E?A-650/4.74-019-a
June 1974
Environmental Monitoring Series
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EPA-650/4-74-019-0
COLLABORATIVE TESTING
OF METHODS FOR MEASUREMENTS
OF N02 IN AMBIENT AIR
VOLUME 1 - REPORT OF TESTING
by
Paul C. Constant, Jr., Michael C. Sharp and George W. Scheil
Midwest Research Institute
425 Volker Boulevard
Kansas City, Missouri 64110
Contract No. 68-02-1363
ROAP No. 26AAF
Program Element No. 1HA327
EPA Project Officer: John H . Margeson
Quality Assurance and Environmental Monitoring Laboratory
National Environmental'Research Center
Research Triangle Park, North Carolina 27711
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
June 1974
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This report has been reviewed by the Environmental Protection Agency
and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Agency,
nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
11
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FOREWORD
This program, "Collaborative Testing of Methods for Measurement
of N02 in Ambient Air," is being conducted under the Environmental Protection
Agency (EPA) Contract No. 68-02-1363, which is Midwest Research Institute
(MRI) Project No. 3823-C. The program is concerned with the evaluation
of the following four methods with regard to their reliability and bias:
1. Sodium-Arsenite,
2. TGS-ANSA,
3. Continuous-Saltzman, and
4. Chemiluminescence.
The collaborative study covered by this two-volume report is of
the sodium-arsenite procedure, which is a tentative manual method. In
summary, MRl's responsibility was to develop an N02, ambient-air sampling
system for use with the four methods, provide the test site and facilities
thereon where the collaborative tests would be conducted, select the collab-
orators with regard to the program, prepare a plan of test for the collabora-
tive test, schedule testing, coordinate the test, retrieve field data and
results from the collaborators' analysis of their samples, statistically
analyze their results, and report its findings to EPA. The 10 collaborators
who participated in the sodium-arsenite collaborative test are:
Air and Industrial Hygiene Laboratory
California Department of Health
2151 Berkeley Way
Berkeley, California 94704
Kansas City Pollution Control Laboratory
2 Northeast 32nd Street
Kansas City, Missouri 64116
Kennecott Copper Corporation
Post Office Box 11299
Salt Lake City, Utah 84111
Los Angeles County
Air Pollution Control District
434 South San Pedro Street
Los Angeles, California 90013
Kentucky Division of Air Pollution
311 East Main Street
Frankfort, Kentucky 40601
Mecklenburg County Health Department
1200 Blythe Boulevard
Charlotte, North Carolina 28203
National Bureau of Standards
B 326 Chemistry Building
Washington, D.C. 20234
Institute of Gas Technology
3424 South State Street
Chicago, Illinois 60616
City of Philadelphia
Air Management Services Laboratory
1501 East Lycoming Street
Philadelphia, Pennsylvania 19124
Texas Air Control Board
8520 Shoal Creek Boulevard
Austin, Texas 79758
iii
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This volume, Volume 1 of the report of test, summarizes MRI's and
the collaborators' activities. It describes the development of the NC>2,
ambient-air sampling system, which covers the general concept of the system,
design considerations, the design of the system and the system checkout.
Following this there are discussions on the test site, the selection of
collaborators, the formal statistical design including the presentation of
factors and parameters that were considered, the collaborators' field sam-
pling at the test site, the collaborators' analysis of their samples--
both test and standard samples--MRl's statistical analyses of the collabo-
rators' results, conclusions and recommendations. Appendices contain a
copy of the tentative, sodium-arsenite method, information on the permeation
tubes prepared for this program by the National Bureau of Standards, cali-
bration of components of the sampling system, written communiques with
collaborators, instructions for collaborators, MRI's field, operational,
data-log sheets, and collaborators' analysis instrumentation and comments.
Volume 2 of this report of tests contains only the collaborators'
field data sheets for the four-run, 240-test sample, collaborative test.
The following individuals of the collaborating organizations are
acknowledged for their excellent work in the sodium-arsenite collaborative
test:
Texas Air Control Board
Mr. Fernando Martinez, field sampling and laboratory analysis
National Bureau of Standards
Mr. Bob Deardorff, field sampling and laboratory analysis
Mecklenburg County Health Department
Mr. James T. Ward, field sampling and laboratory analysis
Kentucky Division of Air Pollution
Ms. Diana Dunker, field sampling and laboratory analysis
California Department of Health
Mr. Kenneth Smith, field sampling and laboratory analysis
Kennecott Copper Corporation
Mr. Lynn Hutchinson, field sampling and laboratory analysis
City of Philadelphia
Mr. Donald Kutys, field sampling and laboratory analysis
Los Angeles County Air Pollution Control District
Mr. Abe Moore, field sampling
Ms. Violeta Vita, laboratory analysis
iv
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Kansas City Air Pollution Control Laboratory
Mr. Glenn Smith, field sampling and laboratory analysis
Institute of Gas Technology
Mr. Jon Zimmer, field sampling
Ms. Eugenia Mann, laboratory analysis
Special acknowledgements are made to the National Bureau of
Standards and to Mr. Ernest E. Hughes and Dr. John K. Taylor of NBS who
provided the NC^ permeation tubes for this collaborative test; and to
Dr. John B. Clements, Chief, Methods Standardization Branch, National En-
vironmental Research Center, Environmental Protection Agency, and Mr. John
H. Margeson, Government Project Officer, Methods Standardization Branch, for
their valuable suggestions in planning and design.
This MRI collaborative program is being conducted under the
management and technical supervision of Paul C. Constant, Jr., Head,
Environmental Measurements Section of MRl's Physical Sciences Division,
who is the Program Manager. Those who contributed to this test are:
development of the NC>2, ambient-air sampling system - Dr. Chatten Cowherd, Jr.
Mr. Fred Bergman, Mr. Emile Baladi, and Mr. Wallace Yocum; experimental
design and statistical analysis - Mr. Michael C. Sharp; and preparation and
operation of test facilities - Dr. George W. Scheil, Mr. John LaShelle,
Mr. Donald Gushing, and Mr. Edward Cartwright, Jr.
Approved for:
MIDWEST RESSARC
H. II. HubbaVd, Directc
Physical Sciences Divijsion
9 September 1974
v
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TABLE OF CONTENTS
Summary 1
I. Introduction 3
II. N02 Ambient-Air Sampling System 4
A. General Concept 4
B. Design Consideration 6
C. System Design 7
D. System Checkout 18
III. Test Site 23
IV. Selection of Collaborators 25
V. Statistical Design 29
A. General Considerations and Comments 29
B. The Formal Design 31
VI. Collaborators' Field Sampling 33
VII. Analyses of Samples 39
A. Analyses Performed by the Collaborators 39
B. Collaborators' Results 40
C. Analysis of Samples by MRI 40
D. Test Site Operational Measurement Data 43
VIII. Statistical Analysis of Collaborators' Results 43
A. Analysis of the Spiked N02 Measurements 49
B. Summary Discussion 53
C. Analysis of the Unspiked Ambient N02 Measurements. . . 54
IX. Conclusions 55
X. Recommendations 56
Appendix A - Tentative Method for the Determination of Nitrogen
Dioxide in the Atmosphere (Sodium-Arsenite
Procedure) 57
vi
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TABLE OF CONTENTS (Continued)
Page
Appendix B - Data on the Permeation Tubes Used as the Source of the
Spiked Levels of N02 ................. 69
Appendix C - Calibration of the Venturi and Dry-Gas Meter ...... 71
Appendix D - Written Communications with Potential Collaborators . . 75
Appendix E - Instructions for Collaborators - N02 Collaborative Test :
Sodium-Arsenite Method ................ 79
Appendix F - NC>2, Ambient-Air Sampling System Operational Data:
Test Log Sheets ................... 87
Appendix G - Collaborators' Analysis Instrumentation and Comments. . 101
LIST OF FIGURES
No. Title Page
1 N02j Ambient-Air Sampling System Concept ........... 5
2 Final Design of the N02, Ambient-Air Sampling System ..... 8
3 Annotated Photographs of the N02» Ambient-Air Sampling System
in Operation ........................ 9
4 Ambient-Air Stream Splitter ................. 12
5 Photographs of the N0£ Bleed-In Unit--Assembled and
Disassembled ........................ 14
6 Schematic Drawing of the N02 Permeation Tube Assembly .... 16
7 Schematic Drawing and Photographs of the Diffuser ...... 17
8 Schematic Drawing and Photographs of the Sampling Manifold. . 19
9 Venturi and Dry-Gas Meter Calibration System ......... 21
10 Collaborative Test Site: MRl's Field Station ........ 24
vii
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TABLE OF CONTENTS (Continued)
LIST OF FIGURES (Concluded)
No. Title Page
11 Photographs of the Test Facility 26
12 Collaborators' Sampling Areas at the Test Site 27
13 Photograph of Field Personnel of the N02 Collaborative Test
(Sodium-Arsenite Method); MRI Field Station; 4-8 February
1974 34
14 Photographs of Collaborators Preparing for a Run and Their
Sampling Trains in Operation 35
15 Photographs of Collaborators' Sampling Trains 37
16 Nitrogen Dioxide Data Sheets--Sodium-Arsenite Method 38
17 Typical Scan of Unreacted NEDA Solutions That Gave a Broad
Absorption Peak at 320 nm 44
18 Typical Scan of Unreacted NEDA Solution That Gave Minor
Absorption Peaks, as Well as a Major Absorption Peak at
320 nm 45
19 Collaborator Percent Bias Per Level of N02 51
A-l Sampling Train 67
A-2 Calibration Setup of Flowmeter 68
LIST OF TABLES
No. Title Page
I Sodium-Arsenite Collaborative Test Schedule 36
II Collaborator Results from Collaborative Test Using the
Sodium-Arsenite Method 41
III Data on NEDA Materials Used in the Sodium-Arsenite Method,
Absorption Peak Investigation 42
viii
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TABLE OF CONTENTS (Concluded)
LIST OF TABLES (Concluded)
No. Title Page
IV R Versus N02 Level 47
V Analysis of Variance (All 10 Collaborators) 48
VI Analysis of Variance (Collaborators A and I Deleted) 48
VII Bias (ug/m3) Per N02 Level 49
VIII Collaborator Biases (ug/m3) - All N02 Levels 50
IX Collaborator Percent Bias Per Level 50
X Components of Variance (All N02 Levels) 52
XI Measurement Error (o-e) Per N02 Level 53
XII Analysis of Variance of Unspiked Ambient N02 Measurements . . 54
XIII Comparison Unspiked Ambient Vs Spiked Components of Variance. 55
F-I Run No. 1 - Operational Data and Information on Ambient
Conditions at Test Site 89
F-II Run No. 2 - Operational Data and Information on Ambient
Conditions at Test Site 90
F-III Run No. 3 - Operational Data and Information on Ambient
Conditions at Test Site 91
F-IV Run No. 4 - Operational Data and Information on Ambient
Conditions at Test Site 92
G-I Analysis Instrumentation Used by Collaborators 102
IX
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SUMMARY
A collaborative test was conducted by MRI in the Greater Kansas
City Area during the week of 4 February 1974. Ten organizations partici-
pated in this test of the "Tentative Method for the Determination of
Nitrogen Dioxide in the Atmosphere (Sodium-Arsenite Procedure)." All
collaborators sampled simultaneously from the NC>2, ambient-air sampling
system that was developed by Midwest Research Institute (MRI) specifically
for this collaborative test program. For each of the four 24-hr runs
(each of a different average N02 level: 84.1, 113.2, 228.3 and 311.7
jig/m-^), each collaborator drew six samples simultaneously; four from the
NC^-spiked section and two from the unspiked (ambient-air) section of the
sampling system. Each collaborator was given, for analysis with his test
samples, two standard samples (one N02 and one blank) that were prepared
by MRI.
The N0~ challenge levels were obtained from permeation tubes
that were developed by the National Bureau of Standards.
The collaborators analyzed the test and the standard samples at
their home laboratories, and submitted their results to MRI. MRI checked
the collaborators' calculated results and found no gross errors. The
collaborators' results were then statistically analyzed.
The collaborators sampled from both the spiked and unspiked lines
of the N02j ambient-air sampling system, providing two sets of collabora-
tors' results. The two sets of results were used to determine true values
of the levels of NC>2 that comprised the challenges to the collaborators'
sampling trains. In addition, for both sets of results, there was an
analysis of variance made to determine biases and components of variances--
the variances of repeated observations and variances between collaborators.
The bias to the NCU determinations is relatively small--approx-
imately 3%--and it was independent of the NC>2 level.
