&EPA
           United States
           Environmental Protection
           Agency
           Environmental Monitoring and Support EPA-600/4-78-024
           Laboratory         May 1978
           Research Triangle Park NIC 27711
          Research and Development
A Technical
Assistance
Document

Use of the Flame
Photometric
Detector Method
for Measurement of
Sulfur Dioxide
in Ambient Air

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                RESEARCH REPORTING SERIES

Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology.  Elimination of traditional grouping  was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:

      1.  Environmental  Health Effects Research
      2.  Environmental  Protection Technology
      3.  Ecological Research
      4.  Environmental  Monitoring
      5.  Socioeconomic Environmental Studies
      6.  Scientific and Technical Assessment Reports (STAR)
      7.  Interagency Energy-Environment Research and Development
      8.  "Special" Reports
      9.  Miscellaneous Reports

This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and  instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations.  It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia  22161.

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                                                EPA-600/4-78-024
                                                May 1978
 USE OF THE FLAME PHOTOMETRIC DETECTOR METHOD

FOR MEASUREMENT OF SULFUR DIOXIDE IN AMBIENT AIR

         A TECHNICAL ASSISTANCE DOCUMENT
                          by
                      W. Gary Eaton
                 Research Triangle Institute
          Research Triangle Park, North Carolina 27709
                 Contract No. 68-02-2433
                    EPA Project Officer
                    John H. Margeson
                  Quality Assurance Branch
        Environmental Monitoring and Support Laboratory
          Research Triangle Park, North Carolina 27711
                       Prepared for

   ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
          OFFICE OF RESEARCH AND DEVELOPMENT
         U.S. ENVIRONMENTAL PROTECTION AGENCY
           RESEARCH TRIANGLE PARK, N.C. 27711

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                         DISCLAIMER

  This report has been reviewed by the Environmental Monitoring and
Support Laboratory,  U.S.  Environmental  Protection Agency,  and
approved for publication. Mention of trade names or commercial prod-
ucts does not constitute endorsement or recommendation for use.

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                                   PREFACE

  Sulfur dioxide is a pollutant for which national primary and secondary ambient air
quality standards have been established by the Environmental Protection Agency. In
order to insure that the standards (as specified in the Code of Federal Regulations (CFR)
Title 40, Chapter I, Part 50) are not  exceeded, continuous monitoring is sometimes
used.
  This technical assistance document (TAD) is intended to serve as a sourcebook of in-
formation and outlines of good practices for operation and calibration of S02 analyzers
based on the measurement principle of the flame photometric detection (FPD) method.
Critical parameters  are identified which affect the operation and calibration of FPD
analyzers. This document can  be used  with older analyzers which measure "total"
sulfur, as well as newer models which  are improved in  specificity for SO2 and have
been designated as  "equivalent methods" by EPA.
  The reader should note that the techniques for generation of S02 calibration stand-
ards and  zero air (discussed in Section 3.0)  may be used in conjunction with any am-
bient air SO2 analyzer, not just FPD S02 analyzers.
  Many of the items discussed in this  document are based on findings from a literature
search, interviews and communications  with FPD manufacturers and users, results of
laboratory calibrations and experiments, and trial field use of the document.
  This document is to be used by technical personnel in conjunction with the manufac-
turer's instruction manual and  the appropriate  sections of EPA  Quality Assurance
Handbook for Air Pollution Measurement Systems - Volume II (EPA-600/4-77-027a).
  This TAD is divided into six major sections: introduction, installation and startup of
an FPD S02  analyzer; generation of S02 calibration standards and  zero air; calibration
of the FPD; procedural aids; references and index.
  It is recommended that the user of this document first read  it entirely and make note
of points which relate to his specific brand of analyzer. Index tabs can be attached to
pages of special interest so they can be found again quickly. Note that precautionary or
emphasized  material in this document is set apart from the text by being enclosed in
"boxes."
  The user's attention is called particularly to the following topics covered in this docu-
ment:
                       Topic                                  Section

       Nonequivalent FPD analyzers                          1.3.3
       Temperature and humidity control                     2.2.2
       Ambient air sampling                                 2.2.4
       Safe use of hydrogen                                 2.3.3, 2.3.4
       Generation of calibration standards and                3.0
         zero air
       Carbon dioxide interferences                          3.6.3
       Zero,  span, and multipoint calibration                  4.0
       Airflow measurements and corrections                 5.0

                                      iii

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IV

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                            ACKNOWLEDGMENTS

  This document was written under Contract No. 68-02-2433 for the Environmental
Protection Agency. The support of this agency is gratefully acknowledged as is the ad-
vice and guidance of the Project Officer, John H.  Margeson.
  Laboratory studies and preparation of this document were carried out in the Systems
and Measurements Division of RTI under the general direction of Mr.  J. J. B. Worth,
Group III Vice President, and Mr. J. B. Tommerdahl, Division Director. Mr. C. E. Decker,
Manager,  Environmental Measurements  Department, was Laboratory Supervisor for
this contract. RTI staff members G. Maier, E. Pedudo, F. Smith, D. Strait and R. Wright
reviewed the document and made many helpful suggestions. Messrs. R. Denyszyn, F.
Dimmock, and  L. Hackworth each aided  in the laboratory trials and experiments.
  Special acknowledgment is made to  Messrs. R.  Baumgardner, F, McElroy, F. Smith,
and D.  vonLehmden,  members of EPA's  Environmental  Monitoring and  Support
Laboratory, for their advice and critical review of the document.  Dr. M. Cher; Mr. D.
Brittain, EPA Region  IV; and Mr. B. Towns, EPA Region X are also acknowledged.
  Grateful appreciation  is also  extended to representatives  of manufacturers  of
analyzers, calibration equipment, permeation devices, and specialty gases who were
most  cooperative in  discussing many topics in the document and reviewing the
manuscript itself.  Included in this group are Mr. C. Laird of the Bendix Corporation,
Dr.  Q. Stahel of Meloy Laboratories, Inc., and Mr. D. Lucero of Monitor Labs, Inc.

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VI

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                                  ABSTRACT

  This Technical Assistance Document is intended to serve as a source-book of infor-
mation and outlines of good practice for operation and calibration of ambient air SO2
detection analyzers based on the measurement principle of Flame Photometric Detec-
tion  (FPD). This is  accomplished through the identification and control of critical
parameters affecting the operation and calibration of FPD analyzers. The document
may be used with analyzers which  measure total sulfur,  as well as  with new S02-
specific models which have been designated as equivalent methods by EPA,
  This document is to be used in conjunction with the instrument manufacturer's in-
struction manual. The document consists of six sections: (1) Introduction to FPD prin-
ciple, (2) Installation  and startup of the analyzer,  (3) Calibration sources and their air
supplies, (4) Procedures for multipoint dynamic calibration, (5) Procedural aids, and (6)
References and Index.
  This report was submitted in fulfillment of Contract No.  68-02-2433 by Research
Triangle Institute under the sponsorship of the Environmental Protection Agency.
                                      VII

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VIII

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                                  CONTENTS
Preface	r	  iii
Acknowledgments 	 	    v
Abstract	vii
Figures	xiii
Tables	   xv

Section 1.0 - Introduction  	    1
     1.1  Flame Photometric Detection of Sulfur:  Basic Principles  .   .    1
     1.2  Application of FPD to Continuous Detection of S02 in
          Ambient Air   	    4
          1.2.1  Background:  Principles of Operation 	    4
     1.3  Commercially Available FPD Ambient Air S02 Analyzers  ....    8
          1.3.1  Manufacturers and Their Instruments  	    8
          1.3.2  Compliance Monitoring-Reference and
                 Equivalent Methods   	    9
          1.3.3  Recommendations for Use of Nonequivalent
                 FPD Sulfur Analyzers 	   10
     1.4  Calibration Gas Delivery System:  Sources of S02  ....... .  ..........  .14
     1.5  Recordkeeping, Maintenance, and Quality Control 	   14

Section 2.0 - Installation and Startup of the FPD S02 Analyzer  ....   17
     2.1  Introduction	   17
     2.2  Requirements of the Facility Which Houses the Analyzer  ...   17
          2.2.1  Electrical Requirements  	   18
          2.2.2  Temperature and Humidity Control Requirements  ....   18
          2.2.3  Spatial Requirements 	   20
          2.2.4  Ambient Air Sampling Requirements  	  ...   20
     2.3  Installation of an FPD S02 Analyzer	   22
          2.3.1  Unpacking the Analyzer	   22
          2.3.2  Electrical and Pneumatic Connections 	   22
          2.3.3  Guidelines for the Safe Use of Hydrogen Cylinders  .   .   26
          2.3.4  Procedures and Safety Precautions for Use of
                 Electrolytic Hydrogen Generators   	  .   .   29
     2.4  Startup of an FPD S02 Analyzer	   31
          2.4.1  Power On; Warmup Times	   31
          2.4.2  "Peaking Up"  Response Prior to Calibration  	   32

Section 3.0 - Generation of S02 Calibration Standards and Zero Air  .   .   35
     3.1  Introduction	   35
     3.2  Clean Air Sources for S02 Calibration Systems 	   36
          3.2.1  Zero Air Generators	   36
          3.2.2  Compressed Air Cylinders	   .   39
                                      IX

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     3.3  Permeation Tubes and Devices Containing Liquefied
          S02:  Characteristics and Use	                   39
          3.3.1  Introduction   	'•'-'.'.'.'.'.'.'.'.'.   39
          3.3.2  Description of NBS Permeation Tubes   .........   40
     3.4  Calibration Systems Based on Permeation Devices:
          Description and Explanation of Use	   45
          3.4.1  Custom-built Laboratory Systems Employing
                 Permeation Tubes   	   45
          3.4.2  Commercial Systems Employing Permeation Tubes
                 or Devices   	   49
          3.4.3  Explanation of Use of Permeation Device
                 Calibration Systems  	   54
          3.4.4  Computation of S02 Concentrations From
                 Permeation Tubes 	   58
     3.5  Calibration by Use of Compressed Gas Cylinders
          Containing S02 in Nitrogen or Air	   60
          3.5.1  General	   60
          3.5.2  Equipment Specifications and Use	   61
          3.5.3  Guidelines for Use of S02 Dilution Systems	   65
     3.6  Other Factors Affecting the S02 Output From Dynamic
          Calibration Systems and/or the Response of FPD S02
          Analyzers   	   67
          3.6.1  Temperature at Which the Permeation Tube is Used ...   67
          3.6.2  Air Flow Rate and Clean Air Supply	   67
          3.6.3  Carbon Dioxide Interference in the FPD
                 Method for Sulfur Dioxide  	   68
          3.6.4  Percentage of Oxygen in Calibration Air	   72
     3.7  Summary of FPD S02 Calibration Source Parameters Which
          Must be Operator-Controlled   	   73

Section 4.0 - Calibration of the Flame Photometric Detector for
            S02 in Ambient Air	   81
     4.1  Introduction to Calibration	   81
          4-1.1  Qualitative and Quantitative Analyses    	   81
          4.1.2  Definition of Calibration; Requirements for
                 Calibration    	   82
          4.1.3  Recordkeeping	      83
     4.2  Preliminary Steps	  .  .   84
     4.3  Zero and Span Check	'  '  '   g^
     4.4  Maintenance and Replacement Operations  	          95
     4.5  Multipoint Calibration of an FPD S02 Analyzer Equipped
          with a Linearized Output	          gg
     4.6  Supplementary Instructions for Particular FPD Analyzers         113
          4-6.1  Bendix Model 8300:   Electronic Zero and              '
                 Operational  Zero   	         -,-,0
          4.6.2  Use of the Optional Log-Linear Output of Meioy
                 FPD Analyzers	             115
          4.6.3  Data Correction Due to Baseline Offset of the
                 Meloy Lab's  Model SA 185 Output	           118
     4.7  Summary of FPD Analyzer Parameters Which Must Be  	
          Operator-Controlled   	

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Section 5.0 - Procedural Aids   	131
     5.1  Introduction	131
     5.2  Soap Film Flowmeter, SFFM, or Bubble Flowmeter  	   132
     5.3  Mercury Column Barometer, Fortin Type 	   136
     5.4  Water Manometer, U-Tube 	   139
     5.5  Steps for Correcting Airflow to Standard Temperature and
          Pressure^	141
     5.6  Ascarite  Method for C02 Determination  	   141
          5.6.1  Procedure	143

References	145

Index   	147

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                                   FIGURES

Number                                                                  Page

1.1  S2 emission bands observed in a shielded air-hydrogen flame  ...     3
1.2  Gas flow diagram of continuous flame photometric detector
     for S02 in ambient air	     5
1.3  Flame photometric detector (FPD) sulfur response
     characteristics (Monitor Labs FPD) 	     7
2.1  Detailed views of various ways for connecting 1/8 in. o.d.  Teflon
     sampling lines to manifold 	    21
2.2  Typical installation of FPD S02 analyzer	    23
2.3  Hydrogen regulator assembly and CGA cylinder connector #350  ...    27
3.1  Zero air generator suitable for FPD S02 zero and calibration ...    37
3.2  National Bureau of Standards standard reference material
     S02 permeation tube	    41
3.3  National Bureau of Standards sulfur dioxide permeation
     tube certificate   	    42
3.4  Example of custom made laboratory permeation tube assembly for
     calibration of S02 analyzers .....  	    46
3.5  Laboratory clean air supply  	    47
3.6  Schematic diagram of a portable S02 calibrator with internal
     air supply   	    50
3.7  Schematic diagram of multipollutant calibrator 	    51
3.8  Concentration of S02 versus time.   Low-level S02 in air;
     treated aluminum cylinder  	    62
3.9  Assembly for dilution of S02 from cylinder of S02
     for use in calibration or span check	    64
3.10 Variation of FPD analyzer response with air oxygen
     content at a fixed S02 concentration of 0.0806 ppm	    74
4.1  Sampling line filter holder and filter of all-Teflon
     construction   	    97
4.2  Calibration trace of linearized output.   FPD ambient air
     S02 analyzer	101
4.3  Calibration curve for linearized FPD S02 analyzer  	   110
4.4  Log-log output of the Meloy Mode]  SA 185 FPD S02 analyzer  ....   116
4.5  Log-linear plot of calibration data, Meloy Model SA 185-2A
     FPD S02 analyzer   	117
5.1  Soap film flowmeter	133
5.2  Water manometer, "U" tube	   140
5.3  Ascarite  sampling train for C02 determination 	   144
                                     xn i

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XIV

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                                   TABLES

Number
1.1  Performance specifications for automated methods for S02 	    11
3.1  Certified permeation rates for National Bureau of Standards
     permeation tube No. 33-64	    44
3.2  Typical errors due to temperature variation of an S02
     permeation tube	    68
3.3  Evaluation of C02 interference in total sulfur measurements
     using FPD analyzers    	    70
3.4  FPD analyzer response, ppm S02, in the presence and
     absence of carbon dioxide  	    71
3.5  Retention of C02 on commonly employed scrubber materials 	    73
3.6  S02 calibration source parameters which must be operator-
     controlled in order to obtain valid data	    76
4.1  Barometric pressure at various altitudes 	    92
4.2  Typical effect of an offset of 0.065 V (0.01 ppm)	120
4.3  Typical effect of an offset of 0.147 V (0.015 ppm) 	  .  .   121
4.4  FPD analyzer parameters which must be operator-
     controlled in order to obtain valid data   	122
5.1  Vapor pressure of water at various temperatures, mm Hg 	   142
                                     xv

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XVI

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                                  SECTION 1.0
                                 INTRODUCTION

1.1  FLAME PHOTOMETRIC DETECTION OF SULFUR:   BASIC PRINCIPLES
     Many elements give characteristic emission spectra when burned in a
flame.  Absorption of energy from the flame allows a ground-state atom or
molecule to reach a higher energy level or an excited state.  The excited-
state atom or molecule contains excess energy and may return to its ground
state by emitting light.  The wavelength and intensity of this light are the
basis for selective and quantitative analysis of different elements or com-
pounds.
     When a sulfur-containing compound (inorganic or organic) is burned in a
flame, a minor product is the excited-state diatomic molecular sulfur spe-
cies, S2*.  The asterisk (*) indicates the species is excited, that is, has
energy in excess of that of the unexcited, ground-state, S2 species.  The
S2* species is inclined to seek a lower energy level  and one mechanism by
which S2* reverts to its ground state is by a chemiluminescent process.  By
this process light energy is emitted with the spectral characteristics shown
in Figure l.l.1'2'3  Two equations describing this are:

               sulfur-containing molecules 	^. S2*              (1)
                                            in flame
                   S2*        	+     S2     + light, hv       (2)
         (excited electronic state)        (normal electronic state)
     The left-hand side of equation 2 shows the excited state S2* species.
The right-hand side shows the products of the decomposition of S2*.  The
products are the unexcited S2 species and a quantity of light energy, i.e.,
photons (hence the name "photometric" detector).   The "detector" portion of
the flame photometric detector is a photomultiplier tube, which senses the
light energy emission intensity and converts it to an equivalent electrical

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current which is proportional to the original concentration of S02 (or other
sulfur-containing gas) in the air sample.
     The S2 emission system is broad-based and falls mainly in the region
2,769 to 6,166 A.  Figure 1.1 shows a portion of the emission spectrum.  The
peak of the spectrum is around 380 nm (3,840 A).   Narrow-band pass filters
are commonly used in detector assemblies to allow only light near the peak
region to pass.
     The formation of the S2 molecule in the flame occurs when two S atoms
combine in the presence of a "third body" (denoted by M), equation 3:
                         S + S + M       S2 + M.                         (3)
     Hydrogen and hydroxyl radicals, also produced by the flame, react with
S2 to produce the excited state S2* species4'5'6  (equations 4,5).
                         H + H + S2      S2* + H2                       (4)
                        OH + H + S2      S2* + H20                      (5)
     The intensity of the chemi luminescence or light produced by S2* as
described  by equation 2 is proportional  to the S2* concentration, [S2*],
equation 6:
                          light intensity = k [S2*].                      (6)
     As stated  above, formation of S2 depends on  reaction between two S
atoms  in the presence of a third body, M (another gaseous atom or molecule).
For  reaction to  occur, the two S atoms must collide simultaneously with M.
It can be  shown  that the number of collisions (and therefore potential
reactions  between two sulfur atoms) is proportional  to the square of their
concentration. 7
     Therefore  the rate of formation of the S2* molecular species will be
proportional to  the square of the S atom concentration, equation 7,  which in
turn depends on  the concentration of the sulfur-containing molecule.
     Thus, for a continuous S02 analyzer based on flame photometry, the
 light energy produced by decaying S2* and received by the photomultiplier
tube is predicted to be proportional to the square of the S02 concentration

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                                                   384
                                        374
                              364
C/3
yt


LU
<
_l
LU
CC
                    355
               350
                                                            394
                                                                    405
                                                                           415
                                                                                  427
                                       WAVELENGTH, nm
          Figure 1.1.  82  emission bands  observed  in  a  shielded  air-hydrogen  flame.

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     The exact theoretical exponential factor of 2 is not usually found.
Instead, a lower value is found.   This diminishment is caused by variation
in flame conditions and by self-collisional quenching processes without
chemiluminescence.
1.2  APPLICATION OF FPD TO CONTINUOUS DETECTION OF S02 IN AMBIENT AIR
1.2.1  Background:   Principles of Operation
     Application of the flame photometric technique to measure sulfur gases
in air was first disclosed in a German patent issued to Draegerwerk and
Drager.8  Crider9 in 1965 and Brody and Chaney10 in 1966 further optimized
the  FPD technique for analysis of a variety of sulfur-containing compounds.
     Ambient air FPD S02 analyzers are designed to supply a sample of air
continuously to the flame photometric detector.   The air sample serves as
the  source of oxygen to support the combustion of the hydrogen fuel and to
maintain the flame.  To achieve sensitivity, stability, and selectivity, the
continuous analyzer must possess certain pneumatic, electronic, and physical
features.11
     Figure 1.2 illustrates the gas flow pathways of a typical continuous
FPD  analyzer for S02 in ambient air.  A vented evacuation pump, located
downstream of the burner, pulls the air sample or calibration gas into the
analyzer through TeflonT tubing.   The sample passes through a 5-micron pore
size Teflon particulate filter (caution:  use only the manufacturer's spec-
ified filter arrangement), a rotameter, a three-way solenoid valve, an
optional H2S scrubber assembly,12 and finally enters the burner block where
it combines with hydrogen and supports the flame.  The sample rotameter is
used only when flows are checked; normally it is bypassed by use of the
solenoid valve.  The H2S scrubber is a required item on EPA-designated
"equivalent method" units.  It removes H2S and allows S02 to pass.   This
improves the specificity of the analyzer.  Without the scrubber, the unit is
a "total sulfur" analyzer and responds to almost all sulfur compounds that
reach the flame.
     The fuel, hydrogen, enters through stainless steel tubing from a pres-
surized source.  It first passes through a solenoid valve (which will close
Co.
     ^"Teflon" is a registered trademark of E.I. Du Pont de Nemours &

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                                                      ADJUSTABLE NEEDLE
                                                      VALVE OR LIMITING
                                                          ORIFICE
                                                    PARTICULATE FILTER
                                                       (-100 MICRON)
        EVACUATION PUMP
  VENT
                                                                                    f     I-
                                                                          DILUTION AIR IN
                                                            H2GAUGE
                                                            0 60 PSIG
FLAME PHOTOMETRIC
DETECTOR ASSEMBLY
SHUT-OFF
SOLENOID VALVE (H2)
                                                                                                     HYDROGEN IN
en
          H2SSCRUBBER
          ASSEMBLY EPA
          DESIGNATED EQUI
          VALENT UNITS
          ONLY  	
                                                   HYDROGEN
                                                   ROTAMETER
                                       HYDROGEN
                                       PRESSURE
                                       REGULATOR
                                                 TFE SAMPLE
                                                 SOLENOID VALVE
                                           SAMPLE
                                           ROTAMETER
                                                                                    I—I
                                                                                5 MICRON TEFLON
                                                                                PARTICULATE FILTER
                                                                          AIR SAMPLE OR
                                                                          CALIBRATION
                                                                          GAS IN
                           Figure 1.2.   Gas flow diagram of continuous flame  photometric  detector
                                                    for S02 in ambient air.

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automatically if the flame should go out, thus preventing a hazardous build-
up of hydrogen), then through a pressure regulator and gauge, through a
flow-indicating rotameter, and then through a flow-1imiting plug or capil-
lary tube to the burner.   To achieve a steady flow of hydrogen, the plug or
capillary is usually located within an oven, where it is maintained at a
constant temperature.
     The third flow of gas is dilution air.   Room air is pulled into the
analyzer by the evacuation pump.   It first passes through a particulate
filter, then through an adjustable needle valve or limiting orifice, and
finally meets and dilutes the vapors that are being pulled from the flame
chamber.  This dilution prevents  condensation of unwanted water vapor and
corrosive products from the flame.
     The flame photometric detector itself is housed in a temperature-
controlled cell.  It is made up of three functional subsystems:  the burner
or flame holder, the flame chamber, and the photomultiplier tube.   Air
carrying sulfur-containing molecules enters through the bottom of the
burner.  The burner provides a support for the flame.   The flame is sur-
rounded by hydrogen, which is enclosed by the flame chamber.   This arrange-
ment produces a cool hydrogen-air flame, which is well-suited for the forma-
tion of the S2* molecular species.   It is a hydrogen hyperventilated dif-
fusion flame.  One wall of the flame chamber is a clear optical window and
narrow bandpass optical filter through which the photomultiplier tube (PMT)
measures the light emission intensity from the S2* species at wavelengths
near 394 nm and converts  it to an equivalent electrical  current.   The PMT is
temperature controlled.  A regulated high-voltage power supply stabilizes
the PMT output.
     The output current of the PMT is approximately proportional  to the
square (the 2nd power) of the concentration of the sulfur present  in the
sample.13
                    response  ~  (sulfur atom concentration)2
     The actual exponential value is generally somewhat less  than  2, usually
between 1.7 and 1.9.  Figure 1.3 illustrates the chemiluminescent  S * emis-
sion intensity - sulfur concentration relationship for the 400-380 nm (4 000-
3,800 A) region.  Note that the PMT currents and sulfur dioxide concentr -

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   1,000
s   100 _
O

X
     10-
                                                                   DETECTOR RESPONSE FACTOR (n) -1.86
                                                                                                I
                                          n-B
n-7
n-6
,0-10            10-9               10-°               ID'7               10"°              10


 CHEMILUMINESCENT S2 EMISSION INTENSITY EXPRESSED AS PHOTOMULTIPLIER TUBE OUTPUT CURRENT, AMPS
,-B
          Figure 1.3.  Flame photometric detector (FPD)  sulfur response characteristics
                                        (Monitor  Labs FPD).

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tions are plotted on a log-log graph.  Note that the slope of the line  is
1.86, fairly near the theoretical slope of 2.00.  Beyond concentrations of
about 1 ppm, the S2* species returns to its ground state without chemi-
luminescense by a self-collisional quenching process.  At sulfur dioxide
levels of 1 ppm and higher,  the FPD signal current begins to deviate from
the square relationship and the slope of the line in Figure 1.3 increases
rapidly.  In other words, the response of the analyzer does not change  much
as the sulfur dioxide concentration increases.
     The log-log output form of Figure 1.3 is seldom used with ambient  air
analyzers.  Instead the signal  is treated electronically such that a linear-
ized signal is obtained.   This enables a linear relation between analyzer
response (e.g., output volts) and sulfur dioxide concentration (ppm) to be
plotted on  linear graph paper.   See Figure 4-3 for an example of such a
plot.
1.3  COMMERCIALLY AVAILABLE FPD AMBIENT AIR S02 ANALYZERS
1.3.1   Manufacturers and Their Instruments
     At the present time (1978) there are three major U.S.  manufacturers of
continuous-type FPD analyzers for total sulfur and/or sulfur dioxide in
ambient air.  These are:
     1.   The Bendix Corporation, Environmental and Process Instruments
          Division, Drawer 831, Lewisburg, WV  24901
     2.   Meloy Laboratories, Incorporated, 6715 Electronic Drive, Spring-
          field, VA  22151
     3.   Monitor Labs,  Incorporated, 4202 Sorrento Valley Blvd.,  San Diego,
          CA  92121
     A  fourth manufacturer, Tracer, Incorporated, 6500 Tracer Lane,  Austin
TX 78721, offers a gas chromatography-flame photometry analyzer,  which
separates sulfur compounds prior to FPD detection.   A "total  sulfur" mode is
also available wherein the sample bypasses the column and goes directly to
the  FPD.
     Performance, operational, and configurational  specifications  are avail-
able from each manufacturer on a full line of FPD analyzers and options
Each of the manufacturers of continuous analyzers has one or more  analv
which has been designated as an "equivalent method" by EPA or i<=  a r.  ^-j /
                                                           «•  is  a candidate

                                     8

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for designation.  This designation is discussed in Section 1.3.2.  Such
designation means only that the analyzer meets certain minimum standards.
Competitive differences exist between FPD analyzers.  Thus, the need for a
careful selection process based on the individual air-monitoring situation
is very important.
     Indeed, if new S02 ambient air monitoring equipment is to be purchased,
consideration should also be given to other methods of S02 detection that
have been designated as equivalent methods or are candidates for designa-
tion.  Such measurement methods include amperometric analyzers (Phillips
Instruments, Incorporated), second derivative spectroscopy (Lear-Siegler
Corporation), and pulsed UV fluorescence analysis (Thermo-Electron Corpora-
tion and Beckman Instrument Corporation).
1.3.2  Compliance Monitoring-Reference and Equivalent Methods
     Certain air pollution control agencies, such as State agencies, are
required to monitor the ambient air to determine compliance with National
Ambient Air Quality Standards.  The standards are given in Title 40, Chapter
1, Part 50 of the Code of Federal Regulations.  Specific monitoring require-
ments  are given in Part 51.  An amendment to Part 51 was issued on February
18, 1975 (40 CFR 7043), and requires that for purposes of compliance monitor-
ing "each method for measuring S02, CO, or photochemical oxidant .  . .  shall
be a reference method or equivalent method ..."  An exception to this
requirement allows automated analyzers purchased prior to February 18,  1976,
to be  used until February 18, 1980.
     The definitions and qualifications of reference and equivalent methods
are given in 40 CFR Part 53.  For S02, the reference method is a manual
method and is completely specified in Appendix A of 40 CFR Part 50.  Thus,
all other methods for S02 compliance measurement must be designated as
equivalent methods by EPA.  A notice of each method designated as equivalent
is published in the Federal Register.  A current list of all designated
reference and equivalent methods is maintained by EPA and may be obtained
                                    f
from EPA Regional Offices or from the Environmental Monitoring and Support
Laboratory, Department E, MD-76, Research Triangle Park, NC  27711.
     Sellers of designated methods for sulfur dioxide must comply with
certain conditions, one of which is that the analyzer must function within

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the limits of the performance specifications given in Table 1.1 for at  least
1 year after delivery when maintained and operated in accordance with the
operation manual. Aside from occasional breakdowns or malfunctions, consist-
ent or repeated noncompliance with any of these specificatons should be
reported to EPA at the address given previously.
     For automated methods, a designation applies to any analyzer that  is
identical to the analyzer described in the designation.   In many cases,
analyzers manufactured prior to the designation may be upgraded (e.g., by
minor modification or by substitution of a new operation or instruction
manual) so as to be identical to the designated method and thus achieve
designated status at a modest cost.  The manufacturer should be consulted to
determine the feasibility of such upgrading.   Any modification to a refer-
ence or equivalent method made by a user must be approved by EPA if the
designated status is to be maintained.
1.3.3  Recommendations for Use of Nonequivalent FPD Sulfur Analyzers
     As was mentioned in the last section, older FPD analyzers may be up-
graded and, thus, achieve designated status at modest cost.   Any modifi-
cations should be done after consultation with the manufacturer and obtain-
ing EPA approval.
     This section contains recommendations for modifications and procedural
changes to make older FPD sulfur analyzers more sensitive and more specific
for S02.  It must be emphasized that making these modifications yourself
does not make your analyzer an equivalent method.   However,  for noncom-
pliance monitoring and until such time as an equivalency-designated instru-
ment is necessary, these steps should help give better data.
     Replace all sampling lines.   All sampling lines leading from the moni-
toring station ambient air manifold to the rear of the analyzer should be
cleaned or replaced entirely with new cleaned Teflon tubing.   This mainte-
nance is necessary because the S02 in the sample can be  adsorbed or reduced
chemically be dirt, oil, and other debris on the tube wall.   Frequency of
tubing replacement should be determined by visual  inspection of the line.
Any fittings which are made of metal or plastic and come into contact with
the sample should be either replaced with Teflon fittings or bored out so
the Teflon tube passes continuously through the fitting.   Tubing inside the
                                     10

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                  Table 1.1.   Performance specifications for automated methods for S02
Performance parameter
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.





