f/EPA
01',
United States
Environmental Protection
Agency
Environmental Monitoring System,
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S4-81-025 Sept. 1981
Project Summary
National Performance Audit
Program: 1979 Proficiency
Surveys for Sulfur Dioxide,
Nitrogen Dioxide, Carbon
Monoxide, Sulfate, Nitrate,
Lead and High Volume Flow
B. I. Bennett, R. L. Lampe, and J. C. Puzak
The Quality Assurance Division of
the Environmental Monitoring Sys-
tems Laboratory, Research Triangle
Park, North Carolina, administers
semiannual Surveys of Analytical
Proficiency for sulfur dioxide, nitrogen
dioxide, carbon monoxide, sulfate,
nitrate, and lead. Sample materials
which simulate ambient air pollution
samples as closely as possible are
furnished to participating laboratories.
Surveys of high volume sample flow
rates are conducted annually using a
modified orifice.
The Quality Assurance Division
assures that samples are stable, of
uniform composition, and are repre-
sentative of pollutant concentration
levels encountered under field sam-
pling conditions and that all materials
conform to prescribed standards of
accuracy. Sample materials are re-
quired to be similar enough to true air
pollution matrices not to introduce
unrealistic conditions of sample prep-
aration or impose handling techniques
that are not a part of the normal
monitoring and analytical activity. A
major survey objective is to assess
routine analytical performance. An
individual report is promptly returned
to each participant after results are
evaluated by the Quality Assurance
Division.
This Project Summary was devel-
oped by EPA's Environmental Moni-
toring Systems Laboratory, Research
Triangle Park, NC. to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
The 1979 Proficiency Surveys con-
tinue the regular surveys by the Environ-
mental Monitoring Systems Laboratory
(EMSL) of agencies which routinely
collect and analyze ambient air samples.
Sample materials which are furnished
for this purpose are designed to simulate
as closely as possible several types of
collected air pollution samples. The
samples furnished by the EPA are used
to test only the analytical portion of the
total air monitoring capability, and do
not deal with errors from sample col-
lection, flow rate error, transportation,
handling, storage, and data processing.
Rankings in the surveys, except as may
occasionally be due to unpropitious
circumstances, reflect the effectiveness
of internal quality assurance programs.
The Proficiency Surveys allow EPA to
assess the quality of air pollution anal-
yses in general and permit the partici-
pants to compare their own work with
that of their peers.
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Participants in the surveys are solicited
by the Regional Quality Control Coordi-
nator in each of the ten Regions. Once a
laboratory enrolls in a survey for a
particular pollutant, it is automatically
notified of subsequent surveys for the
pollutant. The surveys are conducted by
the Quality Assurance Division (QAD)/
EMSL, Environmental Research Center,
Research Triangle Park, North Carolina,
27711, with the assistance and coop-
eration of the EPA Regional Offices.
Inquiries and applications to participate
should be directed to that address.
Included in the surveys were represent-
atives of federal, state, local, industrial
and foreign facilities.
Soon after a roster is established,
instructional information and unknown
sample materials are mailed. Surveys
are presently conducted twice a year for
carbon monoxide (CO), sulfur dioxide
(802), nitrogen dioxide (NOz), lead (Pb)
on filter strips, sulfate (SO*) and nitrate
(NOi) on filter strips and once a year for
hi-vol flow. A report is issued to each
laboratory indicating the reported value
and an historical frequency distribution
of test results. A comprehensive report
is prepared yearly summarizing the
survey results of that year.
Before 1979, the surveys provided
target and sample ranges that defined
the sphere of all creditable results.
Under that system, results falling within
the sample range indicated a fine anal-
ytical job and results within the wider
target range were respectably good.
This format enjoyed wide favor due to
the clear, explicit and uncontestable
tableau it presented for scoring any
single test result.
Beginning with the 1979 survey year,
in an effort to enable comparison of
individual results with those of peer
laboratories, format was modified by
presenting cumulative frequency distri-
butions of the results of earlier surveys.