The major conclusions that can be drawn from the results of this
collaborative test are:
1. The NC>2, ambient-air sampling system developed by MRI is an
effective system for use in collaborative testing of manual methods such
as the sodium-arsenite procedure.
2. The "Tentative Method for the Determination of Nitrogen Dioxide
in the Atmosphere (Sodium-Arsenite Procedure)" is adequately written for
those knowledgeable of sampling and analysis techniques as presented therein.
1
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3. If the tentative sodium-arsenite procedure as given in
Appendix A of this report is followed by people knowledgeable of the sam-
pling and analysis techniques given therein, then such a person will ob-
tain results that are on the average 6.2 ug/m3 too low, ± 16 ug/m3, over
the range 50-300 ug/nP. If a set of such people, each sampling indepen-
dently, follow the method, then results will be on the average 6.2 ug/m3
too low, ± 22 ug/m3.
Based upon the conclusions that have been drawn from the results
of this collaborative test, it is recommended that:
1. The same NC^ sampling system be used in the evaluation of the
remaining NCL methods to be tested;
2. The data sets to be obtained from the subsequent methods to be
evaluated be based on experimental designs, test procedures and sampling
system operational procedures as similar as possible to those of the sodium-
arsenite collaborative test so that comparisons of the methods are based on
similar criteria; and
3. No further analysis be made of the results from the sodium-
arsenite method until the results from the other three methods are obtained.
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I. INTRODUCTION
The Methods Standardization Branch, National Environmental Re-
search Center of the Environmental Protection Agency (EPA) is engaged in
a program to evaluate methods for measuring NOo in ambient air. Midwest
Research Institute (MRI) is working for EPA under Contract No. 68-02-1363
to provide EPA data on the reliability and bias of the following four
methods: sodium-arsenite and TGS-ANSA, which are manual methods; and
continuous-saltzman and chemiluminescent, which are instrumental methods.
To achieve this objective, a collaborative testing program is being
conducted that will assess interlaboratory as well as intralaboratory testing.
In summary, MRI in the execution of this program, selects the collaborators,
provides sampling locations and facilities thereon, orients the collaborators
relative to the program, prepares a plan of test for each method tested,
schedules testing, coordinates the collaborative tests, retrieves field
data and results of the collaborators' chemical analyses of their field
samples, statistically analyzes results received from the collaborators, and
reports results of the program to EPA.
These activities were performed by MRI on its first test undertaken
on the contract. The method investigated was the "Tentative Method for the
Determination of Nitrogen Dioxide in the Atmosphere (Sodium-Arsenite Procedure),"
dated November 1973. A copy of the writeup of this method is given in Appendix
A.
The program was initiated on 30 June 1973, and the first collabora-
tive test took place at MRl's field station in Kansas City, Missouri, during
4-8 February 1974 with 10 different collaborators. The interim period was
devoted to the preparation for this test. A major task of the preparation
activity was the development of a precise N02, ambient-air sampling system
that could be housed indoors and be suitable for all four methods.
The two major phases of the test program were sampling and analy-
ses. The sampling phase covered the field test where the collaborators
collected their samples from the ambient-air sampling system. The analy-
ses phase covered the chemical analyses of field samples by the collabora-
tors and the statistical analyses of their results by MRI. After the
field test, the collaborators returned to their home laboratories where
they analyzed their samples and reported their results to MRI. Then MRI
performed its statistical analysis and prepared this report of the sodium-
arsenite collaborative test.
This report covers the collaborative test of the tentative
sodium-arsenite method in the following order: Section II discusses the
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NCU, ambient-air sampling system MRI developed for this program, covering
the general concept of the system, the design considerations, the system
design, and the system checkout. Section III describes the test site and
the facilities that were used at this site. Section IV discusses how the
collaborators were selected and who they are. Section V presents the fac-
tors and parameters that were considered in the formal experimental design
as well as the formal design. Section VI summarizes the test activities
during the collaborative test. Section VII discusses the analyses that
were performed by the collaborators. The collaborators' results are pre-
sented in this section as well as the analysis MRI conducted and the op-
erational measurement data MRI took during the test. Section VIII dis-
cusses the statistical analysis of the collaborators' results and presents
the results from this analysis, which includes biases and components of
variance. Sections IX and X present conclusions and recommendations, re-
spectively. The appendices contain a copy of the tentative sodium-arsenite
method, data on the permeation tubes that were used as the source of NC>2 in
the spiked section of the sampling system, information concerning the cali-
bration of the venturi and dry-gas meter, copies of written communiques MRI
had with the collaborators, a copy of the test instructions that were given
to the collaborators, the NC^, ambient-air sampling system's operational
data, and collaborators' instrumentation and their comments on the method.
II. N02, AMBIENT-AIR SAMPLING SYSTEM
A. General Concept
In the evaluation of a method by on-site collaborative testing,
it is imperative that all collaborators sample the same air. To achieve
this, the following concept was used: Outdoor ambient air is drawn into
the sampling system through a single tube, as shown in Figure 1. The air
is divided downstream into two sections — spiked and unspiked for ambient
air. A controlled flow at a specific value exists in the spiked section;
a comparable amount in the unspiked section, but the latter is uncontrolled.
Temperature-controlled permeation tubes provide the source of NC>2 which is
injected into the spiked section at a desired level. The N02 is then thor-
oughly mixed with the ambient air in a mixing unit--a diffuser. The mixture
is then equilibrated before Lt reaches the sampling station where the col-
laborators sample from identical ports—all to be subjected to the same gas
flow (spiked plus ambient). A continuous monitor is attached to monitor
the gas at the spiked and unspiked sampling levels to monitor the integrity
of the spike. The collaborators sample ambient air simultaneously at an
identical sampling manifold that is at a similar location of the unspiked
section. The gas in both sections is then exhausted to the outdoors.
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B. Design Consideration
The design of the NK^, ambient-air sampling system was based on
the following information and considerations:
1. The flow rate of each of the four methods to be tested is
approximately 0.2 liter/min, with a maximum of 1 liter/min for some of the
instruments that would be used in the instrumental methods.
2. The sampling period of each manual method is 24 hr; each
instrumental method is preferably 24 hr, but could be less.
3. N02 permeation tubes whose rates are approximately 2 ug/min,
which are furnished by the government, will be the source for the spiked
levels of N02. These tubes are to be operated at 25.1°C ± 0.2°C.
4. The number of collaborators for each collaborative test is to
be 10.
5. The maximum number of samples taken simultaneously by each
collaborator during each run of a manual method is four spiked and two
ambient (unspiked) for a total of six samples per collaborator per run.
The multiplicity of samples per run--both spiked and unspiked--is to pro-
vide replicates.
6. The NOo range of concern is 50-300 ug/m3, which is representa-
tive of ambient conditions.
7. There wi]1 be four different N02 spiked levels: high, low,
and two medium. Each level will be maintained throughout the run's period,
within the accuracy of the system.
8. The test period is to be no more than 6 days, which is based
upon the consensus of potential collaborators surveyed.
9. The overall NOo sampling system accuracy is to be 5% or better.
10. The flow control in the spiked section is to be 2% or better.
11. Flow parameters of the spiked section are to be measured.
12. One N09/N0 chemiluminescent device, switched between spiked
and unspiked sampling manifolds (or stations), is to be used as a monitor-
ing instrument.
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13. Only one person from each collaborator's organization will
be needed in the field for each method.
14. There is to be turbulent flow in the spiked section between
the point of injection of the spiked levels of NC>2 and the diffuser to pro-
vide mixing of the spiked N0~ with the ambient air. The diffuser insures
proper mixing. Up to 207o of the stream in each section—spiked and ambient
air--can be sampled to (1) insure that there is capacity in the main stream
to provide each collaborator with his needs in case there is a problem with
one or more collaborators drawing an excess amount and (2) allow the quan-
tity of spiked flow to be drawn from the center of the spiked line where
there is assurance of equilibration. There is to be a minimum amount of
adsorption of the spiked NOo on surfaces, from its source to and including
the sampling manifold. By using Teflon or glass as the material in which
the gases come into contact and by maintaining a high gas flowrate, which
allows for extremely short resident times, adsorbtivity of NC>2 on surfaces
and reaction to water vapor and other losses are insignificant.
15. Each section—spiked and unspiked--is to be similar, includ-
ing material and geometric aspects.
16. Each section is to be under positive pressure so that no
unwanted air would be pulled into the system in case there was a leak.
17. Collaborators' equipment size, configuration and power re-
quirements must be met.
18. Environmental effects on operation of sampling system must
be considered.
C. System Design
The final design of the NOo, ambient-air system is shown in a
general schematic form in Figure 2. Annotated photographs of this operational
system are given in Figure 3.
The input to the system is located outdoors about 2 m above ground
level and approximately 30 m from the building. A valve at the intake of
the 2-in. aluminum tubing provides resistance to the flow of ambient air to
keep the Model 8700 DMP "Tornado" blower at a stable revolution per minute,
and to serve as a gross flow control. A variac insidQ the building serves as
an operational vernier flow control. The blower is located at the input end
of the system to provide positive pressure in the system. It is located out-
doors to keep out the intensive noise it generates and is housed as shown in
Photographs 1 and 3 of Figure 3 to protect it from the elements.
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The line from the blower to the splitter is 2 -in. diameter, aluminum
pipe. It is sufficiently long to serve as a trap for any excess moisture and
to bring the ambient air to room temperature. The splitter is also made of
aluminum. This splitter, shown in Figure 4, reduces large-scale turbulance
from the blower and divides the ambient air stream between the spiked and
unspiked 1-in. diameter aluminum lines with a controlled quantity of
method sampling rate (number of samples x number of
collaborators + monitor number + purge number) _
w in /mm - percent flow drawn through sampling manifold
0.2 jfc/min x (4 samples x 10 collaborators + 1 NO/N02
monitor + purge-line flow) _
percent flow drawn through sampling manifold
0.15
to the venturi, where the air flow in the spiked line is continuously
measured and recorded. The monitor number and the purge number are flows
attributable to the continuous monitor and the purge line of the system,
respectively. The flow on each line—the spiked and the unspiked--is
turbulent—Reynolds number > 2,100--with the Reynolds number being
Q _ Q xfc /rain x 1, OOP cm311
JA. — - —:~^T— *^
0.785 x 0.15 cm^/sec x D sec x 60 sec/min
, 1,000 9 = MOO x 60 =
7.065 D 7.065 x 2.1
Since the spiked and unspiked sections are identical except that
the spiked section also contains the monitoring points 1, 2, 3, 4, and 5
identified in Figure 3 and the NC>2 permeation tube system, only the spiked
section will be discussed.
From the splitter, the spiked line connects to a Singer Al-175
dry-gas meter, which is made by the American Meter Company. (See Photo-
graph 9 of Figure 3.) This flow meter has a pressure drop of 10 mm of
water. Thus, only the input gas-flow temperature and pressure are mea-
sured to correct the flow readings to obtain the true volume of ambient
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air delivered during a test run. This volume is determined from the flow
measured by the meter and the duration of the run, which is measured by an
accurate clock.
The output of the flow meter is connected, as shown in Photographs
7 and 9 of Figure 3, to a stainless steel venturi, which was designed for a
flow of 60 liters/min. This venturi is used as a general flow control de-
vice, and a backup for the gas volume as determined from the gas meter and
associated measurements, which are made by a strain gage pressure trans-
ducer and thermocouples — see Point 5 of Figure 3(A). Both the pressure
drop of the venturi and the temperature of the pressure transducer are re-
corded on analog recorders. The control of the venturi is handled by mon-
itoring its pressure drop. When the value deviates from a reference value,
60 liters/min flow, the flow can be changed appropriately by making an
appropriate adjustment of the variac control in the blower.
The flow temperature measurement (Point 4 of Figure 3(A)) is
actually the gas-flow temperature at the output of the gas meter and at
the input to the venturi, since those two units are physically close
together (about 12.5 cm apart). This temperature measurement can be used
in obtaining accurate gas-flow values.
The output of the venturi is a few centimeters from the input of
the N0£ bleed-in unit as shown in Photograph 9 of Figure 3. These two
units are connected by 10-in. diameter aluminum tubing. From the input of
the N0£ bleed-in unit through the sampling manifold, the system is made of
Teflon.