Caen i nueryerenu — — —-_—-— — 	 	
luuai interierent ——__-— — .


limit
OUA> OT upper range
limit
Lag time 	



limit
80% of upper range 	
limit
Units!
.

	 do 	
	 	 ____/-i,-,___________

	 	 	 	 ___.4.->__ ___ _
	 do 	
do


	 	 	 	 _H/\-_— _ 	 	
~ao



.
	 Parts per million
	 do 	
Sulfur
dioxide
0-0.5
0.005
0.01
±0.02
0.06
±0.02
±20.0
± 5.0
20
15
15
0.01
0.015
Definitions
and test
procedures
§53.23(a).
§53.23(b).
§53.23(c).
__ ££."} O'ifri}
SDJ. £3{Q).
§53.23(e).
§53.23(e).
§53.23(e).
§53.23(e).
§53.23(e).
§53.23(e).
_ 0 CO OO f r\ "\
s^-j- ^ov.ej.
 Table 1.1 is reproduced from a portion of Table B-l of CFR 40 Part 53.
fTo convert from parts per million to micrograms per cubic meter at 25° C and 760 mm Hg,  multiply by
 M/0.02447, where M is the molecular weight of the gas:   M = 64 for SO,

-------
analyzer that leads to air flow rotameters and to the burner block should
also be removed and replaced.   The sample should not pass through the rotam-
eter during normal sample monitoring operations since S02 gas is removed by
the rotameter components; it should bypass the rotameter.  Any solenoid
valves which are in the sample line should have Teflon interiors and should
be cleaned or replaced if dirty.   A Teflon holder with membrane filter, such
as the "Mace" filter (available from the Mace Corporation, S. El Monte, CA
91733), mounted in the sampling line will minimize particulate accumulation.
     Clean burner block and "window."  The burner block of most FPD analyz-
ers can be removed and disassembled.   Accumulated dust and corrosion are
removed (use fine steel wool)  and the surfaces and fittings are cleaned with
mild soap and water.  It is advisable to replace any "0" rings with new ones
at this time.  Use only the manufacturer's recommended "0" rings since
others may tend to cold-flow or otherwise lose their sealing properties.
For example, the Me Toy model SA-285 requires Viton "0" rings.  Next, rinse
the parts with deionized water and then allow them to dry.  It may be nec-
essary to replace the thermocouple sensor and the ignitor wire or glowplug
at this time.  If the thermocouple is removed or replaced, be sure it is
re-installed identically to the original thermocouple.   If the polarity of
the leads is reversed, the circuitry controlling the H2 solenoid may actuate
and stop the hydrogen flow, giving a flame-out.   Also check the operability
of burner block heating elements and replace them if necessary.   Between the
flame and the photomultiplier tube are a clear "window" and a 394 ± 20 nm
optical filter.  Examine each for cloudiness, staining, or pitting, and
clean or replace them as necessary.  This will allow more light to reach the
PM tube.  Some manufacturers suggest that the burner block be flushed with
certain solvents and then dried.   This procedure is outlined in the manu-
facturer's instruction manual  and may be used.
     Overhaul or replace sample pump.  If the analyzer contains a pump, it
is probably a small bellows pump or diaphragm pump.   Over long periods of
use, these pumps develop problems in the diaphragm area (due to dust and
general fatigue), and variable flows result.   Replace any worn parts and
reseal the pump properly.  A new valve assembly may be required for bellows
pumps.  Consult the pump manufacturer's maintenance instructions regarding
allowable vacuum pressure and flow rate limits.   If an external  pump is
                                     12

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used, be sure it is of sufficient capacity to do the job and that it oper-
ates smoothly.
     Install filter on dilution air entry.  Older models may not have par-
ti cul ate filters on the dilution air entry at the rear of the analyzer.  To
minimize particle and dust entrainment, which might alter the dilution flow
rate, install a simple in-line filter.  The filter should pass air easily so
that adequate flow is maintained.  Porous paper filters mounted in small
plastic holders work well.
     Install H2S scrubber.   The H2S scrubber is an item which seldom accom-
panied older FPD analyzers since they were designed as "total sulfur" moni-
tors.  Today, each of the three major FPD analyzer manufacturers provides
separate H2S scrubbers, which can be purchased and installed on older ana-
lyzers.  These  scrubbers remove H2S but allow S02 to pass unaffected.
     Clean  or replace and recalibrate rotameters.  Most analyzers have
hydrogen fuel and air sample rotameters to indicate flow rates.  After long
usage, these  rotameters may  become dirty and dusty and require disassembly
and cleaning.   Methanol  is suggested as a cleaning solvent.  Use it in a
ventilated  area since methanol is toxic.  After drying and reassembly, the
rotameter should be  calibrated (or the certified calibration curve, which
accompanied the rotameter, should be verified) by comparison to a certified
soap film flowmeter,  spirometer, or wet test meter.  For normal ambient air
monitoring, the air  sample should bypass the rotameter and flow directly to
the flame compartment.
      Electronic checks.   If  there is reason to suspect that the electronics
need repair or  coarse adjustment, a qualified electronic technician or
service  representative  should examine and test the analyzer.  Adjustments
may be made prior to the  calibration procedure.
      Calibration procedure.   Some users of older FPD analyzers may be accus-
tomed to  calibrating an  analyzer by simply "zeroing" and "spanning" the ana-
 lyzer.   This  practice  is  discouraged.
      To  operate an  analyzer  designated as an "equivalent method," a more
detailed  monthly  calibration, which  includes a zero point, span point, and
three  or  more  intermediate concentration points,  is initially  recommended.
If possible,  one  or  more  of  the calibration points should  be  representative
of the concentration levels  that are  actually being experienced  in the
                                      13

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ambient air.   Use of multiple calibration points shows the linearity (or
lack of linearity) of the analyzer's response.   A lack of linearity can be
corrected by adjustment of the linearization circuitry as specified by the
manufacturer.   The use of graphical  display of calibration data and least
squares regression equation computations are suggested.   Details for carry-
ing out such a calibration are given in Section 4.0 of this document.
1.4  CALIBRATION GAS DELIVERY SYSTEM:  SOURCES OF S02
     A reliable and accurate system of delivering known concentrations of
S02 calibration gas to the FPD analyzer is a necessity.   Several commercial
systems are available.  They usually employ permeation tubes or devices as
S02 sources.  The temperature of the tube or device is controlled by use of
a thermostatted water or air bath or other method.   Calibrators may also be
fabricated by the user.  Desirable characteristics  of dynamic S02 calibra-
tors and general  instructions for their use are given in Section 3.0 of this
document.
     The source of S02 should be an NBS-certified permeation tube or another
tube or device whose permeation rate is traceable to an NBS Standard Refer-
ence Material tube.  Sources of air for dilution of permeation tube effluent
are also discussed in Section 3.0.   Particular attention should be given to
both the C02 and 02 content of diluent air.   The use of S02 in air from
compressed gas cylinders is also discussed in Section 3.0.
1.5  RECORDKEEPING, MAINTENANCE, AND QUALITY CONTROL
     Proper recording of all data from calibrations, zero and span checks,
etc., is essential to overall data quality.   This document does not give a
format for data recording, but does emphasize when  data should be recorded.
     Preventive maintenance and major maintenance items  are only noted in
this document.   The user should refer to the analyzer's  instruction manual
for details of maintenance and troubleshooting procedures.
     Quality control and quality assurance are most important to insure
production of good data.   A major aspect of quality control is calibration.
This is treated thoroughly in this document.   For other aspects of quality
control and assurance, the reader is referred to the EPA publications
"Quality Assurance Handbook for Air Pollution Measurement Systems, Volume I,
                                     14

-------
Principles" (EPA-600/9-76-005, March, 1976) and "Quality Assurance Handbook
for Air Pollution Measurement Systems, Volume II, Ambient Air Specific
Methods" (EPA-600/4-77-027a, May, 1977).
                                      15

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16

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                                  SECTION 2.0
                INSTALLATION AND STARTUP OF THE FPD S02 ANALYZER

2.1  INTRODUCTION
     Correct installation and startup of an FPD S02 analyzer is the first
step of an ambient air monitoring program for S02-  In addition to a well-
equipped tool box, brass, stainless steel and Teflon tubing, compression
fittings, signal cable, hydrogen fuel, and a hydrogen regulator will be
required.  Flow-measuring devices such as a selection of rotameters and a
soap film flowmeter are necessary.  A wet test meter and a mass flowmeter
are useful, especially in the laboratory.  A stopwatch, hand calculator, and
a recorder or digital voltmeter will also be required.
     If the analyzer is to be installed and used in a laboratory, the neces-
sary equipment for calibration, etc., will generally be available.   If the
analyzer is to be installed at a field station (unattended operation), it is
recommended that the analyzer first be unpacked, checked, set up, cali-
brated, and operated for several days at the central laboratory.   This
procedure will contribute to better understanding of the analyzer and will
demonstrate its proper calibration and operation before field usage.  The
analyzer is then taken to the field site, installed, and calibrated.
          VERY IMPORTANT:  before beginning any installation procedures,
          first read the manufacturer's operation and maintenance
          manual for your FPD analyzer.  Become familiar with the lo-
          cation and function of all controls and gas and electrical
          connections.  If the original manual is lost or misplaced,
          order a replacement.
2.2  REQUIREMENTS OF THE FACILITY WHICH HOUSES THE ANALYZER
     The room, trailer, or shelter which houses the analyzer will probably
also house other ambient air monitors, calibration systems, meteorological
                                     17

-------
systems, strip chart recorders, and perhaps a magnetic tape data acquisition
system.
     The physical facility housing the FPD analyzer should meet certain
requirements so that optimum analyzer performance is obtained.
2.2.1  Electrical Requirements
          Note:   before connecting any power to your FPD analyzer, be
          certain that all switches for power, pump, etc., are in the
          OFF position.  Unusual power surges have been known to cause
          damage to photomultiplier tubes and other analyzer components.
     Commercial instruments operate over the voltage range 105-125 on 60 Hz,
single phase power.  Be sure there are no voltage fluctuations in the line.
If such fluctuations are suspected, the power company can detect and perhaps
correct the problem.  Power requirements vary from 250 to 500 W.   For rea-
sons of safety (prevention of electrical shock),  proper operation of the
analyzer, and warranty requirements, it is essential that adequate power be
present for the monitoring site and that power be supplied to the analyzer
through the conventionally grounded 3-pin power plug supplied with the
analyzer.  This ground must not be defeated by cutting off the round pin on
the power cable.   If the instrument must be operated from the two-contact
outlet, grounding  is preserved by using a three-conductor to two-conductor
adapter and connecting the adapter wire to a suitable ground such as a cold
water pipe or a grounding rod (embedded in soil).   The use of extension
cords is not recommended unless they are of the heavy duty type.
2.2.2  Temperature and Humidity Control Requirements
     Each of the commercially available instruments is designed to operate
(with minimal effect on instrument drift) over the temperature range 20° -
30° C (74° - 86° F)  and over the range 10° - 40° C with possibly signifi-
cant degradation in the noise, precision, and drift specifications
     Other ambient air monitors will have similar temperature range require-
ments.   The best environment is an air-conditioned/heated room with a ther-
mostat that maintains the room temperature somewhere in the range 20°
30° C.   A temperature of 25° C (77° F) is ideal since this is the "standard"
temperature for air sampling.  If the instrument is rack-mounted, it is
                                     18

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important that the rack enclosure be properly ventilated.  The temperature
inside enclosed relay racks which are not ventilated may be as much as 15° -
25° C above laboratory ambient temperatures.
     One must be careful not to let the temperature inside the laboratory or
sampling site facility fall too low, as this can cause water from the moist
ambient air to condense in the station air sampling manifold and possibly
condense in the sampling lines leading to the instruments.   This will cause
removal of S02.  Deflect the cold air from air conditioners or relocate the
air conditioner away from the manifolds and sampling lines.  If condensation
problems persist,  it may be necessary to insulate and slightly heat the
station sampling manifold and instrument sampling line.
     All of the above variations in temperature may cause the instrument to
respond in an erratic, drifting, manner, due to temperature changes across
the burner block assembly.
     Another note  on temperature effects concerns the exhaust or vent line
from the flame photometric detector.  Since hydrogen is being burned in the
flame  chamber, water is produced and exhausted from the instrument.  Dilu-
tion air mixes with the water-laden hot exhaust gases to reduce the amount
of water per volume of air to a point below the dew point at normal room
temperatures.  If  the temperature of the facility is low enough to cause
condensation of this water, a "plug" of water may form in the vent line.
This will cause the sample flow of the analyzer to vary since both dilution
air and sample air are pulled in with the same pump and disturbance of one
flow affects the other.  To avoid this, a 6.4 mm (0.25 in.) o.d. exhaust
line (polyethylene is acceptable) should be installed in such a way that
drainage of water  always occurs and no points exist where water can stand in
the line.
     The exhaust line should be vented to a point outside the building or to
a vent system whose ultimate exit is well away from the sample inlet source
and occupied enclosed areas.  In this way excess hydrogen will be safely
vented to the ambient air if the instrument's flame is extinguished and the
instrument has no  hydrogen solenoid shutoff or the solenoid fails.  The
length of the exhaust line should be minimal.  If the length is changed it
should be done just prior to a multipoint calibration.  If the exhaust line
leads  to the outside ambient air, proper drainage should be maintained
                                     19

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outside, too.  Extremely cold weather may cause condensation and freezing of
water in the line with subsequent disruption or change of air flows.  The
tube may be insulated by covering it with plastic tubing having an inside
diameter slightly larger than the outside diameter of the exhaust tube.
2.2.3  Spatial Requirements
     Adequate space should be allotted for analyzer operation and calibra-
tion.  If the instrument (or instrument modules) is rack-mounted, there
should be sufficient space around the rack to allow free circulation of air
to provide good heat dissipation.  The bench mount configuration is quite
handy as it allows convenient access to the interior of the analyzer for
maintenance and adjustment.
     In either case, sufficient room should be available adjacent to the
analyzer to locate a sulfur calibration source and associated equipment such
as bubble flowmeters and mass flowmeters.  It is a good idea, if space
permits, to have easy access to the rear panel of the analyzer so that
electrical and pneumatic lines and in-line filters and scrubbers can be
easily checked or changed.
2.2.4  Ambient Air Sampling Requirements
     Air should be brought into the sampling station through an ambient air
sampling manifold of glass or Teflon construction.   A 60-100 cfm (free air)
blower motor is located at one end to pull the air sample into the station
at the rate of several cubic feet per minute and exhaust the excess air to
the outside.  The blower motor should be easily accessible for periodic
checks of its proper operation.  The glassware of the manifold itself should
be disassembled and cleaned from time to time, especially when dust and dirt
buildup becomes noticeable.  Clean it with warm water and rinse with deion-
ized water.  The Teflon sampling line of the analyzer is connected to the
manifold.  Figure 2.1 illustrates several ways to make this connection.
Whatever way is used, it should be compatible with both the ambient air and
calibration manifolds.  Air inlets of calibration systems which "manufac-
ture" zero air for use with permeation tubes or other calibration gas
sources are also connected to the sampling manifold.  In this way, ambient
                                     20

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       SAMPLING OR CALIBRATION MANIFOLD
BALL/SOCKET JOINT ^
HELD BY SPRING-   "
LOADED CLAMP
       1/4 IN. OD
       GLASSTUBE-
 1/4 IN. TO 1/8 IN.
 TEFLON REDUCING
 UNION

 1/8 IN. OD TEFLON
 SAMPLING LINE TO
 INSTRUMENT
                     •SAMPLING TUBE EXTENDS THROUGH THE
                      GLASS CONNECTOR INTO THE MANIFOLD
                  V
1/4 IN. OD GLASS TUBING, DRAWN DOWN
AT ONE END SO THAT A 1/8 IN. OD TUBE
JUST PASSES THROUGH
                      LARGER TYGON TUBING (OR EQUIVALENT)

                     (SMALLER TYGON TUBING (OR EQUIVALENT)

                     • 1/8" OD TEFLON SAMPLING LINE
         SAMPLING OR CALIBRATION MANIFOLD
      PLASTIC CAP,
               *
   TEFLON-COATED
   COMPRESSION
   GASKET
HREADED GLASS FITTING'

1/4 IN. OD TEFLON
OR GLASS TUBE
1/4 IN. TO 1/8 IN.
TEFLON UNION
                                    1/8 IN. OD TEFLON
                                    SAMPLING LINE TO
                                    INSTRUMENT
           1/4 IN. OD GLASS TUBING, DRAWN DOWN
          • AT ONE END SO THAT A 1/8 IN. OD TUBE
           JUST PASSES THROUGH
                                                                - LARGER TYGON TUBING
                                                                 SMALLER TYGON TUBING
   Figure 2.1.   Detailed  views of  various ways  for connecting 1/8  in.  o.d.
                         Teflon sampling lines  to manifold.
                                          21

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levels of carbon dioxide (C02) are supplied to the instrument.  Refer to
Section 3.0 for a discussion of the C02 effect on FPD analyzers.
     Do not sample ambient air by running lengths of Teflon tubing from the
instrument to the exterior of the station.  Such long lines give problems
with pressure balance and moisture condensation and collect dust.  They also
are awkward to use during calibration and zero and span checks.
     Detailed instructions for installation of sampling manifolds are given
in EPA document EPA-600/4-77-027a, "Quality Assurance Handbook for Air
Pollution Measurement Systems-Volume II, Ambient Air Specific Methods."
2.3  INSTALLATION OF AN FPD S02 ANALYZER
2.3.1  Unpacking the Analyzer
     Upon receipt, the analyzer should be unpackaged and examined for damage
such as scratched surfaces, broken or bent control knobs, etc.  Check the
contents of the package against the packing slip which accompanies the
parcel.  If there are shipping deficiencies, report them to the manufac-
turer; if there is damage from shipping, report this to the freight carrier
and file a claim.
     Prior to applying any power to the analyzer, it is a good idea to
remove the cover of the analyzer and visually inspect the interior.   All
analyzers contain electronic "cards" or "boards" which plug into special
sockets; there is a chance one may be loose or not in place.   Refer to the
manufacturer's operation and service manual for directions for handling and
replacing electronic boards.
     Some instruments may also have the sampling pump "tied-down" for ship-
ping purposes.  Remove any such tie-down straps.  Again, if there is any
doubt concerning the location of components of an analyzer, refer to the
manufacturer's manual.
     Save the shipping box or crate in the event the analyzer may have to be
returned to the manufacturer or be moved to another site.
2.3.2  Electrical and Pneumatic Connections
     Electrical and pneumatic (gas) connecting terminals are located on the
rear panel of most FPD S02 analyzers.  Figure 2.2 illustrates a typical
installation.
                                     22

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PO
CO
RECORDER
SIGNAL
CABLE
PRIMARY--,
POWER ^
VENT




DIGITAL
VOLTMETER
(OPTIONAL)



1/8IN. ODSTAINL
_ STEEL TUBING
ANALYZER INLET
RECORDER AND/OR
DATA SYSTEM SIGNAL _^
OUTLET SAMPLE HJ h 	 £
INLET 1 F
H2S SCRUBBER
1 PI IMP 1 "C3 INLET FOR
PUMP | ^DILUTION AIR
1 r^-1 PARTICULATE
v. IM nn DI-II VCTHVI PMP FILTER
TWO STAGE
REGULATOR \
HYDROGEN
CYLINDER OR
GENERATOR
ESS

_ 1/8 IN. OD TEFLON
1 « *\AMPI

TEFLON
FILTER
                      TUBING
                                                 DILUTION
                                                 AIR IN
                           Figure 2.2.   Typical  installation of FPD  S02  analyzer.

-------
2.3.2.1  Electrical Connections
     On the rear of each kind of FPD S02 analyzer will be a terminal strip
for electrical output connections to a recorder and/or data acquisition
system (DAS).   Connections to the screws on this terminal strip are best
made with no.  6 spade lugs (available from electrical supply houses) which
have been carefully connected to the signal cable.   The cable interconnect-
ing the analyzer to the recorder or DAS should be shielded twin lead wire
(commonly called control, instrumentation, or signal cable) and should be of
minimal length, less than 15 m (50 ft).   The shield portion of the cable
should be connected to the signal low at the analyzer and left unconnected
at the recorder or DAS end.   If the recorder or DAS is equipped with a
guarded input, refer to its manual for proper interconnection instructions.
     Special connectors or plugs may be required for connection to the
recording device.   Avoid any sort of wire splicing that involves twisting
wires together and wrapping with tape.  A continuous length of wire is
preferred.  If splicing is necessary, a good quality soldering job should be
done and the wire reinsulated.  The use of the mechanical compression con-
nectors, such as "sta-kons," is acceptable.
2.3.2.2  Pneumatic (Gas) Connections
     Any of the commercial FPD S02 analyzers will require connection of at
least three gas lines to the rear panel  of the analyzer.   These are the
ambient air sample line, the hydrogen fuel line, and the  exhaust gas line.
Be sure to follow the manufacturer's directions for use of tube connectors
and compression fittings so that a leak-free assembly is  obtained.
     Ambient air sample line and filter.   All manufacturers specify the use
of 3.2 mm (1/8 in.)  o.d. x 0.76 mm (0.030 in.) thick wall Teflon tubing.   A
roll of this should be available.  Be sure this tubing is clean and has not
been used previously.  Do not use copper, steel, polyethylene or other
plastics for sample tubing!   Tubing of uncertain cleanliness may be cleaned
by passing reagent grade methanol (methyl alcohol,  a poison) through it and
then drying the tube interior with clean, dry nitrogen or air.   Certain tube
connecting fitting (Swagelok , Parker-Hannifin®, Gyrolok®, etc.) may be
needed.   Use only Teflon fittings or all-glass connecting devices.
                                    24

-------
     The length of the sampling tube should not be excessive.  Usually a
length of 1.5 m (4 to 6 ft) is ample to reach the station sampling manifold.
Use this line for both sampling and calibration.
     It is recommended that an all-Teflon particulate filter be installed in
the instrument sampling line.  The filter should be a Teflon membrane with 5 u
or less pore size.  Its holder should be constructed from a solid piece of
Teflon or metal which is completely lined with Teflon.  A suggested model is
the Mace filter holder, series 930 (available from the Mace Corporation,
S. El Monte, CA 91733) used in conjunction with 5 u Teflon membrane filters,
catalog no. 425-0001 (see Figure 4.1).  Use of non-Teflon filters can de-
stroy the S02 sample and may cause pressure problems in the analyzer's
pneumatic system.  Consult the manufacturer for his specific recommenda-
tions.  The membrane filter should be replaced at the time of calibration,
or more often if the instrument is located in a particularly dirty environ-
ment.
     Exhaust gas line.  The instrument's exhaust line should be 6.3 mm (1/4
in.) or greater o.d. polyethylene tubing.  Since moisture may accumulate in
this line, be sure it is installed in such a way that drainage will always
occur.  In some older FPD models, the exhaust line is connected to an exter-
nal pump which has its own exhaust line.  Any exhaust lines should be of the
minimum length required to exhaust gases from the station.
     Hydrogen fuel  line.  It is recommended for safety reasons that connec-
tion of the hydrogen supply (from a compressed gas cylinder or an electro-
lytic hydrogen generator) to the analyzer be made only through clean, dry
stainless  steel tubing.  The tubing should be 3.2 mm (1/8 in.) o.d.  Use
stainless  steel fittings.  The hydrogen, if supplied from a cylinder, should
be of "prepurified" grade or an equivalent or better grade.   Percent purity
is 99.95 or better.
     The regulator used with the compressed hydrogen cylinder should be a
two-stage metal diaphragm brass regulator with a delivery pressure range
between 0 and 150 psig and should be equipped with CGA no. 350 cylinder
valve outlet.  This regulator must be free of sulfur-containing materials in
its construction.  Brass, stainless steel, and Kel-F or Teflon are suitable
materials for internal construction.  This regulator should be dedicated to
use with H2.  A shut-off valve should also be included.  A very important
                                     25

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safety consideration would be the installation of a flow-limiting orifice
near the regulator to limit the flow in case a leak or rupture occurs.  A
hydrogen regulator assembly is shown in Figure 2.3.
     Observe the following safety requirements in the handling and use of
hydrogen since it is an explosive material.
2.3.3  Guidelines for the Safe Use of Hydrogen Cylinders
     Hydrogen is a highly flammable gas which is colorless, odorless, and
tasteless.   It burns in air with a flame that is almost invisible.  Its
chemical formula is H2, its molecular weight is 2.016, and it is flammable
in the 4 to 75% (by volume) range in air.   A temperature of 585° C (1,085° F)
is required for auto-ignition in mixtures of air or oxygen at atmospheric
pressure.  A spark can of course cause ignition at ambient temperatures.
Electrical relays, contact closures, etc.  are causes of sparks.
     Precautions for handling and storing of hydrogen cylinders
     The major hazard associated with the handling of hydrogen is its flam-
mability.  Be certain to follow these rules when handling hydrogen cylin-
ders:
     1.   Never use cylinders of hydrogen in areas where flames, excessive
          heat, or sparks may occur.
     2.   Utilize only explosion-proof equipment, and spark-proof tools in
          areas where hydrogen is handled.
     3.   Ground all equipment and lines used with hydrogen.
     4.   Never use a flame to detect hydrogen leaks—use water or a
                                                        aj>fc
          commercial liquid leak detector such as "SNOOP ."
     5.   Do not store reserve stocks of hydrogen with cylinders containing
          oxygen or other highly oxidizing or combustible materials.
     Precautions for H9 cylinder use with FPD analyzers
     1.   Never move a hydrogen cylinder unless the regulator is removed
          and the cylinder cap is in position.   Use a cylinder cart and
          chain the tank to it.   Gloves and safety glasses or full face
          shield should be worn when moving tanks.
     2.   Do not expose the H2 tank to mechanical stress by dropping it
          to the ground or dropping it from truck tailgates.
                                    26

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       SHUTOFF
       VALVE
                                            NOTE THE INDENTIONS IN THESE FITTINGS -
                                            INDICATES "LEFT-HANDED" THREADS
COMPRESSION
FITTINGS
            FLOW LIMITING
              ORIFICE
                                                                                           CYLINDER VALVE
                                                                                           SAFETY NUT
                                                                                           (DO NOT REMOVE)
CLEAN 1/8" O.D.
STAINLESS STEEL
TUBING
TWO STAGE METAL
DIAPHRAGM
REGULATOR
CYLINDER
OUTLET CAP
                    CYLINDER VALVE
                    OUTLET CGA #350
                                                                                   •^—

                                                                                    \
                                                                                       HYDROGEN
                                                                                       CYLINDER
            Figure 2.3.   Hydrogen regulator assembly and CGA  cylinder connecter #350.

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3.    Locate the hydrogen cylinder in a well-ventilated area.   If this
     is inside a building, be sure the tank is separated from nearby
     oxygen- or air-containing tanks.   The H2 tank may also be located
     outside the building.  If outside, keep the tank protected from
     the weather, from sources of heat, flame, or sparks,  and separate
     from oxygen or air cylinders.
4.    Properly secure the hydrogen cylinder to a permanent  or semi-
     permanent structure (such as a railing attached to the wall  studs
     or to a laboratory benchtop) using a cylinder clamp with strap or
     chain.  Be certain to have the cylinder properly secured before
     removing the cylinder cap and attaching a regulator.
5.    The hydrogen cylinder and all  equipment and lines associated with
     it should be electrically grounded.   The three-wire grounding
     system of the analyzer grounds the analyzer and connections.
6.    Never open the tank output valve  or the regulator valve before
     connection is made to the analyzer.   Self-ignition (auto-ignition)
     of the escaping hydrogen may occur.   When the cylinder valve ^s
     open, open it all the way (counterclockwise) until  turning stops.
     Leakage may occur at intermediate positions.
7.    Connect the H2 cylinder to the fuel  entry port at the rear of the
     analyzer using only 3.2 mm (1/8 in.) o.d.  stainless steel lines.
     Leak test the lines only with  water or commercial leak check solu-
     tions such as "SNOOP ."  To pressurize the line for a leak test:
     (a) verify that all connections are made and are tight from the
     cylinder outlet to the rear of the analyzer (test by  snugging the
     fittings with wrenches); (b) be certain the analyzer  is off so
     that the H2-shut-off solenoid  is  closed, be certain the hydrogen
     regulator is closed (i.e., the pressure-adjusting knob or handle
     is rotated counterclockwise until it moves freely); (c) quickly
     open or "crack" the cylinder regulator's main valve,  watch the
     pressure rise in the gauge nearer the tank (the pressure in a new
     H2 tank at 21° C (70° F) is about 2,200 psig), and then immedi-
     ately close the cylinder valve.   If the gauge pressure decays as
     you watch, there is a leak in  the regulator's connection to the
     cylinder or a leak through the regulator.   If no leaks are indi-
                               28

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          cated, the pressure on the second gauge should be set to some
          point (say, 40 psig or the FPD analyzer's suggested setting).
          This will pressurize the line up to the instrument H2 shutoff
          solenoid.  Any major leaks will be indicated by a rapid decay of
          pressure in the regulator gauge.  Check for small leaks by apply-
          ing leak-detector solution around each connection and watching for
          small bubbles to form as the hydrogen escapes.
     8.    Never loosen or disconnect any hydrogen fitting or connector while
          the hydrogen is under pressure.  Always cut the hydrogen off at
          the tank and allow the system to "bleed" down to ambient pressure.
     9.    In the event a major leak occurs while the hydrogen is under pres-
          sure, turn off the cylinder valve if possible and leave the sta-
          tion.  Leave the door open for ventilation.   Cut off electrical
          power at the breaker box outside the station.
     10.  When connecting the regulator to the cylinder,  do not confuse the
          cylinder safety nut with the metal outlet cap which is frequently
          installed on the cylinder outlet.  The safety nut connects di-
          rectly to the valve inlet and once it is removed, the flow of gas
          cannot be stopped.  Refer to Figure 2.3.
2.3.4  Procedures and Safety Precautions for Use of Electrolytic
       Hydrogen Generators
     Electrochemical hydrogen generators produce hydrogen (H2) (and oxygen
(02)), by electrolysis of water.  As with any hydrogen supply, one must be
cautious in the use of the generator.   Become thoroughly familiar with the
manufacturer's operation and maintenance manual before using your hydrogen
generator.  Practice preventive maintenance.
     It is recommended that the hydrogen generator be dedicated to use with
the flame photometric detector and not shared with other analyzers.   If two
or more analyzers do share the same hydrogen generator,  be sure that ade-
quate pressure regulation and flow control is maintained to each analyzer.
     All hydrogen generators, of course, produce oxygen concurrently.  In
some generators the oxygen is vented and not used.  In others, the oxygen is
dried and stored (under pressure) for laboratory use.   The most trouble-free
                                    29

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operation for FPD analyzers has been found with generators intended for

hydrogen production only.
     Certain precautions must be observed for successful, long-term, and

safe use of hydrogen generators.  Important points are:

     1.    Do not defeat the grounding three-wire power cord.

     2.    Fill the solution reservoir of the generator only with

          the manufacturer's specified solution.
     4.

     5.
          Exercise caution not to overfill  the reservoir.   If
          it is overfilled, water may be forced through the
          hydrogen line to the instrument.   Follow the manufac-
          turer's instructions.
          Some generators use only deionized distilled water.   If
          water containing metallic impurities is used, the electro-
          chemical cell will  be damaged or contaminated.   Deionization
          of the water may be required in the generator reservoir.
          Keep deionization bags or cartridges fresh.
          Other generators use caustic solutions of sodium hydroxide,
          or acidic solutions.  Exercise care in handling these
          solutions.
Do not operate a hydrogen generator in a sealed or unvented room.

Do not use near open flames or other sources of ignition.
Never allow the 02 vent line to be obstructed.

Check the water or electrolytic solution level  often.   If the
level gets low, the generator will cut off.

When first turning on the generator, allow it to develop a normal
internal pressure before connecting to analyzers.