In any survey, some of the results are
far removed from the rest of the reported
measurements and this small body of
egregious data may be safely excluded.
After the obviously inconsistent data
are removed, objective judgments need
to be made about values that are ques-
tionable. The standard chosen for the
1979 surveys was the Chauvenet's
Criterion.
This criterion is based on the normal
distribution and advises rejection of an
extreme observation if the probability of
occurrence of such deviation from the
mean of the n measurements is less
than 1/2n. The rationale for this criterion
is that inclusion of spurious data vitiates
test results by biasing both the survey
mean and precision, whereas removal
of good measurements merely excludes
some of the data.
The sulfur dioxide sample material
was composed of freeze-dried mixtures
of sodium sulfite and potassium tetra-
chloromercurate (TCM) contained in 5-
ml glass ampoules. Sample sets con-
sisted of five ampoules containing 4 to
64 micrograms Oug) of SO2 equivalent
per container. The sample material was
stored at -20°C to sustain the integrity
of the SOz activity, which was confirmed
by periodic retesting. Analyses were
performed by the reference method for
the determination of S02 in the atmo-
sphere (pararosaniline method). The
sample, when solubilized in 0.04N TCM
forms a dichlorosulfitomercurate com-
plex. This complex is reacted with
pararosaniline and formaldehyde to
form intensely colored pararosaniline
sulfonic acid.
The nitrogen dioxide samples con-
sisted of 5 mL of aqueous sodium nitrite
contained in glass ampoules where a
set consisted of five ampoules. When
mixed with caustic absorbing reagent,
the samples simulated ambient samples
ranging in concentration from 0.17 to
1.00 (jg/mL.
Samples of carbon monoxide were
offered as compressed gas mixtures of
CO and artificial air. Also contained in
each sample was 2 ppm of methane
(CH*) and approximately 365 ppm of
carbon dioxide (C02). Aluminum cylinders
were used in the surveys. Sample
concentrations ranged from 3 to 44 ppm
of CO. Each participant received a set of
three cylinders, one from each of three
concentration levels.
Sulfate-nitrate samples consisted of
1.9 x 20cm (0.75 x 8 in.(glass fiber filter
strips with depositions of potassium
sulfate (KzSO4) and lead nitrate (PfafNOafe).
Filter strips samples included concen-
trations of various S0< and NOs concen-
trations. Each strip was contained in a
sealed plastic envelope. The concentra-
tions of suifate ranged from approxi-
mately 1.5 to 29 fjg/m3. Nitrate levels
spanned between 1.5 and 12/ug/m3.
Concentrations were determined using
the requisite filter dimensions of 20 x
25.4 cm (8 x 10 in.) and a collected air
volume of 2000 m3. It can be shown that
the process of gravimetric preparation
and transfer of a well-characterized
homogeneous solution of chemical
constituents can be accomplished with
more precision and accuracy than would
be obtained from the chemical analysis
of spiked filter strips. Therefore, the
reted) values were obtained theoretically
from the deduced mass of inorganic
salts deposited on the filters. Verification
analyses assured that the accuracy and
precision of the samples were within
prescribed limits.
Lead samples were composed of 1.9x
29 cm (0.75 x 8 in.) glass fiber filter
strips with depositions of lead nitrate
(PbtNOsh). Filter strip sample sets
contained combinations of different
lead concentrations, each in a sealed
plastic envelope. The lead content
ranged in concentration from 1.5 to
12.9 fjg/m3. Concentrations were cal-
culated presuming that the samples
were collected on the prescribed 20 x
25.4 cm (8 x 10 in.) hi-vol filter with a
total air volume of 2000 m3.
To evaluate hi-vol flow, a single
reference flow device (ReF) was supplied
to each participating agency. Organiza-
tions were instructed to check as many
hi-vol sampling units as feasible within
the allotted time. The unit received by
each laboratory consisted of a modified
orifice, wind deflector, manometer, and
resistance plates designed to alter flow
rates.
During measurement of the air flow of
a hi-vol sampler, the ReF was mounted
on top of the sampler replacing the filter
face plate. A wind deflector was neces-
sary to prevent fluctuation in the readings
due to wind blowing across the orifice.
