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10.0 Calculations of TSP Concentration.

10.1 Determine the average sampler flow rate during the sampling period according to either 10.1.1 or 10.1.2 below.

10.1.1 For a sampler without a continuous flow recorder, determine the appropriate expression to be used from table 2 corresponding to the one from table 1 used in step 9.3.9. Using this appropriate expression, determine Qstd for the initial flow rate from the sampler calibration curve, either graphically or from the transposed regression equation:

Qstd =

1/m ([Appropriate expression from table 2]-b)

Similarly, determine Qstd from the final flow reading, and calculate the average flow Qstd as one-half the sum of the initial and final flow rates.

10.1.2 For a sampler with a continuous flow recorder, determine the average flow rate device reading, I, for the period. Determine the appropriate expression from table 2 corresponding to the one from table 1 used in step 9.3.9. Then using this expression and the average flow rate reading, determine Qstd from the sampler calibration curve, either graphically or from the transposed regression equation:

Qstd =

1/m ([Appropriate expression from table 2]-b)

If the trace shows substantial flow change during the sampling period, greater accuracy may be achieved by dividing the sampling period into intervals and calculating an average reading before determining Qstd.

10.2 Calculate the total air volume sampled as:

V-Qstd×t

where:

V = total air volume sampled, in standard volume units, std m 3 /;

Qstd = average standard flow rate, std m 3 /min;

t = sampling time, min.

10.3 Calculate and report the particulate matter concentration as:


where:

TSP = mass concentration of total suspended particulate matter, µg/std m 3 ;

Wi = initial weight of clean filter, g;

Wf = final weight of exposed filter, g;

V = air volume sampled, converted to standard conditions, std m 3 ,

10 6 = conversion of g to µg.

10.4 If desired, the actual particulate matter concentration (see Section 2.2) can be calculated as follows:

(TSP)a=TSP (P3/Pstd)(298/T3)

where:

(TSP)a = actual concentration at field conditions, µg/m 3 ;

TSP = concentration at standard conditions, µg/std m 3 ;

P3 = average barometric pressure during sampling period, mm Hg;

Pstd = 760 mn Hg (or 101 kPa);

T3 = average ambient temperature during sampling period, K.

11.0 References.

1. Quality Assurance Handbook for Air Pollution Measurement Systems, Volume I, Principles. EPA–600/9–76–005, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, 1976.

2. Quality Assurance Handbook for Air Pollution Measurement Systems, Volume II, Ambient Air Specific Methods. EPA–600/4–77–027a, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, 1977.

3. Wedding, J. B., A. R. McFarland, and J. E. Cernak. Large Particle Collection Characteristics of Ambient Aerosol Samplers. Environ. Sci. Technol. 11:387–390, 1977.

4. McKee, H. C., et al. Collaborative Testing of Methods to Measure Air Pollutants, I. The High-Volume Method for Suspended Particulate Matter. J. Air Poll. Cont. Assoc., 22 (342), 1972.

5. Clement, R. E., and F. W. Karasek. Sample Composition Changes in Sampling and Analysis of Organic Compounds in Aerosols. The Intern. J. Environ. Anal. Chem., 7:109, 1979.

6. Lee, R. E., Jr., and J. Wagman. A Sampling Anomaly in the Determination of Atmospheric Sulfuric Concentration. Am. Ind. Hygiene Assoc. J., 27:266, 1966.

7. Appel, B. R., et al. Interference Effects in Sampling Particulate Nitrate in Ambient Air. Atmospheric Environment, 13:319, 1979.

8. Tierney, G. P., and W. D. Conner. Hygroscopic Effects on Weight Determinations of Particulates Collected on Glass-Fiber Filters. Am. Ind. Hygiene Assoc. J., 28:363, 1967.

9. Chahal, H. S., and D. J. Romano. High-Volume Sampling Effect of Windborne Particulate Matter Deposited During Idle Periods. J. Air Poll. Cont. Assoc., Vol. 26 (885), 1976.

10. Patterson, R. K. Aerosol Contamination from High-Volume Sampler Exhaust. J. Air Poll. Cont. Assoc., Vol. 30 (169), 1980.

11. EPA Test Procedures for Determining pH and Integrity of High-Volume Air Filters. QAD/M–80.01. Available from the Methods Standardization Branch, Quality Assurance Division, Environmental Monitoring Systems Laboratory (MD–77), U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, 1980.

