EPA/600/A-92/115
92-99.12
Stability of Air Toxic Gases Listed
in Title III Clean Air Act Amendments
R.K.M. Jayanty
Research Triangle Institute
Research Triangle Park, NC 27709
L.B. Jaffe
Research Triangle Institute
Research Triangle Park, NC 27709
J.R. Albritton
Research Triangle Institute
Research Triangle Park, NC 27709
M.D. Jackson
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
M.R. Midgett
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
The information in this document has been funded wholly or in
part by the United States Environmental Protection Agency under
contract 68-02-4550 to Research Triangle Institute. It has been
subjected to Agency review and approved for publication. Mention
of trade names or commercial products does not constitute
endorsement or recommendation for use.
T.

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92-99.12
INTRODUCTION
Under Title III of the 1990 Clean Air Act Amendments, the
U.S. Environmental Protection Agency (EPA) has recently proposed
Test Method 301 entitled "Field Validation of Emission
Concentrations from Stationary Sources."1 This method, as
specified in the applicable subpart of the Amendments, is to be
used whenever a source owner or operator proposes a test method
to meet an EPA requirement for which a validated method is not
available. This method includes procedures for determining and
documenting the quality, i.e., systematic error (bias) and random
error (precision), of the measured concentrations of the source
emissions. In proposed Test Method 301, the requirement was
added that a performance audit material must be analyzed if it is
available. The method also stated that the analyst shall sample
and analyze the performance audit sample three times according to
the instructions provided with the audit sample. Therefore,
EPA's Atmospheric Research and Exposure Assessment Laboratory has
initiated a program to develop stable and accurate organic
standards (listed in Title III, 1990 Clean Air Act Amendments)
for use in performance audits. The Research Triangle Institute
(RTI), under contract to EPA, has responded to this need by
developing a repository of 59 gaseous organic compounds in
compressed gas cylinders and recyclable aluminum containers
(Scotty IV). Three concentration ranges were selected: low (20
to 200 ppb), mid-level (0.5 to 5 ppm), and high (5 to 50 ppm).
The recyclable aluminum containers were obtained only in the low
concentration range with pressures generally below 400 psig. The
compressed gas cylinders contain pressures up to 2000 psig.
In order to ensure that the concentration of each gas
standard had not changed, each standard was analyzed periodically
for stability. The gas mixtures were analyzed initially by the
manufacturer before shipment to RTI. Upon receipt from the gas
manufacturer, RTI analyzed the gas mixtures to verify the
manufacturer's certified analysis. Subsequently, the gas
mixtures were analyzed periodically (analyzed at 2 to 4 months,
12 months, and thereafter yearly) to determine any change in
concentration of the organic compounds.
Compressed gas cylinders containing toxic organics at ppm
and ppb levels that have been used successfully for performance
audits during environmental measurements are described
extensively in the literature.2*6 A list of organic standards
that are currently available for Test Method 301, the procedures
used to determine the stability of the gas mixtures, and examples
of stability data are given in this paper. In addition, the
usefulness and the stability of organic compounds in Scotty IV
containers are described.
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92-99.12
AUDIT MATERIALS CURRENTLY AVAIIABLE
In 1990, Title III of the Clean Air Act Amendments listed
189 air toxics for which EPA must develop Maximum Achievable
Control Technology (MACT) regulations. Fifty-nine gaseous
organic compounds out of 189 compounds were selected. The
selected compounds were used to perform the stability study and
as audit materials to conduct performance audits during field