Change the desiccant cartridge often to maintain dry hydrogen gas.

Be careful to reseal the desiccant cartridge carefully so it is

leak-tight.   Do not apply pressure to plastic parts with wrenches

or other tools.  To do so may cause cracking or stress lines and
H2 leakage could result.

Minimize the volume of hydrogen stored in lines and desiccant

cartridges by minimizing the size of the line and the hydrogen
pressure.
                                    30

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2.4  STARTUP OF AN FPD S02 ANALYZER
2.4.1  Power On; Warmup Times
     With newer models of FPD S02 analyzers, only the main power  switch  (and
perhaps an electronics switch) needs to be turned on.  The air and fuel
ignite automatically in a preprogrammed sequence.  Since  hydrogen gas does
not flow to the analyzer until the power  is turned on (the safety solenoid
is closed in the power off mode), it may  take several attempts before the
flame lights.  Most analyzers have a front panel lamp which  indicates when
the flame is lighted.
     With older model analyzers,  it is necessary to  ignite the flame man-
ually by depressing a switch which activates a  "glow-plug" in the burner
chamber.  At times, it may be difficult to ignite the flame.  One procedure
to follow is this:  engage the flame-out  override feature; turn the hydrogen
flow rate almost off by adjusting the hydrogen  needle valve  or rotameter on
the instrument's front panel; depress the ignite switch;  slowly increase the
hydrogen flow while you continue  to activate the ignite switch; when a "pop"
is heard, or the ball of the hydrogen rotameter "bounces," release the
ignite  switch.  Complete this operation in 5 seconds or less.  Do not at-
tempt to start  ignition when any  flow of  hydrogen is present.  Rapid igni-
tion may damage the combustion chamber.   If the flame is  burning, the indi-
cator lamp will be unlighted and  the hydrogen rotameter will continue to
indicate flow.  Reset the rotameter ball  to the desired or preset position.
A  significant change in hydrogen  flow can alter the  calibration.
     Some older models of Meloy analyzers have  the following feature which
should  be noted:  a flame-out occurs (i.e., the H2 solenoid  closed) when the
analyzer response voltage became  negative.  New models have  a temperature
sensor  to detect an actual flame-out and  cause  the H2 solenoid to close.
Other early models lacked the hydrogen shut-off solenoid  feature.  If the
flame went out, H2 continued to flow.  For such analyzers, be sure to vent
the exhaust to  the outside of the station.
     A  certain  length of time will be required  for the hydrogen to purge the
air which may be present in the lines and give  a mixture  suitable for igni-
tion at the burner tip.  Other flame-out  problems may be  due to irregular  or
mismatched H2/air sample flows, water condensation in the burner  compart-
                                     31

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ment, or a damaged or corroded burner tip, or mis-adjusted cams on instru-
ments equipped with timers.   Refer to the manufacturer's instruction manual
for servicing and cleaning of burner compartments.
     Warmup times may vary from instrument to instrument.   It is a good idea
to allow 24 hours before beginning calibration.   A stable zero air or span
gas trace on a strip chart recorder is a useful  indicator of instrument
stability.
     Some analyzers have a flowmeter (rotameter) which indicates the flow of
sample air through the instrument.  Use this only for establishing or veri-
fying a flow rate.  Bypass this rotameter (by deactivating a solenoid valve)
during the time of calibration or ambient air sampling.
2.4.2  "Peaking Up" Response Prior to Calibration
     After the flame has burned for a few minutes,  the air flow and the
hydrogen flow should be adjusted to the manufacturer's recommended settings.
The hydrogen flow is generally set by use of a rotameter.   The sample air
flow may also be set with a rotameter.  This sample air rotameter should be
bypassed in normal operation.  A soap film flowmeter or mass flowmeter may
also be used to determine and set the sample flow rate.   Flow rates are
generally around 150-200 cmVmin.
     Certain early models of Bendix analyzers have a burner tip whose height
can be altered.  The tip is threaded and can be  moved up and down.   This
height is set at the factory. However, if the burner block is disassembled
and cleaned, it may be necessary to test the analyzer with the burner tip at
several different heights to optimize the signal.   Consult your Bendix
service representative for advice on the most efficient way to optimize the
signal.
     After the analyzer has warmed up, the operator proceeds to the calibra-
tion of the analyzer, described in Section 4.0 of this document.   Calibra-
tion devices to generate known S02 concentrations are described in Section
3.0.
     With new analyzers, the manufacturer supplies a "checkout sheet," which
gives the results of the manufacturer's calibration and electrical constants
for the particular analyzer.   This sheet should  be consulted during the
initial calibration procedure.   If your results  do not agree fairly closely
                                     32

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with the checkout sheet, the instrument may be damaged or improperly in-
stalled or your calibration and measurement system may be in error.
                                     33

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34

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                                 SECTION 3.0
            GENERATION OF S02 CALIBRATION STANDARDS AND ZERO AIR

3.1  INTRODUCTION
     The accuracy and validity of data derived from any air monitoring
instrument is dependent upon the type and extent of quality control prac-
tices and procedures.  Instrument calibration is the first element of data
quality control and is the key to comparison and utilization of data pro-
duced by federal, state, local, and private air sampling networks.
     Any monitoring instrument, such as the continuous FPD S02 analyzer, is
subject to drift and variation in internal parameters and will need periodic
calibration.
     The recommended method of calibration is a direct, dynamic calibration
utilizing the same pollutant species in the same air diluent as is being
monitored.  In the dynamic method, a known amount of pure or concentrated
gaseous pollutant is mixed with diluting air as the mixture is used.   A
dynamic calibration of ambient air analyzers should generally be a multiple
point calibration.  That a multipoint calibration be performed is especially
important in the case of the FPD, since its response is approximately propor-
tional to the second power of S02 concentration and the more points,  the
better the calibration curve can be established.  This calibration should be
performed at the site of the analyzer (i.e., "in the field").   Reliable,
portable equipment makes this possible.  Many FPD analyzers now have linear-
ized responses.  Multipoint calibration is still important since in this way
the operator will know that the linearization circuitry is properly ad-
justed.   Another way to determine linearity is by simulating S02 response
with a picoamp source.  Consult the manufacturer's literature for details.
     This section of the technical assistance document will discuss cali-
brator systems which may be used for generation of S02 gas standards for
                                     35

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calibration of FPD as well as other types of S02 analyzers.   The reproduci-
bility, reliability, and accuracy of any system depends heavily on four
aspects:   reliable, known, certified sources of S02 (preferably NBS certi-
fied or NBS traceable); stable and accurately known temperatures of S02
permeating devices; known flow rates of dilution air; a proper source of zero
or diluent air.
3.2  CLEAN AIR SOURCES FOR S02 CALIBRATION SYSTEMS
     A source of clean, dry, sulfur-free air is necessary for various uses
in all dynamic calibration systems.   With FPD S02 analyzers, it is obvious
that air, rather than nitrogen or some other inert gas, must be used since
otherwise the detector flame would be extinguished.   The nomenclature de-
scribing diluent air varies.  Zero air is the name used when the clean air
is sampled by the analyzer to allow the setting of the zero  concentration
signal output.  Diluent air is the name given to air used to dilute a stream
of air containing relatively high concentrations of S02.   Sweep air or purge
air  is the term used when clean air sweeps or purges the effluent from a
permeation tube or device.
     This air must have certain characteristics in order to  be employed in
calibration of FPD S02 analyzers.   Its water vapor content must be at levels
where condensation does not occur; it must possess the ambient percentage
(20.94) of oxygen found in air (since the flame of an FPD is sensitive to
the oxygen/nitrogen ratio); it must retain ambient concentration levels of
carbon dioxide, C02, (since the FPD has some degree of sensitivity to C02);
and of course it must be free of all sulfur-containing compounds.
     Since the same source of air is often used to prepare zero and cali-
bration gas for other pollutant monitors, removal of other pollutants is
another desirable feature.
3.2.1  Zero Air Generators
     Figure 3.1 shows the basic components and general specifications of a
zero air generator which will produce air suitable for use in calibration of
FPD S02 analyzers.14  Greater details on this system are given in the refer-
ence.  Such a system is suitable for 99 percent removal of nitric oxide, NO,
N02) S02, H2S, and other pollutant gases.  It allows C02 in  ambient air to
pass through unaffected.

                                    36

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        OUTDOOR AMBIENT
        AIR IN
                             (1) INERT SURFACES,
                               METAL OR
                               TEFLON.
                               PUMP SUCH
                               AS METAL
                               BELLOWS OR
                               DIAPHRAGM
                               PUMP
(DUV LAMP
(2) [03] a 0.3
  ppm AT 16
  6pm IN AIR
(3) INERT INTERNAL
  SURFACES
(4) LOW PRESSURE
  DROP, <10cm
  H20
(1) ACTIVATED CHARCOAL;
  6-12 MESH ACTIVATED
  COCONUT SHELL
  CHARCOAL
(2)TURBULENT FLOW
(3) LENGTH TO DIAMETER
  RATIO >5
(4) LOW PRESSURE DROP,
  <10 cm H20
(5) LONG SCRUBBING
  CAPACITY LIFETIME-
  40 HOURS OR
  LONGER WITH
  CONTINUOUS
  OPERATION
co
000
HPARTICULATELJ |_| DRYING LJ OX|D|ZER
FILTER
o
(1) LOW PRESSURE DROP,
<10 cm H20.
FILTER SUCH AS
15 MICRON BRASS
OR TEFLON
MATERIAL





"""" COLUMN 1 1
o
(1) INDICATING
SILICA GEL,
ACTIVATED,
3-8 MESH
(2) TURBULENT FLOW
(3) LENGTH TO
DIAMETER RATIO
>5
(4) LOW PRESSURE
DROP, <1 Ocm
H20
u — u
O
(1) INERT INTERNAL
SURFACES.
(2) LONG AIR RESI-
DENCE TIME
@16 £pm
(3)>98% REACTION
COMPLETION
(4) LOW PRESSURE
DROP, <10 cm
H20

S02 SCRUBBER
(ONE OR MORE)!



ZERO A
TO FLO!
CONTRC
ROT AMI
AND PEI
TION DE
COMPAR


                    Figure 3.1.   Zero air generator suitable for FPD  S02 zero  and calibration.

-------
     The oxidizer and reactor components are not required for zero gas
production for S02 analyzers; they are present to remove NO by reaction with
ozone and conversion to N02 which is removed by the charcoal.   Thus the
system may be used as a zero air source for calibration of NO  monitors.
                                                             /\
     There are many types of clean air supplies in use which process ambient
air.  Unfortunately, not all of them can be used to supply zero or diluent
air to any type of ambient air analyzer.   The definition of zero air has a
meaning not only in terms of the pollutant response of the analyzer, but
also in terms of the analyzer's interferent molecular responses.  For the
case of the FPD S02 analyzer, zero air must not contain sulfur compounds but
must contain ambient C02 levels.  For instance, it has been found that
heatless air dryer clean air systems are not suitable as calibration air
sources for the FPD analyzer.  This is because the heatless air dryer system
selectively retains C02 on the molecular sieve dryer column, and the back-
flush cycle prevents C02 from passing through the system.
     If the air supply requires drying, a Drierite (TM) or silica gel scrub-
ber is suggested.  These materials have been shown to pass C02 without
diminishment.  The Perma-Pure (TM) dryer is also an acceptable alternative.
     Any air supply which contains Ascarite, soda lime or other air scrub-
bers known to remove C02 cannot be used.   Regenerative molecular sieve
dryers cannot be used.   Activated alumina dryers or scrubbers  should also
not be used since alumina is partially selective in absorption of C02.
     If the C02 content of the air produced by the clean air system(s) in
your laboratory is unknown, it should be determined and compared to ambient
air concentrations determined simultaneously.
          Ambient air for the clean air system should be obtained
          from outside the station (the station's sampling manifold
          is a convenient source) not from within the station or
          laboratory since room air will have elevated concentra-
          tions of C02.   The C02 content of the air produced by the
          clean air supply should be determined and compared to the
          C02 content of ambient air.
     A gravimetric procedure for determination of C02 concentration in air
(by absorption of C02 on Ascarite) is given in Section 5.0 of this document.
Determinations done simultaneously on air from the calibration system and
                                    38

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from ambient air should match fairly well.  If the C02 content from the
calibration system is much lower than that of ambient air, the system should
be improved.
3.2.2  Compressed Air Cylinders
     Compressed air cylinders or other compressed air supplies are also used
to supply air for calibration purposes.   It is important that this air have
the following properties for use with FPD analyzers:
     a.   The same 02 and N2 percentage composition as ambient air (20.94%
          02, 78.08% N2).
     b.   A C02 content similar to that of ambient air, somewhere between
          300 and 350 ppm.  If the average C02 at a particular monitoring
          site is significantly greater than 350 ppm, then the cylinder
          should contain the higher level.  One way to specify this when
          ordering would be to order a specialty gas mixture of C02 (350
          ppm) in zero air.
If this air contains sulfur compounds and/or particulate matter, it must be
cleaned by passage through an activated charcoal scrubber system and/or a
particulate filter.
     For calibration systems based on dilution of high level cylinder con-
centrations of S02 in air or nitrogen, the presence of ambient concentra-
tions  of C02 within the S02 standard cylinder is not necessary if the sam-
ple: air dilution ratio is small (such as 1:500) and the diluent air is zero
air containing ambient concentrations of  C02.
     On the other hand, if low-level S02  in air cylinders are used for
calibration or audit checks, the cylinder should contain ambient levels of
C02 since the contents of the cylinder will be routed directly to the cali-
bration manifold with little or no dilution.
3.3  PERMEATION TUBES AND DEVICES CONTAINING LIQUEFIED S02:
     CHARACTERISTICS AND USE
3.3.1  Introduction
     A liquifiable gas, when enclosed in  an inert plastic tube (i.e.,
Teflon), escapes by permeating the wall at a constant, reproducible,
temperature-dependent rate.  The rate of  escape of gaseous S02 from a
                                     39

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permeation tube is determined gravimetrically.   The weight loss of the tube
is equated to the weight of the escaping material.   Further background
information concerning the theory, construction, and behavior of permeation
tubes or devices can be found in the literature.15'16'17'18'19
     Today, most S02 permeation tubes are purchased directly from suppliers
with the rate of permeation (stated in micrograms/minute or nanograms/minute)
pre-established.  For ambient air calibration work, a reliable source of
permeation tubes in the United States is the National Bureau of Standards
(NBS).  The NBS permeation tube is in fact a Standard Reference Material,
SRM.  If another supplier is employed, be sure to request a calibration
certificate which states that the tube's permeation rate is traceable to NBS
Standard Reference Material.
     Some calibrators may use only special permeation devices.  These are
not tubes but are wafers or cylinders.  Such devices should also be pur-
chased with certificates of traceability to NBS standards or be compared in
the laboratory to an NBS Standard Reference Material.
3.3.2  Description of NBS Permeation Tubes
     The National Bureau of Standards supplies three different size S02
permeation tubes.  A diagram of a tube is shown in Figure 3.2.  Each tube is
calibrated individually and is certified as a Standard Reference Material
(SRM).  They are:
          SRM No.        Size      Nominal Permeation Rate at 25° C
           1627           2 cm          0.56 micrograms/minute
           1626           5 cm          1.4  micrograms/minute
           1625          10 cm          2.8  micrograms/minute
     Figure 3.3  is a copy of the NBS Certificate for SRM No. 1626.  It lists
the method of calibration of the tube and gives use and storage information.
     Table 3.1 is a copy of a table which shows the relationship between
temperature and permeation rate for an actual NBS permeation tube.  The
table also gives an equation of the form log R = mt + b which can be used to
compute permeation rates at other temperatures within the range of certifi-
cation.  Caution!  This equation applies only to tube number 33-64.
                                     40

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                       TEFLON TUBE
\
'5mm
                       TEFLON PLUG


                    RETAINING COLLAR INDICATING
                    TUBE I.D. NUMBER "33-64"
                                                       LIQUEFIED SO2 GAS
                    RETAINING COLLAR
                    INDICATING TUBE
                    CONTENTS, "SO2"
               Figure 3.2.  National  Bureau  of  Standards  standard reference material
                                       S02 permeation  tube.

-------
    National  Bureau  of  Standards
                          Certificate
       Standard  Reference Material  1626
         Sulfur  Dioxide  Permeation Tube
                (Individually  Calibrated)
                       E. E. Hughes and W. P. Schmidt
  This Standard Reference Material consists of a 5 cm sulfur dioxide permeation tube, individually calibrated, for use in the
preparation of gases of known sulfur dioxide content. It is intended for standardization of apparatus and procedures used in air
pollution and related chemical analyses. Permeation rates for temperatures in the range of 20 to 30° C are given in the table ac-
companying each tube.

  The tabulated values result from determinations of the permeation rates for the specified tube, using the method described on
the reverse of this certificate. The uncertainty of the certified permeation rates, based on the results of the calibration of approx-
imately 25 tubes, is less than ± 0.5 percent at 25° C and does not exceed ± 1.0 percent at 20 and 30° C. respectively.

  Experiments in this laborabory have shown that the calibration remains valid as long as visible amounts of liquid sulfur diox-
ide remain in the tube.

  The calibration measurements were made by E. E. Hughes and W. P. Schmidt, Analytical Chemistry Division, NBS Institute
for Materials Research.

  The overall direction and coordination of the technical measurements leading for certification were performed under the chair-
manship of J. K. Taylor.

  The technical and support aspects involved in the preparation, certification, and issuance of this Standard Reference Material
were coordinated through the Office of Standard Reference Materials by T. W. Mears.
Washington, D. C. 20234                                           j. Pau| Cali( chief
August 12, 1971                                         Office of Standard Reference Materials
           Figure 3.3.   National Bureau of Standards  sulfur dioxide
                        permeation tube certificate
                                     42

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                                                  CALIBRATION

   This tube was individually calibrated by gravimetric determination of weight losses at 20, 25, and 30° C, respectively. The
tube was held at constant temperature for several days at each level, and the permeation rate was determined by weighing the
tubes at 24-hour intervals, using a micro-balance. The measured rates were fitted by the method of least squares to an equation of
the type log R  = mt  + b. The resulting equation, given on the table accompanying the tube, was used to calculate the values of
the permeation rates.

   The precision of calibration was estimated from measurements on approximately  25 tubes in this lot at each calibration
temperature. The uncertainties indicated are the approximate half width of the 95 percent confidence interval. It is believed that
the systematic errors concerned with the calibration are negligible.

                                                       USE

   This tube can be used to produce known concentrations of sulfur dioxide in a gas stream when both the temperature and flow
rate of the gas stream are known. Apparatus and techniques for this purpose are described in references [3] and [4] and should be
consulted for operational details. Because of the large temperature coefficient of the permeation rate, approximately 9 percent
per degree Celsius, the temperature must be maintained constant and measured accurately to 0.1° C to provide concentrations
consistent with the calibration uncertainty.

   It is recommended that the tube temperature be held constant during use and that desired concentration levels be achieved by
adjustment of the flow rate. If it is necessary to vary the concentration by changing the tube temperature, a suitable time interval
must be allowed for equilibrium of the permeation rate to be re-established. For changes of 1 or 2 degrees Celsius, a period of 3
hours should suffice. For changes of 10 degrees or when removed from low temperature storage, a period of 24 hours is advisable.

   This permeation tube is a stable and relatively rugged source of sulfur dioxide and no extreme measures are necessary to en-
sure that the  calibration of the tube will be maintained during its  useful life. However, it should be treated with the  care
necessary to assure the user that no change occurs in the character of the tube. Precautions should be exercised to prevent con-
tamination  of the outer surface during handling. The tube should be protected from high concentrations of water vapor during
storage and use. A relative humidity of 10 percent should have no effect on the permeation rate within the calibration uncertain-
ty.

                                                    STORAGE

   The useful  life of this certified sulfur dioxide permeation tube is about 9 months. Storage at lower temperatures will prolong
the life. However, it should be protected from moisture during  storage. On removal from low temperature storage, the tube
should be equilibrated  at the operating temperature for at least  24 hours, before use as an analytical standard.

                                                  PRECAUTION

   This permeation tube contains liquid sulfur dioxide at a pressure of about 4 atmospheres at room temperature. While no
failures have occured during use, there is the possibility of rupture due to internal pressure. However, it is believed that normal
handling of the tubes at temperatures up to and slightly exceeding 35° C does not constitute a hazard.

                                            SELECTED REFERENCES

[]] A. E. O'Keeffe and G. C. Ortman, Anal.  Chem. 38, 760 (1966).
[2] F. P. Scaringelli, S.  A. Frey, and B. E. Saltzman, Amer. Ind. Hyg. Assoc. J. 28, 260 (1967).
[3] Health Laboratory Science 7, No. 1, 4 (1970).
[4] F. P. Scaringelli, A. E. O'Keeffe, E. Rosenberg,  and J. P. Bell, Anal. Chem. 42, 871 (1970).
[5] J. K. Taylor, Ed.,  NBS Technical Note 545, December 1970.
                    Figure  3.3.    National  Bureau  of Standards  sulfur  dioxide
                                     permeation  tube  certificate  (con.)
                                                     43

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          Table 3.1.  Certified permeation  rates for  National  Bureau of
                         Standards permeation tube  No. 33-64.

             CERTIFIED PERMEATION RATES FOR TUBE  NO. 33- 64
                 TEMPERATURE C    PERMEATION RATE, SO2
                                      MICROGRAM/MIN
                     20.00                  .832
                     21.00                  .899
                     22.00                  .972
                     23.00                 1.050
CAUTION!               24.00                 1.135               CAUTION!
EXAMPLE               25.00                 1.227               EXAMPLE
 ONLY!                26.00                 1.326                 ONLY!
                     27.00                 1.433
                     28.00                 1.549
                     29.00                 1.674
                     30.00                 1.810
          THE PERMEATION RATE IS REPRESENTED BY THE EQUATION
                         LOG R = M(273.15+T)-B
      WHERE M = .033759, B = 9.97634 AND T IS TEMPERATURE IN DEGREES C
      THIS EQUATION MAY BE USED TO CALCULATE RATES AT INTERMEDIATE
      TEMPERATURES, NOT TABULATED, AND TO ESTIMATE VALUES AT
      TEMPERATURES NOT MORE THAN 2 DEGREES C. BEYOND THE RANGE OF THE
      TABLE. HOWEVER, THE TUBE IS NOT CERTIFIED FOR TEMPERATURES
      OUTSIDE THE RANGE GIVEN IN THE TABLE.

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3.4  CALIBRATION SYSTEMS BASED ON  PERMEATION  DEVICES:   DESCRIPTION
     AND EXPLANATION OF USE
3.4.1  Custom-built Laboratory Systems  Employing  Permeation Tubes
     Many S02 calibration  gas sources have  been custom-built  for laboratory
use.  Such systems generally employ  water baths for  temperature control and
glass condensers as permeation tube  holders.   Such systems are inconvenient
for use in the  field because of  their bulk  and fragility.  A  system suitable
for generation  of S02  atmospheres  (and  with minor modification, H2S and N02)
is shown  in  Figure 3.4.  A schematic of a  laboratory clean air supply is
shown in  Figure 3.5.   The  numbered components of  the system are discussed
below.
     The  system shown  in Figure  3.5  is  built  around  a "Forma  Temp Jr."
constant  temperature water circulating  bath (1),  which has an approximate 8
liter (2  gallon) capacity, controls  water temperature to ±0.1°C, by alternate
heating and  cooling, has a variable  temperature range of 15 to 35°C, and has
a  positive displacement type recirculating  pump (2)  with a 1  1/min liquid
flow rate.   The heating/cooling  portion of  the bath  is modified by adding a
proportional  temperature controller  No.  71  (3) and control dial manufactured
by RFL Industries, Boonton,  New  Jersey  07005.  The electronic components of
the controller  are somewhat temperature sensitive.   By mounting the con-
troller on a block of  aluminum through  which  water circulates, temperature
stability is achieved.  The water  returns to  the  bath through tube (4).  For
temperature  control at or  near 25° C, approximately  30 volts  is supplied to
the heater (5)  at all  times to "buck" the effect  of  the refrigerated cooler
(6) and cooler  coils (7) which are on at all  times.   The temperature con-
troller applies varying smaller  voltages in response to the platinum sensor
(8).  If  the need for  additional water  circulation in the tank is indicated,
a  motorized  stirrer (9) should be  added.
     Water from the constant temperature bath flows  through rubber tubing to
one or more  water-jacketed,  large-bore  glass  condensers (10).  The glass
condensers are  at a constant temperature and  keep the airstream moving
through them at a constant temperature  too.  Keep the length  of tubing used
to supply water to a minimum. The  straight  condenser (Liebig  or West type)
houses the permeation  tube (11)  and  the glass thermometer  (12).  The ther-
mometer gives the temperature of the air and  the  permeation tube.  An NBS

                                     45

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SWEEP AIR FROM
CLEAN AIR
SUPPLY
                                                                                  CALIBRATION MANIFOLD

                                                                                                  VENT
                                                                                                 SAMPLING LINE
                                                                                                 TO ANALYZER
                                                        1 LITER VOLUME
                                                        MIXING BULB
  Components are described by number in the text.
                 Figure  3.4.   Example of custom-made laboratory permeation tube assembly
                                      for calibration of S02  analyzers.

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    Catalytic
    Converter

Iron-Constantan
        Sensor
  Heater
         \
    Temperature
      Readout
                                                                 Proportional
                                                                 Temperature
                                                                •Controller
                                                                 (Temp. Set for
                                                                 315° C; 600° F)
              Vent (Avoids Pressure Buildup
           "" if Valves are Closed Downstream)

           Critical Orifice
           200 ml/min
           Air Bleed
                                                                                               ShutofT
                                                                                               Valve
                                                      Pressure
                                                      Regulator
Pressure
Gauge
                                       Drierite


                                    • Purafil
                  o
                                                                                           Shutoff
                                                                                           Valve
                                                         Permapure.
                                                         Dryer
 Pressure
* Regulator
                                                  Two Stage
                                                  Pressure
                                                  Regulator
                                                           Oil-less
                                                       Compressor •
                                                           Pump
        Canister of Activated
        Charcoal and Filter
                                           f
                                       Mass Flow
                                       Controller
           ->- Air
             Out for
             Zero or
            Dilution
                                                                                                       T
                                                                                                       Ambient
                                                                                                       Air In
                                                            Air Out to
                                                            Permeation
                                                            Tube System
                                 Figure  3.5.    Laboratory clean  air  supply.

                                                         47

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certified thermometer or one traceable to NBS standards should be employed.
A useful thermometer is one having a range of 24 to 25° C in 0.005° C divi-
sions, since many commercial as well as NBS S02 permeation tubes are cer-
tified and used over the range 20-30°C.  The all glass thermometer may be
placed in the same compartment as the permeation tube.  The water flows- from
the condenser to a sealed glass cylinder (13).   Attached to the cylinder is
a stainless steel thermocouple well (14) and, within the well, a platinum
sensor (8).  Water leaves the glass cylinder, goes through an aluminum block
beneath the temperature controller, and then returns to the bath.
     Air from the laboratory clean air supply enters the bath through a
length of 6.3 mm (1/4 in.) o.d. copper tubing (15).   Approximately I meter
(3 feet) of the tubing is coiled and submerged beneath the water of the
bath.  The coil serves as a heat exchange element to bring the flushing or
carrier air to nearly the same temperature as the permeation tube.   Appro-
priate fittings connect the copper tube to the clean air supply and to a
precision needle valve (16).  The needle valve connects to a precision
rotameter (17) having a flow range between zero and 500 cc/minute.   The air
then enters one end of the water jacketed condenser.  The condenser has been
modified so that the air will be at the temperature of the permeation tube
when it enters the permeation tube compartment.   This modification (18)
consists of a short length of 0.25 inch o.d.  glass tube attached to a 3 inch
length of coiled 3.2 mm (1/8 in.) o.d. glass tubing.  All of the coiled
glass is surrounded by water.  The air then flows across the permeation tube
and exits the condenser via either a standard taper ground glass connector
(19) or a ball and socket joint.  Connected to the glass fitting is a length
of 6.3 mm (1/4 in.) o.d. corrugated or conventional, straight-walled Teflon
tubing (20).  Air containing S02 flows through this tubing to a mixing flask
at which point it combines with diluent air to produce the desired low
concentration of S02.
     All of the water and air lines associated with this system are wrapped
in sponge rubber insulation (21) to maintain temperature stability.  The
glass condensers are also wrapped in sponge rubber.
     Flow across the permeation tube is adjusted to approximately 200
cc/min.   Flow is maintained at all times unless the tube is removed.
                                    48

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     Attention should be given to the  air  supply  used with the  laboratory
system.   Ambient levels of 02 (20.94%)  and C02  (-350 ppm) should be present
in both the flushing or carrier  air and the  diluent or zero air.  The air
supply system shown in Figure 3.5 is designed to  run continuously.  The
source of air should be "outside" ambient  air to  ensure that 02 and C02
levels in the calibration gas are equivalent to those levels in the actual
"outside" sample air.
3.4.2  Commercial Systems Employing Permeation Tubes or Devices
     Many brands and types of S02-producing  "calibrators" are available
commercially.  All of them depend on control of the temperature of the
permeation tube or device and control  of the flow of air across the tube and
the flow of diluent air in order to produce  a known final concentration of
S02 in air within the calibration manifold.  Figure 3.6 is a schematic of
the components of a typical  calibrator intended for S02 production only.
Figure 3.7 is a schematic of a more elaborate calibrator system intended for
multi-pollutant calibration  work.  Refer to  Section 3.2 for further dis-
cussion of zero air supplies for calibrators intended for use with FPD S02
analyzers.
     The temperature of the  permeation tube  or  device is set and controlled
in one of several ways.  Some systems  employ a  small recirculating water
bath.  Many systems have a thermostatted "air bath" in which the permeation
device holder is mounted.  Others employ heated metal blocks.  Whatever the
system, it is important that the temperature be known and controllable to
±0,1° C since the permeation rate of a tube  or  device is extremely sensitive
to temperature (see Table 3.2).
     The flow of air across  the  permeation device as well as the flow of
diluent air is regulated in  one  or more of several ways.  The simplest
systems have a rotameter and an  adjustable needle valve to set and control
the air flows.  Such rotameters  must be calibrated and checked frequently.
A rotameter should be calibrated "in-line,"  that  is, while it is an in-
stalled part of the system,  and  not separate from the calibration system.
Do not rely solely on a "calibration curve"  for the rotameter.  Use a soap
film flowmeter or wet test meter to check  flows.  More sophisticated systems
employ critical orifices or  long lengths of  stainless steel capillary tubing
                                     49

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                                                       SAMPLE LINE
                                                       TO ANALYZER
;

•


(
\
IV
ROTAMETER F
MIXING
FLASK
en
o
   CAPILLARY
   RESTRICTOR'
                                                       PRESSURE
                                                       REGULATOR
                                                                            CALIBRATION MANIFOLD
                                                                            AND SAMPLE OUTLETS

                                                                             VENT
                                                                      HEATED PERMEATION
                                                                      CHAMBER
                                                                          PRESSURE
                                                                           RELIEF
                                                                           VALVE
                                                                                                   s AMBIENT
                                                                                                   \AIRINLET
                                                                                 PISTON COMPRESSOR PUMP.
                                                                                 OIL-LESS, TEFLON-LINED
                                           FILTER CONTAINING
                                           ACTIVATED CHARCOAL
                                           ANDPARTICULATE
                                           SCRUBBER
                            NEEDLE
                            VALVE
                                                                             •EXCESS WATER DRAIN

          Figure 3.6.   Schematic  diagram of a portable  S02 calibrator with  internal air  supply.