12. Smith, F., P. S. Wohlschlegel, R. S. C. Rogers, and D. J. Mulligan. Investigation of Flow Rate Calibration Procedures Associated with the High-Volume Method for Determination of Suspended Particulates. EPA–600/4–78–047, U.S. Environmental Protection Agency, Research Triangle Park, NC, June 1978.


[47 FR 54912, Dec. 6, 1982; 48 FR 17355, Apr. 22, 1983]

Appendix C to Part 50—Measurement Principle and Calibration Procedure for the Measurement of Carbon Monoxide in the Atmosphere (Non-Dispersive Infrared Photometry)
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Measurement Principle

1. Measurements are based on the absorption of infrared radiation by carbon monoxide (CO) in a non-dispersive photometer. Infrared energy from a source is passed through a cell containing the gas sample to be analyzed, and the quantitative absorption of energy by CO in the sample cell is measured by a suitable detector. The photometer is sensitized to CO by employing CO gas in either the detector or in a filter cell in the optical path, thereby limiting the measured absorption to one or more of the characteristic wavelengths at which CO strongly absorbs. Optical filters or other means may also be used to limit sensitivity of the photometer to a narrow band of interest. Various schemes may be used to provide a suitable zero reference for the photometer. The measured absorption is converted to an electrical output signal, which is related to the concentration of CO in the measurement cell.

2. 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.

3. Sampling considerations.

The use of a particle filter on the sample inlet line of an NDIR CO analyzer is optional and left to the discretion of the user or the manufacturer. Use of filter should depend on the analyzer's susceptibility to interference, malfunction, or damage due to particles.

Calibration Procedure

1. Principle. Either of two methods may be used for dynamic multipoint calibration of CO analyzers:

(1) One method uses a single certified standard cylinder of CO, diluted as necessary with zero air, to obtain the various calibration concentrations needed.

(2) The other method uses individual certified standard cylinders of CO for each concentration needed. Additional information on calibration may be found in Section 2.0.9 of Reference 1.

2. Apparatus. The major components and typical configurations of the calibration systems for the two calibration methods are shown in Figures 1 and 2.

2.1 Flow controller(s). Device capable of adjusting and regulating flow rates. Flow rates for the dilution method (Figure 1) must be regulated to ±1%.

2.2 Flow meter(s). Calibrated flow meter capable of measuring and monitoring flow rates. Flow rates for the dilution method (Figure 1) must be measured with an accuracy of ±2% of the measured value.

2.3 Pressure regulator(s) for standard CO cylinder(s). Regulator must have nonreactive diaphragm and internal parts and a suitable delivery pressure.

2.4 Mixing chamber. A chamber designed to provide thorough mixing of CO and diluent air for the dilution method.

2.5 Output manifold. The output manifold 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.

3. Reagents.

3.1 CO concentration standard(s). Cylinder(s) of CO in air containing appropriate concentrations(s) of CO suitable for the selected operating range of the analyzer under calibration; CO standards for the dilution method may be contained in a nitrogen matrix if the zero air dilution ratio is not less than 100:1. The assay of the cylinder(s) must be traceable either to a National Bureau of Standards (NBS) CO in air Standard Reference Material (SRM) or to an NBS/EPA-approved commercially available Certified Reference Material (CRM). CRM's are described in Reference 2, and a list of CRM sources is available from the address shown for Reference 2. A recommended protocol for certifying CO gas cylinders against either a CO SRM or a CRM is given in Reference 1. CO gas cylinders should be recertified on a regular basis as determined by the local quality control program.

3.2 Dilution gas (zero air). Air, free of contaminants which will cause a detectable response on the CO analyzer. The zero air should contain <0.1 ppm CO. A procedure for generating zero air is given in Reference 1.

4. Procedure Using Dynamic Dilution Method.

4.1 Assemble a dynamic calibration system such as the one shown in Figure 1. All calibration gases including zero air must be introduced into the sample inlet of the analyzer system. For specific operating instructions refer to the manufacturer's manual.

4.2 Insure that all flowmeters are properly calibrated, under the conditions of use, if appropriate, against an authoritative standard such as a soap-bubble meter or wet-test meter. All volumetric flowrates should be corrected to 25 °C and 760 mm Hg (101 kPa). A discussion on calibration of flowmeters is given in Reference 1.

4.3 Select the operating range of the CO analyzer to be calibrated.

4.4 Connect the signal output of the CO analyzer to the input of the strip chart recorder or other data collection device. All adjustments to the analyzer should be based on the appropriate strip chart or data device readings. References to analyzer responses in the procedure given below refer to recorder or data device responses.