validation of emission concentrations from stationary sources.
Table I lists these compounds, which are currently available in
TABLE I. Organic cylinder gases currently available
for clean air act aegulations.	
Available Gases
Acetaldehyde
Acetonitrile
Acrolein
Allyl chloride
Benzene
Bromoform
Bromomethane
Bis (2-chloromethyl) ether
Carbon disulfide
Carbon tetrachloride
Carbonyl sulfide
Chlorobenzene
2 Chloro-l,3-butadiene
Chloroform
Chloromethyl benzene
Chloroprene
Cumene
1,2-Dibromoethane
1,2-Dichloroethane
1,1-Dichloroethane
1.1-Dichloroethylene
Dichloroethyl ether
1.2-Dichloropropane
1.3-Dichloropropane
1.4-Dioxane
Ethylene oxide
Ethyl benzene
Ethyl chloride
Ethyl acrylate
Hexane
Hexachloroethane
Hexachloro 1,3-butadiene
Isooctane
Methanol
Methyl bromide
Methyl chloride
Methylene chloride
Methyl ethyl ketone
Methyl isobutyl ketone
Methyl iodide
Methyl methacrylate
Methyl-t-butyl ether
2-Nitropropane
Perchloroethylene
Perchloroethane
Propylene oxide
Propanol
Propionaldehyde
Styrene
1,1,2,2-Tetrachloroethane
Toluene
Trichloroethylene
1,2,4-Trichlorobenzene
1,1,2-Trichloroethane
2,2,4-Trimethylpentane
Vinyl acetate
Vinyl bromide
Vinyl chloride
p-Xylene
the audit repository. Each compound was prepared in compressed
gas cylinders in a balance gas of nitrogen. The Scotty IV"s
contained only the low concentration range.
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92-99.12
EXPERIMENTAL PROCEDURES
The principal objective of this study was to determine the
stability of gas mixtures in compressed gas cylinders and
recyclable containers (Scotty IV) over time. All measurements
were made by gas chromatography (GC) using flame ionization (FID)
and flame photometric (FPD) detectors.
INSTRUMENTATION
Analyses of gas mixtures above the 1-ppm level were
performed with a Hewlett-Packard 5880 GC with a FID and a FPD.
The FPD was used principally for measurement of sulfur-containing
species. Gaseous samples were injected onto the appropriate
column using a six-port Valco gas sampling valve constructed of
Hastalloy C (high nickel content and low absorptive properties)
mounted near the injection port. The valve was equipped with
interchangeable sample loops to allow the injection of a fixed
volume of gas. After separation of the compound from nitrogen,
the detector response was integrated electronically. GC
conditions for analysis have been described in a separate
report.4
Analyses of gas mixtures below the 1-ppm level (e.g., "100
ppb mixtures in compressed gas cylinders and recyclable
containers) were performed using a Nutech automated cryotrapping
apparatus configured to a Hewlett-Packard 5880A GC equipped with
a subambient oven controller and flame ionization and electron
capture detectors (FID/ECD). The carrier gas outlet flow from
the column was split approximately 10:1 between the FID and ECD
using a vitreous silica outlet splitter. Both the FID and the
ECD signals were processed with the HP-5880A Level 4 processors.
STANDARDIZATION AND MEASUREMENT
The GC for the gas mixtures was calibrated using appropriate
calibration standards comprised of known concentrations of gases
in nitrogen. The preparation method for or source of calibration
standards varied depending on the compound involved. National
Institute of Standards and Technology-Standard Reference
Materials (NIST-SRMs) of benzene and perchloroethylene were used
to calibrate the GC for those two compounds.
When NIST-SRMs were not available, known concentrations of
analytes were generated from permeation tubes or from pure
compounds. The calibration gases for hydrogen sulfide, vinyl
chloride, and ethylene oxide were generated using a permeation
tube/dilution system. For all other compounds, the calibration
standard preparation technique consisted of syringe injection of
known quantities of pure (<99.95%) organic compound into an
evacuated blank checked stainless steel canister of known volume.
The canister was then filled with pure nitrogen, and its final
pressure was measured with a Heise-gauge. The concentration of
the gas mixture was calculated using the Ideal Gas Law. The
4