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                                          Chamber Air

                                          Scrubber
                                                                      Permeation

                                                                      Tube Holder
                                                                              Manifold

                                                                            Connection
   Air Supply

   Inlet
C7I
                UOOL
                oooc
                oooc
                oooc
                oooc
                oooc
                oooc
                oooc
                oooc
                oooc
                oooc
                oooc
                oooc
                oooc
                                                        3-Way

                                                        Valve
                                                               Instrument

                                                                 Outlet
                      3-Way

                      Teflon

                      Solenoid

                      Valve
     Chamber

     Rotameter

     & Control
Permeation Oven
Chamber

 Vent
                              #1 Dilution

                               Rotameter

                               & Control
          3-Way

          Teflon

          Solenoid

          Valve
#2 Dilution

 Rotameter

 & Control
                         ooou
                         oooo
                         oooo
                         oooo
                         oooo
                         ooo~
                         oooo
                         oooo
                         oooo
                         oooc
                         oooc
                         oooc
                         oooc
                         oooc
                                                                                                                     3-Way

                                                                                                                     Valve
Overflow Vent

to Outside
                        Dilution

                        Scrubber
                       Figure 3.7.   Schematic diagram of multipoTlutant calibrator.   (Adapted  from

                                      Metronics Association,  Inc.   "Dynacalibrator").

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to control  air flow.   Oftentimes regulators and pressure dials are present
so that flow can be re-established by "dialing in" a certain pressure on the
capillary tube or a network of tubes.   Even with these systems, calibration
and frequent checks of air flow versus pressure setting are necessary.  Some
calibrators have mass flow controllers which can be set to deliver pre-
determined mass flows of air.   Since mass flowmeters are not infallible,
they too must be calibrated or verified and rechecked periodically.  Mass
flowmeters often exhibit a temperature sensitivity; thus it is important
to operate them at controlled, reproducible temperatures.
     All flow measurements taken must be corrected to standard conditions of
pressure and temperature:   760 mm Hg and 25°C for air pollution work.   If a
soap film flowmeter or wet test meter is used, do not neglect to correct for
the effect of water vapor (explained in Section 5, Procedural Aids) since
the calibration air is usually quite dry and picks up water vapor while a
flow is being established.
     The following features are recommended for consideration in a commer-
cial S02 "calibrator" which employs a permeation tube or device.
1.   The presence of a means for temperature control  and verification.  Some
     "calibrators" have a fixed, unchangeable temperature.   If temperature
     can be varied, a thumbwheel or digital  system for accurately setting
     and resetting temperatures should be present.   A device (such as  flash-
     ing light or meter/needles) should be present to indicate when the
     desired temperature has been attained or when the desired temperature
     is not present.   Attainment of the temperature of course does not mean
     that the permeation tube or device has also attained equilibrium.
     Generally, an additional  24 to 48 hours should be allowed for permea-
     tion tube equilibrium.
     Ideally, an accurate thermometer or thermistor should be embedded in
     the permeation tube compartment so that any temperature variations can
     be read directly.   This thermometer or thermistor should be installed
     in such a way that upon removal and replacement, it is seated in  ex-
     actly the same geometrical configuration.   In other words, it should be
     impossible for the operator to re-install  the thermometer or thermistor
     in any way except the correct way.   If a temperature sensing device is
     not included, the calibrator should have some way to allow the operator

                                    52

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     to reproducibly place a temperature measuring device  in the vicinity of
     the permeation device.
2.    The permeation tube or device  should be easily  inserted and removed.
     Connections to the permeation  tube holder  should be leak-tight and
     easily retightened and repositioned.  All  lines downstream of the
     permeation tube oven should be of Teflon or glass construction.
3.    Air flow controllers and  indicators should be of the  highest quality
     and be capable of being set reproducibly.  For  instance, pressure
     gauges should have accurately  divided fine graduations and rotameters
     should be of sufficient length (12 inches  preferred)  to give good
     resolution in reading.
4.    For field use in calibration of  ambient air monitors, the "portability
     option" is highly recommended.   This option permits a car battery to
     supply power to the "calibrator" to keep the oven warm and equilibrated
     and to run a small pump to allow continuous passage of air over the
     permeation tube or device.  If such an option is not  used, it is neces-
     sary to either remove the permeation tube  or purge the system for some
     time before use since the high concentrations of S02  which have built
     up will be released slowly from  Teflon components.  It is also, of
     course, necessary to re-equilibrate the permeation tube or device at
     the desired temperature.  While  the permeation  tube or device is warm-
     ing up (equilibrating), a flow of air should pass over the tube or
     device.
5.   For field use, an internal source of air is desirable.  Usually a small
     diaphragm or bellows pump is employed.  This does away with the neces-
     sity of providing an external  air source and gives a  reproducible
     source of air from site to site.  Certain  precautions must be taken
     when using such an air supply.   Necessary  scrubbers and filters must be
     changed periodically.  The 02  and C02 content of the  air produced must
     be characterized and be maintained near the values for ambient air.
     Provisions must be included for  drying the air  and venting any excess
     moisture buildup caused by compression of  air by the  pump.  The flow of
     air from such internal sources must be stable.  The best systems employ
     differential pressure regulators.  Such regulators can give very stable
                                     53

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     flow and can be used with internal  air supplies or external air sup-
     plies such as compressed air cylinders.
6.    Since the "calibrator" is often used as  a source of zero air, it is
     recommended that some sort of zero  air by-pass loop be present.   In
     this way the permeation tube compartment is either by-passed or its
     effluent is flushed.
7.    The possibility for use of an NBS Standard Reference Material permea-
     tion tube in the calibrator should  be considered.   Not all calibrators
     offer this feature since other permeation tubes or devices are either
     of smaller dimensions than NBS tubes or  operate at higher temperatures
     than those specified for NBS tubes.   If  your calibrator does not have
     this feature, it is recommended that a line of traceability of your
     system to another system which does use  an NBS tube be established.
     Also, permeation tubes or devices may be purchased which are traceable
     to NBS Standard Reference Materials.
8.    The possible range of S02 concentrations and the range of air flows
     desired is also a consideration.   Various S02 analyzers require differ-
     ent sample flow rates.
3.4.3  Explanation of Use of Permeation  Device Calibration Systems
     The instructions listed below can be applied to most permeation device
type calibration systems for S02.  Use the operation manual for your par-
ticular calibrator in conjunction with these  instructions and explanations.
1.    Unpack and inspect the calibrator.   Always perform an inspection if the
     calibrator has been shipped to a new location.   Inspect the apparatus
     (especially the flowmeters and needle valves) for shipping damage.
     Look inside the case for evidence of broken or loose mixing tees or
     bulbs, loose electronic boards, etc.
2.    Make electrical connections.  First, be  sure that all power switches
     are in the "off" position or "stand by"  position.   Connect the power
     switch to a 115V AC socket using a  grounded 3-prong plug.   Turn the
     main power switch to "on" and check the  following:   internal air supply
     pump is on; the fan for air circulation  is on and the fan blades spin
     freely; the heater for the permeation tube bath or oven is on.  This
     should be indicated by a temperature light or dial.  Turn off the main
     power.
                                    54

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3-    Connect the air supply to  the  calibrator.   If  the calibrator has  its
     own internal zero air supply,  connect  the  inlet  of  the air supply pump
     to the station sampling  manifold  so  that ambient air  is treated by the
     cleanup system.  If  a separate air supply  system is used, connect its
     inlet to an outdoor  ambient air source.  Do not  use room air since rt
     will nave a high C02 concentration.  See Sections 3.2 and 3.6.3 for
     discussion of  zero  air  supplies  and  the  C02  interference effect.
4.   Install the permeation  tube  or permeation  device.  Your commercial
     calibrator unit's operations manual  will list  the sizes and types of
     permeation devices  which  may be  used.  Before  unpacking the permeation
     tube or device,  have  the  calibrator  and  the  clean air supply on and
     have a flow of air  (about 100 cc/min or  greater) passing through the
     permeation tube  holder.   Under dust-free and oil-free conditions,
     remove the permeation device from its shipping container in a venti-
     lated area, preferably  a  fume hood.   Immediately transfer the tube to
     the permeation holder of  your calibrator and seal it in.  If the per-
     meation device has  been stored under refrigeration, allow at least 24
     hours equilibration time  in  the  case of  NBS  tubes and longer times with
     other devices.   Note  that some manufacturers do not recommend storage
     of permeation  devices at  low temperature.
      It  is  most important to properly seal  the permeation  holder.  If "0"
      rings  or other sealing devices are used,  be careful not  to misalign
      them.   Threaded Teflon parts must be tightened carefully to avoid
      leaks.   Avoid stripping the threads.   Teflon tape  may be used to insure
      a good seal.   Even a small  leak in the permeation  tube compartment will
      cause  a dramatic change in  concentration  output since relatively high
      concentrations of S02 are present prior to dilution.   Place the permea-
      tion tube (or tubes) in the holder in such a way that the tube does not
      obstruct entry or exit of sweep air.
 5.    Allow  sufficient warmup time for oven and permeation  device.  Install
      the permeation device in its holder,  set  the temperature controller to
      the point recommended or desired for use  with the  permeation device,
      and allow the oven to warmup at least  12-14 hours; 24 hours is better.
      Allow  the permeation tube or device to equilibrate 24 to 72 hours
                                     55

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     depending on initial  conditions and type of device.   Maintain a flow of
     clean air through the permeation chamber during this time.  Consult the
     manufacturer's literature for specific recommendations.   Once the oven
     and permeation tube are equilibrated it is recommended that the system
     remain "on"  or in "standby"  and that air be flushed across the permea-
     tion device  continuously.
     The actual  temperature of the operating permeation tube must be known
     with certainty.   The calibrator should be equipped with an accurate
     (preferably  NBS - traceable) temperature indicator of some kind - a
     thermometer, thermocouple or thermistor.   Thermistors or thermocouples
     may be purchased and installed in most calibrators.   Such devices may
     be purchased from Omega Engineering, Inc., Stamford, Conn. , 06907.
6.   Set and verify flows.  The calibrator will have a needle valve or
     pressure regulator or perhaps a mass flow controller to control  the
     diluent air flow.  With rotameters, the position of the ball  indicates
     the flow.  By convention, scale readings are usually taken at the
     center of the ball.  If your calibrator employs rotameters, a calibra-
     tion curve will be provided by the manufacturer.   This curve  should
     have been established under or related to the normal conditions  of
     25° C and 760 mm Hg.
     When used to measure air flow rates, the main variable in rotameters is
     density.  Assuming that the air is dry after passage through  the filter
     and scrubber assembly, it is only necessary to correct the indicated
     flow for temperature and pressure effects.
     At an altitude of 1.5 km (5000 ft), a rotameter will read about  9% low
     as compared to sea level.  A reading at 25° C instead of 0° C will
     cause the rotameter to read 5% low.  Because the effects depend  on a
     variety of factors, it is recommended that for precise work you  prepare
     your own calibration curve.   Use displacement techniques (soap film
     flowmeter, wet test meter, etc.) and correct for the effect of water
     vapor.  These same techniques should be used to verify the flow rate on
     mass flowmeters and pressure regulator-orifice systems.
7-   Interface the calibration system with the FPD SO? analyzer.  Disconnect
     the FPD analyzer's Teflon ambient air sampling line from the  station

                                    56

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     ambient air sampling manifold and connect it to the calibration sys-
     tem's manifold.  Be certain to supply excess sample flow through the
     calibration manifold to prevent dilution of the calibration gas by room
     air.   About 500 cc/min excess (0.5 liters/rain) is suggested as a mini-
     mum.   Thus, if the instrument's sample flow rate is 250 cc/min, the
     overall flow from the calibrator should be at least 0.75 to 1.0
     liter/min.  Use only cleaned Teflon or glass materials to construct the
     calibration manifold.  All excess calibration gas should be vented.
     Refer to Figures 3.6 and 3.7.
8-    Provide zero air to the analyzer.  By having the diluent air bypass the
     permeation tube compartment or by venting the permeation compartment
     contents, zero air is supplied to the analyzer.   Allow sufficient time
     for a stable zero trace to be established.  Set the analyzer to the
     desired zero point (refer to Section 4).
9.    Provide span gas and intermediate concentrations of S02 to the
     analyzer. By adjusting the total flow (usually only the diluent air)
     different concentrations of S02 can be generated.  The concentration of
     S02 at various flow rates can be computed from equations given in Sec-
     tion 3.4.4.  Remember that the flows should be checked by displacement
     methods (soap  film flowmeter or wet test meter) from time to time.
     Rotameters, pressure gauges, and mass flowmeters are subject to error
     and variation  and need periodic verification.  Also check the flow at
     the output of  the calibration manifold to detect possible leaks in the
     calibration system.
     Always remember that S02 is a hazardous pollutant.  Do not expose
     yourself to the calibration gas; do provide a wel1-ventilated work
     environment.   All excess calibration gas should be vented.  This may be
     done by connecting the calibration manifold to the station sampling
     manifold exhaust.  Use large diameter tubing; avoid high vacuum ex-
     hausts.
10.  Shutdown and maintenance.  If the calibrator is shut down for any
     length of time, the permeation tube or device should be removed and
     stored in a desiccated container.  The main areas for maintenance of
     calibrators are:  replacement of scrubber materials (such as silica gel
                                     57

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     and activated charcoal) on a time-of-use basis; cleanliness of valves
     and rotameters; verification of correct operation of heaters and
     temperature sensors; verification of correctness of flow and temper-
     ature measuring devices.
3.4.4  Computation of S02 Concentrations From Permeation Tubes
     The output of a permeation tube or device is converted to concentration
in parts per million (ppm) using the following equation:

          r =      (R) (MV)
                   (F) (MW)
where:     C =  Concentration in ppm by volume at 25° C and 1 atmosphere
               (760 mm Hg)
          R =  Permeation rate, micrograms/minute (pg/min)
         MV =  Molar volume (24.45 liters at standard conditions of 25° C
               and 760 mm Hg)
          F =  Total flow rate of air (purge air plus diluent air),
               liters/minute (at standard conditions of 25°  C and 760 mm Hg)
         MW =  Molecular weight of the permeating gas (MW S02 = 64).
     Example Calculation A - What is the ppm output of NBS permeation tube
     33-64 (see Table 3.1) under the following calibration conditions?
          Permeation tube oven temperature:   22.5° C
          Purge air flow rate  by soap film flow rate measurement:   180
          cc/min
          Dilution air flow rate by soap film flowmeter measurement:   4500
          cc/min
          Room air temperature:   28.0° C
          Barometric pressure:   750 mm Hg
     Step 1:   determine the permeation rate,  R,  at 22.5°  C using the  equation
     given in Table 3.1.
          LOG R = M(273.15 + t) - B
          LOG R = 0.033759 (273.15 + 22.5) -  9.97634
          LOG R = 0.004508
     From a table of five-place common logarithms:
          ANTILOG of 0.004508  = 1.010 micrograms/minute = R
                                    58

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Step 2:  determine the total  air flow and correct it to the conditions
25° C and  760  mm Hg.

     Total  air flow = 180 + 4500 = 4680 cc/min

                                  = 4.680 liters/minute
Apply this equation to convert the measured flow to the standard  con-

ditions  of 25° C and  760 mm Hg pressure (refer to section  5.0  for an
example):

                                   298.15
where:

      FS =  Flow rate at standard conditions  in liters/minute

      F  =  Measured total  flow rate of air carrying  S02  from the
           calibrator,  liters/minute

      P  =  Barometric pressure in mm Hg (inches  of mercury may also
           be  used provided 29.92 inches of  mercury  is used in the
           denominator, replacing 760 mm Hg)

      P1 =  Vapor pressure  of water,  mm Hg (or  inches Hg  if P is
           measured in inches Hg) at temperature t (refer to table
           in  section 5 or to a handbook of  tables).  This correction
           is  made only when a soap film flowmeter or wet test meter
           is  employed.  Assuming the relative humidity  of the metered
           air is 100%, this corrects for the  vapor pressure of water.
      t  =  Temperature of  the calibration air  in degrees C (or the room
           air temperature of the laboratory).
Thus:
                            750 - 28.35         298.15
              =   4.680   x
           F  =   4.400  liters/minute
          C  =
                 (F)  (MW)

                 (1.010)(24.45)   _    (1.010 ug/min)(24.45 ul/umole)
                  (4.400)(64)           (4.400  l/min)(64
          C  =  0.088 (Jl/l   or  0.088 ppm

Example Calculation B - What is the concentration of S02 expressed as

micrograms/standard cubic meter (|jg/sm3) at the conditions given in

Example Calculation A?

                                59

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     Use this  equation:    Cm  =  R_  x  1000

     where:
               C   =  Concentration,  jjg/sm3

     Thus:
               c   =    1.010 Hfl/mlnute       1000 v  3  =  229.5
                m     4.400 liters/minute
               Cm  =  229.5 |jg/sm3
     Or, since 1 ppm S02 = 2615 ug/m3 at normal  temperature and pressure
     (25° C, 760 mm Hg), then:
               0.088 ppm x 2615 ug/m3 = 230  ug/m3
3.5  CALIBRATION BY USE OF COMPRESSED GAS CYLINDERS CONTAINING S02 IN
     NITROGEN OR AIR
3.5.1  General
     At present, the permeation tube  is the  most reliable and accurate
source of S02 calibration gas.   However, recent  advances in compressed gas
technology have made available special treated cylinders of S02 in air or
nitrogen at high (50-500 ppm) or low  (<1-10  ppm) concentrations.   For ex-
ample, the National Bureau of Standards has  produced four primary standard
S02 in N2 mixtures intended for use in the calibration of instruments used
in the analysis of sulfur dioxide in  stack gases.   These mixtures have been
shown to be stable for long periods of time  (certified for one year) when
packaged in treated aluminum cylinders.  Because the NBS Standard Reference
Materials mentioned above are at high concentration levels (480 to 2521 ppm)
and are diluted by nitrogen instead of air,  they are not useful for cali-
bration of ambient air FPD analyzers.  NBS is, however, studying the sta-
bility of cylinders containing lower  (50 ppm or  less) concentrations of S02
in air.  This study may result in a new Standard Reference Material.
     Today, several specialty gas producers  supply mixtures of S02 in air at
concentrations ranging down to ambient levels.  The higher level mixtures
(100 ppm) have been found to be quite stable,20'21 and can be diluted with
                                    60

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clean air to ambient  levels  for use.   Cylinders of 10 ppm  (or  less) S02 in
air have also exhibited  temperature and pressure stability with  no appre-
ciable decay in mixture  concentration in one study.20  However,  recent field
use of similar mixtures  has  revealed that low levels  of S02  in air (usually
below 50 ppm) in cylinders are  not always stable and  tend  to decay in a
short period of time.22   This decay is illustrated in Figure 3.8.
     Due to such concentration  uncertainties,  cylinders containing very low,
ambient level S02  concentrations in air (i.e.,  less than 50 ppm) are not
recommended for general  calibration use at this time.   They are  useful for
audits if standardized prior to and after field use and an accounting is
made of any  decay in concentration.   The higher concentration S02 in air
cylinders (50-100  ppm and greater) are useful  for calibrations and audits
and a list of good practices and procedures for their use  is given below.
It is recommended  that the cylinder's concentration be  established by com-
parison to an NBS  S02 permeation tube system (i.e., establish traceability).
3.5.2  Equipment Specifications and Use
     SO 9 Cylinder.  At the present time,  the most stable mixtures of S02 in
air or nitrogen have  been prepared in treated  aluminum  cylinders.  Conven-
tional steel cylinders are not  acceptable.   CGA valve outlets vary.   NBS
treated aluminum cylinders have CGA 350 outlets;  other  tanks have CGA 330 or
660 valve outlets.
     Cylinders may be shipped and stored in the same  way as any  other which
contains a toxic gas.  If the cylinder has been shipped or stored under
temperature conditions very  much different from those inside the laboratory
or air monitoring  station where it will  be used,  an equilibration step is
required.  The cylinder  is placed in the laboratory or  station at least 24
to 48 hours prior  to  use.  It is a good idea to let the cylinder, the at-
tached regulator,  and any dilution assemblies  equilibrate  in the sampling
station at least overnight,  under even the best of conditions.
     Regulator for SO, Cylinder.   The regulator should  be  a high purity,
corrosion-resistant,  stainless  steel  model  with the correct CGA  fitting.
Further specifications are:
          Diaphragm constructed of type 316 stainless steel or other non-
          corroding metal; seals and seats of Teflon  or Kel-F.
                                     61

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en
ro
    oc
    o
    CJ

     CM
    o
    00
        10 -
                                                                      2 = -1.9 D + 82.1

                                                                      r =-0.9903
                                           10
12
14
16
18
                                                                            20
                                 22
                                 24
                                 26
                                 28
                                                                                                            30
                                                                 32
                                                       DAY (D)


                          Figure 3.8.  Concentration of  SOa versus time.   Low-level  S02 in air;
                                                treated aluminum cylinder.22

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          Two stage regulator preferred over one  stage.
          Pressure gauges should be as small as possible with ranges of 0 to
          3000 and -30 to 100 psig.
          Regulator should be equipped with a purge assembly option.  The
          diaphragm of the regulator should be fully supported to permit
          evacuation of the regulator without damage to the diaphragm.
     Examples of acceptable regulators include Matheson's Series 3800 two
stage stainless steel regulator, Airco's Model 52 and Model 57 series,  and
Linde's Model UP-G.  Other manufacturers offer similar equipment.  This
regulator should be dedicated for  use only with S02 mixtures.  Furthermore,
an individual regulator should be  used only with  cylinders of approximately
the same concentrations.  For example, a regulator used to deliver 100 ppm
concentrations should not be used  to deliver much higher levels (such as
2500 ppm).  To do so may cause a buildup of S02 on internal regulator parts
which would require lengthy purging prior to re-use with lower concentration
cylinders.
     Dilution Assembly and Clean Air Source.  Many commercial units are
available which can dilute a small flow of S02 with clean air.   A system may
also be built.  Such systems may employ limiting  orifices or capillary
networks to achieve a steady, low  flow of S02.  Passage of S02  mixtures
through a rotameter is not recommended because S02 may be removed on its
surfaces.
     The air supplied to the dilution assembly should be regulated so that a
series of known flow rates can be  obtained.  This is accomplished with
needle valves, critical orifices,  capillary tubes, or a mass flow con-
troller.  Clean air supplied to a  flame photometric detector should contain
ambient levels of C02.
     The flow rates of both the S02 and the clean air should be determined
with a calibrated soap film flowmeter or other calibrated meter.   The final
concentration is established based on the corrected flow rates.
     Assembly of Components.  Figure 3.9 shows a  suggested layout for
assembly of the cylinder, clean air supply, mixing devices and manifold.
The arrangement is quite similar to that employed in permeation tube sys-
tems.
                                     63

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cr>
 Cylinder
Containing
 100 ppm
    or
 Greater
 S02  in
   Air
                                              Stainless Steel, High Purity
                                              Corrosion Resistant Regulator


                                              Stainless Steel Regulator Outlet
                                              i Valve (metal bellows toggle valve
                                              with Teflon seat recommended)

                                                     Precision Regulator
                                                     for Critical Pressure
                                                     Adjustment
                                                           Short Length of Teflon
                                                           or Stainless Steel Tubing
                                                                Regulated Flow Clean
                                                                Air Supply and/or
                                                                Dilution Assembly
                                     Purge Port
                                     and Shutoff
                                     Valve
                                       Box Containing Flow
                                       Limiting Orifice or
                                       Capillary (may be
                                       included in commercial
                                       dilution assembly)
                                                                                                             Excess
                                                                                                       ,  ^  Sample
                                                                                                       I  ^  Vent to
                                                                                                             Outside Air
                     Ambient Air In
                      .Sampling Line
                       to Analyzer
                                               Glass Mixing
                                               Bulbs 150 cc
                                               Volume
Glass Calibration Manifold with
Unused Ports Capped
                                               S02ln

                                               Dilution
                                               Air In
                                                                   Detail of Glass Mixing Bulb
                                      Figure  3.9.   Assembly for  dilution  of  862  from  cylinder  for use
                                                              in  calibration  or  span  check.

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3.5.3  Guidelines for  Use  of  SO,  Dilution Systems
1.    Allow the cylinder, attached regulator,  and dilution assembly  to  equil-
     ibrate in the  laboratory for 24-48 hours prior to use so  that  tempera-
     ture equilibrium  is reached.
2.    During this equilibrium  period,  the tank's regulator should  be thor-
     oughly flushed and  conditioned with S02.   It is important to remove any
     gaseous or surface  adhering  water from the internal  parts to avoid S02
     removal.  If the  regulator is "wet," its effect on S02  concentration
     will be noted  by  a  slowly increasing signal  response on the  continuous
     S02 analyzer.   To expedite the removal  of water,  the purge assembly of
     the regulator  is  used in one or both of the following ways.
     a.   Pressurization/Evacuation
          (1)  Attach  a  small vacuum pump to the purge assembly fitting.
               Close the purge assembly valve.   Close  the regulator outlet
               valve.
          (2)  Open the  cylinder  valve and pressurize  the regulator.   Adjust
               the  regulator  control  valve to pressurize  the low  pressure
               gauge.  Close  the  cylinder valve.
          (3)  Turn on the pump,  open the purge assembly  valve and  pull a
               vacuum  on the  regulator for 1 minute.   The low  pressure gauge
               should  read a  negative value.   Close the purge  assembly
               valve.
          (4)  Repeat  the  pressurization/evacuation procedure  4 or  5 times.
               Remove  the  pump, and pressurize the regulator with the  S02
               mixture.   Close the cylinder valve until ready  for use.
     b.   Purge with dry air  or nitrogen
          Attach  a  cylinder of clean, very dry, nitrogen  or  air to  the purge
          port.   Open  the  purge port valve and regulator  outlet valve.
          Allow a  low  flow of gas to purge through the regulator  for 20-30
          minutes.
After  the regulator has  been  purged and conditioned, it should be left
attached to  the S02 cylinder, and filled with the S02  mixture.  If  it  must
be  removed,  the regulator  may be  protected from moisture  by  immediately
capping or plugging the  CGA outlet and closing all valves.
                                     65

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3.    The concentration of a new cylinder of S02 in air (or nitrogen) should
     be re-established prior to actual  field use by comparing its outlet to
     that of a permeation type calibration system whose permeation tube or
     device is an NBS Standard Reference Material or is traceable to an NBS
     permeation tube.   An experienced person should conduct or oversee this
     operation.
     This is done by first calibrating  a continuous S02 analyzer with a
     permeation tube system.   Next the  diluted gas from the S02 cylinder is
     sampled by the analyzer and,  after stabilization of the signal, the
     concentration value is recorded.    If a FPD analyzer is used, the air
     supplied to the permeation tube calibrator and the dilution assembly
     must have the same C02 content as  the outside ambient air.   Since the
     dilution factor is known, the tank concentration can be calculated and
     compared to the manufacturer's analysis.   If the value so obtained is
     significantly lower than that stated on the cylinder, first check the
     dilution system for leaks or  interferences to S02  detectability.   If no
     fault is found, it is probable that the tank S02 level has decayed.
Example calculation:
          FL  S02 flow rate from  tank:   10 cc/minute
          F2,  Dilution air flow rate:   1420 cc/min
          R,   Calibrated analyzer response:   0.42 ppm
Thus:     [S02], ppm = (R)  r*F   *

          [S02], ppm = (0.42)   142°Q+ 10

          [S02], ppm (cylinder) = 60.06
4.   The cylinder may now be taken to ambient  air monitoring stations for
     use as a calibration, span check, or audit device.   Dilution air at
     each station should be processed ambient  air so  that the diluent air
     contains ambient levels of C02  when  FPD analyzers  are calibrated.
          CAUTION.   Allow sufficient time for  temperature equilibration of
     the cylinder at each monitoring station.
                                    66

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     The S02 tank is used for multipoint  calibration  in  much the same way as
     the permeation tube.  The  dilution air flow is varied  to give different
     concentrations of S02; when  the  S02  supply  line  is  disconnected or
     vented, the dilution air serves  as a source of zero air.
5.    The concentration stability  of such  S02  cylinders should be checked
     from time to time by returning the cylinder to a central laboratory for
     redetermination of  its concentration by  comparison  to  an NBS permeation
     system.  This should be done at  least quarterly  for long-term studies
     and monthly for shorter term efforts.   Replace the  tank when the pres-
    1 sure reaches 500 psig.
3.6  OTHER  FACTORS AFFECTING THE  S02  OUTPUT FROM DYNAMIC CALIBRATION
     SYSTEMS AND/OR THE  RESPONSE  OF FPD S02 ANALYZERS
3.6.1  Temperature at Which the Permeation Tube  is Used
     The temperature at  which the permeation  tube is  used must be precisely
known and controlled to  within  ±0.1°  C of the value selected.  Knowledge of
the correct temperature  is very important since  the permeation rate of tubes
increases (or decreases) in a logarithmic fashion with change in tempera-
tures. Table 3.2  illustrates the  errors that  are introduced for a typical
tube when the temperature  is unknowingly  varied  from  an  assumed value of
25.0° C.
3.6.2  Air  Flow Rate and Clean  Air Supply
     The rate of air flow  (cc/minute  or liters/minute) across the permeation
device must be known.  This is  established by calibration of the dilution
air flow rate with a soap  film  flowmeter, wet test meter, or an air mass
flowmeter.  Each of these measuring devices must  itself have been recently
calibrated  and referenced  to an NBS traceable standard of volume.19  See
Section 5 for a discussion of the use and calibration of air flow measuring
devices.  Many calibration systems split  the  clean air supply and send a
small portion of the flow  over  the permeation device  and a  large portion to
combine with the S02-laden air  coming from the permeation tube compartment.
The gases leaving the permeation  tube compartment contain S02 at relatively
high levels.  A small change in the flow  rate across  the tube would not
affect the  final concentration  significantly since it would be small com-
pared to the total flow.  However, a  ]eak in  the permeation tube compartment

                                      67

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           Table  3.2.   Typical  errors  due  to  temperature variation
                          of  an S02  permeation  tube
Temperature
°C
25.0
25.1
25.5
26.0
27.0
Permeation Rate
|jg/minute
2.62
2.64
2.72
2.83
3.05
Concentration *
at 760 mm, 25° C Error1
(Dilution at 12 liters/minute) Percent
|jg/m3
218
220
227
236
255
ppm
0.083
0.084
0.087
0.090
0.097

0
1
4
8
17
      Assuming the operator thought  the  temperature  was  at 25.0°C  and was
attempting to obtain 0.083 ppm S02

or in the lines leading to the dilution  air  would  cause  a  large  decrease in
the S02 concentration since S02 at high  concentrations would  be  escaping.
     Certain materials such as stainless steel,  dirty surfaces,  and non-
Teflon filters usually cause a diminishment  of S02 by adsorption or reac-
tion.  Use only glass or Teflon tubing and Teflon  filters  in  your  calibra-
tion system.
     An essential  part of the calibration system is  its  supply of  clean, dry
S02-free, zero air.  This air must be like ambient air  in  two important
respects:  the oxygen and nitrogen content must  be the  same as ambient air,
and the C02 content should be similar to that in ambient air  (300-350 ppm).
The oxygen/nitrogen ratio affects the flame  of the FPD,  and the  presence of
C02 in ambient air will depress the  signal if C02  was not  present  in the
calibration gas.
3.6.3  Carbon Dioxide Interference  in the FPD Method for Sulfur  Dioxide
3.6.3.1  Nature of the Problem
     A problem often encountered with FPD analysis of S02  and associated
calibration procedures is the negative span  interference or "quenching"
caused by ambient C02.  The best solution to the problem,  at  present, is to
provide ambient levels of C02 in the calibration gas.
                                     68

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     That the problem  exists  is  shown  by  the  results of  recent audits23
conducted at various ambient  air measuring  facilities, Table 3.3.
     Part of the variance  in  response  to  the  audit  concentrations can be
attributed to factors  other than C02 interference.  However, quantitative
examination of  the  audited calibration system's  C02 output often revealed
C02 concentrations  much  less  than ambient levels.   Minimization of the C02
interference depends on  having ambient levels of C02 present in the calibra-
tion gas.
     Carbon dioxide is naturally present  in the  ambient  atmosphere at aver-
age concentrations  of  300-350 ppm.   There are variations with height, time
of day and season.24   Near sources of  C02,  concentration variations may be
significantly greater  than those of rural ambient air.   For instance, at
ground level, near  a densely  populated and heavily traveled area of a city,
the levels of C02  in air would be higher  than that in  the countryside.
     The C02 does  not  react with or remove the S02.  Its effect on the
signal is probably  due to collisional  quenching  processes which inhibit the
formation of the excited state S2* molecule or deactivate the excited state
S2* molecule prior  to  chemiluminescent emission.

