United States
Environmental Protection
Agency
Environmental Monitoring Systems
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S4-83-008 May 1983
Project Summary
Validation and Improvement of
EPA Reference Method 25-
Determination of Gaseous
Nonmethane Organic Emissions
as Carbon
G. B. Howe, S. K. Gangwal, and R K. M. Jayanty
EPA Reference Method 25 for mea-
surement of total gaseous nonmethane
organics as carbon in source emissions
is being evaluated. Details are given of
the evaluation of a commercial non-
methane organic analyzer (Byron Model
401); design, construction, and testing
of a sample collection and conditioning
system; and two field tests of the
method using dual identical sampling
trains at a textile plant and a plywood
veneer plant. Recommendations are
made to improve and modify the method.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems Laboratory. Research Triangle
Park, NC, to announce key findings of
the research project that is fully doc-
umented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
On October 5, 1979, under Section III
of the amended Clean Air Act the U.S.
Environmental Protection Agency (EPA)
proposed standards limiting the emissions
of volatile organic compounds (VOC) from
new, modified, and reconstructed auto-
mobile and light-duty surface-coating
operations within assembly plants. The
standards were based on EPA's determina-
tion that such emissions contribute signif-
icantly to air pollution by acting as pre-
cursors for formation of ozone and other
photochemical oxidants that impact ad-
versely on health and welfare.
The proposed standards include a method
for measuring VOC emissions—EPA Ref-
erence Method 25. Method 25 involves
first withdrawing an emission sample from
the source stack through a chilled conden-
sate trap and into an evacuated sample
tank The total gaseous nonmethane organics
(NMO) are then determined by combining
the results obtained from separate analyses
of the condensate trap and sample tank
fractions. The organic contents of the
condensate trap are oxidized and quantita-
tively collected in an evacuated vessel, and
an aliquot of the resulting C02 is reduced
to methane and measured by a flame
ionization detector (FID). An aliquot of the
gas collected in the sample tank is intro-
duced into a gas chromatographic (GC)
system to separate the nonmethane or-
ganics from carbon monoxide (CO), carbon
dioxide (C02), and methane (CH4). After
this separation, the NMOs are oxidized to
C02, reduced to CH4, and measured by an
FID. In this way, variations in FID response
to different compounds are eliminated,
and all carbon is measured as methane.
Application of the method revealed de-
ficiencies that affect the accuracy and
reproducibility of the results. As a result
the present investigation was undertaken
to systematically evaluate EPA Reference
Method 25 and to recommend further
modifications to improve the accuracy,
precision, and reliability of the data collected
In addition to a laboratory evaluation, two
field tests of the method were conducted
to determine the quality of the data that
can be expected using Method 25.
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Results and Discussion
All necessary system components for
constructing the sampling, condensate
recovery, and conditioning systems were
obtained and assembled. Byron Model
401 was chosen for NMO and C02 analysis
because of its availability.
Complete experimental details of sys-
tem design and construction are available
in the project report and are not repeated
here. Laboratory evaluation consisted of
separate evaluations of the sampling sys-
tem, the NMO analyzer (Byron Model
401), and the condensate recovery and
conditioning system. Two field tests were
also conducted, one at a textile plant and
the other at a veneer plywood plant
In the laboratory evaluation, the sampling
system yielded a recovery of 99.9 pe'rcent
and a relative standard deviation of 0.08
percent for a dilute propane in air mixture
sampled through a manifold. The accuracy
of the dead volume data of the sampling
train was a point of concern. The error is
directly proportional to the dead volume of
the sampling system from the probe tip to
the sampling container and inversely pro-
portional to the volume of the sampling
container. However, the error can be
determined experimentally and a correction
applied, as was done during the second
field test.
The laboratory evaluation of the NMO
analyzer showed excellent linearity for
some organic compounds over concen-
tration changes of as much as three orders
of magnitude, but the responses to dif-
ferent organics tested ranged over a factor
of three, as shown in Table 1. Possible
reasons for unequal responses are incom-
plete oxidation (carbon laydown) on the
catalyst modules, interaction of the air
carrier gas with the organic on the GC
columns, and severe tailing of compounds
resulting in inaccurate integration. The
Model 401 was linear for C02 measure-
ment over 2.5 orders of magnitude. The
implication of the above findings was that
the NMO would yield more accurate results
for organics that are trapped (and eventually
converted to C02 prior to measurement)
rather than for organics that are measured
in the gaseous form from the sampling
container. A modified NMO analyzer that
would alleviate the problem of unequal
carbon responses was designed and briefly
described in the report This analyzer will
be built and evaluated in future studies.
Laboratory evaluation of the condensate
recovery and conditioning system was
carried out according to procedures speci-
fied by EPA Method 25. The system
passed the requirements of the method
with a system C02 blank of 6.1 ppm.
Table 1. Variation of the Byron Model 40 J Analyzer Response to Various Organic Compounds
Compound
Trichloroethylene
Ethylene
Methyl acetate
Ethane
Freon 1 13
Carbontetrachloride
Isopropyl alcohol
Decane
Acetyl acetone
Nonane
Amyl acetate
Tetrahydrofuran
Tetrahydropyran
Naphthalene
Propane
Toluene
Hexane
Methanol
Propylene
Benzene
Concentration
range, ppmC
10 -
50 -
600 -
150 -
60 -
60 -
40
40,000
1,300
1,400
30
20
300
260
400
455
350
500
60
25
9,000
128
330
100
30
600
Relative
response"
603
473
215
608
652
859
365
864
428
825
787
436
451
721
470
805
429
272
463
647
*Area counts/ppmC
catalyst oxidation efficiency of greater than
96 percent, and carbon recovery of greater
than 90 percent for hexane and toluene
subjected to trapping in both liquid
(equivalent C02 < 10,000 ppm) and
gaseous forms.
