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

-------

-------

-------

-------