4.5 Adjust the calibration system to deliver zero air to 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 a stable respose is obtained. After the response has stabilized, adjust the analyzer zero control. Offsetting the analyzer zero adjustments to +5 percent of scale is recommended to facilitate observing negative zero drift. Record the stable zero air response as ZCO.

4.6 Adjust the zero air flow and the CO flow from the standard CO cylinder to provide a diluted CO concentration of approximately 80 percent of the upper range limit (URL) of the operating range of the analyzer. 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. The exact CO concentration is calculated from:


where:

[CO]OUT = diluted CO concentration at the output manifold, ppm;

[CO]STD = concentration of the undiluted CO standard, ppm;

FCO = flow rate of the CO standard corrected to 25 °C and 760 mm Hg, (101 kPa), L/min; and

FD = flow rate of the dilution air corrected to 25 °C and 760 mm Hg, (101 kPa), L/min.

Sample this CO concentration until a stable response is obtained. Adjust the analyzer span control to obtain a recorder response as indicated below:

Recorder response (percent scale) =


where:

URL = nominal upper range limit of the analyzer's operating range, and

ZCO = analyzer response to zero air, % scale.

If substantial adjustment of the analyzer span control is required, it may be necessary to recheck the zero and span adjustments by repeating Steps 4.5 and 4.6. Record the CO concentration and the analyzer's response. 4.7 Generate several additional concentrations (at least three evenly spaced points across the remaining scale are suggested to verify linearity) by decreasing FCO or increasing FD. Be sure the total flow exceeds the analyzer's total flow demand. For each concentration generated, calculate the exact CO concentration using Equation (1). Record the concentration and the analyzer's response for each concentration. Plot the analyzer responses versus the corresponding CO concentrations and draw or calculate the calibration curve.

5. Procedure Using Multiple Cylinder Method. Use the procedure for the dynamic dilution method with the following changes:

5.1 Use a multi-cylinder system such as the typical one shown in Figure 2.

5.2 The flowmeter need not be accurately calibrated, provided the flow in the output manifold exceeds the analyzer's flow demand.

5.3 The various CO calibration concentrations required in Steps 4.6 and 4.7 are obtained without dilution by selecting the appropriate certified standard cylinder.

References

1. Quality Assurance Handbook for Air Pollution Measurement Systems, Volume II—Ambient Air Specific Methods, EPA–600/4–77–027a, U.S. Environmental Protection Agency, Environmental Monitoring Systems Laboratory, Research Triangle Park, NC 27711, 1977.

2. A procedure for Establishing Traceability of Gas Mixtures to Certain National Bureau of Standards Standard Reference Materials. EPA–600/7–81–010, U.S. Environmental Protection Agency, Environmental Monitoring Systems Laboratory (MD–77), Research Triangle Park, NC 27711, January 1981.


[47 FR 54922, Dec. 6, 1982; 48 FR 17355, Apr. 22, 1983]

Appendix D to Part 50—Measurement Principle and Calibration Procedure for the Measurement of Ozone in the Atmosphere
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Measurement Principle

1. Ambient air and ethylene are delivered simultaneously to a mixing zone where the ozone in the air reacts with the ethylene to emit light, which is detected by a photomultiplier tube. The resulting photocurrent is amplified and is either read directly or displayed on a recorder.

2. 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 and calibrated as follows:

Calibration Procedure

1. Principle. The calibration procedure is based on the photometric assay of ozone (O3) concentrations in a dynamic flow system. The concentration of O3 in an absorption cell is determined from a measurement of the amount of 254 nm light absorbed by the sample. This determination requires knowledge of (1) the absorption coefficient (a) of O3 at 254 nm, (2) the optical path length (l) through the sample, (3) the transmittance of the sample at a wavelength of 254 nm, and (4) the temperature (T) and pressure (P) of the sample. The transmittance is defined as the ratio I/I0, where I is the intensity of light which passes through the cell and is sensed by the detector when the cell contains an O3 sample, and I0 is the intensity of light which passes through the cell and is sensed by the detector when the cell contains zero air. It is assumed that all conditions of the system, except for the contents of the absorption cell, are identical during measurement of I and I0. The quantities defined above are related by the Beer-Lambert absorption law,


where:

a = absorption coefficient of O3 at 254 nm=308 ±4 atm-1 cm-1 at 0 °C and 760 torr. 3 (1,2,3,4,5,6,7)

c = O3 concentration in atmospheres

l = optical path length in cm

In practice, a stable O3 generator is used to produce O3 concentrations over the required range. Each O3 concentration is determined from the measurement of the transmittance (I/I0) of the sample at 254 nm with a photometer of path length l and calculated from the equation,


The calculated O3 concentrations must be corrected for O3 losses which may occur in the photometer and for the temperature and pressure of the sample.