The N0£ bleed-in unit, as shown in Figure 3(A) and Photographs
7 and 9 of Figure 3, receives ambient air from the venturi and a level of
N02 (a spike) from the t^ permeation-tube assembly (see Figures A and B,
and Photographs 8a-c of Figure 3). Detailed photographs of this bleed-in
unit are given in Figure 5. Photograph 1 of Figure 5 is a close-up showing
the assembled Teflon unit with its metal holding/mounting plates. The gas
stream, or ambient air, enters the opening to the right and passes through
the unit, mixing with the spiked level of N02 which exits through the
tapered smaller tubing shown as concentric to the output of the bleed-in
unit at the left of Photograph 1 of Figure 5. The vertical tube of this
bleed-in unit accepts the NC^ gas from the permeation-tube assembly. This
spiked gas flows downward through this tube, making a 90-degree turn in its
tubing which is inside the unit (as can be seen from Photograph 2 of Figure 5),
and after a short run, mixes with the ambient air as stated before.
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Photo 1 - Detail of NC>2 Bleed-In Unit with Vertical
Tube from Permeation Assembly, Chamber with Central
Tapered Pickup Tube and Stainless Steel Mounting
Components.
Photo 2 - Close-Up Showing Machined Chamber with
Pickup for Bleed-In in Place.
Figure 5 - Photographs of the N02 Bleed-In Unit-
Assembled and Disassembled
14
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The NC>2 permeation system is shown in Figure 6 and Photographs
8a-c of Figure 3 where details of the system are given in the captions of
these photographs. The nitrogen carrier gas is used to flush the N02 into
the system. It is passed through a charcoal and soda-lime scrubber before
it is delivered to the N02 permeation tubes. Also, the flow is set by
means of control valves and rotameters. This flow is monitored during sys-
tem operation. The carrier gas is then fed into four separate branches to
achieve different levels of NC^- (More detail on the permeation tubes and
their arrangements in the branches is given in Appendix B.) The N02 per-
meation tubesi/ are arranged in these four different branches to provide
approximately 50, 100, 200, and 300 ug/m^ flow of N02. Branch 1 has four
permeation tubes, Branch 2 has five permeation tubes, Branch 3 has two per-
meation tubes, and Branch 4 has two permeation tubes. An ASTM calibrated
thermometer (0.1°C or better accuracy) is an integral part of each permeation
tube branch. Each set of permeation tubes is enclosed in a glass tube which
has an inlet for the nitrogen carrier gas and an outlet for the nitrogen
carrier gas/NO? mixture. These NC^ permeation tube enclosure units are
immersed in a temperature-controlled water bath for operation at 25.1°C.
If the temperature of this bath were to vary more than 0.2°C, a correction
would be made from the following relationship:
Log r = 0.034857 (273.12 + T) - 10.29198
where T = temperature in °C of the permeation tube environment, and
r = the permeation rate.
The ambient air and the NO^ flow from the bleed-in unit to the
diffuser where they are well mixed. The diffuser is a few centimeters down-
stream from the bleed-in unit, as shown in Photograph 9 of Figure 3. At
the diffuser, shown schematically and in the photograph in Figure 7, the
gases enter the diffuser through the Teflon tubing (Section A of the
schematic drawing of Figure 6), pass into the spiraled tube and through
its angled holes into the space outside the tube. The flow continues
through the holes in the prescreen block, Item D of the schematic, and
then through a series of Teflon screens, Item E.
!_/ "Operation Characteristics of NC^ Permeation Devices," by Harry L.
Rook, Ernie E. Hughes of NBS, Washington, D.C., and Robert S. Fuerst
and John Margeson of EPA, Research Triangle Park, North Carolina. A
paper presented before the Division of Environmental Chemistry,
American Chemical Society, Los Angeles, California, 31 March - 5
April 1974.
15
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Nitrogen Gas
Shutoff Valve
Charcoal & Soda Lime Filter
Control Valves
Rotameters
NO2 Permeation
Tube Holders
Thermometers
Temperature Controlled
Water Bath
Control Valves
to NC>2 Bleed In Unit on
Spiked Line (See Figure 3)
Figure 6 - Schematic Drawing of the NC>2 Permeation Tube Assembly
16
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The homogeneous mixture passes through an equilibration section that
is Teflon tubing 1.0 m long. This section of tubing provides the final
equilibrated concentration. This tubing is connected to the input of the
sampling manifold. (See Photographs 10 and 11 of Figure 3.)
The 45-port sampling manifold is constructed of Teflon except for
its metal plates which are entirely external. Photographs 1-3 of Figure 8,
which show external and internal views of the sampling manifold and a sche-
matic drawing, describe the operation of the manifold. The stream of the
homogeneous mixture of ambient air and a spiked level of NC>2 flows through
the bottom portion of the manifold, into the exhaust line. Section A of
the manifold is in the pickup tube through which flows the total volume of
gas sampled by the collaborators. The inlet to this pickup tube is located
such that this volume is drawn from the central portion of the main stream.
The sampled volume flows past a mixing impeller (B) and then into the main
chamber (C) of the manifold. In this chamber, the flow is spread evenly to
the 45 symetrically located exit channels (D). The gas in the main chamber
that is not drawn through the exit channels to the collaborator ports flows
out the exhaust duct or purge line which has a control valve. Both exhaust
lines from the manifold join downstream to form a common exhaust tube, which
also contains a flow control valve.
One port of each sampling manifold is used to monitor the pressure
in the sampling manifold to determine if it remains positive (see schematic
drawing of Figure 3). Another port of each manifold is used to monitor the
N02 and NO levels being sampled by the collaborators. A Bendix Model 8101 B
chemiluminescence NO-N02-NOX analyzer is used for this and is switched be-
tween the spiked and unspiked manifolds. (See Photograph 12 of Figure 3.)
D. System Checkout
Readying the system for the collaborative test comprised three
principal areas of activity: (1) determination of levels of NO and N02>
both ambient and inside the building; (2) checkout of the sampling system,
including monitoring devices and test instrumentation; and (3) checkout of
the sampling system as an operational system. These three areas are dis-
cussed below.
1. Ambient levels of NO and NO?: Ambient levels of nitrogen oxides
at the test site were generally low, but there were considerable variations at
these levels. Since the test site is located in a rural area south of Kansas
City where there is very little industry, the primary factors that influence
NOX levels at the site are wind speed and wind direction.
18
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During tests of NC) levels using MRI' s Bendix Model 8101 B chemi-
A.
luminescence NO-N02-NOX analyzer for 24-hr monitoring, the lowest levels were
found when the wind was from the south. Both NO and NC>2 seldom exceeded
20 ug/mr when the wind was from the south, and periods of more than 1-hr
duration were measured when readings were indistinguishable from the purified
zero gas used to calibrate the analyzer.
With northerly winds, NCL levels were generally between 30 and 50
pg/m-' and NO levels were approximately 10 ug/m^. As expected, the ambient
levels followed an inverse relation with respect to wind speed. The highest
daily readings were coincident with the morning and evening rush hours.
These peak levels generally began at about 7:00 AM and again at 5:00 PM and
lasted between 2 to 4 hr.
The highest recorded levels of N0£ occurred under calm wind con-
ditions when the light vehicular traffic in the vicinity of the test station
generated levels in excess of 100 ug/m^. NO levels did not exceed N02 levels
at this site.
The ambient background levels at the test site were quite typical.
Over a 24-hr period, average N02 levels were 10-50 ug/nP, and NO levels were
of the order 10-20 ug/m3. During any 24-hr period, maximum N02 levels were
generally several times higher than the minimum levels. Indoor readings
were similar but did not show the sudden changes often found when monitor-
ing outdoor levels.
2. Subsystems and units: The venturi and dry-gas meter were
calibrated using a 1.0-ft^/rev., wet-test meter, as shown in Figure 9.
Refer to Appendix C for further information concerning the calibration
method.
The operation of the centrifugal blower was checked by operating
it at the normal flowrate for several days. Very little brush wear was
found after this period. The only long-term drift found was a slight de-
crease in flowrate. A compensation for this increase was easily made by
adjusting the Variac control.
The thermocouples were calibrated using a null-point potentiometer
before and after the collaborative test. Checks of the gas temperature before
and after the dry-gas meter revealed no differences in readings so that a
single thermometer after the gas meter was used.
Recorders were checked by MRl's electronics shop and these recorders
were operated successfully over a period of several days on the sampling sys-
tem prior to the test.
20
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Splitter
Wet Test
Meter
Temp
Reading
Spiked
Line Bubbler
NC>2 Bleed-in
Venturi
Pressure
Reading
Figure 9 - Venturi and Dry-Gas Meter Calibration System
21
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Flowmeters of the permeation tube assembly that measure the nitrogen
flow were calibrated by the manufacturer to 1% accuracy. Thermometers that
were used to measure the gas temperature in the permeation tube holders are
ASTM type that are accurate to within 0.1°C. The permeation tubes used were
calibrated by the National Bureau of Standards and checked by EPA. (See
Appendix B.) The entire permeation assembly from the tube holders to the
pickup fitting, where the spiked gas enters the main gas stream, was checked
for leaks with Snoop and found to be airtight. A check of NO levels in the
x o
tanks of prepurified nitrogen carrier gas found no NOo and 40 ug/nr3 NO. The
entire system was checked by running it continuously for several days. Water
addition to the constant temperature bath was the only maintenance required.
The temperature variation of the permeation tube bath during this time was
less than 0.1°C.
The Bendix NO Analyzer was checked at MRI by a Bendix field repre-
X
sentative. The difference in spiked and unspiked readings agreed within 107o
of the calculated spike levels at all levels. The instrument was stable
and reliable when operated continuously at the levels found during normal
testing. Checks with calibration gases reveal that the catalytic converter
efficiency does fall off sharply above 400 ug/rn-^.
The symmetry of the sampling ports was checked in two ways. The
primary way was that the pressure drop at each port was measured under the
normal load of 200 cc/min. This test showed that all ports gave a pressure
drop of 1.5 cm of water ± 0.5 cm. Such a pressure drop may bt considered
to be insignificant and should have no effect on sample flows from the
ports.
A second way was to connect the N02 monitor to ports of the spiked
and unspiked sampling manifolds and measure the level of NO 2 in micrograms
per cubic meter. This was done in two ways: the system under a load, e.g.,
a spiked level of approximately 350 ug/m^; and an unloaded condition where
just ambient air was passed through each section—spiked and unspiked--of
the NOo sampling system. In both cases, the N0£ monitor showed no variation
between ports when connected to four ports spaced equally about the manifold.
3. System operation: Identical materials and dimensions are used
on the spiked and unspiked sections of the N02 sampling system. Handling and
treatment of all components was also identical.
Flowrates of the spiked and unspiked sides were within 10% of each
other with all dampers open. In normal operation, the exhaust dampers are
adjusted to give a positive pressure of 2-4 mm of water at the sample manifolds.
Once set, this pressure is stable.
22
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The rise and fall times to equilibrium in response to changes in
a spike level were checked. Rise time was less than 15 min and fall time
was less than 5 min (when permeation tubes were disconnected). The fall
time is essentially that of the analyzer response time, allowing for the
purge time of the sample lines. The rise time is longer than the fall time
because of the increased pressure that the carrier gas stream must work
against when a set of permeation tubes are connected. Some flow reversal
in the permeation tube holders occurs after connection.
Since the response times were essentially limited by flowrates
and instrument response, no observable adsorption effects were noted.
Checks of NOX levels found at the sampling ports agreed, within normal
accuracy limits, with those measured outside the building. At the 50-
ug/nP level both readings were within 5 jig/m-^ (0.57o of full scale) which
is within the accuracy of the monitoring instrument. Thus, the unspiked
samples at the sample ports accurately reflect ambient levels, and the
sampling system may be considered to be inert with respect to
III. TEST SITE
The general criteria one would use in selecting a site include the
ambient level of NC^ and variation thereof, general meteorological and
climatological conditions, work facilities for the collaborators (adequate
space, facilities, housing, etc.), cooperation of the organization furnishing
the site, logistic aspects, and local lodging accommodations.
The levels of N02 required are those representative of ambient N02
conditions, which are in the range of a few micrograms per cubic meter to
300 ug/m^. These levels could be achieved at one site with a low level of
N02 by spiking the ambient air with various levels of N02 in a manifold sam-
pling system (see Section II, Part A).
MRl's field station (see Figure 10), which is located in a rural
area south of Kansas City, meets all the criteria and was selected as the test
site. The N0«, ambient-air sampling station is housed in Building 3 shown in
Figure 10. The input to the sampling system is located outside the building
near the roadway (see Photograph 3 of Figure 3).
The test facilities are described in conjunction with the sampling
system in Section II, Part C. Photographs of the facilities are given in
Figure 11. Photograph 1 shows the circular tables that house the sampling
manifolds and the collaborators' sampling trains. Each table--spiked and
unspiked--has a multiplicity of AC power receptacles, with each collaborator
23
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having its own branch of outlets. Each branch has its own circuit breaker
and branch indicator (see Photograph 2 of Figure 11). This arrangement is
to protect one collaborator from another in case one collaborator may have
a power failure due to faulty equipment.
