EPA-R2-73-246 TENTATIVE METHOD FOR THE CALIBRATION OF NITRIC OXIDE, NITROGEN DIOXIDE, AND OZONE ANALYZERS BY GAS PHASE TITRATION by K. A. Rehme, B. E. Martin, and J. A. Hodgeson Chemistry and Physics Laboratory National Environmental Research Center Research Triangle Park, North Carolina 27711 Program Element No. 1A1010 NATIONAL ENVIRONMENTAL RESEARCH CENTER Office of Research and Monitoring U.S. Environmental Protection Agency Research Triangle Park, North Carolina 27711 March 1974 ------- This report has been reviewed by the Environmental Protection Agency and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. Publication No. EPA-R2-73-246 ------- CONTENTS Page ABSTRACT v PRINCIPLE AND APPLICABILITY 1 RANGES 4 INTERFERENCES 4 PRECISION , ACCURACY , AND STABILITY 5 REAGENTS 7 PROCEDURE 7 GLOSSARY 14 REFERENCES 15 LIST OF FIGURES Figure 1. Flow Scheme for Calibration of NO, NO2, NOX, and 03 Monitors by Gas Phase Titration 2 2 . Gas Phase Titration of NO with O 9 111 ------- ------- ABSTRACT A detailed procedural description of a technique developed and ap- plied within the U. S. Environmental Protection Agency for the dynamic calibration of ambient air monitors for ozone, nitric oxide, and nitrogen dioxide is presented. A gas phase titration technique utilizing the rapid gas phase reaction between nitric oxide and ozone is used in such a manner that, with the concentration of one of the three gases known, the concentrations of the other two are determined. Initially a cylinder of nitric oxide in nitrogen is standardized by gas phase titration with ozone, in concentrations that have been determined iodometrically. Cylinder nitric oxide is then used as a secondary standard for routine calibrations. Ozone is added to excess nitric oxide in the dynamic calibration system, and a chemiluminescent nitric oxide monitor is used as an indicator of changes in concentration. The decrease observed on the spanned nitric oxirlc monitor upon addition of ozone is equivalent to the concentration of nitric oxide consumed, the concentration of ozone added and the nitrogen dioxide concentration produced. The advantages of the procedure are that a primary standard for only one of the gases is required and that rapid and routine calibrations of ozone, nitric oxide, and nitrogen dioxide monitors may be performed at a common manifold. ------- ------- TENTATIVE METHOD FOR THE CALIBRATION OF NITRIC OXIDE, NITROGEN DIOXIDE, AND OZONE ANALYZERS BY GAS PHASE TITRATION PRINCIPLE AND APPLICABILITY Basic Principle The following paragraphs describe, in general terras, a gas phase technique for the dynamic calibration of ambient air monitors for nitric oxide (NO), nitrogen dioxide (NO.), total oxides of nitrogen (NOX), and ozone (0^). The technique basically utilizes the rapid gas phase reaction between NO and 0-j to produce a stoichiometric quantity of NO- in accordance 1 n with the following equation: ' NO 4- 03 = N02 + 02 k = 1.0 X 107 liters moles"1 sec"1 The quantitative nature of the reaction is used in such a manner that, with the concentration of one of the three basic components known, the con- centrations of the other two are determined. As illustrated in Figure 1, NO from a calibrated cylinder of NO in nitrogen (N2) (50 to 100 parts per million) is diluted with a constant flow of clean air to provide NO concentrations at the exit manifold in the range from 0.05 to 1 ppm. Upstream of the point of NO addition, the *5 clean air stream passes through an ozonizer, which produces variable 0, concentrations from 0 to 1 ppm at the sample manifold. Between the point where the ozonized air is mixed with NO (shown in Figure 1) and the sample manifold, a reaction chamber provides a residence time long enough for quantitative reaction to occur when 0. concentrations up to 75 percent of the initial NO concentration are added. 