Two field tests were conducted, one at a
textile plant and the other at a veneer ply-
wood plant. Identical dual sampling sys-
tems were used to test the precision of the
method under conditions of actual appli-
cation. During each test, four sets of
duplicate samples were collected. During
the first field test, a 31-percent relative
standard deviation of the pooled values
was obtained. Several modifications were
made to the sampling train and procedure
for the second field test, which resulted in
a pooled relative standard deviation of 8
percent The most significant modifications
included the use of a needle valve-rotameter
combination for maintaining constant flows
during the test period (instead of just the
needle valve as used in the first field test)
and a modified leak-check procedure with
a dead volume correction. In addition, two
condensate traps in series, one at ice water
temperature and the other at dry ice tem-
perature, were used to circumvent the
possible problem of moisture freeze-out in
the dry ice trap.
The best precision of results from dual
sampling trains was ±1.45 percent for
sample #4 from the second field test The
carbon concentration in the polyester cloth
drier exhaust ranged from 200 to 750
ppmC and that in the veneer drier exhaust
ranged from 4,700 to 6,700 ppmC.
Conclusions
Laboratory evaluations of EPA Reference
Method 25 revealed that recoveries of
organic gases exceeded 90 percent when
several standardized mixtures of these
gases in air or nitrogen were analyzed. At
first, poor precision was encountered in
field testing. When dual trains were
employed to sample a fabric finishing
plant effluent stream, a 31 -percent relative
standard deviation (RSD) was obtained for
the pooled values. These results prompted
modification of the sampling trains, im-
provement of the condensible organics
recovery procedure, and introduction of a
sampling train dead volume correction.
When these techniques were employed in
the sampling of the effluent from a plywood
veneer dryer using dual sampling trains,
the pooled values yielded an 8-percent
RSD.
The Byron Model 401 analyzer showed
excellent linearity for a variety of organic
compounds, with the linear range extend-
ing over three orders of magnitude in
some instances. However, the response
to samples of different compounds con-
taining equal ppmC was found to be
different. Incomplete oxidation of organic
compounds to C02 within the analyzer
and peak tailing appear to be among the
many causes that may have contributed to
the unequivalent response. This response
variability is expected to result in inaccu-
racies for measurement of the volatile por-
tion of the sample that is not captured by
the condensate trap and ends up in the
sample tank. The variability of response.
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however, should have no effect on the
precision of results for samples collected
via the dual sampling trains.
Recommendations
Many of the problems with the Byron
Model 401 analyzer might be alleviated to
some extent by constructing an improved
NMO analyzer.
1. Using only one column in tho Byron
Model 401 instead of the three may
substantially reduce the peak tailing
problems by reducing the dead volume.
2. A more efficient catalyst, such as the
hopcalite oxidizing catalyst used in the
liquid condensate recovery and condi-
tioning system instead of the proprie-
tary catalyst used in the Byron instru-
ment may solve the problem of re-
sponse variability associated with in-
complete oxidation of organics.
3. Finally, an inert carrier gas such as
helium or nitrogen used in the chromat-
ographic portion of the analyzer instead
of air may result in reduced interaction
with the column material. A 60/80
'mesh Porapak-N (Waters Associates)
column could be used to separate the
NMO from C02 and other gases. The
column would first elute C02 then the
.N MOs would be backf lushed out of the
column into an oxidation-reduction sys-
tem and finally to an FID. This design
would be much simpler than that origi-
nally shown in Method 2 5 as described
in the Federal Register.
The use of a Heise bourdon tube pressure
gauge in place of the U-tube mercury
manometer is also recommended. Its
advantages include ease of use, portability,
and ruggedness and it is adequately ac-
curate for making sample tank pressure
measurements.
The reuse of the sample tank as the
intermediate collection vessel during con-
densate recovery and conditioning would
eliminate the necessity of measuring tank
volumes and the associated error. This
action is possible because the intermediate
collection vessel volumn (Vv) and the
sample tank volume (Vs) cancel out in the
calculation of condensible organic con-
centrations (Cc) if these volumes are equal
for Method 25 equation derivations. Before
the sample tank is reused, however, it
should be flushed adequately with clean
air to remove any remaining CC^.
The Federal Register procedure speci-
fies that during recovery of the condensate
trap sample, the dry ice must be removed
from the trap before switching the carrier
gas flow through the trap. This method
can create problems of clogged rotameters
and sample loss because the trap gases
begin to expand when the dry ice is
removed. If the carrier gas is switched into
this pressurized trap, water vapor or or-
ganics could expand back into the rotam-
eters. Therefore, the carrier gas should
be passed through the condensate trap
before the dry ice is removed.
G. B. Howe, S. K. Gangwal. and R. K. M. Jayanty are with Research Triangle
Institute, Research Triangle Park, NC 27709.
Joseph E. Knoll is the EPA Project Officer (see below).
The complete report, entitled "Validation and Improvement of EPA Reference
Method 25—Determination of Gaseous Nonmethane Organic Emissions as
Carbon," (Order No. PB 83-191 00 7; Cost: $11.50. 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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