Photograph 3 of Figure 11 gives a close-up view of some of the
collaborators' trains positioned in their table areas (see Figure 11).
Photograph 4 of Figure 11 gives a view of part of the bulletin board where
test instructions and general information was posted.
Photographs 1, 2, and 3 of Figure 11 show that the windows on the
north side of the building were boarded to keep electromagnetic radiation
from entering the building. With this blockage and a temperature control
system in the building, the 25.1°C permeation bath was able to be maintained
at that temperature throughout the four 24-hr runs with no detectable devia-
tion from the 25.1°C temperature, except for a few hours when the deviation
was 0.1°C.
IV. SELECTION OF COLLABORATORS
A principal activity was to compile a list of potential collabora-
tors and from this list select 10 to perform the testing according to the
tentative sodium-arsenite method. Information was obtained from EPA (names
and addresses of 150 organizations) and from MRl's files to compile a list
of nearly 200 potential collaborators.
A letter was sent to 162 organizations seeking their desire to
participate as a volunteer collaborator on this test-and-evaluation program.
Attachments to this letter were (1) a "Collaborator Form" to be completed
which surveyed their experience with the four methods, methods they had used,
equipment they could make available for the tests, acceptable length of test
period, etc., and (2) a copy of the method writeup for the first collaborative
test--the sodium-arsenite method. A copy of this letter and the collaborator
form are given in Appendix D.
A majority of the responses indicated the desire that a test period
for a method be no more than 6 days.
Ten organizations were selected for the sodium-arsenite collabora-
tive test from the 39 organizations that responded in the affirmative to
participate in the test. The selection was based upon the following criteria:
25
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SPIKED
SAMPLING MANIFOLD
COLLABORATOR
AREAS *
* For Unspiked Manifold--Colaborator areas marked in reverse
order—counter clockwise.
Figure 12 - Collaborators' Sampling Areas at the Test Site
27
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1. Willingness to participate on a volunteer basis,
2. Technical capabilities,
3. Related past experience,
4. Availability,
5. Ability to furnish sampling equipment, instruments, and mate-
rials required to perform the test strictly according to the method, and
6. Type of organization (industrial, educational, governmental--
local, state, federal—etc.) .
The information needed to make the selection based on the above criteria
was obtained from the collaborator forms that were returned, and from sub-
sequent telephone conversations with the candidate collaborators.
The 10 organizations selected as collaborators for the sodium-
arsenite collaborative test were:
TEXAS AIR CONTROL BOARD
8520 Shoal Creek Boulevard
Austin, Texas 78758
512-451-5711
1 j t
(Jimmie S. Payne, Mr. Fernando Martinez±j-=-' )
Air and Industrial Hygiene Laboratory
CALIFORNIA DEPARTMENT OF HEALTH
2151 Berkeley Way
Berkeley, California 94704
415-843-7900
(Mr. Emil R. de Vera, Mr. Kenneth Smith-
MECKLENBURG COUNTY HEALTH DEPARTMENT
1200 Blythe Boulevard
Charlotte, North Carolina 28203
704-374-2607 ^ o/
(Mr. James T.
NATIONAL BUREAU OF STANDARDS
Chemistry Building
Washington, D.C. 20234
301-921-2886
(Dr. John K. Taylor, Mr. Bob
Deardorf f ±jj=.' )
CITY OF PHILADELPHIA
Air Management Services Laboratory
1501 East Lycoming Street
Philadelphia, Pennsylvania 19124
215-288-5177 i o/
(Mr. Donald
KENTUCKY DIVISION OF AIR POLLUTION
311 East Main Street
Frankfort, Kentucky 40601
502-564-4446
(Ms. Diana Dunker
2/
*—
I/ These individuals performed the sampling at the field site.
2/ These individuals performed the analyses of the samples.
28
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KENNECOTT COPPER CORPORATION
Post Office Box 11299
Salt Lake City, Utah 84111
801-322-1533
(Dr. Robert J. Heaney, Mr. Lynn
Hutchinson —*-=•' )
LOS ANGELES COUNTY AIR POLLUTION CONTROL
DISTRICT
434 South San Pedro Street
Los Angeles, California 90013
213-974-7573
(Mr. Abe B. Moore,—' Ms. Violeta Vita—')
KANSAS CITY AIR POLLUTION CONTROL
LABORATORY
2 Northeast 32nd Street
Kansas City, Missouri 64116
816-274-1206
(Mr. Glenn Smith—2— )
INSTITUTE OF GAS TECHNOLOGY
3424 South State Street
Chicago, Illinois 60616
312-225-9600
(Mr. Robert A. Macriss, Mr. Jon
Zimmer,—' Ms. Eugenia Mann— )
These organizations will be referred to as Collaborators A through
J, without defining which is A, B, etc., to allow the organizational data to
remain anonymous.
V. STATISTICAL DESIGN
A. General Considerations and Comments
The purpose of this collaborative test was to determine the pre-
cision and bias of the sodium-arsenite method. A major element of the
collaborative test was to have an experimental design that would allow this
purpose to be met. Considerations that formed the bases of this design,
which is given later in this section in a formal manner, are:
1. Challenge (spike) levels of N02»
2. Ambient levels of N02,
3. True values of N02,
4. Sampling time of a run,
5. Test period of the method,
6. Number of collaborators,
7. Number of samples per run,
8. Interferences,
9. Adsorptivity,
10. Sampling ports, and
11. Instrumentation.
!_/ These individuals performed the sampling at the field site.
2_/ These individuals performed the analyses of the samples.
29
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Challenge level of NO? is an experimental design variate. The
following four levels of challenge were selected based upon the normal
range of values found in ambient air on a 24-hr average basis: one low
level in the order of 50 ug/m3; two medium levels, one near 100 ug/m^ and
the second near 200 ug/m3; and one high level of approximately 300 ug/m^.
A challenge level should be steady state, or continuous at a specific
level, plus or minus acceptable deviations — less than ± 2%. The source
of N02 was permeation tubes constructed and calibrated by the National
Bureau of Standards. (See Appendix B.)
Ambient levels should be representative, preferably less than
10 ug/nr^. Since the ambient levels are the actual ambient levels of N02
at the test site, those levels present during the time of testing may vary
some from this criteria (see Section II, Part D). The ambient levels will
be mixed with the challenge Levels to provide the spiked challenges. There
will be just ambient challenges which are identical with the ambient por-
tion of the spiked challenges. The collaborators will sample both spiked
and ambient challenges simultaneously.
For a run, the true value of N02 sampled by the collaborators will
be taken as the NCL spiked level generated by the permeation tube assembly
plus the average value of the. ambient challenges sampled by the 10 collabora-
tors.
The sodium-arsenite method requires a sampling period to be 24
hr.
From the survey for volunteer collaborators, it was determined
that 6 days would be the limit for a test period o£ a method. Thus con-
sidering this period, the mandatory 24-hr sampling period (or a run), travel
time, and orientation, set-up and switch-over time (time in between runs),
four runs would be the maximum possible.
Ten collaborators were deemed a sufficient number to obtain a cross-
section of the population of the type organizations that would be involved in
sampling N0?, be within acceptable project costs, and provide statistical
significance with the results.
Replicate samples are desirable and generally needed. In this test,
replication is constrained by the test period and the duration of a run, and
thus any replicates must be of the nature of simultaneous sampling by collab-
orators using as near identical trains as possible. This type replication,
in turn, has constraints, which include principally the number of collabora-
tors, space limitations at the test site, size of the NOn sampling system
and cost limitations. Naturally some of these are interdependent.
30
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An important consideration for the sodium-arsenite method is that
of interferences, such as NO and ratios such as NC>2/NO and NC>2/0 . These
factors will vary depending upon geographic location, time of year, etc.
The interference consideration was not included in the experimental design,
since EPA told MRI that it had been covered by EPA's work.
Adsorptivity is of concern because of the possibility of error
in the NC>2 level received by the collaborators' sampling devices in contrast
to the known level of the challenge--from both the standpoints of increasing
and decreasing the challenge level from run to run. Teflon material was used
from the NCL bleed-in port through the sampling manifold to minimize if not
eliminate the adsorptivity factor. For further assurance, prior to commencing
a run, the challenge could be run for a sufficiently long period so that all
surfaces exposed would have adsorbed their limit or lost their limit of
deadsorbance. Both aspects were covered; Teflon was used in the construction
and sufficiently long challenges were made to the system prior to commencing
a run.
The port-to-port effect did not need to be incorporated in the
il
1:
Part D).
experimental design because results of the evaluation of the NO , ambient-
air sampling system indicated that all ports were identical (see Section II,
The major considerations with regard to instrumentation for the
sodium-arsenite collaborative test were: (1) MRI would only instruct the
collaborators that they were to use the sampling equipment and calibra-
tion equipment specified in the method writeup, and (2) MRI's monitoring
instrumentation and test instrumentation used in the calculation of the
ambient-air system was sufficiently reliable and accurate. In both cases,
all requirements were met.
To minimize bias, which was of keen concern, the collaborators
would need to prepare absorbing reagent, etc., at their home laboratories.
The only purpose of going to the field site would be to collect samples.
Then the samples taken in the field would be returned to the collaborators'
home laboratories to be analyzed to eliminate any bias from the chemical
analysis phase of the collaborative test.
B. The Formal Design
The N02 data are collected according to a two-way analysis of
variance model with the analysis of primary interest being estimation of
the components of variance and the bias. Thus, the mean square errors can
be constructed.
31
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Specifically, we have:
Xijk = » " Ci + Lj + CLij
where u = overall mean,
C-^ = ifck collaborator (i = 1,..., 10; C. is a random factor),
Lj = jth level of N02 (j = 1,..., 4; L, is a fixed factor),
CL. . = collaborator-level interaction,
ew-i n = error term (k = 1,..., 4V ij),
t~V\ t~Ti t~h
X.., = k response observed by iun collaborator on jcn level.
The expected mean squares are:
E (MSC) = o£ + 16 o£, E (MSL) = ^ + 4 °CL + 4° °L' E ^CL5 = ae + 4 °CL
and
E (MSe) = o-
Although the F-tests for significant effects were performed for
completeness, the primary object is the components of variance analysis; in
particular, the components cr (variance of repeated observations) and
-------
In any analysis of variance the homeoscedastic assumption must be
validated. It was found that the measurement error was not uniform through-
out the experiment but also not proportional to the level of N0£. Therefore,
no data transformation was made.
Outliers were deleted before analysis, and the frequency of them
noted. Due to computational errors, two of the 10 collaborators contributed
unduly to the bias. Therefore, the data were analyzed with and without
their presence.
VI. COLLABORATORS' FIELD SAMPLING
The collaborative test took place at the MRI Deramus Field Station
I/
(see Figures 3, 10, and 11) during 4-8 February 1974.— The 10 collaborators
named on pages 29 and 30 started the test at 0830, 4 February, with an
orientation (see Figure 13). The N02» ambient-air sampling system they used
was shown and explained to them. The written instructions that comprise
Appendix E were given to and discussed with the collaborators. After this
orientation period the collaborators set up their sampling trains in prepa-
ration for the first run (see Figures 13 and 14). They were ready to start
sampling at 11:50 AM, 2 hr ahead of schedule. The actual schedule of the
four runs that took place is given in Table I. All 10 collaborators cleared
the site by 1500, Friday afternoon, 8 February. There were no system opera-
tional problems or collaborator operational problems.
Each run was 24 hr in duration. The collaborators were at the
site from 2 to 3 hr prior to the start of a run, or completion of a run.
They stayed through the changeover to the subsequent run and from 1 to 2
hr thereafter.
From only observations and no communications controls, MRI ascer-
tained that all collaborators followed the sampling procedures given in the
method writeup, with only minor deviations. Figures 14 and 15 give photo-
graphs of collaborators preparing their equipment for a test, some of the
sampling train setups, and these trains in operation.
Field data were recorded in duplicate by the collaborators on
data sheets designed by MRI for this test (see Figure 16). A copy of this
data sheet was collected from each collaborator after the completion of
a run, and before a subsequent run would be started. The collaborators
retained their copies for recording subsequent analysis work at their home
laboratories.
I/ The sodium-arsenite test was first scheduled for the first part of January
1974. A change in the schedule for the development of the N02, ambient -
air sampling system necessitated rescheduling the test.
33
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Front Row: Diana Dunker, Bob Deardorff, Fernando Martinez, Abe Moore,
Paul Constant JL/, James Ward
Back Row: Jon Zimmer, Lynn Hutchinson, Glenn Smith, Donald Kutys,
John Margeson JL/, George Scheil_L/, John LaShelle _L7,
Kenneth Smith
_L7 MRI personnel.