1 ------- o oj CO -C Q. c/> co CD >, _O CO O E o E CO O TJ c CO X O CM O 2 O 2 ~o c o TO L_ .O co o E o> o O) ILL ------- Upstream of the ozonizer, the air stream is split so that 10 per- cent of the flow passes through the 0, source and 90 percent through a bypass line. The ozonized 10 percent flow mixes directly with the NO stream and recombines with the 90 percent bypass flow downstream of the reaction vessel. The stream is split in order to produce locally high concentrations of 0, and NO in the reaction chamber ([O.j], reaction chamber •= 10 X [0-,], sample manifold), which in turn provides a quanti- tative reaction within a small volume. The concentrations produced at the manifold are independent of the ratio of bypass flow to source flow and depend only on total flow rate. When excess NO is present, the amount of 0, added is equivalent to (1) the amount of NO consumed and (2) the concentration of N02 formed. This interrelation is fundamental among concentrations of the three gases. An outline of the general calibration scheme follows. The standard cylinder of NO in N2 is initially recalibrated by the use of gas phase titration (GPT) with 0-, concentrations that have been analyzed by iodometry (this procedure is discussed in more detail later). An acceptable alter- native method, not described, for cylinder calibration would be by com- parison of N02 concentrations produced by GPT with the output of a gravi- metrically calibrated permeation tube. Once the NO concentration in the cylinder has been confirmed, this cylinder may be used over its lifetime to provide a working standard for routine calibrations. In routine calibrations, NO analyzers are calibrated by dynamic flow dilution of the cylinder gas. To calibrate NO and 0 analyzers, a constant concentration of 110 at approximately 1 ppm is produced in the ------- flow system. Ozone is added in increments from the variable 0., source. The incremental decreases of NO, observed on the spanned NO detector, are then equivalent to the concentrations produced by the on source, and serve to calibrate the source. Since N02 produced is equivalent to 0- consumed, the calibrated 0, source also serves as a calibrated NO. source when NO is present in excess. Application of Technique This technique has been designed primarily for the calibration of chemiluminescent analyzers for NO, NO,,, NO and 0~. Any detector that has a rapid and linear response to !!0 could be used as the indicator in tlva OPT step. With minor modifications in the flow scheme shown in Figure 1, any 0^ analyzer could be used as the concentration indicator. Since OPT is used to provide a working calibration of the 0., source, any tyoe of 0_ or oxidant analvzer may be calibrated. Only those tynes of N09 analyzers that do not respond to 110 may be calibrated, since the 7?07 calibration samples will contain a small excess of NO. "RANGES The procedures described in this document apply to the generation of calibration samples for NO in the range from 0.05 to 1 ppra, for 0 in the range from 0 to 0.5 ppm, and for NO in the range of 0 to 0.5 ppm. INTERFERENCES No other interfering gases are present in calibration samples produced for 0- and NO. Nitrogen dioxide analyzers that suffer interference "A "spanned NO detector" is an instrument that has been calibrated with a known concentration of NO; the output reads directly in concentration units. ------- from NO cannot be calibrated bv this method, since some NO is present in the NO^ calibration sample produced. PRECISION, ACCURACY, AND STABILITY Precision The definition of the term precision as applied to the genera- tion of calibration gases is generally uncertain at present. A given concentration of any of the three gases (NO, NO™, 0,) can, however, be generated from day-to-day with an estimated reproducibility of + 2 percent. Accuracy The accuracy in the concentrations of the calibration gases produced (NO, N00, or 0 ) is estimated to be + 3 percent. This value is determined by the accuracy of the primary calibration scheme used, in this case iodometric 0^ analysis. Stability The concentrations of calibration gases produced by CPT are stable to within + 1 percent over a 1-hour period. APPARATUS Figure 1, a schematic of the GPT apparatus, shows the placement of most of the components listed below: 1. Air Flow Controller. A device capable of maintaining constant air flow; e.g., a differential pressure regulator. 2. Air Flow-meter. A flowmeter capable of monitoring air flows between 0 and 10 liters per minute; also a wet test meter or volumetric soap bubble meter for calibration and absolute flow measurements in this range. 3. Pressure Regulator for Standard NO Cylinder. All regulators ------- used should have stainless steel internal parts with teflon or Kel-F seats. 