External Review Draft
February 1980
Draft
Do Not Quote or Cite
Facts and Issues Associated
with the Need for a
Hydrocarbon Criteria Document
NOTICE
This document is a preliminary draft. It has not been formally released by EPA and should not at this stage be
construed to represent Agency policy. It is being circulated for comment on its technical accuracy and policy
implications.
Environmental Criteria and Assessment Office
Office of Health and Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, N. C. 27711
-------
External Review Draft
February 1980
Draft
Do Not Quote or Cite
Facts and Issues Associated
with the Need for a
Hydrocarbon Criteria Document
NOTICE
This document is a preliminary draft. It has not been formally released by EPA and should not at this stage be
construed to represent Agency policy. It is being circulated for comment on its technical accuracy and policy
implications.
Environmental Criteria and Assessment Office
Office of Health and Environmental Assessment
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, N. C. 27711
-------
HCT2 JOB E 2-22-80
NOTICE
EPA Project Officer on this document is Dr. Robert M. Bruce. Correspondence
relating to the subject matter of the document should be addressed to:
Dr. Robert M. Bruce
Environmental Criteria and Assessment Office (MD-52)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
n
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HCT2 JOB C 2-22-80
CONTENTS
AUTHORS AND REVIEWERS v
1. SUMMARY AND CONCLUSIONS 1-1
1.1 INTRODUCTION 1-1
1.2 BACKGROUND INFORMATION 1-2
1.3 CONTRIBUTION OF HYDROCARBONS TO OXIDANT FORMATION 1-5
1.4 MEASUREMENT METHODOLOGY 1-6
1.5 SOURCES AND EMISSIONS 1-7
1.6 AMBIENT AIR CONCENTRATIONS 1-8
1.7 HYDROCARBON/OXIDANT RELATIONSHIP 1-10
1.8 HEALTH AND WELFARE EFFECTS OF HYDROCARBON 1-13
2. RECOMMENDATIONS 2-1
3. INTRODUCTION 3-1
3.1 BASIS FOR AIR QUALITY CRITERIA AND NATIONAL AMBIENT
AIR QUALITY STANDARDS 3-1
3.2 BASIS AND NATURE OF PRESENT REVIEW OF CRITERIA FOR
HYDROCARBONS 3-2
4. BACKGROUND INFORMATION 4-1
4.1 UNIQUE CHARACTERISTICS OF CRITERIA AND STANDARDS
FOR HYDROCARBONS 4-1
4.2 NEED FOR A CRITERIA DOCUMENT FOR HYDROCARBONS 4-3
5. SUMMARY OF 1970 CRITERIA FOR HYDROCARBONS 5-1
5.1 CONTRIBUTION OF HYDROCARBONS TO FORMATION OF
PHOTOCHEMICAL OXIDANTS 5-1
5.2 MEASUREMENT METHODOLOGY 5-5
5.3 SOURCES AND EMISSIONS OF HYDROCARBONS 5-7
5.4 AMBIENT AIR CONCENTRATIONS 5-8
5.5 HYDROCARBON/OXIDANT RELATIONSHIPS 5-17
5.6 HEALTH EFFECTS 5-23
5.7 WELFARE EFFECTS 5-38
6. SCIENTIFIC DATA BASE ON HYDROCARBONS, 1970 THROUGH PRESENT .... 6-1
6.1 CONTRIBUTION OF HYDROCARBONS TO OXIDANT FORMATION 6-1
6.2 MEASUREMENT METHODOLOGY 6-2
6.3 SOURCES AND EMISSIONS OF HYDROCARBONS 6-14
6.3.1 General 6-14
6.3.2 Natural Sources and Emissions 6-20
6.3.3 Manmade Sources and Emissions 6-21
6.4 AMBIENT AIR CONCENTRATIONS 6-56
6.5 HYDROCARBON/OXIDANT RELATIONSHIP 6-91
6.5.1 Factors Affecting the Hydrocarbon-Ozone
Relationship 6-94
6.5.2 Models for Determining Hydrocarbon Emission
Reductions 6-103
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HCT2 JOB C 2-22-80
6.6 HEALTH EFFECTS 6-108
6.6.1 Aliphatic Hydrocarbons 6-109
6.6.2 Alicyclic Hydrocarbons 6-117
6.6.3 Aromatic Hydrocarbons 6-118
6.6.4 Hydrocarbon Mixtures-Gasoline 6-121
6.6.5 Miscellaneous Hydrocarbons 6-125
6.6.6 Health Effects Summary 6-130
6.7 WELFARE EFFECTS 6-133
6.7.1 Welfare Effects Summary 6-138
REFERENCES 7-1
i v
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HCT4/G 1
TABLES
5-1. Some hydrocarbons identified in ambient air 5-10
5-2. Average hydrocarbon compositon, 218 ambient air samples, Los
Angeles, 1965 5-12
5-3. Average and highest concentration measured for various aromatic
hydrocarbons in Los Angeles, 26 days, September through November,
1966 5-13
5-4. Range of yearly maximum 1-hour average concentrations of
aldehydes, Los Angeles County stations, 1951 through 1957. . . . 5-15
5-5. Average formaldehyde and acrolein concentrations by time of day
in Los Angeles, September 25 through November 15, 1961 5-18
5-6. Toxicity of saturated aliphatic hydrocarbons 5-27
5-7. Toxicity of unsaturated aliphatic hydrocarbons 5-29
5-8. Toxicity of alicyclic hydrocarbons: comparative effects of
chronic and acute exposure in air 5-31
5-9. Toxicity of aromatic hydrocarbons: comparative effects of acute
and chronic exposure in air 5-33
5-10. Principal mixtures containing paraffin hydrocarbons 5-37
5-11. Human response to gasoline vapors distilling below 230°F .... 5-39
5-12. Comparative phytotoxicity of unsaturated carbon gases 5-41
5-13. Dosage-response relationships of various plants to ethylene. . . 5-43
5-14. American Industrial Hygiene Association recommended standards
for ethylene 5-44
6-1. Percentage difference from known concentrations of nonmethane
hydrocarbons obtained by sixteen users 6-4
6-2. Summary of national estimates of volatile organic emissions,
1970-1977 6-15
6-3. National estimates of volatile organic emissions, 1977, by
source category 6-16
6-4A. Emissions of volatile organic compounds from stationary external
combustion sources 6-24
6-4B. Emissions of volatile organic compounds from stationary source
internal combustion engines 6-25
6-4C. Emissions of volatile organic compounds from manufacture of
selected chemicals/products 6-26
6-4D. Emissions of volatile organic compounds from sanitary landfills. 6-28
6-4E. Emissions of volatile organic compounds from general use of
domestic solvents 6-30
6-4F. Emissions of volatile organic compounds from domestic and
commercial use of pesticides 6-31
6-4G. Emissions of volatile organic compounds from the use of
architectural surface coatings 6-32
6-4H. Emissions of volatile organic compounds from forest fires and
from open burning of agricultural/landscape wastes 6-34
6-5. Nationwide estimates of VOC emissions from transportation sources,
1970 through 1977 6-35
6-6. Summary data on gasoline composition, reported as weight percent 6-38
6-7. Average gasoline vapor composition 6-39
6-8. Predominant hydrocarbons in exhaust emissions from gasoline-
fueled autos 6-41
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HCT4/G 2
6-9. Summary of exhaust emission data for uncontrolled and catalyst-
equipped gasoline-fueled cars by model year 6-43
6-10. Increase in aromatic aldehyde emission rates for gasoline cars
with increase in fuel aromaticity 6-46
6-11. Total hydrocarbon emission rates on (ECE test cycle) for car
fueled with gasoline, methanol, or a 15% methanol-85% gasoline
mixture 6-47
6-12. Emission rates for hydrocarbons in exhaust from two diesel
vehicles 6-51
6-13. Aldehyde emissions from diesel vehicles operating on five
different fuels, 1975 FTP 6-52
6-14. Comparison of reactivities of different types of organics. . . . 6-54
6-15. Classification of organics with respect to oxidant-related
reactivity in urban atmospheres 6-55
6-15A. Ambient air concentrations of hydrocarbons reported by Graedel . 6-58
6-16. Frequency distributions for 6-to-9 a.m. nonmethane hydrocarbon
concentrations at CAMP sites, 1967 through 1972 6-61
6-R. Trends in 6-to9- a.m. nonmethane hydrocarbons at two sites
in the California South Coast Air Basin, 1967 through 1977 . . . 6-64
6-S. Maximum and Average 6-to-9 a.m. nonmethane hydrocarbon
concentrations at four sites in California South Coast Air
Basin, June through September 1975 6-65
6-17. Total nonmethane hydrocarbon concentrations in 2-hour samples
measured by gas chromatography at urban site in St. Louis for 6
days, September 13-25, 1972 6-67
6-18. Total nonmethane hydrocarbon concentrations in 2-hour samples
measured by gas chromatography at urban site in St. Louis for 4
days, June 21-July 8, 1973 6-68
6-19. 24-hour average hydrocarbon concentrations measured by gas
chromatography at urban site in St. Louis, September 13, 1972. . 6-69
6-20. 24-Hour average individual hydrocarbon measurements at
Wilmington, Ohio, July 18, 1974, determined by gas
chromotography 6-74
6-21. Concentrations of total nonmethane hydrocarbons, methane,
and selected oxygenates in eleven 2-hour and two 1-hour
samples taken over 24 hours, July 18, 1974, Wilmington, Ohio . . 6-76
6-22. 24-Hour average individual hydrocarbon concentrations
measured by gas chromotography, Boston area, 1975 6-77
6-23. Total nonmethane hydrocarbon concentrations in Houston by
time of day for 23 days, July 3-29, 1976 6-80
6-24. Concentrations of hydrocarbons by class in air samples 6-81
6-25. Concentrations of individual hydrocarbons in air samples
collected in Houston on September 11, 1973 6-82
6-Y. Average percentage composition of hydrocarbons in ambient air
at selected sites in Houston (1978) and St. Louis (1972
and 1977), 6-to -9 a.m. period 6-86
6-Z. Effect of wind direction on hydrocarbon composition at site 03
(Houston) 6-87
6-26. Mean values and ranges in aromatic hydrocarbon concentrations
in West Germany, July 1976 6-90
6-X. Some factors that affect the photochemical formation of ozone
from precursors 6-96
vi
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HCT4/G 3
6-27. Comparison of reactivities of different types of organics. . . . 6-100
6-28. Classification of organics with respect to oxidant-related
reactivity in urban atmospheres 6-102
6-29. Effects of alkane vapor exposure on humans 6-112
6-30. Effects of alkane vapor exposure on animals 6-114
6-31. Human experience: Exposure to gasoline vapors 6-123
6-32. Suggested hygienic standard for various hydrocarbon
solvent mixtures based on inhalation toxicity studies
of animals and sensory response of human subjects 6-128
6-33. Houston study ethylene levels 6-135
vn
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HCT4/G 4
FIGURES
5-1. Nonmethane hydrocarbons by flame ionization analyzer, averaged
by hour of day over several months for four cities 5-16
5-2. Hourly aldehyde concentrations at two Los Angeles sites,
October 22, 1968 5'19
5-3. Maximum daily oxidant as a function of early morning total
hydrocarbons, 1966-1968, for CAMP stations; May through October
1967 for Los Angeles 5"21
5-4. Required hydrocarbon emission, control as a function of
photochemical oxidant concentration 2' ^'^
6-1. Density of population in U.S. in 1975 by state, no. people/mi. . 6-18
6-2. Density of total nonmethane hydrocarbon (VOC) emissions in U.S.
in 1975 by state, tons/mi. 6-19
6-3. Distribution of diesel hydrocarbon exhaust emissions, by molecular
weight, between gas-phase and particulate forms 6-49
6-4. Distribution of hydrocarbons, by molecular weight, in diesel fuel
and lubricant 6~50
6-5. Nonmethane hydrocarbon trends in Los Angeles, 1963 through 1972. 6-62
6-6. Sum of nonmethane hydrocarbon concentrations versus number of
samples for two ground sites used in the 1974 Midwest Oxidant
Transport Study 6-72
6-7. Occurrence of gas-phase hydrocarbons, by carbon number, in
gasoline, exhaust, and urban ambient air 6-92
6-8. Calculated gasoline threshold limit value, reflecting impact
of present vs. newly promulgated TLV standard as a function
of the liquid volume percent benzene in the gasoline 6-126
6-9. Geographic location of the grab sample collection sites 6-137
vi 11
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HCT2 JOB E 2-22-80
AUTHORS AND REVIEWERS
The authors of this document were:
Ms. Beverly E. Til ton
Environmental Criteria and Assessment Office
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. Robert M. Bruce
Environmental Criteria and Assessment Office
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
The following persons within EPA reviewed the first draft of this
document and submitted comments:
Dr. Paul Altshuller
Senior Scientific Advisor to the Assistant
Administrator for Research and Development (MD-59)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Dr. John Burchard
Senior ORD Official
Director
Industrial Environmental Research Laboratory (MD-60)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Mr. Alfred H. Campbell
Strategies and Air Standards Division,
OAQPS (MD-12)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Ms. Josephine Cooper
Special Assistant to the Assistant Administrator
for Research and Development (RD-672)
U.S. Environmental Protection Agency
Washington, DC 20460
Dr. Basil Dimitriades
Deputy Director
Environmental Sciences Research Laboratory (MD-59)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Mr. Edward J. Li 11 is
Monitoring and Data Analysis Division,
OAQPS (MD-14)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
IX
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HCT2 JOB E 2-22-80
Mr. Frank McElroy
Environmental Monitoring Support Laboratory (MD-77)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Mr. John O'Connor
Strategies and Air Standards Division, OAQPS (MD-12)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Mr. Patrick K. O'Hare
Office of General Counsel (A-133)
U.S. Environmental Protection Agency
Washington, DC 20460
Mr. Joseph Padgett
Director
Strategies and Air Standards Division
OAQPS (MD-12)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Mr. Johnnie Pearson
Control Programs Development Division
OAQPS (MD-15)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Mr. Charles H. Ris III
Assistant Director for Planning
Office of Health and Environmental
Assessment (RD-689)
Office of Research and Development
U.S. Environmental Protection Agency
Washington, DC 20460
Mr. Matthew Van Hook
Office of General Counsel (A-133)
U.S. Environmental Protection Agency
Washington, DC 20460
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HCT1 JOB K 2-21-80
1. SUMMARY AND CONCLUSIONS
1.1 INTRODUCTION
Section 109(d)(l) of the Clean Air Act, added by the 1977 amendments,
requires that EPA thoroughly review each 5 years the criteria for those pollutants
listed under Section 108 and regulated by National Ambient Air Quality Standards
(NAAQS) under Section 109. According to this requirement, the first such
review of the criteria and standards for hydrocarbons must be completed by
December 31, 1980. Most reviews of the criteria for regulated pollutants have
led to revisions of the existing criteria documents. In the revision process,
thorough evaluation is made of comprehensive scientific information that will
form the basis for a decision on the need for and nature of any revisions to
the National Ambient Air Quality Standard (NAAQS) for the pollutant under
consideration. Preliminary review in 1979, however, of the criteria for
hydrocarbons published in 1970 and of the data base on hydrocarbons compiled
since 1970 called into question the fruitfulness of revising the criteria
document for hydrocarbons. Rather, that review indicated the preferability of
preparing a paper that would address certain key issues and that would serve
as a basis on which EPA can decide (1) whether to make a regulatory decision
without further development of criteria for hydrocarbons; or (2) whether a
full criteria document on hydrocarbons is needed as a basis for a subsequent
regulatory decision. Section 4 presents the rationale behind preparation of
an issue paper in lieu of a full criteria document.
The 1970 air quality criteria document covered only those organic compounds
that are composed solely of carbon and hydrogen and that occur in the atmosphere
in the gas phase. These compounds, hundreds of which have been identified as
being emitted into the atmosphere, are collectively referred to as hydrocarbons.
1-1
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HCT1 JOB K 2-21-80
Hydrocarbons are a specific class of organic compounds, so that all hydrocarbons
are organic compounds but not all organic compounds are hydrocarbons. The
1970 criteria document excluded compounds such as substituted or derivatized
hydrocarbons, e.g., halogenated hydrocarbons. It also excluded all organic
compounds, hydrocarbon or nonhydrocarbon, that occur in the atmosphere in
aerosol or particulate form. It included a brief treatment of aldehydes to
ensure coverage of this class of secondary pollutants formed from hydrocarbons
in the atmosphere.
Similarly, this issue paper covers only volatile hydrocarbons as defined
in the 1970 criteria document and, thus, as covered by the 1971 NAAQS for
hydrocarbons. Aldehydes are generally excluded from this paper since they
are not covered by the NAAQS for hydrocarbons and since the 1978 criteria
document for ozone and other photochemical oxidants included information on
the photochemistry and health effects of aldehydes. Furthermore, the National
Academy of Sciences is presently conducting a review of these aspects of aldehyde
air pollutants for EPA. At the conclusion of the NAS review, EPA will determine
whether further assessment should be conducted as a basis for possible regulatory
action on aldehydes. EPA is currently preparing separate documents that
assess the health effects of a number of nonhydrocarbon organic compounds,
e.g., perchloroethylene, trichloroethylene, ethylene dichloride, acrylonitrile,
and vinylidene chloride.