2. Applicability. This procedure is applicable to the calibration of ambient air O3 analyzers, either directly or by means of a transfer standard certified by this procedure. Transfer standards must meet the requirements and specifications set forth in Reference 8.

3. Apparatus. A complete UV calibration system consists of an ozone generator, an output port or manifold, a photometer, an appropriate source of zero air, and other components as necessary. The configuration must provide a stable ozone concentration at the system output and allow the photometer to accurately assay the output concentration to the precision specified for the photometer (3.1). Figure 1 shows a commonly used configuration and serves to illustrate the calibration procedure which follows. Other configurations may require appropriate variations in the procedural steps. All connections between components in the calibration system downstream of the O3 generator should be of glass, Teflon, or other relatively inert materials. Additional information regarding the assembly of a UV photometric calibration apparatus is given in Reference 9. For certification of transfer standards which provide their own source of O3, the transfer standard may replace the O3 generator and possibly other components shown in Figure 1; see Reference 8 for guidance.

3.1 UV photometer. The photometer consists of a low-pressure mercury discharge lamp, (optional) collimation optics, an absorption cell, a detector, and signal-processing electronics, as illustrated in Figure 1. It must be capable of measuring the transmittance, I/I0, at a wavelength of 254 nm with sufficient precision such that the standard deviation of the concentration measurements does not exceed the greater of 0.005 ppm or 3% of the concentration. Because the low-pressure mercury lamp radiates at several wavelengths, the photometer must incorporate suitable means to assure that no O3 is generated in the cell by the lamp, and that at least 99.5% of the radiation sensed by the detector is 254 nm radiation. (This can be readily achieved by prudent selection of optical filter and detector response characteristics.) The length of the light path through the absorption cell must be known with an accuracy of at least 99.5%. In addition, the cell and associated plumbing must be designed to minimize loss of O3 from contact with cell walls and gas handling components. See Reference 9 for additional information.

3.2 Air flow controllers. Devices capable of regulating air flows as necessary to meet the output stability and photometer precision requirements.

3.3 Ozone generator. Device capable of generating stable levels of O3 over the required concentration range.

3.4 Output manifold. The output manifold should be constructed of glass, Teflon, or other relatively inert material, and should be of sufficient diameter to insure a negligible pressure drop at the photometer connection and other output ports. The system must have a vent designed to insure atmospheric pressure in the manifold and to prevent ambient air from entering the manifold.

3.5 Two-way valve. Manual or automatic valve, or other means to switch the photometer flow between zero air and the O3 concentration.

3.6 Temperature indicator. Accurate to ±1 °C.

3.7 Barometer or pressure indicator. Accurate to ±2 torr.

4. Reagents.

4.1 Zero air. The zero air must be free of contaminants which would cause a detectable response from the O3 analyzer, and it should be free of NO, C2 H4, and other species which react with O3. A procedure for generating suitable zero air is given in Reference 9. As shown in Figure 1, the zero air supplied to the photometer cell for the I0 reference measurement must be derived from the same source as the zero air used for generation of the ozone concentration to be assayed (I measurement). When using the photometer to certify a transfer standard having its own source of ozone, see Reference 8 for guidance on meeting this requirement.

5. Procedure.

5.1 General operation. The calibration photometer must be dedicated exclusively to use as a calibration standard. It should always be used with clean, filtered calibration gases, and never used for ambient air sampling. Consideration should be given to locating the calibration photometer in a clean laboratory where it can be stationary, protected from physical shock, operated by a responsible analyst, and used as a common standard for all field calibrations via transfer standards.

5.2 Preparation. Proper operation of the photometer is of critical importance to the accuracy of this procedure. The following steps will help to verify proper operation. The steps are not necessarily required prior to each use of the photometer. Upon initial operation of the photometer, these steps should be carried out frequently, with all quantitative results or indications recorded in a chronological record either in tabular form or plotted on a graphical chart. As the performance and stability record of the photometer is established, the frequency of these steps may be reduced consistent with the documented stability of the photometer.