    S2*   +   C02 	*•  S2   +  C02  (without chemi luminescent emission)

Overall, this  results  in an apparent lowering of the  FPD S02 concentration
output signal,  i.e.,  a negative span interference.
     Table  3.4  shows  analyzer response results for a  modern 1976 model ambi-
ent air  S02  FPD analyzer.   One set of data was established  in the presence
of ambient  C02, ~350  ppm, the other in the absence of C02.  Note that the
percent  response increase at different S02 concentration levels  is  about the
same,  17%,  when the C02  is removed.
     All commercially available continuous FPD S02 analyzers  show this C02
effect to varying extents (see Table 3.3).  The effect is not  observed in
analyzers which chromatographically separate S02 from other atmospheric
gases  (e.g.,  C02).
                                      69

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Table 3.3.   Evaluation of C02 interference in total
      sulfur measurements using FPD analyzers23
S02
Audit
Instrument Concen-
Brand tration
(ppb)
50
A 99
151
51
A 101
150
59
B 103
150
59
B 103
150
50
C 100
150
65
C 127
188
50
D 99
149
49
D 102
151

Measured
0 ppm
C02
(ppb)
51
107
180
49
111
170
53
108
148
53
107
149
45
91
138
61
126
190
46
95
149
40
91
146


TS Concentrations
360 ppm
C02
(ppb)
41
92
149
41
90
142
49
100
142
50
101
145
46
90
135
58
116
174
44
88
135
38
87
132
750 ppm
C02
(ppb)
34
78
129
34
74
119
44
92
135
48
101
140
46
82
114
53
101
150
43
84
126
35
84
131

% Change
0 ppm C02

360 ppm CO
-20%
-14%
-17%
-16%
-19%
-16%
-8%
-7%
-4%
-6%
-6%
-3%
+2%
-1%
-2%
-5%
-8%
-8%
-4%
-7%
-9%
-5%
-4%
-10%

From
Measurement

2 750 ppm C02
-33%
-17%
-28%
-31%
-33%
-30%
-17%
-15%
-9%
-9%
-6%
-6%
+2%
-10%
-17%
-13%
-20%
-21%
-7%
-12%
-15%
-13%
-8%
-10%
                       70

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             Table 3.4.   FPD analyzer response, ppm S02)  in the
                   presence and absence of carbon dioxide.

Perm tube
Predicted
S02 , ppm

0.0
0.437
0.338
0.278
0.144
0.099
0.078
Instrument
Response,
Volts
(C02 present/
C02 absent)
0.0135/0.014
0.875/1.032
0.678/0.795
0.540/0.630
0.283/0.335
0.191/0.225
0.149/0.176
Calculated^
S02 , ppm
(C02 present
at 350 ppm)

0.006
0.439
0.340
0.271
0.142
0.096
0.075

Calculated^
S02 , ppm
(C02 absent)

0.007
0.518
0.399
0.316
0.168
0.113
0.088

% Response
Increase,
(C02 absent)

_
18.0
17.3
16.6
15.5
17.7
17.3
      Calculated based on least squares regression calibration equation
established in the presence of ~350 ppm C02.
3.6.3.2  Minimization of the C02 Interference
     The C02 interference can be minimized by dynamically calibrating the
analyzer with S02 in air mixtures containing ambient levels of C02 (~350
ppm). Then, when the analyzer is returned to ambient air, it will  "see"
approximately the same amount of C02 and the effect will be the same as
during calibration.  In this way the C02 interference has been "nulled out"
or compensated for by the calibration zero and span adjustments.
     It should be noted that calibration and rechecks of calibration will
not uncover the presence of a C02 interference.  For instance, one might
calibrate with air mixed with S02 containing no C02.  The calibration may  be
repeated and give excellent agreement with the first calibration.   However,
when the analyzer is returned to ambient air, an immediate quenching of the
S02 signal occurs.
     Of course, if the concentration of C02  in the  air  used for calibration
purposes changes dramatically from  one calibration  to the next, there can be
a noticeable difference between successive calibration  span values.  This
effect could be mistaken for instrument span drift  or calibration gas inac-
curacy.
                                     71

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     To ensure that ambient levels of C02 are included in the calibration
gases, a calibration system should be set up which uses on-site outside
ambient air (which is scrubbed free of sulfur compounds but not C02) as a
source of zero and dilution air.
     Ambient air, taken from outside the sampling station, must be used and
can be obtained from the station sampling manifold.   Do not use room air.
Room air C02 levels may be much higher than those of ambient air.   If the
analyzer is calibrated with air containing C02 levels higher than in ambient
air, the response to S02 upon return to ambient air will  be greater than
during calibration, resulting in an apparent positive interference.
     A zero air generator suitable for FPD zero and calibration work is
shown in Figure 3.1, Section 3.2.1.  A laboratory experiment was carried out
to determine the amount of C02 which passes through commonly employed scrub-
bers.  A 3.8 x 15 cm (1.5 x 6 inch) cylindrical column contained the scrub-
ber material; flow rate of the air/C02 mixture through the system was 1
liter per minute.  Analysis was by gas chromatography.   Results are sum-
marized in Table 3.5.
     The results show that the S02-scrubbing agent,  activated coconut char-
coal, does not retain C02 significantly, especially if it is conditioned
prior to use.  The drying agents, "Drierite" (TM) and silica gel,  pass C02
quantitatively.  Molecular sieves (which are often found in heatless air
dryers) completely remove C02 and should not be used.   Soda lime and "As-
carite" (TM) also absorb C02 completely and should not be used as scrubber
material.
     Parameters for the operation of individual clean air systems should be
optimized by the user.  The dimensions of the scrubber cartridge and the
amount of material packed inside will be dictated by the air flow rate, the
length of time the system is used before repacking the scrubbers,  and the
concentration of pollutants present in the ambient air.
     Most commercial calibration systems intended for use in calibrating
ambient level FPD S02 monitors will normally have a nominal total  air flow
of from 2-5  liters/minute.
3.6.4  Percentage of Oxygen in Calibration Air
     The flame photometric detector has been shown to give a varying re-
sponse to S02 when air supplied to the flame has a varying oxygen content.
                                     72

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                   Table 3.5.   Retention of C02 on commonly
                         employed  scrubber materials.
Scrubber material
    C02, ppm
prior to scrubber
  C02, ppm
after scrubber
Exposure time,
  minutes
Activated coconut
charcoal, 6-14 mesh,
taken directly from
new container.  56g.
        350
    245
                                           88
Activated coconut
charcoal, 6-18 mesh,
conditioned for 16.5
hrs. at 300°C in air.
56g.
        350
    345
                                           80
"Drierite"  (TM),
10-20 mesh.
20g.
        350
    347
     32
Molecular sieves,
Type 5A, 8-12 mesh.
28g.
        350
                     32
Silica gel, indica-
ting, coarse mesh.
67g.
        350
    350
    150
The use of scrubbed ambient  air  for  zero and dilution is recommended in

order to avoid this problem.   If cylinder air is used, it should contain the

correct ambient percentage of  oxygen (20.94) and nitrogen (78.9).   Meatless

air dryers may also slightly alter the oxygen content of ambient air.

     Figure 3.10 illustrates the variation in response of an FPD analyzer to

a fixed concentration of S02 diluted by air of varying oxygen content.

3.7  SUMMARY OF FPD S02 CALIBRATION  SOURCE PARAMETERS WHICH MUST BE
     OPERATOR-CONTROLLED

     Table 3.6 presents a checklist  of calibration source parameters which

must be operator-controlled  in order to obtain valid data from FPD S02
                                     73

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   21
   20
   19
ID
X
o
   18
    17
    16
                 17
0.0806 ppm (20.94% 02)
 18
                                           0.0876 PPM (19.4% 0.
                                                         0.0941 PPM (17.73% 0,)
                                                                         0.10114 PPM (16.18% 0,
19
20
21
22
23
                          ANALYZER RESPONSE, mv (0-100 mv FULL SCALE)


     Figure 3.10.   Variation of FPD  analyzer response  with  air oxygen content
                      at a  fixed SOa concentration of  0.0806  ppm.
                                         74

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analyzers.  The table lists the parameter, how the operator controls  the
parameter, how  lack of control can be identified, and how the parameter may
be brought into control.
                                       75

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01
             Table 3.6.  S02 calibration source parameters which must be operator-controlled
                                      in order to obtain valid data



 PARAMETER

      Knowledge of the permeation rate of S02 from tube or device

 How Operator Controls Parameter
      1.    Purchase NBS certified S02 permeation tubes; use as received or employ for establishing trace-
           ability of other tubes or devices.

      2.    Purchase other tubes or devices which:

           a.   Are certified by their manufacturer as being calibrated by use of NBS or NBS- traceable
               materials.

           b.   Can be compared to S02 standard atmospheres generated in your laboratory by use of
               NBS permeation tubes.

      3.    Exercise care in storage, handling, and use of permeation tubes.

 How Operator May Identify Lack of Control

           The expected output of the tube or device changes with time and no other factor can be identi-
      fied  (temperature, flow, etc.) which could cause the problem.

           The outlet from the tube or device does not agree with the expected value when the calibration
      system is compared to another system which uses an NBS certified tube.

           The tube contains no visible liquid S02 or is visibly cracked or  split, or  is visibly oily
     or dirty.

How Operator May Bring Parameter Into Control

     A defective permeation tube cannot be  repaired, it must be replaced.

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             Table 3.6.  S02 calibration source parameters which must be operator-controlled
                                  in order to obtain valid data (continued)


PARAMETER

     Temperature of permeation tube bath or holder


How Operator Controls Parameter

     Some commercial permeation tube or device type calibration systems have an adjustable dial or
     thumbwheel to set the temperature of the air bath or compartment which contains the permeation
     device.  Other systems are preset at some temperature (such as 35°C) and cannot be adjusted.
     Temperatures in systems employing recirculating water (or other fluid) are set using controls
     of the constant temperature water bath.

How Operator May Identify Lack of Control
          A small change in the temperature of the permeation tube will  cause a change in the concen-
     tration of S02 produced.  This is one indication of temperature variation.   Also check the
     thermocouple signal output of the system for indication of drift.   Some calibration sources have
     a meter which  indicates whether temperatures are being controlled or not.   Check it.
          If it is possible to do so, a thermometer (of NBS or ASTM accuracy) with at least ±0.1°C
     graduations should be placed in the permeation tube compartment with the mercury bulb located
     next to the permeation tube while air is flowing across the permeation tube.   A thermocouple or
     thermistor may also be used as a temperature sensor.

How Operator May Bring Parameter Into Control
          If heating and cooling devices are unstable or defective, replace them and calibrate the
     temperature output with a thermometer or thermocouple/thermistor arrangement.   If unable to
     calibrate temperatures, compare the system's S02 output to that of  an  independent S02  source
     which  has been temperature calibrated and which uses NBS permeation tubes.
          If a temperature-adjustable system is operating satisfactorily but is  only out of calibra-
     tion,  make adjustments and recalibrate the system.

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                    Table 3.6.  S02 calibration source parameters which must be operator-controlled
                                         in order to obtain valid data (continued)


        PARAMETER
             Flow  rate of purge air and dilution air


        How Operator Controls Parameter
             Control is usually by use of resettable pressure regulators and/or rotameters which are coupled
             to restrictive capillaries and orifices.  Such pressure settings and rotameter readings must
             be correlated with actual flow rate by flow calibration.

        How Operator May Identify Lack of Control
             An increase in total air flow will result in a decrease in S02 concentration.

             A decrease in total air flow will result in an increase in S02 concentration.
00
        How Operator May Bring Parameter Into Control

                  First, check the dial settings on the calibration system's pressure gauges and rotameters to
             be sure they are at the desired settings.  If they are wrong, next check the pressure at the source
             of the air supply, tank or compressor.  If too low, increase the tank pressure, replace the tank
             or correct the compressor problem.  Be sure compression pumps are operating.
                  Second, check the calibration and analyzer system for leaks.  Use leak detection solution on
             pressurized lines only.
                  If the pressure gauges or rotameters are simply misadjusted, reset them.
                  It is most important that no leaks occur in the permeation tube holder since S02 will be
             vented in large concentration.   By use of a bubble flowmeter, this flow should be established
             and rechecked occasionally.  This is done by breaking into the line downstream of the permeation
             holder.   The dilution air flow settings (gauge or rotameter) must also be matched with actual
            air flow by calibration with a bubble flowmeter or wet test meter.
                 Two ways to check for system leaks are suggested:  1.  measure flow at the inlet and outlet
            and compare;  2.  plug the outlet and pressurize the system with air, then use leak detector solution.

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             Table 3.6.  S02 calibration source parameters which  must be operator-controlled
                                  in order to obtain valid data (continued)


PARAMETER

     Interferences to S02 concentration or response of  FPD analyzer

     The major problems are caused by:

     1.   Use of stainless steel tubing or other tubing besides Teflon  or glass  (causes  loss of S02
          and/or slow analyzer response).

     2.   Water condensation in zero and/or dilution air (causes  loss of S02).

     3.   Wrong 02:N2 ratio in zero and dilution air (causes variability of flame and may  increase
          or decrease response to S02).

     4.   Zero or less than ambient amounts of C02 in the zero and/or dilution air (causes an apparent
          diminishment in S02 concentration when analyzer is returned to  ambient air).

     5.   Pressurization of the S02 calibration manifold.


How Operator Controls  Parameter

     1.   Use only Teflon or glass to  deliver S02 to analyzer.

     2.   Provide air  free of condensation by use of scrubbers, or in the case of compressed ambient
          air, provide route for excess liquid water to escape from compression chamber.

     3.   Use S02-free ambient air where possible.  If  compressed cylinder air is used,  specify that
          it be  ambient compressed air.  If synthetic air (prepared from 02 + N2)is used, request an
          analysis of  contents.  The desired concentrations are:   20.9% 02, 78.9% N2, and 350 ppm C02.

     4.   Use dry, S02-free ambient air where possible.  Air supply system must be such  that the ambient
          air C02 content is maintained.  If compressed air from cylinders is used,  ambient C02  levels
          (350 ppm)  should be present.  Analysis for C02 should be requested.

     5.   Provide restriction-free venting of the calibration manifold.   If a vacuum is  used at the  vent,
          be certain it is a light, gentle vacuum which will  not cause a partial  vacuum  to occur within
          the calibration manifold.

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                   Table 3.6.   S02 calibration source parameters which must be  operator-controlled
                                      in order to obtain valid data (continued)


      How Operator May Identify Lack of Control

           1.   Inspect tubing and fittings of calibration systems.
           2.   Moisture droplets appear in tubing.   Moisture scrubber is exhausted.   If an indicating drier
                is used (such as indicating Drierite or silica gel),  the color  will  change from blue to pink
                as it becomes exhausted.

           3.   A sudden change occurs in instrument response to S02  (increase  or decrease) immediately after
                attachment of a new source of zero air.

           4.   Chemically measure the amount of C02 in your zero air at the calibration manifold (see
                Section 5 for instructions).

           5.   Attach a water manometer pressure gauge to one of the calibration manifold outlets.   No
                pressure or vacuum should register.   Momentarily remove any vent lines,  etc.  and continue
o               to sample a known S02 concentration with the FPD.   If any change in  response occurs, the
                presence of the vent tube, etc. must have been causing an effect.

      How Operator May Bring Parameter Into Control

           1.   Replace all tubings, fittings with Teflon and/or glass material.

           2.   Provide vent or other route for excess water to escape from pressurization system.  Add a
                water scrubber (such as Drierite or silica gel) to your zero air system; replace exhausted
                drying agent.

           3.   Specify that your zero air contain 20.9%, 78.9% N2, 350 ppm C02.

           4.   Use a system which does not scrub C02 from ambient air if ambient air is scrubbed and used
                as a source of zero air.  If compressed cylinder air is used, be sure C02 is part of the mix-
                ture (request analysis if necessary).

           5.    Remove any restrictions to proper venting of the calibration manifold.  Use a light,
                gentle vacuum at the vent.



                                                                                                CONCLUDED

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                                 SECTION 4.0
   CALIBRATION OF THE  FLAME PHOTOMETRIC DETECTOR  FOR  S02  IN AMBIENT AIR

4.1  INTRODUCTION TO CALIBRATION
4.1.1  Qualitative  and Quantitative  Analyses
     The qualitative basis  for any analytical  method  is the occurrence of a
change in some property of  the analytical  system  when the compound you wish
to determine  is  added.
     The flame photometric  detection of S02 is a  qualitative procedure.
When S02 reaches the H2/air flame, processes  occur which produce an excited-
state S2 molecule.  This molecule  loses its excess energy by emitting  light,
and this light is sensed by a photomultiplier tube.   The amperage signal
from the photomultiplier tube is converted electronically to a voltage
signal, which is displayed  on a voltmeter  or  a stripchart recorder.
     It is  understood  that  the analytical  method  must be specific for the
compound being determined.   This is  another way of saying the analytical
method for  compound A  has no positive or negative interferences from compounds
B, C, D, etc.  However, in  practice, most  analytical  methods suffer inter-
ferences.   Without  modification, flame photometry is  not specific for S02
detection.  When burned in  a hydrogen-rich flame, any sulfur-containing gas
may produce the  excited-state S2 molecule,  which  decays and emits light with
a range of  wavelengths centering around 394 nm.   To be certain that the
light of other wavelengths  does not  reach  the photomultiplier tube, a 394-nm
narrow band pass optical  filter is used.   This makes  the FPD highly selective
for detection of sulfur-containing compounds.   In a further step, the  FPD is
made highly specific for S02 by the  use of a  "scrubber," which removes H2S
from the sample  air stream  while allowing  S02 to  pass unaffected.  A chroma-
tography column  can also separate  S02 from unwanted compounds.
     A qualitative  analysis can become a quantitative analysis.  A quantita-
tive analysis is one which  not only  tells  you what compound, but also  how
much of that  compound  is  present.  To assign  a value  to an unknown concentra-

                                      81

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tion, the change or response of the analytical system to the unknown is
compared to predetermined responses obtained for a sample containing none of
the compound (known as a blank or zero) and a series of samples of known
concentration.   The concentrations which are known have been previously
established by another analytical method.   This set of known concentrations
is sometimes called a set of standards.  The process of obtaining the analyt-
ical system's responses for the members of a set of standards is often
called standardization of the analytical method.   Another term describing
this process is calibration.
4.1.2  Definition of Calibration; Requirements for Calibration
     In general terms, calibration is the process of precisely relating the
magnitude (size) of the response of the analytical system to the concentra-
tion of the compound being measured.   To achieve a valid calibration, two
major requirements must be met.
     1.   The response of the analytical method to different concentrations
          of standard should be as reproducible and unvarying as possible.
          This is achieved by careful control of parameters affecting re-
          sponse.  Furthermore, the effects of any interferences on response
          must be accounted for.
     2.   The concentration of the compound used as a standard for calibra-
          tion must be known with a high degree of accuracy.  This degree of
          accuracy must be within the limits of sensitivity of the analytical
          method.  The standards must be sampled by the analytical method in
          the same way that unknown samples are taken.
     To meet these two major requirements, careful control of parameters
affecting the calibration standards (discussed in Section 3.0) and the
analytical method (discussed in this section) must be maintained.
     The meaning of the word "calibration" as applied to an automated analyzer
such as the FPD S02 must be clearly understood.  Calibration for automated
methods refers to a complete multipoint characterization of the analyzer's
response to an accurate, reliable standard over the entire analyzer range.
A "zero and span operation" consists of a baseline check with clean air and
a one-point check of analyzer response.  Zero and span is not an acceptable
basis for calibration.
                                    82

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     An FPD S02 analyzer  should  be  calibrated  on-site upon installation and
at intervals thereafter.  Monthly calibrations are suggested; calibration
every 2 weeks may be best in  some cases.  Zero and span checks should be
performed more frequently-daily if possible.  These procedures, along with
maintenance and preventive  maintenance  are  important parts of an air-monitoring
system's quality control  program and are  essential in maintaining the accuracy
and reliability of  air quality data.
     It is important that the FPD analyzer  be  operated during calibration
under conditions identical  to those in  its  normal ambient air sampling mode
of operation.  No modifications  or  alterations should be made to the ana-
lyzer's components, flow  system, prescribed flow rate, or other parameters.
Concentrations of S02  intended for  calibration must be generated continuously
by means entirely independent of the analyzer.  The flow rate of the calibra-
tion gas must exceed the  sample  flow rate of the analyzer.  The calibration
gas should flow through a manifold  and  the  analyzer should draw its sample
through the regular ambient air  sampling  line, which is attached to a port
of the vented calibration manifold.
     This section of the  TAD covers more  than  just a procedure for multipoint
calibration of an FPD  analyzer.  Also included are suggested steps for
station maintenance and recordkeeping,  how  to  conduct a zero and span check,
a short section on  maintenance and  replacement operations, and a checklist
of FPD analyzer parameters  and their control.
     The procedure  for multipoint calibration  of an FPD analyzer is neces-
sarily general.  Where analyzer-specific  instructions or explanations are
necessary, the reader  is  referred to supplementary information located at
the end of the procedure  and to  the manufacturer's instruction manual.
     Special explanatory  and precautionary  material in the text is set apart
by being enclosed in blocks.
4.1.3.  Recordkeeping
     A permanent record should be  kept on all  activities  relating to calibra-
tion and maintenance of the FPD  analyzer.  The date and time intervals should
be clearly noted.   Also keep records on such items as:  maintenance of cali-
bration devices, calibration gases, hydrogen supplies, other analyzers, and
the monitoring station itself.   Also, record your  name in  the  notebook, on
the stripchart, etc.

                                      83

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     A hardbound laboratory notebook is highly recommended.  Make legible
entries in ink; cross through erroneous entries with a single line.   Many
users find calibration and maintenance forms useful since they remind the
operator to perform certain steps.   If such forms are used, a copy should be
pasted or taped into the notebook along with calibration curves and equations.
     The stripchart record should also be marked.  A short description of
the action taken should be given.  Times should be noted and marked clearly
with a line or arrow.
4.2  PRELIMINARY STEPS
     Before calibrating the FPD S02 analyzer, certain preliminary steps are
taken.  All of these steps are carried out before any adjustments are made
to the analyzer, the calibration system, the data recording system, or other
laboratory equipment serving the analyzer.  In this way, any changes that
have occurred  in the total analytical system since the last calibration or
check  can be recognized and recorded.  By examining this record over a
period of time, problems of the analyzer (such as varying sample flow rate),
the calibrator (such as temperature drift), or the station environment (such
as inadequate  temperature control) can be recognized and corrected.
      1.   Survey station condition.  Check temperature/humidity control,
          cleanliness of station ambient air inlet, etc.  Record findings in
          station  logbook.
      2.   FPD  Analyzer online, warmed up.  Before calibrating an FPD ana-
           lyzer, the electronics and flame should have been on (sampling
          mode) for  at least 24  hours.
           If this  is  an  initial calibration of a new  instrument,  a
           good practice  is  to  test the analyzer for 5 to 7  days
           while conducting  an  accelerated program of  zero,  span,
           and multipoint calibrations.   In other words, during
           this first  week,  calibrate the instrument about three
           times and carefully  compare results from one calibration
           to the next to detect sources  of error or drift,  which
           need correction prior to recording ambient  air data.
      3.    Calibration  system  online, warmed up.   If a calibration  system
           employing  a  permeation tube or device  is to be  used,  the following
           steps  must be  completed  before calibration begins:
                                     84

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The permeation tube or device must have been installed in its
compartment and the constant temperature air or water bath
must have been in operation at the desired temperature for at
least 24 to 48 hours if the tube or device is initially at a
temperature 10° C different from that of the oven.  If its
temperature is only 1° or 2° C different from that of the
oven, 3 hours of equilibration time may be adequate.  Shorter
or longer times may be required and these times can only be
deduced by experience.  During equilibration a low flow of
clean air (sweep air) must pass over the permeation device.
Without this air flow, large concentrations of S02 will build
up in the permeation compartment and lengthy purging with
clean air will be necessary.
The source of clean, S02-free air (used for zero air, sweep
air, and diluent air) must be in a state of readiness.  If
heated scrubbers (such as catalytic oxidizers) are used, such
devices should be powered, warmed up, and producing clean air
prior to use with the calibrator.  Spent cartridges of chemi-
cal scrubbers should be replaced with equivalent materials,
dirty filters should be replaced and conditioned, and water
condensation traps  should be emptied.  Dirty or sticking
rotameters should be disassembled and cleaned, dried, reassem-
bled, and recalibrated.  It  is easier to perform such mainte-
nance in the central  laboratory rather than at the field
site.  Record all maintenance activities in the station
logbook or in a  notebook devoted to the calibration system.
      NOTE:   Following any maintenance  or  replace-
      ment activities on the calibration system,  it
      is  important to:
      (1)   Double check all connections for  air
           leaks.
      (2)   Check the zero air output from  the  system
           to be certain that the new chemical
           scrubbers are not off-gasing any  sulfur-
           containing compounds.   In other words,
                      85

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               does the FPD signal increase dramatically
               on "zero" air after the scrubbers are re-
               placed?  If it does, the scrubber packing
               or holder is contaminated and must be re-
               placed.

          (3)  Compare +he instrument response to the
               zero air produced by the new scrubber
               system with the response to zero air from
               the previous scrubber system.   If the
               response is significantly lower for the
               new scrubber than for the old, this
               indicates that the old scrubber system
               was exhausted and was allowing SO^ to
               pass.   Record any significant variations
               and make a report to the data validation
               section since some prior data may need to
               be voided.

          (4)  Be certain that the flow rates of zero,
               sweep, and diluent air have not been
               altered.   Redetermine flow rates if
               necessary.
d.
The relation between the settings of rotameters or pressure

dials of the calibration system and the flow rate of dilution
air and permeation tube sweep air should be established by

calibration of the air flow with a wet-test meter or soap
film flowmeter.   See Section 5 for an explanation of the use

of these devices.   All measured flow rates should be corrected

to standard temperature and pressure conditions, 25° C, 760
mm Hg.   See Section 5 for the procedure for correcting air
flow rates to STP.