1.2 BACKGROUND INFORMATION
Hydrocarbons are unique among the seven pollutants or classes of pollutants
listed under Section 108 and regulated under Section 109 of the Clean Air Act.
All pollutants regulated by NAAQS except for hydrocarbons are thought to have
direct deleterious effects on public health, and, in some instances, on public
welfare as well. The criteria developed in 1970 for hydrocarbons showed
clearly, however, that hydrocarbons do not directly produce deleterious effects
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HCT1 JOB K 2-21-80
on public health or welfare. Instead, the criteria showed that hydrocarbons
indirectly cause adverse health and welfare effects through their contribution
to the formation of photochemical oxidants in general and of ozone in particular.
Thus, hydrocarbons were the only pollutant or pollutant class regulated under
Section 109 solely for the purpose of controlling their secondary atmospheric
products.
This approach resulted in an NAAQS that is unique among the seven existing
NAAQS in the following respects: (1) it was not based on the health or welfare
effects of hydrocarbons, either singly or as a class; (2) ,it was accompanied
by a measurement method that is not as specific for the regulated pollutant as
the methods available for other criteria pollutants; (3) it was intended to
serve solely as a guide in helping States determine hydrocarbon emission
reductions needed to attain the 1971 oxidant standard; (4) it was not intended
to be an enforceable standard having the same regulatory weight and function
as the other standards; and for that reason it has not been enforced, no State
Implementation Plans for its attainment have been required, and no routine
monitoring of ambient air levels of nonmethane hydrocarbons have been required
under the hydrocarbon standard. In keeping with its intended function as a
guide for achieving the oxidant standard (which is now a standard for ozone),
the level selected for the 1971 NAAQS for hydrocarbons was fixed by the level
selected for the oxidant standard, and was determined through the application
of an empirical model derived from aerometric data in conjunction with the
atmospheric dispersion-related equation used in the linear rollback model.
In preparing this issue paper, it was necessary once again to review the
criteria for hydrocarbons that were developed in 1970. It was clear from this
review that the contribution of hydrocarbons to the formation of ozone and
1-3
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HCT1 JOB K 2-21-80
other photochemical oxidants was the sole scientific basis for regulating
hydrocarbons under Section 109 of the Clean Air Act. No adverse effects on
health or welfare from hydrocarbons were established in the 1970 air quality
criteria document. EPA also recognized as a result of its recent review that
the answers to three basic and specific questions regarding hydrocarbons will
provide the pivotal criteria upon which the Agency can base a regulatory
decision on hydrocarbons. The first of these questions was settled scienti-
fically and legally when the criteria for ozone and other photochemical oxidants
were revised in 1978 and a new ozone standard promulgated in 1979. Likewise,
the replacement in 1979 of Appendix J with other models settled scientifically
and legally the question of the validity of the method used in 1970 to quantify
the relationship between precursor hydrocarbons and ozone and other photochemical
oxidants. Thus, these two questions are restated here only to focus the
reader's attention on those scientific questions relevant to regulatory decisions
regarding hydrocarbons as precursors to ozone and oxidants. These two questions,
plus an extremely important third question, are:
1. According to present knowledge, do gas-phase hydrocarbons—as a
class—contribute to the formation of ozone and other photochemical
oxidants?
2. According to present knowledge, can the attainment and maintenance
of a uniform, nationwide ambient air concentration of volatile
nonmethane hydrocarbons ensure the attainment and maintainance of
the ozone standard?
3. According to present knowledge, do gas-phase hydrocarbons—as a
class—cause adverse effects on public health or welfare?
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HCT1 JOB K 2-21-80
These basic questions are addressed in this paper using the data base on
hydrocarbons from 1970 through the present. The following additional questions,
pertinent but subsidiary, are also addressed, using the same data base:
4. What analytical methods are available for ambient air hydrocarbons?
How accurate and specific are they?
5. What is the relationship between measurements of hydrocarbon mass in
the ambient air and consequent oxidant pollution? That is, do
monitoring methods for hydrocarbons reflect the oxidant-forming
potential of hydrocarbon mixtures in the ambient air?
6. What are the major sources of hydrocarbon emissions to the atmosphere?
7. What kind of hydrocarbons are emitted from these sources?
8. What are the levels of emissions from the major sources?
9. What are the ambient air levels of hydrocarbons as a class and of
certain individual hydrocarbons or subclasses of hydrocarbons?
10. Have any subclasses of gas-phase hydrocarbons (aliphatics, alicyclics,
aromatics, and mixtures) been demonstrated to have adverse health or
welfare effects—as a subclass? If so, what kind and at what levels?
11. Have any individual hydrocarbons been shown to have adverse health
or welfare effects? If so, what kind and at what levels?
The answers to these questions are provided and documented in Sections 5 and
6. The sections that follow summarize those chapters and are presented according
to the organization of Sections 5 and 6.
1.3 CONTRIBUTION OF HYDROCARBONS TO OXIDANT FORMATION
The information presented in Sections 5.1 and 6.1 substantiates that
most, if not all, gas-phase hydrocarbons participate in a complex series of
photochemical reactions that give rise to the formation of ozone and other
1-5
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HCT1 JOB K 2-21-80
photochemical oxidants in ambient air. Evidence accumulated from both experi-
mental and theoretical research over the past decade strongly supports the
position that reducing the emissions of hydrocarbons will reduce ambient air
concentrations of ozone. Research results continue to indicate, however, that
the hydrocarbon-ozone relationship is exceedingly complex and that it is
dependent upon many factors, including the ratio of nonmethane hydrocarbons to
nitrogen oxides. Research has increasingly corroborated over the past decade
that volatile organic compounds other than hydrocarbons are also photochemically
reactive in the production of ozone and other photochemical oxidants. The
answer, then, to the first question addressed in this document is that gas-
phase hydrocarbons, along with other compounds, do indeed serve as precursdrs
to ozone and other photochemical oxidants in the ambient air.
1.4 MEASUREMENT METHODOLOGY
Routine measurements of total and nonmethane hydrocarbons in ambient air
are made using continuous monitoring analyzers that employ a flame-ionization
detector (FID) as the sensing element. This method is the EPA-adopted method
promulgated when the 1971 NAAQS for HC was promulgated. Nonmethane hydrocarbon
concentrations are determined by separating methane chromatographically from
the remaining hydrocarbons in the ambient air sample and determining the
methane concentration separately. Subtraction of the value for methane yields
the nonmethane hydrocarbon concentration. The methane concentration is of no
particular interest since methane is photochemically nonreactive.
The FID is sensitive to a fraction of a part-per-million (ppm) carbon,
expressed as methane. The FID is not specific for hydrocarbons alone but
responds to any C-H or C-C bonds. Thus, though it is often referred to as a
nonmethane hydrocarbon (NMHC) method, the FID method is more appropriately
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HCT1 JOB K 2-21-80
called a nonmethane organic compound (NMOC) method. The values obtained by
this method are a measurement of the mass of the hydrocarbons in ambient air,
o
expressed as ppm carbon or as micrograms of carbon per cubic meter (|jg/n> )•
The values give no indication of the kind of hydrocarbons measured or the mole
concentration of total hydrocarbons measured.
A collaborative study in 1974 by 16 different users of the EPA reference
method (FID) showed that at the level of the NAAQS for HC, 160 Mg/m3 (0.24
ppm) C, the majority of the measurements were in error by 50 to 100 percent,
with no consistent bias. At higher hydrocarbon concentrations, the measurement
error is considerably less, only 0 to 20 percent.
Gas chromatography (GC) is a more specific method than the FID analyzer
and is the only method available for measurement of individual hydrocarbons.
It is more specific because individual compounds can be identified and peaks
resulting from the presence of organic compounds other than hydrocarbons can
be excluded from the determination of total nonmethane hydrocarbons. GC
techniques are sensitive to the part-per-billion (ppb) level. GC techniques
are more sophisticated and time-consuming, however, than the FID analyzer and
do not lend themselves to continuous monitoring or to long-term analysis of
hydrocarbons in ambient air.
1.5 SOURCES AND EMISSIONS
As noted in the preceding section (1.4), FID measurement methods are not
specific for hydrocarbons but may give a positive response to the presence of
many other organic compounds, even though that response may be a reduced
response. Also, as noted in Section 1.3, many volatile organic compounds
besides hydrocarbons participate in the atmospheric photochemical reactions
that give rise to ozone and other photochemical oxidants. The Environmental
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HCT1 JOB K 2-21-80
Protection Agency in recent years has for these reasons included hydrocarbon
source and emissions data under the broader category of volatile organic
compounds (VOC).
Volatile organic compounds are emitted from both natural and manmade
sources. Methane emissions from natural sources in the United States have
been estimated at about 5 x 10 tons/year. Emissions of isoprene and terpenes
13
from vegetation in the United States have been estimated to be 6.5 x 10
grams/year. Methane is considered to be photochemically inert, but isoprene
and terpenes can alternately act as scavengers of ozone or, under different
conditions, as precursors of ozone. At ratios of NMHC/NO commonly found in
rural areas, where the bulk of natural emissions occur, isoprene and terpenes
are unlikely to act as precursors but instead will react with ozone to consume
it.
On a nationwide basis, manmade emissions of volatile organic compounds
from all sources were estimated to be 28.3 metric tons/year in 1977, a decrease
of about 3 percent since 1970. In 1977, the major source of volatile organic
emissions was transportation (41 percent), followed by industrial processes
(36 percent), and miscellaneous organic solvent use (3.7 percent). Emissions
due to evaporative losses and industrial processes increased from 1970 through
1977, but emissions from highway vehicles decreased by about 7 percent over
the same period as a result of the use of control devices. The decrease in
vehicle emissions occurred in spite of an estimated 30 percent increase in
motor vehicle miles traveled during that period.
Within the categories of industrial processes and miscellaneous sources
of VOC emissions, chemical manufacturing, industrial solvent use, and miscellaneous
solvent use (domestic and commercial) together resulted in VOC emissions of
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HCT1 JOB K 2-21-80
about 9.1 x 106 metric tons in 1977, nearly the total of VOC emissions produced
by highway vehicles (9.9 x 10 metric/tons year). As stated earlier, hydrocarbons
are just one class of those compounds categorized by EPA as volatile organic
compounds. A rough estimate of the percentage of VOC emissions that are
actually hydrocarbon emissions may be obtained by assuming that emissions from
chemical manufacturing and from industrial and miscellaneous organic solvent
use are 100 percent non-hydrocarbon VOC. While this assumption is not wholly
accurate, it is also true that exceptions to it are more than likely offset by
non-hydrocarbon VOC emissions such as oxygenated or even halogenated hydrocarbons
from highway vehicles, stationary source fuel combustion, oil and gas production
and marketing, and miscellaneous combustion sources. Given the basic assumption,
non-hydrocarbon emissions may represent as much as 32 percent of the total VOC
emissions estimated for 1977 (9.1 x 106 MT/yr out of 28.3 x 106 MT/yr).
1.6 AMBIENT AIR CONCENTRATIONS
The monitoring of hydrocarbons that is conducted by the States is for the
purpose of determining reductions in HC emissions needed to control oxidant
levels and is not required for purposes of enforcing the HC NAAQS. Therefore,
the hydrocarbon monitoring by the states is largely for the purpose of obtaining
ambient air data that can be used as input to the respective models used to
determine the percentage reductions in HC emissions that are needed to attain
and maintain the NAAQS for ozone.
Since routine monitoring has not been required, most of the data available
have been obtained from field studies conducted by EPA. Data presented in
this document were obtained from these field studies as well as from the open
literature. In general, the ambient air data are reported as parts per million
or parts per billion carbon (ppm or ppb C), whereas data reported by physicians
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HCT1 JOB K 2-21-80
and toxicologists in animal and human exposure studies are generally expressed
as ppm or ppb compound.
In a recent compendium of ambient air data on gas-phase hydrocarbons by
Graedel (Section 6), the detection of over 1000 organic compounds is documented
according to class of hydrocarbon and source. The most abundant hydrocarbon
by far is methane, with a range of 1.3 to 4 ppm; ethylene and acetylene are
second and third, respectively, with concentrations in the ppb range. The
most abundant of the alkanes are ethane, propane, butane, pentane, and isopentane,
with upper limits all above 50 ppb but less than 200 ppb. The most abundant
unsaturated alkenes and alkynes are ethylene and acetylene, with concentrations
ranging from 227 to 700 ppb as the upper limit, with all other concentrations
less than 52 ppb. In comparison to all the other hydrocarbon classes, the
alicyclic compounds are very limited in number and the combined concentrations
are very low. Excluding benzene, toluene, and the xylenes, the upper limit
concentrations of individual aromatics is less than 22 ppb. Benzene concentrations
range from 0.025 to 57 ppb; toluene ranges from 0.005 to 129 ppb; and the
xylenes range from 0.5 to 61 ppb.
Many of the published detailed studies of organic compounds in the urban
atmosphere were conducted in the 1960s. Results of those studies were summarized
and discussed in the 1970 criteria document for hydrocarbons. Published data
on total NMHC levels in urban atmosphere from 1970 through the present are
relatively abundant, but most of these data suffer from considerable measurement
error since they were obtained with FID instrumentation. Data obtained by EPA
in field studies in St. Louis and Houston are representative of urban atmospheres;
however, the atmospheric hydrocarbon burdens of these two cities are influenced
by different sources. St. Louis is dominated by automotive-related sources
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whereas Houston is influenced by both automotive and industrial emissions.
Data reported in this document for the greater Boston area are representative
of HC concentrations found in suburban areas and data reported for Wilmington,
Ohio, are representative of levels found in rural areas. The Houston area has
a greater number of hydrocarbon-polluting industries than St. Louis or the
Boston area (suburban site), and certainly more than the rural area represented
by Wilmington, Ohio, even though local influences there
include a refinery.
In general, the individual hydrocarbon concentrations observed in the
field studies conducted by EPA were less than the upper limits quoted by
Graedel, though in a few cases the values were higher. Typical concentrations
of total nonmethane hydrocarbons (EPA studies) in urban atmospheres are in the
range of 0.1 to 3 ppm C. Concentrations in rural areas range from 0.04 to 0.2
ppm C.
1.7 HYDROCARBON/OXIDANT RELATIONSHIP
The qualitative aspects of hydrocarbon-oxidant relationships are better
understood now than in 1970 when the hydrocarbon criteria document was published.
Factors affecting the atmospheric photochemical processes were treated in
detail in the 1978 criteria document for ozone and other photochemical oxidants.
That document also gave in detail other qualitative and quantitative information
on the precursor-oxidant relationship, including information on the photochemical
products to be expected from specific organic precursors and the reaction
rates, where known, for the formation of those products. Such information has
therefore been discussed only briefly in this paper. Among those physical
factors having important, even profound, influence on the photochemical
formation of ozone and other photochemical oxidants are: temperature, sunlight
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intensity, spectral distribution of sunlight, occurrence and persistence of
inversions, and other meteorologic, geographic, or climatologic factors.
Among the chemical factors that are important influences are the initial
precursor concentrations (including background levels); composition of the
NMHC mix in ambient air and the relative reactivities of the species present;
and the NMHC/NO ratio. (In this context, NMHC actually refers to nonmethane
J\
organic compounds, NMOC.) Data on precursor-oxidant relationships, including
both theoretical and empirical data, corroborate that a reduction in NMOC will
result in reductions in ambient air concentrations of ozone and other photo-
chemical oxidants. Available reactivity data indicate that all hydrocarbons
that participate in the formation of peroxyacyl nitrates also participate in
the formation of ozone, even though reactivities of the various hydrocarbons
may differ with respect to the different oxidant products.
It is with respect to quantifying the precursor-oxidant relationship that
the relative disparity between the 1970 and 1979 data bases becomes apparent.
The term "relative disparity" is used here because the Administrator acknowledged
in the 1970 criteria document and the promulgation of the 1971 standard the
limitations of models available then for describing the relationship between
hydrocarbons and oxidants. The Appendix J model was the best one available in
1970 when the air quality criteria document was written; and in using it in
its 1971 standard-setting process, EPA made the most effective use it could of
available data describing the hydrocarbon-oxidant relationship. An attempt
has been made in Sections 5 and 6 of this paper to note key characteristics
and shortcomings of the Appendix J method for determining reductions in hydro-
carbon emissions needed to achieve the 1971 NAAQS for oxidant. It must be
emphasized, however, that EPA has since replaced this method by the promulgation
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of other models because data obtained since 1970 have substantiated the
theoretical inadequacies of the Appendix J method.