4. Nitric Oxide Flowmeter. A flowmeter capable of monitoring NO flows between 0 and 100 cubic centimeters per minute (cm^/rain) and a 25-cm^ soap-bubble meter for absolute flow measurements in this range. The NO flow must be measured and controlled within an accuracy of + 2 percent. 5. Capillary Restriction. Glass or stainless steel capillary of sufficient length and internal diameter to allow approximately 1.0 liter/rain of air to flow through the 0 generator at a total air flow of 10 liters/min. 6. Ozone Generator. The 0-j source consists of a quartz tube into which O-^-free air is introduced and then irradiated with a stable low-pressure mercury lamp. The level of irradiation is controlled by an adjustable aluminum sleeve that fits around the lamp. Ozone concentrations are varied by adjustment of this sleeve. At a fixed level of irradiation, 03 is produced at a constant rate. This generator is described completely in Reference 3. 7. Reaction Chamber and Mixing Bulb. The reaction chamber and 3 mixing bulb are Kjeldahl mixing bulbs with volumes of 150 cm . 8. Sample Manifold. A multiport all-glass manifold is recommended. All connections in the calibration system should be glass or teflon. 9. Nitric Oxide Detector. An NO monitor is used as an indicator in the calibration procedure. The detector should be of the chemiluminescent type that is based on the light-producing 6 ------- reaction between NO and 0-j at reduced^ »-* or atmospheric pressure. Detectors of this type are available commercially from several companies. 10. lodometric Calibration Apparatus. The iodometric apparatus required for the primary calibration of the NO cylinder is described in the Federal Register. REAGENTS 1. Nitric Oxide Standard Cylinder. Cylinder containing 100 ppm NO in NT with less than 1 pnin N09. 2. Clean Air Supply. Cvlinder air or purified air containing no more than 0.002 ppm of NO, NO., and 0 . 3. Reagents for Potassium Iodide (KI) Procedure. (See Reference 7 for a list of these reagents.) PROCEDURE Primary Calibration of the NO Cylinder^ Ozone Oenerator Calibration — A multipoint calibration of the 0-j generator is obtained by the use of the neutral-buffered KI procedure as described in the Federal register. Cas Phase Titration — The NO concentration in the cylinder is deter- mined as follows: 1. With the MO flow off, set the clean air flow at a value of approximately 5 liters/min; measure and record the absolute air flow, FO< 2. Generate approximately 1.0 ppm NO by dilution and span the instrument on a range of 0 to 1 ppm. (If a 100 ppm range is available, the NO monitor may be spanned directly with cylinder gas.) 7 ------- 3. Measure and record the NO cylinder flow rate, F.._, with soap- bubble meter in-line as described in the section below entitled Calibration of NO Monitors (0 to 1.0 ppm Range). 4. Record the initial detector reading and then add approximately 0.1 ppm O.j by opening the sleeve on the 03 generator. 5. Allow the NO response to stabilize and record the resultant detector readings. f>. Adjust sleeve to obtain 0.2 ppm 0^ and allow NO response to stabilize. 7. Continue this procedure until up to 0.8 ppm 0, has been added in a stepwise fashion. 8. Remeasure the NO flow rate. Calculation — The calculation method is as follows: 1. As illustrated in the example given in Figure 2, plot the NO detector readings in ppm (y axis) versus 0~ concentration added (x axis). 2. Draw a straight line from the y axis through the linear portion of the titration curve and extrapolate to the x axis. (The i concentration at the x axis intercept, CQ, is the 0-j concen- tration equivalent to the initial diluted NO concentration.) 3. Calculate the cylinder NO concentration by the following equation: FQ X CQ CMO = FNO where C^Q = cylinder NO concentration, ppm FNQ = measured NO flow, cm /min CQ = equivalence point 0-j concentration, ppm •3 F = total clean air flow, cm /min. ------- o Q_ o: cc o a o 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 03 CONCENTRATION, ppm (K I METHOD) Figure 2. Gas phase titration of NO with 03. ------- Procedure for Routine Calibration of NO, N02» NOX, and 0^ Monitors The following procedure is recommended for routine calibration: 7ero Adjustment — 1. Allow all instruments to sample clean air until a stable re- sponse is obtained. (Clean air supply should contain no more than 0.002 ppm of NO, 110 , and 0_.) 