If the permeation tube has not been used for some time,

examine it visually to be sure liquid S02 is still present.
Order calibrated permeation tubes or devices in plenty of

time to provide replacement.  As long as 4 months may be

required to receive an NBS-certified permeation tube.  See
Section 3 for information concerning permeation tubes and
devices.
                          86

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Determine any time discrepancy between the recorder and the
local time.   Over a period of days, the recorder drive mecha-
nism may lag behind or speed up with respect to local time.
This could be due to power failure, an inaccurate chart drive
mechanism, or to Hnding, or slippage of the chart paper on
the drive mechanism.  Note the time discrepancy in the station
logbook, determine its cause, and take corrective action.
Remove the stripchart roll and examine the ambient air trace
(and any automatic zero or span checks) for the previous 24
hours.  Look for evidence of power failure, flameout and
automatic reignition, unusually high values, unusually low
values (such as a straight zero baseline), and noisy signals.
     Such information is helpful in determining the
     present status of the analyzer and will indi-
     cate whether further warmup time is necessary
     before calibration.  The stripchart roll
     should be clearly marked with the station
     number and inclusive times and dates and
     forwarded to the person responsible for data
     analysis.
Check the ink supply of the recorder.   Add ink and clean the
system as necessary.  Replace the stripchart roll with a new
one.  Move the paper and start the pen at the desired time
mark, and record the station name, date, and time on the
stripchart.
If a data acquisition system (DAS) is being used, remove the
magnetic tape cartridge and insert a new one.  Some operators
may prefer to leave the old tape in place, recording data,
until the multipoint calibration is complete.  Others may
prefer to have the new calibration data entered on the new
tape.  If the calibration data are entered on the new tape,
later application of the calibration equation to the raw data
points acquired during calibration should give the correct
calibration values if the scan or integrating interval of the
                     88

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          DAS is short enough.  This serves as a check on the integrity
          of the data acquisition system and the computer program,
          which treats the raw data.
               Always take adequate notes of time on, time
               off, any analyzer response scale changes made,
               periods of calibration, etc.  See that these
               notes reach the person responsible for magne-
               tic tape data workup and interpretation so
               that signal variations due to calibration,
               zero, span, power failures, etc., are recog-
               nized and not confused with ambient air data.
6.    Connect the stripchart recorder to analyzer.  If a recorder is not
     already in place, connect one to the analyzer.  Be sure the range
     of the recorder matches that of the analyzer output.   It is recom-
     mended that the recorder baseline be offset to create a live zero
     for instruments having both positive and negative signal output.
     This is done by calibrating the recorder so a zero voltage input
     corresponds to 5 percent of the full-scale chart (i.e., 5 chart
     divisions if the paper has 100 divisions).  A digital voltmeter
     may also be connected at this time.  This will also permit the
     identification of negative zero drifts during calibration.
          A good practice  is to  use  shielded cables to make
          signal connections.  Consult the recorder manufac-
          turer's manual for instructions.  Since the recorder
          trace is often used  as the permanent  record for the
          data, the operator must be aware of the potential
          for error by problems  such as:

            a.  Recorder "dead band" error,
            b.  Noisy trace due  to improper gain adjustment,
            c.  Loading error  caused by  the recorder and/or
                the voltmeter, and
            d.  Erroneously set  zero and span points.
                                89

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     Recorders and voltmeters should be carefully checked and cali-
     brated to avoid such errors.   Refer any questions or problems to
     an experienced electronics technician.   Records should be kept of
     recorder and voltmeter calibrations and adjustments or repairs.
     Preventive maintenance programs should include recorders, data
     acquisition systems, and electronic measurement devices.
7.    Obtain station temperature and pressure.   In order to correct any
     measured volumetric flow rates to standard temperature (25° C) and
     pressure (760 mm Hg or 29.92 in.  Hg),  the temperature of the cali-
     bration air sample and the barometric  pressure at the site must be
     known.
     The temperature of the calibration gas is best determined by in-
     serting a precision-grade glass thermometer into the calibration
     manifold.  Once a steady temperature is attained, record the value
     and remove the thermometer.   The room  air temperature of the
     station may also be used, but it is possibly a less accurate
     reading than that taken directly from  the manifold.
     The atmospheric pressure is best obtained by reading a mercury
     column barometer or aneroid barometer  which is located  in the
     sampling station and has been in place long enough to achieve
     temperature equilibrium.  Refer to Section 5 for instruction in
     the use and reading of barometers.
     The nearest airport that maintains atmospheric pressure data may
     be called for information.  Be sure that you ask for the actual
     "station pressure," not the pressure used by aviators, which has
     been  corrected to sea level.
          EXAMPLE.  A call was placed to the local airport
          weather service on March 22.  The recorded an-
          nouncement stated the pressure was 29.60 in. Hg at
          2:00 p.m.  This is the value for aviators.
          According to the meterologist on duty, the actual
          station pressure at 2:00 p.m. was 29.185 in. Hg.
          This latter value is the one to be used in volu-
          metric correction equations.
                                90

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         The pressure at a site may be  approximated by reference to a table
         listing barometric pressure  at various altitudes.  The elevation
         of the site must be  known.   See Table 4.1.
               EXAMPLE.   An  ambient air sampling  station  is  lo-
               cated  at  an altitude of 2,058  feet above sea  level.
               What is the average pressure at the site in mm Hg?
               From Table 4.1,  Psite = 27.70  + .02 =  27.72 in. Hg
               (25.4  mm/inch) (27.72 in.  Hg)  = 704 mm Hg.
          Be aware that significant temperature and pressure  changes  can
          occur during the timeframe of a calibration.   If a  barometer  is
          present in the station, a reading should also be recorded at  the
          conclusion of the calibration.  A significant change may explain
          minor variations in instrument response since the instrument
          sampling rate is not mass-flow controlled.
4.3  ZERO AND SPAN CHECK
     A zero and span check consists of  a determination of an analyzer's
baseline response to clean air and to a single S02 span point.  In this way,
certain analyzer malfunctions and drift that occur between calibrations may
be detected.  A zero and  span check should be conducted daily if possible
and just prior to a multipoint calibration.  Only  slight adjustments should
be made to  the zero pot;  no  adjustments should be  made to the span pot.  A
zero and span check should not be confused with  a  multipoint calibration.
Zero and span data should not be used  as a basis for data workup.  Zero and
span data are very useful  to help an operator  keep track  of daily zero and
span drifts.   In  contrast to a multipoint  calibration, a  zero and span check
uses only two points  and  perhaps uses  a less accurate, less  reliable,  or
nondynamic  S02  standard.
     Often  a zero air source is  included within  the analyzer.   Zero  air  is
supplied  by having the analyzer's  sample pump  pull air through  a charcoal-
filled cartridge.   By activating a solenoid  valve, the air sample is pulled
through the cartridge rather than  through  the  ambient air sample line.
Thus,  the path of the built-in  zero air is not the same as that followed by
ambient air.   The span gas may  also enter by a path other than that used for

                                     91

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Table 4.1.  Barometric pressure at various altitudes.
Barometric
pressure, B
inches

23.50
.60
.70
.80
.90
24.00
.10
.20
.30
.40
24.50
.60
.70
.80
.90
25.00
.10
.20
.30
.40
25.50
.60
.70
.80
.90
26.00
.10
.20
.30
.40
26.50
.60
.70
.80
.90
27.00
.10
.20
.30
.40
27.50
.60
.70
.80
.90
28.00
.10
.20
.30
.40
28.50
.60
.70
.80
.90
29.00
.10
.20
.30
.40
29.50
.60
.70
.80
.90
30.00
.10
.20
.30
.40
30.50
.60
.70
.80
0
Feet
6,546
6,431
6,316
6,202
6,088
5,974
5,861
5,749
5,637
5,525
5,414
5,303
5,193
5,083
4,974
4,865
4,756
4,648
4,540
4,433
4,326
4,220
4,114
4,009
3,903
3,799
3,694
3,590
3,487
3,384
3,281
3,179
3,077
2,975
2,874
2,773
2,672
2,572
2,473
2,373
2,274
2,176
2,077
1,980
1,872
1,784
1,688
1,591
1,495
1,399
1,303
1,208
1,113
1,019
925
831
737
644
551
458
366
274
182
91
0
-91
-181
-271
-361
-451
-540
-629
-718
-806
0.01
Feet
6,535
6,420
6,305
6,190
6,076
5,963
5,850
5,737
5,625
5,514
5,403
5,292
5,182
5,072
4,963
4,854
4,745
4,637
4,530
4,423
4,316
4,209
4,104
3,998
3,893
3,788
3,684
3,580
3,477
3,373
3,270 •
3,168
3,066
2,965
2,864
2,763
2,662
2,562
2,463
2,363
2.264
2,166
2,067
1,970
1,872
1,775
1,678
1,581
1,485
1,389
1,294
1,199
1,104
1,009
915
821
728
635
542
449
357
265
173
+82
-9
-100
-190
-280
-370
-460
-549
-638
-727
-815
0.02
Feet
6,523
6,408
6,293
6,179
6,065
5,952
5,839
5,726
5,614
5,503
5,392
5,281
5,171
5,061
4,952
4,843
4,735
4,627
4,519
4,412
4,305
4,199
4,093
3,988
3,882
3,778
3,674
3,570
3,466
3,363
3,260
3,158
3,056
2,955
2,854
2,753
2,652
2,552
2,453
2,353
2,254
2,156
2,058
1,960
1,862
1,765
1,668
1,572
1,476
1,380
1,284
1,189
1,094
1,000
906
812
718
625
532
440
348
256
164
+73
-18
-109
-199
-289
-379
-469
-558
-647
-735
-824
0.03
Feti
6,512
6,397
6,282
6,167
6,054
5,940
5,827
5,715
5,603
5,492
5,381
5,270
5,160
5,050
4,941
4,832
4,724
4,616
4,508
4,401
4,295
4,188
4,082
3,977
3,872
3,767
3,663
3,559
3,456
3,353
3,250
3,148
3,046
2,945
2,843
2,743
2,642
2,542
2,443
2,343
2,245
2,146
2,048
1,950
1,852
1,755
1,659
1,562
1,466
1,370
1,275
1.180
1,085
990
896
803
709
616
523
431
338
247
155
+64
-27
-118
-208
-298
-388
-478
-567
-656
-744
-833
0.04
Feet
6,500
6,385
6,270
6,156
6,042
5,929
5,816
5,704
5,593
5,480
5,369
5,259
5,149
5,039
4,930
4,821
4,713
4,605
4,498
4,391
4,284
4,178
4,072
3,966
3,861
3,757
3,653
3,549
3,446
3,343
3,240
3,138
3,036
2,934
2,833
2,733
2,632
2,532
2,433
2,334
2,235
2,136
2,038
1,940
1,843
1,746
1,649
1,552
1,456
1,361
1,265
1,170
1,075
981
887
794
700
607
514
421
329
237
146
+ 55
-36
-127
-217
-307
-397
-486
-576
-665
-753
-841
0.05
Feet
6,489
6,374
6,259
6,145
6,031
5,918
5,805
5,693
5,581
5,469
5,358
5,248
5,138
5,028
4,919
4,810
4,702
4,594
4,487
4,380
4,273
4,167
4,061
3,956
3,851
3,746
3,642
3,539
3,435
3,332
3,230
3,128
3,026
2,924
2,823
2,723
2,622
2,522
2,423
2,324
2,225
2,126
2,028
1,930
1,833
1,736
1,639
1,543
1,447
1,351
1,256
1,161
1,066
972
878
784
690
597
505
412
320
228
137
+45
-45
-136
-226
-316
-406
-495
-585
-673
-762
-850
0.06
Feet
6,477
6,362
6,247
6,133
6,020
5,906
5,794
5,681
5,570
5,458
5,347
5,237
5,127
5,017
4,908
4,800
4,691
4,584
4,476
4,369
4,263
4,156
4,051
3,945
3,841
3,736
3,632
3,528
3,425
3,322
3,219
3,117
3,016
2,914
2,813
2,713
2,612
2,512
2,413
2,314
2,215
2.116
2,018
1,921
1,823
1,726
1,630
1,533
1,437
1,342
1,246
1,151
1,057
962
868
775
681
588
495
403
311
219
128
+36
-55
-145
-235
-325
-415
-504
-593
-682
-771
-859
0.07
Feet
6,466
6,351
6,236
6,122
6,008
5,895
5,782
5,670
5,558
5,447
5,336
5,226
5,116
5,006
4,897
4,789
4,681
4,573
4,465
4,358
4,252
4,146
4,040
3,935
3,830
3,726
3,622
3,518
3,415
3,312
3,209
3,107
3,005
2,904
2,803
2,703
2,602
2,502
2,403
2,304
2,205
2,107
2,009
1,911
1,814
1,717
1,620
1,524
1,428
1,332
1,237
1,142
1,047
953
859
765
672
579
486
394
302
210
118
+27
-64
-154
-244
-334
-424
-513
-602
-691
-780
-868
0.08
Feet
6,454
6,339
6,225
6,110
5,997
5,884
5,771
5,659
5,547
5.436
5,325
5,215
5,105
4,995
4,886
4,778
4,070
4,562
4,455
4,348
4,241
4,135
4,030
3,924
3,820
3,715
3,611
3,508
3,404
3,301
3,199
3,097
2,995
2,894
2,793
2,692
2,592
2,493
2,393
2,294
2,195
2,097
1,999
1,901
1,804
1,707
1,610
1,514
1,418
1,322
1,227
1,132
1,038
943
849
756
663
570
477
384
292
201
109
+18
-73
-163
-253
-343
-433
-522
-611
-700
-788
-877
0.09
Feet
6,443
6,328
6,213
6,099
5,986
5,872
5,760
5,648
5,536
5,425
5,314
5,204
5,094
4,985
4,876
4,767
4,659
4,551
4,444
4,337
4,231
4,125
4,019
3,914
3,809
3,705
3,601
3,497
3,394
3,291
3,189
3,087
2,985
2,884
2,783
2,682
2,582
2,483
2,383
2,284
2,185
2,087
1,989
1,891
1,794
1,697
1,601
1,504
1,408
1,313
1,218
1,123
1,028
934
840
746
653
560
468
375
283
192
100
+9
-82
-172
-262
-352
-442
-531
-620
-709
-797
-885
                          92

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ambient air.  The source  of  the  span gas  may  be  a  tank or other single-point
S02 supply.  The analyzer may  have a programmable  clock wired to solenoid
valves so that zero  and span operations occur at preset times without the
need for operator assistance.
     It is possible  to set up  a  dynamic calibration  system which will supply
zero air and one or  two span concentrations to the ambient air sampling line
at preset intervals.  At  least one manufacturer  (Metronics) offers such a
system.
     Suggested steps and  explanations for performing zero and span opera-
tions  are listed below.
     1.   Zero check.  Manually  or automatically switch the analyzer sample
          control  (if the analyzer is so  equipped) to the zero position.
          Mark the  stripchart  with time,  date, and action.  Enter the same
          information in  the notebook.  If the zero  point is entered auto-
          matically in the operator's absence, be  sure to note later the
          date, duration, etc.,  on the stripchart  and in the station logbook.
          Be  sure  that the person ultimately  responsible for data reduction
          and analysis  is made aware of these operations so that such time
           intervals are accounted for.  If an automatic data acquisition
          system  is used, be sure that it does not treat the zero and span
           readings  as ambient  data.
          Allow sufficient time  for a stable  zero  signal to occur.  If the
           system  is automated, program the clock for ample time.  If the
          zero air source requires warmup, allow time for this, too.  Make
           no  adjustments  to  the  analyzer  at  this time.
                NOTE.  The system used for the multipoint calibra-
                tion may also serve as a zero and span source.
                First, be certain the system is warmed up and flows
                are calibrated.  Then connect the analyzer to the
                calibration manifold in the same way as in a multi-
                point calibration.
                Such a zero and span operation is often performed
                just prior to a multipoint calibration.  In this
                way, changes in analyzer response since the last
                                     93

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              	 __ ___ ^_ 	  	 __  __^  ,.„.„,_ _.	 _„,  ^^  -_T_  -,—,  ^_ ^.i,,,  I,— _ •• "|
              [multipoint calibration are determined by an accurate,
              [ reliable,  dynamic calibration source.	|
     2-    Span check(s).   Set up the span gas supply so that an accurately

          known concentration of approximately 80 percent of full scale is

          generated.   Turn on the single-point span gas supply by manual or

          automatic means.   Mark the stripchart and enter time, date, and

          action in the notebook.
     Follow all the manufacturer's instructions for installation and use of

the span gas source.   Allow sufficient time for the span gas supply to

equilibrate and for the response of the analyzer to stabilize.   With auto-

mated systems, program the clock for ample time.   Make no adjustments to the

analyzer.
          NOTE.  The system used for the multipoint calibration
          may also serve as a span check source.   If possible, the
          same span concentration as used during the last multi-
          point calibration should be generated so a direct com-
          parison can be made.   If this cannot be done, the con-
          centration that is generated should be compared to the
          expected value (or voltage) based on the calibration
          curve or calibration equation established for the most
          recent prior calibration.   This comparison could be made
          by: (1) solving the least squares regression equation
          for the expected response (mv, volts, or chart divisions)
          to the known S02 span concentration you are generating,
          or (2) finding the expected response on a carefully
          drawn calibration graph of the analyzer response versus
          S02 concentration.
     3.   Disconnect the zero and span system.   Be certain that the analyzer

          ceases to sample zero or span gas and is returned to ambient air.

          When the span check ends, allow sufficient time for the analyzer

          response to "recover" from the span signal.   This will be evident

          from the stripchart trace.   The time at which recovery is complete

          should be recorded as the "end time" for zero and span operation.

          This will also be the time at which valid ambient air data are
                                    94

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          again recorded.  Denoting this time  is particularly important when
          an automatic data acquisition system is used.
     4-   Correct problems indicated by zero,  span data.  As a general rule,
          no adjustments are made to the zero  and span settings of an ana-
          lyzer during a zero and span check.   This is because of several
          reasons.  The zero or  span source  is  often not as accurate as the
          dynamic calibration system.  Minor variations (noise) in instru-
          ment zero and span response are expected and cannot be adjusted
          out.  Large changes in atmospheric pressure or C02 levels of
          cleaned ambient air can affect the span signal somewhat and daily
          adjustment cannot compensate for this.
          If gross variations (greater than 5  percent, the percent allowable
          drift for an EPA equivalent-designated instrument) are noted in
          either the zero or span check, or if  the zero or span is slowly
          but steadily changing  in one direction over a period of days,
          action should be taken.  First, check the zero and span sources
          for reliability by comparison to calibration standards or by
          performing a dynamic calibration.  If they are correct, the ana-
          lyzer itself needs corrective maintenance and a multipoint cali-
          bration.
4.4  MAINTENANCE AND REPLACEMENT OPERATIONS
     Following the zero and span check and just prior to a multipoint dy-
namic calibration, maintenance and replacement  activities are carried out.
Any maintenance on the station itself (such as  air conditioning adjustment
or cleaning of ambient air intake) is also done at this time.  A record of
all items replaced or adjustments made should  be entered in an appropriate
notebook or logbook.  A supply of replacement  gases, filters, and parts
should be maintained at the central laboratory.
     It is suggested that the following minor  maintenance and replacement
steps be performed prior to each monthly multipoint calibration.  Special
conditions such as dusty environments may necessitate more frequent main-
tenance.
     1.   Check gas supplies.  Replace empty or near-empty gas cylinders of
          hydrogen, air, or others.  Service H2 generators by adding water
                                     95

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     or electrolyte.   Refer to the manufacturer's instruction manual.
     If the FPD analyzer flames-out when the H2 supply is replaced,
     relight the flame as soon as  possible to avoid long restabili-
     zation times.
          Check all  connections between the H2 supply and the analyzer
     to be certain they are leaktight.   Use a liquid leak detector.
2.    Replace filters;  clean or replace  sampling lines.   Often a Teflon
     membrane filter and Teflon filter  holder are located in the ambient
     air sampling line leading to  the analyzer.  Some operators make a
     practice of replacing this filter  prior to each multipoint dynamic
     calibration.   Do not allow too much particulate matter to build up
     on the filter before replacing it.   Replace the filter and clean
     the holder prior to calibration.   Figure 4-1 shows a typical
     filter and holder and gives directions for its assembly.
          CAUTION.   Be sure the Teflon filter is seated
          properly and the filter holder is reassembled
          tightly.   If not, a leak will  exist and particles
          may reach the FPD burner.   Exercise care not to
          overtighten Teflon threaded connections.   If the
          thread are stripped, a poor seal  results.
     Another filter which may need to be replaced is located at the
     rear of the analyzer at the dilution air entry.  Replace it with
     an identical filter.  Some analyzers have a coarse sintered brass
     filter located on the pump inside the case.  The sintered filter
     should be replaced after about 1 year of continuous operation.
          CAUTION.  The dilution air filter holder is often
          attached to a hypodermic needle which pierces a
          rubber  septum and acts as a critical orifice.  This
          supplies a constant flow of dilution air to dilute
          the moist burner exhaust air and prevent unwanted
          water condensation.
          If the  needle must be removed to replace the filter
          holder, be sure it is put back exactly as it was.
          Be careful not to obstruct the needle by clogging
          it with a piece of rubber septum material.  If the
                                96

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                          CALIBRATION OR
                          AMBIENT AIR INLET
10
                TEFLON
                FILTER
                             TO ANALYZER
             Figure  4.1.   Sampling line filter holder and filter of all-Teflon construction,

-------
          needle  is  replaced,  the  new one should be of exact-
          ly the  same  length  and gauge as the old one in
          order to avoid large flow changes.   If the rubber
          septum  is  cracked or not seated properly, replace
          it too.
          CAUTION.   If the  dilution air filter is replaced
          with one  quite  different from the original,  flow
          changes  in both the  dilution  air and the sample air
          may occur.   Calibration  errors,  flameout,  and other
          problems  may also occur.
     The ambient air sample line  itself,  3.2 mm (1/8 in) o.d.  Teflon,
     may occasionally need replacement because of a buildup of parti-
     cles or occurrence of "kinks"  in  the line.   If so,  cut and install
     a new piece of exactly the same  length as the one it replaces.
     Use only Teflon fittings;  check  all  fittings for tightness.   Any
     new tube or filter will  require  a conditioning period with S02
     before a stable, steady signal is attained.
     The lines may also be cleaned  by  removing them, flushing with pure
     methanol (methyl alcohol,  a  poison), and venting zero air or dry
     nitrogen through the tube  until  it is dry.   Recondition the lines
     with S02 calibration gas.
3.    Leak check.  Any pneumatic connections that were untightened
     during maintenance and replacement should be leak-checked.  Use a
     liquid leak detector or pure water.   Wipe off the fluid after
     testing.
4.    Perform other maintenance.   Any  maintenance or repair of the
     stripchart recorder and the  data  acquisition system should be done
     at this time.
5.    Adjust instrument flow rates.
     a.   Carefully adjust the  hydrogen flow rate control knob.  Hydro-
          gen flow will be indicated  by a pressure gauge or rotameter
          or both.   Set the gauge or  rotameter to the position speci-
          fied in the operating manual.  Record both the old and new
          settings in notebook.
                               98

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          b.    Carefully adjust the air sample flow rate control knob.  Some
               analyzers, such as the Meloy Model 285 and the Monitor Labs
               Model 8450 have preset sample flow rates which cannot be
               adjusted.  Sample flow will be indicated by a rotameter, but
               usually only when the analyzer is in the zero mode.   Set the
               rotameter to the manufacturer's suggested setting.  Determine
               the actual ambient mode flow rate by attaching the analyzer
               sampling line to the upper part of a soap film flowmeter.
               Refer to Section 5 for explanation of use.  Record the flow
               value in the notebook.
     Any major maintenance on the FPD analyzer should be done prior to cali-
bration.  Be sure to allow enough time for the analyzer to warm up again
before beginning calibration.  Consult the manufacturer's instruction manual
for details of major maintenance operations.  Major maintenance items include:
     1.   Sample pump overhaul or replacement,
     2.   Photomultiplier tube replacement,
     3.   Solenoid valve replacement,
     4.   H2S scrubber  replacement or reconditioning,
     5.   Cleaning or replacement of rotameters or gauges,
     6.   Cleaning of the burner block, and
     7.   Cleaning or replacement of the cooling fans.
4.5  MULTIPOINT CALIBRATION OF AN FPD S02 ANALYZER EQUIPPED WITH
     A LINEARIZED OUTPUT
     A multipoint calibration must be performed when the analyzer is first
set up and periodically thereafter.  The frequency of calibration will de-
pend upon the type of sample the analyzer receives, the environmental condi-
tions under which the analyzer operates, and the requirements for data
accuracy.  Only by performing frequent calibrations (at least monthly) can
the reliability and accuracy of air quality data be maintained and assessed.
Dramatic changes in calibration results alert the user to problems with the
analyzer or calibrator.  Periodic calibrations are an important part of the
quality control and quality assurance aspects of an air monitoring program.
     The following procedure is intended for use with instruments that are
designed to sample the ambient atmosphere for S02.  Under these conditions,
                                     99

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the S02 level often will be low (often 0.1 ppm or less) and measurements of
the highest accuracy are sought.  To help insure the accuracy of the data,
the analyzer should be operated under controlled environmental conditions of
temperature, voltage, and humidity, and the calibration procedure should be
performed frequently.
     A multipoint calibration should be performed soon after receipt of a
new analyzer and monthly thereafter.  In addition, a multipoint calibration
should be carried out:
     1.   Following any adjustments or replacements of amplifier assemblies,
          power supply boards, temperature control boards, or photomulti-
          plier tube;
     2.   If for any reason the air sample flow rate or hydrogen flow rate
          is adjusted from previously set or recommended values (these flows
          affect the flame and, thus, affect the response); and
     3.   If the burner assembly or any Teflon lines are cleaned or re-
          placed.
     A dynamic calibration should always be performed at the site of the
analyzer.   Do not calibrate an  instrument at one location, move it to another,
and  expect  the calibration to "hold."
     Step-by-step instructions  for dynamic calibration of a typical FPD S02
analyzer  (using the  linearized  output) are given below.  Each step is numbered.
Special explanations or precautions are given immediately following the in-
structions.  Figure  4.2 is a reproduction of the stripchart trace of a
typical multipoint calibration  and should be consulted as one proceeds with
the  calibration.
     1.   Verify that PRELIMINARY STEPS. ZERO AND SPAN CHECK. AND MAINTENANCE
          AND REPLACEMENT steps are complete.  Record all actions and results
           in a notebook or the  calibration logbook.
     2.    Interface  the analyzer and the calibration system.  Disconnect the
          analyzer's Teflon ambient air sampling line from the station
          ambient air sampling  manifold and connect it to the calibration
          system manifold.
                The  ambient  air  sampling  line  should be  used  for
                calibration  purposes.   In this way  the calibration
                                     100
n
ion

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    TIME MARK
    1700 EST
                RETURN TO AMBIENT AIR
                                                 ^_ ENTER 6TH CALIBRATION
                                               	1 -POINT (0.075 PPM)
                                                                      ENTER 5TH CALIBRATION
                                                                      POINT (0.1 SO PPM]
                                                                                        ENTER 4TH CALIBRATION
                                                                                        POINT (0.225 PPM)
                                                                               STABILIZATION
                                                                               PERIOD
                                                                                                              CALIBRATION
                                                                                                              POINT
                                                                                                          I	10.375 PPMI
                ~ ENTER SPAN GAS AGAIN (0.400 PPM)

                MAKE MINOR ZERO ADJUSTMENT
                                                                                            SPAN GAS
                                                                                            STABILIZATION
                                                                                            PERIOD
                ENTER SPAN GAS (0,400 PPM SOj)
                                                                       INDICATES APPROXIMATE POINT IN TIME TO READ
                                                                       STRIP CHART AND DVM; RECORD VALUES
    X^   I ADJUST ANALYZER ZERO POT
                                                                       READINGS AT THESE POINTS ARE USED TO CONSTRUCT
                                                                       CALIBRATION CURVE AND TO DERIVE THE LEAST
                                                                       SQUARES REGRESSION EQUATION OF THE CALIBRATION
                                                                       LINE
                        ZERO AIR
                        STABILIZATION
                        PERIOD
                                                                       NOTE:  CHART SPEED IS 6 INCHES/HOUR
                            ENTER ZERO AIR (0.000 PPM S02>
                                       j
                            AMBIENT AIR {-
TIME MARK
1600 EST '
VOLTS
                                                                                                                     0.460
                                                                                                                     0.90
                       Figure  4.2.    Calibration  trace of  linearized  output.
                                         FPD  ambient  air  S02 analyzer.
                                                              101

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          gas passes through the same pathway (including the
          Teflon particulate filter) as the ambient air and
          the same pressures and flow rates are maintained.
          Do not change the length of the Teflon sampling
          line.
          Use of other zero or span gas entry ports to the
          instrument is not recommended for multipoint cali-
          bration.   Use such ports only for zero and span
          checks.                                     	
3.    Sample zero air.   Leave the analyzer in the sample mode and allow

     it to sample zero air from the calibration manifold until a stable

     reading on the stripchart trace or voltmeter is obtained.  Record

     the voltage reading or stripchart reading (number of divisions or

     percent of full scale) in the notebook.   Compare the zero gas

     reading to the value set at the previous calibration.   The values

     should be nearly the same if no significant zero drift has occurred.

     Do not adjust zero pot at this time.
          Be certain that your zero air meets  all  require-
          ments for zero air.   It should not contain sulfur
          compounds or large amounts of water  vapor.   It
          should contain = 350 ppm (or ambient levels of)
          C02.   The oxygen/nitrogen percentage composition
          must be the same as in ambient air.   Refer to
          Section 3.0 for a discussion of the  carbon dioxide
          effect and the composition of zero air.

          The zero airflow must be in excess of the analyzer
          sample flow demand,  preferably 50 percent greater.
          Thus, if an analyzer's sample flow is 200 cmVmin,
          the zero airflow must be at least 300 cmVmin.
          Do not pressurize the calibration manifold since
          this will  alter the analyzer's response.   See
          Figure 3.6 or 3.7 for an illustration of correct
          installation of a calibration manifold.   Provide
          unobstructed exhaust of excess air.   Do  not allow
          back diffusion of room air.   The pressure (as
          measured at the calibration manifold) must not
          exceed 1 inch of water, either positive  or negative,
                               102

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     from the ambient pressure.  Use a water manometer
     for measuring pressure.  Refer to Section 5.0 for
     instructions on its use.
     As long as 30 minutes or more may be required to
     obtain a stable zero baseline.  This is usually the
     case when a high S02 concentration has been sampled
     just prior to sampling zero air.  The analyzer
     should have been on for at least 24 hours prior to
     calibration.
Set the zero of the analyzer.  Set the front panel zero adjust pot

so that the analyzer output, as measured by the digital voltmeter,

DVM, reads 0.000 V or the value given by the manufacturer for the

linearized output.  (For example:  0.000 V for Monitor Labs Model
8450; 0.014 volts for Meloy Labs Model SA-185-2A.)  Do not set

zero by adjusting the recorder zero.
     PRECAUTION!  If your FPD S02 analyzer is a model
     8300 manufactured by the Bendix Corporation, do not
     adjust the front panel zero adjust.  Internal
     adjustments of the nonsulfur suppression pot may be
     required.  Refer to the Bendix operation manual for
     assistance or see Section 4.6.1 for procedures and
     explanations.  Calibration of Bendix FPD analyzers
     continues with Step 5.
     If your analyzer is manufactured by Meloy Labora-
     tories and you wish to use the log output instead
     of the linearized output, refer to Section 4.6.2
     for further details.  Instructions for offsetting
     zero of Meloy instruments are given in Section
     4.6.3.
The pen of the stripchart  recorder should trace a line at the
point on the chart paper corresponding to 0.000 V (or the voltage
value assigned to zero ppm S02)-  Stripchart divisions, percent of
                           103

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     full  scale chart readings, or ppm S02 values taken from the re-
     corder may be used instead of voltmeter readings.   Be certain the
     recorder itself is properly zeroed, spanned, and its response is
     linear.   See Figure 4.2 for an example of voltage and ppm S02
     readings assigned to a stripchart.
     Allow a few minutes following zero pot adjustment to be sure a
     stable voltage is obtained, then "lock" the zero pot and record
     the voltage value in notebook.
          Sometimes the process of "locking"  the zero pot
          causes a slight change in the setting.   Be aware of
          this and make necessary adjustments.
          If an unusually large adjustment is necessary,  or
          if the zero point cannot be set by adjustment of
          the pot:
          a.    Be sure the analyzer has been given sufficient
               time to stabilize on zero air (check strip
               chart for no further change in slope of the
               trace).
          b.    Be sure there is no source of S02  or other
               sulfur compound entering the zero  air.
          c.    Be sure the charcoal scrubber for  the zero air
               supply is fresh.
          d.    Be sure the flame is lighted.
          e.    Consult manual  or manufacturer for trouble-
               shooting and servicing procedures.
5.    Sample SQ9 span gas.   Adjust the flow rate of the calibration
     assembly to produce an S02 span gas of concentration equal to
     approximately 80 percent of the value of the analyzer's range.
     The usual ranges used are 0 to 0.5 or 0 to 1.0 ppm.   If, for
     example, the analyzer is set to a 0-0.5 ppm range, 80 percent of
     the range would be (0.80) (0.5) =0.4 ppm.   Generate this concen-
     tration (0.400 ppm) or an accurately known value close to it.  Use
                               104

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     this as the span gas concentration.  Instructions are given in
     Section 3.0.  Sample the span gas until a stable signal is obtained
     (as indicated by the stripchart trace).  Record the voltage value
     or stripchart reading  in the notebook as "unadjusted span" value.
          A permeation tube type calibrator, whose tube is
          traceable to NBS standards, is recommended for
          generating all S02 concentrations for span and
          intermediate concentrations.  Be certain the diluent
          air (carrier air) is of the same composition as the
          zero air.  See Section 3.0 for details of the use
          of such calibration devices, calculation of the S02
          concentration, and the use of S02 from cylinders as
          calibration gases.

          Provide a flow of span gas that is at least 50
          percent in excess of the analyzer's flow require-
          ment.
          As long as 30 minutes may be required for signal
          stabilization, especially if the analyzer is new or
          if new tubing or a new H2S scrubber has been in-
          stalled, stabilization may take several hours.
          This is due to the "conditioning" of "active sites"
          in the Teflon line and scrubber by S02.  Usually
          10-15 minutes should suffice for stabilization.
          If the analyzer response goes "offscale" and does
          not soon return, remove the sampling line from the
          manifold momentarily and check to see if the ana-
          lyzer and recorder are on the correct range.  Also,
          check the dilution air flow setting of the cali-
          brator.

          Another cause of offscale readings is excess S02
          from a permeation tube that has remained in its
          compartment without air passing over it continuous-
          ly.  If this is the case, the calibrator must be
          flushed with clean air for some hours before the
          calculated concentration is obtained.
6.    Compare "unadjusted span" value to previous calibration results.

