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ADDENDA A. Suggested Performance Specifications for Atmospheric Analyzers for Hydrocarbons Corrected for Methane:
0.3 mg./m.“ (0-5 p.p.m.)
THC. 03 mg./m.: (0-5 p.p.m.)
CHA Output (minimum)
0-10 mv. full scale. Minimum detectable sensitivi 0.1 p.p.m. THC.
0.1 p.p.m. CH. Zero drift (maximum). Not to exceed 1 percent/24
hours. Span drift (maximum). Not to exceed 1 percent/24
hours. Precision (minimum).
+0.5 percent. Operational period (minimum).. 3 days. Operating temperature range 5.40* C.
(minimum). Operating humidity range 10-100 percent.
(minimum). Linearity (maximum)..
1 percent of full scale.
B. Suggested Definitions of Performance Specifications: Range-The minimum and maximum meas
urement limits. Output-Electrical signal which is propor
tional to the measurement; intended for connection to readout or data processing devices. Usually expressed as millivolts or
milliamps full scale at a given impedence. Full Scale-The maximum measuring limit
for a given range. Minimum Detectable Sensitivity-The
smallest amount of input concentration that can be detected as the concentration
approaches zero. Accuracy–The degree of agreement be
tween a measured value and the true value; usually expressed at $ percent of
full scale. Lag Time-The time interval from a step
change in input concentration at the instrument inlet to the first corresponding
change in the instrument output. Time to 90 Percent Response-The time in
terval from a step change in the input
concentration at the instrument inlet to a reading of 90 percent of the ultimate re
corded concentration. Rise Time (90 percent)-The interval be
tween initial response time and time to 90 percent response after a step decrease in
the inlet concentration. Zero Drift-The change in instrument
output over a stated time period, usually 24 hours, of unadjusted continuous operation, when the input concentration is zero; usually expressed as percent full
scale. Span Drift-The change in instrument
output over a stated time period, usually 24 hours, of unadjusted continuous operation, when the input concentration is a stated upscale value; usually expressed as
percent full scale. Precision-The degree of agreement be
tween repeated measurements of the same concentration. It is expressed as the average deviation of the single results from
the mean. Operational Period-The period of time
over which the instrument can be expected to operate unattended within specifica
tions. Noise-Spontaneous deviations from a mean
output not caused by input concentration
changes. Interference-An undesired positive or neg
ative output caused by a substance other
than the one being measured. Interference Equivalent–The portion of in
dicated input concentration due to the
presence of an interferent. Operating Temperature Range-The range
of ambient temperatures over which the instrument will meet all performance specifications. Operating Humidity Range—The range of
ambient relative humidity over which the instrument will meet all performance
specifications. Linearity-The maximum deviation between
an actual instrument reading and the reading predicted by a straight line drawn between upper and lower calibration points.
(36 FR 22394, Nov. 25, 1971)
APPENDIX F-MEASUREMENT PRINCIPLE
AND CALIBRATION PROCEDURE FOR
Principle and Applicability
1. Atmospheric concentrations of nitrogen dioxide (NO,) 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 (0,). (1,2,3) NO, is first quantitatively reduced to NO(4,5,6) by means of a converter. NO, which commonly exists in ambient air together with NO,, passes through the converter unchanged causing a resultant total NO, concentration equal to NO+NO,. 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+NO,) to yield the final NO, measurement. The NO and NO+NO, 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/NO/NO, 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 NO, and valid NO, measurements may be obtained. In certain geographical areas, where the concentration of these potential interferences is known or suspected to be high relative to NO,, the use of an equivalent method for the measurement of NO, is recommended.
2.2 The use of integrating flasks on the sample inlet line of chemiluminescence NO/ NO,/NO, 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 NO, measurements resulting from the reaction of ambient levels of NO and O, in the sampling system.
2.3 The use of particulate filters on the sample inlet line of chemiluminescence NO/ NO,/NO, analyzers is optional and left to the discretion of the user or the manufac
turer. 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 NO, 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 Og.