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92-99.12
sample was diluted further by depressurization and
repressurization with pure nitrogen to achieve its desired
concentration. A standard was prepared fresh for each time
period. For each of these approaches, multipoint calibration
curves were prepared each time a cylinder gas was analyzed.
ANALYTICAL QUALITY CONTROL
As a quality control check on the accuracy of calibration
mixtures prepared by the pressure-dilution technique, NIST-SRMs
of benzene or propane in nitrogen were analyzed by GC-FID against
selected compound calibration standards. The prepared
calibration mixture was used to establish the detector response
on a ppm-carbon basis.
During both the ppm- and ppb-level cylinder gas analyses,
replicate injections of both the audit cylinder gases and the
calibration standards were performed until the relative standard
deviation of replicate injections was less than 1 percent.
RESULTS AND DISCUSSION
Stability Studies - Cylinder Gases
The data collected over time from the measurement of
cylinder concentrations were used to estimate the stabilities of
the organic gases. Cylinder gas stability data are important for
several reasons. First, audit materials used by Federal, State,
and local governmental agencies must be stable to be considered
reliable standards for auditing measurement methods during
regulatory compliance emission tests. Second, if organic gases
in cylinders are stable, other investigators may more readily use
cylinder gases as calibration standards and/or quality control
check samples. Finally, if cylinder contents are stable,
government agencies may conduct performance audits to assess the
accuracy of the measurement methods being developed during tests
for operating permits under Title III of the 1990 Clean Air Act
Amendments.
The term "stability," as it pertains to the study of gaseous
compounds, is defined as the change in concentration with time
for a given cylinder at a specified concentration range. To
ensure that the concentration of each gas standard had not
changed, each standard was analyzed periodically for stability.
A two-tiered stability assessment was conducted. In the first
tier, on each standard, the commercial gas manufacturer conducted
one or two analyses prior to shipment. Once a gas standard was
received from the gas manufacturer, it was analyzed as soon as
within one month, then reanalyzed periodically to determine any
change in concentration.
The stability data obtained to date for 30 of the organics
(listed in the Clean Air Act Regulations) in the ppm-level gas
cylinders have been published in a status report. An example of
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92-99,12
stability data for selected organic cylinder gases is shown in
Table II. (The stability studies for the remaining 29 compounds
are in progress.) An examination of the stability data for many
of the organics in the ppm-level cylinder gases shows that the
TABLE II. Example of stability data for selected ppm-level
gases in compressed gas cylinders.	
Day
Benzene
Toluene
Chloroform
Perehloro-
ethylene
Vinyl
Chloride
Cone.
9.14a
9. 0a
9.81"
7.98a
8.52®
Dateb
5/4/78
3/29/83
1/10/86
7/6/79
10/1/79
Cone.
9.10
8.51
8.92
8.40
7.85
Dayc
132
744
534
52
700
Cone.
7.80
8.04
9.45
7.92
8.41
Day
302
1063
756
376
1812
Cone.
8.50
9.07
9.74
7.94
8.15
Day
1005
1548
1077
1818
2524
Cone.
8.17
9.37
9.54
6.88
8.13
Day
1209
1766
1201
2440
2914
Cone.
8.42
9.12
9.91
7.83
7.60
Day
2162
2092
2020
2901
3088
Cone.
8.40
8.79
9.44
7.68
7.79
Day
2784
2597
____
3118
3404
Cone.
8.72
9.44
————
7.39
7.66
Day
3326
2915
____
3580
3844
Cone.
8.88
9.07
	