     Using the previous calibration curve or equation and the "unad-
                                105

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justed span" reading  determined in Step 5, determine the  concen-
tration of S02 being  indicated by the analyzer.  Compare  this
result to the calculated  span  gas concentration being  used in Step
5.  The calculated concentration is based on the permeation device
output and measured dilution airflow rates.   Compute the  percent
difference between the  two  values.
     Example calculation.   Based on the previous multi-
     point calibration curve,  the indicated S02 span
     concentration  is measured as 0.392 ppm.   The concen-
     tration based  on the  permeation tube weight loss
     and known dilution  flow rates, is 0.430 ppm.
     Thus:
       Indicated Concentration - Calculated Concentration  ,„„     ..••*•
       	x 100 = percent deviation
              Calculated Concentration
                  0.392-0.430 x1nu = -8.84 percent
                     0.430
If the values are within ±10  percent,  proceed to Step 7.

If the present span concentration  is  greater than ±10 percent of
the value predicted by the previous calibration data, a problem
may exist in the present calibration  setup, a problem was present
at the last calibration, or the  analyzer has drifted significantly
and needs maintenance.  Check the  present calibration using the
following steps.

Check the calibration system  for:
a.   Proper dilution airflow  setting  (redetermine actual
     airflow if necessary and recalculate S02 concen-
     tration if an error was  made).
b.   Sufficient airflow to the analyzer.   (50 percent
     excess flow is desirable.)
c.   Proper temperature and temperature control of
     permeation oven.
                           106

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     d.   Line voltage variations.

     e.   Leaks.

     f.   Permeation tube  integrity.

     g.   Proper C02 content of diluent air.

     Check the FPD Analyzer for:

     a.   Correct and stable sample flow rate.

     b.   Correct H2 flow  rate.

     c.   Obstruction-free exhaust.

     Check the recorder for correct span.
          If no fault  is found  in any of these checks, the
          analyzer may need electronic adjustment.  Refer to
          the manufacturer's manual or consult the manu-
          facturer.  It is also possible that the previous
          calibration  was in error; it should be reviewed for
          errors.
7.    Set the analyzer span.  Calculate the expected analyzer voltage

     output and/or recorder response (chart divisions or percent of

     full scale) for the calculated concentration of span gas.   Adjust

     the front panel span pot so that the linearized output reads the

     correct value on the DVM and/or the stripchart.
          Example computation.  If the analyzer is set on the
          0-0.5 ppm range and has a 0-1 V linearized output,
          and the calibration system is set to give 0.400 ppm
          S02, the predicted voltage is computed as follows:
          calibrator span, ppm
          analyzer range, ppm
          0.400 ppm
          0.500 ppm
analyzer full  _  voltage
scale voltage  ~  span point
output


  I volt    =    0.800 V
          The recorder should trace a steady line at an
          upscale point.  If the recorder is on the 0-1 V
          range, the stripchart has 100 chart divisions, and
          the recorder zero is set at 5 percent of full scale
          (i.e., five chart divisions), then 0.400 ppm S02
          should give a trace at:
                                107

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                       x  (100 divisions) + (5 divisions)  =
           80.0 + 5 = 85.0 chart divisions
           Refer to Figure 4.2 for illustration.
 8.    If the span adjustment required in Step 7 was appreciable (±5
      percent of the expected value), return the analyzer to zero air
      (Step 3), allow the analyzer to stabilize, and make necessary
      adjustments of the zero pot.
 9.    Return to the span gas, allow the analyzer response to stabilize,
      and make necessary adjustments of the span pot.
10.    Repeat zero and span gas operations until  it is no longer necessary
      to adjust the zero or span pots.
11.    Adjust the calibrator flow rates  to generate in succession the
      following standard S02 calibration levels  (expressed as percent of
      instrument range):

      approximate percent of range      ppm,  if 0.5 ppm range
                    75
                    60
                    45
                    30
                    15
0.375
0.300
0.225
0.150
0.075
      Other levels  may be  introduced  if desired.   Values  less than 0.100
      ppm are suggested since  ambient S02  concentrations  are usually in
      this range.   Values  less than 0.040  ppm  (40  ppb)  are very slow to
      give a stable response.

      Important!  Make no  adjustments to the zero  or  span pots while
      these points  are being entered.

      Record the voltage or stripchart response  for each  level.
                                108

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           Introduction of an S02 concentration equal to
           exactly 75 percent, 60 percent, etc. of full scale
           range is not necessary.  What is important and
           necessary is that these concentrations be equally
           spaced over the range; be within ±5 percent of the
           75 percent, 60 percent, etc., level; and that the
           concentration be prepared with accuracy (within
           0.001 ppm).
           Allow sufficient time for each S02 level to stabi-
           lize ("level off" as indicated by the stripchart)
           before proceeding to the next value.
           The instrument response time and stabilization time
           will be slower at the lower concentration values.
12.   Construct a plot of the calibration data on graph paper.  Refer to
      Figure 4.3 as an example.
      a.   Use a high quality graph paper with fine graduation marks so
           that data points may  be clearly entered.  A good choice is
           18 x 25 cm graph paper with 10 x 10 divisions to the centi-
           meter.
      b.   Assign the S02 concentration values to the x-axis  (horizontal
           axis).  These are the calculated values from the calibration
           system.  Subdivide the x-axis in ppm extending from zero to
           the analyzer's full scale  range.  Units of microgratns of S02
           per cubic meter (ug/m3) may also be plotted; 1 ppm S02 =
           2,615 ug/m3 S02 at 1  atmosphere (760 mm Hg) and 25° C.
           Assign the analyzer response (V or mV or percent of scale) to
           the y-axis (vertical  axis) and subdivide this axis into
           portions of the full  scale output for the particular analyzer
           (0-1 V, 0-100 mV, etc.).
      c.   Enter the zero and span values on the graph, also  enter all
           intermediate calibration values.
      d.   Check the quality of  the calibration curve in the  following
           way:
                With the aid of  a straightedge  (ruler, etc.)  connect  the
                zero and span points  with a  light pencil line.
                                  109

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                                                       LEAST SQUARES OF LINE OF BEST FIT
                                                       LEAST SQUARES LINEAR REGRESSION EQUATION IS:
                                                                VOLTAGE = 1.992 [SOjI - 0.0054

                                                       [S02],ppm        0.437  0.338  0.278  0.144  0.099 0.078
                                                       RESPONSE, VOLTS  0.875  0.686  0.555  0.292  0.198 0.155
     0.1
0.2                        0.3
 S02 CONCENTRATION, PPM (x-AXIS)
                                                                                   0.4
                                                                                                             0.5
Figure  4.3.   Calibration curve  for linearized FPD S02 analyzer.

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                Look at the positions of the intermediate calibration
                points with respect to the straight line.  The inter-
                mediate points should fall on or very near the line.  If
                they are all off, either above or below the line, this
                may suggest:
                     The span point is incorrectly set.   Recheck the air
                     flow and calculations used for spans.
                     The zero point is incorrectly set.
                     The linearization circuitry of the FPD analyzer is
                in need of adjustment.  Refer to operation manual or to
                manufacturer for aid.  All possible error sources should
                be investigated before adjustments are made to the
                linearization circuitry.   Unless you are thoroughly
                familiar with this circuitry, it is best to consult the
                manufacturer for advice.
13.   Determine the calibration equation.  Determine,  or have determined
      by someone, the equation for the least squares line of best fit
      for all the calibration points, including zero and span.
           Many hand-held calculators now have the capacity to
           compute the least squares linear regression equation.
      The equation will be of the form  y = mx + b where:
           y = analyzer response (V),
           m = slope of calibration line (V per ppm),
           x = concentration of S02 (ppm), and
           b = intercept of the calibration line with the y-axis (V).
      Using this equation, calculate the location of any two points on
      the line (one point near zero, one point near full scale).  Con-
      nect these points with a light line and extend the line through
      the y-axis as well as beyond the span point.  This line should
      pass through or very near to the intermediate calibration points,
      the span point, and the zero point.  Refer to Figure 4.3.
                                 Ill

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               Apply the equation to convert voltage signals stored on a

          data acquisition system to concentration units.   Forward the

          calibration record and the least squares regression equation (if

          computed) to your supervisor or to the data processing department.

          This equation will be used to treat the signals  stored in a DAS

          until the time of the next calibration.

          The equation may also be used to solve for ppm S02 concentrations

          corresponding to voltage values taken manually from the stripchart.

          If the calibration points lie on or very close to the calibration

          curve, the S02 values may be read directly from  the stripchart.

Example calculations:


               x-axis                                      y-axis

          S02, ppm, from                          Linear response,  volts
          permeation tube                       (0-1 V output;  analyzer
           calibration                                range 0-0.5 ppm)


         0.0    zero air                    +0.0136  (set  with  zero pot)
         0.437  span gas                     0.875   (set  with  span pot)
         0.338                               0.686
         0.278                               0.555
         0.144                               0.292
         0.099                               0.198
         0.078                               0.155

     Least squares linear regression equation is:

                       voltage = 1.9921 [S02] + 0.0054

     or, rearranging:

                         [S02]ppm  .
Thus, for example, if a known concentration of S02 of 0.500 ppm is sampled
by the analyzer, the expected response is:

               voltage = 1.9921 (0.500 ppm) + 0.0054
                          voltage = 1.001

As another example, if a voltage value of 0.300 is obtained, the equation
says that the concentration of S02 is:
                                    112

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                   - 0.300 - 0.0054    _ nyio
                   - ~	 =  0.148 ppm
               ppm        1.9921
    14.    Return the analyzer  sampling  line  to the station sampling mani-
          fold and ambient air.  Make note of this action and the time in
          the notebook.
4.6  SUPPLEMENTARY INSTRUCTIONS  FOR  PARTICULAR FPD ANALYZERS
4.6.1  Bendix Model 8300:  Electronic Zero and Operational Zero
     The Bendix Model 8300 FPD S02 analyzers have two adjustable zero pots
which serve different purposes.  One is  located on the front panel; it is an
electronic zero and is adjusted  only when the flame of the FPD is extinguished.
The second zero,  located  inside  the  cabinet, is often called the nonsulfur
suppression adjustment, and  is adjusted  only when the flame is burning and
zero air is being sampled.   If your  instrument is a new model (not Model
8300) the following instructions do  not  apply.  For instance, the Model 8303
would not use these instructions.
4.6.1.1  Front panel electronic  zero adjustment
     Adjustment of the front panel electronic zero must be made while the
flame is extinguished.  The  following steps  are taken from the Bendix oper-
ation manual.
     1.   Extinguish the  flame by pulling the PULL TO TEST hydrogen diverter
          valve fully out.   Be cautious  when venting hydrogen.  A tube
          should be attached to  the  vent to  carry the hydrogen to the out-
          side air.
     2.   When the flame  is  out, if  a positive output is  indicated by the
          voltmeter or recorder, adjust the  ZERO adjustment pot on the front
          panel of the analyzer  for  a zero indication on  the voltmeter or
          recorder.  This adjustment corrects for the offset of the ampli-
          fiers in the Exponential Amplifier Card.
               NOTE:   Usually the ten-turn ZERO adjustment pot
               indicator dial is factory-set at midscale;  -500,
               and will  give  a 0.001 V output when the 0-1 V range
               output  (located on the rear panel) is connected to
                                     113

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               Apply the equation to convert voltage signals stored on a

          data acquisition system to concentration units.  Forward the

          calibration record and the least squares regression equation (if

          computed) to your supervisor or to the data processing department.

          This equation will be used to treat the signals stored in a DAS

          until the time of the next calibration.

          The equation may also be used to solve for ppm S02 concentrations

          corresponding to voltage values taken manually from the stripchart.

          If the calibration points lie on or very close to the calibration

          curve, the S02 values may be read directly from the stripchart.

Example calculations:


               x-axis                                      y-axis

          S02, ppm, from                          Linear response,  volts
          permeation tube                       (0-1 V output;  analyzer
           calibration                                range 0-0.5 ppm)


         0.0    zero air                    +0.0136  (set with  zero pot)
         0.437  span gas                     0.875   (set with  span pot)
         0.338                               0.686
         0.278                               0.555
         0.144                               0.292
         0.099                               0.198
         0.078                               0.155

     Least squares linear regression equation is:

                       voltage = 1.9921 [S02] + 0.0054

     or, rearranging:

                         L"s°2]™m  - voltage - 0.0054
                              Ppm  "      1.9921


Thus, for example, if a known concentration of S02 of 0.500 ppm is  sampled
by the analyzer, the expected response is:

               voltage = 1.9921 (0.500 ppm) + 0.0054
                          voltage = 1.001

As another example, if a voltage value of 0,300 is obtained,  the equation
says that the concentration of S02 is:
                                    112

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                   - 0-300 -  0-0054  _  .  ,.0
              J	—  =  0.148  ppm
               ppm        1.9921
    14.   Return the analyzer  sampling  line  to the station sampling mani-
          fold and ambient air.  Make note of this action and the time in
          the notebook.
4.6  SUPPLEMENTARY INSTRUCTIONS  FOR  PARTICULAR FPD ANALYZERS
4-6.1  Bendix Model 8300:  Electronic Zero and Operational Zero
     The Bendix Model  8300 FPD S02 analyzers have two adjustable zero pots
which  serve different  purposes.  One is  located on the front panel; it is an
electronic zero and is  adjusted  only when the flame of the FPD is extinguished.
The second zero, located  inside  the  cabinet, is often called the nonsulfur
suppression adjustment, and  is adjusted  only when the flame is burning and
zero air is being sampled.   If your  instrument is a new model (not Model
8300)  the following instructions do  not  apply.  For instance, the Model 8303
would  not use these instructions.
4.6.1.1  Front panel electronic  zero adjustment
     Adjustment of the  front panel electronic zero must be made while the
flame  is extinguished.  The  following steps  are taken from the Bendix oper-
ation  manual.
     1.   Extinguish the  flame by pulling the PULL TO TEST hydrogen diverter
          valve fully  out.   Be cautious  when venting hydrogen.  A tube
          should be attached to  the  vent to  carry the hydrogen to the out-
          side air.
     2.   When the flame  is  out, if  a positive output is  indicated by the
          voltmeter or recorder, adjust the  ZERO adjustment pot on the front
          panel of the  analyzer  for  a zero  indication on  the  voltmeter or
          recorder.  This adjustment corrects for the offset  of the ampli-
          fiers in the  Exponential Amplifier Card.
                NOTE:   Usually the ten-turn ZERO adjustment pot
                indicator dial  is factory-set at midscale;  -500,
                and  will  give a 0.001 V output when the 0-1 V range
                output (located on the rear panel) is connected to
                                     113

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     1.
     2.
               a digital  voltmeter.   If the voltmeter or recorder
               indicates  that adjustment is necessary, the ZERO
               pot should require adjustment by only a few divi-
               sions.
     3.    If a 5 percent offset of full  scale and zero of the analyzer is

          desired,  use the front panel  ZERO adjustment pot at this time.

          For example, if the analyzer  is  in the 0-1 ppm range and has a 0-1

          voltage output, the pot should be adjusted until the voltmeter or

          recorder indicates 0.050 V (50 mV).   This gives a "live zero."

          See comments in Section 4.6.3  describing the effects of this zero

          offset on the data.
     4.    After electronic zero adjustment is complete,  return the hydrogen

          diverter valve to the "in" position and relight the flame.

4.6.1.2  Internal operational  zero (Nonsulfur Suppression) adjustment
The instrument should be on,  the flame should be lighted,  and the
instrument should be sampling zero air.
Carefully remove the top cover of the analyzer and adjust  the
NONSULFUR SUPPRESSION pot (located on an interior panel  of the
instrument) until a zero voltage is indicated on the voltmeter or
recorder.   This adjustment is very critical.   Extreme misadjust-
ment can cause a negative voltage readout.   Misadjustment  also
tends to cause nonlinear response, especially at low levels.
               WARNING.   The NONSULFUR SUPPRESSION  pot is  the
               biasing pot for the  photomultiplier  tube log  ampli-
               fier.   If it is turned  too  far negative, it will
               bias the amplifier in an OFF  position  and a certain
               concentration of S02 will be  required  to turn the
               amplifier on.   This, in effect,  causes loss of
               detection of low-level  sulfur concentrations.

               If the pot adjustment is too  positive  it will cause
               the amplifier to come on and  show a  positive  re-
               sponse in the absence of of S02.   In this condi-
               tion,  nonlinear behavior is also observed.
     3.    Operate the instrument on,zero  air for 30  minutes  to be sure there
          is  no zero  drift.
                                    114

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     4.   Return to the  calibration procedure,  Section 4.5 of this document,
          and continue with  the  span adjustment.
4-6.2  Use of the Optional Log-Li near Output  of Meloy FPD Analyzers
     There are several signal  outputs available from various models of the
Meloy  (or the earlier Melpar)  FPD  S02 analyzer.   These are the log-log
output (plotted as  log of amperage versus  log of concentration), and the
linearized output (plotted as  linear voltage  versus  linear concentration).
     The  linearized output is  most commonly used and most instruments are
purchased with the  optional  linearization  circuit included.  Linearizing
circuitry "packages" are also  available.   A discussion of the log-log and
log-linear outputs  is given  below.
4.6.2.1   Log-log output
     The  output signal from  the  photomultiplier tube is  in the form of an
electrical current.  This signal  is an exponential function which plots
linearly  versus concentration  on log-log paper  with a slope of 1.4 to 2.0,
depending on  the burner  characteristics.   Figure 4.4 shows a log-log plot of
S02  concentration,  ppm,  versus the photomultiplier current output of a
typical Meloy FPD S02 analyzer.
     The  log-log output  is not commonly available on Meloy ambient air
analyzers.  The output more  commonly available  at the rear panel is the
log-linear output discussed  below.
4.6.2.2   Log-linear output
     Meloy Laboratories  employs  a  patented amplifier which converts the
current from  the PM tube to  a  voltage.  This  amplifier also has a log re-
sponse which  is adjustable so  that a 0-1 V output may represent up to six
decades of input current.  By  using this log/linear amplifier, a wide dy-
namic  range is obtained  with excellent readability for low S02 concentra-
tions.
     Figure 4.5 is  a plot of typical calibration data, and shows S02 concen-
tration, ppm, versus the voltage output from  the log/linear amplifier.  In
this particular instrument,  a  voltage output  of 0.000 V  corresponds to 0.000
ppm  S02 and 1.000 V to 0.500 ppm S02.   Note that the output is plotted on
semi log graph.  The S02  concentration is plotted on the  logarithmic x-axis,
the  analysis response, volts,  is entered using  the linear y-axis.

                                     115

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          LOG-LOG OUTPUT
                                        1 0.08 ppm

                             0  10 20 30  40 50 60 70 80 90  100
         TYPICAL ANALYZER
        CALIBRATION CURVE
CHART RECORDED READINGS
Figure 4.4.   Log-log output of the  Meloy Model  SA 185
                   FPD  S02 analyzer.
                            116

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   1.0





   0.9





   0.8



c/»

5  0.7
o
>


!5  0.6
Q.





   "
    0.3
 cd  0.2




    0.1
ta
o
       1.0
                                                         0.1




                                                  Concentration, ppm
                                                                                                             0.01
    Figure 4.5.   Log-linear  plot of calibration data, Meloy model  SA 185-2A FPD  S02 analyzer.

-------
     Other concentrations of S02 may be read from the curve if the voltage
output of the calibrated analyzer is known.   For example, a voltage output
of 0.460 corresponds to an S02 concentration of 0.048 ppm.
     If data are recorded on linear stripchart paper, the concentration
value cannot be read directly from the chart.   Instead the voltage value (or
alternatively, the number of chart divisions)  is read from the stripchart
and the ppm (or ug/m3) value taken from the calibration curve (e.g., Figure
4.5).  Logarithmic stripchart paper may also be used.  Concentration values
are then read directly from the chart.
     If log/linear voltage data are stored on  magnetic tape by a data acqui-
sition system, an equation must be employed to convert the raw voltage
signal to physical units.  Such an equation is developed in Section 4.6.3 of
this document.
4.6.3  Data Correction Due to Baseline Offset  of the Meloy Lab's Model
       SA 185 Output

     Some users may prefer to offset the "zero" baseline output of Meloy
Model SA 185 FPD sulfur analyzers to some point higher on the output voltage
scale to allow observation of any negative drift which might occur.   Indeed,
in the early models, which use electronic rather than thermal flame-off
detection, such negative drift can cause hydrogen shutoff with subsequent
unnecessary downtime.
     When offset is used, the data of the normalized logarithmic output are
no longer applicable and an error, the magnitude of which depends on the
amount of offset, is introduced into the data  being collected.
     The maximum error occurs at the lower levels of concentration due to
the nature of the logarithmic curve.  The mathematical expression used to
calculate the effect is given below.  Correction tables, calculated from
that expression, for offset voltages of +0.065 V (0.01 ppm) and +0.147 V
(0.015 ppm) for a typical SA 185 calibration curve are also provided.   In
the data shown with a 0.01 ppm offset the precision error is no greater than
+0.003 ppm and is reduced, in the area of 0.04 ppm, to insignificance (+0.001
ppm).
     Two possibilities for data correction exist.  First, a gross error of
approximately 0.003 ppm can be subtracted from all readings below 0.040 ppm.
                                    118

-------
Second, an exact correction based on an equation  and  the calibration curve
supplied with your  unit(s)  can be used either manually or with a computer,
if that type of data treatment is desired.   A computer can be programmed
easily to correct each data point or to provide a correction table.
     There is a third possibility.   It is to accept the readings without
correction,  knowing that a  possible error of +0.004 ppm at very low concen-
trations exists but is not  significant enough to  cause concern.
     The equation used to determine actual  concentration versus output
signal when  the baseline (zero gas value) is offset (that is, the output
zero value is greater than  zero) is:

                       [S02] = 0.007260 [eVRA - eV0A]B

where:
      [S0?] = actual concentration, ppm
         e  = natural logarithm base = 2.71828
        Vp  = output signal  voltage with sample divided by output voltage
              at 1 ppm (Full Scale)
        Vn  = output voltage with zero gas introduced  to analyzer divided
              by output voltage at 1 ppm (Full Scale)
         A  = 1.0695 [In (A-j/Ag)]
            - (4.6052)
         B     [In (A^/Ag)]

        A   = current output in amps from calibration  curve  at  1 ppm S02
        A   = current output in amps from calibration  curve  at  0.010 ppm S02
        In   = natural log of value in parenthesis

      An example of the equation  use and the resulting error using  a typical
 calibration curve is:

           A  = 4.55 x 10"9 amps  at  0.01 pptn S02
 and                     _c                  __
           A  = 3.85 x 10   amps  at  1.0 ppm  SU2
                                      119

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therefore:
         A   = 9.0433
           A = 1.0695 (9.0433) = 9.672
             _ (4.6052)  _ Q 5Q92
           8 ' (9.0433)  ~ °-5092
with a baseline offset of 0.065 V (0.01 ppm on the meter):
          eV  = e(0-065) (0'672)  = 1.875
using this "typical calibration curve" data for Table 4.2 were prepared.  As
can be seen from Table 4.2, the error is only 0.003 ppm when the meter or
output reads 0.020.  The error quickly decreases so that at a reading of
0.05 ppm or greater there is essentially no error due to the offset (a
%0.001 ppm variation is attributed to mathematical error due to rounding
off).
     Table 4.3 shows the effect of a 0.015 ppm offset.   The error, although
greater at very low concentrations, becomes insignificant at 0.07 ppm concen-
tration level.
     Table 4.2.  Typical effect of an offset of 0.065 V (0.01 ppm)
VR
0.065
0.206
0.288
0.346
0.392
0.533
0.673
0.756
0.859
0.928
1.000
Meter Reading
S02 (ppm)
0.01
0.02
0.03
0.04
0.05
0.10
0.20
0.30
0.50
0.70
1.00
Actual
Concentration (ppm)
0.000
0.017
0.028
0.039
0.049
0.100
0.199
0.300
0.499
0.701
1.000
Error
(ppm)
Not Applicable
+0.003
+0.002
+0.001
+0.001
0
+0.001
0
+0.001
-0.001
0
                                    120

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     Table 4.3.   Typical effect of an offset of 0.147 V (0.015 ppm)
v Meter Reading
R S02 (ppm)
0.147
0.206
0.288
0.346
0.392
0.533
0.673
0.756
0.859
0.928
1.000
0.015
0.020
0.030
0.040
0.050
0.100
0.200
0.300
0.500
0.700
1.000
Actual
(ppm)
0.000
0.013
0.026
0.037
0.048
0.100
0.199
0.300
0.499
0.701
0.999
Error
(ppm)
Not Applicable
+0. 007
+0.004
+0.003
+0.002
0
+0.001
0
+0.001
-0.001
+0.001
4.7  SUMMARY OF FPD ANALYZER PARAMETERS WHICH MUST BE OPERATOR-CONTROLLED
     Operator-controlled parameters relating to the operation of an ambient
air S02 FPD analyzer are summarized in Table 4.4.  The table lists the
parameter, how the operator controls the parameter, how the operator may
identify lack of control of the parameter, and how the operator may bring
the parameter into control.
                                     121

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                  Table 4.4  FPD analyzer parameters which must  be  operator-controlled
                                      in order to obtain valid data
PARAMETER
     Air sample flow rate, cc/minute
How Operator Controls Parameter

     Needle Valve.  (NOTE:  Monitor Labs Model  8450 and Meloy Model  285  have  a  preset  control  which
     operator cannot adjust.)

How Operator May Identify Lack of Control

     1.   Test airflow to sample inlet with calibrated bubble flowmeter  or calibrated  mass  flowmeter.
          After correction to 760 mm Hg, 25°C,  compare to previous  determination  and/or  manufacturer's
          setting.

     2.   Check the instrument's calibrated air rotameter and compare setting with that  found  at last
          calibration.   (NOTE:   Most air rotameters measure zero air from internal source and  not
          the actual sample flow; therefore, use flowmeter check in addition  to rotameter check.) After
          long periods of use,  rotameters may exhibit "sag."  The rotameter ball  will  move  to  a new
          location, but the same flow rate will continue.   This is  caused by  a  combination  of  electro-
          static effects and scratching of the  rotameter column by  the rotameter float.

How Operator May Bring Parameter Into Control

     1.   Remove any obstructions to flow.   (Dirty Teflon filter, dirty, kinked,  or bent Teflon tubing,
          dirt-plugged orifice, defective Teflon solenoid valve, plugged or bent exhaust line,
          plugged dilution air inlet orifice and/or filter, Teflon  tubing squeezed shut  by  compression
          fitting, etc.)

     2.   Eliminate any leaks in sample flow system.   (Ill-fitting  particulate  filter, loose compression
          fitting, loose or poor connection of sampling line to sampling manifold, leaking solenoid
          valve, loose connection to sampling pump, etc.)

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                        Table  4.4.   FPD  analyzer  parameters which  must  be  operator-controlled
                                      in  order  to  obtain  valid  data (continued)



      How  Operator  May  Bring  Parameter Into  Control  (continued)

           3.    Verify  sample pump  performance.  (Sample  pumps  periodically need  new  diaphragms  or valve
                assemblies.   Dust particles  can affect  the  flow and the  flow will  vary  with  length of
                pump operation.)

           4.    Check burner  assembly components for water  vapor condensation and  corrosion.   (Verify
                heater operation  and clean or replace corroded  components.)
ro

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                  Table 4.4.  FPD analyzer parameters which must be operator-controlled
                                in order to obtain valid data (continued)
PARAMETER
     Hydrogen flow rate, cc/minute
How Operator Controls Parameter
     Hydrogen pressure regulator and gauge.   (Some older analyzers have a needle valve control  or a
     pressure regulator with no gauge.   These adjustments are in addition to the pressure regulator
     and gauge located at the hydrogen tank or generator.)

How Operator May Identify Lack of Control
     1.   Check the instrument's calibrated H2 rotameter and compare setting with that found at last
          calibration, and/or with manufacturer's suggested setting.  Be certain the rotameter is
          not "sticking."

     2.   Disconnect hydrogen feed at burner assembly, override the hydrogen shutoff control, and
          measure flow with bubble flowmeter or calibrated hydrogen mass flowmeter.   (Caution!   Hydrogen
          is a flammable gas; provide adequate ventilation.)  Compare with previously determined H2
          flow rates.

How Operator May Bring Parameter Into Control

     1.   Check hydrogen source (cylinder or generator) for adequate pressure and pressure setting.

     2.   Be certain H2 solenoid is not sticking shut.

     3.   Check for obstructions to flow (bent metal tubing).  Check for leaks with leak detector
          solution.

     4.   Check burner assembly for corrosion.

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en
                  Table 4.4.  FPD analyzer parameters  which must be operator-controlled
                                in order to obtain  valid data (continued)



PARAMETER

     Interferences to S0g Detectability

     1.   Sulfur compounds  other than  S02
     2.   Carbon dioxide
     3.   Water condensation
     4.   Stainless steel or plastic tubing in  sampling  line
     5.   S02 removed in the presence  of 03 in  heated  H2S silver scrubber

How Operator Controls Parameter

     1.   The positive  interference of sulfur compounds  other than  S02  is eliminated  by  use  of a scrubber
          which  is available from the  instrument manufacturer.   Determine or estimate the  average con-
          centration  of H2S for the area in ppm.  Use  the manufacturer's  ppm-hours  rating  of scrubber
          to compute  expected  lifetime for the  area.

     2.   The  negative  interference of carbon dioxide  is  minimized  by calibration with air containing
          ambient  levels of C02.  (Refer to discussion of clean  air supplies for FPD  calibration,
          Section  3.3.)

      3.   The  negative  effect  of water condensation in manifold  and sampling lines  is minimized
          by proper  temperature and humidity control of  the  room housing  the analyzer.

      4.    Stainless  steel,  rubber, polyethylene, etc., tubing is  never  used as a sample line
           since  S02  absorbs and reacts.  Use only Teflon.

      5.    Keep H2S scrubber temperature as low  as possible to obtain optimum performance.  Instruments
           equipped with unheated scrubbers show less interference.

 How Operator May Identify  Lack of Control
      1.    Challenge  the scrubber with  a low level of H2S  and check  for  analyzer response.  If response
           occurs,  scrubber  is  not effective.

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                            Table 4.4.   FPD analyzer parameters  which  must  be operator-controlled
                                          in order to obtain  valid  data  (continued)
ro
How Operator May Identify Lack of Control (continued)
     2.    Perform independent calibration check (make no adjustments) of analyzer with calibration system
          known to have =350 ppm C02 present.   Compare calibration curves and see if the analyzer's
          response has diminished.   (Refer to Section 3.0,  Effects of C02.)

     3.    S02 concentration at time of pre-calibration check is lower than expected.   Visible moisture
          present in sample line or station manifold.

     4.    Inspect analyzer and sampling lines for proper material  (Teflon).

     5.    Challenge analyzer with S02, then with S02 plus 03.

How Operator May Bring Parameter Into Control

     1.    Replace or clean the scrubber according to manufacturer's instructions.

     2.    Perform calibration with ambient level of C02 present in the calibration gas.  (See Section 5.0
          for a procedure for determination of ambient levels of C02.)