2. After the response has stabilized, make proper zero adjustments. Calibration of MO Monitors (0 to 1.0 ppm Range) — 1. Span the chemiluminescent NO detector on a range of 0 to 1,0 ppm generating an NO concentration in the range of 0.9 to 1.0 ppm by flow dilution. (The flow rate of NO added must be measured accurately, preferably with a soap-bubble meter in- line; i.e., meter the NO flow into the bubble meter and from the bubble meter into the system.) 2. After accurately measuring the NO flow, remove the bubble meter, and meter the NO flow directly into the system. 3. Calculate the exact MO concentration added by: [NO] = FNO X CNO FT where [NO] = diluted NO concentration, ppm CNO " cylinder N0 concentration, ppm 3 F = NO flow rate, cm /min F = total flow at manifold, cm3/min " FNO •*" F0 o F = total clean air flow, cnr/min. 10 ------- 4. After £h« NO instrument response has stabilized, adjust the instrument snan control until the instrument output reads directly the concentration calculated above. 5. Decrease the NO flow rate to yield a decreased NO concentration. 6. Calculate the concentration added and record the NO instrument response. 7. Repeat at several concentration values in the range of 0 to 1.0 ppm. 8. Plot instrument response versus calculated NO concentrations and draw the NO calibration curve. (If the initial instrument span is accomplished accurately, direct readout of concen- tration should be possible without reference to the calibra- tion curve.) Calibration of NO,, Monitors (0 to 0.5 ppm Range) — 1. Adjust the NO flow rate to establish 1.00 ppm NO as measured on the NO monitor. 2. Open the sleeve on the 0 generator to add enough 0 to decrease the NO response to 0.5 ppm. (Note and record the sleeve setting on the 0 generator. This action results in the generation of 0.5 ppm NO™, which is used to span the N0? instruments.) 3. Allow the response of each N02 instrument to stabilize and ad- just the span controls to give a direct readout of 0.5 ppm. 4. Decrease the added 0 concentration by adjustment of the sleeve on the 0_ generator, again noting and recording the sleeve setting on the 0_ generator. (Allow the instrument responses to stabilize before measuring.) The decrease in response on the NO monitor yields the concentration of NO^ generated and 11 ------- the Oo source concentration. [NO.,]. = [03]i = [NO]Q - [N0]i where [NO] » initial NO concentration measured on NO o monitor, ppm = MO concentration after 0 addition, ppm .^ resultant NO concentration, ppm = added 0^ concentration, ppm 5. Repeat at several added 0, concentrations to obtain a multipoint calibration in the range of 0 to 0.5 ppm. 6. Plot the NO., instrument response versus the NO., concentration as determined abov^ and draw the NO. calibration curve. Calibration of 0, Monitors (0 to 0.5 ppm Range) — The calibration of the 0-j source, as described earlier, was determined by observation of the decreases on the NO monitor as a function of sleeve setting. The following steps are recommended for calibration of 0^ monitors: 1. In order to obtain [(^L, the output of the source, corrected for dilution of 0, by the NO flow rate, multiply each of the differential readings obtained above by the ratio F^,/Fg. (The ratio Ff/Fg normally represents a small correction factor; e.g., FT/FQ = 1.02 for CNO = 50 ppm and FQ « 5 liters /min.) f°3li = VF0 X [03]i - FT/FQ [N02]. 2. Plot these corrected 0 concentrations versus sleeve setting to yield a calibration curve for the 0.. source. 3. With the NO flow off, open the sleeve to the setting required to pive 0.5 ppm as determined by the calibration curve above. 12 ------- 4. Adjust the instrument span control to give a full-scale read- out of 0.5 ppm. 5. Reduce the sleeve setting in increments to give a series of 0-j concentrations in the range of 0 to 0.5 ppm. 6. Plot instrument response versus 0 concentration determined from the n source calibration curve. 7. Draw the calibration curve for the 0_ monitor. 13 ------- GLOSSARY dm /min Cubic centimeters per minute C Cvlinder NO concentration, ppm NO " F^ NO flow rate, cmVmin FQ Total clean air flow, cm-Vmin FT Total flow at manifold, cm^/rain GPT Gas phase titration NO Nitric oxide N02 Nitrogen dioxide NO,, Total oxides of nitrogen J\. [NO] Diluted NO concentration, ppm NO concentration after 0-j addition, ppm . Resultant NO concentration, ppm [NO] Initial NO concentration measured on NO monitor, ppm o 0^ Ozone [0,]^ Added 0., concentration, ppm t [0-]^ 0^ output corrected for flow dilution, ppm 14 ------- REFERENCES 1. Hodgeson, J. A., R. E. Baumgardner, B. E. Martin, and K. A. Rehme. Stoichiometry in the Neutral lodoraetric Procedure for Ozone by Gas- Phase Titration with Nitric Oxide. Anal.Chem. ^3_(8) :1123-1126, July 1971. 