2J EPA Project Monitor.
Figure 13 - Photograph of Field Personnel of the N02 Collaborative Test
(Sodium-Arsenite Method); MRI Field Station; 4-8 February 1974
34
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TABLE I
SODIUM-ARSENITE COLLABORATIVE TEST SCHEDULE
N02 Spiked Level Date/Time
Run (yig/m^) Started Completed
1 311 2-4-74 at 1153 2-5-74 at 1153
2 94.7 2-5-74 at 1229 2-6-74 at 1229
3 203 2-6-74 at 1302 2-7-74 at 1302
4 56.1 2-7-74 at 1330 2-8-74 at 1330
36
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Figure 15 - Photographs of Collaborators' Sampling Trains
37
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MRI DERAMUS; FIELD STATION - K.C. MO.
NITROGEN DIOXIDE DATA SHEET - SODIUM ARSENITE METHOD
Sampling
Collaborator Run Number
Sampled by Sampling Port Number
Sampling Train No.
Bubbler Identification No.
Rotameter Description (make, model, etc.,)
Rotameter reading at start at finish type of ball
Start:Date Time Finish:Date Time
o
Sampling duration (min) Sample flow rate (cm /min)
Total air volume sampled (m )
Remarks:
Analysis
Date of Analysis
Analyzed by: Person Organization
Standardization plot slope (absorbance units/ug N02/ml)_
Absorbance of sample against blank (540 nm) Aliquot (ml)
N02 Concentration (ug/m^)
Remarks:
Figure 16 - Nitrogen Dioxide Data Sheets—Sodium-Arsenite Method
38
-------
During 31 January - 1 February--just prior to the start of the
test on Monday, 4 February--MRI prepared standard samples. These samples
were drawn from the spiked line (a challenge from the M^ permeation tube
source) into absorbing solutions which were contained in 150-ml impingers.
The solutions from all impingers were mixed to provide a homogeneous sample.
Individual samples were then prepared for the collaborators and MRI. Each
collaborator was given one N0£ sample and one blank (absorbing solution only)
to be analyzed at the home laboratory along with his test samples. MRI
followed the method in preparing for sampling and sampling with the excep-
tion that the trains were scaled upward.
The samples taken by the collaborators, as well as MRI's standard
samples given to them, were either taken with them when they returned home,
or shipped to them by MRI. The samples were shipped via air mail on different
days to insure against loss of all samples of a collaborator in case a ship-
ment was lost or destroyed.
MRI had a laboratory supervisor who was in charge of the N02>
ambient-air system operation. He was on duty from 0800 to 1700 each day,
which was the period of run starts and completions. He was available any-
time during the 24-hr runs, if any problems arose, as was the program manager.
There was a technician on duty throughout each run at all times
during the test. These people monitored the sampling system operation,
recording operational data and general observations. A general log book was
kept as well as the log sheets for operational data. Copies of these log
sheets are given in Appendix F.
VII. ANALYSES OF SAMPLES
This section discusses the analyses performed by the collaborators
and by MRI. The collaborators' analyses were of the samples they took during
the test from both the spiked and unspiked lines, and the standard samples
prepared by MRI and given to them. For each of the four test runs in the
field, each collaborator had four spiked samples and two unspiked samples.
In addition, each collaborator had two standard samples—one blank and one N02-
A. Analyses Performed by the Collaborators
The collaborators performed the analyses of their samples accord-
ing to the procedures given in the Sodium-Arsenite Method, with two exceptions:
(1) on 5 February 1974 all collaborators were asked to measure the absorbance
39
-------
at 530 run rather than 540 as stated in the method writeup (see Section VII.B.
for more details); and (2) Collaborator A who corrected his results for pres-
sure and temperature. In eight out of 10 cases, the collaborators' represen-
tative who performed the field sampling also performed the analyses of the
samples at the collaborators' home laboratory. Only Collaborators B and C
had a different person perform the analyses of the samples. Information on
the collaborators' analysis instrumentation as well as their comments on the
test are given in Appendix G.
B. Collaborators' Results
The one primary set of results the collaborators furnished MRI is
the results of their chemical analysis of their samples. These data*which
include calibration and absorbance data relating to these results, as well
as raw field data that resulted from sampling in the field, are given in
Volume II of this report.
For convenience, these final results of the collaborators' analyses
are summarized in Table II. There are two sections to Table II: the top
portion that gives measurements from the test samples taken by the collabora-
tors; and the bottom portion that gives the results of the collaborators'
analyses of the standard samples given them. Column 1 of the top portion of
Table II gives the N02 level that is mixed with the ambient air to form the
run's challenge. It does not include the quantity of N02 that was present
in the ambient air (see Section VIII for information on the "True Value").
Column 2 and suceeding even columns provide the NC>2 values the collaborators
measured during each run. There are six values per run; two are from the two
samples taken from the ambient air (unspiked) manifold; and four from the
spiked manifold (each collaborator pulled all six of his 24-hr samples simul-
taneously). Column 3 and succeeding odd columns provide the values MRI ob-
tained when it checked the collaborators' calculations.
MRI's check of the collaborators' result was a gross overall check
to determine if there were major errors due to, for example, misplacement of
the decimal point. Minor difference could be attributed to the reading of
the collaborators' calibration curves.
C. Analysis of Samples by MRI
Standard samples* prepared by MRI as well as some samples MRI ob-
tained from the NO , ambient air sampling system just prior to the collabora-
tive test were analyzed by MRI according to the Sodium-Arsenite Method, using
These were from the same solutions as were the standard samples given to
the collaborators.
40
-------
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41
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a Varian-Cary Model 118 UV-Visible Scanning Spectrophotometer. The results
of this analysis showed that maximum absorption occurred at 530 nm, rather
than 540 nm as stated in the method writeup. The set of samples that gave
the 530-nm peak was processed using Product No. N-21, Lot No. 711520 which
was taken from a bottle that had been previously used and had been on the
shelf for an unknown time. When a capsule of NEDA Product No. N-30, Lot No.
790988, Sample 2 of Table III was used, a 542-nm peak was obtained. Thus,
the question arose as to which peak was the correct one.
TABLE III
DATA ON NEDA MATERIALS USED IN THE SODIUM-ARSENITE
METHOD, ABSORPTION PEAK INVESTIGATION
Sample
No.
Source
Product
No.
Lot No. Form
J. T. Baker Chemical
Company
Matheson, Coleman & Bell
Manufacturing Chemists
Wavelength for
Method
(nm)
1 Fisher Scientific Company N-21 711520 Powder
2 Fisher Scientific Company N-30 790988 Capsule
3 Fisher Scientific Company N-30 730606 Capsule
R-702 304001 Powder
530
542
542
542
NX230 Not identified powder 542
In an attempt to gain an explanation for the difference in wave-
lengths, a limited investigation was undertaken using two additional sources
of NEDA material (Samples 4 and 5 of Table III) plus a new sample (No. 3) from
the original source purchased specifically for this investigation. A solu-
tion of NEDA was made from each of these materials, and each solution was
reacted, according to the Sodium-Arsenite Method, with a solution containing
0.1 ug N02~/ml. Each resulting colored solution was scanned between 575 and
500 nm using the Varian-Cary Spectrophotometer. Using the three new samples
the reacted solutions peaked at 542 nm, similar to what Lot 790988 had given.
42
-------
As a further point of investigation, a diluted solution of unreacted
NEDA* from each of the five samples noted in Table III was scanned, using the
same Varian-Cary Spectrophotometer. The solution prepared from Samples 2
through 5 gave the results shown in Figure 17--a broad absorption band at 320
nm. The solution prepared from Sample 1 had four minor absorption bands--
peaking at 305, 290, 280 and 268 nm--in addition to the major band of 320 nm.
These latter results are shown in Figure 18.
To check the effect of possible pH variations on the maximum absorp-
tion of the NEDA solutions, the absorbance of a sample mixed with reagents as
per the method was first run from 520-550 nm on a Beckman DU. Maximum absorbance
was found to be 540 nm. The pH was 1.9. To the remaining portion of this
sample (40 ml), 10 millimoles of NaOH was added in an attempt to raise the
pH. The pH changed to 3.0 after the addition and the maximum absorbance
remained at 540 nm. From this test, the solution is very well buffered by
the phosphoric acid and the absorption maximum is not affected by reasonable
pH variations.
Results of this limited investigation suggest that impurities in
the NEDA material may be the cause of the different absorption peaks.
D. Test Site Operational Measurement Data
The results of monitoring the N02 ambient-air sampling system
during the four runs of this test are given in Appendix F. These data are
summarized in Tables F-I through F-IV of Appendix F, for Runs 1 through 4.
Column 1 of these tables gives the date and time measurements were made;
Columns 2 through 10 give NOo sampling system data; Columns 11 through 15
give calculated flow rates and spike levels; and Columns 16 through 21 give
information on ambient conditions at the test site.
VIII. STATISTICAL ANALYSIS OF COLLABORATORS' RESULTS
The collaborators sampled from both the spiked and unspiked lines
of the N02 ambient-air sampling system, providing two sets of collaborators'
results. The two sets of results were used to determine true values of the
levels of NOn that comprised the challenges to the collaborators' sampling
trains. In addition, for both sets of results, there was an analysis of
variance made to estimate biases and components of variances--the variances
of repeated observations and variances between collaborators.
* NEDA = N-(l-naphthyl)-ethylenediamine dihydrochloride.
43
-------
200
250
350
WAVELENGTH, nm
400
Figure 17 - Typical Scan of Unreacted NEDA Solutions
That Gave a Broad Absorption Peak at 320 nm
44
-------
1.0
0.9
0.8
0.7
0.6
U
Z
S 0.5
O
0.4
0.3
0.2
0.1
J I
250 300 350
WAVELENGTH, nm
400
Figure 18 - Typical Scan of Unreacted NEDA Solution That Gave Minor Absorption
Peaks, as Well as a Major Absorption Peak at 320 nm
45
-------
An analysis of variance model for the collaborative test is:
Xijk = V- + Ci + Lj + CLij + ek(ij)»
where |i = over all mean
C-j^ = itn collaborator, i = 1, . . . , 10
LJ = jth N02 level, j = 1, . . . , 4
ek(ii)= residual error in k measurement in ij cell
k = 1, . . . , 4 V- ij
CL.ji = collaborator "level interaction
X^.i = ijktn bias, i.e., ijkt^1 determination - true value.
The NC>2 level is a fixed factor, but the collaborators are considered
to be a random factor; i.e., the 10 collaborators numbered A through J used in
the experiment are considered a sample drawn from a population of possible
collaborators. Thus, the expected mean squares (EMS) are:
Term EMS
ae + 16
CL a? + 4 a£r
40
The true value is the spiked level of N02 plus the ambient N02—the
ambient level, of course, being unknown. Therefore, a true value is taken
as the spiked amount plus the average ambient determination of all collabora-
tors. For example, the true level 1 of N02 is taken as 311.7 ug/nr>, because
299 |-ig/m N02 were spiked and the average ambient reading from the 10 col-
O
laborators was 12.7 p,g/m .
An individual response is a bias (collaborator's reading of spiked
line minus the true value). For example, Collaborator A's first reading of
level 1 in the spiked line was 270.6 ug/m3, so Xm = 270.6 - 311.7 = -41.1
ug/m3, etc. Since subtracting the true value is merely coding the data, the
components of variance are unaffected by the use of biases rather than spiked
readings as the response.
46
-------
There was one missing data point (Xj^)' an<^ two other readings
' ^832 ) were discarded as outliers.* Thus, three artificial readings
were inserted (via minimizing a|) an2 level are probably more realistic than the total
-------
TABLE V
ANALYSIS OF VARIANCE
(All 10 Collaborators)
Source
C
L
CL
e
dF
9
3
27
117
SS
31,415.2
3,165.6
16,341.3
8,215.6
MS
3,490.58
1,055.21
605.23
70.22
F
49.71
1.74
8.62
—
dF = Degrees of freedom.
SS = Sum of squares.
MS = Mean square.
F = F ratio or F test.
TABLE VI
ANALYSIS OF VARIANCE
(Collaborators A and
Source
C
L
CL
e
dF
7
3
21
94
SS
7,406.9
704.2
11,335.0
6,256.0
I Deleted)
MS
1,058.
234.
539.
66.
12
72
76
55
dF = Degrees of freedom.
SS = Sum of squares.
MS = Mean square.
F = F ratio or F test.