5.2.1 Instruction manual: Carry out all set up and adjustment procedures or checks as described in the operation or instruction manual associated with the photometer.

5.2.2 System check: Check the photometer system for integrity, leaks, cleanliness, proper flowrates, etc. Service or replace filters and zero air scrubbers or other consumable materials, as necessary.

5.2.3 Linearity: Verify that the photometer manufacturer has adequately established that the linearity error of the photometer is less than 3%, or test the linearity by dilution as follows: Generate and assay an O3 concentration near the upper range limit of the system (0.5 or 1.0 ppm), then accurately dilute that concentration with zero air and reassay it. Repeat at several different dilution ratios. Compare the assay of the original concentration with the assay of the diluted concentration divided by the dilution ratio, as follows


where:

E = linearity error, percent

A1 = assay of the original concentration

A2 = assay of the diluted concentration

R = dilution ratio = flow of original concentration divided by the total flow

The linearity error must be less than 5%. Since the accuracy of the measured flow-rates will affect the linearity error as measured this way, the test is not necessarily conclusive. Additional information on verifying linearity is contained in Reference 9.

5.2.4 Intercomparison: When possible, the photometer should be occasionally intercompared, either directly or via transfer standards, with calibration photometers used by other agencies or laboratories.

5.2.5 Ozone losses: Some portion of the O3 may be lost upon contact with the photometer cell walls and gas handling components. The magnitude of this loss must be determined and used to correct the calculated O3 concentration. This loss must not exceed 5%. Some guidelines for quantitatively determining this loss are discussed in Reference 9.

5.3 Assay of O3 concentrations.

5.3.1 Allow the photometer system to warm up and stabilizer.

5.3.2 Verify that the flowrate through the photometer absorption cell, F allows the cell to be flushed in a reasonably short period of time (2 liter/min is a typical flow). The precision of the measurements is inversely related to the time required for flushing, since the photometer drift error increases with time.

5.3.3 Insure that the flowrate into the output manifold is at least 1 liter/min greater than the total flowrate required by the photometer and any other flow demand connected to the manifold.

5.3.4 Insure that the flowrate of zero air, Fz, is at least 1 liter/min greater than the flowrate required by the photometer.

5.3.5 With zero air flowing in the output manifold, actuate the two-way valve to allow the photometer to sample first the manifold zero air, then Fz. The two photometer readings must be equal (I=Io).

Note: In some commercially available photometers, the operation of the two-way valve and various other operations in section 5.3 may be carried out automatically by the photometer.

5.3.6 Adjust the O3 generator to produce an O3 concentration as needed.

5.3.7 Actuate the two-way valve to allow the photometer to sample zero air until the absorption cell is thoroughly flushed and record the stable measured value of Io.

5.3.8 Actuate the two-way valve to allow the photometer to sample the ozone concentration until the absorption cell is thoroughly flushed and record the stable measured value of I.

5.3.9 Record the temperature and pressure of the sample in the photometer absorption cell. (See Reference 9 for guidance.)

5.3.10 Calculate the O3 concentration from equation 4. An average of several determinations will provide better precision.


where:

[O3]OUT = O3 concentration, ppm

a = absorption coefficient of O3 at 254 nm=308 atm-1 cm-1 at 0 °C and 760 torr

l = optical path length, cm

T = sample temperature, K

P = sample pressure, torr

L = correction factor for O3 losses from 5.2.5=(1-fraction O3 lost).

Note: Some commercial photometers may automatically evaluate all or part of equation 4. It is the operator's responsibility to verify that all of the information required for equation 4 is obtained, either automatically by the photometer or manually. For “automatic” photometers which evaluate the first term of equation 4 based on a linear approximation, a manual correction may be required, particularly at higher O3 levels. See the photometer instruction manual and Reference 9 for guidance.

5.3.11 Obtain additional O3 concentration standards as necessary by repeating steps 5.3.6 to 5.3.10 or by Option 1.

5.4 Certification of transfer standards. A transfer standard is certified by relating the output of the transfer standard to one or more ozone standards as determined according to section 5.3. The exact procedure varies depending on the nature and design of the transfer standard. Consult Reference 8 for guidance.

5.5 Calibration of ozone analyzers. Ozone analyzers are calibrated as follows, using ozone standards obtained directly according to section 5.3 or by means of a certified transfer standard.

