A GUIDE FOR THE EVALUATION OF ATMOSPHERIC ANALYZERS
by
P.K. Mueller, Ph.D.
¥. Tokiwa
E.R. deVera
W.J. Wehrmeister
1. Belsky
S. Twiss
M. Imada
EPA Contract 68-02-0214
Project Officers
J.B. Clements, Ph.D.
T.W. Stanley
Prepared For
Environmental Protection Agency
Research Triangle Park, NC 27711
Air and Industrial Hygiene Laboratory, Laboratory Program
California State Department of Public Health
Berkeley, California 94704
June 1973
-------
This report has been reviewed by the Environmental
Protection Agency and approved for publication.
Approval does not signify that the contents
necessarily reflect the views and policies of
the Agency nor does mention of tradenames or
commercial products constitute endorsement or
recommendation for use.
-------
TABLE OF CONTENTS
CHAPTER PAGE
Acknowledgement i
Abstract ii
Preface ili-lv
1.0 Introduction 1
2.0 Manufacturer's Specifications 2
2.1 Introduction 2
2.2 Class I 3
2.3 Class II 4
3.0 Operating Instructions 7
3.1 Introduction 7
3.2 Identification 7
3.3 ' Operation and Hiintainanca Section 3
3.4 .Field Repair or Service Section 15
4.0 Procedures for Determining Performance 19
4.1 General 19
4.2 Physical Characteristics 27
4.3 Instrument Operating Instructions - 28
4.4 Calibration 30
4.5 Linearity 32
4.6 Measuring Range 36
4.7 - Calibration Accuracy 37
4.8 Drift at Zero 38;
4.9 . Drift at Span 39
4.10 Noise 41
-------
TABLE OF CONTENTS
CHAPTER PAGE
4.11 Precision and Response Times 44
4.12 Pulse Time . 49
4.13 Lower Detectable Limit 50
4.14 Analyzer Deadband 52
4.15 Warm-up Time 53
4.16 Interferences 55
4.17 Operating Temperature Range 58
4.18 Operating Voltage S.ange 60
4.19 Unattended Operation 62
5.0 Gas Generation 80
5.1 Principle and Scope 80
5.2 Apparatus 82
5.3 ' Operation 93
5.4 References 94
6.0 Calibration Procedure for Automated Atmospheric
Oxidant and Ozone Analyzers 107
6.1 Principle and Scope 107
6.2 Range 108
6.3 Interferences 109
6.4 Precision, Accuracy and Stability 109
6.5 Apparatus 110
6.6 Reagents and Gases 114
6.7 Spectrophotometer Calibration 120
6.8 Dynamic Calibration 121
-------
TABLE OF CONTENTS
CHAPTER • PAGE
8.5 Apparatus 175
8.6 Reagents and Gases 178
8.7 Spectrophotometer Calibration 179
8.8 Dynamic Calibration 180
8.9 .Static Calibration 187
8.10 Reconciling Static and Dynamic Calibrations 188
8.11 References 190
9.0 Calibration Procedure for Automated Atmospheric
Carbon Monoxide Analyzers 194
9.1 Principle and Scope 194
9.2 Range 195
9.3 Interferences 195
9.4 • Pre'cision, Accuracy and Stability 196
9.5 Apparatus '197
9.6 Reagents and Gases • 199
9.7 Preparation of Calibrating Gases 201
9.8 Dynamic Calibration 203
9.9 References 207
.10.0 Air Analyzer Terminology 210
-------
TABLE OF CONTENTS
CHAPTER FACE
6.9 Static Calibration 126
6.10 Reconciling Static and Dynamic Calibrations 132
6.11 Basis for Calculations 133
6.12 References 135
7.0 Calibration Procedure for Automated Atmospheric
Nitrogen Dioxide and Nitric Oxide Analyzers 140
7.1 Principle and Scope 140
7.2 Range 141
7.3 Interferences 142
7.4 Precision, Accuracy and Stability 142
7.5 Apparatus 143
<
7-6 Reagents and Gases . 149
7.7 Spectrophotometer Calibration 152
7.8 Dynamic Calibration 153
7.9 Static Calibration 160
7.10 Reconciling Static and Dynamic Calibrations 165
7.11 References 166
8.0 Calibration Procedure for Automated Atmospheric
Sulfur Dioxide Analyzers
8.1 Principle and Scope
8.2 Range
8.3 Interferences 2.74
8.4 Precision, Accuracy and Stability '
-------
LIST OF TABLES
Title Page
4-1 Manufacturer's Data Sheet 65
4-II Analyzer Summary Sheet and Test Results 68
4-III Instrument Operating Instructions 71
4-IV Linearity Summary Sheet 73
4-V Worksheet for Linear Equation . 74
4-VI Worksheet for Response Times 75
4-VII , Worksheet for Precision 76
4-VIII Interferent Test Concentrations * 77
4-IX Ppm vs. yg/iu Conversion Factors for Selected Gases 79
5-1 Measuring Ranges and Sampling Rates of Common
Air Analyzers 96
5-II Methods far Generating and Determining Gas
Concentrations 97-98
5-III Absorbers for Producing Zero Air Up to 30 1/min. 99-101
-------
LIST OF ILLUSTRATIONS
FIGURE PAGE
5-1 Diagram of gas mixing apparatus 102
5-II Configurations of gas mixing chambers 103
5-III Gas permeation apparatus 104
5-IV Permeation device holder 105
5-V Ozone Generator 106
6-1 Gas generating apparatus for calibrating
ozone analyzers. 137
6-II Ozone generator 138
6-III Sampling train for referee ozone analysis 139
7-1 Gas generating system for calibrating NO and
N02 analysers. 169
7-II Sampling train for referee NO and N02 analysis. 170
7-III Calibrating solution dispenser 171
8-1 Gas generating system for calibrating S02
analyzers. 192
8-II Sampling train for referee S02 analysis. 193
9-1 Primary dilution system for CO in bags. 208
9-II Secondary dilution system for calibrating CO
analyzers. 209
10-1 Diagram showing visual representation and
interpretation of noise an time delays in
analyzer response. 235
10-11 Diagram of pulse time 235
-------
ACKNOWLEDGEMENT
The authors wish to acknowledge the assistance of many individuals
and organizations whose comments and suggestions made this guide
possible. The contributions of Dr. John B. Clements and
Mr. Thomas W. Stanley who served as project officers; the technical
staff of the National Environmental Research Center, RTF;
Mr. Jay Sinnett, Office of Monitoring, EPA; the technical specialists
of the Air and Industrial Hygiene Laboratory; Dr. Ernest Yeager,
Case Western Reserve University: and Messrs. John Kinosian and
K. Nishikawa of the California Air Resources Board were especially
helpful. Drs. -Albert Rocklin and Lionel Farber served as editorial
consultants. 'Our deepest thanks go to the many air analyzer
manufacturers and representatives for their assistance and loan
of their instruments without which the validity of this guide could
not have been established.
-------
ABSTRACT
Intelligent selection and application of atmospheric analyzers
require complete, consistent, cohesive and unequivocal information
regarding the physical and performance characteristics of these
instruments. This guide is designed for use by operating personnel
and provides 1) definitions for selected terms in air monitoring ?
2) a listing of physical and performance characteristics for which
Information is needed, 3) recommended criteria for operating
instructions, 4) test procedures for evaluating physical and
performance characteristics of air analyzers and 5) procedures
for the calibration of analyzers for carbon monoxide, nitric
oxide, nitrogen dioxide, ozone and oxidant, and sulfur dioxide.
-------
PREFACE
To assess air quality and to determine compliance with legally
established air quality standards, noxious components such as carbon
monoxide, oxidant, nitrogen dioxide, nitric oxide, sulfur dioxide,
hydrocarbons and suspended particulate matter have been monitored
in many areas of the country. Effective April 30, 1971, the federal
Environmental Protection Agency (EPA) has promulgated primary and
secondary air quality standards and regulations for all the above
pollutants except nitric oxide (Federal Register, 36, No. 84, April
1971). Additional regulations (Federal Register 36, No. 158, August
1971) require the States to follow a demanding time schedule to
achieve compliance with the primary and secondary standards. The
regulation!? r.learly state that these rules :rs.y not in any way be
considered so as to permit deterioration of existing air quality that
is already well within the confines of the standards. The federal
regulations further specify that pollutants shall be measured by
prescribed reference methods or methods which have been demonstrated
to be equivalent to the satisfaction of EPA. This requirement
indicates that equivalency with the reference procedure must be
demonstrated for current and. future air pollutant sampling and
analysis systems. ,
A substantial increase in air monitoring programs is thus in-
evitable in order to determine short and long term trends, to assess
ill.
-------
the effectiveness of control programs, to substantiate compliance
and to insure maintenance of existing clean air environments. Fara
lei to this increase in surveillance activity will be a growing
demand for air monitoring instrumentation accompanied by foreseeable
advances and changes in air analyzer technology. In order to deal
competently with this anticipated situation, meaningful information
is necessary to provide guidelines for the selection and use of air
monitoring instrument including'instructions on proper instal-
lation and maintenance. Only by proper application of well-tested
performance evaluation procedures for air analyzers can one expect
;
to acquire valid and reliable aerometric data.
It is therefore gratifying that EPA chose to provide our laboratory,
which has decades of collective and productive experience with air
pollution measurements, with resources to develop and test system-
atically procedures for the evaluation of atmospheric analyzer per-
formance. -It is also rewarding to realize that some results of our
efforts have been included in the promulgation of federal register
specifications for carbon monoxide and oxidant analyzers even be-
fore details of our work were finalized. I trust that results being
produced now will be even more generally useful. Any comments re-
garding the utility of these procedures and deficiencies and
omissions in this guide are welcome.
Peter K. Mueller, Ph.D.
Principal Investigator
June 1973
iv
-------
1.0 INTRODUCTION
For measuring air pollutants, a variety of commercial monitoring
instruments are available. For intelligent selection and appli-
cation of these instruments, reliable information concerning the
physical and performance characteristics of these instruments is
necessary. The information provided must be complete, consistent,
cohesive and unequivocal. The terms used to describe these
characteristics should be specific and well-defined. The com-
parison, selection and application of such instruments are
enhanced when the specifications cover the same parameters
»
and are based on uniform instrument evaluation.
To meet some of these needs, this guide, which is designed for use
by operating personnel, 1) provides definitions for selected terms
commonly used in the description of air monitoring practices and
instrumentation, 2) lists specific physical and performance character-
istics for which information is routinely needed, 3) recommends the
format and information to be included in instrument operating
instructions, 4) describes test procedures fcr evaluating physical
and performance characteristics of automated analyzers for atmospheric
monitoring and 5) provides procedures for the calibration of atmo-
spheric analyzers for carbon monoxide, nitric oxide, nitrogen dioxide,
ozone and oxidant, and sulfur dioxide.
-------
2.0 MANUFACTURER'S SPECIFICATIONS
2.1 INTRODUCTION
The purpose of this chapter is to achieve uniformity by reducing
the wide variations that now exists in published air analyzer
specifications by delineating a list of required specifications
and other pertinent information under two categories, designated
here as Class I and Class II. The Class I category is intended
to cover the minimum number of parameters the manufacturer
should furnish so that the prospective user can judge the potential
suitability of the instrument and can decide if further investigation
is warranted. It is not expected to provide sufficient information
to justify a purchase. Class I specifications are designed for adver-
tisements in technical journals, product bulletins, new product
flyers, and news articles.
The Class II category includes information required for complete
identification and characterization of the instrument on which a
decision concerning the purchase can be based. It is intended
primarily for presentation in manufacturers' instrument brochures,
specification sheets and instruction manuals. In all cases,
manufacturers should provide realistic and accurate performance
data and describe their instruments in clearly defined terms, such
—2—
-------
2.3.1 Instrument Description
a. Measurement principle - a detailed description of the principle
on which the measurement is based. Where appropriate, diagrams and
photographs should be used (see b below).
b. Drawings - block, logic, or schematic diagrams of the basic com-
ponents and of the important electrical, sample, solution, and
optical pathways, with an explanation of the function of each.
Photographs may also be used.
V
c. Optional auxiliary equipment for use with the instrument.
d. Sale price of basic unit, optional equipment and accessory
items.
i
2.3.2 Installation and Operation
a. Physical size and shape of the instrument, with space require-
ments for its installation, operation, and maintenance including
allowances for auxiliary items and swinging space for doors and
access panels.
b. Weight of each subunit making up the complete instrument.
c. Environmental requirements including the range of temperatures,
humidity and, especially in the case of portable instruments,
—5~
-------
vibration conditions over which the instrument will meet stated^
performance specifications.
d. Air sampling requirements including sample flow rates and
permissible differences in sample line pressure.
e. A list, with consumption rates, of all solutions, reagents,
and gases required for start up, operation, and maintenance,
but not including lubricating oils, or other materials for
preventive maintenance.
f. A brief description and recommended frequency of .the calibration
procedure(s).
2.3.3 Performanc e Charac ter is tics
a. Dynamic response including lag time, rise time, fall time, and
pulse time.
b. Output signal characteristics with respect to: 1) type (elect-
rical, mechanical, optical, etc.), 2) magnitude (voltage, current,
frequency, resistance, etc.), 3) linearity (arithmetic, exponential,
other function), 4) impedance, and 5) noise.
c. Audible noise.
-6-
-------
3.0 OPERATING INSTRUCTIONS
3.1 INTRODUCTION
Most instruments require information and directions concerning their
proper operation and use. To insure this, each instrument should be
delivered with a manual of operating instructions. The manual should
contain a section on: 1) operation and maintenance and 2) field repair
or service. These sections may be separately bound.
3.2 IDENTIFICATION
The manual should be identified with the model number of the instru-
ment and should be current for that model. Separately bound portions
should be individually identified with the model number. Loose leaf
manuals should have the model number appear on every leaf. Corrections
or revisions should be clearly marked. Where the manual covers several
models, the. model number of the instrument to which it applies should
be clearly indicated.
The manual should be provided with a convenient reference form listing
the model number, serial number or run number, special options and
modifications, location and telephone numbers of the manufacturer's
representative and nearest service or repair center.
—7—
-------
3.3 OPERATION AND MAINTENANCE SECTION
This section should provide information and instructions regarding
principles, installation, initial start-up, hazards, calibration,
sampling, maintenance actions, and limited trouble shooting, and
should describe or contain any warranties or guarantees. Addi-
tionally, a section should be provided dealing with delivery, unpacking,
and installation of the instrument. This section should be accessible
to the purchaser at or before the time of delivery of the instrument
and should define whether the purchaser may, in the absence of an
authorized manufacturer's representative:
s. Unpack the unit
b. Install the unit
c. Operate'the unit
d. Relocate the unit
The Operation and Maintenance Section should cover, but is not limited
to the following topics:
3.3.1 Delivery and Unpacking Instructions
The manual should furnish details concerning shipment acceptance. A
set of instructions for the orderly unpacking and inspection of the
instrument should cover the following topics:
-8-
-------
a. Unpacking
b. Warnings concerning dangers to the instrument and/or personnel
during' unpacking.
c. Inspection
d. Procedures to be followed when the instrument arrives in damaged
condition, when parts are missing, or when wrong parts have been
sent.
3.3.2 Installation and Assembly
The manual should describe the utilities and the physical environment
that are required and should provide instructions for moving, mounting,
and installing the instrument, including details for connecting
together various components and for attachment to utilities. The
following topics should be covered:
a. Electric requirements - voltage, power consumption (or current
drain), frequency, number of phases, grounding.
b. Other utilities - fuel gas, hydrogen, Oxygen, other gases, water,
vacuum, drains.' These should be qualified by specifications for
the quality or purity and limitations on flow capacity and pres-
sure .
c. Physical environment - limitations on temperature, humidity,
vibration, light; requirements for shielding or isolation of the
-9-
-------
instrument; provision of exhaust vents for safety and comfort;
clearance or space needed for the operation and maintenance of
the instrument.
d. Working surfaces and material of construction of surroundings -
floor and bench support, floor covering, bench top, bench height,
supporting struts or other suggested bracing.
&. Interconnection of instrument sections and attachments to utilities
electrical, mechanical, pneumatic.
3e3.3 Hazards and Precautions
The manual should specify any hazards which could potentially injure
personnel or damage the instrument. Warnings should be placed both
in the manual and at appropriate locations on or in the instrument.
The instrument should be equipped with, or provisions made for the
attachment of, effective exhaust and effluent disposal devices. Clear
instructions and warnings concerning proper disposal of any potentially
hazardous discharges should be provided where appropriate on the
instrument arid in the manual. Tests for leaks on all lines, valves,
and control devices exposed to hazardous fluids such as compressed,-
flammable, toxic or corrosive gases and liquids must be specified.
Emergency shut-down procedures should be clearly described.
-10-
-------
3.3.4 Application, Principle of Operation, and Scope
The manual should describe what the instrument measures, state the
useful measuring range(s) and explain the principle of operation.
Where appropriate, the description should include sketches, block
diagrams or other pictorial representations of the instrument, the
units comprising it, and the function of each. The effect of
potential interferents should be described.
3.3.5 Air Sampling Requirements
The method of air sampling and any additional equipment required should
be described. Where the instrument is intended for connection to an
external sampling probe, the recommended probe materials, velocities
and residence times, and dimensions should be specified. The pre-
ferred range of air sampling rates should be stated, and the permissible
variations in sampling rate and air pressure should be given.
3.3.6 Ou;tpu: t_S i gna1
Most instruments are designed to be coupled with signal processing
and presentation devices such as recorders, integrators, analogue
and digital displays, computers, and telemetry systems. The selection
of an appropriate signal processing device depends on the characteristics
of the output signal from the instrument. Therefore, the manufacturer
should specify the signal as to:
-11-
-------
a. Type - mechanical, electrical, optical, acoustical
B. Characteristic - voltage, current, frequency, continuity
(steady or chopped)
c. Linearity - arithmetic, logarithmic, etc.
d. "Matching requirement - output impedance, resistance, back
pressure. Instructions should be given for detecting and
isolating response difficulties arising from mismatching of
the signal source and the signal presentation device.
3.3.7 Specification
A technical summary of the instrument's physical and performance
characteristics under various conditions, as well as information
concerning input, output, power requirements, reagents, and
utilities as listed in 2.2 and 2.3, should be provided.
3.3.8 Start-up and Operation
A precise, abbreviated summary of the operational procedures should be
provided in the manual and printed on the instrument or on a permanent
card affixed to the instrument. Photographs or illustrations de-
picting various views of the instrument including the controls suitably
labeled are helpful.
Instructions for placing the unit in operation should include:
-12-
-------
a. Procedures for procuring, preparing, and installing reagents,
gases, and other consumable items.
b. Identification, purpose of and procedures for operating all
controls, and adjustments.
c. Prestart-up checks
d. Step-wise start-up and shut-down procedure
e. Directions for making response checks and adjustments.
3.3.9 Calibration
Instructions and recommended frequency for precise calibration of
the instrument should be provided. These should include a description
of the reference method and a list of the necessary equipment and
calibrating standard materials. Sources, quality, specifications,
/
and literature references should be included where appropriate,
3.3.10 Maintenance
A routine servicing schedule should be provided. This should in-
clude a check list of inspection points and maintenance procedures,
a timetable for carrying out the servicing operations, and a form
for keeping maintenance and repair records.
-13-
-------
Where the manufacturer wishes to restrict certain maintenance
operations to specially qualified or authorized personnel, the
nature of the qualifications or authorization should be described,
the responsibilities of both the manufacturer and the purchaser
should be stated clearly, and the arrangements for maintenance
should be specified.
A recommended list of spare parts and subassemblies to be kept on
hand should also be provided, with emphasis on those replacement items
that fail frequently or are difficult to procure.
3.3.11 Troubleshooting
Check procedures to be followed in the event o± instrument ±ailure
should be provided. Procedures should include instructions for
disassembly and reassembly along with warnings concerning possible
damage or contamination to components and steps for isolating and
checking components, sections or areas to determine the probable
cause of failure, and methods for remedy. This may be accomplished
with a chart which outlines the symptoms, the typical cause of
failure, the unit or units which may be involved, and the recom-
mended course of action.
3.3.12 Service Information
A detailed statement regarding the. manufacturer's repair policy
should include:
-14-
-------
a. Repairs which may be performed by the user or local service-
man.
b. Repairs which are to be done only by the manufacturer because
they are too difficult and/or hazardous.
c. Locations and telephone number of manufacturer's repair centers,
d. Acceptable packing procedures for returning the instrument or
parts thereof to the manufacturer for repair.
3.3.13 Warranty
Any guarantee or warranty should be a part of the manual and should
clearly state which actions by the user will negate such warranty
either completely or in part.
Availability of routine maintenance and emergency repair contracts
should be stated. The manufacturer should also specify the time
during which repair parts will continue to be available.
*
3,4 FIELD BEPAIR OR SERVICE SECTION
The Field Repair or Service Section should provide detailed infor-
mation to diagnose instrument failure which will permit qualified
instrument servicemen to repair and restore the. instrument to oper-
ation. It should include, but not be limited to, the following
topics:
-15-
-------
3.A.I Physical Description
A general description of the physical and operational characteristics
of the instrument should include:
a. A physical description of the complete instrument.
b« A diagram showing the external view with all items such as meters,
knobs, switches, lights, jacks and plugs labeled.
c. A physical description, of each subassembly.
d. Identification, effect of controls, and adjustments for ope-
rating, calibrating, tuning, aligning, etc., each subassembly.
e. An illustration of the interior view with the cover removed and
with adequate labels for tubes, transistors, resistors, circuit
boards, capacitors, photometers, cells, motors, etc. Color
coding and views showing more than one level may be helpful.
/
3.4.2 Mechanical Description
A description of the function and operation of significant optical
or mechanical units should include:
a. Diagrams of optical systems, explanations of their function,
and detailed instruction for adjustment.
b. Diagrams of sampling and solution flow systems, descriptions of
their operation, and procedures for calibration and adjustment.
-16-
-------
c. Descriptions and diagrams of servo-motors, pumps, fans, cir-
culators, heaters, etc.
d. A list of mechanical parts and acceptable commercial substitutes
(if any) along with parts, numbers and descriptions.
e. A list of recommended spare parts to be kept on hand to replace
those that fail frequently or that are difficult to procure.
3.4.3 Electrical/Electronic Description
A general discussion and description of the purpose and operational
characteristics of each unit and subassembly should include:
a. Legible, comprehensive schematic and block or logic wiring
diagrams for the power and the electronic circuits.
b. The physical location of each part in the instrument.
c. Identity of the test points to be used in making voltage, re-
sistance, capacitance, continuity and waveform checks.
d. The voltages and waveforms expected or required between test
points.
e. A list of suggested spare electrical or electronic parts to be
-17-
-------
kept on hand, especially those that are likely to fail without
warning or that are difficult to obtain.
f. Warnings concerning potential hazards.
3.4.4 MaJor_Calibration and Adjjas^tTnent
Major overhaul, repair or replacement of components may cause a shift
in the instrument's response which exceeds the range of normal oper-
ational adjustments. Some instruments provide wider range or coarse
adjustments which can be used to compensate, for such shifts. These
adjustments may be locked or factory sealed to prevent unauthorized
or inadvertent tampering. NOTE: The analyzer calibration should be
checked with calibrating gases when changes in the coarse adjustments
are made.
Procedures for major calibration and adjustment should include:
a. A list of recommended equipment, special tools, chemicals,
gases, materials and standards.
b. Description and location of adjustment screws, potentio-
meters, trimmers, etc.
c. An explanation of the purpose for each step in the calibration
procedure and directions for making necessary adjustments and
response checks during calibration.
-18-
-------
4.0 PROCEDURES FOR DETERMINING PERFORMANCE
4.1 GENERAL
4.1.1 Application
This chapter contains test procedures for determining the performance
of air monitoring instruments. The procedures are designed to estab-
lish the analyzers' physical and operational characteristics such as
size, measuring range, noise, lower detectable limit, drifts, lags in
• response, etc. Procedures for assessing the adequacy of the instru-
ments' operating instructions are also provided.
4.1.2 Gas Generation'
Suggested procedures and systems for generating the test gases required
for determining analyzer performance are given in Chapter 5 (Gas Gener-
ation) . To insure a stable output, the temperature of the environment
surrounding the gas generation system should be maintained to within
± 1 C (2°F). When permeation devices are employed, the temperature of
the device and the air passing over the device should be maintained
within ± 0.1°C. The concentration of all test gases generated should be
verified as directed in Step 4 of 4.1.6.
-19-
-------
4.1.3 Test Facility Requirement^
1. Conduct all tests except that for the operating temperature
range at 21 ± 1°C (70 ± 2CF).
2. To assess the effect of temperature changes on analyzer per-
formance, the test facility should be capable of providing temper-
atures between 4°C (39°F) and 43°C (110°) and within ± 1.0°C (2°F).
- An air conditioned room may be used, provided the range of temper-
atures required for the tests can be attained.
3. The performance of most analyzers does not appear to be affected
by exposure to the range of humidities normally encountered in
air conditioned environments. Control of humidity in the test
environment, therefore, is not required.
4. The test facility should be sufficiently large to permit the
testing of the analyzer(s) and have ample cooling capacity to
absorb the heat generated by work personnel and the analyzer(s).
5. Conduct all tests except those involving response to powerline
voltage at 117 ± 2 VAC and 60 ± 1 Hz.
4.1.4 Data Recording, Key Words and Symbols
1. Forms; Suggested forms for entering and recording results of the
tests are shown in Tables 4-1, II and III at the end of this chapter
-20-
-------
2* Keywords and Symbols; Except as noted in Test 4.5 and 4.11, the
following words and symbols are used in all equations and test
procedures. For definitions of related terms, see Chapter 10,
Air Analyzer Terminology.
a = intercept in the general form Y = a + bX
b = slope: the ratio of the analyzer output to
pollutant concentration
b = the slope derived from the manufacturer's calibration
m r
procedure.
•r\
C - pollutant concentration (ppm, pg/nr , etc.)
CV = coefficient of variation
FS = full scale: the maximum pollutant concentration that
can be measured on a given range. It is usually specified by
the instrument manufacturer.
I = interferent
IE - interference equivalent
-21-
-------
LDL = lower detectable, limit
OTR = operating temperature range
OVR = operating voltage range
ppin = the volume (y£) of pollutant per volume (liters) of
air at the standard conditions of 25°C and 760 torr.
R = response: the instrument's output readings after con-
version to concentration units (pg/m^, ppm, etc.)
Referee method = one of the procedures in this guide used
to verify the concentration of the test gas.
Span = an instrument reading or test gas concentration equal
to 80 ±5% of full scale
t = time (hr, min, sec)
H» Ss5 V fc-r t-95> tf = See Test 4-n
T = temperature (°C, °F)
UO - unattended operation
X = symbol for pollutant concentration in Test 4.5
-22-
-------
Y « reading or readout: the instrument's output in the data
display units such as chart or meter readings before conversion
to concentration units
A _
Y - expected reading: the analyzer output reading expected,
based on the response previously obtained with concentrations
of calibrating gases.
Units: the concentrations for all gases are expressed as
ppm (pl/e,). Convert ppm to yg/m^ as follows:
3 _ mol. wt. x 10-*
yg/nr = ppm x
24.47
or refer to Table 4-IX.
4.1.5 Installation and Start-up;
1. Install the analyzer(s) in the test facility described in 4.1.3
according to the instrument operating instructions. Maintain an
operations log book for the analyzer and the test facility.
Include in the analyzer log the following information in addition
to the items listed in Table 4-1, Manufacturer's Data Sheet:
(
a. Date of delivery
b. Description of special options obtained with or modifications
cade to the analyzer
c. Service information including the name of person to contact
-23-
-------
d. Summary of warranty conditions and requirements
e. Record of adjustments and calibrations performed including
settings of flowmeters, graduated dials, step switches, etc.
£, Record of all routine and non-routine maintenance and overhaul
actions
g. Descriptions of instrument malfunctions encountered and corrective
actions taken. State cause of malfunction when known.
2. Connect the output of the analyzer to a data acquisition system
such as strip chart recorder, printer, digital readout, etc.
