DETERMINATION OF TOTAL GASEOUS
NONMETHANE ORGANIC EMISSIONS AS CARBON
SUMMARY OF COMMENTS AND RESPONSES
Emission Measurement Branch
Emission Standards and Engineering Division
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
August 1987
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TA3LE OF CONTENTS
Page
Chapter 1. Introduction 2
Chapter 2. Summary of Changes Since Proposal 3
Chapter 3. Summary of Comments and Responses 4
Table 1. List of Acronyms Used in Summary of Comments
and Responses 1
Table 2. List of Commenters. 16
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Taole 1. LIST OF ACRONYMS UStJ
EPA - Environmental Protection Agency
VOC - Volatile Organic compounds
NSPS - New Source Performance Standards
QA - Quality Assurance
VOC - Volatile Organic Compounds
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>.apter 1
INTRODUCTION
On November 7, 1986, the U.S. Environmental Protection Agency (EPA)
published in the Federal Register (51 FR 40448) the revised Method 25,
"Determination of Total Gaseous Nonmethane Organic Emissions as Car-Don."
This method was proposed under the authority of Sections 101, 111, li<:,
116, and 301 of the Clean Air Act, as amended.
Public comments were solicited at the time of proposal. To provide
interested persons the opportunity for oral presentations of data, v^ews,
or arguments concerning the proposed revisions of the test method, a
public hearing was scheduled for December 22, 1986, at the Research
Triangle Park, North Carolina, but no person desired to make an oral
presentation. The public comment period was from November 7, 1986, to
January 21, 1987.
Three comment letters were received concerning issues relative to the
proposed test methods. A detailed d.iscussion of these comments and
responses is summarized in this document. The comments have been carefully
considered, and appropriate changes have been made in the proposed
revision.
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Chapter 2
SUMMARY OF CHANGES SINCE PROPOSAL
The following changes have been made in the revised method since
proposal:
1. Section 4.1.1 has been added to include a contamination cne<;:<
of the sampling equipment.
2. Section 4.1.2 has been revised to allow the use of a vacuum
gauge in place of a mercury manometer for measuring system pressure in
the field.
3. Section 4.1.4 has been revised to reduce the leak check period
from 10 to 5 minutes.
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Chapter 3
SUMMARY OF COMMENTS AND RESPONSES
Commenter IV-D-1
1.1 Comment: Although it was not the intent of the writers of the
method that it be applied universally to any source emitting volatile
organics, past practice has shown that State and local -egulatory agencies,
and even the EPA, will adopt the method without regard for its limitea
applicability. Thus, it behooves the EPA to write reference methods t'lal
have applicability beyond a narrow scope of specific sources. An arbitrary
method with diminished value should be avoided.
For the method to be applicable to a wide range of sources not
covered by new source performance standards (NSPS), or studied during tne
development of these changes, the method should be written in the form of
'general guidelines. These would take the form of a stringent quality
assurance (QA) program to insure acceptable performance for the sources to
be sampled. The changes in the method needed to make it applicable to
specific sources would then be sanctioned, rather than have poor or
meaningless data delivered with a rigid procedure. Thus, much data al-eady
collected using variations of the present Method 25 wi11 maintain izs
validity.
Response: We agree that it was not our intent that the metnod be
applied universally to any source emitting volatile organic compounds
(VOC). we also agree that it would be beneficial if the method could be
written to have a broad applicability to all types of sources, but we do
not agree that this should be done at the expense of the method's accuracy
and precision at those sources for which it is the compliance test method.
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Our experience v/ith performance guidelines for "lec.iod ^3 ;j cia: t :e> /;.'-
become so cumbersome that the method would not be useable for routine
testing. However, this does not preclude any individual or organization
from performing the necessary testing to demonstrate that their procedures
or equipment are adequate for the requirements of Method 25.
Commenter IV-0-1
1.2 Comment: The intent of the filter system is to remove
condensible organic and other particulate material from the sample gas.
The filter temperature was chosen to correspond to the filter temperature
of EPA Method 5, which was selected to prevent collection of sulfjric acid
mists on the filter and has nothing to do with photochemical reactivity of
volatile organic materials. This arbitrary filter temperature should oe
replaced with one consistent with removal of condensible organics or
particulate that does not react photochemically to form ozone.
Some organic compounds that condense in the atmosphere and, therefore,
do not react pho-tochemically, pass through a filter at 250°F and are
measured by the method. This biases the measurement to the high side.
These materials should be excluded from the sample. We suggest that the
filter temperature be reduced to 190°F. Even at this temperature, some
nonphotochemical ly reactive condensible organic materials will pass th-i
filter and be measured, but the potential problem of the sample gas
temperature falling below the dew point will be avoided.