The characteristics of newer models (AQSM, EKMA, statistical, and linear
rollback) for determining necessary reductions in hydrocarbon emissions have
been briefly summarized in Section 6. It is apparent that the models give
different results, as stated by EPA when it promulgated the 1979 NAAQS for
ozone. It is also apparent that no one model can serve all localities. EPA
is in the process of issuing additional information on precursor/oxidant
models to the States to be used in preparing revisions to State Implementation
Plans.
No model is available that can quantify the relationship between HC
emissions and ozone across the entire nation. The relationship between HC
precursor emissions and oxidant air quality is such that the attainment and
maintenance of a nationally applied ozone standard depend upon HC emission
reductions specifically tailored in accordance with the HC mix (profile), HC
levels, NO levels, HC/NO ratio, and meteorological parameters of local or,
r\ J\.
at most, regional areas. The most fundamental and sophisticated of the models,
the photochemical diffusion models (air quality simulation models, AQSM),
relate hydrocarbon emissions directly to ozone air quality by means of chemical
reaction mechanisms coupled with meteorological factors. These AQSMs require
meteorological and emissions data, disaggregated spatially and temporally, for
the specific area or region in which ozone levels are to be controlled.
Irrespective of which of the EPA-prescribed models may be used, however,
an important point to be made is that all of the models are used to determine
needed reductions in emissions rather than reductions in ambient air levels of
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hydrocarbons. In all the models, the relationship being determined is that
between hydrocarbon emissions and ozone concentrations in ambient air. To
link ozone concentrations to a fixed hydrocarbon concentration in air nation-
wide would not be consonant with what is now known about the atmospheric
reactions and processes that result in the formation of ozone, many of which
are dependent upon meteorological and source characteristics that are by
nature local, o,r perhaps regional, but not national. Thus, according to
present knowledge, the relationship between hydrocarbon precursors and resulting
ambient air levels of ozone and other oxidants is not uniform or monotonic
across the nation and cannot be described on a nationwide basis. Rather, it
can be quantified with any degree of accuracy only on a local, area-specific
basis. The scientific evidence accumulated since 1971 has invalidated the
concept that any one ambient air level of hydrocarbons can be derived that
describes nationwide the relationship between hydrocarbon emissions and resulting
ozone/oxidant ambient air levels or that in any way numerically controls
ambient air levels of ozone/oxidant nationwide.
1.8 HEALTH AND WELFARE EFFECTS OF HYDROCARBONS
The criteria developed by EPA in 1970 for hydrocarbons provided no health
data directly related to ambient levels of gaseous or volatile hydrocarbons as
a pollutant class. The only direct adverse effect attributable at that time
to gas-phase hydrocarbons at levels approximating ambient air concentrations
was the vegetation damage from ethylene; however, this effect was limited to
certain species of plants and certain areas of the country and was by no means
a problem nationwide. The sole purpose of prescribing a nonmethane hydrocarbon
standard was to control the ambient levels of specific smog components such
that the oxidant standard would be met.
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Since the original data base was developed, the criteria document published,
and the standards promulgated for hydrocarbons, nearly 10 years have passed.
A review of the literature since 1970 reveals once again that hydrocarbons, as
a class, do not present a significant potential for adverse health or welfare
effects at the present detectable levels but that hydrocarbons should be
controlled or restricted on the basis of their contribution to photochemical
sinog and the resultant health and welfare effects of the smog products.
In order for any direct effects on health to be observed from exposure to
hydrocarbons, as a class, in the ambient air, the present levels of all gas-phase
hydrocarbons would have to be increased by hundreds to thousand of times. One
member of this class, however, is present in ambient air at levels that represent
a potential for adverse health effects.
This compound, benzene, is a unique aromatic hydrocarbon, and has been
implicated in three pathological conditions; namely, leukemia, pancytopenia,
and chromosomal aberrations. The concern over benzene as a leukemogen and as
the cause of other severe systemic toxicities at low exposure levels has been
widely recognized, as evidenced by the facts that EPA has listed it as a
hazardous pollutant under Section 112 of the Clean Air Act, that NIOSH recently
recommended a much more stringent standard for occupational exposure, and that
Runion (Section 6) has reexamined the practical impact of such a benzene
standard in relation to gasoline exposure as expressed by TLV values.
The leukemogenic nature of benzene is specific to the structure of this
aromatic hydrocarbon. The insertion of an alkyl substituent into the benzene
nucleus to give, e.g., methyl benzene (toluene), completely changes the route
by which the substituted compound is metabolized and changes the resulting
chronic toxicity to the point that toluene lacks the potential to cause
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hematological damage. The toxicity of the xylenes is even greater than that
of benzene or toluene in acute exposures, but less than that of benzene and
toluene in chronic exposures.
Relative to benzene, the remaining hydrocarbons, whether they occur as
mixtures (Carpenter's solvents) or as individual hydrocarbons, can in general
be tolerated at elevated concentration levels. In the case of the aliphatic
hydrocarbons, no threshold limit values have been assigned to the collective1
class of hydrocarbons known as the "simple asphyxiants" since their tolerable
concentrations in air are limited only by the percentage (18 percent) of
available oxygen. Until recently, the C&-Cg alkanes were considered innocuous
as evidenced by TLV's of 500 ppm or more; however, NIOSH has now recommended
o
that a TLV limit of 350 mg/m be established for total C5-Cg alkanes—which
includes pentane, hexane, heptane, and octane—based upon chronic neurological
disorders. On a volume-to-volume basis, these concentrations are equal to
about 120 ppm pentane, 100 ppm hexane, 85 ppm heptane, and 75 ppm octane. No
studies suggest that any of the gas-phase aliphatics are carcinogenic, mutagenic,
or teratogenic in humans or experimental animals; nor is there any reason to
suspect that they will be found to produce such effects based on their chemical
structures relative to known compounds that exhibit these effects. Alkanes
and alkenes, based on limited bioassay data, have been classified as non-
carcinogenic; however, some of the long-chain (C..- or greater) aliphatic
hydrocarbons have been implicated as cocarcinogens or tumor promoters, based
on mouse skin experiments. These long-chain aliphatics are not generally
emitted as gases and are not generally encountered in the atmosphere in the
gas phase.
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Toxicologically, the alicyclic compounds, as a class, resemble the pre-
viously discussed aliphatic hydrocarbons, in that they act as general anesthe-
tics and central nervous system depressants with a relatively low order of
acute toxicity. No occupational or epidemiological evidence was found to
indicate that naphthenes (alicyclic components of gasoline and other hydro-
carbon mixtures) give rise to systemic effects nor are they implicated as
hematopoietic toxicants. Unlike the aliphatic hydrocarbons, the degree of
toxicity of the alicyclic hydrocarbons does not correlate with structural
characteristics. Naphthene vapors at high concentrations cause irritation of
the mucous membranes, with the saturated hydrocarbons generally causing less
irritation than the corresponding unsaturated. No studies were found regarding
the carcinogenic, mutagenic, or teratogenic potential of any alicyclic hydro-
carbons.
Studies by Carpenter (Section 6) on miscellaneous hydrocarbon mixtures
lend additional support to the concept that the majority of aliphatic and
aromatic hydrocarbons, with the exception of benzene, appear to be relatively
nontoxic, even when encountered as mixtures. The lowest suggested hygienic
standard for these solvent mixtures was 90 ppm based upon inhalation studies
with animals in a lethal atmosphere and based upon the sensory response of human
subjects. (As Section 6 shows, typical concentrations of total nonmethane
hydrocarbons in urban atmospheres are in the range of 0.1 to 3 ppm C. Concen-
trations in rural areas range from 0.04 to 0.2 ppm C.)
No welfare effects are produced by hydrocarbons as a class at or near
ambient levels. The effects of a specific hydrocarbon, ethylene, on vegetation
have been well documented. In specific areas of the country, due to a combina-
tion of meteorological conditions and vehicle exhaust emissions, the levels of
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ethylene in the ambient air have resulted in damage to ornamental plant species.
However, ethylene does not appear to be a problem nationwide; and the use of
catalytic converters on autos, especially improved ones expected in the future,
may alleviate the problem, if not eliminate it. Now, as in 1970, there are
certain areas of the country that have air standards for dealing with local
problems from ethylene. California has an air quality standard for ethylene,
for example, which was adopted in 1962 prior to the promulgation of the air
quality standard addressing hydrocarbons.
In summary, with the exception of benzene and ethylene, hydrocarbons do
not appear to cause adverse health or welfare effects.
The majority of studies used to support the present health effects position
on hydrocarbons are studies of acute exposures. Thus, it may be advantageous
to encourage additional research studies under conditions of chronic exposure
to low levels of individual hydrocarbons and mixtures to ensure against any
long-term effects that are not obvious under acute exposure conditions. #s
more information develops in the future, the health and welfare effects of
individual hydrocarbons may have to be determined and documented in separate
assessment reports.
In conclusion, there is no scientific evidence to indicate the need for
preparing a full criteria document for hydrocarbons, since now, as in 1970, an
air quality standard for hydrocarbons cannot be supported based on the health
and welfare effects of hydrocarbons as a class.
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2. RECOMMENDATIONS
Based upon its review of the literature and the scientific evidence
accumulated, ECAO recommends that the appropriate offices and laboratories of
EPA do the following:
1. Make a regulatory decision on the national ambient air quality
standard for hydrocarbons, without further documentation of
criteria. In the future, address hydrocarbons as precursors to
photochemical oxidants in the ozone/oxidant criteria document.
2. Study and document the effects of ethylene on plants, but as a
low-priority item. The effects of ethylene on plants are
nonspecific and resemble the effects of certain other pollutants, of
other environmental factors, and of some plant diseases. Since
gasoline-powered vehicles are its primary source, ethylene is a
ubiquitous pollutant. Ethylene damage to plants is not an acute
problem nationwide, however, because ethylene-sensitive species--
mostly ornamentals--are grown only in certain localities. Also, the
use of catalytic converters on autos, especially improved ones
expected in the future, may alleviate the problem if not eliminate
it.
3. Investigate the need for documenting the health effects of
aldehydes. Secondary aldehydes formed in the atmosphere from the
oxidation of hydrocarbons will be controlled to the extent that
hydrocarbon precursors to oxidants are controlled. Aldehydes are
also primary pollutants, however, and as such are emitted directly
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into the atmosphere from a variety of sources. Some of the aldehydes
(e.g., formaldehyde) are photochemically reactive and may be deleterious
to human health. The decision to document the effects of aldehydes
should probably wait on the completion by NAS of its document on
aldehydes.
4. Study the need for preparing a health assessment document on gasoline
vapor.
5. Inasmuch as chronic exposure data are lacking, consider initiation
by EPA of research on the long-term health effects of low levels of
individual hydrocarbons selected on the basis of toxicologic effects
coupled with ambient air concentrations. If evidence for adverse
health effects accrues from such research or in the open literature,
document the health effects of individual hydrocarbons on a case-by-case
basis to determine the need for their individual regulation.
6. Available data indicate that volatile organic emissions, including
those of hydrocarbons, from some stationary sources are poorly
characterized with respect to the magnitude of emissions and, in
some instances, even species. Efforts to identify magnitude and
species of HC emissions from stationary sources should be intensified,
so that any changes in qualitative profiles of emissions resulting
from technologic changes, fuel conversion, etc., can be detected
before such changes are pervasive enough to affect profiles of
ambient air HC. As species and the magnitude of emissions are
identified, study on a continuing basis the need for preparing
health assessment documents on individual compounds.
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7. Continue development of an accurate and reliable field instrument
for measurement of total nonmethane organic compounds (NMOC) in
ambient air. Develop instrumentation for source emission measure-
ments of NMOC, possibly including instrumentation for measuring
fluxes in organic vapors from evaporation losses. Continue to
refine methodology and instrumentation specific for measurements
of individual nonmethane hydrocarbons in ambient air.
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3. INTRODUCTION
3.1 BASIS FOR AIR QUALITY CRITERIA AND NATIONAL AMBIENT AIR QUALITY STANDARDS
Passage of the Clean Air Act Amendments of 1970 marked the initiation of
the present role of the Federal government in air quality management. This
legislation requires the Administrator to publish a list that includes each
air pollutant--
(A) which in his judgment has an adverse effect on public
health and welfare;
(B) the presence of which in the ambient air results from
numerous or diverse mobile or stationary sources; and
(C) for which air quality criteria had not been issued
before the date of enactment of the Clean Air Amendments of
1970, but for which he plans to issue air quality criteria under
this section.
These amendments further require the Administrator to develop criteria for all
pollutants listed. The criteria are to reflect accurately the latest scienti-
fic knowledge useful in indicating the kind and extent of all identifiable
effects on public health or welfare that result from exposure to each of the
pollutants listed. The criteria are to include information on (1) known or
anticipated adverse effects of the pollutants on welfare; (2) interactions
between the criteria pollutant and other pollutants in the atmosphere if those
interactions will result in adverse effects on public health or welfare; and
(3) variables, including atmospheric conditions, that may alter the effects of
the listed pollutant on public health or welfare. Though criteria have his-
torically been issued in the form of criteria documents, the Clean Air Act
does not specify the form in which criteria must be issued.
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Simultaneously with the issuance of criteria, the Administrator is to
provide to the States and appropriate air pollution control agencies informa-
tion on techniques for controlling the criteria pollutant. In addition, the
Administrator must simultaneously propose primary and secondary national
ambient air quality standards that specify levels of air quality that, based
on the criteria issued and according to the Administrator's judgment, should
not be exceeded if public health and welfare, respectively, are to be
protected. After a suitable period of public comment and review (<90 days),
the Administrator is required to promulgate primary and secondary national air
quality standards, with such modifications as he deems appropriate.
3.2 BASIS AND NATURE OF PRESENT REVIEW OF CRITERIA FOR HYDROCARBONS
Section 109(d)(l), added to the Clean Air Act in 1977, requires that EPA
review each 5 years, or more often if evidence warrants it, the criteria for
those pollutants listed under Section 108 and regulated by National Ambient
Air Quality Standards (NAAQS) under Section 109. According to this require-
ment, the first such review of the criteria and standards for hydrocarbons
must be completed by December 31, 1980.
The Environmental Criteria and Assessment Office therefore initiated
earlier this year the appropriate literature searches and review procedures,
only to come to the realization that available current data on hydrocarbons do
not substantially alter, on two of three major issues, the scientific
position on hydrocarbons that prevailed when the first criteria document for
2
hydrocarbons was written in 1970. Furthermore, preliminary review of the
criteria developed in 1970, and of the data base on hydrocarbons compiled
since then, called into question the fruitfulness of revising the criteria
document for hydrocarbons. Instead, that review indicated the preferability
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of preparing an issue paper that would serve as a basis on which the Agency
can decide (1) whether to make the appropriate regulatory decision without
further development of criteria for hydrocarbons; or (2) whether a full criteria
document on hydrocarbons is needed to serve as a basis for a subsequent regulatory
decision.
To fulfill its purpose, this issue paper is essentially threefold in
nature: (1) it presents those aspects of hydrocarbons and of the NAAQS for
hydrocarbons that are unique among the criteria pollutants and the standards
regulating them; (2) it presents a brief review of the key criteria developed
in 1970 and used in the standard-setting process of 1971; and (3) it examines
the 1970-1979 data on hydrocarbons that are pertinent to those key criteria.
This paper is based on a comprehensive survey of available health and welfare
effects information, but the paper itself is not intended to be an exhaustive
review of all aspects of hydrocarbon pollution. Rather, in areas other than
health and welfare effects, an attempt has been made to review those aspects
of hydrocarbon pollution pertinent to the criteria developed in 1970 and to
present only those established facts that represent a scientific consensus of
present knowledge concerning hydrocarbons. The health and welfare effects
information presented is the result of a thorough screening of the literature
and is given in as concise a form as possible.
It must be emphasized that the 1970 criteria document for hydrocarbons
covered only those organic compounds that are composed solely of carbon and
hydrogen and that occur in the atmosphere in the gas phase. It excluded other
gas-phase organics such as substituted or derivatized hydrocarbons; e.g.,
halogenated hydrocarbons. It also excluded all organic compounds, whether
hydrocarbon or nonhydrocarbon, that occur in the atmosphere in aerosol or
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HCT1 JOB J 2-20-80
particulate form. It included a brief treatment of aldehydes to ensure
coverage of this class of secondary pollutants formed from hydrocarbons in the
atmosphere. It did not cover the oxidants, since that class of secondary
pollutants formed from hydrocarbons was treated in a separate criteria document
for photochemical oxidants.
Similarly, this issue paper covers only gas-phase hydrocarbons as defined
in the 1970 criteria document; that is, compounds of carbon and hydrogen
ranging in carbon number from 1 to about 12- (C-^ - C12). Aldehydes are treated
quite briefly, since the 1978 criteria document for ozone and other photo-
chemical oxidants included information on the photochemistry and health effects
of aldehydes. In addition, the National Academy of Sciences is presently
conducting a review of these aspects of aldehydes for EPA. At the conclusion
of this review, EPA will determine whether further assessment should be conducted
as a basis for possible regulatory action on aldehydes. Other volatile organic
compounds are excluded from this issue paper because they were not covered by
the 1970 criteria document or by the 1971 NAAQS for hydrocarbons; and because
EPA is currently preparing separate documents that assess the health effects
of a number of organic compounds, e.g., perchloroethylene, trichloroethylene,
ethylene dichloride, acrylonitrile, and vinylidene chloride.