F
15.90
< 1.00
8.11
48
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A. Analysis of the Spiked NC>2 Measurements
A discussion of Tables V and VI (a discussion of biases) will
follow, and then the components of variance analysis will be presented. In
all the following discussions only the eight collaborators free of computa-
tional errors will be used.
1. Biases: Collaborators differ significantly in their average
bias, and the "calibration curves" (bias versus level) for the various col-
laborators are significantly nonparallel. However, bias is not a function
of the level of NC^.
In general, collaborators read about 6.2 pg/m3 low (see Table VII)
The collaborators can be divided into five groups* with one collaborator (J)
reading without bias. Two collaborators read with a positive bias, and
seven collaborators (including A and I) have a negative bias. (See Table
VIII).
TABLE VII
BIAS (ug/m3) PER N02 LEVEL
N02
LI (311.7)
L2 (133.2)
L3 (228,3)
L4 (84.1)
All levels
(average 184.3)
Eight Collaborators
Bias
-9
-4
-5
-5
-6
.7
.7
.7
.1
.2
% True
3
4
2
5
3
* Via the Fisher method.
49
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TABLE VIII
COLLABORATOR BIASES (ug/m3) - ALL N02 LEVELS
Average Bias Bias/True
Collaborator (ug/m3)
B -25.1 13.6 1
C --8.7 4.7 3
D 6.4 3.5 5
E -6.1 3.3 3
F -16.6 9.0 2
G -4.9 2.7 3
H 6.0 3.3 5
J 0.6k/ 0.3 4
The CL interaction term is significant, i.e., the bias versus
level curves per collaborator are not all parallel. (See
Table IX and Figure 19.)
a/ Members of a group do not differ significantly in
average bias.
b_/ Not significantly different from zero.
TABLE IX
COLLABORATOR PERCENT BIAS PER LEVEL
Collaborator 84.1 ug/m3 113.2 ug/m3 228.3 ug/m3 311.7 ug/m3
B -14 -12 -15 -13
C -5 -5 -5 -5
D -2-3 93
E -3 -1 -3 -4
F -12 -13 -9 -6
G -5 -4 -1 -2
H 2334
J 1211
50
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Note that almost all the CL interaction is due to the variable
bias per level exhibited by Collaborator D. In other words, although there
is a significant CL interaction, seven of the eight collaborators produced
a relatively uniform percent bias, irrespective of the NC>2 level.
9 9
2. Components of variance: The components of variance cr~ and a
1 99
are shown in Table X. The components is just as physically realistic, so
that a set of collaborators could be said to read 6.2 ug/m3 too low,
± 31.4 ug/m3 (vcr| + a£ + cfci =15.7 ug/m3). The customary definition
of reproducibility is preserved in the text.
52
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TABLE XI
MEASUREMENT ERROR (cre) PER N02 LEVEL
NC>2 Level Eight Collaborators
84.1 ug/m3 5.38
113.2 ug/m3 7.25
228.3 ug/m3 9.80
311.7 ug/m3 9.33
The values of cre in Table XI are probably better to use (in con-
junction with 2 level.
After copies of the data were sent to all collaborators, Collab-
orator I noticed its large negative bias and found the reason for it. Thus,
Collaborator I corrected its readings, after being shown in effect that it
was biased. Since Collaborator I presumably would not have discovered its
error if it alone had performed the experiment, the results computed from its
mistaken readings are the ones heretofore reported and discussed.
B. Summary Discussion
There is a general bias to the NO determinations, but is is rela-
tively small (•** 3%) and independent of the N02 level. (Unless, of course,
a computational bias is inserted.) Various collaborators differ in the amount
of bias shown, but this variability is also relatively small, i.e., the
variance between collaborator means is not too large (crc ^ 4% true value).
The measurement errors are essentially uniform for all collabora-
tors, but do depend on the N02 level. The measurement error is about the
same size as the collaborator error if no computational errors are made
(cr «w 4% true value). There is a significant difference between collabora-
tors in bias vs N02 level curves. However, eight of 10 collaborators exhibit
a uniform percent bias over all N02 levels, so that the method (as opposed
to all collaborators) seems to produce a reasonably linear performance over
the range of N02 examined.
53
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It should be remembered that a "replicate" in this experiment was
not, strictly speaking, a true replicate, i.e., a complete duplicate of
determination of NC>2. This was necessary for practical consideration in
running the experiment, but since all replicates were performed simultaneously
the estimated 2 Measurements
The ambient N02 determinations can, of course, also be considered
as a response and subjected to the analysis of variance. Thus CT| and OQ
can be estimated for ambient measurements, and these components of variance
compared to their counterparts for the spiked level readings. Also, the
rank order of collaborators when measuring ambient NOo can be compared to
the order of collaborators when measuring spiked NCU .
The analysis of variance is shown in Table XII. The comparison
between unspiked ambient and spiked components of variance is displayed in
Table XIII. The relative size of ae vs
-------
TABLE XIII
COMPARISON UNSPIKED AMBIENT VS SPIKED COMPONENTS OF VARIANCE
(eight collaborators)
ae CTC ae/cre CV(e) (7.) CV(C)
Ambient 2.19 2.93 1.34 8.8 11.7
Spiked 8.16 11.13 1.36 4.4 6.0
The correlation between collaborators rank order (relative bias)
for the spiked and ambient level is significant, but not overwhelming
(r = + 0.77); that is, the biases in determining NC>2 concentration appear
to exist in approximately the same fashion per collaborator whether ambient
levels or spiked levels are observed.
IX. CONCLUSIONS
The major conclusions that can be drawn from the results of this
collaborative test are:
1. The N02, ambient-air sampling system developed by MRI is an
effective system for use in collaborative testing of manual methods such
as the sodium-arsenite procedure.
2. The "Tentative Method for the Determination of Nitrogen Dioxide
in the Atmosphere (Sodium-Arsenite Procedure)" is adequately written for those
knowledgeable of sampling and analysis techniques as presented therein.
3. If the tentative sodium-arsenite procedure as given in Appen-
dix A of this report is followed by people knowledgeable of the sampling
and analysis techniques given therein, then such persons will obtain results
that are on the average 6.2 ug/rn-^ too low, ± 16 ug/nP, over the range 50-
300 ug/m.3. If a set of such people, each sampling independently, follow the
method, then results will be on the average 6.2 ug/m^ too low, ± 22
55
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X. RECOMMENDATIONS
Based upon the conclusions that have been drawn from the results
of this collaborative test, it is recommended that:
1. The same N02 sampling system be used in the evaluation of the
remaining N02 methods to be tested;
2. The data sets to be obtained from the subsequent methods to
be evaluated be based on experimental designs, test procedures and sampling
system operational procedures as similar as possible to those of the sodium-
arsenite collaborative test so that comparisons of the methods are based on
similar criteria; and
3. No further analysis be made of the results from the sodium-
arsenite method until the results from the other three methods are obtained.
56
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APPENDIX A
TENTATIVE METHOD FOR THE DETERMINATION
OF NITROGEN DIOXIDE IN THE ATMOSPHERE
(SODIUM-ARSENITE PROCEDURE)
57
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ENVIRONMENTAL PROTECTION AGENCY
METHODS STANDARDIZATION BRANCH
QUALITY ASSURANCE AND ENVIRONMENTAL MONITORING LABORATORY
NATIONAL ENVIRONMENTAL RESEARCH CENTER
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
NOVEMBER 1973
TENTATIVE METHOD FOR THE DETERMINATION OF NITROGEN DIOXIDE
IN THE ATMOSPHERE (SODIUM ARSENITE PROCEDURE)9
A tentative method is one which has been carefully drafted from
available experimental information, reviewed editorially within
the Methods Standardization Branch and has undergone extensive
laboratory evaluation. The method is still under investigation
and therefore, is subject to revision.
58
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1. Principle and Applicability
1.1 Nitrogen dioxide is collected by bubbling air through a sodium
hydroxide-sodium arsenite solution to form a stable solution of sodium
nitrite. The nitrite ion produced during sampling is reacted with phos-
phoric acid, sulfanilamide, and N-l-(naphthyl)ethylenediamine dihydro-
chloride to form an azo dye and then determined colorimetrically.
1.2 The method is applicable to collection of 24-hour samples in
the field and subsequent analysis in the laboratory.
2. Range and Sensitivity
2.1 The range of the analysis is 0.04 to 2.0 vg NO^/ml . Beer's law
is obeyed through this range (0 to 1.0 absorbance units). With 50 ml
absorbing reagent and a sampling rate of 200 cm /min for 24-hours, the
3 ?
range of the method is 20 to 750 pg/m (0.01 to 0.4 ppm) nitrogen dioxide/
2,2 'A concentr-iti Ti of 0 *"•" v" NOo/^l will Tod'jce an 9bsorb?nC6 0"f
approximately 0.02 with 1-cm cells.
3. Interferences
3.1 Nitric oxide is a positive interferent. The presence of NO can
2
increase the N02 response by 5 to 15% of the N02 sampled.
3.2 The interference of sulfur dioxide is eliminated by converting
4
it to sulfate ion with hydrogen peroxide before analysis.
4. Precision, Accuracy and Stability
4.1 The relative standard deviations for sampling N02 concentrations
of 78, 105 and 329 pg/m3 are 3, 4 and 2%, respectively.
59
-------
4.2 No accuracy data are available.
4.3 Collected samples are stable for at least 6 weeks.
5, Apparatus
5.1 Sampling. A diagram of a suggested sampling apparatus is
shown in Figure A-I.
5.1.1 Probe. Teflon, polypropylene, or glass tube with a polypropylene
or glass funnel at the end.
5.1.2 Absorption Tube. Polypropylene tubes 164 x 32 mm, equipped
with polypropylene two-port closures. Rubber stoppers cause high and vary-
ing blank values and should not be used. A glass-tube restricted orifice
is used to disperse the gas. The tube, approximately 8 mm O.D.-6 mm I.D.,
should be 152 mm long with the end drawn out to 0.3 * 0.8 mm I.D. The tube
should be positioned so as to allow a clearance of 6 mm from the bottom of
the absorber.
5.1.3 Moisture Trap. Polypropylene tube equipped with two-port
closure. The entrance port of the closure is fitted with tubing that extends
to the bottom of the trap. The unit is loosely packed with glass wool to
prevent moisture entrainment.
5.1.4 Membrane Filter. Of 0.8 to 2.0 microns porosity.
5.1.5 Flow Control Device. Any device capable of maintaining a con-
stant flow through the sampling solution between 180-220 cm /min. A typical
flow control device is a 27 gauge hypodermic needle, three-eights inch long.
(Most 27 gauge needles will give flow rates in this range.) The device
used should be protected from particulate matter. A membrane filter is
60
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suggested. Change filter after collecting 10 samples.
5.1.6 Air Pump. Capable of maintaining a pressure differential
of at least 0.6-0.7 of an atmosphere across the flow control device.
This value includes the minimum useful differential, 0.53 atmospheres,
plus a safety factor to allow for variations in atmospheric pressure.
5.1.7 Calibration Equipment. - Flowmeter for measuring airflows up
to 275 cm /min. within +_2%, stopwatch, and a precision wet test meter
(1 liter/revolution).
5.2 Analysis
5.2.1 Volumetric Flasks. 50, 100, 200, 250, 500, 1,000 ml.
5.2.2 Graduated Cylinder. 1,000ml.
5.2.3 Pipets. 1, 2, 5, 10, 15 ml volumetric; 2 ml, graduated in
1/10 ml intervals.
5.2.4 Test Tubes, approximately 20 x 150 mm.
5.2.5 Spectrophotometer. Capable of measuring absorbance at 540 nm.
6. Reagents
6.1 Sampling
6.1.1 Sodium Hydroxide. ACS Reagent Grade.
6.1.2 Sodium Arsenite. ACS Reagent Grade.
6.1.3 Absorbing Reagent. Dissolve 4.0 g sodium hydroxide in distill-
ed water, add 1.0 g of sodium arsenite and dilute to 1,000 ml with distill-
ed water.
6.2 Analysis
6.2.1 Sulf anil amide. Melting point,. 165-167°C.
61
-------
6.2.2 N-(1-Naphthy!)-ethylenediamine dihydrochlon'de (NEDA). Best
grade available.
6.2.3 Hydrogen Peroxide. ACS Reagent Grade, 30%.
6.2.4 Sodium Nitrite. Assay of 97% NaNCL or greater.
6.2.5 Phosphoric Acid. ACS Reagent Grade, 85%.
6.2.6 Sulfanilamide Solution. Dissolve 20 g sulfanilamide in 700
ml distilled water. Add, with mixing, 50 ml concentrated phosphoric acid and
dilute to 1,000 ml. This solution is stable for one month, if refrigerated.