The resistance plates, when inserted
into the ReF, simulated various filter
loading conditions.
Conclusions
Sulfur Dioxide
Proficiency Surveys for SO2 were
conducted in April and October 1979.
Approximately 100 participants com-
pleted each of the surveys. The para-
rosaniline method predominated with
80 percent of the laboratories using that
procedure. No systematic discrepancies
or substantial bias existed in the S02
surveys. Comparison by the t test showed
that differences in the means of the
preponderant methods were not statis-
tically significant. Within the purview of
the semiannual proficiency surveys, the
two methods do not differ with regard to
variability, according to the F test.
Participation in the April 1979 SOz
survey decreased by 12 percent from
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the previous year; the October 1979
survey continuing at about the same
level. The reduction was largely ac-
counted for by decreased use of the
pararosaniline method by state agencies.
The number of users of the pararosani-
line method stabilized at around 1 00.
Survey results are summarized in
Table 1, with all methods included.
Nitrogen Dioxide
Proficiency Surveys for NOa were
conducted in June and December 1 979.
Approximately 90 participants completed
the first survey, and close to 80 the
Qpponrl
3dd>UI IU.
The predominant analytical method
was the manual sodium arsenite color -
imetric procedure; 72.7 percent of the
0679 respondents used it. Slightly
fewer reported using the manual method
in the 1279 survey. Around 21 percent
of respondents used the automated
sodium arsenite method. The manual
and automated Saltzman and TGS-
ANSA manual methods made up the
balance of the test methods. No system-
atic discrepancies or substantial bias
was apparent in the NOa surveys.
Survey results are summarized in
Table 2, with all methods included.
Carbon Monoxide
Proficiency Surveys for CO were
conducted in March and September
1979. Operational assessment of ap-
proximately 300 instruments were
included in each of the two semiannual
surveys. The NDIR method was employed
by approximately 90 percent of the
survey respondents. No systematic dis-
crepancies or substantial bias was iden-
tified in the CO surveys.
Of the test methods listed on the
survey information forms, the NDIR
method dominated, with 91 percent of
the laboratories using that method in
the 0379 survey and 87 percent in the
0979 test. Facilities using the GC method
increased from 6 to 12 percent during
the biannual testing period. Other
methods were reported being used by
approximately 2 percent of the respon-
dents. The 1979 and previous survey
results lead to the conclusion that the
precision of the GC method is subordi-
nate to that of the NDIR method. This
conclusion is verified by application of
the statistical F test to the data obtained.
Survey results are listed in Table 3,
with all methods included.
Table 1 . Summary of Sulfur Dioxide Proficiency Surveys
Expected
Sample value
no. Respondents* (Jig/m3
Survey 0479 (April 1979)
1 100 13.9
3 105 93.3
4 103 148.3
5 105 212.7
Survey 1079 (October 1979)
1 101 13.5
2 103 38.5
3 102 80.0
4 103 125.
5 104 165.
*With outliers removed.
Survey
mean
/jg/m3
14.15
92.56
154.30
214.48
12.63
35.80
77.26
125.24
165.62
Survey
std. dev.
ug/m3
4.85
7.97
10.45
15.03
5.00
6.57
8.14
11.31
14.16
Survey interval
ug/m3
2.17- 25.76
70.74-109.10
126.51-175.68
1 70.80-256.99
1.08- 33.30
10.13- 54.10
48.14-108.40
88.00-166.50
104.22-206.97
Table 2. Summary of Nitrogen Dioxide Proficiency Surveys
Expected
Sample value
no. Respondents* /jg/mL
Survey 0679 (June 1979)
1 88 0.259
2 88 0.405
3 88 0.514
4 87 0.700
5 86 0.935
Survey 1279 (December 1979)
1 76 0.172
2 78 0.342
3 76 0.595
4 77 0. 746
5 76 1.000
*With outliers removed.