7.69
7.49
Day
3549

____
3834
4265
Cone.
9.17
— — ——
_____
7.37
7.67
Day
3887

____
4323

Cone.
8.89
— — —
———
7.38
—	—
Day
4778
— — —
__—
		
— — ——
Cone.
8.80
—		
	
	

a = Manufacturer1s analysis
b = Date of RTI first analysis.
c = Number of days since RTI1s first analysis.
6

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92-99.12
results varied by less than 10 percent over a period of up to ten
years. This variation results primarily from random error during
the stability analytical measurements. The possible sources of
experimental errors in the measurement process that contribute to
this variability include: (1) the variability of the
instrumentation used for analysis (2) the stability of the
calibration standards and (3) the accuracy of independently-
produced calibration standards where NIST-SRMs do not exist.
Estimates of day-to-day measurement uncertainty
(repeatability) for all components have not been performed.
However, the measurement uncertainties for the halocarbons and
eight other organics have been published in the open
literature.2,3 The measurement uncertainty varied from less than
1 percent to 10 percent depending on the compound, and a major
portion of the uncertainty was attributed to the method of
preparation of the calibration standard. The uncertainty of the
GC analysis was determined to be less than 2 percent by multiple
injections of the gas during same-day analyses.
Stability Studies - Cylinder Gases vs. scotty IV Containers
As noted, RTI has obtained organic gases at 20- to
200-ppb ranges in both compressed gas cylinders and recyclable
containers (Scotty IV) to determine their stabilities.
Recyclable containers (Scotty IV) are especially suitable for
holding audit materials for a number of reasons including
simplicity, portability, and low cost. However, the stability of
organic compounds in these containers is not well established.
Hence, stability studies of the 59 organic compounds in both
compressed gas cylinders and Scotty IV containers have been
initiated. Table III summarizes the results of the stability
studies of organic gases in compressed gas cylinders and Scotty
IV containers. An examination of the data indicates that the
stability in Scotty IV containers depends on the type of compound
held; in general, many compounds (23 out of 59) were found to be
unstable relative to those in compressed gas cylinders. Ten of
the 59 organic compounds (Acetaldehyde, 1,3-dichloropropane,
ethylene oxide (below 100 ppb), propylene oxide (below 100 ppb),
ethyl aerylate, hexachloro-1,3-butadiene, methanol, propanol,
propionaldehyde, and 1,2,4-trichlorobenzene) were found to be
unstable in cylinders as well as in Scotty IV containers; thus
they are not suitable as audit materials.
SUMMARY AND CONCLUSIONS
Compressed gas cylinders containing 59 gaseous organic
compounds at three concentration levels have been evaluated for
use in calibration and performance audits during source emissions
measurements. Stability studies indicate that many of these
organic compounds have been found to be stable in compressed gas
cylinders but unstable for certain compounds in recyclable
containers. A compound was rated stable if the concentration did
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92-99.12
Table III. Summary of stability of organic cylinder gases 3-
Ft.3 Scotty IV containers vs. 150-FT.3 compressed
gas cylinders at ppb levels.a,b

3-ft.3
150-ft.3
Compound
Scottv IV
Cylinders
Acetaldehyde
Unstable
Unstable
Acetonitrile
Unstable
X
Acrolein
Unstable
X
Allyl chloride
X
X
Benzene
X
X
Bromoform
X
X
Bromomethane
N/A
X
Bis (2-Chloromethyl)ether
Unstable
X
Carbon disulfide
X
X
Carbon tetrachloride
X
X
Carbonyl sulfide
X
X
Chlorobenzene
X
X
2-Chloro-l,3-butadieneb
N/A
N/A
Chloroform
X
X
Chloromethyl benzene
Unstable
X
Chloroprene
N/A
N/A
Cumene
X
X
1; 2-Dibromoethane
Unstable
X
1,2-Dichloroethane
X
X
1,1-Dichloro-ethylane
X
X
1,1-Dichloro-ethylene
X
X
1;1-Dichloroethyl ether
Unstable
X
1, 2-Dichloro-propane
X
X
1,3-Dichloro-propane
Unstable
Unstable
1,4-Dioxane
Unstable
X
Ethylene oxide
Unstable
Unstable
Ethyl benzene
X
X
Ethyl chloride
X
X
Ethyl acrylate
Unstable
Unstable
Hexane
X
X
Hexachloro-ethanec
N/A
N/A
Hexachloro 1,3-Butadiene
Unstable
Unstable
Isooctane
X
X
Methanol
Unstable
Unstable
Methyl bromide
X
X
Methyl chloride
X
X
Methylene chloride
X
X
Methyl ethyl ketone
Unstable
X
Methyl isobutyl ketone
Unstable
X
Methyl iodide
X
X
Methyl methacrylate
X
X
Methyl-t-butylether
X
X
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92-99,12
Table III (Continued)
Compound
2-Nitropropane
Perchloro-ethylene
Perchloro-ethane
Propylene oxide
Propanol
Propionaldehyde
Styrene
1,1,2,2-Tetrachloroethane
Toluene
Trichloro-ethylene
1,2,4-Tri-chlorobenzene
1,1,2-Tri-chloroethane
2,2,4-Tri-methylpentane
Vinyl acetate
Vinyl bromide
Vinyl chloride
Xylene	
X = stable; N/A = not analyzed
a = nominal concentration 20-200 ppb
b = Reactive
c = Encountered analytical problems
not change by 10 percent over its period of testing ( up to ten
years). Ten compounds (acetaldehyde, 1,3-dichloropropane,
ethylene oxide, propylene oxide, ethyl acrylate, hexachloro-1,3-
butadiene, methanol, propanol, propionaldehyde, and 1,2,4-
trichlorobenzene) were found to be unstable in cylinders as well
as in Scotty IV containers and are therefore not recommended for
use as audit materials.
DISCLAIMER
The information in this document has been funded wholly or in
part by the United States Environmental Protection Agency under
contract 68-02-4550 to Research Triangle Institute. It has been
subjected to Agency review and approved for publication. Mention
of trade names or commercial products does not constitute
endorsement or recommendation for use.
REFERENCES
1.	"Field Validation of Emission Concentrations from Stationary
Sources," Method 301 Federal Register , U.S. Government
Printing Office, Washington, June 1991, Vol.56, pp. 114.
2.	R.K.M. Jayanty, C.B. Parker, C.E. Decker, et al., "Quality
Assurance for Emissions Analysis Systems," ES&T 17(6):(1983).
3-ft.3
Scottv IV
Unstable
X
N/A
Unstable
Unstable
Unstable
X
Unstable
X
X
Unstable
X
N/A
Unstable
X
X
Unstable
150-ft.3
Cylinders
X
X
N/A
Unstable
Unstable
Unstable
X
X
X
X
Unstable
X
N/A
X
X
X
X
9