When a strip chart recorder is used, the following minimum
specifications are needed:
&. Chart v?idth — 10 inch
b. Chart speeds - 1,2 and 5 inch/hr or
2.5, 5 and 12.5 cm/hr
c. Zero offset - ± 10% FS
d. Span adjust - ± 50% FS
e. Linearity - 0.5% FS
f. Deadband - 0.5% FS
g. Accuracy - i 0.1% FS
-24-
-------
Verify the recorder's accuracy, linearity and deadband using a
millivolt potentiometer or other appropriate test equipment.
Any other type data acquisition system should be capable of
providing data equal to or superior to those obtained with the
recorder.
NOTE: During the operating temperature range tests, locate the
data acquisition system outside the test facility.
3. Calibrate or verify all gas and reagent flows which affect analyser
response with measuring devices such as a wet test meter, dry gas
meter, a calibrated rotaraeter for gas flows and a graduated buret,
cylinder or volumetric pipet for liquid reagent flows in conjunction
with a timing device such as a stopwatch,
4. Turn the instrument on. Operate for 24 hours or longer before
tests are begun. The 24-hour warm-up time may be shortened
when so stated in the operating instructions. For determination
of warm-up time, see Test 4.15.
4.1.6 General Procedures
1. After proper warm-up and stabilization while sampling zero air,
proceed with the testing. Begin recording analyzer readings
when stable response has been attained. (Look for a rapid
-25-
-------
response an apparent steady state which subsequently shifts
upward or downward one or two hours later.) Inability of the
analyzer to attain stable response within two hours after the
start of any test except Test 4.15, Warm-Up Time, indicates
possible instrument malfunction or faults in analyzer design.
Discontinue testing and correct any problems before resuming
the test. Consult the instrument operating instructions and/or
manufacturers to resolve the problem(s). At the conclusion of
each test, check the instrument response with zero air. For
some tests, the zero response may be set at a level greater
than zero. Average the initial and final zero responses to
obtain the analyzer baseline.
Unless otherwise specified, when the difference between the
initial and final baseline readings in a test is greater than 2%
of full scale the test results are considered invalid and the
test should be repeated.
A second invalidation indicates excessive instrument drift.
Discontinue the test and correct the unit as above before
- resuming.
2. Set the instrument controls to provide the desired measuring
range. For an instrument with multiple range selection, Tests
4.4 through 4.19 should be performed on each range. When
setting the analyzer measuring range, sampling a pollutant gas
concentration (span gas) is required. Refer to Chapters 6, 7,
8 and 9 for details.
-26-
-------
3. Unless otherwise specifled„ set the instrument to read 5% of full
scale while sampling zero air and 85% while sampling a span gas
equal to 80% of full scale. This permits observation of
negative responses.
4. Verify concentration of each test gas by a referee method.
Collect the samples from the delivery system as close as practical
to the sample intake of the instrument under test. Suggested
procedures for verification are given in Chapter 5 (Gas Generation)
5. At the conclusion of each test, subtract the average zero reading
from the analyzer reading Y and convert to concentration units
R by dividing Y by the calibration slope b obtained in Table 4-IV
as follows:
R-I
6. Enter all results obtained in Tests 4.2 to 4.19 under the appro-
priate sections in Table 4-II, Column B, and in Table III.
4.2 PHYSICAL CHARACTERISTICS
4.2.1 Definition: the manufacturer, model, description, application,
detection principle, and published performance specifications of an
analyzer.
4.2.2 Procedure: during installation and start-up, enter the manufacturer's
-27-
-------
published information under the appropriate items in Table 4-1 and
in Column A of Table 4-II. For range, see Test 4.6.
1. Weight: determine the weight of each unit of the instrument and
the total weight of the complete instrument.
2. Size: measure the overall dimensions of each unit of the instru-
ment. Include all protruding items such as knobs, meters, handles,
flanges, and feet which project beyond the instrument case or
housing.
3. Space requirements: measure the dimensions required for the
operation and maintenance of the instrument. These include the
space needed for all auxiliary items and equipment such as pumps,
reagent-containers, and swing-out space for cabinet doors and
panels.
4.3 INSTRUMENT OPERATING INSTRUCTIONS
4'3.1 Definition: a set of directions which provides information regarding
the measuring principle, details of design, proper installation,
application, operation, maintenance, service and repair of an analyzer.
(See Chapter 3 for specifics which ought to be furnished.)
;
4.3.2 Procedure; based on the experiences encountered during installation
and start-up, assess the operating instructions as follows:
-28-
-------
1. Study the requirements given in Chapter 3 (Operating Instructions>.
2. Inspect the operating instructions to determine which of the
topics listed in Table 4-III are included.
3. Assess the adequacy and completeness of the information given
for each topic in the instructions by assigning a numerical value
between 0 and 10 to each topic according to the following scale.
SCORE BASIS
0
1-2
3-5
6-8
9-10
Missing
Poor
Fair
Good
Excellent
NOTE: Assign a score of 2 to instructions that are not current.
Assign a score of 1 to instructions which do not apply to
the instrument designated.
4. Enter the results in Table 4-III. The maximum score is 320.
In general, a score of 300 or greater is excellent, between
200 to 300 is adequate, and less than 200 is poor.
-29-
-------
4.4 CALIBRATION
4.4.1 Definitions:
1. Calibration: the determination of the analyzer response when a
series of calibrating gas concentrations are introduced to the
analyzer inlet or artificial stimuli are presented to the detector.
a. Calibration, dynamic: a performance test of the entire
analyzer under simulated conditions in which the response to
a calibrating gas over a known concentration range is deter-
mined, When reconciled with a static calibration, dynamic
calibration also serves to verify 1) the correctness of
reagent and sample air flow rates, 2) the efficiency of
sample collection, 3) the integrity of the analyzer's
plumbing and 4) the quality of any reagents aud/or reactants,
b. Calibration, static: the determination of the analyzer, response
when artificial stimuli such as standard calibrating solutions,
resistors, screens, optical filters, electrical signals, are
applied directly to the analyzer detector. It is a performance
test for the detection and signal presentation components of
the instrument and is primarily applicable to analyzers using
colorimetric and conductimetric detection schemes. It is not
a substitute for the dynamic calibration.
-30-
-------
4.4.2 Procedure:
1. After proper warm-up'(See Test 4.1.6, Step 1), calibrate the
analyzer for each measuring range as directed in the instrument
operating instructions.
2. In the absence of specific calibration instructions, use the
applicable calibration procedures in Chapters 6, 7, 8 or 9-
3. Set any instrument controls so that the instrument output reads
5% of full scale while sampling zero air and reads 85% of full
scale while sampling a calibrating gas equal to 80% of full scale.
/
4. The calibration should consist of at least six concentration
levels including 0, 50, and 80 percent of full scale.
5. Plot the net instrument readings Y on the vertical axis and the
pollutant concentrations C on *the horizontal axis of an appropriate
graph paper (rectilinear, semilog, log).
4.4.3 Calculations;
1. Use the method of least squares to determine the slope b and
intercept a of the straight line that fits the data best as
directed in Test 4.5.
-31-
-------
2. , The slope of the dynamic calibration curve should correspond within
10% of any static calibration curve. Differences greater than
10% indicate problems with accuracy which may be related to sampling
efficiency, leaks, malfunction in the analyzer, or reagent quality.
Consult the operating instructions and/or the manufacturer to
solve the problem(s) before proceeding with the tests.
4.5 LINEARITY
The following procedure is designed to discriminate between linear
. and non-linear relationships and to determine the nature of arithmetical!
/
or exponentially linear response functions.
1. Deviation Pattern: the configuration of the differences (+ or -)
of the individual calibration points from the best-fit, least
square line, based on the calibration points. The pattern may
be random or non-random.
A
2. Maximum Deviation: the absolute difference (Y - Y) of the point
max
of maximum departure from the best-fit line expressed as percent
of full scale.
3. Linear Response: when the analyzer response to a series of inputs
covering a specified concentration range is expressed as the
of a straight line and the maximum deviation of the calibration
-32-
-------
points from this line is less than 4%, the response is considered
linear.
4. Non-linear Response: when the deviation pattern suggests non-
random scatter of the calibration points about the best-fit
calibration line and the maximum deviation observed is 4% or
more, the response is considered non-linear.
4.5.2 Procedure:
1. Prepare a seven-column table as illustrated in Table 4-IV,
Linearity Summary Sheet.
2. From the data collected in Test 4.4, enter the input pollutant
concentrations X in column a and the corresponding analyzer
readings, Y, in column b.
3. From the data in columns a and b, calculate the sums, sums of
squares and sums of cross products necessary for fitting the least
squares line to the calibration points. Enter the results in
columns c, d and e.
4. In Table 4-V, Worksheet For Linear Relation, enter the vsums
from Table 4-IV and perform the operations indicated in Steps 1
through 11 to calculate the least squares line best fitting the
-33-
-------
calibration points. This worksheet produces a line of the form:
A
Y = a -f bX
5. Calculate the expected reading Y predicted by the equation for each
input concentration and enter, the results in column f, Table 4-TV.
6. Calculate the difference between the analyzer reading Y (column b)
A
and the expected reading Y (column f) and record the positive and
negative differences in column g,
<
7. Inspect the sequence of the +'s and -'s in column,g. Assess the
general pattern of the sequence. This pattern can be:
a. a random series of positive and negative values, e.g.,
H—hf-—(-, suggesting a linear function.
b. negative, positive, then negative, e.g., —HH— suggesting
a convex function.
c. positive, negative, followed by positive, e.g., -H H-,
suggesting a concave function.
A
8. Select the largest value Y from column e (Y - Y) .
max 6 max '
Calculate the maximum deviation as % of full scale (FS) :
-34-
-------
Y) x 100
Max dev =
FS
4.5.3 Determination of Linearity
1. Inspect the results for the deviation pattern and maximum
deviation obtained in Steps 7 and 8 above.
2. When the response is linear, proceed to Step 5 below.
3. When the response is non-linear, logarithmic transformation
of the concentration and/or the response readings may yield
a linear function. Log-linear response patterns may be of the
forms:
log Y = a + b log X (logarithmic)
and
log Y = a + b X
or (semi-logarithmic)
Y = a + b log X
To test these possibilities, convert the values in columns a
and/or b of'Table 4-IV to their logarithms and proceed with
Steps 3 through 8 of 4.5.2.
4. When the results still suggests the response is non-linear, place
a check mark in the square designated "non-linear" in Table 4-IV and
-35-
-------
enter the word "non-linear" and a dash for "maximum deviation"
in column B of Table 4-II.
NOTE: Due to the wide variety of relationships possible, the deri-
vation of equations that fit hyperbolic and transcendental relation-
ships are usually not feasible. Such relationships may be repre-
sented by graphically fitting the best line through the calibration
points. The resulting curve may then be used as a template to
transform the net analyzer reading to concentration.
5. 'A linear relationship exists when the maximum deviation is less than
of 4% or when there is a random deviation pattern.
6. Based on the conclusions from Step 5 above, place a check mark in
the appropriate square (linear, non-linear or linear with poor
precision) in Table 4-IV and enter the corresponding term and
maximum deviation value in column B of Table 4-11.
4.6 MEASURING RANGE
4.6.1 Definition: the nominal minimum and jnaximum concentrations which the
instrument is capable of measuring. Many analyzers provide multiple
range selection capability for greater accuracy and ease of interpre-
tation. Range is usually specified by stating the lower and upper
pollutant concentrations that can be measured, as for example 0 to 1 p
or 0 to 5 ppm.
-36-
-------
4.6.2 Procedure; Record the manufacturer's stated measuring range in con-
centration units in column A, Table 4-II by stating the lower limit
first, then the upper limit: e.g., 0 to 1 ppm, 0 to 10 ppm. For
instruments with multiple range selection, record all ranges. No
test is required.
4.7 CALIBRATION ACCURACY
This test applies to instruments calibrated according to the manufacturers'
procedures and for those the manufacturers state no calibration is
required.
4.7.1 Definition.; the deviation between the slope b of the curve obtained by
the. inanufacturer or with his calibration procedure and the slope b
obtained with a calibrating gas. It is expressed in percent.
4.7.2 Procedure:
1. From the manufacturer's calibration, determine the slope bm using
the procedure described in Test 4.5.
2. Compare bn with the slope b obtained in Test 4.5.
4.7.3 Calculation;
1. Calculate the accuracy in percent as follows:
—37—
-------
b — bjn
Accuracy, % ~ x 100
bm
2. Enter the result in column B of Table 4-II.
4.8 DRIFT AT ZERO
4.8.1 Definition: the deviation in analyzer output during a stated time
period, usually 24 hours, of unadjusted continuous operation when
sampling zero air. It is expressed in percent of full scale.
4.8.2 Procedure:
1. After proper warm-up (See 4.1.6, Step 1) on zero air, record the
reading Y and the time t ,
2. Continue sampling zero air for 24 hours. Make no isanual adjust-
ments to the electronic and/or gas and reagent flows during this
test. Automatic adjustments which are a part of the normal
instrument operation are permitted.
3. Determine and record the reading Ym when the maximum departure
from the baseline occurred and the reading ¥24 at the end of 24
hours.
4. For instruments with multiple range selection, repeat Steps 1
through 3 for each range.
-38-
-------
4.8.3 Calculations:
1. Convert YQ, Yffl and Y2/, to concentration units RQ, Rffl and R24 as
directed in Step 5 of 4.1.6.
2. Calculate the maximum zero drift in percent of full scale and
the drift at the end of 24 hours as follows:
R - R
m o
a. Max zero drift, % = —— x 100
FS
RO / —' R
24 o
b. 24 hr zero drift, % = — x 100
FS
c. Enter the results in Table 4-II. Report values less than twice
the noise as zero (see Test 4.10 for noise at zero).
4.9 DRIFT AT SPAN (80% FULL SCALE)
4.9.1 Definition; the deviation in analyzer output during a stated time
period, usually 24 hours, of unadjusted continuous operation when
sampling a span gas equal to 80% of full scale. It is expressed as
percent full scale.
4.9.2 Procedure:
1. After proper warm-up (See 4.1.6, Step 1) on zero air, record the
zero baseline reading YQ. Generate a pollutant test gas equal to
\
80 ± 5% of full scale. Verify the pollutant concentration COQ by
-39-
-------
the referee method specified in Chapter 5, Table 5-11. Switch
the analyzer inlet to sample the test gas. Sample until the
instrument reading indicates a stable reading YgQ at the test .
gas concentration. At this time, start and record the time tQ.
2. Continue to sample for 24 hours. Make no manual adjustments to
the electronics, gas or reagent flows during this test. Automatic
adjustments which are part of the normal instrument operation are
permitted.
3. At the end of the 24 hour test period, verify the pollutant concenti
tion as in Step 1 above and switch the inlet to sample zero air.
4. Determine and record the reading Ym when the maximum departure
from Y occurred and the reading Y£ at the end of 24 hours.
5. For instruments with multiple range selection, repeat Steps 1
through 4 for each range.
4.9.3 Calculations;
1. Convert YgQ, Ym and Y24 to concentration units Rg0, f^ and £94
as directed in 4.1.6, Step 5.
2. Calculate the maximum drift in percent of full scale and the drilt
at the end of 24 hours as follows:
-40-
-------
Rm " R80
Max span drift, % - — —- x 100
FS
R ~ R
b. 24 Hr span drift, % = — 9. x 100
FS
c. Enter the results in Table 4-II. Values less than twice the
noise are reported as zero (see Test 4.10 for noise at span).
4.10 NOISE
4.10.1 Definition: unwanted, spontaneous, short-term variations in analyzer
response about the mean output, not caused by variations in pollutant
concentration. It is expressed as percent of full scale.
4;10.2 Procedure;
1. Noise at zero:
a. Examine the analyzer readings during the first 30-ininute interval
from the data in Test 4.8. Select the maximum reading Y, and
the minimum reading Y£ during this period.
b. Convert Y^ and Y? to concentration units R-^ and R£ as directed
in 4.1.6, Step 5.
-41-
-------
c. Calculate the noise at zero in percent of full scale as follows;
i - o
Noise at zero, % = x 100
FS
d. Enter the result in Table 4-11.
i
e. For -analyzers with multiple range selection, determine the
noise at zero for each range.
2. Noise at 50%
a. After proper warm-up (See 4.1.6, Step 1) on zero air, generate a
pollutant test gas concentration equal to 50 ± 5% of full scale.
Switch the analyzer inlet to sample the test gas. Verify the
pollutant concentration and record the reading YCQ when a stable
rea'ding is obtained .
b. Continue to sample for one hour. Examine the readings during
the first 30 minutes from the one-hour period. Select the
maximum reading Y, and the minimum reading ^L^ during this
interval.
c. Convert Y^ and Y- to concentration units R, and R«.
d. Calculate the noise at 50% of full scale in percent of full seal
as follows:
-42-
-------
Noise at 50% of FS » -1-1—1 x 10Q
FS
e. Enter the result in Table 4-II.
f. For analyzers with multiple range selection, determine the
noise at 50% on each range.
3. Noise at Span:
a. Examine the readings during the first 30 minutes from the data
in Step 2 of Test 4.9.2. Select the maximum reading Y^ and
mini mum reading Y£.
b. Convert T^ and Y£ to concentration units Hi and R2.
c. Calculate the noise at span as follows:
R! - R2
Noise at span = — x 100
FS
d. Enter the result in Table 4-II.
e. For instruments with multiple range selection, determine
the noise at span for each ranges
-43-
-------
4.11 PRECISION AM) RESPONSE TIMES
The tests for determining time delays in analyzer response (lag, rise,
fall, etc.) are conducted in conjunction with the measurement of
precision.
4.11.1 Definitions:
1. Precision: the variability in repeated measurements of the same
pollutant concentration expressed as the coefficient of variation,
i.e., the standard deviation of the individual results expressed
as a percent of the mean.
2. Response Times (See Figure 10-1)
a. Lag time (initial response time), t.: the interval between the
time to, when a step changer (increase or decrease) in pollutant
concentration is made, to the time t.^ when the instrument indi-
cates a response equal to twice the noise.
b. Time to 95%, tg5: the interval between the time tQ, when a
steP increase in pollutant concentration is made, to the time tjj
when the instrument indicates a response equal to 95% of the step
chance.
-44-
-------
t f= t- ~ f-
95 C95% o
Similarly, tgQ corresponds to the time to indicate 90% and
t!00 ttie time to indicate 100% of the step change.
c. Rise time, tr: the interval between the time to 100% (t100)
and the lag time (t.).
£r "
d. Time to -95%, t_qc: the interval between the time t when
a step decrease in pollutant concentration is made to the time
t new when the instrument indicates -95% of the step change.
Similarly, t_QQ corresponds to the time to indicate -90% and
t-100 ttie time to indicate -100% of the step change.
e. Fall time, t,.: the interval between the time to -100% Ct_-,Qg)
and the lag time (t,,) . Fall time is not necessarily equal to
rise time.
tf = t-100 " t£
-45-
-------
4.11.2 Procedure:
Note: For this test, a timing device is required with a resolution of
at least 0.1 second, such as a watch with a sweep second hand or a sto]
watch.
1. After proper warm-up (See 4.1.6, Step 1), sample zero air until a
stable baseline concentration RQ (after conversion from reading-Y)
is recorded,
2. Generate a test gas equal to 50 ± 5% of full scale. Switch the
instrument inlet from the zero gas line to the test gas line.
(NOTE: Some instruments are equipped with controls for switching
from sampling ambient air to sampling zero air. These should not
be used for determining response times as they may introduce
v
additional lag times which are not part of normal operation.)
Verify the pollutant concentration C.-Q and note the instrument
response ^Q- Switch the instrument inlet to sample zero air.
3. When a stable response on zero air is obtained, switch the
, inlet to sample the test gas and begin the time to(up) by
starting the timer or noting the time.
4. When the analyzer indicates a change in response equal to twice
the nqise (see Step 1 in Test 4.10.2 for noise at zero), note
and record the time t.
-46-
-------
5. Similarly, note and record the times tg^ and t-^Q when the instrument
indicates 95% and 100% of R5Q.
6. Switch the inlet to sample zero air and begin the time tQ(down)
by starting the timer or noting the time.
Similarly record the times for the analyzer to indicate a change
equal to twice the noise (tj_) and the times to reach -95% (t_^^)
and -100% (t_100) of %Q* Note: See SteP 2 in Procedure 4.10.2
for noise at 50% FS.
7. Repeat Steps 3 through 6 nine more times.
4.11.3 Calculations:
1. Response Times:
a. From the data in Steps 3 through 7, determine the time intervals
required for the instrument to respond to a step increase in con-
centration for each trial as follows:
Lag time up, t^ = t^ - to(up)
Time to 95%, tg5 = tg5% - to(up)
Time to 100%, t100 - t100% - t0(up)
-47-
-------
Rise time, tr - t1QO - t&
b. Record the values in Table 4-IV.
c. Conversely, determine the time intervals required for the
instrument to respond to a step decrease in pollutant concen-
trations for each trial as follows:
Lag time, down, t_^ = t. - tQ(down)
Time to -95%, t_95 = t_95% - to(down)
Time to -100%, t_100 = t_100% - tQ(down)
Fall time, tf = t_
10Q
d. Record the values in Table 4-VI.
e. Perform the operations indicated in Table 4-VT and determine
the mean time and coefficient of variation for each response
time characteristic. Enter the results in Table 4-II.
2. Precision:
Perform the operations indicated in Table 4-VII and determine the
coefficient of variation CV at 50% of full scale. Enter the res«-
in Table 4-II.
-48-
-------
4,12 PULSE TIME
4.12.1 Definition: the minimum time a pollutant concentration must persist for
the analyzer to register a peak response equal to the pollutant
concentration (See Figure 10-11).
4.12.2 Procedure;
1. After proper warm-up (See 4.1.6, Step 1) on zero air, record the
zero baseline response RQ.
2. Generate a test gas equal to 50 ± 5% of full scale*. Switch the
analyzer inlet to sample the test gas and record the time t .
Continue timing and record the time t-jnny when the instrument
indicates 100% of R5Q.
/
3. Switch the inlet to sample zero air. From the data in Step 2,
determine
t!00 ~ t!00% to
4. Switch the inlet to sample the test gas and record the time tQ.
Continue sampling for a. period equal to 90% of t-^Qy and quickly
switch the inlet to zero air. The peak instrument reading may be
equal to or less than RT-
-49-
-------
5. When the reading Is less then R5Q, repeat Step 4 but increase
the sampling time. This time can be approximated by interpolating
between t9Q and t10Q. Repeat Step 4 until the minimum sampling time
t . for the analyzer to indicate RCA is obtained.
min J 50
6. When the reading in Step 4 equals R50, repeat Step 4 but reduce
the sampling time by increments of 10% of tj_QQ until a response of
less than R5Q is obtained. Repeat Step 5 above until t^^ is
obtained.
4.12.3 Calculations:
Determine the pulse time t from the data in Steps 5 and 6 as follows:
Enter the results in Table 4-II.
4.13 LOWER DETECTABLE LIMIT
4.13.1 Definition; the smallest pollutant concentration which produces a
signal equal to twice the noise. It is expressed in concentration
units.
-50-
-------
4.13.2 Procedure:
1. After proper warm-up (See 4.1.6, Step 1) on zero air, record the
zero baseline response R . Obtain the noise at zero from the data
in Step 1 of 4.10.2.
2. Generate a test gas concentration equal to between 5 and 10% o':
full scale. Switch the inlet to sample the test gas. Verify
the pollutant concentration C and record the response R.
3. Based on the response R, calculate the approximate concentration C
which will produce a response R^ equal to twice the noise. Adjust
the pollutant and/or diluent gas flowrates to produce this concen-
tration. Continue to sample and note the analyzer response.
4. When the response R^ obtained in Step 3 is greater than twice the
noise, decrease the pollutant concentration Cm stepwise until a
response equal to twice the noise is obtained.
5. Conversely, when the response R_ obtained in Step 3 is less than
twice the noise, increase the concentration Cm stepwise until a
response R_ equal to twice the noise is obtained.
4.13.3 Calculations;
From the data in Steps 4 or 5 above, enter the smallest concentration
C that produced a response equal to twice the noise in Table 4-II as
min
-51-
-------
the lower detectable limit (LDL).
LDL «* C .
mxn
4.14 ANALYZER DEADBAND
4.14.1 Definition: the range, in percent of full scale, through which the
-•—"""• •• •• —..— \
pollutant concentration may be varied without initiating a response
equal to or greater than twice the noise. (The term deadband is
commonly applied to servo-systems such as recorders but can be applied
to continuous analyzers as well.)
4.14.2 Procedure;
1. After proper warm-up (See 4.1.6, Step 1) on zero air, record the
zero baseline response Ro.
2. Generate a test gas equal to 50 ± 5% of full scale. Switch the
analyzer inlet to sample the test gas. Verify the pollutant concen-
tration CCQ and record the response £50•
3. Increase the test gas concentration to 65 ± 5% of full scale by
varying the pollutant and/or diluent gas flowrates. Verify the
pollutant concentration CW and record the analyzer response Rgc-
4. Obtain the noise at 50% FS from the data in 4.10.2, Step 2.
-------
5. By interpolating between R^Q and R,.^, determine the concentration
CJL that will produce an increase in response (AR) from RcQ equal
to twice the noise. Generate concentration CT as in Step 3 above.
Note the instrument response. The change from RrQ should be equal
to twice the noise. If not, repeat the procedure but adjust the
concentration so that the analyzer produces a change in response
equal to twice the noise.
6- Restore the test gas to the concentration C^Q as used in Step 2 and
record the response R5Q.
7. Repeat Steps 3, 4, and 5 using a test gas concentration equal
to 35 ± 5% of full scale. Verify the pollutant concentration C_
and similarly determine the concentration Co that will produce a
decrease in response from R-, equal to twice the noise.
4.14.3 Calculations: determine the analyzer deadband in percent of full scale
as follows:
(C1 - C2>
Analyzer Deadband, % = 2 100
FS
Enter the results in Table 4-II.
4.15 WARM-UP TIME
4.15.1 Definition: ^the elapsed time necessary after start-up for the analyzer
to meet performance specifications when it has been shut down for at
least 24 hours.
-53-
-------
4.15.2 Procedure:
1. After proper warm-up (See 4.1.6, Step 1) on zero air, record the
zero baseline response R .
2. Generate a test gas equal to 50 ± 10% of full scale. Switch the
analyzer inlet to sample the test gas. Verify the pollutant con-
centration Cr0 and record the instrument response B-cn-
3. Switch the inlet to sample zero air. When a stable respor.se is
obtained, turn the instrument off for at least 24 hours. Continue
generation of the test gas.
4. Restart the analyzer, switch the inlet to the test gas and record
the time t .
5. Record the time t when a stable response at R,-,, is obtained.
(Precaution: Watch for a rapid response to an apparent steady
state reading which subsequently shifts upward or downward within
an hour or two later to a new stable reading.)
•4.15.3 Calculations: determine x
-------
4.16 INTERFERENCES
4.16.1 Definition:
1. Interference equivalent IE: that portion of the indicated pollutant
concentration caused by the presence of an interferent. It Is
expressed as the ratio, in percent, of the indicated concentration
R^ with respect to the concentration of interferent C^.
2. Interferent: a substance or condition other than the one being
measured which modifies or perturbs the output of an analyzer.
9
3. Prefilters: filters or scrubbers designed to remove interferents.
These are used by some air analyzers to increase the specificitv of
detection.
4.16.2 Procedure;
1. General: Test atmospheres containing interferents are generated
by mixing each interferent with the pollutant. The interferents
and their concentrations to be used for most of the currently avail-
able detection methods are listed in Table 4-VIII. Procedures for
verifying their concentrations are given in Table 5-II in Chapter 5.
Tests with interferents known to react in the gas phase with the
pollutant are conducted in the absence of the pollutant. The
addition of the interferent to the gas system should not alter the
pollutant concentration.
-55-
-------
2. Prefliters: Any prefliters should be replaced or serviced as
directed in the instrument's operating instructions. In addition,
the instrument should sample an interferent concentration equal
to the value specified in Table 4-VIII through the prefilter for
at least six continuous hours.
3. Test Gases:
In addition to the zero air (Z) for analyzer warm-up, generate
three test gases:
a. P = flow of zero air containing pollutant which when mixed
with I or A will produce the desired pollutant test
concentration.
b. I = flow of interferent gas required to produce the inter-
ferent concentration specified in Table 4-VIII when mixed
with P.
c. A ~ flow of zero air equal to flow I.
To permit measurement of negative responses, adjust the analyzer
zero baseline, if possible, to read 10% of full scale.