There is no need for the Method 25 filter temperature to correspond
to that of Method 5. There is no relationship between organic emissions
and particulate emissions. Each test method reports its results in units
that are not comparable. If the agency wants to measure the condensible
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organic .naterial in the emissions, It should designate a inet.icc 'idS'r-e:
do so. There are satisfactory methods in use for this purpose that coula
. be appropriated. We suggest the Oregon Department of Environmental
Quality Method 7.
Response: We do not agree that all photochemically reactive organic
compounds must be gases at ambient temperatures. Even those compounds that
are normally liquids at ambient temperature may have a significant vapor
pressure and thus exist partly in the gas phase as evidenced by the
evaporation of organic liquids stored in open containers. If the filtration
temperature were reduced from 250°F to 190°F, we believe that conpounds
that should be counted as VOC would be artificially excluded from the
sample.
Commenter IV-D-1
1.3 Comment: The filtering system could be greatly simplified and
the oven design improved. The design of these components should not be
rigidly specified such that possible improvements are precluded. For
example, the solvents used to clean the probe and filter system between
samples should be thoroughly removed before assembly of the equipment to
preclude contamination of the sample. The long purge time could then be
eliminated. As another example, it would be desirable to reduce the volur-e
of the filtering system so that the error in sample volume would then be
less than 1 percent. The filter system volume could be reduced further by
using 1/8-inch tubing throughout except for thermocouple wells. A 3/8-inch
filter holder can be constructed of Swagelok parts. This would eliminate
the need for a quarter of the equipment that would be hauled to the
sampling'site. Lastly, we see no need for an elbow in the probe.
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: There is no requirement in tne method to clean the prooe
and filter system between samples so this was not a factor in determining
the length of purge time. The purge time of 10 minutes was chosen to
insure that the sampling system was thoroughly purged with sample gas and
at equilibrium and does not seem excessive. Since there is a sample p.,.-^
before sampling begins, there is no error in sample volume and the voi.^e
of the filtering system is not critical.
The elbow at the end of the probe allows the opening of the probe to
be pointed away from the direction of sample gas flow to reduce the amoun:
of particulate matter entering the sampling system..
Commenter IV-D-1
1.4 Comment: The leak check can be reduced from lu minutes to
5 minutes. For a probe system with 0.1 liters volume, a sample size of
3 liters, and a leak rate of 1 percent, the pressure would change 19 mm in
5 minutes. Reducing the probe system volume would reduce the time needed
to conduct the leak check. It should be noted that a leak can be detected
in the same manner by pressurizing the system, with the added advantage
that in the event of a leak, its location can be easily found by wetting
the component connections and looking for bubbles.
ResP°nse: We a9ree that the leak-check procedure can be reduced from
10 minutes to 5 minutes. The method has been revised to reflect this.
While a leak check could be conducted under positive pressure, it is
more appropriate to conduct the leak check under vacuum which is how the
sample train would be operated while collecting the sample.
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Commencer IV-D-i
1.5 Comment: The proposed sampling procedure ignores the need for
isokinetic sampling if participate is present. If the stack temperature :s
less than the filter temperature, condensed organic material, if present,
will be disproportionately sampled. If the stack temperature is g^eate"
than the filter temperature, a nonisokinetic sampling system can be 'jsea.
A lower filter temperature would reduce the need for isokinecio
sampling. The filter temperature would be lower than the stack teuro erasure
in more situations. Also, errors induced by nonisokinetic sampling when
the filter temperature is greater than the stack temperature would be
reduced because the difference in temperature would be smaller and the
amount of particulate volatilized in the sampling train would be less.
Response: We believe that isokinetic sampling is not necessary
because particles formed by condensation are typically submicron in
size and will behave as a gas. Thus, even if the sample is not collected
isokinetically, it will not contain a disproportionate amount of
condensed organic matter.
Commenter IV-D-1
1.6 Comment: Mercury manometers are not suitable for field use.
A vacuum gauge is suitable to estimate vacuums in the field. The initial
and final tank pressures can be measured before leaving and upon return to
the laboratory. We routinely hold evacuated sample tanks for several weeks
without experiencing even small leaks.
Response: We agree that a vacuum gauge of sufficient accuracy would be
suitable to measure vacuum in the field. The method has been revised to
reflect this.
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Commenter IV-0-1; Commenter IV-D-2
1.7 Comment: A post-test leak check should not be eliminated, a
'post-test leak check is necessary to assure sample integrity. If the
promulgated method incorporates the elaborate filter system, a post-test
leak check will be even more of a necessity considering the number of
connections suggested in the proposal.