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92-99.12
3.	G.B. Howe, R.K.M. Jayanty, A. V. Rao, et al., "Evaluation of
Selected Gaseous Halocarbons for Use in Source Test
Performance Audits," JAPCA 33(9):(1983).
4.	J.R. Albritton, S.B. Tompkins, R.K.M. Jayanty, et al.,
Stability of Parts-Per-Million Organic Cylinder Gases and
Results of Source Test Analysis Audits. Status Report No. 13,
Research Triangle Institute, Research Triangle Park, August
1991.
5.	Y.H. Straley, S.B. Tompkins and R.K.M. Jayanty, Stability of
Parts-Per-Billion Hazardous Organic Cylinder Gases and
Performance Audit Results of Source Test and Ambient Air
Measurement Systems. Status Report No. 8, Research Triangle
Institute, Research Triangle Park, October 1991.
6.	R.K.M. Jayanty, J.R. Albritton, Y.H. Straley et al.,
"Stability of PPB and PPM Organic Cylinder Gases Used for
Calibration and Audits," accepted for publication in JA&WMA
(1992).
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TECHNICAL REPORT DATA
1. REPORT NO.
EPA/600/A-92/115
2.
3' PB9 2-188812
4. TITLE AND SUBTITLE
Stability of Air Toxic Gases Listed in Title III
Clean Air Act Amendments
5.REPORT DATE
6.PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
R.K.M. Jayanty, L.B. Jaffe, J.R. Albritton, M.D.
Jackson and M.R. Midgett
8.PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute
Research Triangle Park, NC 27709
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-4550
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Research and Development
Atmospheric Research and Exposure Assessment
Laboratory
Research Triangle Park, NC 27711
13.TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A repository of 59 organic compounds has been established by the U.S.
Environmental Protection Agency (EPA) for use as gas standards in performance
audits during field validation of emission concentrations from stationary sources.
These compounds are listed in Title III of the 1990 Clean Air Act Amendment. The
compounds are prepared in compressed gas cylinders and recyclable aluminum
containers. Three concentration ranges were selected: low (20 to 200 ppb), mid-
level (0.5 to 5 ppm), and high (5 to 50 ppm). The recyclable aluminum containers
were only prepared in the low range, and pressures were generally below 400 psig.
The compressed gas cylinders contained pressures up to 2000 psig. In this program
to ensure that the concentration of each gas standard had not changed, each
standard was analyzed periodically for stability. The gas mixtures were analyzed
by the manufacturer before shipment. They were then analyzed upon receipt, and
reanalyzed periodically to determine any change in concentration. The stability
data obtained to date indicates that many compounds are stable in the compressed
gas cylinders; however, some of the compounds in the recyclable containers are not
stable.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.IDENTIFIERS/ OPEN ENDED TERMS
c.COSATI



18. DISTRIBUTION STATEMENT
19. SECURITY CLASS (This ReDort)
Unclassified
21.NO. OF PAGES
11
20. SECURITY CLASS (This Pajte)
Unclassifed
22. PRICE

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