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4. BACKGROUND INFORMATION
4.1 UNIQUE CHARACTERISTICS OF CRITERIA AND STANDARDS FOR HYDROCARBONS
Originally listed as a criteria pollutant pursuant to the Clean Air Act
of 1970, hydrocarbons are regulated by a National Ambient Air Quality Standard
that specifies that nonmethane hydrocarbons in the ambient air shall not
o
exceed 0.24 ppm C (160 ug/m ), maximum 3-hour average concentration (6-to-9
4
a.m.), more than once per year.
The NAAQS for hydrocarbons is one of six NAAQS promulgated in April 1971
4
pursuant to Section 109. Of the six NAAQS promulgated in 1971, three governed
individual or narrow chemical classes of pollutants—carbon monoxide, nitrogen
dioxide, and sulfur oxides; and three governed broad classes of pollutants—
photochemical oxidants, total suspended particulates, and gas-phase hydro-
carbons. Of the pollutants regulated as classes, hydrocarbons constitute the
most diverse and heterogeneous group in terms of (1) their health effects at
high occupational levels, (2) the secondary pollutants they give rise to, and
(3) the rates at which they react in the atmosphere. Hydrocarbons constitute
the largest and most chemically heterogeneous class of pollutants regulated by
one standard.
Hydrocarbons are unique among the seven pollutants or classes of pollutants
listed under Section 108 and regulated under Section 109 of the Clean Air Act.
All pollutants regulated by NAAQS except for hydrocarbons are thought to have
direct deleterious effects on public health, and, in some instances, on public
4
welfare as well. The criteria developed in 1970 for hydrocarbons showed
4-1
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HCT1 JOB H 2-20-80
clearly, however, that hydrocarbons do not directly produce deleterious effects
ry
on public health or welfare. The criteria showed instead that hydrocarbons
indirectly cause adverse health and welfare effects through their contribution
to the formation of photochemical oxidants in general and of ozone in particular.
Thus, hydrocarbons are the only pollutant or pollutant class regulated under
Section 109 for the sole purpose of controlling their secondary atmospheric
products. Hydrocarbons are the only regulated pollutants that do not produce
direct adverse effects in a human receptor but which instead produce direct
effects on receptors that are other chemical species in the ambient air. The
ambient air may be considered the receptor for which a hydrocarbon dose-
response relationship must be determined.
These unique characteristics of hydrocarbons and of the criteria for
hydrocarbons have combined to result in an NAAQS for hydrocarbons (HC) that
differs from the other NAAQS. The HC NAAQS is unique among the seven existing
NAAQS for the principal reasons listed below:
1. The NAAQS for HC was not based upon demonstration of adverse effects
4 5
of HC on human health or welfare. '
2. The NAAQS for HC was based solely on the role that HC play in the
atmospheric photochemical reactions that produce ozone and other
oxidants. HC were regulated in 1971 strictly on the basis that they
4 %
are precursors to photochemical oxidants. '
3. The NAAQS for HC was prescribed solely "to provide guidance in
formulating emission control strategies for attainment and maintenance
of the national standard for photochemical oxidants."4 It was not
intended to be an enforceable standard comparable to the other
NAAQS, but was intended to serve as a point of departure to be used
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in determining the reductions in HC emissions needed for achievement
and maintenance of the oxidant standard (now an ozone standard,
since a standard for ozone was promulgated in place of the oxidant
standard in February 1979).
All other pollutants or classes of pollutants for which NAAQS exist are
regulated on the basis of their direct adverse effects on health or on both
health and welfare. Except for hydrocarbons, no other precursor to a regulated
pollutant is regulated by its own separate NAAQS.
4.2 NEED FOR A CRITERIA DOCUMENT FOR HYDROCARBONS
Air quality criteria are descriptors of the relationship that exists
between a pollutant in the ambient air and the effects caused by that pollutant
in a specific receptor or receptor population. Criteria, as described by the
1 3
Clean Air Act, ' must reflect the latest scientific knowledge available and
must identify the effects of a given pollutant expected from the presence of
that pollutant in the air. Where possible, criteria are expressed as a dose-
response relationship. Since the 1971 NAAQS for hydrocarbons was based on the
contribution of hydrocarbons to the formation in ambient air of photochemical
oxidants, the dose-response function that was derived was a quantitative
relationship between hydrocarbon emissions and the resulting levels of photo-
chemical oxidants formed.
Consequently, the first question asked in EPA's current review of the
1970 criteria and of the 1970 to 1979 data base was whether present knowledge
confirms that hydrocarbons in ambient air contribute to or result in the
formation of ozone and other photochemical oxidants. The second question
asked, as the logical outgrowth of the first, was whether the relationship
between precursor hydrocarbons and the resulting oxidant pollution formed was
known to be the same as that expressed in the 1970 criteria document and
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promulgated in 1971, in a different form, as the relationship to be used by
the States in attaining and maintaining the oxidant standard. The revision of
the air quality criteria for ozone and other photochemical oxidants and the
subsequent promulgation in 1979 of the current ozone standard provided answers
to both these questions.6 Though both these questions are basic and crucial
to any regulatory decision on hydrocarbons, they are not sufficient by themselves.
The third basic and crucial question that must be asked is whether hydrocarbons,
as a class, produce any direct adverse health or welfare effects.
A comprehensive review of all aspects of hydrocarbon pollution in ambient
air would be counterproductive since the three questions or issues delineated
above are the pivotal issues to be resolved. First, such a review would be
precluded on the basis of the volume of information alone, given the number of
hydrocarbons that have been detected in ambient air. Second, and most important,
there is no known gas-phase hydrocarbon that can serve as a surrogate for the
entire class of compounds, as an index of the ambient air level of the entire
class, or as an index of the oxidant-forming potential of hydrocarbon mixtures
in ambient air. Consequently, even if a dose-response relationship were
derived for a single hydrocarbon, this criterion would be of no value in a
review of the existing class standard. It would be useful only for regulatory
decisions and action with respect to that individual compound.
In view of these facts, EPA believes that a full criteria document for
hydrocarbons is not appropriate. This issue paper offers and documents answers
to the three basic questions posed above, answers that constitute the pivotal
criteria needed to review the NAAQS for hydrocarbons. If scientific review of
this issue paper should prove the answers given to be inadequate, or should
raise other key questions that must be answered, EPA will undertake the necessary
documentation, either in a revised issue paper or in a criteria document.
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5. SUMMARY OF 1970 CRITERIA FOR HYDROCARBONS
This section sets forth in summary form the criteria for hydrocarbons
that were published in 1970 and upon which the NAAQS for hydrocarbons promulgated
in 1971 was based. This review of the pertinent findings of the 1970 criteria
document is presented here to provide background for understanding the basis
of the present NAAQS for hydrocarbons and to facilitate comparison of that
basis with the current data base on hydrocarbons.
5.1 CONTRIBUTION OF HYDROCARBONS TO FORMATION OF PHOTOCHEMICAL OXIDANTS
The hydrocarbons covered by the air quality criteria document of 1970,
and thus by the NAAQS as well, were only those compounds consisting of carbon
2
and hydrogen that occur in the gas phase in ambient air. In this context,
hydrocarbons having a carbon number greater than about 12 were not covered,
since they generally are not encountered as gases in the atmosphere in other
2
than miniscule amounts. The measurement methodology promulgated at the time
the standard was set is not specific for hydrocarbons, but rather is specific
for C-H and C-C bonds, which are found in many volatile organic compounds
2
(VOC) other than hydrocarbons. Nevertheless, since the criteria document
covered specifically hydrocarbons, as defined above, and since the methodology
2
was promulgated for the purpose of measuring nonmethane hydrocarbons (NMHC),
this issue paper is restricted to that class of compounds.
2
As stated in the 1970 document, the ultimate products of the photooxidation
of HC in ambient atmospheres would probably be carbon dioxide and water vapor,
if a parcel of air were irradiated by sunlight long enough. Complete oxidation
of hydrocarbons in an air parcel does not occur, however, because of shortened
5-1
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HCT3/C 2-19-80
irradiation time, transport, diffusion, the infusion of "fresh" emissions,
etc. At any given time, then, the photooxidation products of hydrocarbons
that reside in the ambient air consist of various intermediates in the
oxidation process. These intermediates are all capable of further reaction
and degradation.
Hydrocarbons become involved in the production of the photochemical air
pollution complex not because of their exposure to sunlight, however, but
2
because of their reaction with other components of the atmosphere. The
processes by which hydrocarbons participate in the formation of ozone and
other photochemical oxidants have been reviewed in detail in two recent EPA
documents, Air Quality Criteria for Ozone and Other Photochemical Oxidants
(1978),7 and Air Quality Criteria for Nitrogen Oxides (1979).8 In addition,
the chemistry of oxidant formation and of the role of organic compounds,
including hydrocarbons, in those processes has been reviewed in two National
9 10
Academy of Sciences documents. ' The description given below is a highly
simplified version of the complex chemical reactions that actually occur in
the atmosphere. It is presented merely to underscore the fact that gas-phase
hydrocarbons do contribute to the formation of ozone and other photochemical
oxidants.
The photochemical oxidants observed in the atmosphere are ozone (OO;
«3
nitrogen dioxide (N02); and peroxyacetyl nitrate (PAN).9 Several other
substances, such as hydrogen peroxide (H202), may be classified as
photochemical oxidants, but their common presence in smog is not well
Q
established. Of these oxidants—all of which are secondary pollutants formed
as a result of chemical reactions in the atmosphere—ozone occurs in the
highest concentrations.
5-2
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HCT3/C 2-19-80
Ozone is the product of a three-body process in which atomic oxygen
reacts with molecular oxygen in the presence of a third body, or molecule (M),
to form ozone plus the altered third body:
0 + 02 + M +03+M (5-1)
The third molecule is usually a nitrogen compound or oxygen. The atomic
oxygen that serves as a reactant in the above equation is generated largely,
if not solely, from the photolysis of nitrogen dioxide (N02):
N02 + hv -> 0 + NO (5-2)
These two reactions together form a mechanism for ozone formation in the
atmosphere, a mechanism that is completed by an additional reaction in which
N02 is regenerated:
NO + 03 •*• N02 + 02 (5-3)
The role of hydrocarbons in promoting reactions 5-1 through 5-3 is complex,
and at the time of the 1970 document was not very well understood. Although
of central importance in smog chemistry, reactions (5-1) through (5-3) by
9
themselves do not explain the atmospheric buildup of ozone. If only these
three reactions were important, the photodissociation of nitrogen dioxide
would rapidly establish a small, steady-state concentration of ozone expressed
by the equation:
kl [N02] (5-4)
^ *>
[0 ] =
[NO]
The photolysis of nitrogen dioxide alone then, does not explain the atmospheric
q
accumulation of ozone, even though it is the mechanism of ozone formation.
The dominant factor in this system is the ratio of N0« to NO. Once the conversion
5-3
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HCT3/C 2-19-80
of NO to N0? is explained, the ozone concentration follows the ratio of N02 to
q
NO concentrations given in equation (5-4). What was inexplicable until about
1970 was the rapidity of oxidation of NO to N02 and the continuing conversion
of NO into N02 during the buildup of ozone, because this defies the relatively
simple theoretical relationship described in equation (5-4).
Early laboratory studies had implicated hydrocarbons, especially olefins,
in the formation of ozone by showing that both ozone and ground-state atomic
oxygen would attack reactive hydrocarbons. Modeling and smog-chamber
simulations have since shown that significant oxidant formation occurs with
nitrogen oxides (NO ) plus aldehydes, NOV plus nonmethane alkenes, or even NO
xx x
Q
plus carbon monoxide (CO) in moist air. Though the mechanism had barely been
suggested when the 1970 criteria document was written, it is now known that
hydrocarbons—along with the other oxidizable pollutants such as aldehydes and
CO—serve the function of regenerating free radicals that react with oxygen in
Q
the air to form alkylperoxy and hydroperoxy radicals. These radicals react
with NO to form NO,,:
H02 + NO •* OH + N02 (5-5)
or
R02 + NO -> OH + N0£
Thus, these oxidizable pollutants can be thought of as pumping the nitric
oxide to nitrogen dioxide. In the process, hydrocarbons become degraded to
other compounds, some of which are also photochemically reactive, such as
formaldehyde. The amount of "pumping" that can be done, and thus the amount
of oxidant formed, depends in a nonlinear manner on both the reactivity of the
oxidizable pollutant-in this case, hydrocarbons—and its concentration.
Advances made since 1970 in understanding the reaction mechanisms involved are
summarized in Section 6.
5-4
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HCT3/C 2-19-80
5.2 MEASUREMENT METHODOLOGY
As stated in the 1970 air quality criteria document for hydrocarbons, the
complexity of the mixtures of hydrocarbons present in ambient air demands
sophisticated instrumentation and techniques for measurement. In 1970 a
technique was already available for the measurement of the concentration of
total hydrocarbons in ambient air. Originally developed as a detector for gas
chromatography, this flame ionization technique (FID) was adapted for total
hydrocarbon analysis around 1960. In the technique, a sensitive electrometer
detects the increase in ion intensity resulting from the introduction into a
hydrogen flame of a sample of air containing any organic compound (e.g.,
hydrocarbons, aldehydes, alcohols). The response is approximately in proportion
to the number of organically bound carbon atoms in the sample, but its response
to carbon atoms in different compounds is nonlinear. That is, the response of
the detector to different classes of hydrocarbons is variable and the response
12
appears to fall off rapidly with increasing carbon number. FID data are
usually expressed as the calibration gas used: for example, parts per million
of carbon as methane. The fact that FID response may be, and often is, related
to different reference compounds (methane, propane, butane, etc.) further
12
complicates the comparability, interpretation, and usefulness of FID data.
Carbon atoms bound to oxygen, nitrogen, or halogens give reduced or no response.
The instrument responds to hydrocarbon derivatives approximately according to
the proportion of carbon atoms bound to carbon or hydrogen. There is no
response to nitrogen, carbon monoxide, carbon dioxide, or water vapor; but
there is an oxygen effect, which can be minimized by appropriate operating
conditions.
The response of the FID is rapid and, with careful calibration, is sensi-
tive to a fraction of a ppm carbon as methane. Variations in FID response to
5-5
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HCT3/C 2-19-80
various hydrocarbons and derivatives detract from the comparability and
usefulness of FID data. Practically all continuous hydrocarbon analyzers in
use in 1970 utilized the flame ionization detector as the sensing element.
The value of the data obtained from measuring total hydrocarbon
concentrations is limited. The high background level of naturally occurring
methane obscures variations in levels of other hydrocarbon species which,
unlike methane, participate in photochemical reactions and are therefore of
principal interest. Consequently, methods for measuring methane separately
and determining nonmethane hydrocarbons by subtraction of the methane values
2
had been attempted by 1970 and had met with some success. Many of the
nonmethane hydrocarbon data obtained prior to 1970 were data obtained by use
12
of a relatively crude carbon absorber to separate out the methane. At the
time the NAAQS for hydrocarbons was promulgated, EPA promulgated as the
Federal Reference Method an FID method for determining nonmethane
hydrocarbons. In the EPA method, which was developed around 1970 and which
represented a major improvement over the carbon absorber, the air sample
containing methane and carbon monoxide is passed quantitatively through a
stripper column to a gas chromatographic column that separates the two gases.
The methane is eluted first and is passed unchanged into the FID. (The CO is
eluted into a catalytic reduction tube where it is reduced to methane and is
subsequently measured by the FID. The CO measurement is not needed in
measuring NMHC.) The NMHC concentration is obtained by subtracting the
5
methane value from the total hydrocarbon concentration. The method is
applicable to the semicontinuous measurement of hydrocarbons corrected for
methane in the ambient air. This method has been incorrectly called a "total
hydrocarbon (THC)" measurement method, when in fact the FID also responds to
oxygenated compounds such as alcohols and aldehydes having >2 carbon atoms,
5-6
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HCT3/C 2-19-80
as well as to other volatile organic compounds (VOC). Nevertheless, in the
absence of a suitable method specific for hydrocarbons, EPA promulgated this
method in 1971 as the best available method, and thus the method of choice,
2 4
for the measurement of total hydrocarbons and of npnmethane hydrocarbons. '
Other methods available in 1970 for the measurement of hydrocarbons
included spectrometric and gas chromatographic techniques. Available spectro-
metric methods for total and specific analyses were complex and generally
insensitive. Gas chromatographic techniques, while providing the requisite
sensitivity and specificity for the measurement of individual
hydrocarbons, ' required a high degree of operator skill and experience.
Furthermore, they were applicable only to short-term analyses because of the
2
time, effort, and skill involved in data reduction.