2. Pehme, K. A., B. E. Martin, and J. A. Hodgeson. The Application of Gas-Phase Titration in the Simultaneous Calibration of NO, H02, NOX, and Oj Atmospheric Monitors. Office of Research and Monitoring, U. S. Environmental Protection Agency. (Presented at the 164th American Chemical Society National Meeting. New York City. September 1972). 3. Hodgeson, J. A., R. K. Stevens, and B. E. Martin. A Stable Ozone Source Applicable as a Secondary Standard for Calibration of Atmospheric Monitors. In: Air Quality Instrumentation, Scales, J. W. (ed.). Pittsburg, Instrument Society of America, 1972. p. 149-158. 4. Fontijn, A., A. J. Sabadell, and R. J, Ronco. Homogeneous Chemi- luminescent Measurement of Nitric Oxide with Ozone. Anal.Chem. ^2:575-579, May 1970. 5. Stedman, D. H., E. E. Daby, F. Stuhl, and H. Niki. Analysis of Ozone and Nitric Oxide by a Chemiluminescent Method in Laboratory and Atmo- spheric Studies of Photochemical Smog. J. Air Pollut.Contr.Assoc. j!2.:260-263, April 1972. 6. Hodgeson, J. A., K. A. Rehme, B. E. Martin, and R. K. Stevens. Measurements for Atmospheric Oxides of Nitrogen and Ammonia by Chemi- luininescence. Office of Research and Monitoring, U. S. Environmental Protection Agency (Presented at 1972 Air Pollution Control Association, Miami. June 1972), 15 ------- 7. National Primary and Secondary Ambient Air Quality Standards. Federal Register, Vol. 36, No. 228, p. 22392-22395, November 25, 1971. 16 ------- TECHNICAL REPORT DATA (Please read Instructions on the reverse before completing) 1 REPORT NO. EPA-R2-73-246 3. RECIPIENT'S ACCESSION-NO. 4 TITLE AND SUBTITLE Tentative Method for the Calibration of Nitric Oxide, Nitrogen Dioxide,1 and Ozone Analyzers by Gas Phase Titration 5. REPORT DATE March, 1974 6. PERFORMING ORGANIZATION CODE 7 AUTHOR(S) Kenneth A. Rehme, Barry E. Martin, Jimmie A. Hodgeson* *NERC-Las Vegas, Nevada 8. PERFORMING ORGANIZATION REPORT NO. 9 PERFORMING ORGANIZATION NAME AND ADDRESS Chemistry and Physics Laboratory National Environmental Research Center Office of Research and Monitoring U. S. Environmental Protection Agench, RTPj N. C. 27711 10. PROGRAM ELEMENT NO. 1A1010 11. CONTRACT/GRANT NO. 12. SPONSORING AGENCY NAME AND ADDRESS 13. TYPE OF REPORT AND PERIOD COVERED Final 14. SPONSORING AGENCY CODE 15. SUPPLEMENTARY NOTES 16. ABSTRACT A detailed procedural description of a technique developed and applied within the U. S. Environmental Protection Agency for the dynamic calibration of ambient air monitors for ozone, nitric oxide, and nitrogen dioxide is presented. A gas phase titration technique utilizing the rapid gas phase reaction between nitric oxide and ozone is used in such a manner that, with the concentration of one of the three gases known, the concentrations of the other two are determined. Initially a cylinder of nitric oxide in nitrogen is standardized by gas phase titration with ozone, in concentrations that have been determined iodometrically. Cylinder nitric oxide is then used as a secondary standard for routine calibrations. Ozone is added to excess nitric oxide in the dynamic calibration system, and a chemiluminescent nitric oxide monitor is used as an indicator of changes in concentration. The decrease observed on the spanned nitric oxide monitor upon addition of ozone is equivalent to the concentration of nitric oxide consumed, the concentration of ozone added and the nitrogen dioxide concentration produced. The advantages of the procedure are that a primary standard for only one of the gases is required and that rapid and routine calibrations of ozone, nitric oxide, and nitrogen dioxide monitors may be performed at a common manifold. KEY WORDS AND DOCUMENT ANALYSIS DESCRIPTORS b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group Calibration Nitric Oxide Nitrogen Dioxide Ozone Gas Phase Titration 3. DISTRIBUTION STATEMENT NTIS; APTIC (EPA) "Release Unlimited" 19. SECURITY CLASS (ThisReport) Unclassified 21. NO. OF PAGES 21 20. SECURITY CLASS (Thispage) Unclassified 22. PRICE EPA Form 2220-1 (9-73) 17 ------- ------- ------- ------- |