppm NO in N2 with less than 1 ppm NO2. If this
cylinder is used as the reference standard, the cylinder must be
traceable to an SRM or CRM as specified in 2.3.1. If an NO2
permeation device is used as the reference standard, the NO
cylinder must be certified against the NO2 standard according to
the procedure given in Reference 13. The cylinder should be
recertified on a regular basis as determined by the local quality
control program.
2.3.3 Zero air. Air, free of contaminants which might
react with NO or NO2 or cause a detectable response on the
NO/NOX/NO2 analyzer. When using permeation devices that are
sensitive to moisture, the zero air passing across the permeation
device must be dry to avoid surface reactions on the device. (Refer
to the supplier's instructions for use of the permeation device.) A
procedure for generating zero air is given in reference 13.
2.4 Procedure.
2.4.1 Assemble the calibration apparatus such as the typical one
shown in Figure 2.
2.4.2 Insure that all flowmeters are calibrated under the
conditions of use against a reliable standard such as a soap bubble
meter or wet-test meter. All volumetric flowrates should be
corrected to 25 °C and 760 mm Hg. A discussion on the calibration
of flowmeters is given in reference 13.
2.4.3 Install the permeation device in the constant temperature
chamber. Provide a small fixed air flow (200-400 scm 3/min) across
the device. The permeation device should always have a continuous
air flow across it to prevent large buildup of NO2 in the system
and a consequent restabilization period. Record the flowrate as FP.
Allow the device to stabilize at the calibration temperature for at
least 24 hours. The temperature must be adjusted and controlled to
within ±0.1 °C or less of the calibration temperature as monitored
with the temperature measuring device.
2.4.4 Precautions must be taken to remove O2 and other
contaminants from the NO pressure regulator and delivery system
prior to the start of calibration to avoid any conversion of the
standard NO to NO2. Failure to do so can cause significant errors
in calibration. This problem may be minimized by
(1) Carefully evacuating the regulator, when possible, after the
regulator has been connected to the cylinder and before opening the
cylinder valve;
(2) Thoroughly flushing the regulator and delivery system with
NO after opening the cylinder valve;
(3) Not removing the regulator from the cylinder between
calibrations unless absolutely necessary. Further discussion of
these procedures is given in reference 13.
2.4.5 Select the operating range of the NO/NOX NO2 analyzer to
be calibrated. In order to obtain maximum precision and accuracy
for NO2 calibration, all three channels of the analyzer should be
set to the same range. If operation of the NO and NOX channels on
higher ranges is desired, subsequent recalibration of the NO and
NOX channels on the higher ranges is recommended.
Note:
Some analyzer designs may require identical ranges for NO, NOX,
and NO2 during operation of the analyzer.
2.4.6 Connect the recorder output cable(s) of the NO/NOX/NO2
analyzer to the input terminals of the strip chart recorder(s). All
adjustments to the analyzer should be performed based on the
appropriate strip chart readings. References to analyzer responses
in the procedures given below refer to recorder responses.
2.4.7 Switch the valve to vent the flow from the permeation
device and adjust the diluent air flowrate, FD, to provide zero air
at the output manifold. The total air flow must exceed the total
demand of the analyzer(s) connected to the output manifold to
insure that no ambient air is pulled into the manifold vent. Allow
the analyzer to sample zero air until stable NO, NOX, and NO2
responses are obtained. After the responses have stabilized, adjust
the analyzer zero control(s).
Note:
Some analyzers may have separate zero controls for NO, NOX, and
NO2. Other analyzers may have separate zero controls only for NO
and NOX, while still others may have only one zero common control
to all three channels.
Offsetting the analyzer zero adjustments to + 5% of scale is
recommended to facilitate observing negative zero drift. Record the
stable zero air responses as ZNO, ZNOX, and ZNO2.
2.4.8 Preparation of NO and NOX calibration
curves.
2.4.8.1 Adjustment of NO span control. Adjust the NO flow
from the standard NO cylinder to generate an NO concentration of
approximately 80% of the upper range limit (URL) of the NO range.
The exact NO concentration is calculated from:
where: [NO]OUT = diluted NO concentration at
the output manifold, ppm
FNO = NO flowrate, scm 3/min
[NO]STD = concentration of the undiluted NO standard, ppm
FD
= diluent air flowrate, scm 3/min Sample this NO concentration
until the NO and NOX responses have stabilized. Adjust the NO span
control to obtain a recorder response as indicated below: recorder
response (% scale) =
where:
URL = nominal upper range limit of the NO channel, ppm Note:
Some analyzers may have separate span controls for NO, NOX, and
NO2. Other analyzers may have separate span controls only for NO
and NOX, while still others may have only one span control common
to all three channels. When only one span control is available, the
span adjustment is made on the NO channel of the analyzer.