Response: At the beginning of the run, the system vacuum is at its
highest and the potential for leaks is greatest. This is the most
critical time for leak checking the sampling train. If no leaks are
detected at this point, it is very unlikely that any wou-d develop during
sampling. At the end of the sampling period, the vacuum remaining in the
cylinder will be near zero and the potential for leaks in the system will
be very low. Also if a post-test leak check were added, it would lengthen
the time required to complete a test and would be very unlikely to add any
additional information.
1.8 Comment: A trap burnout temperature of 2(JO°C is specified by
the proposed method. This temperature may suffice for the more volatile
solvents. However, in some sources, specifically some for which there
are no NSPS, organic material captured in the cryogenic trap may pyrolyze
rather than vaporize at these temperatures and will not be recovered.
To insure complete removal of organic material, the traps should be
heated to 600°C. At this temperature, carbon residuals left by pyrolysis
of heavy organics are burned to carbon dioxide and removed from the trap.
The EPA chose the 200°C trap heating temperature out of fear from C02 would
diffuse through the stainless steel trap at higher temperatures and
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contain: nata tne sa.np'e. Ae ha/a -leva" had a p-oi'e;:, f.-j.r.C-'; ::•-.; -..
into the traps at 60U°C trap heating temperatures. Our experience was
that trap blanks of less than 5 ppm were readily achieved at the 600°C
temperature, even when the trap was bathed in C02 from an acetylene torch
EPA's own studies did not indicate a problem with C02 diffusion ;ito :,ie
trap when heated to 60U°C.
Resp_on_se: Because the sample is filtered at 121JC, all mate^'a "is
reaching the condensate trap must be a gas at that temperature. We
believe that a material which can exist as a gas at 121°C will be
vaporized easily when heated to 200°C. At the same time, a tempest j~o
of 200°C should be low enough to avoid decomposing the sample during the
vaporization process. Thus, the 20U°C temperature was chosen because it
provided a temperature that was high enough to vaporize the sample while
minimizing any problems due to decomposition from temperatures that are
too high. Diffusion of C02 through stainless steel at high temperatures
was not a factor in choosing a heating temperature.
Commenter IV-D-1
1.9 Comment_: Materials other than chromia on alumina are superior
catalysts. An oxygen donating cacu'ys-; s«ic:i as manyanese ;i^ije, , j«.;
be allowed so that when more organics are present than oxygen is available,
the catalyst will provide the additional oxygen -»c'j :-?<-; * ; ^n^rt 3.: ' c
the organic carbon to carbon dioxide.
The EPA contractor developing this method evaluated manganese dioxide
as an oxidation catalyst but found it unacceptable. However, the
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contractor evaluated tne catalyst ac an i napprcpri ate cpe"i:~i"iG i-'-Cc~;~, .~;
(4o4°C). The chromia on alumina also failed to perform adequately at tn:s
temperature. When operated at the proper temperature (6bO°C), manganese
dioxide is a superior catalyst to chromium on alumina because of its
oxygen donating properties.
The manganese dioxide catalyst does degrade at temperatures above
700°C. Thus, proper temperature control is necessary.
Chromia on alumina tends to spread the peaks. Sharper peaks from toe
chromatography can be obtained with manganese dioxide. The EPA contractor
reported a peak asymmetry factor of 1.38 for the chromia on alumina
catalysts. The National Council of the Paper Industry for Air and Stream
Improvements, Inc. found a peak asymmetry of 1.24 for the manganese dioxide
catalyst. A factor of 1.0 indicates asymmetrical peak, and is preferred.
The sharper peaks allow for more accurate determination of the
concentrations.
Use of an oxygen donating catalyst alleviates the need for adding
oxygen or air to the carrier gas prior to the oxidation catalyst, thus
simplifying the analysis system. It avoids an additional hazard in ^he
work place. There is SJ.""f icient oxygen ',rt c.ie sample i; - Hj -eye'ic*- :,x-
the catalyst upon each injection. We have used a manganese dioxide
catalyst for several years without "egeneration nth r!~ )th,?r ^har Vr1-.:.
in the sample. We believe that ;ne manganese Jiox:de Cacalyst -:noun
be specified, or at least be allowed, provided that the QA portion of the
method is satisfied.
Response: Although there is good evidence that manganese dioxide
based catalysts have limited ability to oxidize organic compounds in an
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overloading. There is also evidence that, in the absence of sufficient
oxygen, some of the organic material is converted to carbon which deposits
on the surface of the catalyst and is subsequently converted to carbon
dioxide when sufficient oxygen is present. It appears that this process
does not always go to completion and may, over a period time, leaa to loss
of oxidation efficiency. Even though manganese dioxide has the ability to
donate oxygen for oxidation in an oxygen poor environment, it would still
be necessary to add auxiliary oxygen to ensure good performance with
samples having high organic levels. Thus, it's ability to donate oxygen
does not give it any special advantage over other catalysts.