5.3 SOURCES AND EMISSIONS OF HYDROCARBONS
Hydrocarbons in the ambient air arise from both natural and man-made
(technologic) sources. The presence of hydrocarbons from natural sources was
established in 1948 with the measurement of background methane
concentrations. Although most natural hydrocarbons arise from biological
sources, small and highly localized quantities of methane and a few other
lower-molecular-weight hydrocarbons are emitted by geothermal areas, coal
2
fields, natural gas and petroleum fields, and natural fires.
Some estimates of natural methane and of terpenes and isoprene from
vegetation were available in 1970. Koyama, in 1963, conservatively estimated
8 18
the worldwide emission of natural methane to be 3 x 10 tons per year.
Worldwide emissions of volatile terpenes and isoprenes from vegetation were
8 19
estimated in 1965 by Rasmussen and Went at 4.4 x 10 tons per year. No
estimate of natural emissions in the United States alone was given in the 1970
2
document.
5-7
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HCT3/C 2-19-80
Total nationwide manmade emissions of hydrocarbons and related organic
compounds were estimated at 32 x 106 tons for 1968. Transportation (mobile
sources) accounted for 52 percent of this estimate. Miscellaneous sources,
principally solvent evaporation, constituted the second largest category of
sources and contributed 27 percent of these emissions. Industrial processes
were third, with 14 percent; solid waste disposal was fourth, with 5 percent;
2
and fuel combustion in stationary sources was fifth, with 2 percent.
Local emissions for 22 metropolitan areas, as opposed to total nationwide
emissions, were estimated to range from about 0.05 to 1.3 million tons per
year, depending on the area. Transportation sources accounted for 37 to about
99 percent of local emissions, and process losses—solvent evaporation and
industrial processes combined—accounted for 1 to 63 percent. Thus, total
hydrocarbon emissions in 1968, the base year used in the 1970 criteria
document, originated primarily from the inefficient combustion of volatile
20
fuel and from the use of hydrocarbons as process raw materials.
Conventional automobiles (gasoline-powered, internal combustion engines)
potentially emit gas-phase hydrocarbons from four sources: engine exhaust,
2
crankcase blow-by, carburetor evaporation, and fuel tank evaporation.
Positive crankcase ventilation (PCV) systems were introduced in 1963 that
21
virtually eliminated crankcase blow-by emissions. Emissions from the other
three sources were not yet controlled to any appreciable extent in 1968, so
that uncontrolled conventional automobiles constituted most of the aggregate
of passenger cars and other light-duty vehicles at that time.
5.4 AMBIENT AIR CONCENTRATIONS
Methane concentrations were reported in the 1970 document to range
o
generally from about 0.7 to 1.0 mg/m (1.0 to 1.5 ppm), but to occur often at
5-8
-------
HCT3/C 2-19-80
2
levels as high as 4 mg/m (6 ppm) in populous areas. Yearly averages of
monthly maximum 1-hour average total hydrocarbon concentrations, which
included methane, ranged from 8 to 17 ppm (as carbon) at stations of the
2
Continuous Air Monitoring Projects (CAMP) network for 1962 through 1967. Few
data were available in 1970 for comparing nonmethane hydrocarbon (NMHC)
2
concentrations at various geographic locations. From the data available in
1968 from the CAMP network, 24-hour average NMHC concentrations, averaged over
several months, were about 0.5 to 0.8 ppm C in Washington, D.C.; about 0.6 to
1.5 ppm C in Denver; about 0.8 to 1.3 ppm C in St. Louis; and about 0.6 to 1.3
ppm C in Chicago. a In urban areas, the ratio of nonmethane hydrocarbons to
methane was estimated at 0.6 in Cincinnati and at 1.9 in Los Angeles in 1964.
The higher ratio in Los Angeles may have been a reflection of the greater
2
traffic density in that city.
In a series of 200 samples taken in one urban location, average con-
centrations of the most abundant hydrocarbons were (in ppm as C): methane,
3.22; toluene, 0.37; n-butane, 0.26; isopentane, 0.21; ethane, 0.20; benzene,
0.19; n-pentane, 0.18; propane, 0.15; and ethylene, 0.12. Among classes of
hydrocarbons, alkanes predominated even when methane levels were excluded.
They were followed, in order, by aromatics, olefins, acetylene, and alicyclics.
Detailed hydrocarbon data for samples taken in Los Angeles in 1965, as
pO—OC
determined by gas chromatography, are shown in Tables 5-1 through 5-3.
The hydrocarbons that appear on these tables are typically found in most urban
areas. The quantitative profiles differ from one urban area to the next;
however, the qualitative profiles do not vary widely in urban areas influenced
predominantly by automobile emissions. Examination of these qualitative
profiles and comparison with whole gasoline and gasoline vapor constituents
5-9
-------
HCT3/C 2-19-80
TABLE 5-1. SOME HYDROCARBONS IDENTIFIED IN AMBIENT AIR
22-24
Carbon
number
1
2
2
2
3
3
3
3
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
5
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
7
Class
Al kane
AT kane
AT kene
Al kyne
Al kane
Al kene
Al kene
Al kyne
Al kane
Al kane
Al kene
Al kene
Al kene
Al kene
Alkene
Al kane
Al kane
Alkene
Al kene
Alkene
Al kene
Al kene
Al kene
Al kene
Cycloalkane
Cycloalkene
Al kane
Al kane
Al kane
Al kane
Alkane
Al kene
Al kene
Alkene
Al kene
Al kene
Al kene
Al kene
Al kene
Aromatic
Cycloalkane
Cycloalkane
Al kane
Compound
Methane
Ethane
Ethyl ene
Acetylene
Propane
Propylene
Propadiene
Methyl acetylene
Butane
Isobutane
1-Butene
cis-2-Butene
trans-2-Butene
Isobutene
1,3-Butadiene
Pentane
Isopentane
1-Pentene
cis-2-Pentene
trans-2-Pentene
2-Methyl-l-butene
2-Methyl-2-butene
3-Methyl-l-butene
2-Methyl -1 , 3-butadiene
Cyclopentane
Cyclopentene
Hexane
2-Methyl pentane
3-Methylpentane
2, 2-Dimethyl butane
2, 3-Dimethyl butane
1-Hexene
cis-2-Hexene
trans-2-Hexene
cls-3-Hexene
trans-3-Hexene
2-Methyl -1-pentene
4-Methyl -1-pentene
4-Methyl -2-pentene
Benzene
Cyclohexane
Methyl cycl opentane
2-Methyl hexane
5-10
-------
HCT3/C 2-19-80
TABLE 5-1 (continued)
Carbon
number
Class
Compound
7
7
7
7
8
8
10
Alkane 3-Methylhexane
Alkane 2,3-Dimethylpentane
Alkane 2,4-Dimethylpentane
Aromatic Toluene
Alkane 2,2,4-Trimethylpentane
Aromatic o-Xylene
m-Xylene
p_-Xylene
Aromatic m-Ethyltoluene
£-Ethyltoluene
1,2,4-Trimethyl benzene
1,3,5-Trimethy1benzene
Aromatic sec-Butyl benzene
5-11
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HCT3/C 2-19-80
TABLE 5-2. AVERAGE HYDROCARBON COMPOSITION,
218 AMBIENT AIR SAMPLES,
LOS ANGELES, 196525
Concentration
Compound
Methane
Ethane
Propane
Isobutane
n-Butane
Isopentane
n-Pentane
2, 2-Dimethyl butane
2-Methylpentane
2, 3-Di methyl butane
Cyclopentane
3-Methylpentane
n-Hexane
Total alkanes (excluding methane)
Ethyl ene
Propene
1-Butene + Isobutylene
trans-2-Butene
cis-2-Butene
1-Pentene
2-Methyl-l-Butene
trans-2-Pentene
cis-2-Pentene
2-Methyl-2-Butene
Propadiene
1,3-Butadiene
Total alkenes
Acetylene
Methyl acetylene
Total acetylene
Benzene
Toluene
Total aromatics
Total
ppm
3.22
0.098
0.049
0.013
0.064
0.043
0.035
0.0012
0.014
0.004
0.008
0.012
•0.3412
0.060
0.018
0.007
0.0014
0.0012
0.002
0.002
0.003
0.0013
0.004
0.0001
0.002
0.1020
0.039
0.0014
0.0404
0.032
0.053
0.0850
3.7886
ppm (as carbon)
3.22
0.20
0.15
0.05
0.26
0.21
0.18
0.01
0.08
0.02
0.05
0.07
1.28
0.12
0.05
0.03
0.01
Negligible
0.01
0.01
0.02
0.01
0.02
Negligible
0.01
0.29
0.08
Negligible
0.08
0.19
0.37
0.56
5.43
Determined by multiplying compound concentration by number of carbon atoms
in the compound.
5-12
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HCT3/C 2-19-80
TABLE 5-3. AVERAGE AND HIGHEST CONCENTRATION MEASURED
FOR VARIOUS AROMATIC HYDROCARBONS IN LOS ANGELES,
yc
26 DAYS, SEPTEMBER THROUGH NOVEMBER, 1966
Average Highest measured
concentration, concentration,
Aromatic hydrocarbon ppm ppm
Benzene 0.015 0.057
Toluene 0.037 0.129
Ethyl benzene 0.006 0.022
£-Xylene 0.006 0.025
m-Xylene 0.016 0.061
o-Xylene 0.008 0.033
ifPropylbenzene 0.003 0.012
n-Propylbenzene 0.002 0.006
3-and 4-Ethyl toluene 0.008 0.027
1,3,5-Trimethylbenzene 0.003 0.011
1,2,4-Trimethylbenzene, and
jhButyl-and s.ec-Butylbenzene 0.009 0.030
tert-Butylbenzene 0.002 0.006
Total aromatics 0.106 0.330
5-13
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HCT3/C 2-19-80
(see Section 6) reveal the important influence of mobile source emissions on
hydrocarbon mixtures in urban atmospheres.
Among the hydrocarbon oxidation products for which ambient air data were
available in 1970, aldehydes were by far the predominating compounds. Total
aldehyde concentrations for Los Angeles for 1951 through 1957, as determined
27
by manual, wet-chemical methods, are shown in Table 5-4. Further study in
1960 in the Los Angeles area showed that concentrations of total aldehydes
ranged up to 0.36 ppm for a 10-minute sample, with formaldehyde not exceeding
3
130 ug/m (0.10 ppm). The maximum acrolein (acrylic aldehyde) value was 25.2
ug/m (0.011 ppm); but most values were less than half that level. Typical
28
aldehyde concentrations were around 0.10 ppm on many days. Yearly maximum
1-hour average aldehyde concentrations in Los Angeles ranged from 0.20 to 1.30
ppm.
The 1970 report documented the diurnal patterns of nonmethane hydrocarbons
for several cities, showing that in most of the urban areas sampled maximum HC
concentrations coincided with the peak traffic period of about 6- to 9-a.m.
29
These diurnal patterns, illustrated in Figure 5-1, do not parallel the
diurnal variations in secondary contaminants, particularly ozone. Instead,
2
secondary pollutants typically show a pronounced maximum in the afternoon.
Insufficient data were available in 1970 to determine seasonal variations in
hydrocarbon concentrations nationwide. Data available then for 17 California
cities showed, however, that in 14 of those cities maximum HC concentrations
(averages of maximum hourly averages) occurred in October or November,
presumably as a consequence of the similar meteorological conditions that
2
prevail along the California coast.
5-14
-------
HCT3/C 2-19-80
TABLE 5-4. RANGE OF YEARLY MAXIMUM 1-HOUR AVERAGE CONCENTRATIONS
OF ALDEHYDES, LOS ANGELES COUNTY STATIONS, 1951 THROUGH 195727
Concentration range, ppm
Year Formaldehyde Total aldehydes
1951 0.05 - 0.12 0.26 - 0.67
1952 0.20 - 0.27
1953 0.25 - 1.20
1954 0.39 - 0.80
1955 0.47 - 1.28
1956 0.51 - 1.30
1957 0.27 - 0.47
5-15
-------
1.5
1.0
0.5
i—i—i—i—i—i—i i i r
CHICAGO
(MAY THROUGH AUGUST AND OCTOBER, 1968)
I I i I I I I I I
1.5
1.0
0.5
2.0
1.5
1.0
0.5
u
a.
a.
of
Z
o
CD
o
o
a
o
<
Z
O
Z
1 1
ST. LOUIS
(MAY THROUGH JULY, SEPTEMBER, AND OCTOBER, 1968)
J^ I I I I I I I I I I
1 I
DENVER
~
=-^._,
(JANUARY
1 1
1 1 1 1 1 1 1 1 1
«-x
• \ X """ "—"""** N*
/ •-.. s •**.
f
THROUGH MARCH, MAY, SEPTEMBER, AND OCTOBER, 1968)
I 1 1 1 1 1 1 1 1
^i
—
0.5
0
1
I I
WASHINGTON,
J 4~"~ m ^" •
(JANUARY
I I
2
.«
I I I
•**" • — -^. . .
I I I I
-.^
THROUGH APRIL AND AUGUST THROUGH OCTOBER
I I I
6 1
— ~ »• »
I I I I
2 6
4 n.m.
I
, 1968)
1
* 4
—
i;
— ^
LOCAL TIME
Figure 5-1. Nonmethane hydrocarbons by flame ionization analyzer, averaged by
hour of day over several months for four cities. 29
5-16
-------
HCT3/C 2-19-80
Diurnal variations in aldehyde concentrations display an early rise, a
broad plateau or maximum through most of the day, and a decrease in the
afternoon. This pattern is shown for formaldehyde and acrolein concentrations
on 0.1
in Los Angeles in Table 5-5, for 1961, and in Figure 5-2, for 1968.
5.5 HYDROCARBON/OXIDANT RELATIONSHIPS
National ambient air quality standards regulate the concentrations of
criteria pollutants in the air. They do not directly regulate emissions,
though emissions are controlled in order to meet NAAQS. In the case of measure-
ments of ambient air concentrations of hydrocarbons, such measurements do not
necessarily reflect emissions of hydrocarbons. At any given time that an
urban atmosphere is being measured, the hydrocarbon concentrations measured
may represent just one point in time—and space—during a dynamic process that
involves the mixing of fresh hydrocarbon emissions (1) with already-reacted
(and thus chemically transformed) hydrocarbons, (2) with relatively unreactive
or slowly reactive hydrocarbons, and (3) with many other pollutants under
various changing meteorologic conditions. Consequently, the major problem
facing atmospheric chemists in 1970, including the authors of the air quality
criteria document, was that of relating hydrocarbon emissions to resulting
oxidant air quality by means of relationships based on ambient air concentra-
2
tions of hydrocarbons. The criteria document stated:
The development of a model to relate emission rates of hydrocarbons
to ambient air quality and then to the secondary products of photochemical
reactions has proved to be an elusive problem. Because of this lack
of an appropriate model, the relationship between hydrocarbon emissions
and subsequent maximum daily oxidant levels must be approached empirically.
The empirical approach adopted is a comparison of 6 to 9 a.m. average
hydrocarbon values with hourly maximum oxidant values attained later
5-17
-------
HCT3/C 2-19-80
TABLE 5-5. AVERAGE FORMALDEHYDE AND ACROLEIN CONCENTRATIONS BY TIME OF DAY IN
30
LOS ANGELES, SEPTEMBER 25 THROUGH NOVEMBER 15, 1961OU
Formaldehyde
Sampling
time
Number of
days
Average
concentration, ppm
Acrolein
Number of
days
Average
concentration,
ppm
7:00 a.m. 7 0.041 2 0.007
8:00 a.m. 18 0.043 3 0.009
9:00 a.m. 21 0.045 3 0.009
10:00 a.m. 28 0.044 5 0.008
11:00 a.m. 27 0.051 5 0.008
Noon 23 0.044 3 0.005
1:00 p.m. 25 0.041 7 0.008
2:00 p.m. 27 0.034 5 0.007
3:00 p.m. 25 0.026 4 0.004
4:00 p.m. 15 0.019 5 0.004
5-18
-------
U. Id
0.16
LU
£ 0.14
£ 0.12
O
_) 0.10
<
u i °-°8
^ y,- 0.06
oi o °-°4
<< 0.02
a o
< LU 0.14
LU O
Q Z 0.12
> O
1 *-* 0.10
3 0.08
5 0.06
Of.
O 0.04
II
0.02
(
I I I I I
— .X*** HUNTINGTON —
i_ «X \ PARK _
i- / X\\
L, ./X/%*\
/ * •* *• »\
— ^ / / v —
-X /..** ALIPHATIC —
^ /* ALDEHYDES
•fSf? - — -FORMALDEHYDE
^ EL MONTE
/ \
I / N I
- x^^ iV~
> . ~~
1
— ^"1.* 1^"""* ~~
— •••* —
1 1 I 1 1
5 12 <
U.U1B
0.016
0.014
0.012
Q
0.010 a
fc
0.008 g
0.006 i-
0.004 *
0.002 ^
OB—
2
O
0.014 U
•^
0.012 -
LU
0.010 ^
0.008 Q
0.006 <
0.004
0.002
•
LOCAL TIME
Figure 5-2. Hourly aldehyde concentrations at two
Los Angeles sites, October 22,1968.31
5-19
-------
HCT3/C 2-19-80
in the day. This approach has validity only because of the dominating
influence of the macro-meteorological variables on both the concentra-
tions of precursors and photochemical products. Furthermore, this
approach can yield useful information only when a large number of
days are considered; this guarantees the inclusion of all possible
combinations of emission rates, meteorological dilution and dispersion
variables, sunlight intensity, and ratios of precursor emissions.