Survey
mean
/jg/mL
0.26
0.40
0.51
0.71
0.95
0.18
0.35
0.59
0.74
0.97
Survey
std. dev.
fjg/mL
0.02
0.02
0.03
0.03
0.04
0.04
0.05
0.07
0.09
0.12
Survey interval
/jg/mL
0.21-0.30
0.34-0.45
0.39-0.62
0.62-0.78
0.83-1.07
0.09-0.44
0. 14-0.55
0.22-0.73
0.18-0.90
0.34-1.16
Table 3. Summary of Carbon Monoxide Proficiency Surveys
Expected
Sample value
no. Respondents* ppm
Survey 0379 (March 1979)
1 291 6.53
2 295 19.8
3 294 43.7
Survey 0979 (September 1979)
1 290 „ 2-98
2 268 14.8
3 297 33.8
*With outliers removed.
Survey
mean
ppm
6.39
20.08
44.14
2.73
14.75
34.14
Survey
std. dev.
ppm
0.53
0.89
1.51
0.48
0.75
1.37
Survey interval
ppm
4.92- 8.50
17.30-23.00
38.23-49.70
1.25- 4.75
12.24-17.30
29.50-39.00
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Sulfate
Proficiency Surveys for S04 were
conducted in February and August
1979. Approximately 60 participants
completed each survey. State and local
agencies composed 70 percent of the
roster of participating laboratories. Six
test methods were employed with
methylthymol blue and the manual
barium chloride procedures dominating.
Other major methods used were the
Sulfa-Ver© and ion chromatography. No
systematic discrepancies occurred. The
barium chloride procedures exhibited
the greatest variability of the test
methods.
Survey results are listed in Table 4,
with all methods included.
Nitrate
Proficiency Surveys for NOi were
conducted in February and August
1979. Approximately 45 participants
completed each of the surveys. Over
half the respondents used the automated
cadmium reduction procedure. In all,
nine analytical methods were reported
in use. Others were ion chromatography,
phenoldisulfonic acid, brucine, specific
ion electrode, Szechrome© and ultra-
violet spectrophotometric procedures.
The averages of all methods were com-
pared by an extension of the analysis of
variance at the 5 percent significance
level. No single method was particularly
bad and no systematic discrepancies
existed.
Survey results are given in Table 5,
including all analytical methods.
Table 4. Summary of Sulfate Proficiency Surveys
Expected
Sample value
no. Respondents* fjg/m3
Survey
mean
ug/m3
Survey
std. dev.
ug/m3
Survey interval
ug/m3
Survey 0279 (February 1979)
0 65 \ 10.50 10.61 2.21 6.65-21.60
1 65 19.50 18.96 1.73 14.10-23.64
2 65 1.50 1.96 1.17 0.30- 5.60
3 65 15.OO 14.74 1.34 11.70-18.03
4 65 24.00 23.80 2.22 16.48-31.80
5 65 6.00 5.75 1.13 3.06- 9.15
Survey 0879 (August 1979)
0
2
3
4
5
*With
59
58
60
58
59
outliers removed.
9.10
28. 8O
23.70
13.10
7.20
8.38
27.42
22.90
12.16
6.77
1.25
2.57
2.58
1.58
1.18
3.00-11.11
20.00-33.60
14.00-30.11
6.45-15.90
3.50-10.13
Table 5. Summary of Nitrate Summary Proficiency Surveys
Sample
no.
Expected
value
Respondents*
Survey
mean
ug/m3
Survey
std. dev.
ug/m3
Survey interval
ug/m3
Survey 0279 (February 1979)
0 50 1.50 1.58 0.41 0.35- 3.39
1 50 3.60 3.52 .0.38 2.53- 4.60
2 50 5.70 5.52 0.52 4.39- 7.29
3 50 12.00 11.54 1.32 7.83-14.79
4 50 7.80 7.60 0.77 5.04- 9.16
5 50 9.90 9.68 0.98 7.32-13.74
Survey 0879 (August 1979)
0 40 3.40
2 39 6.00
3 40 10.2O
4 40 8.30
5 40 1.20
3.44
5.90
9.97
7.94
1.21
0.44
0.51
0.95
0.84
0.27
2.37- 4.40
4.22- 6.88
7.12-11.57
4.99- 9.20
0.36- 1.82
*With outliers removed.