If substantial adjustment of the NO span control is necessary, it
may be necessary to recheck the zero and span adjustments by
repeating steps 2.4.7 and 2.4.8.1. Record the NO concentration and
the analyzer's NO response.
2.4.8.2 Adjustment of NOX span control. When
adjusting the analyzer's NOX span control, the presence of any NO2
impurity in the standard NO cylinder must be taken into account.
Procedures for determining the amount of NO2 impurity in the
standard NO cylinder are given in reference 13. The exact NOX
concentration is calculated from:
where: [NOX]OUT = diluted NOX cencentration at
the output manifold, ppm [NO2]IMP = concentration of NO2 impurity
in the standard NO cylinder, ppm Adjust the NOX span control to
obtain a convenient recorder response as indicated below: recorder
response (% scale)
Note:
If the analyzer has only one span control, the span adjustment
is made on the NO channel and no further adjustment is made here
for NOX.
If substantial adjustment of the NOX span control is necessary, it
may be necessary to recheck the zero and span adjustments by
repeating steps 2.4.7 and 2.4.8.2. Record the NOX concentration and
the analyzer's NOX response.
2.4.8.3 Generate several additional concentrations (at least
five evenly spaced points across the remaining scale are suggested
to verify linearity) by decreasing FNO or increasing FD. For
each concentration generated, calculate the exact NO and NOX
concentrations using equations (16) and (18) respectively. Record
the analyzer's NO and NOX responses for each concentration. Plot
the analyzer responses versus the respective calculated NO and NOX
concentrations and draw or calculate the NO and NOX calibration
curves. For subsequent calibrations where linearity can be assumed,
these curves may be checked with a two-point calibration consisting
of a zero point and NO and NOX concentrations of approximately 80
percent of the URL.
2.4.9 Preparation of NO2 calibration curve.
2.4.9.1 Remove the NO flow. Assuming the NO2 zero has been
properly adjusted while sampling zero air in step 2.4.7, switch the
valve to provide NO2 at the output manifold.
2.4.9.2 Adjust FD to generate an NO2 concentration of
approximately 80 percent of the URL of the NO2 range. The
total air flow must exceed the demand of the analyzer(s) under
calibration. The actual concentration of NO2 is calculated
from:
where: [NO2]OUT = diluted NO2 concentration at
the output manifold, ppm
R = permeation rate, µg/min
K = 0.532 µl NO2/µg NO2 (at 25 °C and 760 mm Hg)
Fp =
air flowrate across permeation device, scm 3/min
FD =
diluent air flowrate, scm 3/min Sample this NO2 concentration until
the NOX and NO2 responses have stabilized. Adjust the NO2 span
control to obtain a recorder response as indicated below: recorder
response (% scale)
Note:
If the analyzer has only one or two span controls, the span
adjustments are made on the NO channel or NO and NOX channels and
no further adjustment is made here for NO2.
If substantial adjustment of the NO2 span control is necessary it
may be necessary to recheck the zero and span adjustments by
repeating steps 2.4.7 and 2.4.9.2. Record the NO2 concentration and
the analyzer's NO2 response. Using the NOX calibration curve
obtained in step 2.4.8, measure and record the NOX concentration as
[NOX]M.
2.4.9.3 Adjust FD to obtain several other concentrations
of NO2 over the NO2 range (at least five evenly spaced points
across the remaining scale are suggested). Calculate each NO2
concentration using equation (20) and record the corresponding
analyzer NO2 and NOX responses. Plot the analyzer's NO2 responses
versus the corresponding calculated NO2 concentrations and draw or
calculate the NO2 calibration curve.
2.4.10 Determination of converter efficiency.
2.4.10.1 Plot [NOX]M (y-axis) versus [NO2]OUT (x-axis) and draw
or calculate the converter efficiency curve. The slope of the curve
times 100 is the average converter efficiency, EC. The
average converter efficiency must be greater than 96 percent; if it
is less than 96 percent, replace or service the converter.
Note:
Supplemental information on calibration and other procedures in
this method are given in reference 13.