-56-
-------
4. Test Procedure Without Pollutant;
a. After proper warm-up (See 4.1.6, Step 1) of the analyzer on zero
air, record the baseline response R .
b. Generate P (containing no pollutant) and I. Mix P with I.
Switch the analyzer to sample the gas mixture. Verify the
interferent concentration C^ and record the response RJ.
c. Switch the analyzer to sample zero air Z. Record the
response RQ.
5. Test Procedure with Pollutant (Omit if interferent and pollutant
cannot be mixed):
a. Generate and mix P and A to produce a pollutant concentration
equal to 50 ± 5% of full scale. Switch the analyzer to sample
the test gas. Verify the pollutant concentration Cp and record
the response R .
b. Generate I and substitute for A to produce the interferent
concentration C-^ used in Step 4b above. Record the response Rp
4.16.3 Calculations:
Determine the interference equivalent IE at pollutant concentration C
P
-57-
-------
as follows:
R. ~ R
IE (when C = 0) = - - - x 100
V»
IE (when Cn ^ 0) = ~ ~ x 100
P Ci
4.17 OPERATING TEMPERATURE RANGE
4.17.1 Definition: the range of ambient temperatures through which the analyzer
will meet performance specifications.
4.17.2 Procedure;
1. Install and operate the analyzer in the test facility (4.1.3). Set
the test' facility controls to provide a temperature (T^i) of 21 ± 1°C
(70 ± 2°F) . Verify the temperature with an appropriate temperature
measuring instrument such as a .laboratory mercury thermometer.
2. After the analyzer is properly warmed up (See 4.1.6, Step 1) or.
zero air, record the zero baseline response R .
3. Generate a test gas concentration equal to 50 ± 5% of full scale.
Switch the analyzer inlet to sample the test gas. Verify the
pollutant concentration CCA and record the response R01 ,
-58-
-------
4. Reset the test facility controls to provide the lowest possible
temperature T^ at or above but not lower than 4°C (39°F).
5. Continue to operate the analyzer until a stable response is
obtained. Record the analyzer response R/.
6. When the difference between R^i and R, is equal to or less than
twice the noise, record the temperature T, and proceed to Step 9
below.
7. Conversely, when the difference is greater than twice the noise,
estimate the temperature T,, at which the change in response will
eaual twice the noise bv interpolation between Tm and T/.
* " ^ JL -r
8. Reset the test facility controls to provide the temperature equal
to T,. Continue to sample as in Step 5 above and note the analyzer
As
response. Repeat Steps 6, 7 and 8 until the temperature T, that
causes a change in response equal to twice the noise is obtained.
9. Restore the temperature of the test facility to T2,. Continue to
sample as in Step 5 until a stable response at R£J is obtained.
10. Reset the test facility controls to provide a temperature T^
as high as possible, but not exceeding 43°C (110°F). Follow
the procedures in Steps 5 through 8 and similarly determine
the upper temperature Th which will produce a change in res-
ponse equal to twice the noise.
-59-
-------
4.17.3 Calculations:
Report the operating temperature range OTR by stating the lower
temperature T£ and the upper temperature Th at which the changes
in response were equal to twice the noise:
OTR = T£ to Th
4.18 OPERATING VOLTAGE RANGE
4.18.1 Definition; the range of powerline voltages through which the
analyzer will meet performance specifications.
4.18.2 Procedure: This test is conducted by first determining the analyzer respm
to a decrease in voltage (from 117 VAC) and second by determining the
response to an increase in voltage.
1. Install a variable transformer between the source of electrical
power and the analyzer. The transformer should have an adjust-
able output between 0 and 140 VAC and be capable of delivering
the amperage requirement of the analyzer.
2. Set the transformer to provide 117 ± 1 VAC. Verify this voltage
V117 and a1"^ subsecluent: t£st voltages with a voltmeter.
3. After proper analyzer warm-up on zero air, record baseline response
V
-60-
-------
4. Generate a test gas concentration equal to 50 ± 10% of full scale
Switch' the analyzer to sample the test gas. Verify the pollutant
concentration C^g and record the analyzer response RIIT-
5. Set the transformer to provide 90 V (VQQ) . Continue to
sample until a stable response is obtained and record RgQ.
6. Determine the difference between the response Rj^y and RQ(V
a. When the difference is equal to or less than twice the noise s
record VQQ and proceed to Step 9 below.
b. When the difference is greater than twice the noise, estimate
the voltage V0 at which the change in response will equal twice
" . Af
the .noise by interpolating between V and V^,-,.
7. Reset the transformer to provide V^. Continue to sample as in
Step 5 until a stable response is obtained. Repeat Steps 6a and
6b until the voltage V. that produces a change in response equal
to twice the noise is obtained. Record V^x.
8. Restore the transformer to V^-jj. Sample as in Step 5 until a stable
response at RCQ is obtained.
9. Adjust the transformer to provide 130 VAC (Vj^g) . Continue to
sample the test gas and determine RJ^Q as in Step 5 above.
-61-
-------
10. Determine the difference between the response R;QJ and
a. When the difference is equal to or less than twice the noise,
record V and proceed to 4.18.3.
b. When the difference is greater than twice the noise, similarly
determine the highest voltage V, which will produce a change
in response equal to twice the noise as in Steps 6 and 7.
11. Repeat Step 8.
4.18.3 Calculations ;:
Report the operating voltage range OYR by stating the lower voltage
(either VQQ or V,,x) first, and then the upper voltage V,™ or V, ,
e.g.,:
OVR = 90 to 130 V
4.19 UNATTENDED OPERATION
4.19.1 Definition: the period of time during which the analyzer can be
expected to operate unattended within the specifications.
4.19.2 Procedure:
Start this test with the maximum amount of consumable items (reagents,
gases, chart paper, etc.) recommended in the instrument operating
-62-
-------
instructions. No manual adjustments to the electronic, gas or reagent
flows are permitted during this test. Automatic adjustments which are
a part of normal instrument operation are permitted at any time.
1. After proper analyzer warm-up (See 4.1.6, Step 1) on zero air,
record zero baseline response R .
2. Generate a test gas concentration equal to 80 ± 5% of full scale.
Switch to sample the test gas. When a stable response is obtained,
verify the pollutant concentration Cgg and record the response Rq^
and the time t .
3. Switch the analyzer to sample ambient air, but continue to generate
the test gas.
4. At the end of 25 hours, switch the analyzer to sample zero air. •
Record the zero baseline and switch to the test gas. "Verify the
pollutant concentration COQ and- record the response B-gQ-
5. Continue Steps 3 and 4 for 100 hrs or until the response at
either:
a. exceeds the manufacturer's stated specifications for noise or
drift at zero and span, or
b. exceeds the noise or drift values obtained in Procedures 4.8,
4.9 or 4.10 or
-63-
-------
c. the unit is no longer operational (i.e., out of supplies,
analyzer stoppage, analyzer breakdown, etc.).
6. Hote the time t
4.19.3 Calculations:
Determine the unattended operation time UO as follows;
U0 '
-64-
-------
TABLE 4-1
MANUFACTURER'S DATA SHEET
Date:
Test Date(s):
A. IDENTIFICATION
1. Manufacturer
Phone
Address
2. Vendor
Address
' 3. Tradename(s) :
5. Serial No(s') :
6. Measurement Principle(s):
B. APPLICATION
1. Pollutant(s) :
C. PHYSICAL
1. Size, Weight:
Description of Unit
Overall Size, and Weight
Phone
4. Model(s):
•Measuring Range
ppm
Dimensions
(W x H x D, cm)
Weight
-65-
-------
TABLE 4-1 (Continued)
2, Space required (H x W x D, cm):
3. Mobility: Mobile Portable
4. Signal Output
Output
Pollutant Range
Stationary
Units
(volt, ma, 0)
Linearity
D. REQUIREMENTS
1. Sampling Rate, 1/min
2. Reagent(s):
Item
3. Utilities
Item
4. Power
Voltage
(AC or DC)
Consumption
Rate (ml/lain)
Storage
Captacity
Consumption Rate
(£/min)
Range
Current
(amp, ma)
Regulation
Required, %
-66-
-------
TABLE 4-1 (Continued)
5. Calibration
Dynamic Static (specify method)
E. SPECIAL FEATURES
-67-
-------
TABLE 4-II
ANALYZER SUMMARY SHEET AND TEST RESULTS
Test Procedure (A)
, Manufacturer's Test Results
Specifications
4.2 Physical Description
a. Weight (kg) _______ _ _________ _ _
b. Size, W x H x D (cm) ___ _ ______ ____________
c. Space Requirements
W x H x D (cm)
4.3 Instrument Operating Instructions
a. Supplied ?
b. Overall score
(see Table 4-III)
4.5 Linearity
a. Response (linear, concave,
convex)
b. Maximum deviation (%FS)
4.6 Range(s), (ppm)
a.
b.
c.
4.7 Accuracy (%)
4.8 Drift at Zero (% FS)
a. 24 hours
b. Maximum
4.9 Drift at Span (% FS) -
a. 24 hours
b. Maximum
-68-
-------
TABLE 4-II (Continued)
Test Procedure (A) (B)
Manufacturer's Test Results
Specifications
4.10 Noise (% FS)
a. at 0%
b. at 50%
c. at-span (80%)
4.11 Precision and Response Times-
taean of 10 trials (sec, min)
and CV, %
a. Lag time (up), t£
b. time to 95%, t
c. time to 100%, t
100
d. rise time, t
e. lag time (down). t
"**J6
f. time to -95%, t_93
g. time to -100%, t
h. fall time, t^
i. precision at 50% FS,
(CV, %)
4.12 Pulse Time, t (inin)
4.13 Lower Detectable Limit (ppm)
4.14 Analyzer Beadband (% FS)
4.15 Warm-up time (min)
4.16 Interferences (IE, %)
Interferents
a. T ^
b.
V
c.
d.
-------
TABLE 4- II (Continued)
Test Procedure , „ ^. D
Manufacturer's Test Results
Specifications
4.17 Operating Temperature Range,
OTR (°C)
4,18 Operating Voltage Range,
OVR (volts)
4.19 Unattended Operation, UO (hr)
-70-
-------
TABLE 4-III
INSTRUMENT OPERATING INSTRUCTIONS
SCORE
1. Instructions supplied
2. Current (up-to-date)
3t Applies to instrument designated ______
4. Includes Operation & Maintenance Section
and Field Repair or Service Section _____
5. Identification
a. Model ______
b. Name, address & phone of manufacturer
c. Name, address & phone of representative or
vendor
d. Name, address & phone of nearest service
center
e. Form for recording serial nos., modifications,
date of purchase, etc. _
6. Operation & Maintenance Instructions
a. Delivery & unpacking instructions
b. Assembly & installation instructions
c. Electrical requirements _____
d. Utilities requirements _____
e. Air sample flow and pressure requirements
f. Environmental requirements
g. Output signal characteristics
h. Start-up & operation instructions
i
i. Calibration procedure & intervals
j. Maintenance procedures & intervals
k. List of recommended spare parts
—71—
-------
TABLE 4-III (Continued)
SCORE
1. Troubleshooting
m. Service information _,
n. Warranty
7. Application
a. Purpose & use of instrument
b. Measuring range(s)
c. Description of operating principle & flow
diagram
• d. Physical and performance specifications
8. Repair Instructions
a. Physical description
b. Mechanical description
c., Electrical/electronic description
d. Calibration & adjustment procedures
e. Field repair procedures
TOTAL SCORE
-72-
-------
Table 4 - IV
LINEARITY SUMMARY SHEET
(a)
X
(input)
2X=
(b)
Y
(analyzer
reading)
" "
2Y=
(c)
X2
2X2=
(d)
Y2
2Y2=
(e)
XY
2XY=
(0
Y
(expected
reading)
1
(8)
Deviation
(b) - (0
Equation of the line:
ANALYZER
READING
= + X InPut
(intercept) (slope) Cone
Deviation pattern
Maximum deviation
LINEARITY: '—' LINEAR - maximum deviation <4% and any deviation pattern
Q NON-LINEAR - maximum deviation">4%, and convex or concave delation pattern
Fl LINEAR (poor precision) - max deviation ^4% and random deviation pattern
-73-
-------
Table 4 - V
WORKSHEET FOR LINEAR RELATION'
X denotes (input concentration]
SX=
Y denotes (analyzer reading)
Number of Points: n =
Step (1) ZXY
(2) (2X)(SY)/n
(3) Sxy = (l)-(2
(4) X = 2X/n
(5) Y = 2Y/n
(6) SX2
(7) (SX)2/n
(8) Sxx = (6)- (7) =
(9) b=_JLy = [3) =
Sxx (8)
(slope)
(10) bX = (9) X (4) =
a = Y-bX
(intercept)
Equation ot the line:
9 = a + bX
* adapted from Natrella, MG: Experimental Statistics. National
Bureau of Standards Handbook No. 91 (1966)
** enter value in Table 4 - IV
-74-
-------
TABLE 4-VI
WORKSHEET FOR RESPONSE TIMES
(a) Et
Trials
n = 10
1
2
3
h
5
6
1
8
9
10
I
(b) Mean = (a) " =
n
(c) Et2
(d) (Zt)2 _ (a)2 =
n n
(e) = (c) - (d)
(+\ , (e)
(f ' ~ n-_i
(g) Std Dev - /(f ) =
(h) cv = 4|4 x 100 =
\°)
Times to Respond (Units )
*i
Ss
*100
... -
t
r
fc~l
'-95
t-100
1
, i . . i
fcf
— —
. . I
-75-
-------
TABLE 4-VII
WOEKSHEET FOR PRECISION
(a) Input Concentration =
ppm
Trials
n = 10
1
2
3
h
5
6
7
8
9
10
TOTAL
Y
net analyzer
reading
R
(c) times Y
H2
Mean Analyzer Reading =
n
(c) Conversion Factor = Ob)
(aj
(d) 2R
(e) Mean Response = (d)
(n)
(g)
(h) = (f) - (g)
(i) - J^LL.
u; n-1
5) .Std Dev = /(i)
CV - (J) X 100
"tef
-------
TABLE 4-VIII
INTERFERENT TEST CONCENTRATIONS
Interferent Concentration-ppma
•.n
Ozone
Pollutant
CO
CO
N02
K02
N02
°3
03
°3
03
03
S02
Measuring
Principle Airanonia
NDIR
Mercury Replacement
Coloriraetric - azo dye
Amperometric
Chemi luminescent - Gas 0.5
Phase
Amperometric
Colorimetric - KI
Electrochemical
Concentration cell
Chemi luminescent - Gas
Phase
Spectrcmetric
Amperometric
Carbon Hydrogen Nitric Nitrogei
Dioxide Chlorine Sulfide Oxide Dioxide
1000
0.1
0*5 0.1 0.5
0.5 ' 0.1 0.5
0.5
0.5 O.lb 0.5b 0.5
' 0.5 0.5b 0.5
0.5 0.5
0.5
0.5 0.1 0.5
0.5
0.5
Sulfur Water
Dioxide Vaporf;
80
80
0.5
80
0.5 80
0.5
0.5
0,5
80
80
80
80
80
1.0
-------
TABLE 4-VIII (Continued)
Interferent Concentration-ppma
Pollutant
S02
S02
S09
Measuring
Principle
Coloriinetric
Conductimetric
Flame Photometric
Ammonia
0.5
0.5
Carbon
Dioxide Chlorine
0.5
0.5
0.5
Hydrogen
Sulfide
0.1
0.1
0.1
• Nitric Nitrogen
Oxide Dioxide
0.5
0,5
0.5
Sulfur Water
Ozone Dioxide Vaporc
1.0
1.0
a. Prepare concentrations to stated value ± 5%,
b. Do not mix with pollutant.
c. % RH.
CO
I
-------
TABLE 4-IX
PPM vs yg/m-3 Conversion Factors For Selected Gases
\Desired
GiveiK
yg/m3
mg/m3
PPM at 25 °C and 760 Torr
M3
1.44 X 10- 3
-
C12
3.45 X 10~4
-
H2S
7.18 X 10~4
-
NO
8.15 X 10"4
-
N02
5.32 X 1(T4
-
°3
5.10 X ID"*
so2
3.82 X 10~4
_
CO
-
0.874
co2
-
0.556
j
vo
I
N. Desired
\
Given\v
I__A,
PPM
!
yg/m3
1
NH3
696
C12
2900.
•V
H2S
1390
NO
1230 v
N02
1880
°3
1960
S02
2620
i.
mg/m^
CO
1.14
i ,
co2
1.80
Multiply the given value by the factor under the appropriate gas to obtain the desired unit,.
-------
5.0 GAS GENERATION
5.1 PRINCIPLES AM) SCOPE
To conduct the analyzer performance tests described in Chapter 4
requires the availability of stable test atmospheres which contain
known concentrations of pollutant and interferent gases for extended
periods (days). In general, a test atmosphere is produced by mixing
a flow of the desired test gas with flows of clean, dry air (zero air).
The test gas may be obtained by dilution of a. concentrated gas from
a permeation device or a cylinder, further dilution of a dilute gas,
or generated from another medium as in the case of oxygen photolysis to
produce ozone. The dilutions are prepared in a gas mixing apparatus
prior to entering a delivery manifold. This manifold is designed to
accommodate simultaneously the sample probe of the analyzer and the
independent referee method (Figure 5-1).
This chapter provides instructions for generating the various pol-
lutant and interferent test gases that are needed. In using these
instructions, previous experience and training in gas dynamics and
trace gas analysis are helpful.
5.1.1 Range
Ths concentration and volume of the test gases required depend on
the measuring range and the sampling rates of the analyzer(s) to be
-80-
-------
tested and the range of the referee method.
Typical analyzer measuring ranges and sampling rates are summarized
in Table 5-1. The concentrations range from 0.01 to 100 ppm and
sampling rates vary from 0.1 to 5.0 1/min.
5.1.2 Interferences
Pure pollutant and interferent gases can be purchased with a purity
of 99% or better. Selective absorbers can be used to remove further
unwanted trace substances. Descriptions of absorbers that have been
found useful are given in Table 5-III. See 5.2.2 for zero air speci-
fications .
5.1.3 Precision
The precision (coefficient of variation) with which the test gas
concentrations can be prepared depends on 1) the nature of the test
• gas and 2) the precision of the method used to establish the concen-
tration. With careful work, a precision between 2 to 5% is achievable
in the preparation of gases such as CO, S02 and N02« A portion of
the error is in the determination of air volumes stemming from the
use of rotameters. A minimum>of 2% error is produced for each rotameter
and the errors are usually additive. Pulsating flows and pressure
differences in the gas generation systems produce some flow variation
which also tends to decrease precision.
-81-
-------
Another source of error is the precision of the referee procedure;
there is little information in this regard. When the referee method
is a colorimetric procedure, the limiting factors are often in the
measurement of the sample air volume and the absorbance of the
colored reagent.
5.2 APPARATUS
This section specifies the equipment components and materials needed
for generating and verifying the test gas concentrations.
*
The gas generating system consists of a) sources of the pollutant
and interferent gases (permeation system, cylinder of gas. ozone
generator, etc.), b) source of zero air, c) a gas mixing apparatus,
d) a delivery manifold and e) provisions for collecting samples for
independent analysis. The individual gas flows - zero air, pollutant
and interferent - are homogenized and delivered to the test analyzer(s).
The procedures for generating the test gases are summarized in Table
5-II along with the referee methods for the verification or establish-
ment of the test gas concentrations. Additional information and dis-
cussion concerning the theoretical and practical aspects of gas gener-
2
ation can be obtained in "Controlled Test Atmospheres" by G. 0. Nelson •
Any gas generation system should meet the following general specificatior
-82-
-------
1. Produce the required pollutant and tnterferent gases.
2. Generate gas concentrations to cover the measuring ranges of the
analyzers to be tested.
3. Provide sufficient gas flow to accommodate the sampling
requirements.
4. Maintain stable output for the required test duration.
5. Simulate rapid (seconds) step changes in gas concentration.
6. Generate multicomponent gas mixtures.
7. Deliver flows of zero air and the test gas simultaneously
through separate ducts.
8. Maintain the difference in pressure at the point of delivery to
± 0.5 inch 1^0 (0.012 Newton/cm^) of atmospheric.
9. Utilize ducts, valves, rotameter, mixing chambers etc. with
surfaces that will not alter the test gas composition.
Mount the components on a chassis for convenience.
-83-
-------
5.2.1 Gas Mixing Apparatus
The gas mixing apparatus consists of an array of flowmeters, metering
valves, a glass mixing chamber and delivery manifold as shown in Figure
5-1.
*• Flowmeters; Calibrated flowmeters are needed to measure a) a flow
of zero air equal to the sum of the flow required by the test
analyzers, the referee procedure and 10% excess, and b) the range
of gas flows required to produce the pollutant and interferent
test concentrations. Glass rotameters are commonly used. Cali-
brate all rotameters in the system with a primary or secondary
standard such as a soap bubble meter, frictionless piston, wet-
test meter, spirometer or dry gas meter.
2. Mixing Chamber; This is a vessel with inlet and outlet ports for
mixing the individual test gases. The configurations of some
typical mixing chambers are shown in Figure 5-II. Design A is
the simplest and is usually adequate, Design B permits the
addition and mixing of several gases simultaneously. When
chambers of other configurations are used, make sure they
accommodate the required gas volumes and flows and provide
2
homogeneous mixtures .
-84-
-------
3. Delivery Manifold: This consists of a borosilicate glass duct
with several ports for sampling the test gas mixture simultan-
eously with the test analyzer (s) and the referee procedure.
i
The inside diameter of the duct and ports should be suffi-
(.
ciently large so that the pressure and flow conditions within
the analyzer will not be altered by more than 2% during sampling
4. Metering Valves: Fine control needle valves should be stain-
less steel or Teflon for pollutant and' interf erent gases and
any material for zero air.
5.2.2 Zero Air Production
The zero air for diluting the test gases should be free of any sub-
stances that will in any way a) alter the test analyzer response,
b) react with the pollutant or the interf erent and c) interfere
in the referee procedure . (NOTE : It is not necessary to remove
substances that are known not to interfere in the test analyzers
and referee measurement methods.) The zero air may be supplied
from cylinders or by filtering of ambient air.
1. Cylinder Zero Mry; Cylinders should be fitted with a two-stage
pressure regulator and a metering valve. For uninterupted operation,
several cylinders may be connected to the same line. While it
-85-
-------
is possible to prepare zero air in .cylinders in the laboratory,
this requires access to a high pressure (1,000 to 2,000 psig)
air compressor.
2. Filtered Zero Air; For diluent flow requirements ^ 7 1/min,
zero air can be prepared by passing ambient air through a
commercial breathing mask filter designed for removing acid
gases and organic vapors. This filter, installed in a special
holder-*, removes NC^j S02, 0^, most other acid and organic
gases and vapors and partially removes NO. It does not re-
move CO or C0£.
To remove substances not eliminated by this filter and to
purify larger air volumes (up to 30 1/min.) the ambient air
is passed through a series of chemical filters designed to
remove specific constituents. The filter materials required,
the purpose of each and the method of preparation are summa-
rized in Table 5-III. To trap particulate matter that might
be released into the air stream, install a glass fiber mat
particle filter just prior to discharging the zero air.
3. Mr Pump (for transport of ambient air) ; Vane, piston or dia-
phragm air pumps are used to furnish the diluent air flow re-
quired for the gas mixing apparatus. Diaphragm-type pumps are
recommended since carbon ring and carbon vane-type pumps may
-86-
-------
release particulate matter into the air stream. Oil lubricated
pumps should not be used. A particle filter is necessary for
vane pumps and is optional with diaphragm types. Diaphragm and
piston pumps often deliver pulsating flows. To minimize or
eliminate such variations, install an expansion tank in the
pump discharge line.
5.2.3 Gas Permeation Apparatus (Figure 5-III)
Using permeation devices as sources for gases require a constant.
temperature bath, a temperature conditioning coil and a permeation
device holder.
I. Constant Temperature B^.th; A. bath in the rangf? of 20 fo Tn°C and
controlled to ± 0.1°C is needed.
2. Temperature Conditioning Coil: A coil of metal tubing is used for
equilibrating the temperature pf the carrier gas. A section of copper
tube 1/4 to 3/8 in. ID (0.64 to 0.95 cm) by 25 to 50 ft (76 to 152 m)
long is usually adequate.
3. Thermometer ; Use a laboratory type thermometer suitable for
measuring between 20 to 30°C with an accuracy of 0.1°C.
4. Permeation Device Holder: The holder is made from a boro-
silicate glass screw-cap test tube with added inlet and out-
let ports (Figure 5-IV) . All connections must be x^ater-tight .
-87-
-------
5. Permeation Device; This is a source for some of the test gases
listed, in Table 5-II. The devices may be purchased * or
o n
prepared in the laboratory0'^.
5.2.4 jCompressed Cylinder Gases
High pressure cylinders containing dilute concentrations of test
gases such as carbon monoxide (CO), carbon dioxide (CO-), nitric
oxide (NO), nitrogen dioxide (N02) and sulfur dioxide CSO£) can be
purchased^!10 or prepared in the laboratory. The concentrations
should be at least twice and preferably 10 to 100 times the desired
test concentration. The maximum useful cylinder concentration is
determined by the gas volumes and rates that can be reasonably
handled by the gas mixing system.
A cylinder -of gas is prepared in the laboratory by transferring the
'appropriate volume of the pure test gas to an evacuated cylinder.
The cylinder is then pressurized with the desired diluent gas. The
transfer is made with a closed system vacuum-pressure manifold" . Care
must be taken to avoid contamination of the pure gas with air and water
vapor or accidental release of the toxic gas into the work environment.
The losses of some test gases are minimised by using stainless steel
containers or containers coated with a non-reactive lining such as
chromium molybdenum, alloy, paraffin or Teflon, or containers with
-88-
-------
"conditioned" surfaces. Conditioning involves repeating filling
and emptying of the container with the test gas until referee analysis"
shows no further changes in concentration occur with time. In
any event, a container previously filled with a particular test
gas should be refilled only with the same test gas and concentration.
In an emergency, cylinders known to have contained gases such as air
or nitrogen may be refilled with a different gas.
Cylinder gases should be analyzed before each use. CO concen-
trations should be verified monthly by independent analysis for
the first six months after purchase or preparation and about every
6 months thereafter. Certification or analysis by the supplier
at the time of preparation is often of little value because changes
have frequently been observed. When cylinder pressures deplete
to 200 to 500 psig; (138 to 345 Newton/cm2) the concentrations of
some gases increase due to wall desorption. The gases should be
analyzed more frequently or preferably the cylinders should be
refilled. After equilibration and confirmation or verification
of the concentrations by referee analysis, the gases are ready for
use. In the case of some gases, notably N02> it may be necessary
before use to bleed the cylinders at 30 to 50 ml/min for up to
two hours to condition the delivery lines.
5.2.5 Ozone Generation
Several commercial ozone generators have recently become available.
An adequate generator can also be assembled in the laboratory with
-89-
-------
readily available components. See Figure 5-V and 6.5.1 in Chapter 6
for the list of equipment. NOTE: The generator in Figure 5-V uses
a larger lamp and chamber than in Figure 6-II to furnish larger gas
volumes for testing several analyzers simultaneously.
Ozone up to 2 ppia is produced by irradiating a stream of zero air
to ultra-violet light from a mercury vapor lamp. A portion of the oxyger
in the air is converted to ozone. The air may be passed through a
chamber in which the lamp is inserted or the lamp may be located
outside the chamber as in Figure 5-V. In this latter design, the
chamber should be of quartz to allow the radiation to pass through.
Depending on the generator design, changes in concentration are obtained
by a) the adjustment of a movable shade over the lamp which controls the
amount of radiation, b) varying the airflow through the chamber,
c) adjusting the lamp voltage or d) dilution of the ozonized air with
zero air. In some designs, the distance between the lamp and chamber
can be varied. The concentrations can be further increased by using
oxygen in place of air.
Although ozone can be obtained dissolved in liquid chlorotri-
fluoromethane (Freon 13)3, it is not recommended because of a) cost,
b) limited durability (days), c) toxicity and d) possibility of
•I n
explosion at temperatures above -20°C .