Although most people who use manganese dioxide catalysts operate them
at 850°C, the manufacturers of two of the most widely used manganese
dioxide-based catalysts recommend that they be operated at temperatures no
higher than 454°C. This is the temperature at which they were operated in
our tests, as well as 850°C.
Even though manganese dioxide may have shown a slightly lower
asymmetry factor than that of chromia on alumina, the difference is not
significant. As a result of our evaluation, we concluded tnat cnro'.rii or,
alumina represented the best choice of a catalyst considering all the
factors that affect a catalyst's oerformance.
Commenter IV-D-1
1.1U Comment: Our experience with nickel reduction catalysts is
that they fail rapidly. Any sample containing sulfur compounds poison the
catalyst. We have used a rhodium catalyst on a variety of sources with no
degradation. We have not replaced our reduction catalyst in 7 years of
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concinua! service, .ve S'jyges: t.ia.1: t.ie rnojiuc, catilys:
at least be allowed provided that the QA portion of the nethod is
satisfied.
Response: We would not expect to collect sulfur containing compounds
from sources where Method 2b is specified as the compliance test -nethod.
We did not evaluate rhodium as a reduction catalyst and could not spec:''/
it as the reduction catalyst for Method 25. However, the rhodium catal /st
could be approved as an alternative if sufficient data were presented to
support its use.
Commenter IV-D-2
2.1 Comment: The proposed method does not address the prooleiTi of
residual contamination in the sampling train which users of Method 25 have
confirmed to De a serious problem. A laboratory confirmation of the
presence of residual contamination from a previous test or laboratory
contamination needs to be specified. The proposal should incorporate a
pretest conditioning and QA check of the sampling equipment which will
contribute to the overall reliability of Method 25. Such a procedure could
consist of baking the probe and trap assembly while purging with a suitable
organic-free gas and performing an analysis on tne trap and Sainp'.e tank.
Response: We agree that such a procedure should be included in
Method 25. We have revised tne nethod to incorporate a c :nt.Tni Tat; on
check.
Commenter IV-D-2
2.2 Comment: The proposed particulate filtration system is
unnecessartly complex since particulate concentrations from applicable
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incorporate this elaborate filtering system is estimated (by EPA in 19db)
to cost approximately $1,700. Although we agree that a filtration system
is needed, we believe that an in-stack filter (as mentioned in the proposal
as an option when electrical systems are prohibited) would be adequate. nw
using an in-stack filter, the probe, from the back half of the filter
holder to the condensate trap, could then be baked along with the trap to
determine the condensible organics as in the present system. The method
could alternatively allow the more elaborate filtration system for problem
sources.
Response: We believe that an in-stack filter system is appropriate
only at those sources where a heated out-of-stack filter would be
prohibited for safety reasons. Because many organic compounds can change
physical state between ambient temperature and 250°F, the temperature at
which the sample is filtered determines whether some organic compounds
are counted as VOC or not. Under these circumstances, we believe that tne
only equitable way to measure VOC emissions is to filter all samples at, the
same filtration temperature regardless of the source's operating
temperature.
Commenter IV-D-2
2.3 Comment: The tolerances ostao1 : shed by E0/n ^jr 0* •; - c a 3 r to '-,-
very stringent for such a complex analytical system. Although we have had
limited experience with the system, we are concerned wirn the achievaoi1ity
of the proposed accuracy standards. We oel ieve the present standards are
adequate and should be maintained.
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Re_sp_pnse: Our laboratory program to Devise trie net.'; a ;-rons : "itc :
that the tolerances proposed in the revised method should be achiavaole
by any well operated system. Relaxing the tolerances would be li,
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OF
Docket Number A-36-U5
Docket Item Number
IV-D-1
IV-D-2
IV-0-3
Commenter/Af f 11 iati oji
John £. Pinkerton, Manager
Ai r Quality Program
National Council of the Paper Lidii
for Air and Stream Improvement, {
260 Madison Avenue
New York, New York 10016
Ben A Brodovicz, Chief
Division of Technical Service and
Monitoring
Department of Environmental Resour
Commonwealth of Pennsylvania
Post Office Box 2063
Harrisburg, Pennsylvania 17120
U.V. Henderson, Associate Director
Environmental Affairs Research and
Environmental Affairs 'epartment
Post Office Box 509
Beacon, New York 125U8
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