When maximum daily oxidant values from such an unrestricted data base
are plotted as a function of the early morning hydrocarbons, a complete
range of oxidant values--starting near zero and ranging up to finite
and limiting values—is observed. Given data for a sufficient number
of days, it becomes apparent that the maximum values of attainable
oxidant are a direct function of the early morning hydrocarbon con-
centration. This upper limit of the maximum daily oxidant concentra-
tion is dependent on the metropolitan geographical area only to the
extent that differences in meteorological variables exist between
these areas. Thus the data from all cities can be plotted on one
graph when defining the oxidant upper limit as a function of early
morning hydrocarbon.
As the document further noted, all available data relating directly
measured nonmethane hydrocarbon concentrations to maximum daily oxidant
2
concentrations were used. For Los Angeles, however, no nonmethane data were
available; and for some stations in each of the other cities nonmethane hydro-
carbon concentrations were derived by applying an empirically determined ratio
32 33
between total and nonmethane hydrocarbons. ' Figure 5-3 shows maximum
oxidant concentrations as a function of 6-to-9-a.m. average total hydrocarbon
concentrations, developed from 326 days of data obtained from five cities.
Direct examination of the data used to develop this plot shows that, at any
given hydrocarbon level, there appears to be a limit to the amount of oxidant
32
that can be generated. Specifically, the data appear to indicate that an
average 6-to-9-a.m. concentration of 0.3 ppm nonmethane hydrocarbon (expressed
as carbon) can be expected to produce a maximum hourly average oxidant con-
32
centration of up to 0.1 ppm. It must be borne in mind, however, that the
aerometric data base underlying this model was obtained by FID measurements
that were subject to all the errors associated with this method.
5-20
-------
W.-KJ
0.25
a
a
£ 0.20
0
X
o
in
O
at
ii i
< 0.15
0
X
^
d
° 0.10
D
3E
X
2
0.05
A
D DENVER
• CINCINNATI
A LOS ANGELES
O PHILADELPHIA
A WASHINGTON
St
^*
• ^
S A
X*
x' a
X* A —
,^ A A
X D
i
a D Am
— /+ A AA —
/O 0 (-
iA D
^A* O A A D D A
/ OA
O A A
y' A O D OAD O A AD A O A
— • AA a AA D A D D O & —
/ DAADO OOA9OA •ODA A «D A
1 D O AOAO0DOOOAAQ0OAD AOAO AD A
0 D AA DAA AOAl
^OA* DBftAftD AttA
— /AD ADA AOA ADA ADA««A«A A«* A • ^ —
/ DD A4DADA AAGADAA ADA«O« A OA O •• AD
ju D AOAAADADADA AA «DA««AD«a ••* A
326 DAYS OF DATA; COINCIDENT
POINTS NOT PLOTTED
6-9 a.m. AVERAGE TOTAL HYDROCARBON
CONCENTRATION, ppm C
Figure 5-3. Maximum daily oxidant as a function of early morning total hydrocarbons, 1966-
1968 for CAMP stations; May through October 1967 for Los Angeles.2
5-21
-------
HCT3/C 2-19-80
A number of caveats for this method of relating hydrocarbon concentra-
2
tions to oxidant concentrations were given in the 1970 hydrocarbon document,
33
in the 1971 air quality criteria document for nitrogen oxides, and in the
journal publication that described the development of the upper-limit curve of
Figure 5-3.32 Schuck et al.32 clearly stated that the upper limit curve is
descriptive rather than predictive. It defines the limit on oxidant associated
with certain levels of ambient hydrocarbons but cannot predict or explain this
32
observed relationship. The nitrogen oxides document of 1971, which discussed
the upper-limit curve in detail, noted that the derivation of an upper limit
curve requires abundant measurements. "Since the upper limit is attained on
only about 1 percent of the days in a year, many days' measurements are needed
in order to provide reasonable assurance that an upper-limit point has actually
33
been observed." The relative paucity of data at the actual curve in Figure 5-3
demonstrates this point.
Nevertheless, since the hydrocarbon standard was promulgated for the
purpose of ensuring the attainment and maintenance of the oxidant standard,
EPA had to prescribe a method for determining the relationship between hydro-
carbon emissions and resulting ambient air concentrations of oxidant. In
response to that need, EPA scientists developed a method that used the
upper-limit curves in conjunction with the dispersion-related equations used
in linear rollback models.
Rollback models embody the principle that reductions in emissions of a
pollutant are reflected by improvements in air quality, as may be shown by a
straight line, a curved line, or a complex surface that expresses some pro-
o
portionality relationship. Linear rollback, though it would result in
improved oxidant air quality, does not accurately describe the relationship
5-22
-------
HCT3/C 2-19-80
between hydrocarbons and oxidant air quality; it is best applied to pollutants
that, unlike hydrocarbons, do not undergo chemical transformations in the
g
atmosphere. Consequently, EPA used the upper-limit curve to derive a type of
modified rollback model for relating maximum 1-hour photochemical oxidant
concentrations to the percentage reduction needed in hydrocarbon emissions in
order to achieve the oxidant standard. The resulting model or method was
promulgated in 1971 as Appendix J. It represented EPA's best attempt, given
the data available and the state of the art of modeling in 1971, to go beyond
relating ambient air HC levels to oxidant levels and to attempt the more
difficult task of relating hydrocarbon emissions to oxidant levels. The
33 34
Appendix J curve is shown as Figure 5-4. ' As discussed in Section 6,
revision of the NAAQS in 1978 for oxidants and promulgation of
an NAAQS for ozone in 1979 led to replacement of the Appendix J model by four
other modeling techniques for use by the States in determining hydrocarbon
reductions necessary to attain the NAAQS for ozone.
5.6 HEALTH EFFECTS
2
The document entitled, Air Quality Criteria for Hydrocarbons, which was
published in 1970, provided no health effects data directly related to ambient
concentrations of gaseous or volatile hydrocarbons as a pollutant class.
Excluded from this health assessment were hydrocarbons (>C,2) and other
organics (e.g., polycyclic organic matter) associated only with suspended
particles in the atmosphere. The only direct adverse effect at that time
attributable to known ambient concentrations of hydrocarbons was the vegetation
damage from ethylene; however, these effects were not nationwide but highly
dependent on the locality and the species of plants grown for retail sales.
The sole purpose of prescribing a nonmethane hydrocarbon air quality standard
5-23
-------
Ul
no
q
\
IU
51
< a
a <
tu a
Ex
i o
z JE
8*
So
<"-
o a
o oc
oc <
a a
> z
X <
Sfe
o
D
O
ui
cc
100
80
_i 60
40
20
0
150
APPENDIX J
MAXIMUM MEASURED 1-hour PHOTOCHEMICAL OXIDANT CONCENTRATION, ppm
0.10
0.15
0.20
0.25
0.30
NOTE: NO HYDROCARBON OR PHOTOCHEMICAL
OXIDANT BACKGROUND ASSUMED
200
250 300 350 400 450 500
MAXIMUM MEASURED 1-hour PHOTOCHEMICAL OXIDANT CONCENTRATION,
550
600
Figure 5-4. Required hydrocarbon emission control as a function of photochemical oxidant concentration.33,34
-------
HCT3/C 2-19-80
g
of 160 (jg/m (0.24 ppm), maximum 3-hr average concentration (6-to-9-a.m.) not
to be exceeded more than once per year, was to control the ambient levels of
specific smog components such that the oxidant standard of 160 ug/m3 (0.08
ppm), maximum 1-hour concentration not to be exceeded more than once a year,
4
would be met. Inherent in the setting of this hydrocarbon standard was the
fact that these specific smog components known as "oxidants" are produced from
hydrocarbons by gas-phase photochemical reactions involving oxides of nitrogen
(NO ), oxygen, and sunlight. To date, the only health effects reported from
/\
exposure to smog products derived directly from hydrocarbons, as opposed to
indirectly derived products such as ozone, at levels approximating those found
in the ambient air, are the irritating effects of aldehydes and peroxyacyl-
nitrates on mucous membranes of the eyes, nose, and throat. The aldehydes
that have been identified as the most effective irritants are acrolein and
formaldehyde, while the peroxyacylnitrates identified as such are the acetyl
and benzoyl derivatives. These smog components (aldehydes, peroxyacylnitrates)
are governed by the control strategy cited in the revisions to the NAAQS for
photochemical oxidants.
The lack in 1970 of a health effects data base directly related to hydro-
carbons at ambient concentrations, either as individual compounds or as a
class, is readily observed from the toxicological and clinical studies discussed
below. These studies were those reviewed in the preparation of the 1970 criteria
2
document for hydrocarbons that served as the basis for the promulgation of
the standards.
The effects observed up to 1970 for hydrocarbons either as a class or as
individual compounds are as follows:
5-25
-------
HCT3/C 2-19-80
1. Aliphatic Hydrocarbons
In general, members of this hydrocarbon series are virtually inert and
produce no demonstrable pathological effects. The first two members of these
alkane hydrocarbons, methane and ethane, are pharmacologitally "inert," belonging
to a group of gases called "simple asphyxiants." These gases can be tolerated
in high concentrations in inspired air; however, above concentrations of
50,000 and 100,000 ppm, one observes systemic effects of ethane and methane,
respectively, due to oxygen deprivation or asphyxia. Pharmacologically, the
aliphatic hydrocarbons above ethane, both saturated and unsaturated, can be
grouped with the general anesthetics in a large class known as the central
nervous system 'depressants. This is particularly true of ethylene, propylene,
and acetylene, which have all been used as anesthetics at high concentrations.
The vapors of the alkane hydrocarbons are mildly irritating to mucous membranes,
the irritation increasing in intensity from pentane to octane. Generally,
alkanes from the pentanes (C,-) through the octanes (CQ) show increasingly
strong narcotic properties which has been correlated with the increased
lipophilia. Narcotic effects may be accompanied by exhilaration, vertigo,
headache, anorexia, incoordination, and nausea. These compounds in general
are relatively inactive toxicologically at concentrations of hundreds to
thousands of times above those levels found in the atmosphere. No effects
were observed at levels below 500 ppm for the alkanes and 1,000 ppm for the
qc
alkenes. These observed effects are summarized in Tables 5-6 and 5-7.
2. Alicyclic Hydrocarbons
Toxicologically, the alicyclic hydrocarbons, both saturated and unsaturated,
are similar to the aliphatic hydrocarbons in that they act as general anesthetics
5-26
-------
HCT3/C 2-19-80
TABLE 5-6. TOXICITY OF SATURATED ALIPHATIC HYDROCARBONS
35
ro
Hydrocarbon Formula
Methane CH4
Ethane C2Hg
Propane C3Hg
Butane ^4^10
Pentane ^5^12
Health effects
No systemic effects.
No systemic effects.
No symptoms after
brief exposure.
Odor not detected.
No irritation,
but slight
dizziness in a
few minutes.
Odor not detected.
No systemic
effects except
drowsiness.
Threshold limit.
Odor readily detectable.
No mucous membrane
Concentration, ppm
<100,000
<50,000
<10,000
<20,000
<100,000
<5,000
10 min. @ 10,000
1,000
5,000
10 min. @ 5,000
% by
volume of air
10
5
1
2
10
0.5
1.0
0.1
0.5
0.5
Subject
man
man
man
man
man
man
man
man
man
Ambient conjugation
1300-4000
0.05-95
12-94
0.01-182
0.023-64
Hexane ^6^14
irritation or other
symptoms.
Narcosis in 5 to 60 min.
Threshold limit.
No symptoms.
Dizziness and
sensation of
giddiness.
Narcosis.
90,000-120,000
500
2,000 @ 10 min.
5,000
30,000
9-12
0.05
0.2
0.5
3.0
mice
man
man
man
mice
4-27
-------
HCT3/C 2-19-80
TABLE 5-6 (continued)
Hydrocarbon
Heptane
Formula Health effects
Convulsions and
death have resulted
from exposures of
equal duration.
C-,H,C Threshold limit.
/ ID
Slight vertigo.
Marked vertigo,
Concentration, ppm
35,000-40,000
500
1,000 @ 6 min.
2,000 @ 4 min.
5,000 @ 4 min.
% by
volume of air
3.5-4.0
0.05
0.1
0.2
0.5
Ambient concentrations,
Subject ppb '
Mice
Man 0.2-34
Man
Man
Man
en
i
ro
Co
hilarity, and
lack of coordination.
Intoxication
characterized by
uncontrolled hilarity
in some individuals and
in others a stupor lasting
for 30 min. after exposure.
These individuals complained
of loss of appetite, slight
nausea, and a taste
resembling gasoline.
5,000 @ 15 min.
0.5
Man
Narcosis.
Convulsions/
death.
ctane C8H18 Threshold limit.
Narcosis in
30-90 min.
No deaths or
convulsions.
10,000-15,000 9
30-60 min.
15,000-20,000 @
30-60 min.
500
6600-13,700
<13,700
for 30-90 min.
1-1.5
1.5-2.0
0.05
0.66-1.37
1.37
Mice
Mice
Man 0.04-3.4
Mice
Mice
Concentrations appearing in the literature up to 1978.
-------
HCT3/C 2-19-80
TABLE 5-7. TOXICITY OF UNSATURATED ALIPHATIC HYDROCARBONS
35
en
i
Hydrocarbon Formula
Ethyl ene C2H2
Propylene C~Hg
1-Butene C.Hg
1,3 Butadiene C4Hg
2-Methyl-l,3- C5Hg
butadiene
(isoprene)
Acetylene CpH^
Health effects
TLVb
MPLC
MPLC
MPLC
TLVb
Only slight eye and
upper respiratory tract
irritation in man.
No deleterious effects
from these exposures;
however, the animals were
slightly anesthetized,
showing a loss of pupillary
reflex. Noisy breathing and
rales were noted.
No narcosis.
MPLC
Slight intoxicating
effect.
Marked intoxication.
Incoordi nation.
Unconsciousness
in 5 min.
Concentration, ppm
1,000
5,500
4,000
4,000
1,000
8,000 @
8 hr
200,000-250,000
once a day for
15-21 days
20,000 for
2 hr
35,000-40,000
5000
100,000
200,000
300,000
350,000
% by
volume of air
0.1
0.55
0.4
0.4
0.1
0.8
20-25
2
3.5-4.0
0.5
10
20
30
35
Ambient concgn^gation
Subject ppb '
Man 0.7-700
Man
Man 1-52
Man 1-6
Man 1-9
Man
Rabbits
Mice 0.2-2.9
Mice
Man 0.2-227
Man
Man
Man
Man
Concentrations appearing in the literature up to 1978.
bTLV - Threshold limit value.
CMPL - Maximum permissible level.
-------
HCT3/C 2-19-80
and central nervous system depressants having a relatively low order of acute
toxicity. Cumulative toxicity from repeated exposure to low atmospheric
concentrations is unlikely because the alicyclics do not tend to accumulate in
body tissues. Massive acute exposure that results in prolonged unconscious-
ness, anoxia, and convulsions may cause central nervous system sequelae similar
to those described as occurring after exposure to volatile aliphatic hydro-
carbons. Like the aliphatic compounds, the alicyclic compounds are generally
biochemically inert, although not biologically inert and are only reactive at
concentrations of 100-1000 higher than those levels found in the ambient air.
The vapors in sufficient concentrations will cause irritation of the mucous
membranes. In general, the saturated hydrocarbons are less irritating than
the corresponding unsaturated compounds. No evidence was found to indicate
that alicyclic hydrocarbons are specific hematopoietic toxicants. Like the
aliphatic compounds, the alicyclic compounds are generally biochemically
inert, though not biologically inert and are only reactive at concentrations
of 100 to 1000 higher than those levels found in the ambient air. Data con-
cerning the toxicity of cyclohexane and methyl eyelohexane are summarized in
Table 5-8.37
3. Aromatic Hydrocarbons
The aromatic hydrocarbons are biochemically and biologically active. The
vapors are more irritating to the mucous membranes than equivalent concentra-
tions of aliphatic or alicyclic groups. Systemic injury can result from the
inhalation of vapors of the aromatic compounds; no effects, however, have been
reported below 25 ppm. This value is 103 times greater than the average
benzene concentration reported in California (Los Angeles) during 1966.