-90-
-------
5.2.6 Humidity Generator
The generator consists of a glass vessel (humidifier) containing
distilled water and a moisture sensor. Humidified air is produced
by passing zero air over the distilled water in the humidifier main-
tained at a fixed temperature between 20 to 30°C so that a
relative humidity between 70 to 80% is produced.
1. Humidifier; This can be a 250 or 500 ml Erlenmeyer or
equivalent flask with an inlet tube extending to within
1 to 2 cm above the water level.
2. Moisture Sensor: A commercially available moisture sensor such
as a LiCl salt type sensor, dew-point detector or continuous
wet and dry bulb recorder may be used.
5.2.7 Sampling and Analysis
The referee procedure generally is a manual method and requires
a sampling train consisting of sampling probes, absorbers, metering
valves, flowmeters, vacuum pumps and traps as shown in Figures 6-III,
7-II and 8-II.
1. Sampling Probes: All sampling lines for the referee procedure
should be of glass or Teflon, and should be as short as possible
to prevent transit losses. Short sections of polyvinylchlori.de
tubing (like Tygon) may be used for-butt-joints only.
-91-
-------
2. Absorbers: All-glass bubblers or midget impingers are described
in the respective referee procedures. The absorbers may be
purchased from major glassware suppliers. For some tests, two
absorbers in series may be needed to insure complete collection
of the air sample. Standard ball-joints are commonly used to
facilitate on-off connections.
3. Air-Vacuum Pump; This is needed to draw up to 2.0 iiters/min
through the absorbers. The pump should be equipped with a
trap and a needle valve at the inlet side to regulate flow.
4. Thermometer; An accuracy of ± 2°C is needed to correct the sampled
gas volumes to standard conditions (25°C, 760 torr).
5. Metering Valve: A fine control needle valve is used to regulate
sample flow.
6* Barometer: This is used to correct the sample gas volumes to
standard conditions and should be accurate to the nearest torr.
7. Flowmeter; A calibrated rotameter to measure gas flows between
0.5 to 3 liters/min within ± 2%.
$• Trap: A vessel which contains glass wool to protect the needle
valve and the vacuum pump from moisture.
-92-
-------
9« Sgectroghotometer; This is used to measure the absorbance of
solutions between 350 to 600 im. The references listed in Table
5-II cite bandpass requirements.
10* Other; Chemicals, reagents and other apparatus needed to perform
the referee analysis are specified in the references listed in
Table 5-II.
5.3 OPERATION OF THE SYSTEM
The test gases and the concentrations needed and the instructions for
generating them are described under the respective tests in Chapter 4.
Information regarding the criteria of components for the gas generating
systems and additional details concerning other methods and equipment
for generating test atmospheres are found in Reference 2.
-93-
-------
5.4 REFERENCES
1. Thomas MA., and Amtower RE: Gas dilution apparatus for
reproducible dynamic gas mixtures in any desired concentration
and complexity. J Air Poll Coiit Assn, 16-618, 1966
2. Nelson GO: Controlled Test Atmospheres. Ann Arbor Science
Publisher, Inc. (1971)
3. Matheson Gas Products, 61 Grove Street, Gloucester, MA 01930
4. Filter Cartridge, (CMC fill), Cat. No. DZ-78006,-Mine Safety Applian
201 North Braddock Avenue, Pittsburgh, PA 15028
5. Filter Holder, End of Line, Cat. No. DZ-78006, Ibid
6. Analytical Instrument Development, Inc., 250 South Franklin Street,
West Chester, PA 19380
7. Metronics Associates, Inc., 3201 Porter Drive, Stanford Industrial P
Palo Alto, CA 94304
8. O'Keeffe AE , Ortman GC: Primary standards for trace gas
analysis. Anal Chem 38, 760 (1966)
-94-
-------
9. Scaringelli FP, O'Keeffe AE, Rosenberg E, Bell JP:
Preparation, of known, concentrations of gases and vapors with
permeation devices calibrated gravimetrically. Anal Chem 42,
871 (1970)
10. Scott Research Laboratories, Inc., Plumsteadville, PA
11. Belsky T: Preparation of low-concentration mixtures of gases,
Air and Industrial Hygiene Lab, Cal State Dept of Publ Hlth,
Berkeley, CA 94704, AIHL Report No. 117 (Jan. 1972)
12. Braker W, Mossiaan AL: Effects of exposure to toxic gases.
Matheson Gas Products, Div Will Ross Co, NJ (July 20, 1970)
-95-
-------
TABLE 5-31
MEASURING RANGES AND SAMPLING RATES OF COMMON AIR ANALYZERS
POLLUTANT
CO
0-.
v
N0/N02
so2
MEASUREMENT
PRINCIPLE
NDIR
Hg replacement
Atnperometrlc
Chemilumines cent
Colorimetric
Electrochemical Cell
IN Absorption
Amperometrie
Chemiluminescent
Colorimetric
Amperometric
Colorimetric
Conductimetric
Flame Photometric
Electrochemical Transducer
MEASURING
RANGE
(Upper Limit)
25 to 100
5 to 50
0.1 to 2
0.02 to 2
0.5 to 5
0.025 to 1
0.5 to 2
0.1 to 2
0.1 to 2
0.1 to 2
0.1 to 2
0.25 to 5
0.5 to 2
0.01 to 1
1 to 5
SAMPLING
RATE
1/min
0.5 to 2.0
8 to 41a
0.15 to 4.0
1.0 to 2.0
0.25 to 4.0
0.10
3.0
0.15 to 3.5
0.2 to 3.5
0.15 to 3.5
0.4 to 1.0
0.1 to 5
0.15
0.2 to 0.5
a Rate of interferent prefilter section. Detector section samples at 1 to 2 liter/mln.
-------
METHODS FOR GENERATING AND DETERMINING GAS CONCENTRATIONS
TEST GAS
1. Ammonia
2. Carbon Dioxide
3. Carbon Monoxide
! 4. Chlorine
VO
•-j
5. lydrogen Sulfide
6. Nitric Oxide
7. Nitrogen Dioxide
GENERATION
Permeation tube and procedure
described for S02 in footnote 3.
A cylinder of zero air containing
10,000 ppm C02. Dilute with zero
air to concentration specified in
Table 4-VIII.
A cylinder of zero air containing
CO concentrations 10 to 100
times those required in the test
procedure. Dilute with zero air
to concentration needed.
Permeation tube and procedure
described for S02 in footnote 3.
Permeation tube, and procedure
similar to that described for
S02 in footnote 3.
Cylinder of nitrogen containing
20 ppm NO and less than 4 ppm
02. Dilute with zero air to
desired concentration.
Cylinder of nitrogen containing
20 ppm N02. Dilute with zero
air to desired concentration.
(NOTE: To condition regulator
and delivery lines, discharge
the N02 at a low (~ 30 ml/min)
rate until the concentration is
stable (usually within one hour).
REFEREE METHOD
Tentative Method of Analysis for Ammonia
in the Atmosphere (Indophenol Method).
42604-01-72T, footnote 1.
Certified analysis by manufacturer, vendor or
independent laboratory.
Certified analysis by manufacturer, vendor or
independent laboratory.
Tentative Method of Analysis for Free Chlorine
Content of the Atmosphere (Methyl Orange Method).
42215-01-70T, pg 282, footnote 2.
Tentative Method of Analysis for Hydrdgen Sulfide
Content of the Atmosphere, 42402-01-70T, pg 426,
footnote 2.
Tentative Method of Analysis for Nitric Oxide
Content of the Atmosphere (Greiss-Saltzman
Reaction), 42601-01-7IT, pg 325, footnote 2.
Tentative Method of Analysis for Nitrogen Dioxide
Content of the Atmosphere (Greiss-Saltzman Reaction)!
42602-01-68T, pg 329, footnote 2.
-------
TABLE 5-II (Cont'd)
TEST GAS
7. Nitrogen Dioxide
(Cont'd)
8. Ozone
GENERATION
Permeation tube and procedure
described for S0£ in footnote 3.
Air in contact with permeation
tube must have a RH <5%. Tube
should be weighed weekly.
Ozone generator - procedure des-
cribed in footnote 3.
REFEREE METHOD
Ibid (preferred) or emission rate certified by
manufacturer, or by independent laboratory.
Tentative Method of Analysis for Oxidizing Sub-
stances in the Atmosphere, 44101-01-70T, pg 351,
footnote 2.
9. Sulfur Dioxide
10. Water
CO
I
Permeation tube and procedure
described in reference method for
footnote 3.
Pass zero air over water at a fixed
temperature between 20 to 30°C to
obtain 80 to 90% RH. Dilute with
zero air to desired RH.
Pararosaniline procedure described in
footnote 3.
Dewpoint detector, calibrated hygrometer or a
wet/dry bulb thermometer.
11. Zero Air
Air containing 21.0 ± 0.5% oxygen and
no, constituents that will 1) react
with the pollutant or interferent gas
2) alter the test analyzer response
and 3) Interfere in the referee pro-
cedure.
Cylinder zero air: certified analysis by
manufacturer or vendor. Filtered zero air:
compare response of referee method and test
analyzer(s) with response obtained with
certified cylinder zero air.
1 Health Lab Sciences, 10:2, 115-118, Apr 1973.
2 Manual of Methods of Ambient Air Sampling and Analysis. Intersociety Committee, 1972. Amer.
Public Health Assn., 1015 - 18th Street N.W., Washington, DC.
3 Part 50 - National Primary and Secondary Ambient Air Quality Standards, Federal Register, Nov. 25,
1972 (26 FR 22384)
-------
TABU. ,'5-IXI
ABSORBERS FOR PRODUCING ZERO AIR UP TO 30 1/mi.n
IATERIAL
PURPOSE
Activated charcoal
(6 x 16 mesh)
Removes many gases such as ozone,
N02, higher molecular weight organic
vapors. Does not remove CO, CC.
NO Oxidizer .
(a) Chromium trioxide
Converts NO to N0£ for subsequent
removal with TEA or soda lime^.
(b) Humidifier
Furnishes water vapor for proper
operation of oxidizer.
PREPARATION
Commercially activated coconut hull charcoal
6 ic 16 meshX Place in 2 inch I.D. x 18 inc
long section of plastic pipe. Use glass
wool plugs to retain charcoal in place.
Plastic pipe caps on each end of cylinder
are drilled and threaded to accept standard
1/2 inch O.D. tube fittings. Containers
of other materials and similar configuration
and volume may be used.
Soak firebrick or alumina 15-40 mesh in a
solution containing 16 g Cr03 in 100 ml of
water. Drain, dry in an oven at 1U5-115°C
for 30 to 60 minutes and cool. Spread a thin
layer of the dry pellets in a dish and
place in a desiccator containing a saturated
salt solution which maintains the relative
humidity between 50 to 70%. The reddish
color changes to a golden orange when equi-
librated. Place in a 1/2 inch I.D. x 15 inch
glass tube. Use glass wool plugs to hold
pellets in place. (Caution: Protect eyes and
skin when handling this material. Do not
breathe oxidizer dust.) Before using, pass
air containing 30 to 70% RH through the
oxidizer for about 1 hour at 0.5 £/min to
condition. Discard when more than
3/4 of the oxidizer bed depth turns brown.
Pass dilute NO air stream over water at a
fixed temperature such that the humidity of
the air stream is maintained within 50 ±
20% R.H.
-------
TABLE 5-HI (Cont'd)
MATERIAL
3. Triethanolamine (TEA)
PURPOSE
Removes NO,
4. Desiccant
Remove water
Carbon Monoxide
Oxidizer (Hopcallte)
Catalytically oxidize CO to C02 for
subsequent removal with Ascarite or
soda lime.
6. C02 Absorber
Remove C02, H20
PREPARATION
Soak firebrick 10-20 mesh in a 20% aqueous
solution of TEA. Drain, spread on a dish.
and dry for 30 to 60 min at
95°C. Pellets should be free-floxd.ng.
Place in a 1/2 inch O.D. (7/16 inch X.D.)
•x 15 inch long polyethylene or stainless
steel tube with standard 1/2 inch O.D,
tube fittings on each end. Use glass
wool plugs to hold the pellets in place.
Commercial 6 x 16 mesh silica gel with
color indicator". Place in 3 inch I.D.
x 24 inch long clear plastic cylinder
capped at both ends. Caps are drilled
and threaded to accommodate standard 1/2
inch O.B. tube fittings. Use glass wool
to hold granules in place. When the. change
in color exceeds 3/4 of the desiccant bed
depth, regenerate by exposing the silica gel
to 120°C atmosphere overnight.
Commercial mixture of copper and manganese
oxides-^. Place granules in a 1/2 inch O.D.
(7/16 inch I.D.) x 15 inch long section of
copper pipe with standard 1/2 inch O.D. tube
fittings on each end. Use glass wool to
hold granules in place.
a.
b.
Soda Lime^: commercial mixture of
calcium and sodium hydroxides; 4 to
8 mesh.
Ascarite^ : a commercial preparation
of sodium hydroxide in an asbestos
matrix, 8-30 mesh.
-------
TABLE 5-IIZ (Cont'd)
ATERIAL PURPOSE PREPARATION
Place soda lime or ascarlte in a 2 Inch
I.D. x 15 inch long section of plastic pipe.
Plastic caps at both ends are drilled and
threaded to accept standard 1/2 inch O.D.
tube fittings.
1 Activated coconut hull charcoal, Type PCB 6 x 16 mesh, Pittsburgh Activated Charcoal, Merk & Co., Inc.
Pittsburgh, PA 15230
2 Silica gel, indicating, 6 x 16 mesh, Grace Davison Chemical, Baltimore, MD 21226
3 Carbon monoxide purifier, (Hopcalite) Model RAF-BCHDI, Robbins Aviation, Inc., Vernon, CA 90058
4 Soda lime, 4-8 mesh, J.T. Baker Chemical Co., Phillipsburg, NJ 08865
5 Ascarite, 8-30 mesh, ibid.
-------
I
M
O
I
Zero Gas Line
Pollutant/Interferent Gas Line
O
Vent«~O
O
Flow
Meter
Zero Air Pollutant Interferent
&
Mixing
Cnamber
Vent
To Test
Analyzers
To Referee
Method
Vent
Figure 5—1. Diagram of gas mixing apparatus.
-------
Ill
o
U)
I
B
Figure 5-II. Configuration of gas mixing chambers.
-------
o
-p-
I
Thermometer
fl
Stirrer
Flowmeter
Control
valve
Water bai:b
Permeation device
Device holder
(glass)
Zero air
Temperature conditioning coil (copper)
Figure 5-III. Gas permeation apparatus.
-------
I
J_a
o
25mm
Outlet
Port
200mm
f
^
Inlet
Port
1
Screw Cap Test Tube
or Culture Tube*
Plastic Screw Cap
(w/Teflon Link)
Threaded to Fit Cap
* Kimble Glass Co., Div. Owens-Illinois, Toledo, Ohio.
Cat. No. 45066.
Figure 5-IV. Permeation device holder.
-------
Aluminum box enclosure
!
M
O
I
Hi-voltage
power supply
Clean air ~~
or oxygen
Adjustable sleeve
9-in. UV lamp ^
£-tezz2
-1
I
.J
Quartz tube 35mm O.D.
Collar
A
Figure 5-V. Ozone Generator
-------
6.0 CALIBRATION PROCEDURE FOR AUTOMATED ATMOSPHERIC
OX3DANT AND OZONE ANALYZERS
6.1 PRINCIPLE AND SCOPE
6.1.1 This procedure is for the calibration of automated atmospheric oxidants
and ozone analyzers. The calibration -may be of two types, dynamic and
static. The dynamic calibration must always be performed by determining
the analyzer response to a series of ozone (03) concentrations. The
procedure is applicable to all oxidant and ozone analyzers and is a
performance test of the entire analyzer under simulated service
conditions. The static calibration is performed by determining the
analyzer response to artificial stimuli such as standard calibrating
solutions, optical filters, screens, electrical signals, resistors,
etc. This calibration is a test of the detection and signal presen-
tation components only and is not a substitute for the dynamic cali-
• bration. It is primarily applicable to analyzers using wet-chemistry
and colorimetry.
6.1.2 Atmospheric oxidants are those airborne compounds that will oxidize
iodide ions in solution to iodine. The predominant oxidant is ozone.
Other oxidants are: nitrogen dioxide, halogens, peroxy compounds,
hydroperoxides, organic nitrites, peroxy nitrates, and hydrogen
peroxide. Sulfur dioxide reduces the iodine in solution. Oxidant
data should be corrected for the effect of nitrogen dioxide and sulfur
dioxide.
-107-
-------
6.1.3 The ozone concentrations for the dynamic calibration are generated
by irradiating a stream of purified air (or oxygen) with ultraviolet
light. Each ozone stream is sampled simultaneously with the instru-
ment and with the manual referee method (neutral potassium iodide1)
to establish the concentration.
6.1.4 Static calibration is accomplished by flowing reagent solutions
containing amounts of iodine (12) equivalent to concentrations of
ozone through the analyzer's detector at the reagent flox-7 conditions
encountered during normal operation. The analyzer responses are
plotted versus equivalent ozone concentrations to obtain the static
calibration curve. The instrument variables, e.g., air and liquid
I
flow rates, may be adjusted after static calibration to make the
output response conform to the pollutant concentration or a simple
multiple or fraction of the concentration in parts per million (ppra)
or micrograms per cubic meter (pg/m^) (spanning). When a static
calibration is not performed, the spanning may be done during the
dynamic calibration.
6.2 RANGE
The range of the calibration procedure is determined by that of the
manual referee method. For a 100 liter sample collected in 10 ml
of absorbing reagent and measured in a 0.5 inch cuvette, the range is
between 0.02 to 1.0 ppm 03 (40 to 2,000 yg 03/m3). The lower limit
-108-
-------
can be extended down to about 0.01 ppm (20 yg/m3) by using a
one inch path cuvette and a 30 minute sampling period. At con-
centrations below 0.05 ppm (100 yg/m3) the manual method may be
less accurate because of the losses of iodine on the glass surface .
The upper limit can be extended up to 10 ppm 03 (20,000 yg 03/m3) by
using 20 ml of absorbing reagent and decreasing the sampling rate
and collection period.
6.3 INTERFERENCES
6.3.1 The zero air used for ozone generation must be free of reducing and
oxidizing substances. Commercial zero air in cylinders is usually
free of such interferents. Chemical absorbers are available that
will remove most interfering compounds when ambient air is used
for zero air. Details for preparing these absorbers are given in
Table 5-III.
6.3,2 Glassware should be cleaned with chromic acid solution since dust
or foreign matter may interfere. Rinse thoroughly with distilled
water. Vessels to contain a dilute iodine solution should be rinsed
just before use with a portion of the solution to avoid losses of
Iodine .
6.4 PRECISION, ACCURACY AND STABILITY
6.4.1 The coefficient of variation of the manual referee method within the
range of 0 to 2 ppm is about ± 5%. The -major error is from the loss
-109-
-------
of iodine. This is reduced by using a second impinger in tandem.
6.4.2 When spanning is possible, any discrepancy between the input and
output may be resolved by adjusting the output of the instrument
to correspond with the value of the calibrating gas or solution.
Where analyzers have no spanning controls, a correction factor
nay be calcxilated to convert the analyzer readings to ozone con-
centrations .
The calibration is based on the 1:1 stoichiometry of the reaction of
Q / t
ozone in the absorbing solution^' > .
03 + 2KI + H20 •> 12 + 2KOH 4- 02 (1)
6.4.3 The absorbance of the reacted KI solutions in the referee procedure
should be read between 15 to 30 minutes after sampling to insure
complete I2 formation and yet avoid fading of iodine color, especially
at low absorbance levels.
6.5 APPARATUS
6.5.1 Ozone Generator (Figure 6-1 and 6-II) The generator should be capable
of producing ozone concentrations in the range of 0.01 to 1.0 ppm
(20 to 200 yg/m3) at a flow rate of at least 5 1/mln.
Commercial ozone generators have recently become available. The ozone
concentration produced varies inversely with the airflow rate, and
-110-
-------
directly with the exposed area of the ultraviolet lamp.
An adequate generator consists of:
1. Ultraviolet Source - Low-pressure mercury lamp such as Ultraviolet
Products, Inc., San Gabriel, California, model PCQ9G-1 or equivalent
(available in lengths from 6.3 to 20 cm or 2-1/2 to 8 inches), with
matching power supply (ballast transformer).
2. Lamp Control - The lamp ballast should be connected to a source
of constant AC voltage to provide a constant lamp output.
3. Lamp Housing - Figure 6-II shows a recommended system for exposing
the air stream to the ultraviolet lamp.
4. Pump (for transport of ambient air) - capable of furnishing the
total airflow requirements of the calibration system plus 10%.
Diaphragm-type pumps are recommended since pumps with carbon
vanes and rings may release particulate matter into the air
stream. A particle filter (glass fiber mat) should be installed
downstream of carbon vane pumps and is optional with diaphragm
pumps.
5. Activated Charcoal Trap - For filtering cylinder air.
See Table 5-III, Item 1.
-Ill-
-------
- F°r measuring airflow past the lamp; meter should be
capable of measuring flows from 1 to 10 liters/min within ± 5%.
Rotameters are most commonly used. They should be calibrated
frequently (at least monthly) with an appropriate flow measuring
device such as a wet test meter, dry gas meter, soap bubble
meter or calibrated rotameter.
7. Sampling Manifold - The manifold is fabricated from borosilicate
glass tube with sampling ports to distribute the calibrating
gas simultaneously to the analyzer (s) and the manual sampling
train. See Figure 6-1.
6.5.2 pH meter - Capable of measuring with a precision of ± 0.02 pH units.
6.5.3 Sampling Probes - The gas lines for conducting the ozone calibrating
mixtures to the analyzer should be of Teflon or glass, and they should
be as short as possible to minimize wall losses. Short sections of
polyvinylchloride tubing may be used to butt join sections of inert
tubing .
6.5.4 Manual Sampling Train:
Assemble the ozone sampling train as shown in Figure 6-III. Use
ground-glass joints upstream from the impingers. Other connections
may be butt-joined with polyvinylchloride tubing.
-112-
-------
1* Absorber - All-glass midget impingers as shown in Figure 6-III
are recommended for collecting the samples for referee analysis.
See Reference 1 for specifications. The impingers may be
purchased from glassware suppliers. Two absorbers in series
are needed to insure complete collection of the sample. Ball-
joint connections are recommended for convenience.
2. Air-vacuum Pump - Capable of drawing 1 liter/min through the
absorbers. The pump should be equipped with a needle valve and
trap at the inlet side to regulate flow.
3. Flowmeter - A calibrated metering device to measure gas flows of
0.5 to 2 liters/min within ± 2%. See Item 6 in 6.5.1 for
calibration requirements.
4. Trap - A vessel containing glass wool to protect needle valve
from moisture.
6.5.5 Miscellaneous
1. Spectrophotometer - Equipped with a bandpass filter of 20 run
or less for measuring the absorbance at 352 nm. Matched 1-cm,
0.5 or 1.0 inch cuvettes should be used.
2' Timer - 0 to 30.0 minutes - for measuring the sampling period
of the referee sample.
-113-
-------
3* Thermometer - With an accuracy of ± 2°C to correct sample volumes
to standard conditions (25°C, 760 torr).
4. Barometer - Accurate to the nearest torr to correct sample volumes
to standard conditions.
6.5.6 Static Calibration
I- Volumetric Flasks - 25, 100, 250, 500, 1000 ml - low actinic
glass.
x
2. Buret - 50 ml.
3. Pipets - 0.5, 1, 2, 3, 4, 10, 25, and 50 ml volumetric.
4. Separatory Funnel - 125 ml, low actinic glass.
5. Iodine Flasks - 300 ml., (3).
6. Oven - maintained at 105°C.
6.6 REAGENTS AND GASES
Purity of chemicals - Unless otherwise indicated, all reagent specifi-
cations shall conform to the Committee on Analytical Reagents of the
-114-
-------
American Chemical Society6. When such reagents are not available,
ascertain that they do not lessen the accuracy of the determination.
6.6.1 Potassium Iodide (KI) - Reagent grade KI often contains a reducing
agent to prevent the oxidation of iodide to iodine on standing. KI
meeting "USP specifications usually contains little or no reducing
agent. While this agent keeps the KI from turning yellow, it
interferes significantly with oxidant and ozone measurement and
calibration. Every lot of KI purchased should be tested before
use. To test, prepare a 10% solution as directed in 6.9.1, Step 2,
in a clear 100 ml volumetric flask. Make sure the pH is between 6.5
to 7.0. Add 0.10 ml of iodine working solution (Item 6.6.11) and mix
well. Observe the iodine color visually or transfer 10 ml to a
cuvette and read at 352 ma in the spectrophotometer. When reducing
agent is present, the absorbance will fade within minutes. Add ^ 10%
hydrogen peroxide (H202) solution dropwise (with a graduated pipet
or buret) to the 10% KI until the loss of absorbance stops. To check
the end-point, again add 0.10 ml of the I2 solution (Item 6.6.11).
The color should not fade. Based on the volume V]_ of the H202 required,
determine the volume V2 of the H202 needed to neutralize the reductant
in 1 liter of 50% KI (Item 6.6.9).
. (50%) (1000 ml) (2)
= CV1' (10%) (100 ml)
Add V2 ml H202 to each liter of the 50% KI 6.6.9 prepared. Verify
that the proper amount of H202 has been added to the batch. A yellow
-115-
-------
color Indicates too much H202 was added and a. new batch should be
prepared. When the solution is colorless, add 0.1 ml of the I2
working solution (Item 6.6.11) forming a slight yellow color that
should not fade. When it does, determine the additional amount of
H202 required. Other KI solutions (1%) should be tested and treated
in a similar manner.
6.6.2 Distilled Water - Double-distilled water should be used for all
reagents. It can be prepared in an all-glass still. Before the
second distillation, add potassium permanganate to the water to
produce a faint pink color and one crystal of barium hydroxide per
liter to make the water alkaline,
6.6.3 Absorbing Solution (1 % KI in 0.1 M phosphate buffer) - Dissolve 13.6 g
of potassium dihydrogen phosphate (KH2PO^), 14.2 g of disodium hydrogen
phosphate (l^HPO^) or 35.8 g of the dodecahydrate salt (Na2HP04'12 B^O)
and 10.0 g of KI in sequence in approximately 750 ml distilled water,
and dilute to 1 liter. Keep at room temperature for at least one day
before use. Measure the pH and adjust to 6.8 ± 0.2 with NaOH pellets
or 10% H-^PO^. This solution can be stored for several months in a
glass-stoppered brown bottle at room temperature without deterioration.
It should not be exposed to direct sunlight.
6.6.4 Standard Arsenious Oxide As20-^ Solution (0.05 N) _ T)ry reaeent grade
As203 at 105° to 115°C for one hour immediately before using. Cool
to room temperature in a desiccator. Accurately weigh 2.473 g in a
-------
small glass-stoppered weighing bottle. Dissolve in 25 ml 1 N NaOH
in a flask or beaker on a steam bath. Add 25 ml 1 N ^SO, . Cool,
transfer quantitatively to a 1000 ml volumetric flask and dilute to
volume. The solution should be neutral to litmus.
(wt. AsoOo)
Kor-ality °
6.6.5 Starch Indicator Soulution (0.2%) - Triturate 0.4 g soluble starch
and approximately 2 mg mercuric iodide (preservative) with a few ml of
water. Add the paste slowly to 200 ml boiling water. Continue boiling
until the solution is clear, allow to cool, and transfer to a glass-
stoppered bottle, Alternatively, a commercial indicator (Thyodene3)
can be used .
6.6.6 Stock Iodine Solution (0.05 N
1. Preparation - Successively dissolve 16 g KI and 3.173 g resublimed
I2 in 25 ml distilled water. When the I2 dissolves, transfer the
solution to a 500 ml glass-stoppered volumetric flask. Dilute to
volume with distilled water and mix thoroughly. Keep at room
temperature at least one day before use) Store the solution in
a dark brown, glass-stoppered bottle away from light. Re-
standardize before use.
^Indicator, Thyodene, Cat. No. T-138, Fisher Scientific Company
-117-
-------
2. Standardization - Accurately pipet 20.0 ml of standard As203
solution (Item 6.6.4) into a 300 ml iodine flask and acidify with
one drop of 10% l^SO^ solution. Add about 2 g solid sodium
bicarbonate (NaHCX^) , and 5 ml starch solution (or 0.1 to 0.5
gm thyodene) as indicator. Titrate with the stock I2 solution
adding 1 ml of 10% I^SO^ near the end-point to saturate the
solution with carbon dioxide. Continue the titration until
a pale blue color is obtained that persists for 30 sec. Cal-
culate the normality of the stock I2 by equation 4.
ml AsoOo X normality AsoOo , ,.