6.2.7 NEDA Solution. Dissolve 0.5 g of NEDA in 500 ml of distilled
water. This solution is stable for one month, if refrigerated and protected
from light.
6.2.8 Hydrogen Peroxide Solution. Dilute 0.2 ml of 30% hydrogen
peroxide to 250 ml with distilled water. This solution ma*' be usec! for ons
month, if protected from light and refrigerated.
6.2.9 Standard Nitrite Solution. Dissolve sufficient desiccated
sodium nitrite and dilute with distilled water to 1,000 ml so that a
solution containing 1,000 yg NOl/ml is obtained. The amount of NaNO? to
use is calculated as follows:
r 1.500 v 100
" —5—
G = Amount of NaNO^ grams.
1.500 = Gravimetric factor in converting N02 into NaNOp.
A = Assay, percent.
62
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7. Procedure
7.1 Sampling. Assemble the sampling apparatus as shown in
Figure 1. Components upstream from the absorption tube may be connected,
where required, with teflon or polypropylene tubing; glass tubing with
dry ball joints; or glass tubing with butt-to-butt joints with tygon,
teflon or polypropylene. Add exactly 50 ml of absorbing reagent to the
calibrated absorption tube (8.1.3). Disconnect funnel, insert calibrated
flowmeter, and measure flow before sampling. If flow rate before sampling
is not between 180 and 220 cm /min, replace the flow control device and/or
check the system for leaks. Start sampling only after obtaining an initial
flow rate in this range. Sample for 24 hours and measure the flow after
the sampling period.
7.2 Analysis. Replace any water lest by evaporation during sampling
by adding distilled water up to the calibration mark on the absorption tube.
Pipet 10 ml of the collected sample into a test tube. Pipet in 1 ml hydrogen
peroxide solution, 10 ml sulfanil amide solution, and 1.4 ml NEDA solution
with thorough mixing after the addition of each reagent. Prepare a blank in
the same manner using 10 ml of unexposed absorbing reagent. After a 10-minute
color-developrrent interval, measure the absorbance at 540 nm against the blank,
Read pg NQ~/ml from the calibration curve (Section 8.2). Samples with an
absorbance greater than 1.0 must be reanalyzed after diluting an aliquot
(less than 10 ml) of the collected sample with unexposed absorbing reagent.
63
-------
8. Calibration and Efficiencies
8.1 Sampling
8.1.1 Calibration of Flowmeter. (See Figure A-2). Using a wet test
meter and a stopwatch, determine the rates of air flow (cm /min) through
the flowmeter at a minimum of four different ball positions. Plot ball
positions versus flow rates.
8.1.2 Flow Control Device. The flow control device results in a
constant rate of air flow through the absorbing solution. The flow rate
is determined in Section 7.1.
8.1.3 Calibration of Absorption Tube. Calibrate the polypropylene
absorption tube (Section 5.1.1) by first pipeting in 50 ml of water or
absorbing reagent. Scribe the level of the meniscus With a sharp object,
r»rv /M »/?y* 4-l*i r\ 3 v*"n "> <.rn '-4*1-1 *» £ d 1 4- 4-' •? r\ 'y**^ *»l?*+ «* ^ *\ *•* r- -»•% *4 <•*• *f^ -*•; •£*£ -4-U *- >s»^^%^f- —
y w w * C I CiiC MIWU MIWII U 1 W I W** c- 1 p 1111^ I r\ 1 11 ^ pUlly Ul IU I L4W Oil CitC C,/%VC J J •
8.2 Calibration Curve. Dilute 5.0 ml of the 1,000 ug NO^/ml
solution to 200 ml with absorbing reagent. This solution contains 25 vg
NO^/ml. Pipet 1, 1, 2, 15, and 20 ml of the 25 vg N0"/ml solution into TOO-,
50-, 50-, 250-, and 250- ml volumetric flasks and dilute to the mark with
absorbing reagent. The solutions contain 0.25, 0.50, 1.00, 1.50 and 2.00
yg NO^/ml, respectively. Run standards as instructed in 7.2, including
the blank. Plot absorbance vs. pg NOZ/ml. A straight line with a slope
of 0.48 +_ 0.02 absorbance units/yg NOl/ml, passing through the origin,
should be obtained.
64 '
-------
8.3 Efficiencies. An overall average efficiency of 82% was
obtained over the range of 40 to 750 yg/m NO^.
9. Calculation
9.1 Sampling
9.1.1 Calculate volume of air sampled.
V = Fl + F2 --6
v i ^ X T X 10 °
3
V = Volume of. air sampled, m .
F, = Measured flow rate before sampling, cm /min.
Fp = Measured flow rate after sampling, cm /min.
T = Time of sampling, min.
/• -5 O
10" = Conversion of cm to m .
9.1.2 Uncorrected Volume. The volume of air sampled is net corrected
to S.T.P. because of the uncertainity associated with 24-hour average
temperature and pressure values.
3
9.2 Calculate the concentration of nitrogen dioxide as yg N0?/m
using:
yg N02/m3 = (yg NOp/ml) X 50
V X 0.82
50 = Volume of absorbing reagent used in sampling, ml.
V c Volume of air sampled, m .
0.82 = Collection efficiency.
9.2.1 If desired, concentration of nitrogen dioxide may be calculated
as p.p.m. N02 using:
p.p.m. N02 = (yg N02/m3) X 5.32 X 10"4
65
-------
10. References
1. Christie,A. A. et^ al_. "Field Methods for the Determination of
Nitrogen Dioxide in Air." Analyst 95, 519-524 (1970).
2. Unpublished results, Environmental Protection Agency, Research
Triangle Park, N. C. 27711.
3. Merryman, E. L. et a]_. "Effects of NO, C02> CH4, H20 and Sodium
Arsenite on NOp Analysis." Presented at the Second Conference on
Natural Gas Research and Technology in Atlanta, Georgia on June 5,
1972.
4. -Jacobs, M. B. and Hochheiser, S., "Continuous Sampling and Ultramicro-
determination of Nitrogen Dioxide in Air," Anal. Chem. 30, 426
(1958).
5. Lodge, J. P. et^ aj_. "The Use of Hypodermic Needles as Critical
Orifices in Air Sampling." J.A.P.C.A., 16, 197-200 (1966).
66
-------
C
•H
cfl
60
C
•H
I
-------
-------
APPENDIX B
DATA ON THE PERMEATION TUBES USED AS THE
SOURCE OF THE SPIKED LEVELS OF N02
69
-------
As shown in Figure 6 of the text (p. 16), there were four branches
to the NC>2 permeation tube assembly. Each branch contained a set of permea-
tion tubes as follows:
Permeation Tube
Rate of N02 ± IS Branch N02*
Branch Number (ug/min) (ug/min) (ug/min)
1 35-8 1.434 0.001
1 35-16 1.597 0.002
1 29-3 1.345 0.002
1 28-10 1.160 0.002
1 5.536
2 34-3 1.195 0.002
2 34-13 1.275 0.002
2 34-6 1.548 0.001
2 34-1 1.226 0.003
2 34-10 1.138 0.001
2 6.382
3 35-13 1.990 0.003
3 29-4 1.210 0.001
3 3.200
4 29-2 1.210 0.001
4 34-12 1.770 0.002
4 2.980
Permeation rates for the above tubes were determined by the
National Bureau of Standards and validated by the Methods Standardization
Branch (MSB) of EPA at 25.1°C before they were given to MRI for use on the
collaborative test.
The combinations of branches used for the four runs of the sodium-
arsenite collaborative test are:
Run No. Date Branches Used
1 February 4-5 1, 2, 3, and 4
2 February 5-6 1
3 February 6-7 1 and 2
4 February 7-8 3
* The sum of the NC>2 generated by each permeation tube in the branch.
70
-------
APPENDIX C
CALIBRATION OF THE VENTURI
AND DRY-GAS METER
71
-------
Q
The venturi and dry-gas meter were calibrated using a 1.0-ft /rev.,
wet-test meter, as shown in Figure 9 (p. 20 of text). The wet-test meter is
connected between the splitter and the dry-gas meter. A bubbler is used
before the wet-test meter to saturate the air with water. The air flow
then proceeds through the venturi to the NOo bleed-in as it does in normal
operation (see Figure 3, p. 9 of text).
Since the saturated air coming from the wet-test meter is not
dried before going into the dry-gas meter, no correction for water vapor
pressure is necessary and only the normal corrections for temperature and
pressure are used. The flowrate of the wet-test meter (to stp) is:
P 294
Flow = Flow (meter reading) x x
sup 76Q T
where T = temperature of wet-test meter + 273, and
P = Patm + pressure of test meter manometer.
The venturi flowrate is dependent on both temperature and pressure.
Therefore Flowgtp is corrected to venturi conditions
760
Flowventuri = FlowstP x ~ x
where T£ = temperature of gas stream + 273, and
P2 = Patm + P(gas stream) *
The dry-gas meter is temperature compensated, so only pressure
corrections are made for its readings and a temperature base of 21°C is used
for calibration. Thus the true flowrate of the dry-gas meter (Fm) is
Flowstp
O
where ? = P + P
atm (gag stream) -
72
-------
The correction factor f to convert f , measured dry-gas meter flow-
rate, to true flowrate is then
f -
" f m
The venturi and dry-gas meter were calibrated at three flowrates;
50, 55, and 60 j^/min. Normal system flowrates are 55-60 ^/min. The cali-
bration factor for the dry-gas meter is constant at the calibration flows
(+ 0.27o). The average value of flow from seven determinations is used in
calculating true flowrates of the system. The plot of venturi AP vs flow-
rate follows a straight line over the range used in calibration. From the
slope and intercept of the line flowrates were calculated.
73
-------
APPENDIX D
WRITTEN.COMMUNICATIONS WITH
POTENTIAL COLLABORATORS
75
-------
Dear Sir:
Your name has been given to Midvest Research Institute (MRI) by the
Environmental Protection Agency (EPA), as having expressed an interest
in becoming a voluntary collaborator in an NOp Testing Program, to be
sponsored by EPA. I am writing to confirm this expression of interest
by your organization.
The objective of this program is to determine the reliability and bias
of four methods for measuring NC>2-ambient air. MRI has the responsibili-
ties for organizing the program, furnishing the test facilities, co-
ordinating the testing, analyzing the results of the collaborators, and
reporting the findings to EPA.
The sodium-arsenite method—the first method to be evaluated—will be
tested in Kansas City, Missouri, during the first part of January 1974.
Ten collaborators are needed for each of the four methods. A tentative
test schedule of the other three methods is given on the attached "Col-
laborator Form."
A writeup of the sodium-arsenite method is enclosed, and provides the
information needed for a collaborator to perform the testing and analyze
the samples he takes.
Each collaborator organization, once chosen, will be reimbursed for travel,
subsistence, lodging, and miscellaneous expenses (e.g., shipment of equipment
and local travel), for the employee sent to Kansas City to perform the
testing. Each collaborator will need to furnish the sampling apparatus
called for in the writeup. For each of the two manual methods, sodium-
arsenite and TGS-ANSA, six sampling trains will be needed. Cases will be
furnished in which to ship field samples to the collaborator's laboratory
for analysis.
We would appreciate your completing and returning to us the Collaborator
Form before November 15.
Sincerely,
Paul C. Constant, Jr., Head
Environmental Measurements Section
Enclosures: (1) Collaborator Form
(2) Tentative Method for the Determination
of Nitrogen Dioxide in the Atmosphere
(Sodium-Arsenite Method)
76
-------
COLABORATOR FORM
1. Methods to Test (Check the ones in which you want to participate
as a collaborator) :
TGS-ANSA Procedure
[ j Chemiluminescent
no
Sodium Arsenite
[ _ | Continuous Saltzman
2. Equipment Available for Test:
Could you furnish six trains for:
Sodium Arsenite : j__j yes
TGS-ANSA: £] yes [] no
Have you a Colorimetric (Continuous Saltzman) Ambient NC>2 Monitor?
LJ yes I I no Make _ Model _
Have you a Chemiluminescent Ambient N(>2 Monitor that you would use?
II yes I I no Make _ Model _
3. Test Period (Each Method) ;
Period acceptable (calendar days) :
[]] 6 days Q] 10 days
4. Methods You Have Used;
| | Sodium Arsenite," Q TGS-ANSA,
(_j Chemiluminescent, ( j Others:
13 days
Continuous Saltzman,
5. Remarks:
6. Company;
Address:
Person to Contact:
Telephone Number;
77
-------
APPENDIX E
INSTRUCTIONS FOR COLLABORATORS
N02 COLLABORATIVE TEST:
SODIUM-ARSENITE METHOD
79
-------
INSTRUCTIONS FOR COLLABORATORS
N02 COLLABORATIVE TEST: SODIUM-ARSENITE METHOD
GENERAL INFORMATION
1. Calibration, sampling, analysis, etc. should be done explicitly
as stated in the November 1973 write-up furnished you on "Tentative Method
for the Determination of Nitrogen Dioxide in the Atmosphere (Sodium Arsenite
Procedure)."