5-30
-------
HCT3/C 2-19-80
TABLE 5-8. TOXICITY OF ALICYCLIC HYDROCARBONS:
COMPARATIVE EFFECTS OF CHRONIC AND ACUTE EXPOSURE IN AIR
37
en
oo
Hydrocarbon Formula Health effects
Cyclohexane3 C6H12 No effect
Minor microscopic
changes in kidneys
and liver
No effect
No fatalities or
signs of injury
Some fatalities
No deaths
Deaths
Methylcvclo- Cf-H,1CH,> No effect
hexane0 D 1J- J No effect
No effect
Minor evidence
of kidney &
liver injury
No fatalities;
lethargy in 50%
25% fatalities
100% fatalities
100% fatalities
Concentration
ppm mg/m3 %
434
786
1243
3300
7400
18,500
18,500
26,600
241
1162
2800
3300
5600
7300
10,000
15,000
1
2
4
11
25
63
63
11
13
22
29
40
60
,491
,710
,270
,439
,419
,548
,548
996
4659
,228
,233
,456
,273
,100
,150
0.
0.
0.
0.
0.
1.
2.
0.
0.
0.
0.
0.
0.
1.
1.
by air
043
078
12
33
74-1.85
85
66
024
116
28
33
56
73
0
5
Exposure
hr days
8
6
6
6
6
8
1
24
24
24
5
6
6
6
70
130
50
50
50
10
1
-
70
70
70
70
28
14
14
min.
Animal
Rabbit
Rabbit
Monkey
Rabbits
Rabbits
Rabbits
Rabbits
Rabbits
Rabbits
Rabbits
Rabbits
Rabbits
Rabbits
Rabbits
Rabbits
Type Ambient 35
study concentrations, ppb
Chronic 3-6
Chronic
Chronic
Chronic
Chronic
Acute
Acute
Chronic 3-7
Chronic
Chronic
Chronic
Chronic
Chronic
Chronic
Acute
Threshold Limit Value for cyclohexane is 400 ppm.
The Threshold Limit Value for methylcyclohexane is 500 ppm.
-------
HCT3/C 2-19-80
It is well established that benzene is an insidious toxicant which has a
destructive effect on the hematopoietic system. Experimental evidence
indicates, however, that the alkyl derivatives of benzene are not capable of
inducing these effects and that benzene is unique among the aromatic hydro-
carbons as a myelotoxicant. This difference in toxicity between benzene and
its alkyl derivatives has been primarily attributed to detoxification of the
derivatives via a different metabolic route. Pharmacologically, the alkyl
benzenes or phenylalkanes can be classified with the central nervous system
depressants.
Toluene is a more potent narcotic and acute toxicant than benzene, but it
38
does not affect the hematological system. Xylenes are more acutely toxic
than benzene or toluene. The comparative effects of acute and chronic exposure
39
to aromatic hydrocarbon vapors in air are shown in Table 5-9.
4. Hydrocarbon Mixtures
Hydrocarbon mixtures produced and consumed in this country include natural
gas, liquid propane gas, petroleum ether, petroleum benzene, petroleum naphtha,
gasoline, mineral spirits, kerosene, jet and turbo fuels, and lubricating
oils.
The physiological response resulting from exposure to these hydrocarbon
mixtures can be judged from their composition (Table 5-10) and the information
given above for their physiological response to the specific hydrocarbons,
40
methane through octane.
Of all the hydrocarbon mixtures, gasoline is undoubtedly the most exten-
sively used and represents the major source of homogeneous hydrocarbons emitted
5-32
-------
HCT3/C 2-19-80
TABLE 5-9. TOXICITY OF AROMATIC HYDROCARBONS:
COMPARATIVE EFFECTS OF ACUTE AND CHRONIC EXPOSURE IN AIR
39
to
co
Hydrocarbon Formula Health effects
Benzene CCHC TLV
b b
Mucous membrane
irritation
Threshold for
affecting central
nervous system
Endurable for
0.5-1.0 hrs.
Prostration
LC 50
Dangerous after
0.5-1.0 hrs.
LC 100
LC 100
Fatal after
5-10 min.
ppm
25
100
370
3000
4700
7400
7500
14,100
17,800
20,000
Concentration
mg/m3 % by air
80
319'
1,180
9,570
14,993
23,606
23,925
44,979
56,782
63,800
0.0025
0.01
0.037
0.3
0.47
0.74
0.75
1.41
1.78
2.0
Exposure
hr days
Acute —
Acute —
Acute —
Acute —
Acute —
Acute —
Acute —
Acute —
Acute —
Acute —
Ambient 3
Subject concentrations, ppb
Man 0.025-57
Man
Mice
Man
Mice
Mice
Man
Mice
Rats
Man
-------
HCT3/C 2-19-80
TABLE 5-9 (continued)
oo
•£»
Hydrocarbon Formula Health effects
Toluene CgH5.CH3 No effect
Mild fatigue, weakness,
confusion, skin
parethesias
Symptoms more
pronounced
Symptoms plus
mental confusion
Also plus nausea,
headache, dizziness
Also plus loss
Concentration
ppm mg/m3 % by air
50-100
200
300
400
600
600
188-377
753
1,130
1,506
2,259
2,259
0.05-0.01
0.02
0.03
0.04
0.06
0.06
Exposure
hr days
Acute —
8 1
8 1
8 1
3 1
8 1
Ambient 3
Subject concentrations, ppb
Man 0.005-129
Man
Man
Man
Man
Man
of coordination,
staggering, gait and
pupils dilated
Same symptoms as
above with after
effects characterized
by severe nervousness,
muscular fatigue and
insomnia
800
3,012 0.08
Man
-------
HCT3/C 2-19-80
TABLE 5-9 (continued)
Concentration Exposure Ambient
Hydrocarbon Formula Health effects ppm mg/m3 % by air hr days Subject concentrations, ppb
Styrene Cj-Hr-CH^H, Threshold limit 100 418
00 * value (TLV)
No effect 650 2714
Eye and nasal 1300 5428
irritation only
w Eye and nasal 1300 5428
i irritation only
tn
10% deaths 1300 5428
Some fatalities; 2500 10,438
varying degrees
of weakness, stupor
incoordi nation, tremor
unconsciousness (in
10 hours)
Unconsciousness in 5000 20,875
1 hour
Unconsciousness 10,000 41,750
in 10 min. , deaths
0.001 Acute --- Man 1.5-5
0.065 8 180 Guinea pig
0.13 8 180 Rat
0.13 8 180 Rabbit
0.13 8 180 Guinea pigs
0.25 8 1 Guinea pig
and rat
0.5 1 1 Guinea pig
and rat
1.0 1/2-1 1 Guinea pig
and rat
36
in 30-60 min.
-------
HCT3/C 2-19-80
TABLE 5-9 (continued)
i
(*>
(Tt
Hydrocarbon Formula
Xylenes CfiH.. (CH-),
(O.M.P) b 4 6 *
i
j
^
Health effects
Threshold for
affecting central
nervous system
Threshold limit
value (TLV)
No hematological
effects
Decreased leukocytes
red blood cells:
increased platelets
Prostration
LC50
LC100
LCinn
ppm
174
200
690
1150
&
4699
9200
12,650
17,250
Concentration
mg/m3 % by air
755
868
2,995
4,991
20,394
39,928
54,901
74,865
0.017
0.02
0.069
0.115
0.469
0.920
1.26
1.72
Exposure
hr days
Acute —
Acute —
8 130
8 55
Acute ---
Acute ---
Acute —
Acute —
Ambient ,
Subject concentrations, ppb
Mice 2.5-119
Man
Rat and
rabbit
Rabbit
Mice
Mice
Mice
Rat
-------
HCT3/C 2-19-80
TABLE 5-10. PRINCIPAL MIXTURES CONTAINING PARAFFIN HYDROCARBONS
40
Mixture
Boiling range, °C
Principal paraffins
Natural gas
LPG ("bottled gas")
Petroleum ether
Petroleum bezin
Petroleum naphtha
Gasoline
Mineral spirits
Kerosene (coal oil)
Jet and turbo fuels
Lubricating oils
Gas at room temp.
Gas at room temp.
20-60
40-90
65-120
36-210
150-210
170-300
40-300
300-700
C1'C2
C3'C4
C4 to C6
C5 to C?
C6 to C8
C5 to C1Q
C? to Cg
Cg tO C^
C5 to C16
C, and up
5-37
-------
HCT3/C 2-19-80
nationwide whether due to evaporative loss or combustion. Gasoline is a
mixture of C4 to C12 hydrocarbons, including paraffins, olefins, naphthenes,
and aromatics over a boiling range of 26°C to 204°C (80°F to 400°F). Alkanes
and aromatics generally constitute the largest fraction, but olefins and
naphthenes are also present. In addition to the 200 hydrocarbons generally
contained in gasoline, nonhydrocarbons (additives) are added to improve engine
performance. The changes in the hydrocarbon composition have not significantly
altered its basic pharmacology and toxicology. An acute exposure to gasoline
vapors will elicit the symptoms and signs of intoxication described for exposure
to heptane. The atmospheric concentrations and the duration of exposure
required to elicit these responses will differ with the composition of the
gasoline. The concentration of gasoline hydrocarbons that causes mucous
membrane irritation will vary with the degree of branching of the paraffins
and the content of alkyl derivatives of benzene and olefins. The foregoing
does not apply to gasolines that contain a significant concentration of benzene,
which appears to be unique among hydrocarbons in its effect on blood-forming
tissues. In light of the variability of the composition of gasolines (blends),
a single threshold limit value was not applicable; however, as a general rule
the contents of the aromatic hydrocarbons and, to a lesser degree, of the
42
additives are used to arrive at the appropriate TLV values. Based on Machle's
summary (Table 5-11) of man's response to air concentrations of the volatile
fraction (<230°F) of unleaded straight-run gasoline, Gerarde recommended 500
40
ppm as a TLV for gasoline in 1962.
5.7 WELFARE EFFECTS
Hydrocarbons were recognized as phytotoxic air pollutants at least as
early as 1871 as a result of injury to green house plants from illuminating
5-38
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HCT3/C 2-19-80
TABLE 5-11. HUMAN RESPONSE TO GASOLINE VAPORS DISTILLING BELOW 230°F43
Concentration,
ppm Exposure time Response
550 1 hr No effects
900 1 hr Slight dizziness and irritation of eyes,
nose, and throat
2,000 1 hr Dizziness, mucous membrane irritation,
and anesthesia
10,000 10 min Nose and throat irritation in 2 min. ;
dizziness in 4 min.; signs of
intoxication in 4 to 10 min.
5-39
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HCT3/C 2-19-80
gas. Renewed interest in hydrocarbons, and ethylene in particular, occurred
in the mid-1950's when ethylene was found to be one of the primary pollutants
in the photochemical reaction complex. Although additional combustion sources
contribute to ethylene in the atmosphere, the internal combustion engine is
the major source of ethylene pollution in metropolitan areas.
The levels found in the ambient air vary according to location, time of
day and weather. Low levels in the range of 3 to 5 ppb have been reported for
2 182
desert areas and Davis, California. ' In contrast, San Francisco air was
reported to contain peaks of 100 ppb for an hour or more on several
occasions;2'183"185 however, the average for this city is 50 ppb.2'183'186 The
187
Pasadena area has, in the past, reported an unusually high value of 500
ppb, while surrounding areas, such as the San Gabriel Valley, have lower peak
o 1 QC
values, i.e., 30 ppb. ' Similarily, on the east coast, Washington, D.C.,
reported average values of 10 to 20 ppb with maximum values near 60 ppb. In
Frederick, Maryland (50 miles west of Washington, D.C.), ethylene levels range
from 1 to 5 ppb. Research on several unsaturated and saturated hydrocarbons
proved that only ethylene had adverse effects on vegetation at atmospheric
concentrations of 1 ppm or less. Concentrations as low as 0.05 ppm have
caused malformations in certain plants and injuries to flowers. This concen-
tration is well within the range measured in ambient atmosphere. Other
unsaturated hydrocarbons produce similar effects, but at concentrations 60 to
44
500 times that of ethylene (Table 5-12). Such concentrations are orders of
magnitude higher than concentrations found in the atmosphere.
Research has demonstrated that ethylene is produced naturally within
tissues of plants and serves as a hormone in regulating growth and development
and other processes such as the ripening of fruit. Thus, ethylene is unique
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HCT3/C 2-19-80
TABLE 5-12. COMPARATIVE PHYTOTOXICITY OF UNSATURATED CARBON GASES44
Gas
Ethyl ene
Acetylene
Propylene
Carbon monoxide
Butyl ene
Minimum concentration
gas producing response
of
, ppm
Sweet peaa Tomato
0.2
250
1,000
5,000
50
0.1
50
50
500
,000
aEffect noted: declination in sweet pea seedlings (3-day exposures).
Effect noted: epinasty in tomato petiole (2-day exposures).
5-41
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HCT3/C 2-19-80
in being an endogenous plant-growth regulator and a serious phytotoxic air
pollutant. A delicate balance between auxin and ethylene in the petiole is
required for normal defoliation; however, an artificial increase in ethylene
through pollution would upset this balance and cause early abscission or
defoliation without noticeable leaf injury. Unfortunately, this plant-growth
inhibitory effect does not characterize ethylene, because other pollutants at
sublethal dosages, as well as some diseases and environmental factors, may
also inhibit growth. The various effects corresponding to different levels of
2
ethylene are illustrated in Table 5-13.
It should be emphasized that data on the phytotoxicity of ethylene were
not used in promulgating a secondary or welfare standard for hydrocarbons, but
like the primary standard, the secondary standard was based on the specifi-
cations of the oxidant standards, which automatically fixed the hydrocarbon
standards. Prior to 1970 various standards for acceptable levels of ethylene
were proposed or adopted. In 1962 the State of California adopted ambient air
o
quality standards for ethylene of 500 ppb (575 ug/m ) for 1 hour or 100 ppb
(115 ug/m ) f°r 8 hours. These are considered "adverse" levels, based on the
45-47
damage to vegetation. The American Industrial Hygiene Association (ACGIH)
48
has also proposed air quality standards for ethylene. Based on insufficient
data at that time, these latter standards were never unequivocally adopted and
served only as guidelines. The recommended standards are given in Table 5-14.
5-42
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HCT3/C 2-19-80
TABLE 5-13. DOSAGE-RESPONSE RELATIONSHIPS OF VARIOUS PLANTS TO ETHYLENE'
Dosage
Response
Abscission
Cotton leaves, square
Cotton leaves
Pepper and tomato
flower buds
Rose leaves
Snapdragon petals
Chlorosis on leaves
Cotton (slight)
Cowpea
Rose
Death of plant
Cowpea
Dry sepal injury
Orchids (severe)
Orchids (typical)
Orchids (slight)
Epi nasty
African marigold
Various plants
Flowers do not open
Carnation
Orchid
Flowers close
Carnation
Growth inhibition
Cotton
Lily family
Various plants
Loss of apical dominance
Cotton
MQ/ra
46-3,435
685
115
345
11,450
575
685
2,290
1,145
2,290
115
46
23
5.75
345
57.5
11.5
1.15
345
3,435
2,290
115
575-1,145
115
575
685
46-3,435
860
2,390
46-3,435
ppm
0.04-3.0
0.6
0.1
0.3
10.0
0.5
0.6
2.0
1.0
2.0
0.1
0.04
0.02
0.005
0.3
0.05
0.01
0.001
0.3
3.0
2.0
0.1
0.5-1.0
0.1
0.5
0.6
0.4-3.0
0.75
2.0
0.04-3.0
Time
Not stated
1 month
Less than
8 hr
120 hr
24 hr
1 hr
1 month
1 day
5 days
10 days
8 hr
8 hr
24 hr
24 hr
1 hr
6 hr
24 hr
20 hr
24 hr
3 hr
10 days
3 days
20 hr
6 hr
12 hr
1 mo
Not stated
7 days
10 days
Not stated
5-43
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HCT3/C 2-19-80
TABLE 5-14. AMERICAN INDUSTRIAL HYGIENE ASSOCIATION
4R-47
RECOMMENDED STANDARDS FOR ETHYLENE
Rural
Residential
Commercial
Industrial
1-hr
M9/m
287.5
575
862.5
1,150
max3
ppm
0.25
0.50
0.75
1.00
8-hr
MQ/m
57.5
115
172.5
230
max3
ppm
0.05
0.10
0.15
0.20
The rural concentrations should not produce adverse effects in the most
sensitive plants. The residential concentrations should produce only slight
injury to the most sensitive plants.
5-44
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HCT6 JOB A 2-19-80
6. SCIENTIFIC DATA BASE ON HYDROCARBONS,
1970 THROUGH PRESENT
6.1 CONTRIBUTION OF HYDROCARBONS TO OXIDANT FORMATION
A brief and highly simplified summary of the role of hydrocarbons in the
formation of photochemical oxidants was presented in Section 5.1. Since
publication of the 1970 criteria document on hydrocarbons, research has produced
new findings in the area of reaction mechanisms but has consistently substantiated
the basic chemistry of oxidant formation as presented in the 1970 document.
The new findings and their significance have been discussed in detail in three
g
recent reviews, Ozone and Other Photochemical Oxidants (NAS, 1976),
Air Quality Criteria for Ozone and Other Photochemical Oxidants (EPA, 1978),
Q
and Air Quality Criteria for Nitrogen Oxides (EPA, Draft, June 1979). Conse-
quently, only brief mention is made here of the significant research findings
of the past decade.