Normality 1.2 = - ^-3 - - - ^-^ (4)
ml I2
The stock I2 solution may also be standardized with 0.025 N
sodium thiosulfate (Na2S2Oo). The ^32820^ solution is in turn
7
standardized with primary standard potassium biiodate (KH(IOo)?)
or potassium dichromate (K^Cr^y) .
6.6.7 Zero Air - This may be obtained from cylinders of high-pressure,
compressed synthetic air, or by filtering ambient air. The air
for generating and diluting the test gas should be free of ozone
and any substances that will in any v?ay a) change the test gas
concentration, b) interfere in the analyzer response or c) interfere
in the referee procedure. An activated carbon filter will remove
most interferents, but when nitric oxide or sulfur dioxide is present
-118-
-------
in the ambient air, a Cr03 oxidizer followed by a soda lime or tri-
ethanolamine filter is necessary to remove them. See Chapter 5, Gas
Generation, for details.
6.6.8 0.5 M Buffer Solution (for static calibration) - Dissolve 71 g (0.5
mole) anhydrous Na2HP04 or 179 g Na2HP04'12 H20, and 68 g KH2P04, in
approximately 750 ml distilled water. Make up to almost one liter.
Measure the pH. When different from pH 6.8 to 7.0, adjust with
NaOH or KOH pellets, granular KH2P04 or 10% H3P04> Dilute to one
liter. Store in an amber bottle and out of direct sunlight. Discard
after two years. When exposure to sunlight is unavoidable, add
0.025 gm of a non-reducing preserving agent, e.g., sodium o-phenyl-
phenate, sodium pentachlorophenate, Trichlorophenate (Dowicide B).
6.6.9 50% Alkaline KI Solution (for static calibration)_ - Dissolve 500 g
of KI (See 6.6.1) in. approximately 750 ml of water. Add a sufficient
amount of concentrated NaOH solution or NaOH pellets to obtain a pH
9 to 11 and make up to one liter. Mix well and store in an amber
bottle out of direct sunlight. Discard after two years.
6.6.10 Iodine Dilute Solution (0.004N I2) - Transfer 40.00 ml of the 0.05 N
I2 stock solution (Item 6.6.6) to a 500 ml low-actinic volumetric
flask with a volumetric pipette. Dilute to volume with distilled water,
Mix well and store out of direct sunlight. Discard after two days.
Calculate the normality of the I2 by equation 5:
(40.00 ml) (N of stock 12)
N of dilute I2 = — — (5)
(500 nil)
-119-
-------
6.6.11 Iodine Working Solution (0.0008N I2: equal to 10 yl 03/ml of solution)
Calculate the volume V^ of dilute I2 (Item 6.6.10) necessary to make •
250 ml of iodine working solution by equation 6:
0.204 (6)
a N of Dilute I2
where 0.204 is a combined constant (See Basis for calculations, 6.11).
Transfer the volume of 0.002 N I2 solution calculated by equation 6
to a 250 ml low-actinic volumetric flask and dilute to volume with
distilled water. Mix well and store out of direct sunlight.
Prepare daily.
1. Prepare 'a series of calibrating solutions between 0.1 to 0.7
Hi 03/rnl by diluting aliquots (i.e., 1, 2, 3 ml) of the I2
working solution (Item 6.6.11) to 100 ml with the 1% KI absorbing
solution (Item 6.6.3). Obtain the spectrophotometer readings at
352 ran. Plot the absorbances versus equivalent yl Oo per ml
on rectilinear graph paper as a check for linearity. Calculate
the slope b of the best-fit curve for the data using the method
of least squares .
2. When a static calibration is to be performed on a colorimetric
Instrument using iodide absorbing solution, prepare a calibration
Table 4-V in Chapter 4.
-120-
-------
curve for the spectrophotometer as in step 1 above bat using
the same reagent formulation as used in the analyzer. This
curve will be used when performing a secondary check on the
accuracy of the calibrating solutions during static cali-
bration (6.9) .
6.8 DYNAMIC CALIBRATION
6.8.1 General
1. When a static calibration (6.9), is to be performed on the
analyzer, it should be done before the dynamic calibration
(6.8) to assure proper operation of its detection and signal
presentation components.
2. When the analyzer to be calibrated has been operating as a
continuous monitor, it is useful to determine the response
near the span level first without changing the span setting
(auditing). When the analyzer response is within 10% of
that obtained in the previous calibration, the calibration
is still valid and a new calibration is not needed. When
the response is greater than 10% from the previous calibration
proceed with the complete calibration. The audit data provide
a record of the calibration drift. Instruments with non-linear
response require the full calibration.
-121-
-------
3. The static and dynamic responses may be compared (reconciled)
to verify the proper operation of the analyzer. See 6.10
for details.
6.8.2 Procedure
1. The analyzer should be in good operating condition and in-
stalled in accordance with manufacturer's instructions.
Operate the analyzer for at least 24 hours to warm-up. This
24 hour warm-up time may be shortened when so stated in the
operating instructions. Adjust air and reagent flows to their
recommended rates or the rates determined from the static
calibration data and verify the flowrates as described in
6.5, Item 6. Record data only after stable response has
been attained. Refer to 4.1.6 in Chapter 4 for determining
stable responses.
2. Place the ozone generation app'aratus (Item 6.5.1) as close as
practical to the analyzer to prevent losses and to minimize
pressure changes in the analyzer sampling duct. Determine the
sample airflow requirements of the analyzer(s) and add the
airflow (1.0 £/min) needed for the referee analysis. Add
about 10% of the total to insure an excess. (NOTE: The
excess ozone stream should be vented or absorbed by a charcoal
filter to avoid exposure to personnel.) In a proper assembly,
connection or disconnection of the analyzers sampling ducts
should not alter the airflow settings of the instruments.
-122-
-------
3. The ozonizer lamp and power supply should be sufficiently
warmed up to Insure a steady ozone output. Some commercial
ozone generators may require -up to two hours for warm-up.
With the ozonizer power supply on and the lamp completely
shielded, flush the system with zero air for several minutes
to remove residual ozone.
4. When a steady analyzer reading is obtained, pipet 10 -ml of
the 1% KI absorbing reagent (Item 6.6.3) into each of the 2
impingers. Assemble the impingers and connect to the
sampling train as shown in Figure 6-III. Draw a sample
from the sampling manifold through the train au 1.0 liter/
min for 30 minutes. Allow the solutions to stand for 15
minutes. Transfer the exposed solution from each impinger,
in turn, to a clean spectrophotometer cuvette and determine
the absorbance of the solution at 352 nm against unexposed
absorbing reagent as the reference blank.
When the absorbance of the solution in the first impinger
is greater than the blank, continue flushing the apparatus
until the absorbance obtained is the same as the blank.
NOTE: Inability to obtain a reading equal to the blank
indicates possible presence of oxidants in the zero air or
low pH (<6.5) of the absorbing solution. Correct problem(s)
before continuing.
-123-
-------
Zero the analyzer by adjusting the analyzer zero controls
so that the output reads zero or reads the desired baseline
value.
5« Generate an ozone gas concentration equal to 80 ± 5% (span
gas) of the analyzer's full scale measuring range. When
the analyzer response is steady, collect two samples of the
gas stream and analyze as described in Step 4 above. Adjust
the sampling period so that the absorbance of the sampling
solution is about midscale (between 0.2 to 0.5) on the
spectrophotometer. Five to ten minutes are usually sufficient.
Do not exceed 30 minutes to avoid iodine losses.
6. Add the two spectrophotometer readings to obtain total absorbance.
From the volume of air sampled and the slope of the spectrophoto-
meter calibration curve (See Step 1 in 6.7), calculate the
ppm 0-j (or yg Og/m ) by equation 7:
n (A) (10 ml)
ppia 03 = (7)
where: A = absorbance of the solution
b = slope of the spectrophotometer calibration curve
obtained in 6.7
Va = volume in liters of sample collected (liters/ruin
X min)
-124-
-------
To convert ppm (yl/1) to pg 03/m3, use equation 8.
Vg 03/ia3 = (1960) (ppm 03) (8)
Usually, the change in the gas volumes of the samples due to
deviation from the standard conditions of 25°C and 760 torr
are small and may be neglected. When the deviations are large
(sufficient to cause a change in gas volume greater than about
5%) correction should be made.
7. The concentrations of the two samples obtained should be within
± 5%. Differences greater than 5% indicates possible unstable
gas concentrations or error in the sample collection and analysis.
Correct these problems before proceeding with the calibration.
8« Determine the net analyzer reading by subtracting the analyzer
baseline reading from the span reading.
9. Adjust, when possible, the analyzer upper limit (span) controls
to give a reading equivalent to the span concentration (spanning).
When the instrument has no span controls, proceed to Step 10
below. Generate zero air and note the analyzer reading. When
the reading is different from the original reading by > 2%, reset
the analyzer to the original baseline and repeat Steps 5 through
9 above. NOTE: When the span and zero controls are not electri-
cally independent, it may be necessary to rezero and respan
iteratively until the proper zero and span settings are obtained.
-125-
-------
10. Generate, in turn, four additional ozone concentrations (10, 20,
40 and 60% of full scale) and determine the ozone concentrations
in duplicate as described in Steps 4 through 8 above. Record
the net analyzer readings by subtracting the baseline reading
from the individual readings.
6.8.3 Treatment ofDynamic Calibration Data
1. Plot the net analyzer readings on the vertical axis versus the
ozone concentrations on the horizontal axis of an appropriate
graph paper (rectilinear, log, semi-log, etc.). Calculate the
slope b
-------
also 6.1.4. The procedures can also be used on other color imetric
KI instruments by using the appropriate reagent formulations.
6.9.1 Procedure
1. Turn the analyzer air and liquid pumps off. Clamp off and
disconnect the reagent line at the air-liquid separator or
other convenient place. Install a 125 ml low-actinic separatory
funnel supported by a ring stand and connect the funnel to the
inlet of the analyzer sample cell with 8 mm ID glass tubing.
Butt-join the tubing with polyvinylchloride tubing. Dis-
connect the sample cell exit line at the inlet to the reagent
reservoir and lead the line to a waste bucket.
When the analyzer uses a solution reference, disconnect the
reagent line at the exit port of the reference cell and recycle
the solution back to the reagent reservoir so that the reagent
flows through the reference cell only. Turn the analyzer
reagent pump on.
2. Prepare 10% KI absorbing solution blank by placing 20 ml of
the 0.5 M buffer reagent (Item 6.6.8) and 20 ml of the 50% alkaline
KI reagent (Item 6.6.9) in a 100 ml low-actinic volumetric flask.
Dilute to volume with distilled water and mix well.
-127-
-------
NOTE: This, and all subsequent 10% KI solutions should be
prepared as needed and used within minutes to prevent inter-
ference from oxidation of iodide to iodine by exposure to air
or light.
3. Rinse the separatory funnel, connecting lines and sample cell
with a small portion (= 10 ml) of the 10% KI blank solution
twice. Fill the separatory funnel with the remainder of the
reagent and adjust the flow through the sample cell to
approximately the flow rate at which the instrument is to
operate (1 ml/min - 20 drops/min). The separatory funnel
stopcock may be used to control the flow. When the analyzer
reading is stable, set the recorder baseline slightly above
the pen indicator stop (or zero) to permit indication of
negative deviations from zero. Record the analyzer baseline
reading and the position of the zero control.
4. Prepare a calibrating solution equal to about 80 ±5% of full
scale with the 10% KI solution as follows: Make up 100 ml
of 10% KI solution and mix well. Transfer a portion to the
cuvette to zero the speetrophotometer at 352 nm. For a.
full scale of 1 ppm, 80% of full scale is 0.80 ppni Oo.
v» =
-128-
-------
where: Vw - volume (ml) of iodine working solution (6.6.11)
Vc = volume of calibrating solution (100 ml)
C « concentration desired, in yl 03/101
C^ = concentration of working solution (10 pi 03/ml)
For example: When the desired calibrating solution is 0.20
ul 03/ml, the volume Vw of the iodine working solution re-
quired is:
(0.20 yl Do/ml)
Vw - (100 ml) — i—- = 2.0 ml (10)
w (10 ul 03/ml)
Pipette the required volume (8.0 ml) of the iodine working
solution (6.6.11) to the remainder of the 10% KI in the
Volumetric flcisk. ZelTO tu5 SpeCtropaOtOUietfcr witu tile
reagent removed earlier then dilute the flask to volume with
the same' blank reagent. Mix well. This solution contains
0.80 yl Oo/ml. Discard the excess blank reagent in the
cuvette.
5. Rinse the cuvette with some of the above solution. Read a
portion of the solution in the spectrophotometer to verify
that the solution contains 0.80 yl 03/ml. When the proper
reading cannot be obtained, check for error in the T£
concentration, error in the dilution process or poor quality
reagent. Correct problem(s) before proceeding with the
calibration.
-129-
-------
6. Rinse, the separately funnel with a small portion of the remaining
0.80 yl 03/ml solution and fill the separatory funnel. Introduce
the solution through the sample cell in the same manner as Step 3
above. Note the analyzer reading and adjust, when possible, the
analyzer to give a reading equivalent to the spaa concentration
(spanning). For instruments with non-linear response, proceed
to Step 8 below.
7. Prepare and introduce blank 10% KI solution and note the analyzer
reading. When the response is different from the original base-
line by > 2% of full scale, reset the analyzer to the original
baseline and repeat Step 3 above. When the zero and span controls
are not electrically independent, it may be necessary to rezero
and respan iteratively until the proper zero and span settings
are obtained.
8. Prepare, in turn, solutions equal to 10, 20, 40, and 60% of full
scale (e.g., 0.10, 0.20 yl O^/ml, etc.) and determine the analyzer
response to each concentration as described in Steps 4 and 5 above.
9. Determine the net responses by subtracting the baseline reading
froia the individual readings. Replumb the analyzer to original
operating condition.
-130-
-------
6.9.2 Treatment of Static Calibration Data
1. Plot the net analyzer readings on the vertical axis versus ul
O-j/ml of the calibrating solutions on the horizontal axis of
an appropriate graph paper (rectilinear, semi-log, log, etc.).
Calculate the slope bg of the static response curve by the
method of least squares0. To determine the linearity of the
response, see Test 4.5 in Chapter 4. A non-linear response
from an instrument normally linear indicates malfunction in the
analyzer or error in the preparation of the calibrating solutions.
Correct the problem(s) before recalibrating.
2.. When a non-linear response is normal, prepare a template as
directed in Step 2 of 6.8.3. An alternate -method is to attempt
to linearize the instrument output by adjusting the electronics
of the photometer by some combination of photocell voltage and
span upper-limit setting until a linear output is found over
the concentration range of interest.
6.9.3 Determination of Sample. Air Flqwrate
For instruments not equipped with adjustable -upper limit or span
controls or when the range of span adjust is insufficient, the slope
of the static calibration can be used to determine the sample airflow
rate that will make the analyzer output correspond to the pollutant
cSee Table 4-V in Chapter 4.
-131-
-------
concentration or a simple fraction or multiple of the concentration
as follows:
where: f = fraction or multiple of the analyzer range desired.
(e.g., 0.5, 1, 2, 3)
Qa = airflow rate, ml /rain
Q = reagent flowrate, ml/min
bs - slope of the static calibration curve obtained in 6.9.2
6.10 RECONCILING STATIC AND DYNAMIC CALIBRATIONS
1. The static calibration slope bg (6.9.2, Step 1) and dynamic cali-
bration slope bj (6.8.3, Step 1) are compared in equation 10
below.
R » -a- x 100
bs
2. Large values of R (> 10%) are indicative of a) error in the
analyzer's air or liquid flowrate, b) leaks or malfunction in
the analyzer, c) poor quality reagents and/or reactants, d)
error in the static or dynamic calibration process/or e) change
in efficiency of sample collection. Consult the analyzer
operating instructions and/or the manufacturer and correct
problem(s) before recalibrating.
-132-
-------
6.11 BASIS FOR CALCULATIONS
The relationship between the standard iodine and ozone and the
constant used in equation 6 (6.6.11) was obtained from the stoichio-
metric equation 1. One mole of ozone produces one mole of iodine
according to the reaction:
03 + 2KI + H20 -*• I2 + 2KOH + 02 (1)
One mole of ozone, however, contains two equivalents (there is a
two electron exchange in the half reaction) :
H20 + 2e~ -»• 20H~ + 02 (11)
Therefores one-half mole of ozone is equal to one equivalent ^eq.j
of iodine. Since one mole of ozone occupies, at 25°C and 760 torr,
24.46 liters, then
I eq. 03 = 12.23 liter 03 - 1 eq. I2
or
12.23 E! 03 = 1 milliequivalent (meq) I2
therefore
10 yl 03 - veq I2 (12)
12.23
_ 10 x 10"3 meq I7 (13)
~ 12.23 H 2
or in terms of solution:
-133-
-------
10 yl 03/ml = 0.8177 x 10~3 meq I2/ml (14)
The volume V,, in ml, of the dilute iodine solution Nj needed
to make 250 ml of a working solution Nw equal to 10 yl O^/ml is
then:
V -, N. = V N (15)
d d w w
V = V "
y, v -
d
(250 ml) (0.8177) (IP"3)
- . -
(Nd)
rr 0>204
then Vd= Nd
ich is the basis for the constant in equation 6.
-134-
-------
6.12 REFERENCES
1. Intersociety Committee: Tentative method for the manual
analysis of oxidizing substances in the atmosphere, no. 44101-
02-7OT. Methods of Air Sampling and Analysis. Washington,
D. C., American Public Health Association, 1972
2. Saltzman BE, Gilbert N: lodometric micr ode termination of
organic oxidants and ozone. Anal Chem 31:1914-1920, 1959
3. Hodgeson JA, Baumgardner RE, Martin BE, Rehme KA: Stoichioiuetry
in the neutral iodornetric procedure for ozone by gas-phase titra-
tion with nitric oxide. Anal Chem 43:1123-1126, July 1971
4. Kopczynski SL, Bufalini JJ: Some observations on stoichiometry
of iodometric analyses of ozone at pH 7.0. Anal Chem 43:1126-
1127, July 1971
5. Dietz RN, Pruzansky J, Smith JD: Effect of pH on the stoichiometry
of the iodometric determination of ozone. Anal Chem 45:402-404,
Feb. 1973
6. ACS Reagent Chemicals, American Chemical Society Specifications.
»
American Chemical Society, Washington, B.C. For suggestions on
-135-
-------
the testing of reagents not listed by the American Chemical
Society, see: Rosin J: Reagent Chemicals and Standards.
New York, D. Van Nostrand Co., Inc., and The United States
Pharmacopoeia.
7. G Fredrick Smith Chemical Co., Columbus, OH 43223
8. JT Baker Chemical Co., Phillipsburg, N.J. 08865
-136-
-------
1
(-•
to
I
Sampling manifold
Ozone source
Vent
Analyzers
Rotameter
Flow
controller
Particle
filter
or
Syn.
zero
air
Ambient air
Air pump
Activated
carbon
filter
Figure 6-1. Gas generating apparatus for calibrating ozone analyzers,
-------
U)
00
I
Hi-voltage
power supply
Clean air •
or oxygen
Aluminum box enclosure
Adjustable sleeve
9-in. UV lamp
Collar
-o
X
1
-«-«_- — «.-«.: 1
rfffiiajinm»nuj-.._r.T...?"ar
^ f
Quartz tube 15mm O.D.
Figure 6-II. Ozone generator.
-------
flexible tubing
Flowmeter
Trap
Needle
valve
Figure 6-III. Sampling train for referee ozone analysis.
-------
7.0 CALIBRATION PROCEDURE FOR AUTOMATED ATMOSPHERIC
NITROGEN DIOXIDE AND NITRIC OXIDE ANALYZERS
7.1 PRINCIPLE AND SCOPE
7.1.1 This procedure is for the calibration of continuous analyzers used
for monitoring atmospheric concentrations of nitrogen dioxide (N02)
and nitric oxide (NO). Analyzers for monitoring both pollutants
concurrently are common. The calibration may be of two types, dy-
namic and static. The dynamic calibration must always be done and
is performed by determining the analyzer response to a series of NO or
K02 concentrations. The dynamic calibration is applicable to all NO,
K02 or NOX, analyzers and is a performance test of the entire instrument
under simulated service conditions. The static calibration is
performed by determining the analyzer response to artificial stimuli
such as standard calibrating solutions, optical filters, screens,
electrical- signals, resistors, etc. This calibration is primarily
applicable to analyzers using wet-chemistry and colorimetry and is
a test of the detection and signal presentation components only.
It is not a substitute for the dynamic calibration.
7.1.2 Each calibrating gas for the dynamic calibration is generated by
mixing a dilute NO or N0£ gas stream or diluting with clean air a
concentrated source such as N02 from a permeation tube or from a
cylinder. Each gas is sampled simultaneously with the analyzer and
1 2
with referee methods: ' to establish the gas concentrations.
-140-
-------
7.1.3 The static- calibration is accomplished by adding known concentrations
of sodium nitrite to measured volumes of the analyzer absorbing
solution. The solutions produce colors with absorbances equivalent
to concentrations of N02- These solutions are flowed through the
analyzer's detector at the reagent flow conditions encountered
during normal operation. The analyzer readings are plotted versus
N0£ concentrations to obtain the static calibration curve. The
instrument variables, e.g., air and liquid flow rates, may be
adjusted after static calibration to make the output response
conform to the pollutant concentration or a simple multiple or
fraction of the concentration in parts per million (ppm) or micro-
*3
grams per cubic meter (yg/m ) (spanning) . When a static is not
performed, the spanning may be done during the dynamic calibration.
7.2 RANGE
The range of the calibration procedure is determined by that of the
referee method. For a 4-liter sample collected in 10 ml of absorbing
solution and measured in a 1.0 inch cuvette, the range is between
o 33
0.01 to 2ppm (10 to 3,760 yg N02/iir' and 12 to 2,450 yg NO/m ) . The
sampling rate may be reduced or the sampling period increased or
decreased to extend or reduce the range.
Continuous colorimetric analyzers for N02 and NO usually measure
these gases in the same range. The linear range for chemiluminescent
NO~N02'analyzers is about 0.005 to 15 ppm (9 to 28,000 yg N02/m3 and
•141-
-------
6 to 18,400 yg NO/m3)^. Amperometric analyzers usually measure con-
centrations from 0.005 to 1 ppm (9 to 1,880 yg N02/m3; 6 to 1,220
yg NO/m3). Sampling rates of these instruments range from 0.15 to
4 1/min.
7.3 INTERFERENCES
7.3.1 The main interference arises from traces of NO in N02 and vice
versa. Zero air and pure streams of NO or N0£ can be obtained by
the use of various combinations of chemical absorbers and con-
") S 6
verters ' * . Details for preparing these absorbers are given in
Table 5-III, Chapter 5.
«**
7.3.2 Relative humidities in excess of 90% for extended periods (> 3 hr)
inactivate the chromium trioxide oxidizer used for converting NO
to N0£ in the manual referee analysis and in some analyzers.
Operating the oxidizer 5°C above ambient temperatures (e.g., by
heating with a 7 W lamp) usually eliminates this problem.
7.4 PRECISION, ACCURACY, AND STABILITY
7.4^.1 A coefficient of variation of 1% can be achieved in the manual
referee analysis with careful work7; the limiting factors are in
the difficulty in measuring the volumes of the air samples and in
reading the absorbance of the colored reagent. Instrumental precision
-142-
-------
will usually decrease between 2 to 5% because of airflow variations.
These variations are produced by pressure changes and unstable or
pulsating flows.
7.4.2 When spanning is possible, any discrepancy between the input and
output may be resolved by adjusting the instrument output to
correspond to the value of the calibrating gas or solution. Where
analyzers have no span controls, a correction factor may be calcu-
lated to convert the analyzer readings to pollutant concentrations.
7.4.3 The absorbing solution used in the manual referee procedure or
the static calibration should be protected from direct sunlight.
Allow 15 minutes for maximum color development and measure the
absorbance within one hour after sampling to minimize any color loss.
7.4.4 A detailed discussion of the various sources of error in calibrating
gas preparation is given in Reference 1, Part I: General Precautions
and Techniques. The minimization of the sources of error is important
to assure high levels of accuracy and precision.
7.5 APPARATUS
A gas generating system (Figure 7-1) capable of providing calibrating
gases in the range of 0.01 to 2 ppm (19 to 3,760 yg N02/m3 or 12 to
2450 yg NO/m^) is needed in the dynamic calibration. The system
consists of a gas dilution apparatus, sources of zero air and NO
-143-
-------
and N02 gases and a sampling train (Figure 7-II) for referee, analysis.
The components and connecting lines used should be sized and assembled
so that the differences in the pressure between the various flow com-
ponents do not exceed 2% overall to prevent errors in flowrate measure-
ments .
7.5.1 Gas Dilution Apparatus
1- Flowmeters - Rotameters with sapphire or stainless steel balls
are used to measure the flow of zero air (0 to 5 liter/min)
and pollutant gas (0 to 1 liter/min). They should be
calibrated frequently (at least once a month)} with an
appropriate flow measuring device such as a wet test meter,
dry gas meter, soap bubble meter or calibrated rotataeter.
2. Connecting gas flow lines - Use 8 mm ID (minimum) borosilicate
glass tubing or 10 ran ID polytetrafluoroethylene (TFE) tubing
for all connections. Flexible" polyvinyl chloride (PVC) tubing
may be used to butt-join sections of inert tubings only. Ball
and socket joints (e.g., 12/5 mm) with 8 mm stems are preferred
for connections that are frequently made and broken such as the
calibrating gas lines to the dilution apparatus and the sampling
ducts to the analyzer(s).
3. Mixing chamber - A cylindrical Kjeldahl type connecting bulb of
200 to 300 ml volume works well. This can also be fabricated
-144-
-------
from bprosilicate glass as shown in Figure 7-1, with standard
12/5 ran balj. connections.
4. NO Oxidizer (CrOo) . p-m _ 1nA . -, ,-n , . c TTV n ,
____ J/ • till a 100 to 150 by 15 urn ID glass tube
with ball connecting ends (see Figure 7-1) to a length of 20
to 80 mm with Cr03 granules (Item 7.6.6). Use glass wool plugs
to hold granules in place. (Caution! Protect eyes and skin
when handling this material. Do not breathe the oxidizer dust.)
Before use, pass air containing 30 to 70% RH at 0.5 1/min
about 1 hr. to condition. Discard when more than 3/4 of the
packing bed depth turns brown.
5. J£uaf~r_, 0 to 30.0 minutes - for measuring the sampling period in
the referee method.
7.5.2 Zero Air Source
The air for diluting the calibrating gases should be free of SO and
N02 and substances that will in any way 1) change the calibrating
gas concentration, 2) interfere in the analyzer response or 3) inter-
fere in the referee procedure. The zero air -may be furnished from
a gas cylinder or by filtering ambient air as indicated in Figure 7-1.
1. Cylinder Zero Air - Cylinders should be fitted with a two-stage
pressure regulator and with fine control needle valves. A
Wv filter (Item 3a) is used when NOX contaminants are present.
-145-
-------
The humidifier (Item 3b) should be used with a pressure relief
ty
valve set between 2 to 5 psig (1.4 to 3.4 newton/cmz) to prevent*
expolsion of glass vessel in case of flow stoppage.
2. -Air Pump (for transport of ambient air) - An oil-less (carbon
vane or diaphragm) air pump capable of delivering between 5
to 10 liters/iain is used. The pump is fitted with a vibration
pad, a fine control needle valve, and a bleed-off valve. A
particle filter should be installed downstream of carbon vane
pumps and is optional with diaghragm types.
3. Air Filter
(a) NOX filter - This is used to remove any NO and NO? from
the air used for zero air. Fill a 30 mm OD by 300 mm long
glass tube to one-half its volume with CrOg oxidizer (Item
7.6.6) and the rest with soda lime (Item 7.6.5). Place the
soda lime on the downstream side of the CrOo. Use glass wool
plugs in both ends to retain the granules. The orange Cr03
granules turns brown with use. Discard when more than 3/4 of
the packing length is brown.