Major equipment required: Stable O, generator. Chemiluminescence NO/NO/NO, 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 O, to produce stoichiometric quantities of NO, in accordance with the following equation: (8) NO+0= »NO,+O,
(1) The quantitative nature of this reaction is such that when the NO concentration is known, the concentration of NO, can be determined. Ozone is added to excess NO in a dynamic calibration system, and the NO channel of the chemiluminescence NO/ NO,/NO, analyzer is used as an indicator of changes in NO concentration. Upon the addition of Os, the decrease in NO concentration observed on the calibrated NO channel is equivalent to the concentration of NO, produced. The amount of NO, generated may be varied by adding variable amounts of O, from a stable uncalibrated O, 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 O, 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 32% 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 O, for reaction with NO to generate NO, concentrations in the range required. Ozone generators of the electric discharge type may produce NO and NO, 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 O, 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.
1.3.1 NO concentration standard. Gas cylinder standard containing 50 to 100 ppm NO in N, with less than 1 ppm NO,. This standard must be traceable to a National Bureau of Standards (NBS) NO in N, Standard Reference Material (SRM 1683 or SRM 1684), an NBS NO, 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 NO, SRM and for determining the amount of NO, impurity in an NO cylinder.
1.3.2 Zero air. Air, free of contaminants which will cause a detectable response on the NO/NO,/NO, analyzer or which might react with either NO, O,, or NO, 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 O, generator air flowrate (F.) and NO flowrate (FNO) (see Figure 1) must be adjusted such that the following relationship holds:
Pr=[NOJRC X to 2.75 ppm-minutes
[NO]ac = [NO, (
< 2 minutes
where: Pr=dynamic parameter specification, de
termined empirically, to insure complete reaction of the available On,
ppm-minute (NOJRC=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/min Fo=O, generator air flowrate, scm/min Vrc=volume of the reaction chamber,
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 (Fr=analyzer demand plus 10 to 50% excess).
(b) Establish (NOJOut as the highest NO concentration (ppm) which will be required at the output manifold. [NO]our should be approximately equivalent to 90% of the upper range limit (URL) of the NO, concentration range to be covered.
(c) Determine Fuo as
Verify that tx < 2 minutes. If not, select a reaction chamber with a smaller Vac.
(g) Compute the diluent air flowrate as
Fp=diluent air flowrate, scm/min
(h) If Fo turns out to be impractical for the desired system, select a reaction chamber having a different Vic and recompute Fo and Fo.
NOTE: A dynamic parameter lower than 2.75 ppm-minutes may be used if it can be determined empirically that quantitative reaction of O, 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.
1.5.1 Assemble & 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 callbration of flowmeters is given in reference 13.
1.5.3 Precautions must be taken to remove O, 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 NO, 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/NO,/NO, analyzer to be calibrated. In order to obtain maximum precision and accuracy for NO, calibration, all three chan. nels of the analyzer should be set to the same range. If operation of the NO and NO, channels on higher ranges is desired, subsequent recalibration of the NO and NO, channels on the higher ranges is recommended.
(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'.
(e) Compute FO as
[NO]ord XFNOX VRC
(f) Compute to as
NOTE: Some analyzer designs may require identical ranges for NO, NO, Bud NO, during operation of the analyzer.
1.5.5 Connect the recorder output cable(s) of the NO/NO,/NO, 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 ana. lyzer 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 O, 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 mani. fold to insure that no ambient air is pulled into the manifold vent. Allow the analyzer to sample zero air until stable NO, NO, and
NO, responses are obtained. After the responses have stabilized, adjust the analyzer zero control(s).
NOTE: Some analyzers may have separate zero controls for NO, NO,, and NO,. Other analyzers may have separate zero controls only for NO and NO,, 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 ZNO.
1.5.8 Preparation of NO and NO, callbration curves.
184.108.40.206 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,Jout=diluted NO, concentration at
the output manifold, ppm (NO2)D=concentration of NO, impurity
in the standard NO cylinder, ppm Adjust the NOx span control to obtain a recorder response as indicated below: recorder response (% scale)=
NO channel, ppm
220.127.116.11 Adjustment of NO, span control. When adjusting the analyzer's NO, span control, the presence of any NO, impurity in the standard NO cylinder must be taken
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 NO, 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 18.104.22.168. Record the NO, concentration and the analyzer's NO, response.
22.214.171.124 Generate several additional concentrations (at least five evenly spaced