Lead
Proficiency Surveys for Pb were con-
ducted in January and July 1979, with
approximately 80 facilities participating.
The atomic absorption method of analy-
sis was virtually the only method used.
No systematic discrepancies or bias was
observed in the Pb surveys.
Table 6 contains the results of the
lead surveys.
Hi-Vol Flow Rate
The Proficiency Survey for hi-vol flow
was conducted in May 1979 with ap-
proximately 1300 sites being tested. Six
measurement methods were listed by
survey participants. The pressure
transducer and rotameter dominated
with 72.6 percent using those methods.
Table 6. Summary of Lead Survey Proficiency Surveys
Expected
Sample value
no. Respondents* ug/m3
Survey
mean
ug/m3
Survey
std. dev.
ug/m3
Survey interval
ug/m3
Survey 0179 (January 1979)
3 76 1.46 1.45 0.16 0.93- 1.95
4 76 3.52 3.46 0.28 2.84- 4.32
5 76 5.39 5.39 0.57 2.88- 6.63
6 76 11.45 11.31 1.15 7.74-14.10
7 76 7.48 7.61 1.10 4.80-12.00
8 76 9.51 9.38 0.96 6.18-11.57
Survey 0779 (July 1979)
0
1
2.
3
4
5
81
81
79
81
80
81
3.53
12.86
5.85
10.39
7.93
1.18
3.53
12.85
5.90
10.42
7.99
1.17
0.29
0.87
0.34
0.91
0.48
0.12
2.34- 4.20
10.59-15.30
4.77- 6.97
7.50-13.80
6.81- 9.97
0.84- 1.50
*With outliers removed.
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Other minor methods, as noted on the
survey cards, were flow gauge, manom-
eter, orifice manometer, and magnehelic
gauge.
The sample ReF's furnished could not
be all the same. Each ReF unit was
calibrated individually and is distinct
from all other units, because flow rates
could not be duplicated precisely enough
among the test devices to establish flow
values that were applicable to all units.
Rather than comparing collective mea-
surements against a common standard,
results from each ReF were compared to
a calibration which was unique for that
unit. The calibrated flow values, or
expected values, developed for each of
five flow constrictor plates, were com-
pared to the values recorded on the
survey forms.
Frequency distributions of the percent
differences between the reported and
expected values for each measurement
pair are shown in Table 7.
Table 7. Percent Difference from Expected Flow Rates
Number of
measurements
Percent of measurements
10%
20%
30%
50%
70%
90%
5902
-9.2
-4.8
-2.6
0.3
3.0
7.4
Recommendations
Since the EPA began administering
the voluntary proficiency surveys in
1973, the program has progressed both
in scope and participation, with approxi-
mately 300 laboratories now receiving
CO survey samples and 1300 sites
taking part in the hi-vol tests. Prompt
return of survey reports by the QAD
signal possible analytical/measurement
problems or confirms the excellence of
ongoing monitoring activities. Timely
notification is considered one of the
essential elements of the survey
program.
Continuance of the surveys will render
valued assistance to existing internal
quality assurance programs by making
accessible a variety of air pollution
standard samples, furnished free of
charge by the U.S. EPA, to a diverse
clientele within the arena of air pollution
monitoring.
US GOVERNMENT PRINTING OFFICE, 1981 —757-012/7345
The EPA authors B. I. Bennett (also the EPA Project Officer, see below). R. L.
Lampe. and J. C. Puzak are with the Environmental Monitoring Systems
Laboratory, Research Triangle Park, NC 27711.
The complete report, entitled "National Performance Audit Program: 1979
Proficiency Surveys for Sulfur Dioxide. Nitrogen Dioxide, Carbon Monoxide,
Sulfate, Nitrate, Lead and High Volume Flow," (Order No. PB 81-239 402;
Cost: $8.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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Fees Paid
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Penalty for Private Use $300
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