(b) Humidifier - This is used to humidify the zero air for the props
operation of the Cr03 oxidizer (7.5.1, Item 4 and Item 3a) and
consists of a 250 ml flask with the inlet tube extending to 2 a
above water level as shown in Figure 7-1 to give a relative
-146-
-------
humidity of 70 to 80%. Install upstream of the NOX filter
(Item 3a) and the air pump (Item 2) and downstream of the
charcoal filter (Item 3c).
(c) Charcoal Filter - See Item 2 in 5.2.2 and Table 5-III for
requirements and preparation.
7.5.3 N02 Permeation Apparatus
Proper operation of permeation devices or tubes (Item 7.6.2) requires
a constant temperature bath maintained within 0.1°C at 20 to 30°C
and equipped with a temperature conditioning coil and permeation
Q
tube holder. The gas permeation systems described for S02° are
»>1 ocv QTIT>I-i ^oKI o fr\r WO,-, cro-no-ra t--i rvn-' C.otrme>f oT a 1 evc:t-ATn<2 J5TP avfl T.1'-iM P
Vb-l-u —f «.£-£.'_«- ^«.l— -I- — ~ -_ ~. V ^ c>>^*«*^*_. , ..- . — — ~ ~~ — j ^ ~- - - . — - —
7.5.4 Ozone Generator (when calibrating chemiluminescent analyzers)
An ozone generator is used in the zero air line to furnish ozone for
converting NO to NC^- This provides a mixture of NO and N02 which
is used to test the efficiency of the N02-to-NO converter in chemi-
luminescent analyzers10. See 7.8.5 for details. Ozone generators
for conversion of NO to N02 are commercially available. One can
also be fabricated by using a low pressure mercury lamp (Ultra-
violet Products, Inc., San Gabriel, Cal., or equivalent) and a
lamp power supply. See 6.5.1 in Chapter 6 for details.
-147-
-------
7.5.5 NO2 Absorber (TEA) - Fill a 20 mm ID by 100 to 150 mm long polyethylene
.inm,,.—,*-V -----— -i ,, m-^, i_ _, INI ^
tube with tubing fittings at both ends with TEA granules (Item 7.6.4),
Hold the granules in place with glass wool plugs. Install the absorber
in the line between the NO source tank and the dilution apparatus.
7.5.6 Spectrophotoaeter or colorimeter - With 2.54 cm (1 inch) cuvettes
for measuring the absorbance at 550 nm.
7.5.7 Manual Samp1ing Train:
Assemble the sampling train as shown in Figure 7-II. "Use ground-
glass joints upstream from the bubbler. Other connections may be
butt-joined with polyvinylchloride tubing.
1. Absorber - All-glass bubbler with a maximum frit pore diameter of
60y as shewn in Figure 7-II or in References 1 and 2 are needed
to collect the samples for referee analysis. Bubblers may be
purchased from suppliers of air pollution equipment and many
glassware suppliers. Ball-joint connections are recommended for
convenience.
2. Air-vacuum Pump - Capable of drawing 0.40 liter/uiin through the
bubbler. The pump should be equipped with a needle valve and
trap at the inlet side to regulate flow.
3. Flowmeter - Calibrated to measure gas flows of 0.5 to 2 liters/
min within ± 2%. See Item 1 in 7.5.1 for calibration requirements.
-------
^* ;*•£§£ ~ A vessel containing glass wool to protect needle valve from
moisture.
7.5.8 Miscellaneous; Other equipment needed to perform the manual reference
sampling operation described in Reference 1 and 2,
7.5.9 CalibratingSolution Dispenser(for static calibration); A solution
dispenser, consisting of one or two lengths (about 50 cm) of small
diameter (about 1.5 mm I.D.) clear polyvinylchloride (F?C) tubing,
a plastic anti-syphon device and a 125 ml low-actinic separatory
funnel as shown in Figure 7-III, is used to deliver the calibrating
solutions under controlled flow conditions by means of furnished
screw clamp(s) on the tubing(s). This (hypodermoclysis) set,
which is intended for administering fluids under the skin, is
inexpensive and can be purchased from medical supply houses.
A similar device can be fabricated from small diameter plastic
tubing, Y connector and screw clamps.
7.6 REAGENTS AND GASES
Purity of Chemicals - Unless otherwise indicated, all reagents
specifications shall conform to the Committee on Analytical Reagents
of the American Chemical Society11. When such reagents are not
available, ascertain that they do not lessen the accuracy of the
determination.
-149-
-------
7.6.1 Cylinder NO; A cylinder of compressed N2 gas containing about 100
ppm NO (122 mg NO/m3), <10 ppm H20 and <3 ppm 02: This mixture is
quite stable when care is taken to exclude air during preparation.
It may be purchased or can be prepared in the laboratory using a
1 O
closed-systems vacuum-pressure manifold . Further dilution of the
gas brings the concentration within the normal range of NO^ analyzers.
Permeation tubes containing NO are not available because of its
low boiling point (-152°C).
7.6.2 NO2.Permeation Devices; Permeation devices containing N0£ may be
purchased13' . Their use usually requires the use of a temperature
controlled bath. While S02 permeation devices can be used as a primary
standard because of their reliable emission rates, HO^ permeation
devices have not yet achieved the same level of reliability. The
exact concentrations produced, therefore, must be established during
calibration by a referee method . Exposure of the tube to water
vapor and wide variations in temperature during operation or storage
may produce marked changes in permeation rates. N02 devices rmay
also be used for calibrating NO analyzers when a N02~to-N0 converter
is used.
7'6'3 °ther Sources of NO and N02; Lower concentrations of NO and N02 in
steel cylinders (about l/10th of those listed in 7.6.1) may be used
but since these substances are unstable at these low levels, the
-150-
-------
concentrations resulting from such -mixtures must be determined by
referee analysis just prior to and/or during calibration.
7.6.4 Triethanolamine (TEA.) ; Soak 1.5 mm (1/16") diameter or 10 to 14 mesh
granules of porous, inert material such as firebrick, alumina, or
xeolites, in 20% aqueous TEA6. Drain, spread on a dish, and dry
for 30 to 60 min at 90 to 95°C. The granules should be free flowing.
7.6.5 Soda Lime - Granules, 4-8 mesh.
7.6.6 Chromium Trioxide (CrOa) CbdLdizer2'6 - Soak 15 to 40 mesh porous
firebrick or alumina in a 16% w/w aqueous CrO^ solution. Drain,
spread on a dish and dry in an oven for 30 to 60 min at 105 to 115°C,
then place the dish in a desiccator containing a saturated salt
solution which maintains the relative humidity between 50 to 70%.
The reddish color changes to a golden orange when properly equili-
brated. CautionI Protect eyes and skin when handling this material.
Do not breathe the oxidizer dust.
7.6.7 NaN02 Stock Solution. Dissolve 2.03 g NaNO£ (a correction is applied
if purity is less than 100%) in distilled water and dilute to 1000 ml
in a volumetric flask. This solution contains the equivalent of
1000 yl N02/ml. The weight of the nitrite is calculated based upon
the empirical observation that 0.72 mole of sodium nitrite produces
the same color as 1 mole of nitrogen dioxide >J--).
-151-
-------
7.6.8 NaN02 Working Solution (10 yl N02/ml) . Dilute 5.00 ml of the stock
NaN02 solution (Item 7.6.7) to 500 ml with distilled water (nitrite
free) in a low-actinic volumetric flask. This working standard is
equal to 10 yl of N02/ml,
7.6.9 A^Si^i^H^l—lSESHLL^,5 Reagents needed to perform the manual referee
analysis are described in Reference 1.
7.7 SPECTROPHOTOMETER CALIBRATION
1. Prepare a series of calibrating solutions equivalent to between
0.04 to 0.20 yl N02/ml by diluting 1,2,3 ml etc of NaN02 working
standard (Item 7.6.8) in 250 ml of the azo-dye absorbing reagent as
directed in Reference 1 and in 7.9, Static Calibration. Allow
15 minutes for full color development and then read the solutions
in the spectrophototueter at 550 nm. Plot the absorbances on the
vertical axis versus yl N02/ml on the horizontal axis of a recti-
linear graph paper as a check for linearity. Calculate the slope
b of best-fit curve for the data using the method of least squares3.
2. When a static calibration is to be performed on the analyzer and
the formulation of the analyzer absorbing solution is different
from that of the referee procedure, obtain a spectrophotometer
calibration factor by diluting aliquots of the NaN02 working
solution with the analyzer reagent as described in Step 1 above.
aSee Chapter 4, Table 4-V.
-152-
-------
7.8 DYNAMIC CALIBRATION
7.8.1 General
1. When a static calibration (7.9) is to be performed on the analyzer,
it should be done before the dynamic (7.8) to assure proper operation
of its detection and signal presentation components. The static and
dynamic responses may be compared (reconciled) to verify the proper
operation of the analyzer. See 7.10 for details.
2. When the analyzer has been operating as continuous monitor, it
is useful to determine the response near the span level first
without changing the span settings (auditing). When the response
is within 10% of the. previous calibration; the calibration is
still valid and a new calibration is not necessary. When the
response is greater than 10%, proceed with the complete cali-
bration. The audit data provide a record of the calibration
drift. Instruments with non-linear response require the full
calibration.
3. Chemiluminescent NOV analyzers with single detectors that measure
JV
N02 by difference (N02 = NOX - NO) are usually equipped with
converters for reducing the N02 to NO. Such instruments must
first be calibrated with NO because the analyzers response to
N02 depend on the efficiency of the converters. See 7.8.5
for details.
-153-
-------
4. The analyzer to be calibrated should be in good operating condition
and installed in accordance with the manufacturer's instructions.
Operate the analyzer for at least 24 hours to warm-up. This 24-hr
warm-up period may be shortened when so stated in the operating
instructions. Adjust the air and reagent flowrates to their
recommended rates or to the rates determined from the static
calibration (7.9) data and verify the rates as described in 7.5.1,
Item 1.
5. Record all data only after stable analyzer response has been
attained. Refer to 4.1.6 in Chapter 4 for determining stable
response.
6. Assemble the gas generating system for generating NO or-N02
as needed. Place the system as close as practical to the
analyzer to prevent losses and to minimize pressure changes
in the analyzer sampling ducts. Calculate the airflow of
the analyzer(s) and add the airflow (400 ml/min) needed for
the referee analysis. Add about 10% of the total to insure
an excess. (NOTE: The excess calibrating gas should be vented
or absorbed by a non-restricting filter to prevent exposure to
personnel.) In a proper assembly connection or disconnection of
the analyzer sampling line should not alter the airflow settings.
-154-
-------
7.8.2 Analyzer Zero
1. Generate a flow of zero air equal to the rate determined in
7.8.1, Step 6 above and sample with the analyzer. When a
stable analyzer reading is obtained, pipet 10 ml of the
azo-dye absorbing reagent in the bubbler (7.5.7, Item I)1.
Assemble the bubbler and connect to the sampling train as shown
in Figure 7-II.
Sample the gas stream according to the manual referee method
for 10 minutes at 400 ml/min. Wait for 15 minutes for color
development and then transfer the solution to a clean 1.0 inch
(2.54 cm) cuvette. Measure the absorbance of the solution at
550 nm on the spectrophotonieter against unexposed absorbing
reagent as blank.
2. When the absorbance of the solution is greater than the blank,
continue flushing the generation system until the absorbance
obtained is the same as the blank. Inability to obtain a
reading equal to the blank indicates interferents in the zero
air. Correct the problem before proceeding.
3. Zero the analyzer by adjusting the analyzer controls so that the
output corresponds to zero or the desired baseline value.
-155-
-------
7.8.3 Generation of N02
1. Connect the source of the NC>2 (NC>2 permeation apparatus 7.5,3 or
the NO cylinder 7.6.1 and ozone generator 7.5.4) as shown in the
gas generation system (Figure 7-1). It -may be necessary before
hookup to bleed the cylinder outside the generation system at a
low flow (30 to 50 ml/min) for one to two hours to condition the
delivery tubing. (NOTE: Bleed the N0£ into a filter to avoid
exposure to personnel).
2. Generate a N02 concentration equal to 80 ± 5% (span gas) of full
scale. When a steady analyzer reading is obtained, collect two
samples of the gas stream and analyze as described in Step 1 of
7.8.2. Adjust the sampling period to keep the absorbance of the
samples at about midscale (0.3 to 0.5 A) on the spectrophotometer.
Five to ten minutes are usually sufficient.
3. From the volume of air sample and the slope of the spectrophotometer
calibration curve, calculate the ppm N0£ as follows:
(A) (10) (1)
ppm = (b) (vj
Where: ppm = concentration (u/D N02 or NO in air
A - absorbance of the solution
b = slope of the spectrophotometer calibration curve
obtained in 7.7.
-156-
-------
Va = volume, In liters, of the gas sample collected (liters/
min X rain) .
<5
To convert ppm to pg/m , use equation 2 for NO and equation 3 for
Ug NO /in3 = ppm NO X 1230 (2)
pg N02/m3 = ppm N02 X 1880 (3)
Usually, the change in the gas volumes of the samples due to deviation
from the standard conditions of 25°C and 760 torr is small and may be
neglected. ,- When the deviations are large (sufficient to cause a
change > 5% in gas volume) , correction should be made.
4. The concentration of duplicate samples should be within 5%.
Differences greater than 5% may be due to unstable gas concentration
or error in sample collection and analysis. Correct these problems
before proceeding with the calibration.
5. Determine the net analyzer reading by subtracting the baseline
reading from the span reading.
6. When possible, adjust the analyzer to give a reading equivalent
to the span N02 concentration obtained in Step 3 above (spanning) .
When the instrument has no span controls, proceed to Step 7 below =
Generate zero air and note the analyzer reading. When the reading
is different from the original baseline reading by > 2%, reset the
-157-
-------
analyzer to the original baseline and repeat Steps 2 through 6
above. NOTE: When the span and zero controls are not electrically
independent, it may be necessary to rezero and respan iteratively
until the proper zero and span settings are obtained.
7. Generate^ in turn, four additional concentrations (10, 20, 30,
40 and 60% of full scale are suggested). Determine the N02
concentrations in duplicate as described in Steps 2 through 4
above. Record the net analyzer responses by subtracting the
baseline reading from the individual readings.
7.8.4 Generation of NO
1, Install the TEA NO^ absorber (Item 7,5.5) at the outlet of the
NO (Item 7.6.1) cylinder to remove any traces of N02« Install
the NO (Cr03) oxidizer (Item 4 in 7.5.1) in the manual sampling
train as shown in Figure 7-II. 'This oxidizes NO to N0£ for
referee analysis. The humidity of the gas stream is controlled
by the humidifier in the zero air line as shown in Figure 7-1.
Connect the cylinder of NO as shown in Fig. 7-1. The rest of
.the calibration follows the same procedure as described for N02
in 7.8.3 above.
2. Determine the NO concentration by equation 1 in Step 3 of 7.8.3.
This procedure is valid because the conversion of NO to N02 is
100% when the CrO-j is used as specified .
-158-
-------
7.8.5 Determination of Converte^j^ffj-ciency (for chemiluminescent analyzers)
1. To determine the converter efficiency of cherailuminescent NCL
and NO analyzers, generate an NO concentration equal to 80 ± 5%
ji
of full scale. Verify the concentration and record the analyzer
readings YNQ and Y in both the NO and NO modes.
2C
2. Oxidize a portion of the NO to NO,, by turning the ozone generator
(Fig 7-1) on and adjust the ozone output so that the NO reading
Y is reduced to about one-half. Record the new NO and NO
'NQ
readings Y'NQ and Y'NO .
1
The decrease in the NO reading (YNQ - Y NQ) is equal to the
input N02 concentration. The analyzer output as N02 is equal
to the difference between the new NO^ and NO readings or
' - Y*
NO,, ' NO'
3. Calculate the conversion efficiency fc by equation 5.
_
f -
Y* - Y'
N0x
. - .
YNO ~ Y. NO
'A ratio f of the output N02 to the input N02 of less than 1.0
indicates the conversion is less than 100% and the converter
should either be corrected or preferably replaced.
-159-
-------
7.8.6 Treatment of DynamicCalibrationData
1. Plot the net analyzer readings for each channel on the vertical
axis versus the ppm NC>2 (7.8.3) or ppm NO (7.8.4) obtained by
manual sampling on the horizontal axis of an appropriate graph
paper (rectilinear, semilog, log, etc.). Calculate the slope
b,j of best-fit curve for the data using the method of least
squares^. To determine the linearity of the response, see Test
4.5 in Chapter 4. A non-linear response from an instrument
normally linear indicates malfunction in the analyzer or error
in the calibration process. Correct problem(s) before
recalibrating.
2. When a non-linear response is normal, draw a smooth line through
the calibration points that fits the data best. From this,
prepare a template to convert the net analyzer readings to
cone en trat ion uni t s.
7.9 STATIC CALIBRATION
The following section pertains to colorimetric analyzers using azo-dye
forming reagents for monitoring NO, N02 or NO^, See also 7.1.3.
7.9.1 Procedure
1. The reagent used in the following procedure should be formulated
in accordance with the manufacturer's recommendations.
bSee Chapter 4, Table 4-V.
-160-
-------
2. Turn the analyzer air and liquid pumps off. Disconnect the
reagent line at the exit port of the photometer reference
cell and recycle the solution to the reagent reservoir. Dis-
connect the spent reagent line at the used-reagent reservoir,
or at the inlet to the reagent recovery carbon column, when so
equipped, and lead it to a waste bucket. Disconnect the
reagent line at the sample cell inlet and connect the delivery
end of a calibrating solution dispenser (Item 7.5.9). Support
the separatory funnel near the instrument on a ring stand.
Turn the analyzer reagent pump on. The reagent now flows only
through the, reference cell. Siphon absorbing solution from
the analyzer reagent reservoir into six 250 ml low-actinic
volumetric flasks and fill almost to the mark.
3. Mark one of the flasks as blank. Pour about 15 ml of the
reagent from the blank into the separatory funnel. Squeeze
out any air bubbles trapped between the funnel and the screw
clamps. Open the screw clamp(s) and flush the connecting
line and cell. Repeat with a second 15 ml portion. Fill
the separatory funnel with the blank reagent and adjust the
discharge rate into the cell at about the same flow rate at which
the analyzer is to operate (1 ml/min equals about 20 drops/
minute). For dual channel analyzer that monitor both pollutants
(NO and NO ) concurrently, Steps 3 through 8 can be performed
simultaneously using the same calibrating solution for both
channels.
-161-
-------
4. While waiting for the instrument reading to stabilize, determine,
by equation 6 s the volumes of working NaN02 solution (Item 7.6.8)
required (in 250 ml) to produce a series of calibrating standards
equal to 10, 20, 40, 60 and 80% of full scale.
(C) C6)
where: C = concentration (in yl N02/ml) desired
Cy = concentration of working solution (10 ul N02/ml)
Vc = volume of calibrating solution (250 ml)
Pipet the required volumes, e.g., 1.0, 2.0, into the five
remaining 250 ml volumetric flasks containing the absorbing
reagent- Dilute .to the mark with the reagent and mix well.
Let stand for 15 min for full color development .
Read the color of a portion of each standard solution with
the previously calibrated spectrophotometer (Item 7.7) to verify
that each standard contains the equivalent yl N02/ml calcu-
lated in Step 4. When the proper readings cannot be obtained,
check for error (s) in the NaN02 concentration, error in the
dilution process or poor quality reagent(s) . Correct problem(s)
before proceeding with the calibration.
5. After the analyzer response has stabilized on the blank reagent,
adjust the analyzer controls to obtain the desired baseline
reading.
-162-
-------
6. Introduce the standard equal tc 80% of full scale as directed in
Step 3 above. When a steady reading is obtained, adjust, when
possible, the analyzer reading to correspond to the concentration,
of standard. For instruments with no span controls, proceed to
Step 8 below.
7. Introduce blank reagent and note the analyzer reading. When the
reading is different from the original baseline by > 2%, reset
the analyzer to the original baseline and repeat Steps 3 and 5.
When the span and zero controls are not electrically independent,
it may be necessary to rezero and respan iteratively until the
proper zero and span settings are obtained.
8. Introduce the remaining calibrating standards in turn and record
the corresponding analyzer readings as described in Step 5.
Determine the net readings by subtracting the baseline reading
from, the individual readings.
7.9.2 Treatment of Static Calibration Data
1. Plot the net analyzer readings on the vertical axis versus ul
N02/ml of the calibrating solutions on the horizontal axis of
an appropriate graph paper (rectilinear, semi-log, log, etc).
Determine the slope bs of the static response curve by the
method of least squaresc. To determine the linearity of the
response, refer to Test 4.5 in Chapter 4. A non-linear response
from an instrument normally linear indicates malfunction in
the analyzer or some error in the preparation of the cali-
cSee Chapter 4, Table 4-V.
-163-
-------
brating solutions. Correct the problem(s) before proceeding
with the calibration.
2. When a non-linear response Is normal, prepare a template as
directed in 7,8.6, Step 2. An alternate method is to attempt
to linearize the instrument output by adjusting the electronics
of the photometer by some combination of photocell voltage and
span upperlimit setting until a linear output is found over the
concentration range of interest.
7.9.3 Determination of Airflow Rate
1. For instruments not equipped with adjustable upper limit or
span controls or when the range of span adjust is insufficient,
the slope of the static calibration curve can be used to establish
the sample airflow rate that will make the analyzer output
correspond to the pollutant concentration or a simple fraction
or multiple fg of the concentration range as follows:
(fs>
Qa " (Qr> TTT (7)
(OQ)
where: Q = airflow rate, ml/rain
ct
Qr = reagent flow rate, ml/min
f = fraction or multiple of the analyzer range desired
s
b - slope of the static calibration curve obtained in 7.9.2
-164-
-------
The NO channel is handled in like manner. Equation 7 is also
useful if the analyzer read-out is in yg/nr^ since the static
calibration curve is then units of absorbance versus yg N02/ml.
7.10 RECONCILING THE STATIC AND DYNAMIC CALIBRATIONS
The static calibration slope bg (7.9.2, Step 1) and the dynamic
calibration slope b^ (7.8.6, Step 1) are compared by equation 8:
lbg - brr|
R » b X 100 (8)
S
Large values of R (£ 10%) are indicative of a) error in the analyzer's
air or reagent flowrate, b) leaks or malfunction in the analyzer,
. e) poor quality reagents, d) error in the static or dynamic calibration
process or e) change in efficiency of collection. Consult the
analyzer operating instructions and/or manufacturer and correct
the problem(s) before recalibrating.
-165-
-------
7.11 REFERENCES
1, Intersociety Committee: Tentative method of analysis for
nitrogen dioxide content of the atmosphere (Griess-Saltzman
reaction). Hlth Lab Sci 6:106, 1969. Reprinted in Methods
of Air Sampling and Analysis. Intersociety Conimitteej p 329-336.
American Public Health Association 1015 Eighteenth Streets N.W.,
Washington, B.C., 1972.
2. Intersociety Committee: Tentative method of analysis for nitric
oxide content of the atmosphere. Hlth Lab Sci 9:71, 1972.
Reprinted in Methods of Air Sampling and Analysis. Intersociety
Committee, p. 325-328. American Public Health Association, 1015
Eighteenth Street, N.W., Washington, B.C., 1972.
3. ASTM: Continuous measurement of nitric oxide, nitrogen dioxide,
and ozone in the atmosphere. Method D 2012-69. Annual Standards.
Part 23, 620-27, November,,1970.
4. Hodgeson JA, Rehme KA, Martin BE, Stevens RK: Measurements for
atmospheric oxide of nitrogen and ammonia by chemiluminescence.
Presented at Air Pollution Control Association Meeting, Miami, FL,
June, 1972.
5. Intersociety Committee: Tentative method for calibration of
continuous colorimetrie analyzers for atmospheric nitrogen dioxiue
and nitric oxide. Hlth Lab Sci 9:4, October, 1972.
-166-
-------
6. Levaggi DA, SIu W, Feldstein M5 Kothny EL: Quantitative
separation of nitric oxide from nitrogen dioxide at atmospheric
concentration ranges. Env Sci Tech 6:250, 1972.
7. Thomas, MA., Amtower RE: Gas dilution apparatus for preparing
reproducible dynamic gas mixtures in any desired concentration
and complexity. J Air Pollut Contr Assn 16-618, 1966.
8. Intersociety Committee: Tentative method of analysis for sulfur
dioxide content of the atmosphere. Hlth Lab Sci 7:4, 1970.
Reprinted in Methods of Air Sampling and Analysis, Intersociety
Committee, p 447-455. American Public Health Assoc., 1015
Eighteenth St., N.W., Washington, B.C., 1972.
9. Saltzman BE, Burg WR, Ranaswamy G: Performance of permeation
tubes as. standard gas sources. Env Sci Tech 5:1121, 1971.
10. Wright B, Jeung E: Simplified calibration procedure for
chemiluminescent NO-NC) analyzers. Presented at the 13th
X
Conference on Methods in Air Pollution and Industrial Hygiene
Studies, California State Department of Health, Berkeley,
California, October 30-31, 1972.
11. ACS Reagent Chemicals, American Chemical Society Specifications.
American Chemical Society, Washington, D.C. For suggestions on
-167-
-------
the testing of reagents not listed by the American Chemical
Society, see: Rosin J: Reagent Chemicals and Standards.
New York, D. Van Nostrand Co., Inc., and The United States
Pharmacopoeia.
12. Belsky T: Preparation of low concentration mixtures of gases,
Air and Industrial Hygiene Laboratory, California State Depart-
ment of Health, Report No. 117, Berkeley, California, January
1972.
13. Metronics Associates, Inc., Palo Alto, CA 94304.
14. Analytical Instrument Development, Inc., 250 South Franklin Street,
Westchester, PA 19380.
15. Scaringelli FP, Rosenberg E, Rehine KA: Comparison of permeation
devices and nitrite ion as standards for the colorimetric determinat
of nitrogen dioxide. Env Sci Tech 4-924, 1970.
-168-
-------
Gas mixing
chambe r
(for NOo stream)
JJ-
CrO~ (for NO stream)
Sampling manifold
M M M
Analyzers
Zero air
eferee
sampling
!train
Air pump
Dilute NO
Humidifier
Dilute N02 (from N02 permeation apparatus)
Ambient
air
Figure 7-1. Gas generating system i'or calibrating NO and N02 analyzers.
-------
Cr03 (for NO stream)
o
i
Absorber
(fritted)
Flexible tubing
To
.air
pump
Needle valve
From gas manifold
-------
Screw Clamp
Connect to Analyzer
Solution Cell Inlet'
Separatory Funnel
125 ml Cap
Hypodermoclysis Set
Connect to Analyzer
Solution Cell Inlet
Flexible
Tubing
Figure 7-III. Calibrating solution dispenser.
-------
8.0 CALIBRATION PROCEDURE FOR AUTOMATED ATMOSPHERIC SULFUR
DIOXIDE ANALYZERS
8.1 PRINCIPLE AND SCOPE
8.1.1 This procedure is for the calibration of continuous atmospheric
sulfur dioxide analyzers. The calibration may be of two types,
dynamic and static. The dynamic calibration must always be done
and is performed by determining the analyzer response to a series
of sulfur dioxide (SO,.,) concentrations. The dynamic calibration is
a performance test of the entire analyzer under simulated service
conditions and is applicable to all S02 analyzers. The static
calibration is performed by determining the analyzer response
to artificial stimuli such as standard calibrating solutions,
optical filters, screens, electrical signals, resistors, etc. This
calibration is a test of the detection and signal presentation com-
ponents only and is primarily applicable to S02 analyzers using wet-
chemistry such as colorimetry and conductimetry. It is not a substitute
for the dynamic calibration.
8.1.2 The calibrating gas for the dynamic calibration may be generated in
two ways. The preferred method is by mixing a stream of S02 from
1 *) *\
an S02 permeation apparatus ''J (Figure 8-1) with clean air.
*3
Alternatively, streams of dilute S02 (50 to 100 ppm; 131 to 262 yg/m )
from a cylinder may be mixed with clean air.
-172-
-------
The calibrating gas is sampled simultaneously with the analyzer and -
with the referee method^ to establish the concentration of the gas.
A permeation tube with a known emission rate can be used as a primary
'standard (see 8.6.1) source of SC>2 gas.