3. Frequency of calibration. The frequency of
calibration, as well as the number of points necessary to establish
the calibration curve and the frequency of other performance
checks, will vary from one analyzer to another. The user's quality
control program should provide guidelines for initial establishment
of these variables and for subsequent alteration as operational
experience is accumulated. Manufacturers of analyzers should
include in their instruction/operation manuals information and
guidance as to these variables and on other matters of operation,
calibration, and quality control.
References
1. A. Fontijn, A. J. Sabadell, and R. J. Ronco, “Homogeneous
Chemiluminescent Measurement of Nitric Oxide with Ozone,” Anal.
Chem., 42, 575 (1970).
2. D. H. Stedman, E. E. Daby, F. Stuhl, and H. Niki, “Analysis
of Ozone and Nitric Oxide by a Chemiluminiscent Method in
Laboratory and Atmospheric Studies of Photochemical Smog,” J. Air
Poll. Control Assoc., 22, 260 (1972).
3. B. E. Martin, J. A. Hodgeson, and R. K. Stevens, “Detection
of Nitric Oxide Chemiluminescence at Atmospheric Pressure,”
Presented at 164th National ACS Meeting, New York City, August
1972.
4. J. A. Hodgeson, K. A. Rehme, B. E. Martin, and R. K. Stevens,
“Measurements for Atmospheric Oxides of Nitrogen and Ammonia by
Chemiluminescence,” Presented at 1972 APCA Meeting, Miami, FL, June
1972.
5. R. K. Stevens and J. A. Hodgeson, “Applications of
Chemiluminescence Reactions to the Measurement of Air Pollutants,”
Anal. Chem., 45, 443A (1973).
6. L. P. Breitenbach and M. Shelef, “Development of a Method for
the Analysis of NO2 and NH3 by NO-Measuring Instruments,” J. Air
Poll. Control Assoc., 23, 128 (1973).
7. A. M. Winer, J. W. Peters, J. P. Smith, and J. N. Pitts, Jr.,
“Response of Commercial Chemiluminescent NO-NO2 Analyzers to Other
Nitrogen-Containing Compounds,” Environ. Sci. Technol., 8, 1118
(1974).
8. K. A. Rehme, B. E. Martin, and J. A. Hodgeson, Tentative
Method for the Calibration of Nitric Oxide, Nitrogen Dioxide, and
Ozone Analyzers by Gas Phase Titration,” EPA-R2-73-246, March
1974.
9. J. A. Hodgeson, R. K. Stevens, and B. E. Martin, “A Stable
Ozone Source Applicable as a Secondary Standard for Calibration of
Atmospheric Monitors,” ISA Transactions, 11, 161 (1972).
10. A. E. O'Keeffe and G. C. Ortman, “Primary Standards for
Trace Gas Analysis,” Anal. Chem., 38, 760 (1966).
11. F. P. Scaringelli, A. E. O'Keeffe, E. Rosenberg, and J. P.
Bell, “Preparation of Known Concentrations of Gases and Vapors with
Permeation Devices Calibrated Gravimetrically,” Anal. Chem., 42,
871 (1970).
12. H. L. Rook, E. E. Hughes, R. S. Fuerst, and J. H. Margeson,
“Operation Characteristics of NO2 Permeation Devices,” Presented at
167th National ACS Meeting, Los Angeles, CA, April 1974.
13. E. C. Ellis, “Technical Assistance Document for the
Chemiluminescence Measurement of Nitrogen Dioxide,”
EPA-E600/4-75-003 (Available in draft form from the United States
Environmental Protection Agency, Department E (MD-76),
Environmental Monitoring and Support Laboratory, Research Triangle
Park, NC 27711).
14. A Procedure for Establishing Traceability of Gas Mixtures to
Certain National Bureau of Standards Standard Reference Materials.
EPA-600/7-81-010, Joint publication by NBS and EPA. Available from
the U.S. Environmental Protection Agency, Environmental Monitoring
Systems Laboratory (MD-77), Research Triangle Park, NC 27711, May
1981.
15. Quality Assurance Handbook for Air Pollution Measurement
Systems, Volume II, Ambient Air Specific Methods. The U.S.
Environmental Protection Agency, Environmental Monitoring Systems
Laboratory, Research Triangle Park, NC 27711. Publication No.
EAP-600/4-77-027a.
[41 FR 52688, Dec.
1, 1976, as amended at 48 FR 2529, Jan. 20, 1983]