     3.    Maintain high enough room temperature such that H20 condensation does not occur.

     4.    Replace steel or plastic tubing with Teflon tubing.

     5.    Use unheated H2S scrubber.  Check temperature control of heated scrubber.

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                  Table 4.4.  FPD analyzer parameters which  must  be  operator-controlled
                                in order to obtain valid  data (continued)



PARAMETER

     Temperatures

     1.   Shelter temperature

     2.   Temperature of analyzer components  (photomultiplier tube housing,  burner block,  and exhaust
          assembly, H2S scrubber)

How Operator Controls Parameter

     1.   Adjust heating/air conditioning controls or shelter.

     2.   Operator  cannot  control temperatures  of analyzer components.

How Operator May  Identify  Lack of Control

     1.   Shelter temperature is outside the  limits of 20-30°C  (68-86°F).

     2.   The  following may indicate lack of  instrument temperature  control.

          a.    Zero or  span signal  is unsteady.  Photomultiplier  tube housing temperature may be
                varying.  This affects the PMT output and  H2  flow  controlling capillaries or
                other pneumatic impedance elements.  Check for proper temperature by use of built-in
                thermocouple or status light of  analyzer.

           b.    Flame will  not light, or moisture droplets appear  in  exhaust line.  This may indicate
                that the  burner block and exhaust manifold have  lost  heat  and allowed condensation to
                occur.   Check thermocouple or  status light.   Touch burner  block and exhaust lines
                cautiously.  They should be very hot.

           c.    H2S  scrubber fails to scrub H2S.  This could  indicate failure of heater element in
                scrubber.

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                           Table 4.4.   FPD analyzer parameters which must be operator-controlled

                                         in order to obtain valid data (continued
ro
oo
         How Operator May Bring Parameter Into Control

              1.    Adjust shelter temperature.


              2.    Replace defective heaters.

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                  Table 4.4.  FPD analyzer parameters which must be operator-controlled
                                in order to obtain valid data (continued)
PARAMETER
     Linearity of signal output
How Operator Controls Parameter

          Adjustments of Linearization Electronic Circuitry.  CAUTION!  Do not adjust without  first
     determining this is truly the problem.  (NOTE:  the linearization circuitry is factory-set  for
     the Monitor Labs Model 8450 and cannot be operator-adjusted.)

How Operator May Identify Lack of Control

          Operator performs multipoint calibration and examines graphical plot of analyzer response for
     departures from linearity.  (Refer to Calibration Section 4.0 and Linearization Procedures, in
     the manufacturer's instruction manual.)

How Operator May Bring Parameter Into Control

          Operator generates S02 calibration gases (zero, span, and intermediate points) and adjusts
      linearization circuitry until linearity is achieved.  (See Linearization Procedures in the
      manufacturer's instruction manual.)  The use of a picoamp source to generate amperage signals
      equal  to  those expected from S02 is another approach to establishing linearity (consult
      manufacturer).


                                                                                          Concluded

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130

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                                  SECTION 5.0
                                PROCEDURAL AIDS
5.1  INTRODUCTION
     Establishing and maintaining  sample and calibration gas flow rates is
essential to obtaining  quality  data  from any ambient air analyzer.  Proce-
dures, explanations, and  precautions for determining and correcting air-
flows are given  in  this section.
     A common piece of  equipment for determining the volumetric flow of a
gas is the soap  film flowmeter  or  bubble flowmeter (Section 5.2).   Such
flowmeters can be bought  commercially or built  in glassblowing shops.   All
soap film flowmeters should  be  calibrated by water displacement or by compar-
ison to a certified soap  film whose  volume  is traceable to NBS standards of
volume.  An example of  a  certified soap film flowmeter is the Hastings Model
HBM-1 which is available  from the  Hastings  Raydist Company, Hampton, Virginia.
     Section 5.3 discusses the  use and care of  the mercury barometer which
is used to determine atmospheric pressure.  Section 5.4 discusses the use of
a water manometer which is used to determine very slight variations in
pressure.  Section  5.5  discusses an  equation to correct volumetric flow
rates to the normal conditions  of  25° C and 760 mm Hg.
     Section 5.6 outlines a  quantitative method for determining the C02
content of ambient  air  or air from clean air supplies.
                                     131

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5.2  SOAP FILM FLOWMETER, SFFM, OR BUBBLE FLOWMETER
       PROCEDURE
RESULTS, EXPLANATION
    PRECAUTION
1.  Choose the size SFFM
    needed for the job.
    Be certain it is cali-
    brated or certified.19
    See Figure 5.1
2.  Place SFFM on level
    spot and secure it
    to prevent tipping.
3.  Fill reservoir
    with soap solution.
4.  Connect SFFM to gas
    tubTng of flowing
    system.
    a.  If source pushes
        gas out, connect
        to lower port of
        SFFM (upper port
        open).
    b.  If source pull
        gas in, connect
        to upper port of
        SFFM (lower port
        open).
    c.  If measuring an
        inline flow, break
        into system and
        connect both

        ports,  making
        closed loop.
If flowmeter volume is
too smal1, one cannot
accurately time the
soap film movement.
About 30-60 seconds
time for measurements
is desirable.
Inaccurate readings
may be obtained if
SFFM is not level.  A
ringstand with soft
clamps is a convenient
holder.

A liquid leak detector,
such as "SNOOP®" is sug-
gested.
Leak-free connection
is essential.   Use one
of the following:
a.  Ground glass ball/
    socket fittings
    and clamp.
b.  Compression fit-
    tings with soft
    rubber or Teflon
    gaskets.
c.  Smaller tubing
    forced tightly in-
    to or over larger
    tubing.
If gas flow rate
is less that 2 cc/
minute, gas dif-
fusion through
soap film is
appreciable.  Do
not use SFFM for
very low flow
measurements.

Do not over-
tighten clamps.
Fill reservoir and
lines to a point
just below lower
air inlet to
SFFM.

Double check the
direction of air
flow.  If soap
solution is
pulled .into an
instrument it
may be ruined.
Use of an inline
liquid trap is
suggested.
   Be cautious
when measuring
toxic or flammable
gases.  Provide
ventilation to
the outside via
6.3 mm (1/4 in.)
tubing.  Work in
a fume hood.
                                    132

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           UPPER PORT
'BUBBLE BREAKER
   TOP GRADUATION LINE
      INTERMEDIATE
      GRADUATION LINE
LOWER GRADUATION LINE	>•
lOOcc
50 cc
                               Occ
    BASE
      LOWER PORT
                                                            RUBBER BULB
                     Figure 5.1.  Soap film flowmeter.
                                        133

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5.2  SOAP FILM FLOWMETER, SFFM, OR BUBBLE FLOWMETER (con.)
       PROCEDURE
RESULTS, EXPLANATION
    PRECAUTION
    Lift soap solution
    reservoir tube or
    depress rubber
    bulb-to create
    soap film bubble.
       Release 10 to
    20 bubbles to wet
    interior surface.

    Measure the flow
    rate of gas
    through the
    SFFM.
       Take three
    separate meas-
    urements.
As the liquid rises
above the lower port
of SFFM, air entering
this port will create
a bubble and carry
the film upward.   At
this point, release
tube or bulb.

Allow all bubbles
to clear the SFFM
column.   With stop-
watch in hand, start
a single uniform
soap film up the
column.
Observe the lower
graduation line of
the SFFM at eye level
and as the film passes
this mark, start the
watch.
   Use suffi-
ciently large
inlet lines to
avoid back-
pressure and
flow change.
   Do not pres-
surize the SFFM
by attaching an
exhaust line
that is too small
in diameter and/
or too long in
length.
   When measuring
inline,  keep con-
nections as short
as possible.

Do not allow the
bubbles to be
carried into
the instrument.
   Use a "bubble
breaker" atop the
SFFM to break
the film surface.

Be sure, to
observe soap
film travel
by sighting
along the plane
of the film.
  Do not touch
the rubber bulb
during a reading.
                                     134

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5.2  SOAP FILM  FLOWMETER,  SFFM, OR BUBBLE FLOWMETER (con.)
       PROCEDURE
RESULTS, EXPLANATION
                                                               PRECAUTION
7.   Compute the volu-
     metric flow rate.
       Average the three
     values to obtain
     final  value.
        Record all data
     calculations in note-
     book.
   Stop the watch
when the soap film
crosses the top
graduation or some
known intermediate
graduation.

Divide the volume of
the flowmeter (or the
volume traversed), cc,
by the time required,
minutes.

Example calculation:

Soap film  traverses
100 cc in  39 seconds.
                                 39 sec   = 0.65 min
                               60 sec/min
If necessary for
comparison, this
volumetric flow
rate should be
corrected to
standard temper-
ature (25° C)
and pressure
(760 mm Hg).
Also correct
for water
vapor pressure.
See Section 5.5.
 8.   Disconnect SFFM
     from and gas
     source.
                                    C(
                               n
                               0.65 mm
                                        =153.8 cc/min
                                is the  uncorrected
                                volume  flow rate.
                              Be certain that
                              all disconnected
                              fittings, etc.
                              are retightened
                              and leak-tested.
                                       135

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5.3  MERCURY COLUMN BAROMETER, FORTIN TYPE
        PROCEDURE
                          RESULTS, EXPLANATION
                                PRECAUTION
1.
2.
3.
Assure that the baro-
meter is mounted pro-
perly, and that the
mercury is clean.
Adjust mercury reser-
voir leveling screw so
liquid mercury just
touches sharp point
of ivory zero point.
Locate the top of
the mercury column,
then tap the baro-
meter case lightly
with fingers.
    Adjust vernier
    plate with notched
    wheel until lower
    edge of vernier
    is in same plane
    as top of mer-
    cury meniscus.
Barometer should be
wall-mounted vertical-
ly and be perpendicular
to a level floor.
Dirty mercury is dull,
tarnished.
This adjusts the
level of mercury in
the cistern to the
same point for each
reading.  A flash-
light provides
helpful illumination.
Adjust until the zero
pointer makes a slight
"dimple" in the mer-
cury pool,  then "back-
off" slightly.

The height of the mer-
cury meniscus (the
curvature of the mer-
cury surface inside a
glass tube) is greater
on a rising barometer
than a falling one.
Tapping brings the
meniscus to an average
height.

This process locates
the top of the mercury
column.
If barometer is
not level or
mercury is dirty,
erroneous read-
ings are obtained.
   Return to
factory if mer-
cury column
contains dirty
mercury.

Do not force
or strain the
adjusting screw. .
                                                        When reading
                                                        barometer, the
                                                        reader's eye
                                                        should be in
                                                        the same hori-
                                                        zontal plane
                                                        as the top of
                                                        the meniscus
                                                        and the lower
                                                        edge of the
                                    136

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5.3  MERCURY COLUMN  BAROMETER,  FORTIN TYPE  (con.
        PROCEDURE
                               RESULTS,  EXPLANATION
                                                          PRECAUTION
5.
Determine  reading  in
English or metric
units.
a.  Read column
    height.
b.  Read fractional
    value  from venier
    scale.
6.
Apply corrections  for
the temperature of the
barometer, and if
desired, gravity.
To read column height,
determine scale value
that lower line of
venier intercepts or
is just above.
Read venier by deter-
mining which one of
the 9 division marks
(1 to 9) intersects
most closely with
scale value lines.

Example:

   Lower line of ver-
nier "crosses" between
755 and 756 mm Hg.
  This says the read-
ing is between 755 and
756 mm Hg.
   The vernier line
marked "8"  matches ex-
actly with the 771 mm
line of the scale.
   Thus, the uncorrect-
ed barometric pressure
is 755.8 mm Hg.

Temperature affects
the expansion of mer-
cury and the scale
metal.
                                                            vernier plate.
                                                            Line your sight
                                                            on the bottom
                                                            of vernier and
                                                            the metal ver-
                                                            nier guide lo-
                                                            cated behind
                                                            the mercury
                                                            column.
If it is desired
convert an English
reading to a metric
reading or vice
                                     137

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5.3  MERCURY COLUMN BAROMETER, FORTIN TYPE (con.)
        PROCEDURE             RESULTS, EXPLANATION            PRECAUTION


                                 Temperature correc-        versa, always
                              tion tables and in-           apply the tempera-
   Use the corrected          instructions for their        ture and gravity
   pressure reading           use for English and           corrections before
   to calculate gas           metric scales accom-          making the con-
   volumes at stan-           pany the barometer or         version.
   dard temperatures          may be found in such
   and pressure.               publications as the
                              Handbook of Chemistry
                              and Physics.
                                 Take the tempera-
                              ture reading from the
                              thermometer attached
                              to the barometer or
                              from a therometer
                              in the same area.
                                    138

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5.4  WATER MANOMETER,  U-TUBE
        PROCEDURE
                           RESULTS,  EXPLANATION
                                                               PRECAUTION
1.
Choose a U-Tube water
or oil manometer.
See Figure 5.2
 4.
Level the manometer
so liquid levels  in
both sides  of  the
"U" are the same.

Attach, by  use of
rubber tubing,  one
side of the "U" to
the manifold or
other item  for which
the pressure differ-
ential is desired.

Read the manometer
establish AP,  inches
of H20 or cm of H20.
As the moving gas
stream sweeps by, a
slight vacuum may be
created.
   If the manifold is
pressurized, a positive
pressure will be shown.

Read the difference in
heights of the water
level in the two sides
of the "U".  See
Figure 5.2
                                                             Manometers  using
                                                             liquids  other
                                                             than water  (such
                                                             as  red oi1) wi11
                                                             have graduations
                                                             different from
                                                             H20 manometers.
                                                             Be  sure  to  use
                                                             the correct fluid.
                                                             Leave  the other
                                                             side of  the "U"
                                                             open to  the at-
                                                             mosphere.
If greater than
1 to 2 inches
H20 pressure is
noted, the FPD
zero stability
may be affected.
Rework any cali-
bration manifolds
which display
such character-
istics.
                                      139

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                                     TUBE CONNECTED TO PORT OF MANIFOLD, ETC.
-IS.
O


                                                                                              THIS END OPEN
                                                                                                ATMOSPHERE

\\\\\\\\\
i
J
t
AP
i
I— -r- P
P2
k /


1
                  AP = 0
           ATMOSPHERIC PRESSURE
    AP= 1.5 INCHES H20
SLIGHT VACUUM ON MANIFOLD
   AP = 1.5 INCHES H20
SLIGHT POSITIVE PRESSURE
IN MANIFOLD, EXCEEDING
ATMOSPHERIC PRESSURE
                                           Figure  5.2.   Water manometer,  "U" tube.

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5.5  STEPS FOR CORRECTING  AIRFLOW TO  STANDARD TEMPERATURE AND PRESSURE
     In air pollution  work,  the  standard  temperature is 25° C; the standard
pressure is 1 atmosphere or  760  mm Hg (29.92 inches Hg).  Almost all flow
measurements taken  by  volumetric displacement methods must be corrected to
standard temperature and pressure for comparisons to other work.  Soap film
flowmeter and wet test meter measurements must also be corrected for the
effect of water  vapor.  Table 5.1 lists the vapor pressure of water (mm Hg)
at various temperatures.
     Apply this  equation to  correct flows:

          F  =  F x  P " P'  x    298'15
           s        760   x  t +  273.15
     where:
          F  =  flow rate at  standard  conditions  in  liters/minute
           j
          F  =  measured flow rate in  liters/minute  by displacement
          P  =  barometric  pressure in mm  Hg
          P' =  vapor pressure of water, mm Hg, at temperature t.
          t  =  air  temperature,  degrees C
     For an example calculation  using this equation, refer to Section 3.4.4.
5.6  ASCARITE®  METHOD  FOR  C02 DETERMINATION
     Average  levels of C02 in ambient air or  in  air from clean air sources
can  be determined gravimetrically by  adsorption  and reaction of C02 on
Ascarite.  The  increase in the weight of  the  tube containing the Ascarite
can  be related  to the  C02  concentration.
     This method is based  on the instructions  given in  the APHA manual,
Methods of Air  Sampling and  Analysis, "Tentative Method for Preparation of
Carbon Monoxide Standard Mixtures," p. 224,  1972.
     Ascarite is available from  most  laboratory  supply  houses.  A mesh of
8-20 is specified for  this procedure.  As Ascarite  collects C02, its  color
changes from brown  to  white  due  to sodium carbonate formation.
                                     141

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       Table 5.1.   Vapor pressure of water  at
             various temperatures, mm Hg
Temp.
°C
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
0.0
17.535
18.650
19.827
21.068
22.377
23.756
25.209
26.739
28.349
30.043
31.824
33.695
35.663
37.729
39.898
42.175
44.563
47.067
49.692
52.442
55.324
58.34
61.50
64.80
68.26
71.88
75.65
79.60
83.71
88.02
92.51
97.20
102.09
107.20
112.51
118.04
123.80
129.82
136.08
142.60
0.2
17.753
18.880
20.070
21.324
22.648
24.039
25.509
27.055
28.680
30.392
32.191
34.082
36.068
38.155
40.344
42.644
45.054
47.582
50.231
53.009
55.91
58.96
62.14
65.48
68.97
72.62
76.43
80.41
84.56
88.90
93.5
98.2
103.1
108.2
113.6
119.1
125.0
131.0
137.3
143.9
0.4
17.974
19.113
20.316
21.583
22.922
24.326
25.812
27.374
29.015
30.745
32.561
34.471
36.477
38.584
40.796
43.117
45.549
48.102
50.774
53.580
56.51
59.58
62.80
66.16
69.69
73.36
77.21
81.23
85.42
89.79
94.4
99.1
104.1
109.3
114.7
120.3
126.2
132.3
138.5
145.2
0.6
18.197
19.349
20.565
21.845
23.198
24.617
26.117
27.696
29.354
31.102
32.934
34.864
36.891
39.018
41.251
43.595
46.050
48.627
51.323
54.156
57.11
60.22
63.46
66.86
70.41
74.12
78.00
82.05
86.28
90.69
95.3
100.1
105.1
110.4
115.8
121.5
127.4
133.5
139.9
146.6
0.8
18.422
19.587
20.815
22.110
23.476
24.912
26.426
28.021
29.697
31.461
33.312
35.261
37.308
39.457
41.710
44.078
46.556
49.157
51.879
54.737
57.72
60.86
64.12
67.56
71.14
74.88
78.80
82.87
87.14
91.59
96.3
101.1
106.2
111.4
116.9
122.6
128.6
134.7
141.2
148.0
Source: Handbook of Chemistry and Physics, 50th Ed.  The Chemical Rubber Co.,
      Cleveland, Ohio.
                            142

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5.6.1  Procedure
     Loosely pack  the  Ascarite  into  15  to  20 cm length (6 to 8 in.) glass or
plastic tubes  having a 1.27  cm  (0.5  in) inside diameter.  Plug the ends with
glass wool and cap to  protect from moisture.  Carefully weigh the tube on an
analytical balance to  the nearest milligram.  Do the same with a tube contain-
ing Drierite.
     Set  up a  sampling train similar to the one shown in Figure 5.3.
     Determine the flow rate into the Ascarite cartridge.  500-1000 cc/min
is a reasonable flow.
     Collect air for  a sufficient length of time to obtain an accurate
weight  difference; about 30-60  minutes. Express the total flow volume in
cubic meters at STP;  express the weight gain in micrograms.  Compute the ppm
value of  C02.
     Example calculation:

           Air  flow rate = 500 cc/min at STP  (25° C, 760 mm Hg)
           Time = 30 minutes
           Total weight gain = 0.0094 grams (9400 ug)
                (total  weight gain = Ascarite tube  gain + Drierite tube gain)
     Thus:
                0.5 liters/min x 30 min = 15  liters =  0.015 m3
                9400 ug  _ X ug
                0.015 m3   1 ms
                X = 626667 ug
      Therefore, since 1798 ug/m3 C02 = 1 ppm C02  at STP
      C02, ppm = 626667 = M8 ppm
                  1798
      In field use, this Ascarite C02 collection system has been  shown to
 have an accuracy of 5 percent or better and a precision of ±12 ppm for
                             22
 co-located sampling systems."
                                      143

-------
          AIR SOURCE IN AT
          KNOWN FLOW RATE
 /
             TUBE CONTAINING
             DRIERITE TO REMOVE
             MOISTURE FROM AIR
         FLOW CONTROL VALVE
PREWEIGHED TUBE
CONTAINING ASCARITE
TO CAPTURE C02
                                                                            PREWEIGHED TUBE CONTAINING
                                                                            DRIERITE TO CAPTURE ANY WATER
                                                                            LEAVING THE ASCARITE CARTRIDGE
METAL BELLOWS
OR DIAPHRAGM
    PUMP
        FLEXIBLE PLASTIC
            TUBING
AIR
OUT
                   Figure 5.3.   Ascarite  sampling train  for C02 determination.

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                                  REFERENCES


1.   R. Mavrodineanu,  ed.,  "Analytical  Flame Spectroscopy,"  Macmillan,
     London, 1970.  p.  282.

2.   P. T. Gilbert,  "Monitoring of Phosphorous and Sulfur by Chemilumine-
     scent Flame  Spectrophotometry,"   Proceedings of Conference  of  Spectro-
     scopy,  Instrumentation,  and Chemistry, San Francisco, October  23,  1964.

3.   J. A. Dean and T.  C.  Rains, Flame  Emission and Atomic Absorption Spec-
     trometry. Vol.  3,  Marcel  Dekker, New York, 1975,  p.  33(h

4.-   A. G. Gaydon and  G.  Whittingham,  "The Spectra of Flames Containing Oxides
     of Sulphur," Proc.  Royal  Soc.  London, Series A,  189,  313 (1947).

5.   A. Fowler and W.  M.  Yaidya, "The Spectrum of the Flame  of Carbon Disulfide,"
     Proc. Royal  Soc.  London.  Series A,  132. 310 (1931).

6.   A. G. Gaydon,  The Spectroscopy of  Flames, John Wiley and Sons,  Inc.,
     New York, 1957, p.  220.

7.   G. W. Castellan,  Physical  Chemistry, Addison-Wesley  Publishing Co.,
     Inc., Reading,  Mass.,  1964. p.  565.

8.   Heinrich Dragerwerk,  and W. Drager,  German patent 1-133918;  date of
     arrival, January  19,  1961; date of patent, July 26,  1962.

9.   W. L. Crider,  "Hydrogen  Flame Emission Spectrophotometry in  Monitoring
     Air for Sulfur Dioxide and Sulfuric Acid Aerosol," Anal.  Chem.  37, 1770
     (1965).

10.  S. S. Brody  and J.  E.  Chaney, "Flame Photometric Detector:   The Appli-
     cation  of a  Specific Detector for  P and for S Compounds - Sensitive to
     Subnanogram  Quantities,"  J. Gas  Chromatog., 4, 42 (1966).

11.  D. P. Lucero and  J.  W.  Paljug, "Monitoring Sulfur Compounds  by Flame
     Photometry," Instrumentation for  Monitoring Air Quality.  American
     Society for  Testing and  Materials,  1976.  pp. 20-35.

12.  R. E. Baumgardner,  T.  A.  Clark,  and R. K. Stevens, "Increased  Specificity
     in the  Measurement of Sulfur Compounds with the Flame Photometric  Detector,
     Anal. Chem.  47, 563 (1975).

13.  R. K. Stevens,  A.  E.  O'Keeffe, and G. C. Ortman, "Absolute  Calibration
     of a Flame Photometric Detector to Volatile Sulfur Compounds at Sub-Part-
     Per-MiTlion  Levels,"  Environ.  Science and Tech., 3,  652 (1969).

                                      145

-------
14.   D.  P. Lucero, "Ultra Low-Level Calibration Gas Generation  by  Multistage
     Dilution Techniques," Calibration jji Air Monitoring, ASTM  STP 598.
     American Society for Testing and Materials, 1976.  pp. 301-319.

15.   Daniel P. Lucero, "Performance Characteristics of Permeation  Tubes,"
     Anal. Chem.  43, 1744 (1971).

16.   A.  E. O'Keeffe and G. C. Ortman, "Primary Standards for Trace Gas
     Analysis," Anal. Chem. 38, 760 (1966).

17.   F.  P. Scaringelli, S. A. Frey, and B. E. Saltzman,  "Evaluation  of
     Teflon Permeation Tubes for Use with Sulfur Dioxide." Amer. Ind. Hygiene
     Assoc. J. 28, 260 (1967).

18.   F.  P. Scaringelli, A. E. O'Keeffe, E. Rosenberg, and J. P. Bell,
     "Preparation of Known Concentrations of Gases and Vapors with Permeation
     Devices Calibrated Gravimetrically."  Anal. Chem. 42, 871  (1970).

19.   G.  0. Nelson, Controlled Test Atmospheres.  Ann Arbor Science Pub-
     lishers, Inc., Ann Arbor, Michigan, 1971.  pp. 134-141.

20.   S.  G. Wechter, "Preparation of Stable Pollution Gas Standards Using
     Treated Aluminum Cylinders."  Calibration jji Air Monitoring,  ASTM
     STP  598.  American Society for Testing and Materials, 1976.   pp. 40-54.

21.   I.  Gellman, "An Investigation of H2S and S02 Calibration Cylinder Gas
     Stability and Their Standardization Using Wet Chemical Techniques."
     Special Report No. 76-06.  National Council of the Paper Industry for
     Air  and Stream Improvement, Inc., August, 1976.

22.   F.  Smith,  Research Triangle Institute, Research Triangle  Park,  N.C.
     Unpublished results, 1976.

23.   D.  J. von Lehmden, "Suppression Effect of C02 on FPD Total Sulfur Air
     Analyzers and Recommended Corrective Action."  Proceedings, Fourth
     Joint Conference on Sensing of Environmental Pollutants.   New Orleans,
     La., November 6-11, 1977.

24.   C.  E. Junge, Air Chemistry and Radioactivity.  Academic Press. New
     York, 1963.   p. 21.
                                     146

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          INDEX
Air, compressed
Alumina
Aluminum cylinder
Ascarite®
Barometer
Barometric pressure
Bendix, analyzer
Burner block
cleaning
description
tip
Calibration
Calibrator
S02 cylinder
S02 tube
Carbon dioxide
quenching
Charcoal, activated
Clean air supply
Data acquisition system
Detector output
linearized
log-linear
log-log
Diatomic sulfur
Dilution air
Drying agents
Drierite
Mole sieves
Silica gel
Dynamic calibration
Electrical requirements
Electrolytic H2
Equivalent methods
Exhaust, FPD
Filters
Dilution air
Sample
Teflon
"Flame-out"
Flame photometer
analyzer
Flowrate
Air sample
Flowmeter
Hydrogen
39
38
61
38, 141
136
90,136
8,113

12
6
32
81,99
49
60
54

68
37,73
36
88

35,129
115
8
J
13,35

38,73
73
38,73
81,99
18
29
9,11
19

13
24,96
24,96
31

5

122
132
124
Hydrogen
Cylinders
Electrolytic
Flame
Fuel
Safe use
Hydrogen sulfide
Scrubber
Humidity control
Ignition, FPD
Installation, FPD
Interferences, S02
Leak tests
Hydrogen
Linearity
MACE® filter
Maintenance
Manifold
Calibration
Connections
Sampling
Manometer
Meloy, analyzer
Molecular sieves
Monitor Labs, analyzer
Multipoint calibration
NBS
Non-equivalent FPD
Oven, permeation
Oxygen/nitrogen ratio
Permeation tube
Installation
Oven
Rate
Temperature
Use
Pneumatic connections
Ambient air
Exhaust
Dilution air
H2 fuel
Portable calibrator
Pressure
Pumps
Repair
Sample

25
29
6
4,25
26

4,13
18
31
17
79, 125
77
28
129
96
95

46,64
21
20
139
8,115
73
8
81,99
40
10
45,49
72
39
55
45,49
58,76
67,77
42

24
25
13
25
53
90

12
12
Quality control
Quenching
Carbon dioxide
Self-collisional
Rack-mounting
Recorder connections
Record-keeping
Regulators, pressure
Evacuation
H2
S02
S2*
Formation
Spectra
Safety
Electrical
Hydrogen
Signal cable
Soap film flowmeter
Soda lime
Span check
Standard Reference
Material
Stripchart recorder
Sulfur dioxide
Cylinders
Permeation devices
Safe use
Temperature control
Analyzer
Station
Thermistor
Thermometer
Tracer, analyzer
14,82

68
8
18
24
14,83

65
25
61

2
3

18
26
24
132
38,72
91

40
24,87

60
39
57
18
127
127
52
52
8
                                           Vapor pressure, H2 0      142
Quality assurance
                        14
"Warm-up" time
   Analyzer
   Calibrator
   Perm tube
Water
   Condensation
   Vapor pressure

Zero air
   Generator
   Requirements
   Supply
Zero check
                                                                  31
                                                                  55
                                                                  42

                                                                  18
                                                                  142
37
36
36
91
          147

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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
 1. REPORT NO,

  EPA-600/4-78-024
                              2.
                                                           3. RECIPIENT'S ACCESSION-NO.
 4. TITLE AND SUBTITLE
     Use of the  Flame Photometric Detector Method for
     Measurement of Sulfur Dioxide in Ambient Air
          A  Technical  Assistance Document   	
                                                   5. REPORT DATE
                                                     May 1978
                                                   6. PERFORMING ORGANIZATION CODE
 7. AUTHOR(S)
                                                           8. PERFORMING ORGANIZATION REPORT NO
     W. Gary  Eaton
 9. PERFORMING ORGANIZATION NAME AND ADDRESS
     Research  Triangle Institute
     Research  Triangle Park, N.C.
                                                   10. PROGRAM ELEMENT NO.

                                                      1 HD 621
                            27709
                                                   11. CONTRACT/GRANT NO.
                                                              68-02-2433
 12. SPONSORING AGENCY NAME AND ADDRESS
     Environmental  Monitoring and Support  Laboratory
     Office  of Research and Development
     U.S.  Environmental Protection Agency
     Research  Triangle Park, N.C.  27711	
                                                   13. TYPE OF REPORT AND PERIOD COVERED

                                                      Final 9/76 -   5/78	
                                                   14. SPONSORING AGENCY CODE

                                                      EPA-ORD
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT
           This  Technical Assistance Document  is  intended to serve as  a  source-
     book  of information and outlines of  good practice for operation  and
     calibration of ambient air S0~ detection analyzers based on the  measurement
     principle  of Flame Photometric Detection (FPD).   This is accomplished
     through the identification and control of critical parameters affecting
     the operation and calibration of FPD analyzers.   The document may  be
     used  with  analyzers which measure total  sulfur,  as well as with  new
     specific models which have been designated  as equivalent methods by
     EPA.
                                                                   so2-
          This  document is to be used in  conjunction with the instrument
     manufacturer's instruction manual.   The  document consists of six  sections:
     (1)  Introduction to FPD principle,  (2)  Installation and startup  of the
     analyzer,  (3)  Calibration sources and  their air supplies, (4) Procedures
     for multipoint dynamic calibration,  (5)  Procedural aids, and (6)  References
     and Index.
 17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b.lDENTIFIERS/OPEN ENDED TERMS
                                                                 c. COSATI Field/Group
     *
     *
Sulfur Dioxide
Air Pollution
     *  Calibrating

     *  Flame  Photometry
Ambient Air

SOp Measurement
S02 Calibration

S02 Permeation  Device

    Quality  Control
07 B

13B

14B

14B
 8. DISTRIBUTION STATEMENT
     Release to  Public
                                              19. SECURITY CLASS (ThisReport)
                                                                 21. NO. OF PAGES
                                                                      147
                                      20. SECURITY CLASS (Thispage)

                                                   i' -FioH	
                                                                         22. PRICE
EPA Form Z220-1 (9-73)

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