5.5.1 Allow sufficient time for the O3 analyzer and the photometer or transfer standard to warmup and stabilize.

5.5.2 Allow the O3 analyzer to sample zero air until a stable response is obtained and adjust the O3 analyzer's zero control. Offsetting the analyzer's zero adjustment to +5% of scale is recommended to facilitate observing negative zero drift. Record the stable zero air response as “Z”.

5.5.3 Generate an O3 concentration standard of approximately 80% of the desired upper range limit (URL) of the O3 analyzer. Allow the O3 analyzer to sample this O3 concentration standard until a stable response is obtained.

5.5.4 Adjust the O3 analyzer's span control to obtain a convenient recorder response as indicated below:

recorder response(%scale)=


where:

URL = upper range limit of the O3 analyzer, ppm

Z = recorder response with zero air, % scale

Record the O3 concentration and the corresponding analyzer response. If substantial adjustment of the span control is necessary, recheck the zero and span adjustments by repeating steps 5.5.2 to 5.5.4.

5.5.5 Generate several other O3 concentration standards (at least 5 others are recommended) over the scale range of the O3 analyzer by adjusting the O3 source or by Option 1. For each O3 concentration standard, record the O3 and the corresponding analyzer response.

5.5.6 Plot the O3 analyzer responses versus the corresponding O3 concentrations and draw the O3 analyzer's calibration curve or calculate the appropriate response factor.

5.5.7 Option 1: The various O3 concentrations required in steps 5.3.11 and 5.5.5 may be obtained by dilution of the O3 concentration generated in steps 5.3.6 and 5.5.3. With this option, accurate flow measurements are required. The dynamic calibration system may be modified as shown in Figure 2 to allow for dilution air to be metered in downstream of the O3 generator. A mixing chamber between the O3 generator and the output manifold is also required. The flowrate through the O3 generator (Fo) and the dilution air flowrate (FD) are measured with a reliable flow or volume standard traceable to NBS. Each O3 concentration generated by dilution is calculated from:


where:

[O3]'OUT = diluted O3 concentration, ppm

F0 = flowrate through the O3 generator, liter/min

FD = diluent air flowrate, liter/min

References

1. E.C.Y. Inn and Y. Tanaka, “Absorption coefficient of Ozone in the Ultraviolet and Visible Regions”, J. Opt. Soc. Am., 43, 870 (1953).

2. A. G. Hearn, “Absorption of Ozone in the Ultraviolet and Visible Regions of the Spectrum”, Proc. Phys. Soc. (London), 78, 932 (1961).

3. W. B. DeMore and O. Raper, “Hartley Band Extinction Coefficients of Ozone in the Gas Phase and in Liquid Nitrogen, Carbon Monoxide, and Argon”, J. Phys. Chem., 68, 412 (1964).

4. M. Griggs, “Absorption Coefficients of Ozone in the Ultraviolet and Visible Regions”, J. Chem. Phys., 49, 857 (1968).

5. K. H. Becker, U. Schurath, and H. Seitz, “Ozone Olefin Reactions in the Gas Phase. 1. Rate Constants and Activation Energies”, Int'l Jour. of Chem. Kinetics, VI, 725 (1974).

6. M. A. A. Clyne and J. A. Coxom, “Kinetic Studies of Oxy-halogen Radical Systems”, Proc. Roy. Soc., A303, 207 (1968).

7. J. W. Simons, R. J. Paur, H. A. Webster, and E. J. Bair, “Ozone Ultraviolet Photolysis. VI. The Ultraviolet Spectrum”, J. Chem. Phys., 59, 1203 (1973).

8. Transfer Standards for Calibration of Ambient Air Monitoring Analyzers for Ozone, EPA publication number EPA–600/4–79–056, EPA, National Exposure Research Laboratory, Department E, (MD–77B), Research Triangle Park, NC 27711.

9. Technical Assistance Document for the Calibration of Ambient Ozone Monitors, EPA publication number EPA–600/4–79–057, EPA, National Exposure Research Laboratory, Department E, (MD–77B), Research Triangle Park, NC 27711.


[44 FR 8224, Feb. 8, 1979, as amended at 62 FR 38895, July 18, 1997]

Appendix E to Part 50 [Reserved]
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Appendix F to Part 50—Measurement Principle and Calibration Procedure for the Measurement of Nitrogen Dioxide in the Atmosphere (Gas Phase Chemiluminescence)
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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.) (continued)