8.1.3 The static calibration is performed by adding known concentrations
of a standard reagent to measured volumes of the analyzer absorbing
solution which provide an effect equivalent to concentrations of S02-
These solutions are flowed through the analyzer detector at the actual
reagent flow conditions encountered during normal operation. The
analyzer readings are plotted versus equivalent S02 concentrations
to obtain a static calibration curve. The instrument variables, e.g.,
air and liquid flow rates, may be adjusted to make the output response
conform to the pollutant concentration or to a simple multiple or
fraction of the concentration in parts per million (ppm) or micrograms
per cubic meter (ug S02/m^) (spanning). When a static calibration is
not performed, the spanning may be done during dynamic calibration.
8.2 RANGE
The range of the calibration procedure is determined by that of the
referee method^. For a 10-liter sample collected in 10 ml of absorbing
solution and measured in a 1.0 inch cuvette, the range is between
0.01 to 10 ppm S02 (0.026 to 26 yg S02/m3).
-373-
-------
The measurement range and the sampling rates of continuous SC^
analyzers vary greatly depending on the detection methods. The
upper limit of the measuring range can vary from 0.2 to 10 ppm
(0.52 to 26 yg/m3) . Sampling rates may vary between 0.015 to 5 1/min,
A descriptive compilation of most of the currently available S02
analyzers is given in Reference 5.
8.3 INTERFERENCES
8.3.1 Interferences are a function of the detection principle as shown in
Table 5-IV, Chapter 5. S02 with purity greater than 99.9% is readily
available. Higher purities are obtainable when required. Zero air
for dilution must be free of SC>2 and other substances that can
potentially interfere in the analyzer detection principle. Selective
absorbers (drying agents, Ascarite for C02> etc.) can be used when-
ever a particular measurement principle requires it. Details for
preparing such absorbers are given in Table 5-III, Chapter 5.
-8.4 PRECISION, ACCURACY, AND STABILITY
8.4.1 With careful work the coefficient of variation at the 95% confidence
level of the pararosaniline referee method is 4.6%^. Careful attention
to the details of the method is critical.
8.4.2 When spanning is possible, any discrepancy between the input and output
may be resolved by adjusting the instrument output to correspond to the
-174-
-------
calibrating gas concentration. Where analyzers have no spanning
controls, a correction factor may be calculated to convert the
analyzer readings to S0£ concentrations.
8.4.3 A detailed discussion of the various sources of error in the prepar-
ation of calibrating gases is given in Reference 7, Part I: General
Precautions and Techniques. The appreciation and minimization of
the sources of errors is important to assure high levels of accuracy
and precision.
8.5 APPARATUS
A gas generation system consisting of sources of S02 and zero air,
.flcvseters, gas mixing chamber, sampling manifold and a sampling train
for referee analysis is needed in the dynamic calibration (Figure
8-1). The system should be capable of providing calibrating gases
between 0.002 to 1.0 ppm (0.005 to 2.6 yg S02/m3). The S02 may be
furnished from an S02 permeation apparatus or from a cylinder of
dilute S0'2 gas.
The components and connecting lines making up the system should be
sized and assembled so that the differences in the gas pressure
between the various components do not exceed 2% overall to prevent
errors in flowrate measurements. Ball and socket joints are con-
venient for. connections that are frequently made and broken.
-175-
-------
8.5.1 S02 Permeation Apparatus; See Figure 8-1. This can also be purchased,
I- Flowmeters ; To measure the flows of zero air (0 to 1 liter/inln)
over the permeation tube. They should be calibrated frequently
(monthly) with wet or dry test meters, soap bubble meter or
calibrated rotameter.
2. Temperature-contro lied Bath ; Maintained at 20 to 30 ± 0.1°C.
It is needed for proper operation of permeation tube 8.6.1.
The baths described for S(>2 ' are acceptable.
3. Need! e valves : for controlling the rate of gas flows. Stainless
steel type is recommended for S02«
4. Thermometer : A laboratory type or other temperature-^raeasuring
device is needed to measure with a precision of 0.1°C or better
the temperature of the constant-temperature bath and the zero
air (carrier gas) flowing over the permeation tube.
8.5.2 Gas Dilution Apparatus (when cylinder S(>2 is used)
•"•• Flowmeters ; To measure the rate of S02 and zero air flow.
Calibrate frequently (at least monthly) as indicated in 8.5.1,
Item 1.
2. Needle Valves : to control gas flow rates. Stainless steel types
are recommended for S(>2.
-176-
-------
3. Mixing Chamber: A cylindrical Kjeldahl type connecting bulb of
200 to 300 ml volume works well. This can also be fabricated
from borosilicate glass as shown in Figure 8-1.
4- Sampling Manifold; Fabricate from borosilicate glass (see Figure
8-1)N. It should contain three or four ports to permit simultaneous
sampling of the calibrating gas stream with the analyzer(s) and
the referee method.
8.5.3 ZeroAir Source
The zero air for diluting the calibrating gas should be free of
S02 and substances that will in any way 1) change the calibrating
gas concentrations, 2) interfere in the analyzer response and 3)
interfere in the referee method. The zero air may be furnished from
a cylinder or by filtering ambient air as indicated in Figure 8-1.
1. Air pump (for transport, of ambient air) - A diaphragm or
carbon vane pump capable of delivering flow rate reqxiireinents
of the total generation system (5 to 10 liters/min) is needed.
A particle filter should be installed on the downstream side of
carbon vane pumps and is optional for diaphragm pumps.
2. Filters for Ambient Air; See 8.6.4
8.5.4 Manual Sampling Train and Apparatus for Referee Analysis: See Reference 4
and Figure 8-II.
-177-
-------
8.5.5 Analytical balance; A laboratory type with a sensitivity of 10 yg
or better is needed for weighing the permeation tube.
8.5.6 Calibrating Solution Dispenser (for static calibration): See 7.5.9
and Figure 7-III in Chapter 7.
8.5.7 Apparatus for static calibration; refer to the manufacturer's in-
structions for a list of the required apparatus.
8.5.8 Absorber (Impingers) ; See Item 1 in 6.5.4 and Figure 6-III in Chapter 6
8.6 REAGENTS AND GASES
Purity of chemicals - Unless otherwise specified, all reagent
specifications shall conform to the committee on Analytical Reagents
o
of the American Chemical Society . When such reagents are not
available, ascertain that they do not lessen the accuracy of the
determination.
8.6.1 S02 Permeation Tubes• Permeation tubes containing S02 are commercially
available in a variety of sizes and permeation (emission) rates^> .
The rates may be either nominal or certified. Certification can be
done by the supplier at additional cost or by the user in his own
laboratory. To assure maximum reliability, these tubes should be
weighed regularly (e.g., at least once a month) and just before use.
Certified tubes can also be obtained from the National Bureau of
Standards.
-178-
-------
8,6.2 Cylinder S02 (50-100 ppm; 131-262 yg/m3): This gas mixture is
further diluted to produce the desired concentrations for calibration.
The concentration produced should never be considered as primary
standard and must always be standardized by the referee method or
compared to the analyzer response obtained with a certified S02
permeation device.
8.6.3 Zero Air: A high-pressure cylinder of synthetic zero air, or
filtered ambient air from an air pump may be used.
8.6.4 Zero Air Filter; Activated charcoal and soda lime used together will
remove residual SO? arid most interferents from the zero gas stream.
Excessive amounts of nitric oxide in ambient air can be removed by
placing a Cr03 oxidizer (Item 4 in 7.5.1) before the soda lime.
Refer to Chapter 7 (calibration method for NO2 and NO) and Table 5-III
for details.
8.6.5 Reagents for Referee Method for 502= see References 4 and 7.
8.6.6 Reagents for Static Calibration; refer to the manufacturer's operating
instructions for a list of required reagents.
8.7 SPECTROPHOTOMETER CALIBRATION
1. Prepare a series of calibrating solutions containing the equivalent
of 0.05 to 0.4 yl S02/ml (i.e., 1,2,3 ml) as directed in the manual
-179-
-------
referee method^. Treat the solutions (Ref 4) and wait 30
minutes for full color development. Determine the absorbance
of the solutions on the spectrophotometer against reagent blank.
2. Plot the net absorbances on the vertical axis versus yl S02/ml
on the horizontal axis of a rectilinear graph paper as a check
for linearity. Calculate the slope b of best-fit curve for the
data using the method of least squares3.
8,8 DYNAMIC CALIBRATION
8.8.1 General
1. When a static calibration (8.9) is to be performed on the
analyzer, it should be done before the dynamic to assure proper
operation of its detection.and signal presentation components.
The static and dynamic responses may be compared (reconciled)
to verify the proper operation of the analyzer and the validity
of the calibration. See 8.10 for details.
2. When the analyzer has been operating as a continuous monitor, it
is useful to determine its response near the span level first
without changing the span settings (auditing). When the response
is within ± 10% of the previous calibration, the calibration is
still valid and a new calibration is not necessary. When the
response is greater than ± 10% proceed with the complete calibration
aSee Chapter 4, Table 4-V
-180-
-------
The audit data provide a record of the calibration drift.
Instruments with non-linear response require the full
calibration.
3. The analyzer to be calibrated should be in good operating
condition and installed in accordance with manufacturer's
instructions. Operate the analyzer for at least 24 hr to
warm-up. This 24-hr warm-up period may be shortened if so
stated in the operating instructions. Adjust the air and
reagent flowrates to their recommended rates or to the rates
determined from the static calibration (8.9) data and verify
the rates as described in 8.5.1, Item 1.
4. Record all data only after stable analyzer response has been
attained. Refer to 4.1.6 in Chapter 4 for determining
stable response.
5. Newly prepared SC>2 permeation "tubes may be used after one day
(24 hr) of equilibration at a constant temperature provided the
concentrations produced are established by the referee method.
A minimum of 30 days is required to establish that the emission
rate is stable and before the emitted concentration can be used
as a primary standard . The tube should be equilibrated for
at least 12 and preferably 24 hours whenever the temperature is
changed by more than ± 5°C. See Reference 7 for general pre-
cautions pertaining to permeation tubes. It is generally desirable
-181-
-------
1 to precondition all 862 gas lines for % to 1 hour by flowing a
stream of dilute S02 through them.
8.8.2 Procedure
1. Place the gas generation system as close as practical to the
analyzer to prevent losses and to minimize pressure changes in
the analyzer sampling duct. Calculate the airflow of the
analyzer and add the airflow needed for the referee analysis
(1.0 to 2.0 liter/min). Add about 10% of the total tp insure
an excess. (NOTE: The excess calibrating gas should be vented
to a hood or absorbed by a soda lime trap to avoid exposure
to personnel.) In a proper assembly, connection or dis-
connection of the analyzer sampling line should not alter the
airflow settings.
2. Generate a flow of zero air equal to the rate determined in
Step 1 above. Pipet the required volume of absorbing reagent
in the impinger (Item 8.5.8) according to the manual referee
method . Connect the impinger to the sampling train as shown
in Figure 8-III. When a stable analyzer response is obtained,
sample the gas stream from the manifold for 30 minutes at the
rate directed in Reference 4. Transfer the exposed solution to
a 25 ml volumetric flask. Develop the color of the solution in
accordance with the referee procedure and read the absorbance
at 560 nm. When the absorbance of the solution is greater than
the blank, continue flushing the g^3 generation system until
the absorbance is obtained the same as the blank. Inability to
-------
obtain a reading equal to the blank indicates interferents in
the zero air. Correct the source of the problem(s) before
proceeding.
Zero the analyzer by adjusting the analyzer controls so that
the output corresponds to zero or the desired reading.
3. Generate an SCU concentration equal to 80 ± 5% (span gas) of the
full scale reading (0.80 ppm for full scale of 1.0 ppm; 2.10
yg SC^/nr* for full scale of 2.62 yg/nP) . When the analyzer
response is steady, record the analyzer reading.
4. When a permeation tube system is used and has been shown by
frequent referee analysis to provide reliable S02 concentrations;
the collection of referee samples may be omitted. The S02 con-
centrations are calculated from the diluent gas flow and permeation
rates by equation 1 or 2.
a) To determine the concentration of SC^ in ppm (yl/1) fr
the permeation tube emission rate, use equation 1.
p (1)
ppm = x
VV 2.62 (Qd)
where P = permeation rate in yg/min.
Qd = rate of zero (diluent) air in liters/min.
om
-183-
-------
b) When the concentration units are desired in yg SC>2/!iP instead-
of ppo> then:
c. 3 (R X 103)
S02/m = -——— C2)
(Qd>
5. To establish the S02 concentration by referee analysis:
a) Collect duplicate samples of the gas stream and analyze
as described in the referee method . Adjust the sampling
period to keep the absorbances of the samples at about
midscale (0,3 to 0.5A) on the spectrophotometer. Five to
30 minutes are usually sufficient. For maximum precision,
place the flasks containing the reacted solutions in a bath
maintained within 2°C of the temperature used during the
development of the spectrophotometer calibrating solutions.
b) From the volume of air sampled and the slope of the spactro-
photometer calibration curve, calculate the ppm SOo as
directed in equation 3.
(A) (10)
ppm =
where: ppm = concentration (yil/1) S02
A - net absorbance of the solution
b = slope of the spectrophotometer calibration curve
obtained in 8,7
-184-
-------
Va = volumes in liters, of the gas sample collected
(liters/min X rain)
To convert ppm to yg/m^, use equation 4
yg S02/m3 = ppm S02 X 2620 (4)
Usually, changes in the gas volume of the samples due to
deviation from the standard conditions of 25°C and 760 torr
are small and may be neglected. When the deviations are
large, (sufficient to cause a change in gas volume greater
than about 5%) correction should be made.
c) The concentrations of the duplicate samples should be within
5%. Differences greater than 5% may be due to unstable gas
concentrations, error or inconsistencies in sample collection
and analysis. Correct these problems before proceeding with
the calibration.
6. When possible, adjust the analyzer to give reading equivalent
to the span S02 concentration (spanning). When the instrument
has no span controls, proceed to Step 7 below. Generate zero air
and note the analyzer reading. When the reading is different
from the original baseline reading by > 2%, reset the analyzer
to read the original baseline and repeat Steps 3 through 6
above. Analyzers with zero and span controls not electrically
independent may have to be respanned and rezeroed iteratively
until the proper zero and span settings are obtained.
-185-
-------
7. Generate, in turn, four additional SC^ concentrations between
the blank and span range (e.g., 10, 20, 40, and 60% of full
scale) and determine the S02 concentrations in duplicate and
analyze as directed in Steps 3 through 5 above. Determine
the net analyzer readings by subtracting the baseline reading
from the individual readings.
8.8.3 TreatmentofDynamic Calibration Data
1. Plot the net analyzer readings on the vertical axis versus the
corresponding SO?, concentrations on the horizontal axis of an
appropriate graph paper (rectilinear, semi-log, log, etc.).
Calculate the slope b^ of the best-fit curve for the data by
the method of least squares . To determine the linearity of
the response, see Test 4.5 in Chapter 4. A non-linear response
from an instrument normally linear indicates analyzer malfunction
or, possibly, errors,in the preparation of the calibrating
gases. Correct the cause of the problem(s) before recalibrating.
2. When a non-linear response is normal, draw a smooth line through
the calibration points that fits the points best. From this,
prepare a template to convert the net analyzer readings to S02
concentrations.
Chapter 4, Table 4-V.
-186-
-------
8.9 STATIC CALIBRATION
The following section pertains to S02 analyzers using wet-chemical
methods (colorimetry and conductimetry) . See also 8.1.3.
8.9.1 Procedure
Prepare calibrating solutions (equivalent to 10, 20, 40, 60, and 80%
of full scale and perform the static calibration according to manu-
facturer's instructions. In the absence of such instructions the
static calibration procedures described in Section 6.9, Chapter 6,
for automated oxidants and ozone analyzers may be used as a guide.
8.9.2 Treatmen^ of_S ta/tic _Calib ration .Data
1. Plot the net analyzer readings on an appropriate graph paper
(rectilinear, seial-log, etc.) against the. equivalent yl S02/ml
of the calibrating solutions. Calculate the slope bs of curve
that best-fits the data by the method of least squares0. To
determine the linearity of the response, see Test 4.5 in Chapter
4. A non-linear response from an instrument normally linear
indicates malfunction in the analyzer or error in the static
calibration process. Correct problem(s) before recalibrating.
2. When a non-linear response is normal, prepare a template as
directed in Step 2 of 8.8.3. An alternate method is to
cSee Chapter 4, Table 4-V.
-187-
-------
attempt to linearize the instrument output by adjusting the
electronics (i.e. photometer, etc.) until a linear output is
found over the range of pollutant concentration of interest.
8.9.3 Determination of Airflow Rate
For instruments not equipped with adjustable upper limit or span
controls or when the range of span adjust is insufficient, the
slope of the static calibration can be used to establish the
sample airflow rate that will make the analyzer output correspond
to the pollutant concentration or a simple fraction or multiple
fs of the concentration range as follows:
«= (Qr)
where: bs'=. slope of the static calibration curve obtained in
8.9.2
Qa = analyzer airflow rate, ml/min.
Qr = analyzer reagent flow rate, ml/min.
fs ~ range factor (e.g., %, 1.0, 2.0)
8.10 RECONCILING THE STATIC AND DYNAMIC CALIBRATIONS
The static calibration slope ba (8.9.2) and the dynamic calibration
s
slope b, (8.8.3) are compared by equation 6:
rl88-
-------
|ts - bdj
R « X 100 (6)
b.
s
Large values of R (> 10%) are indicative of a) error in the analyzer's
air or reagent flowrate, b) leaks or malfunction in the analyzer
c) poor quality reagents, d) error in the static or dynamic calibration
process or e) change in the sample collection efficiency of the
analyzer. Consult the analyzer operating instructions and/or
manufacturer and correct the problem(s) before recalibrating.
-189-
-------
8.11 REFERENCES.
1. O'Keeffe AE, Ortman GO: Primary standards lor trace gas
>
analysis. Anal Chem 38:760, 1966.
2. Scaringelli FP, Frey SA, Saltzman BE: Evaluation of teflon
permeation tubes for use with sulfur dioxide. Amer Ind
Hygiene Assoc J _28_:260, 1967.
3. Scaringelli FP, O'Keeffe AE, Rosenberg E, Bell JP: Preparation
of known concentrations of gases and vapors with permeation
devices calibrated gravimetrically. Anal Chem _42_t871, 1970.
4. Environmental Protection Agency, National primary and secondary
ambient air quality standards, Appendix A: Reference method for
the determination of SO^ in the atmosphere. Fed Reg 36; No. 84,
Friday, April 30, 1971.
5. Environmental Instrumentation Group, Lawrence Berkeley Laboratory,
Univ. of Calif., Berkeley, Calif.: Instrumentation for environ-
mental monitoring, Air, LBL-1, vol.1 (SO-,) Dec. 1, 1971.
6. Pate JB, Ammons BE, Swanson GA, Lodge JP, Jr: Nitrite inter-
ference in spectrophotometric determination of atmospheric
sulfur dioxide. Anal Chem _3J7_:942, 1965.
-190-
-------
7. Intersociety Committee: Methods of air sampling and analysis.
Amer Publ Health Assoc, 1015 18th St., NW, Wash., DC, 1972.
8. ACS Reagent Chemicals, American Chemical Society Specifications.
American Chemical Society, Washington, B.C. For suggestions on
the testing of reagents not listed by the American Chemical .
Society,, see: Rosin J: Reagent Chemicals and Standards.
New York, D. Van Nostrand Co., Inc., and The United States
Pharmacopoeia.
9. Metronics Associates, Inc., Palo Alto, CA 94304.
10. Analytical Instrument Development, Inc., 250 South Franklin Street,
Westchester, PA 19380.
11. National Bureau of Standards, Office of Standard Reference
Materials, Washington, DC 20234.
-191-
-------
Gas nixing
chamber
Sampling manifold
Vent
r i
{ Referee sampling i
train i
Particle Air pump Filter
filter
Ambient air
Gas Dilution Apparatus
SOo Source Apparatus
Permeation device
7
or
Rotameter
Dil,
so2
in
N2
Thermometer-
Constant
temperature bath
(air or water)
Rotameter
Figure 8-1. Gas generating system for calibrating SC^ analyzers,
-------
Flexible tubing
Flowmeter
From sampling
manifold
*• To air pump
Needle
valve
Figure 8-II. Sampling train for referee S02 analysis,
-------
9.0 CALIBRATION PROCEDURE FOR AUTOMATED ATMOSPHERIC
CARBON MONOXIDE ANALYZERS
9.1 PRINCIPLE AND SCOPE
9.1.1 This procedure is for the calibration of continuous atmospheric
carbon monoxide (CO) analyzers that use physical measurement
methods such as nondispersive infrared absorption, etc. The
calibration, known as a dynamic calibration, is performed by
determining the analyzer response to a series of calibrating
gas concentrations containing CO. It is a performance test of
<~ •
the entire analyzer under simulated service conditions.
9.1.2 The calibrating gas concentrations may be generated in several
1 2
ways ' . The most coamon method is to prepare a series of CO
concentrations in plastic bags (primary or batch dilution) or to
prepare or purchase cylinders of compressed air containing CO
concentrations between 10 to 80% of full scale (primary standard).
A wider variety of concentrations may be generated by diluting
50 to 100 ppm (57 to 115 mg/m^) CO from a cylinder with zero air
(secondary dilution).
9.1.3 The instrument operating variables, such as airflow rates, output,
gain, span, can be adjusted during calibration to make the output
reading conform directly to concentration in ppm (yl/1) or mg CO/m
or a simple fraction or multiple of the concentration.
-194-
-------
9.2 RANGE
The range of the calibration procedure depends on the measuring
range(s) and sampling rate(s) of the analyzer(s). The analyzer's
measuring range and sampling rates vary greatly depending on its
design and measurement principle (See Reference 2 and its lists
of references for further details). The commonly used nondispersive
infrared (NDIR) analyzers typically measure in the range of about
0 to 25, 50, or 100 ppm CO (0 to 28.6, 57.3, or 115 mg CO/m3).
Sampling rates are typically between 1 to 2 1/min, but can go
as high as 42 I/minute (See Table 5-1). The semi-continuous gas-
chromatographic CO and methane analyzers measure CO concentrations
between 0 to 1000 ppm (0 to 1145 ing/iir) . Electrochemical analyzers
measure in the same range although they are not much used for
continuous ambient monitoring.
9.3 INTERFERENCES
Carbon monoxide is available with purities of 99.7% or greater.
Higher purities are obtainable for special work. Zero air for
dilution must be free of CO, CC2 and water. Selective, absorbers
(drying agents, Ascarite for C02, etc.) can be used whenever a
i
particular measurement principle requires it. Details for pre-
paring these absorbers are given in Table 5-III.
-195-
-------
9.4 PRECISION, ACCURACY, AND STABILITY
9.4.1 A precision (coefficient of variation) from 2 to 3% is achievable
when preparing repeated primary dilutions of CO in non-rigid, CO-
inert bags in the range of 10 to 100 ppm (12 to 115 rog/m3). The
chief source of error is often in measuring the air volumes. A
minimum of 2% error is produced for each rotameter used and the
errors are approximately additive. When greater precision is
needed, positive displacement, metering pumps can be used.
9.4.2 When spanning is possible, any discrepancy between the input and
analyzer output may be resolved by adjusting the instrument output
to correspond to the concentration of the calibrating gas. Where
analyzers have no spanning controls, a correction factor may be
calculated to convert the analyzer readings to CO concentrations.
9.4.3 Primary dilutions made in non-rigid containers usually cannot be
kept for more than a few (< 5) days due to concentration changes
with time. The concentration of dilute CO (> 50 ppm) stored at
high pressure in steel cylinders lined with chromium molybdenum
alloy should be checked periodically (^ monthly) for one to three
months after preparation and semi-annually thereafter. See 9.6.2
for additional comments.
A detailed discussion of the various sources of error in the
preparation of calibrating gases is given in Reference. 1 in
-196-
-------
Part I: General Precautions and Techniques. The minimization
of the sources of error is important to assure high accuracy
and precision in calibration.
9.5 APPARATUS
The apparatus needed depends on the method chosen. The procedures
listed under 9.7 are the easiest as well as among the most reliable.
.For delivering large (> 40/min) flows, procedure 9.7.3 is preferable,
The fourth, indicated in 9.5.4 and discussed in Reference 1, is less
commonly used, although equally reliable. The zero air may be
furnished from a cylinder or by filtering ambient air as shown
in Figure 9-1.
9.5.1 Primary Standards
Eefer to 9.6.2 for equipment and gases.
9.5.2 Primary Dilution in Bags
1. Bagsi (Scotchpaka)i_: Fabricate or purchase six bags of sufficient
volume (10 to 20 1) to satisfy the volume rate requirement of
the analyzer. Use one bag for each gas concentration.
2. Dilution system (Figure 9-1): consists of a flowmeter for
measuring gas flows between 1 to 5 liters/rain, a needle valve,
Registered trademark of Minnesota Mining & Manufacturing Co. C3M)
for their metallized laminate consisting'of polyester, aluminum,
and polyethylene, Cat. No. 20A20.
-197-
-------
a three-way stopcock for diverting flows, a tee connection with
a rubber septum cap for injection of known volumes of pure CO
and the necessary glassware and ball-and-socket joints. Poly-
vinylchloride tubing may be used to butt-join connections.
The rotameter should be calibrated frequently (monthly) with.
a wet or dry test meter, soap bubble meter or calibrated
rotameter.
3. Gas Sampling syringes"; A 1.00 ml syringe is needed for pre-
paring the CO concentrations in bags.
4. Stopwatch or accuratetiming device.
9.5.3 Secondary Dilution of CylinderCO
1. Dilution system (Figure 9-II); This consists of a mixing
chamber, two flownieters capable of measuring the maximum
flow required by the analyzer(s), two needle valves for flow
control and a delivery manifold containing sampling ports
and a vent for discharging excess calibrating gas and the
necessary glassware and ball-and-socket joints. Rotameters
should be calibrated frequently (monthly) with a wet or dry
test meter, soap bubble meter or calibrated rctameter.
Precision Sampling Corp., Baton Rouge, LA, Series A, or equivalent.
•198-
-------
2. Air pump (for transport of jugbieni^air) : An oil-less (carbon
vane or diaphragm) air pump capable of delivering the flow
rate requirements of the total calibration system plus 10%.
A particle filter should be installed downstream of carbon
vane pumps and is optional for diaphragm types.
9.5.4 C0_ln. Cylinders (Low Pressure); See Reference 1 for apparatus
and method.
9.6
REAGENTS AND GASES
9.6.1 100% Carbon Monoxide, Chem. Pure (> 99.7%): For preparing CO in
bags by Method 9.7.2, Primary Dilution.
9.6.2 Dilute CarbonMonoxide (Primary Standards): High pressure steel
cylinders containing CO concentrations equal to 10, 20, 40$ 60 and
80 ± 5% of full scale in air. Cylinders should be lined with a
chromium molybdenum alloy. Alternatively, the 80% of full scale
cylinder may be used for spanning and for preparing intermediate
Concentrations by Method 9.7.3 (Secondary Dilution). These
mixtures may be purchased or may be prepared in the laboratory
with suitable gases and high-pressure manifold . The CO concen-
trations are established by comparing the analyzer readings
obtained with this gas versus those obtained with 1) a primary
-199-
-------
dilutions 2) certified CO ga.s from another source, or 3) analyzed
-gravimetrically^'^. Certification or analysis by the supplier
at the time of preparation is of little value because of unpre-
dictable changes that frequently occur with time. Verify the
concentration monthly for one to three months after purchase or
preparation, and occasionally (setni-annually) thereafter, NOTE:
Since changes in the CO concentration may occur after the cylinder
/
-------
9.7 PREPARATION OF CALIBRATING GASES
9.7.1 Primary Standards
Equip the zero air cylinder (Item 9.6.3) and each CO cylinder
(Item 9.6.2) with an appropriate pressure reducing regulator, metering
valve and flowmeter. These gases inay be fed directly to the analyzer.
9.7.2 Primary or Batch Dilution in Bags
1. Assemble the dilution system described in Item 2 of 9.5.2
and shown in Figure 9—1. Generate a convenient flow of
zero air (i.e.s 1000 ml/min) . From the volume of the bags
calculate the volume of pure CO (Item 9.6.1) needed to prepare
the desired CO concentration by equation 1. The volume of
diluent zero air depends on the size of the bag and should
not exceed about 80% of the bag volume.
v0 = i x io-6 (vx) (cx) CD
where: V0 = volume of pure CO in ml
Cj = ppm CO desired
Vj_ - volume of zero air and CO added to the bag in ml.