2. Each collaborator will have an area and a set of sampling
ports at both the spiked-sampling-manifold table and at the unspiked table—
see accompanying figure and table below:
Collaborator
I.D. Name
1 Kenneth Smith
2 Diana Dunker
3 James Ward
4 Bob Deardorff
5 Fernando Martinez
6 Glenn Smith
7 Abe Moore
8 Donald Kutys
9 Lynn Hutchinson
10 Jon Cimmer
Spiked Table
Area Ports
Unspiked Table
1
2
3
4
5
6
7
8
9
10
1-4
5-8
9-12
13-16
17-20
25-28
29-32
33-36
37-40
41-44
Area
1
2
3
4
5
6
7
8
9
10
Ports
41-44
37-40
33-36
29-32
25-28
17-20
13-16
9-12
5-8
1-4
3. For each run each collaborator will have six sampling trains
running simultaneously: four in his area on the spiked table and two in his
area on the unspiked table. Each train is to be attached to a separate port
as specified in the above table.
4. Nitrogen Dioxide Data Sheets will be provided—a copy of one
is attached. All information on sampling should be filled in during the
period of the run. The bubbler identification number will be made by MRl's
laboratory supervisor. He will have labels to affix to your samples. The
coding is run number (1-4), followed by port number (1-45), followed by
sampling table designation (S or U for spiked or unspiked), and terminated
in collaborator number (1-10); e.g., 1-6-S-2 for run 1, port 6, spiked table
80
-------
and collaborator 2 (Diana Bunker of Kentucky Division of Air Pollution).
Analysis information is to be filled in at your home laboratory.
5. A copy of the data sheet for each run should be given to MRI's
laboratory supervisor after each run is done.
6. Each collaborator should work independently of each other
collaborator.
7. Shipping containers for the samples (absorbing tubes) will be
available on a loan basis.
8. On the spiked sampling table, a separate power circuit (110-V,
60-cycle, four-outlet strip) is to be used by each collaborator for his
four trains. On the unspiked line one strip will be shared by two collab-
orators. These strips are under the table tops near the periphery of the
tops.
9. MRI will provide each collaborator with two standard samples
(each of a different level of N02). This will raise the total number of
samples to be analyzed by each collaborator to 26: six from each of four
runs plus the two standard samples.
10. Each collaborator should analyze his samples at his home
laboratory according to the tentative method write-up identified in Item 1
above. Results should be recorded on the Nitrogen Dioxide Data Sheets used
in the field.
11. A copy of the completed data sheet on each sample as well
as all calibration data and a complete description of the rotometer and wet-
test meter used must be furnished MRI. All this information is needed by
MRI within 1 month after completion of the field test.
TEST INSTRUCTIONS
1. Prepare your six sampling trains. Place four in your area on
the spiked sampling table and two in your area on the unspiked sampling
table.
2. Prepare a data sheet for each sampling train.
3. Upon notification of "Start testing," from the MRI laboratory
supervisor, connect your trains to the proper ports and start your sampling
according to the procedure in the November 1973 write-up on "Tentative
81
-------
Method for Determination of Nitrogen Dioxide in the Atmosphere (Sodium
Arsenite Procedure)."
4. Upon notification, "Stop testing," from the MRI laboratory
supervisor, terminate test according to the procedure in the method write-up.
NOTES
82
-------
MRI DERAMUS FIELD STATION - K.C. MO.
NITROGEN DIOXIDE DATA SHEET - SODIUM ARSENITE METHOD
Sampling
Collaborator Run Number
Sampled by Sampling Port Number
Sampling Train No.
Bubbler Identification No.
Rotameter Description (make, model, etc.,)
Rotameter reading at start at finish type of ball
Start:Date Time Finish:Date Time
o
Sampling duration (min) Sample flow rate (cm /min)
o
Total air volume sampled (ra )
Remarks:
Analysis
Date of Analysis
Analyzed by: Person Organization
Standardization plot slope (absorbance units/ug N02/ml)
Absorbance of sample against blank (540 nm) Aliquot (ml)
NOo Concentration
Remarks:
83
-------
TRUMAN
CORNERS
HOLIDAY
INN'
FIELD STATION
84
-------
85
-------
APPENDIX F
N02, AMBIENT-AIR SAMPLING SYSTEM OPERATIONAL
DATA: TEST LOG SHEETS
87
-------
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100
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APPENDIX G
COLLABORATORS' ANALYSIS INSTRUMENTATION
AND COMMENTS
101
-------
1. Analysis instrumentation used by the collaborators; The spec-
trophotometric analysis instrumentation used by the collaborators is identified
in Table G-I.
TABLE G-I
ANALYSIS INSTRUMENTATION USED BY COLLABORATORS
Collaborator
A
B
C
D
E
Instrumentation
Bausch & Lcmb 20
Beckman DU
Beckman DB
Beckman DB
Beckman DB
Collaborator
F
G
H
I
Instrumentation
Perkin-Elmer 356
Shimadzu QV-50
Beckman B
Bausch & Lomb 88
Shimadzu QV-50
2. Comments of the collaborators; During the orientation of the
collaborators at the field site, they were asked to provide MRI with comments
on the method write-up, problem areas, etc. Four of the 10 responded with
comments which are given below by collaborator code.
Collaborator A; "The analysis 6 February 1974 were run at 540 nm.
When I ran my standard curve and samples on 14 February 1974, I noted the
absorbance difference between 530 nm and 540 nm was less than 2% on every
sample."
Collaborator E; "All samples were analyzed three times. I am
sending copies of data for all analysis in hopes that they might be of value
to you. The first set of data, with curve and calibration curve attached,
would be what would usually be reported. The second, 20 February, and the
third, 25 February, were simply to verify my own work. Slope for the various
curves were: 12 February - 0.465; 20 February - 0.500; and 25 February -
0.480. Unknown solutions Nos. 15 and 128 were analyzed each time and the
following results were obtained: Sample No. 15 - 1.0 ppm (absorbance 0.5,
slope 0.5; absorbance 0.48, slope 0.48); Sample No. 128 (absorbance zero
for each test). Review of my data shows no consistant bias, and precision
not as good as desired. Although samples varied slightly, unknown remained
constant."
102
-------
Problem areas of concern to our laboratory follow:
"Flowmeter calibration - use of a 1-liter wet test meter is im-
possible for us. We were unable to locate anything smaller than 0.1 CFM.
Wet-test meters are no more accurate than the accuracy of their calibration.
Calibrating a flowmeter at our elevation could introduce serious errors in
air measurements at your elevation. Calibration should have been verified
at the test site.
I would like to question the efficiency figure of 0.82. Samples
run in the 180-190 cc/min area on the spiked line appear to show higher
micrograms per cubic meter readings than those sampled at 220 cc/min.
In the method of analysis, the NEDA addition should be changed.
Addition of fractional amounts (1.4 ml) causes possible errors to enter
which need not occur. A standard addition of 1 or 2 ml can be accomplished
with greater speed and accuracy.
We feel that a fritted glass bubbler should be used, regardless
of cost factors. Better dispersion of gas in the liquid would certainly be
achieved. Change of frit size in cleaning would not be any more critical
than matching restricted orifices to obtain uniform 0.6 mm.
Automation of analysis, using the Technicon Auto Analyzer, resulted
in comparable answers in one-tenth of the time required by hand. All data
submitted to you follow EPA methods verbatim."
Collaborator H; "The samples collected were analyzed in strict ac-
cordance with the method except in the calibration of the rotameter used. The
rotameter was calibrated with a bubblemeter because of the unavailability of the
1-liter wet-test meter as called for in the method.
We found the entire method to be straightforward and simple. No
difficulty was encountered in the analysis."
"Comments and Recommendations on the EPA's
Tentative Method for the Determination of Nitrogen Dioxide
In the Atmosphere (Sodium-Arsenite Method)"
3.1 The "N02" between "the" and "sampled" appears to be a typo-
graphical error. It should be "NO."
4.3 Our experiences indicate that the absorbing solution readily
absorbs N02 from the air. We recommend that "when kept tightly sealed" be
added to the sentence.
103
-------
5.1.2 Drawing out a glass tubing to 0.3 to 0.8 mm ID is a diffi-
cult task. We suggest that common twist drills be used to measure the orifice
diameter. We therefore recommend that the following be inserted after the
fourth sentence: "The orifice diameter should permit a No. 80 drill to pass
through but not a No. 68 drill."
5.2.5 The measurement of absorbance at 540 nm is correct, not at
530 nm as previously suggested during the field sampling phase.
6.2.2 Our experience indicates that at times the slopes of calibra-
tion curves prepared using NEDA from different bottles or lots vary. We
recommend the following sentence be added: "When a new bottle or lot of NEDA
is used, prepare a new standard curve."
7.1 The procedure requires the momentary in-line connection of the
calibrated flowmeter before the actual sampling is begun to assure that the
sampling rate is within 180-220 ml/min. Does this not constitute a false
start?
When measuring the exact flowrate with the calibrated flowmeter
in-line, the bubbling in the .absorbing solution causes the flowmeter ball to
bounce erratically and makes it difficult to obtain an accurate reading. We
do not have a recommendation to alleviate this problem.
7.2 It is inevitable that some water will evaporate from the ab-
sorbing solution during the 24-hr sampling period. We recommend that the lost
water be replaced immediately after sampling to forestall any loss of the con-
centrated sample during transit due to leakage or spillage. Therefore, the
first sentence of this paragraph should be transferred to the end of paragraph
7.1.
The absorbing solution absorbs N0£ from the atmosphere readily.
Therefore, during the color development period, the solution should be capped
tightly. In this respect we find that a 25-ml glass stoppered graduate cylinder
instead of in a test tube minimizes this problem.
It is good analytical practice to record the absorbance reading be-
fore converting it to concentration unit. We therefore recommend that "and
record" be inserted between "measure" and "the" on line 7.
We believe that for better accuracy and consistency the slope of
the calibration curve should be used to convert the absorbance readings to
equivalent concentration units. We therefore recommend that "Read y,g N02~/ml
from the calibration curve (Section 8.2)" on line 8 be deleted and substituted
by "Calculate the M-g N02~/ml by dividing the absorbance by the slope of the
calibration curve obtained in Section 8.2."
104
-------
8.2 No procedure is given on how the slope of the curve is obtained,
We recommend that the average slope be used and calculated as follows:
b =
u-jfc NO 2
9.2 We believe that the 0.82 factor includes not only the sampling
collection efficiency but also includes the conversion factor for the NC>2 gas
to nitrite ion (N02~) in solution. We therefore recommend that it be labeled
"average overall efficiency."
Collaborator I; "Enclosed is the data and results of the NC>2
collaborative test. The samples were run only once, so the final values are
not an average. Also note that I have enclosed a copy of a Modified Christie
Method. By reducing the volume of test reagents used and increasing the con-
centration of them, the sensitivity of this method is increased. This is
the method which we use in o-ur laboratory."
105
-------
TECHNICAL REPORT DATA
(Please reaj limructioiu on ike /vi crsc bi-jorc completing)
\. REPORT NO. 2.
EPA-650/4-74-019a
4. TITLE AMD SUBTITLE
Collaborative Testing of Methods for Measurements of
NC>2 in Ambient Air: Volume 1 - Report of Testing
7. AUTHOR(S)
Paul C. Constant, Jr., Michael C. Sharp,
George W. Scheil
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Midwest Research Institute
425 Volker Boulevard
Kansas City, Missouri 64110
12. SPONSORING AGENCY NAME AND ADDRESS
Office of Research and Development
U.S. Environmental Protection Agency '
Research Triangle Park, North Carolina 27711
3. RECIPIENT'S ACCESSION-NO.
5. REPORT DATE
June 1974
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1 HA 327
11. CONTRACT/GRANT NO.
68-02-1363
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A report on the collaborative test, by 10 organizations, of the "Tentative Method
for the Determination of Nitrogen Dioxide in the Atmosphere (Sodium-Arsenite Pro-
cedure)" to determine th*> oracision and bias of the method. The report covers the
design, collaborators' field sampling, their analysis of samples, statistical anal-
ysis of collaborators1 results, conclusions and recommendations.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI llcld/C.roup
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (Tim Report)
Unclassified
21. NO. OF PACES
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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