-201-
-------
*5
To convert ppm CO to mg CO/irr:
mg C0/m3 - (1.15) (ppm CO) (2)
Usually, the change in gas volumes due to deviation from the
standard conditions of 25°C and 760 torr is small and may be
neglected. When the deviations are large (sufficient to
cause a change > 5% in gas volume), volume corrections should
be made.
2. Connect the bag (with its valve open) to the three-way stopcock.
Carefully fill the gas-tight syringe to the calculated volume V0
tar? f-Ti r>nri=> C.Q. KtjT.t"rV» fh.p stonrnrk to fill thp. h^f? with zero
..«..-.._ ^-.__- —. - _ . — - .. « „ __Jt__- _ . ^
air and begin timing. Insert the syringe needle through the
rubber septum cap on the glass tee and expel the pure CO so that
it merges with the zero air stream. Continue filling the bag
until the predetermined volume Vj is reached, then switch the
three-way stopcock to vent. Seal the valve on the bag and knead
the bag to mix tha gases thoroughly. Empty the contents to a
hood and repeat Step 2 twice. Prepare the four other intermediate
CO concentrations in the same manner. These primary dilutions nay
be prepared in duplicate or larger multiples and the analyzer
responses averaged to insure against errors or to acquire
precision data.
-202-
-------
9.7.3
1. Assemble the dilution system (Item 1 of 9.5.3) as shox^n in
Figure 9-II. Connect the cylinder of dilute CO (Item 9.6.2)
and the zero air source (Item 9.6.3) to the needle valves of
their respective rotameters.
9.8 DYNAMIC CALIBRATION
9.8.1 General
1. When the analyzer to be calibrated has been operating as a.
continuous monitor it is useful to determine its response
near the span level first without changing the span setting
(a'.'dl fi/OP1) - Wh#?t» th«? ?Pfl 1 'v?.(?-Y TP-ftponse is within ± 10% of
the previous calibration, the calibration is still valid and
a new calibration is not needed. When the response is
greater than ± 10% proceed with the complete calibration.
The audit data provide a record of the calibration drift.
Instruments with non-linear response requires the full
calibration,
2. The instrument to be calibrated should be in good operating
condition and installed in accordance with manufacturer's in-
structions. Operate the analyzer for at least 24 hours to
•i
warm-up. This 24-hr warm-up period may be shortened if so
stated in the operating instructions. Adjust the analyzer
-203-
-------
airflow to the recommended sampling rate and verify the rate
as described in 9.5.2s, Item 2.
3. Record all data only after stable, analyzer response has been
attained. Refer to 4.1.6 in Chapter 4 for determining stable
response.
4. Assemble the appropriate generating system (.Items 9.5.1, 9.5.2 or
9o5.3)for generating CO as needed. Place the system as close as
practical to the analyzer to prevent losses and to minimize
pressure changes in the analyzer sampling duct. Calculate
the airflow of the analyzer and, when required, add the airflow
seeded for the referee analysis. Add 10% of the total to insure
an excess. (NOTE: Any excess CO gas streams should be vented
or passed through a CO pxidizer/C02 absorber filter to avoid
exposure to personnel. See Table 5-III for details.) In a
proper assembly, connection or disconnection of the analyzer
sampling line should not alter its airflow reading.
5. Generate a flow of zero air equal to the rate determined in
' Step 4 above. When a stable analyzer reading is obtained,
adjust the analyzer zero control so that the analyzer output
reads zero or the desired baseline reading.
6. Generate a flow of calibrating CO gas equal to SO ± 5% of. full r
scale (span gas). When a stable response is obtained, adjust
-204-
-------
the analyzer controls to give a reading equivalent to the
span. CO concentration. Generate a zero gas. When the zero
reading is different from the original baseline reading by
> 2%, reset the analyzer to read the original baseline and
repeat Steps 5 and 6. When the span and zero controls are
not electrically independent, it may be necessary to rezero
and respan iteratively until the proper zero and span control
settings are obtained.
7. In turn, generate and introduce the four Intermediate CO
concentrations (e.g,, 10, 20, 40 and 60% of full scale)
from the bags or from the dilution system and record the
corresponding instrument readings. Determine the net
analyzer readings by subtracting the baseline reeding
from the individual readings.
9.8.2 Treatment of Dynamic Calibration Data
1. Plot the net analyzer readings on the vertical axis versus
the CO concentrations on the horizontal axis of an appropriate
graph paper. Calculate the slope b of the best-fit curve
for the data by the method of least squares0. To determine
the linearity of the response, see Test 4.5 in Chapter 4. A
non-linear response from an instrument normally linear indicates
C8ee Chapter 4, Table 4-V.
-205-
-------
malfunction or, possibly, errors in the concentrations of the
calibrating gas. Correct the problein(s) and recalibrate.
2» When a non-linear response is normal, draw a smooth line through
the calibration points that fits the data best. From this,
prepare a template to transform the net analyzer readings
to CO concentrations.
-206-
-------
9.9 REFERENCES
1. Intersociety Committee: Methods of Air Sampling and Analysis.
Tentative Method of Preparation of Carbon Monoxide Standard
Mixtures, No. 117, Amer Publ Hlth Assn, Wash., DC (1972).
2. U.S. Dept. of Health, Ed. & Welfare, Publ. Hlth Serv., Envir.
Hlth Serv.: Air Quality Criteria for Carbon Konoxide, Ch. 5,
NAPCA Publ. No. AP-62 (March 1970).
3. Belsky T: Preparation of low-concentration mixtures of gases.
Air & Industrial Hygiene Lab., Cal. State Dept. of Publ. Hlth,
AIHL Report No. 117 (Jan, 1972).
-207-
-------
IT 100% co
Source
Zero
air
Flexible (Scotchpak)
bag
Figure 9-1. Primary dilution system for CO in bags.
-------
10.0 AIR ANALYZER TERMINOLOGY
This chapter contains selected terms commonly used in air monitoring
practices and instrumentation and was developed to promote more effectiv
communication between the various disciplines in air pollution techno log
It is not intended as an all-inclusive glossary of air pollution terms,
The emphasis of terms related to instrument performance applies to the
overall analyzer system and not to the individual components.
For visual representation and interpretation of noise a.nd of the various
time delays in instrument response, see Figure 10-1.
-210-
-------
Absorbent; a.medium, which absorbs the pollutant being measured.
Absorber (contactor, contact'column, scrubber): a device for bringing a
gas stream containing vapors, fumes or particulate matter into intimate
contact with a liquid absorbent usually aqueous. To minimize absorption
of interferents. an absorber design with minimum turbulence and minimum
surface area consistent with absorption of the pollutant is desirable,
Bubbler: an absorber in which the sample gas is introduced below
the surface of a liquid absorbent. For increased efficiency, the
gas stream may be broken up into small bubbles by being forced
through restricted openings as in a perforated sparger or a fritted
glass tip. Bubblers may be tall or short depending on the efficiency
of the absorbing process.
Helical ^coluran; an absorber consisting of a coil of tubing with one
or more turns, usually mounted with its axis vertical. Gas-liquid
flow is co-current and may be up or down the column. High wetted—
surface area is achieved by selecting a tube diameter sufficiently
small to insure that the surface tension of the absorbent will cause
the entire inner surface of the column to become wetted. The coil
is usually glass, but other materials may be used.
Helix insert column: a high-surface-area absorber composed of a
narrow vertical tube with a solid helix, usually of glass or wire,
placed axially and in contact with the interior column wall. Liquid
-211-
-------
absorber passes down the column in a. thin film over the helix. Gas-
liquid flow may be co-current or countercurrent. The helix may also*
be wrapped around a center support with the gas-liquid mixture passing
between it and the column wall.
Impjlnger; an absorber in which sample air is blown or aspirated onto
or below the surface of the liquid absorbent. Absorption is increased
by both high surface area and by turbulence.
Mechanical abs orber: an absorber designed to bring a gas or gases and
liquid absorbent into intimate contact by mechanical agitation. Absorp-
tion is increased by both high surface area and by turbulence.
Packedcolumn; a high-surface-area type absorber, usually a vertical
tubular column loosely filled with an inert medium such as Raschig
rings, helices, crushed or sintered glass, beads or other materials
of various shapes. Gas and liquid flow may be co-current or counter-
current with absorption taking place on wetted surfaces. A single
or a series of sintered glass plates through which the gas-liquid
mixture is passed may be used in place of inert packing.
Spray jet: an absorber in which a liquid absorbent is forced through
an orifice at high velocity and impacted on the inner surface of the
absorbing chamber. Gas is absorbed through mixing and turbulence
created by the impaction. Kinetic energy is imparted to the liquid
by hydraulic pressure, sample air pressure, or by aspiration caused
by the airflow into the chamber.
-212-
-------
Absorption; a process in which one or more pollutants are transferred
from a gas phase to a liquid or solid phase, either by physical dissolution
in, or preferably by chemical reaction with the absorbent. The driving
force is a function of the pollutant partial pressure at the gas-absorbent
interface. The process is favored by high interfacial areas, turbulence,
and high diffusion coefficients and, where the absorption process is
chemical, fast reaction rates and irreversible reactions.
Absorption spectroscopy: see detection methods.
Accu_racy_: (not to be confused with precision) the deviation between the
analyser output in concentration units and true pollutant concentration
which has been established by an accepted reference procedure. Lt is
expressed as a percent of the true 'concentration.
Accuracy, calibration; deviation between the slope b^ of the curve
obtained by the manufacturer's calibration procedure and slope obtained
with calibrating gases expressed as- a percent of the manufacturer's
slope.
Accuracy, monitoring_: deviation between the analyzer response obtained
under actual monitoring conditions to that of a reference procedure when
samples of the same atmosphere are taken at approximately the same time,
It is expressed as a percent of the reference procedure.
Adsorption; a process in which one or more pollutants are transferred from
a fluid to a solid by physical binding to the surface of tlie solid. Adsorpti.o:
-213-
-------
Is usually reversible, the pollutant being released (desorbed) by methods
such as solvent elution} evacuation, or heating.
Amperogie.try: see detection methods.
Analy_zer (also monitor) : a device or an instrument for sampling and
assaying pollutants.
Analyzer deadband: see deadband, analyzer.
Anemometer: an instrument for measuring and indicating wind speed.
Aud_ib1e noi s e (also acoustical noise) : 1) any unwanted sound, 2) an
erratic, intermittent or statistically random acoustical oscillation;
commonly expressed in units of power (decibels) sound pressure (newton
or dyne/square area) or loudness (phones, soness noys).
Auxiliary equipment: accessory items designed but not normally required
for use with an operational analyzer.
Bubbler_: see absorber.
Calibra_ting gas_: zero air or zero gas containing a known concentration
of a pollutant and used for the calibration of an analyzer.
Jga_Mbratingsolution; a solution used for static calibration, of an analyze.
and containing a known concentration of a substance which gives a response
equal to that of a known pollutant concentration,
-214-
-------
Calibration: the determination of the analyzer response when a series
of calibrating gas concentrations are introduced to the analyzer inlet
or artificial stimuli are presented to the detector.
Cali'braetion_8_jdynaiai_c; a, performance test of the entire analyzer
under simulated service conditions in which the response to a
calibrating gas over a known concentration range is determined.
When reconciled with a static calibration, dynamic calibration
also serves to verify 1) the correctness of reagent and sample
air flow rates, 2) the efficiency of sample collection, 3) the
integrity of the analyzer's plumbing and 4) the quality of any
reagents and/or reactaiits.
Calibration, static: the determination of the analyzer response when
artificial .stimuli such as standard calibrating solutionss resistors,
screens, optical filters, electrical signals, are applied directly
to the analyzer detector. It is a performance test of the detection
and signal presentation components of the instrument and is primarily
applicable to analyzers using colorimetric and conductinetric detectors,
_Chemilumines cence- (see chemiluminescent under detection methods): an
emission of light during chemical reaction.
Collection efficiency: the amount of pollutant measured divided by the
amount sampled, usually expressed in percent.
Colorimetry: see detection methods.
-------
Conduct im e t r ; see detection methods.
Contac t column : see absorber .
Contactor : see absorber.
Correlation spectrometry : see detection methods
: see detection methods.
Orifice : see orifice
Deadb and , Ana 1 y z er ; the range , in percent of full scale, through which
the input pollutant concentration may be varied without initiating an
analyzer response greater than twice the noise. (Deadband is commonly
applied to servo-systems such as recorders, but can be applied to
continuous analyzers as well.)
Detection methods: the techniques used to detect and assay pollutants
either directly through physical measurement or indirectly through measure-
ment of a reaction product. Inherent in most detection devices is a
comparison system in which the output from the detector is, at some
convenient stage, compared to or balanced against a reference quantity
such as a known voltage or current, or a color intensity of a reference
solution.
-216-
-------
Absorption spectroaetry (ultraviolet, Visible, infrared, and microwave) :
the detection and assay of pollutants based on the selective absorption
of electromagnetic radiation by the pollutants.
Amperoiaetry (not to be confused with coulometry) : The detection and
assay of pollutants based on the measurement of an electrical current
which is the result of a pollutant reacting in an electrochemical cell.
The potential and mass transport conditions in the cell are usually
adjusted such that the magnitude of the current between electrodes
immersed in the electrolyte is proportional to the pollutant concen-.
tration.
\
' Chemiluminescent Method: the detection and assay of pollutants based
on the emission of light by pollutants during chemical reaction. The
intensity of the light produced is proportional to pollutant concen-
tration .
Colorimetry: the detection and assay of pollutants based on the reaction
with a solution to produce a colored product having an intensity (or
absorbance) proportional to the pollutant concentration.
Conductimetryr the detection and analysis of pollutants based on its
reaction with a solution to produce a change in conductance that is
proportional to the pollutant concentration.
-217-
-------
», : ':'ne detection and analysis of pollutants by
direct comparison and correlation of their spectra with that of known
substances „
Coulometry (not to be confused with amperometry) : the detection and
assay of pollutants by an electrolytic method based on Faraday's Law
wherein the quantity of charge (integral of current x time) required
for the reaction is proportional to the pollutant concentration.
Emission spec trome try : the detection and measurement of pollutants
based on the characteristic spectra emitted when pollutants are excited
by heatj radiation, electrical discharge or other stimuli.
the detection and measurement of pollutants based
on the characteristic spectra emitted when pollutants are excited in
a flame. Narrow band-pass optical filters are frequently used to
isolate a characteristic emission line when -measuring a single
pollutant.
Fluor ime try; the detection and assay of pollutants based on the
characteristic electromagnetic radiation (usually visible light)
emitted during exposure of pollutants to radiation having a wave
length shorter than that emitted (usually visible or ultraviolet
light) .
lonization detector (flame and radiogenic) : a device which detects
ions produced by passage of a substance through a flame or a region
-218-
-------
of radioactive emissions. The flame ionization detector is specific
for combustible organic compounds. The radiogenic detector say be
a highly specific type such as electron capture that responds to
electrophilic compounds (e.g., pesticides) or nonspecific such as
helium ionization that responds to all gases.
Nondispersive infra_red_absor£tion (NDIR) : the detection and measure-
ment of pollutants based on their absorption of infrared radiation
generated in mixed wavelengths. Spectral specificity is obtained by
either a selective detector, optical filters, gas filled interference
cells or by pretreating the sample.
Potentiometry; The detection and assay of pollutants based on the
measurement of the potential of an electrochemical cell under
conditions where the cell potential is determined by the. concentration
of the pollutant absorbed. With unpolarized electrodes, the electro-
motive force is usually a linear function of the log of the pollutant
concentration in the electrolyte surrounding one of the electrodes in
the cell.
Detector (also: sensor, transducer): a device which responds to an input
parameter that is a property of, or an effect caused by, a substance
being measured. The amount of the substance present is indicated as the
deviation of an output parameter from a reference value. The input para-
meter is often light or other electromagnetic radiation, electrical current
-219-
-------
or voltage. The output parameter is frequently voltage, current or resist-
ance. Typical detectors are photocells, infrared bolometers and flame-
ionization detectors.
Drif_t-i- ca lib ration: the change in analyzer calibration which occurs
during a stated time period, usually one week, expressed as percent of
full scale.
Drift at span: the deviation in analyzer output during a stated time
period, usually 24 hours, of unadjusted continuous operation when sampling
a span gas concentration equal to some upscale value, usually 80% of
full scale. It is 'expressed as percent of full scale.
Drift^at zero: the deviation in analyzer output during stated time period,
usually 24 hours, of unadjusted continuous operation when sampling zero
air. It is expressed in percent of full scale.
Dry-gas iseter (bellows or diaphragm meters) : a device which measures the
total volume of a gas passed through it without using liquids.
Emission spectroscopy; see detection methods.
\
Fall time., tf'. see response times.
Flame photometry: see detection methods.
-220-
-------
Flow _ggntr_ol__d_ev 1 c e_s^ : apparatus for regulating fluid flow, usually by
maintaining constant pressure differentials across in-line flow con-
strictors .
ing ....... and metering_devic_e_s_: apparatus used to measure and meter
fluid flow. Most devices determine flow either by -volume displacement or
by methods based on the relationship between the pressure differential
across an orifice or constriction and the rate of fluid flow through that
orifice. Some devices determine total mass transfer by an electrodynamic
method. Examples of devices using these principles are:
1) Volume measuring devices - wet test meters, dry test, meters, bellows
meters, diaphragm meters, etc.
2) Rate measuring devices - rotameters, orifice meters, venturi tubes,
pilot tubes j catharometers , anemometers, volume measuring devices
used in conjunction with time measurement.
Flowmeter (see also rotameter) : any device which measures a rate of
fluid flow. In common practice, the term generally refers to a rotameter.
Fluor ime try: see detection methods.
Full__scale_ (see also range) : the maximum pollutant concentration measure-
able for given range, expressed in units such as yg/m , ppra, }il/l, %.
-221-
-------
Helicalcolumn: see absorber.
Eelix _insert^c_oltmn; see absorber.
Humidity operating range: see operating humidity range.
_Imgiriger_: see absorber.
jngtrjgnent inlet: the opening through which air sample enters the analyzer,
-------
time (initial response time) t^j see response times.
Linearity : a concept which expresses the analyzer response as a mathematical
function of concentration over a specified range. For a linear relationship
this function is the equation of a straight line. A non-linear response
pertains when the deviation of calibration points about a straight line of
best fit suggests non-random scatter and the maximum deviation is greater
than a specified percent of full scale.
Lower detectable limit (not to be confused with sensitivity) : the smallest
pollutant concentration XvThich produces a signal equal to twice the noise.
It is usually expressed in concentration units.
Manufacturer : the company or organization which assembled, fabricated or
otherwise produced the instrument.
Mechanical absorb_e_r_: see absorber.
MobjLlity: a qualitative term used for describing the relative ease with
which an analyzer may be moved about. It encompasses the categories:
portable, mobile, and stationary. All analyzers can be used as stationary
units. Mobile and portable analyzers should have qualities for 1) with-
standing the rigors of vibration and acceleration such as occurs during
transport, 2) tolerating extremes in environmental temperature variations,
and 3) warming-up in less than one hour. Portable units are expected
-223-
-------
in addition to be lightweight, self-contained, and independent of external
utilities such as power, gas, vacuum, and reagents. Instruments intended
for mobile operation should be able to meet all performance specifications
while in motion.
Model; an identifying name or alphanumeric code other than the trade name
assigned by the manufacturer to identify the instrument.
Monitor: sae analyzer.
Noise: unwanted, spontaneous, short term variations in analyzer response
about the mean output not caused by variations in pollutant concentration.
It is usually expressed as percent of full scale (see Figure 10-L).
Koise; audible: see audible noise.
Nondispersive infraredabsorption (NPIR): see detection methods.
Operating humidity range: the range of ambient relative humidity (RH) over
which the instrument will meet performance specifications.
OjH5rating__teirperature range: the range of ambient temperature over -which
the,instrument will meet stated performance specifications.
Operating vibration range: the range, in type and intensity, of mechanical
vibration in units of distance/time^ (cm/sec^) ever which the instrument
-224-
-------
will meet performance specifications. The emphasis is on analyzers designed
for portability in field use in motor vehicles and aircraft.
aperating_voltage_ranget the range of power line voltage over which the
"instrument will meet performance specifications.
Operational^period^ an indication of the time during which a properly main-
tained instrument can be expected to function without failure. This -nay be
expressed as a ratio between a specified operating time and the corre-
sponding off-stream, including maintenance, time during that period; as a
percent "of on-time during a specified operating period; or as an average
time between failures (mean failure rate) determined by dividing a specified
total operating period by the number of failures which can be expected to
occur during that period.
Orifice: an opening through which a fluid can pass and which is shaped
to provide pressure-flow characteristics that can be translated to flow
rate. At rates approaching sonic velocities, the characteristics are
useful for controlling flow (critical orifice).
Output; the final signal, usually electrical (volts, ohcs, amperes), pro-
duced by the instrument after detection of the pollutant being measured.
The signal is a function of the concentration of the pollutant. The
function may be linear; if non-linear, it is usually exponential but,
occasionally it is undefined. (see Lineaiity) The output is -usually-
-225-
-------
fed to a signal presentation device such as a meter, chart recorder, or
data processing device (see signal presentation devices).
Packed column: see absorber.
pollutant: the substance in the atmosphere which the analyzer is
designed to detect.
Portable: see nobility.
PotentiOTietry_: see detection methods.
Precision (not to be confused with accuracy) : the variability in repeated
measurements of the same quantity (e.g., pollutant concentration) expressed
as the coefficient of variation, i.e., the standard deviation of the
individual results expressed as a percent of the mean.
primary standard: a substance with a known property which can be defined,
calculated or measured, and which is readily reproducible. The standard
may be traceable to the National Bureau of Standards or other accepted
standards organizations.
_Pulse_tirae_: see response times.
Range (see also full scale.) : the nominal minimum and maximum concentrations
which the instrument is capable of measuring. Many analyzers provide
-226-
-------
multiple range selection capability for greater accuracy and ease of
Interpretation. It is specified by stating the lower and upper pollutant
concentrations that can be measured as for example 0 to 1 ppm, 0 to 5 ppm.
Readout : the presentation of the instrument output in an observable
display, as for example, with meters, printed numerals or words s
light, stripcharts, etc.
Resolution: the ability to separate two closely spaced events in
space or time at a signal-to-ncise ratio of two expressed as percent
of full scale.
Resp_onse___t_iinea_: (see Figure 10-1) .
ime, t*: the interval between the time to -100% Ct_-j_Q0} and
the lag time (t-j_) « Fall time is not necessarily equal to rise time.
'f " ^100
Lag time_ (initial response tine), t^: the interval between the time
t0, when a step change (increase or decrease) in pollutant concen-
tration is made, to the time t^ when the instrument indicates a
response equal to twice the noise.
- t0
-227-
-------
_Pulse___tlme_: the minimum time a pollutant concentration must persist
for the analyzer to register a peak response equal to the pollutant
concentration (see Figure 10-11).
Rise; time, tr: the interval between the time to 100% (tjj}()) an
-------
Rise timg_, tr: see response times.
Rotameter (variable area f lowmeter) : a flow-measuring device that
operates at constant pressure and consists of a weight or float
in a vertical tapered tube. As the flow rate increases, the float
moves upward to a new equilibrium position in a region of larger
area, the position being related to flow rate.
Sample ; a representative specimen of air collected for the purpose
of determining its pollutant content.
Sample_,_ grab ; a single sample rapidly collected when expedient.
Gaseous grab samples are usually collected in a container or
absorbed on a solid or in a solution within one jninute.
Sample, integrated: a composite of a series of samples or a
continuous flow of sample collected over a finite time period and
representing an average sample for that period. Although losses
may occur, an integrated sample is often stored for some time
before analysis.
S amp ling, au t oma ted ; programmed automatic collection of samples
for later detection and analysis.
1 collection of a composite sample durin
a predetermined total time or until a predetermined total volume
-229-
-------
has been reached, comprising uniformly timed samples separated
by regularly timed intervals. The ratio of on- time versus off-
time is stated.
: collection of grab or of integrated sampled at
random intervals.
Samp ling , s e q'u ent ia 1 : collection of uniformly timed samples that follow
each other at regularly timed intervals.
_Scrubb£r_: see absorber.
Secondary standard: a substance having a property which is calibrated
against a primary standard, to a known accuracy.
Selectively permeable membrane: a film which permits certain pollutants
in an air stream to diffuse faster than others. It is used for
separating or concentrationg those pollutants for subsequent analysis.
_Sensj.tivity (not to be confused with lower detectable limit) : the
instrument signal output response per unit of pollutant concentration.
Signal presentation devices; devices that are used to convert the
analyzer output (the signal from the detection device) to a usable
form, such as meters, recorders, digital readout units, computers,
and other data acquisition systems (see output).
-230-
-------
-1o-noise ratio: the ratio of the magnitude of the input
signal to that of the analyzer noise expressed as percent of full
scale. A ratio of two is usually the smallest value that can be used
with confidence.
J?£gCJL requir emen ts_; the area required for safe installation, operation
and maintenance of an instrument including allowance for all auxiliary
items and equipment such as pumps, reagent containers, etc.s and
swingout space for cabinet access doors and panels.
Span gas; a calibrating gas containing a pollutant concentration
equal to seine up scale value, usually 80% of full scale.
Span solution: a liquid reagent used in the static calibration of
an analyzer containing a concentration of a substance which gives a
response equal to some known pollutant concentration, usually 80%
of full scale.
Spanning: adjustment of the instrument output to a selected readin
when sampling a span gas or when the detector, is subjected to an
artificial stimulus such as a span solution, resistor, screen,
optical filter, or electrical signal.
Spray jet: see ab s or b e r.
-231-
-------
: see
S_t o ck s o lut 1 on : a solution which contains a known concentration of
a standard. This solution may be diluted to provide convenient con-
centrations for use in analysis.
Telemetry_: the conversion of the instrument output into a standardized
signal s and transmission thereof to a distant location for interpretation,
e: see operating temperature range.
Time to_95%, tnci see response times
Timejuo -95_%, t_q~: see response times.
Trad_e_jname; the name used by the manufacturer or \rendor to identify
a particular instrument or series of instruments.
Unattended operation: the period of time during which the instrument
can be expected to operate unattended within specifications.
Vendor: the independent dealer or distributor of the instrument,
instrument supplies, parts and service.
Ventur1_ tube; a tube with a constricted throat formed by a gradually
contracting cone followed by a gradually expanding cone used for
-232-
-------
determining fluid velocity by measurement of differential pressure
at the. throat as the fluid traverses the tube.
Vibration: an oscillatory velocity or acceleration expressed in units
of distance/time ; e.g. cm/sec*".
Vibration operatir..|^rang_e_; see operating vibration range.
Voltage operating range: see operating voltage range.
Warm-up titne: the elapsed time necessary after start-up for the
analyzer to meet performance specifications when it has been shut
clown for at least 24 hours, The. shortest possible warm-up time
(minutes) is desirable for instruments designed for portable field
vise,
Wet-test meter : a volumetric flow measuring dex'ice that measures
the total gas volume by entrapping the gas under a liquid in inverted
cups or vanes attached to a rotor. The buoyancy of the gas causes
rotation of the rotor. The'rotation is proportional to the gas
volume and is indicated directly on a calibrated dial.
Zero air (see zero gas): air containing 21.0 ± 0.5% oxygen and no
substances that will 1) react with the pollutant or interferent gas,
-233-
-------
2) alter the test analyzer response or 3} interfere in the referee
procedure. .
_Zer£_gas_ (see zero air): an artificial atmosphere containing no
pollutants.
Zeroing_ (also zero adjustment): deliberate translation of the analyzer
output or recorded data to a position selected as zero reference while
sampling zero air.
-234-
-------
Figure 10-1
DIAGRAM SHOWING VISUAL REPRESENTATION AND INTERPRETATION
OF TIME DELAYS IN ANALYZER RESPONSE
Pollutant
i in
f Input
loo -T- r- — -?
2X noise
Pollutant
off
Figure 10-11
DIAGRAM OF PULSE TIMI
d
o
rt
O
C
O
Output
Time
------- |