A major accomplishment in recent years is the development of computer
49 50
techniques for simulating the atmospheric smog-forming process. ' Such
techniques have provided a useful tool for identifying and studying those
reactions that play a key mechanistic role and for predicting potentially
important but as yet unidentified reaction products in the ambient atmosphere.
The most important mechanistic finding of recent years is that the hydroxyl
radical (OH')--rather than atomic oxygen, 0( P), and ozone—is probably respon-
sible for most of the hydrocarbon- and aldehyde-consuming processes in the
atmosphere.51'52 Other radicals also, notably oxygen atoms and alkylperoxy
(R02) radicals, are implicated in attacks on and consumption of organic reactants.
The OH, hydroperoxy (HOO, and ROp radicals have also been identified as
6-1
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HCT6 JOB A 2-19-80
having major roles in the oxidation of NO to N02, and some sources of these
radicals in the atmosphere have been identified. In addition, more complete
information is now available to account for the degradation of organic oxidant,
the oxidation of NO to N02, and the formation of organic products in the
ambient atmosphere, for paraffinic and olefinic reactants though not for
aromatics. Another noteworthy mechanistic finding is that some nitrogenated
components of the photochemical smog system, e.g., peroxyacetyl nitrate (PAN),
may have greater roles in atmospheric photochemical processes than thought
earlier.
In addition to new information on reaction mechanisms, new reaction
products have been identified or postulated, including organic compounds and a
number of inorganic nitrogenous acids.
It is apparent from the examples cited above that information generated
since the 1970 criteria document was issued has provided a much more complete
view of probable atmospheric oxidant formation processes and the role of
organic compounds in those processes, though much of the evidence for reaction
mechanisms has been obtained from laboratory studies and remains to be verified
in the ambient atmosphere. The elucidation of atmospheric reaction mechanisms,
along with other research of the past decade, has confirmed that photochemical
oxidants in the ambient air are a function of the presence of hydrocarbons, as
well as other organic compounds and nitrogen oxides, in the atmosphere.
6.2 MEASUREMENT METHODOLOGY
The essential features of the 1971 Federal Reference Method for the
measurement of nonmethane hydrocarbons were described in Section 5.2. Instru-
mentation for total and nonmethane hydrocarbon measurements by flame-ionization
detection has not changed appreciably since 1971. For that reason, this
6-2
-------
HUb JUB A 2-19-80
section mainly presents a critique of the method, based largely on work done
since 1971; and presents some of the problems associated with the application
of mass measurements of hydrocarbons. In addition, information is presented
on the use of gas chromatographic techniques for hydrocarbon measurement and
on developments since 1971 in FID measurement methods.
The EPA reference method for nonmethane hydrocarbons (NMHC) involves the
gas chromatographic separation of methane from total hydrocarbons in an air
sample. This is followed by FID measurement of the separated methane and of
total hydrocarbons containing methane, in aliquots of the same air sample.
The concentration of NMHC is obtained by subtraction of the methane measurement
value. Presently available commercial analyzers are still based on these
principles and provide a measurement of total "nonmethane hydrocarbons" by
subtraction of separate measurements of total hydrocarbons (THC) and methane
in an FID. Methane is measured apart from THC in one of two ways, either by
separation in a chromatographic column or by selective oxidation in a heated
12 14
oxidizer. ' The chromatographic separation of methane that is used in the
originally promulgated Reference Method represents a significant improvement
in methodology over the separation technique used prior to 1970. The catalytic,
selective oxidation of CH. to C0« in a heated oxidizer is a viable alternative
to chromatographic separation of CH. and also represents a significant improvement
12 14
over pre-1970 methods for determining CH. and, thus, NMHC. ' In recogni-
tion of the fact that the FID responds to organically bound carbon in compounds
other than hydrocarbons, the measurement of NMHC is now referred to as nonmethane
organic compound (NMOC) measurement. This nomenclature is more accurate than
the previous nomenclature and will be used where appropriate in the remainder
of this section.
6-3
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HCT6 JOB A 2-19-80
Studies of the FID Federal Reference Method, using commercial analyzers,
have been reviewed in a recent EPA draft report and two such studies are cited
here from that report.
The first of the two studies involved the analysis of known synthetic
mixtures of NMHC in compressed air cylinders by 16 different users of the
54
reference method. The NMHC concentrations tested were 0.23 and 2.90 ppm C.
As shown in Table 6-1, the majority of the measurements of the lower concentra-
tion, which was near the HC NAAQS level of 0.24 ppm C, were in error by 50 to
over 100 percent. At 2.90 ppm C, the majority of the measurements were in
error by only 0 to 20 percent. Thus, the higher the concentrations measured,
the better the accuracy. The major causes of error were the inability of the
instrument to measure low levels of NMHC; the complexity of the instrumentation;
and the inability of the average user to identify and correct problems.
TABLE 6-1. PERCENTAGE DIFFERENCE FROM KNOWN CONCENTRATIONS
OF NONMETHANE HYDROCARBONS OBTAINED BY SIXTEEN USERS54
Known NMHC
concentration
0.23 ppm
2.90 ppm
Percent
>100
6
2
50-100
4
— —
20-50
3
3
10-20
2
2
0-10
1
9
In the second study, aliquots of the same ambient air sample were measured
with five different commercial FID instruments operated by skilled personnel.
Results from different analyzer pairs agreed within 0.1 to 0.5 ppm C. Although
these differences represent only 1 to 5 percent of the full scale of the
instrument (0 to 10 ppm, the range necessary to include all ambient air HC
6-4
-------
HCT6 JOB A 2-19-80
values), and are normal errors for ambient air monitoring, they are quite
large relative to the NAAQS of 0.24 ppm C. As these two studies show, even
under optimum operating conditions, agreement between instruments and measure-
co
ments is poor at low concentrations.
In a fairly recent study conducted for EPA, the reference method was
subjected to a comprehensive evaluation that included testing of six commercial
FID instruments. Generally, results showed poor performance; the major problems
were wide differences in response to different NMHC species and discrepancies
that were apparently related to variations in ambient relative humidity.
In its assessment of the flame ionization detection method and instruments
based on that method, EPA summarized the problems as follows:
1. The FID responds non-uniformly to various organic compounds.
2. The FID response varies with design and operating conditions.
3. The normal FID response is roughly proportional to the "carbon
number" of the compound, but otherwise has little or no relationship
to the photochemical reactivity of the compound.
4. Normal instrumental variability errors are substantially increased
by the need to subtract two separate and independent measurements
and by the need for higher scale ranges to accommodate the THC and
methane concentrations, which can be much higher than the NMOC
difference.
5. The FID is susceptible to zero drift and possible interference from
water vapor.
6. Calibration procedures have not been standardized and calibration
may be based on methane, propane, or other compounds depending on
analyzer design or operator preference.
6-5
-------
HCT6 JOB A 2-19-80
7. The FID requires hydrogen, which presents a degree of operational
hazard.
8. Analyzers using chromatographic separation of methane are operationally
complex and require higher levels of operator training and effort to
maintain than most other types of ambient monitors. These problems
appear to limit the useful sensitivity of currently available analyzers
to a few tenths of 1 ppm (methane equivalent).
The major limitations of the FID measurement method for hydrocarbons
result in some very practical and pertinent consequences that must be mentioned,
if only briefly. First, the high measurement error associated with the method
results in erroneous values for hydrocarbon concentrations in ambient air.
This is particularly true for concentrations in the range of the present NAAQS
for hydrocarbons. This measurement error must be kept in mind when NMHC
ambient air data are compared with exposure data from human or animal toxicity
studies. In addition, the errors associated with FID measurements limit the
confidence that can be placed in the use of the FID method for routine monitoring
and in the use of FID data for predictive purposes or for verification of air
quality trends of emission inventory accuracy. It should be noted, however,
that at higher NMOC levels, e.g., those required for predictive models such as
EKMA (Section 6.5), the errors in NMOC measurements made by current methods
are commensurate with the variability of the models, because they have limited
precision arising from necessary assumptions, estimates, and simplifications.
In many cases, the same NMOC methods have been or will be used to develop or
establish the model.14
Second, the FID technique produces measurements of total mass of NMOC in
ambient air. Measurement of the mass of total NMOC in ambient air, however,
6-6
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HCT6 JOB A 2-19-80
is of somewhat limited utility in the overall control of ozone air quality.
This limited utility is related to three factors: (1) The measurement of
mass alone does not give any indication of the reactivity with respect to ozone
formation of the hydrocarbon mixture measured. (2) Mass measurements cannot
be related to the molar concentration of total hydrocarbons in the air sampled.
(3) Total hydrocarbon mass, without identification of individual hydrocarbons,
does not permit identification of those sources that contribute most heavily
to ozone formation. As stated in the 1970 criteria document for hydrocarbons:
As a consequence of the different reactivities of individual
hydrocarbons, it is impossible to predict accurately the rate of
consumption of hydrocarbons in photochemical air pollution unless
the detailed composition of the hydrocarbon component is known or
can be estimated. Knowledge of the total concentration of hydrocarbons
is insufficient, since two atmospheres having the same total hydrocarbon
measurement may contain individual hydrocarbons of very different
reactivity and thus exhibit very different rates of hydrocarbon
consumption and photochemical air pollution development.
An EPA study on reactivity of hydrocarbons from mobile sources concluded that
since "hydrocarbons do not participate to the same extent in atmospheric
reactions leading to oxidant formation, methods for measurement of more than
mass of emissions are necessary to project adequately the impact of mobile
sources on photochemical pollution." The same is true with respect to the
impact of HC emissions from other sources. It is apparent that FID measurements
are inadequate for the complete characterization of hydrocarbons in ambient
air.
There are applications, however, for which mass measurements of NMOC must
be obtained and for which total NMOC concentrations are the best available measure
of the oxidant-forming potential of organic compounds in the ambient air.
Studies are under way in EPA to develop better methodology for NMOC measurements
for such applications.
6-7
-------
HCT6 JOB A 2-19-80
Consequently, modifications of the FID method as well as the development
of other NMOC methods are in progress, though these methods and techniques
will probably not be available for routine use for several years. These
-ly 14. *iA
developments are briefly summarized below. ' '
In a variation of the present method for chromatographic separation of
methane from nonmethane hydrocarbons, chromatographically separated nonmethane
organics are backflushed and are converted to CO,, rather than methane. The
COp is then measured by conventional infrared methods. This technique is
presently used to measure source concentration levels. It is a direct measure-
ment of NMOC, avoids the FID response problems, and may not require hydrogen.
It has, however, the operational problems of a chromatograph as well as the
sensitivity and response-time problems associated with low-level infrared COp
14
measurement.
Another method for measuring methane is gas filter correlation, an optical
technique which can detect methane specifically without prior separation from
other ambient gases. The total hydrocarbon concentration is measured conven-
tionally by FID, and the NMOC concentration is obtained by difference. This
technique may prove to be a useful alternative to the currently available
selective oxidation technique, but otherwise promises no substantial advantages.
In another approach, a selective oxidizer can be used to separate methane
from NMOC provided CO and COp can be removed from the ambient air sample. In
one such technique, the NMOCs are reduced to methane and the methane concentra-
tion is measured before and after conversion (or with and without conversion
in a dual arrangement) by gas filter correlation. The difference is the NMOC
concentration. In a second technique, the NMOCs are converted to COp and
measured directly by gas filter correlation. This latter approach is highly
6-8
-------
HCT6 JOB A 2-19-80
advantageous as it would avoid almost all the problems associated with conven-
tional NMOC methods. At this point, however, the removal of CO and COp appears
to be a formidable problem. .
EPA is also investigating non-continuous gas chromatographic techniques
in which samples are collected in inert bags and analyzed in a central laboratory
using a gas chromatograph with a special column designed to measure specific
organic compounds. The chromatograph can be calibrated with specific individual
compounds or a single compound, and total hydrocarbons can then be estimated
as CH^ by summing the response for all compounds of interest. In this approach,
samples can be collected by less experienced personnel, stored, and later
brought to the central laboratory for analysis. This technique is a simplified
variation of the GC-mass spectrometry techniques often used to identify arid
measure specific organic compounds for developing and verifying some types of
14
photochemical models. This method would have the disadvantages of problems
associated with storage of ambient air samples as described later in this
section.
In addition to the above methods, more unique approaches for measuring
NMOC have been proposed, including the chemiluminescence method for reactive
hydrocarbons noted above and the use of chlorine atoms to abstract hydrogen
atoms from organic molecules to form CO and COp. These approaches would
require much further research, a redefinition of non-methane hydrocarbons, a
determination of the relationship of these measurements to the photochemical
formation of ozone, and possible modification or adaptation of the photo-
14
chemical models.
Though these methods are under development now, the research in progress
represents a rather recent effort to refine and improve NMOC measurement
6-9
-------
HCT6 JOB A 2-19-80
methodology. The relatively slow development of NMOC methods can be attributed
partly to the fact that the HC NAAQS, in keeping with its guideline nature,
has never been enforced and compliance monitoring is not required under EPA
regulations . In part, however, the relatively slow development of NMOC methodology
can be attributed to a lack of scientific consensus on how NMOC measurements
12
should be defined or expressed. Should they, for example, be related (1)
to molar volume; (2) to mass; (3) to the product of carbon number and molar
12
volume; or (4) to the product of molar volume and some reactivity factor?
Research on NMOC methodology will continue since there exists a demonstrated
need for reliable and accurate, as well as inexpensive, field instrumentation
for measuring total NMOC in ambient air and in source emissions. ' Measurements
of NMOC in ambient air are needed for diverse applications such as (1) analysis
of trends in ozone air quality versus precursor ambient air levels, to determine
efficency of control strategies; (2) verification of emission inventories by
comparison with empirical data; (3) acquisition of input data for models used
to determine reductions in hydrocarbon or volatile organic emissions needed to
achieve and maintain the ozone standard; (4) acquisition of data required for
the prediction of the impact of changes in the spatial configuration of sources,
of the addition of major new sources, or of changes in temporal patterns of
emissions; and (5) possible development of new or revised empirical models,
since some empirical models may have been developed from NMOC of doubtful
quality.
Although there are numerous applications for which total NMOC are useful,
there are also applications for which the detailed hydrocarbon composition,
qualitative and quantitative, of ambient air must be known. Now, as in 1970,
the only method available for compositional analysis of hydrocarbons in ambient
air is gas chromatography (GC). ' It is an accurate and reliable method,
6-10
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HCT6 JOB A 2-19-80
commercially available, for the measurement of individual hydrocarbons, NMHC,
and total hydrocarbons. With flame ionization detection, it is sensitive in
the ppb range. With appropriate columns and temperatures, almost any desired
separation of components can be achieved. A number of factors, however,
preclude the use of gas chromatography for the long-term, routine analysis of
hydrocarbon mixtures in ambient air. First, the instrumentation and its
operation are expensive. Second, the instrumentation is sophisticated and
requires operator skill and experience. Third, data reduction is tedious and
time-consuming. This problem, especially acute in 1971 when the NMHC Federal
Reference Method was promulgated, has been alleviated by the development of
automated systems that reduce, and often eliminate, the need for manual identi-
fication and calculation of the chromatogram peaks. These systems also permit
automatic summation of individual hydrocarbon concentrations. In spite of
these advances, the effort and personnel still needed for data reduction make
this step expensive and time-consuming. Fourth, dynamic calibration with
standards of individual hydrocarbons or hydrocarbon mixtures is required.
When unknowns are encountered, or when resolution of peaks is poor, GC analysis
53
must be supplemented with infrared or mass spectrometry for final identification.
Though calibration and the need for supplementation by spectrometry are
hindrances to the routine use of GC techniques, they also constitute part of
the overall specificity of GC methods that is advantageous in detailed hydrocarbon
analysis. Dynamic calibration with known compounds or mixtures means that
quantitative evaluation of individual chromatogram peaks can be made without
standardization of each compound peak. The concentration of each component
can be computed by using an average per-carbon factor determined from measure-
ments of known concentrations of the identified components. The fact that
GC techniques can be coupled with spectrometric techniques ensures the
6-11
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HCT6 JOB A 2-19-80
confirmation of compound identity; spectrometric techniques in and of themselves
are imprecise for the determination of compounds in a mixture, but coupled
with GC they become valuable in the final identification of organic compounds.
An additional advantage of GC techniques is their sensitivity at the ppb
level. In urban atmospheres, hydrocarbons generally exist at levels high
enough to permit the collection and analysis of samples without pre-concentration.
For analysis for rural air samples, in which hydrocarbons are typically present
in parts-per-billion quantities or fractions therof, cryogenic trapping techniques
are available for the pre-concentration of large samples.
An additional problem exists that complicates the use of gas chromato-
graphy—sampling procedures even for short-term studies. As yet no material
has been found that is ideal for use in fabricating air sample containers.
Flexible bags made of Tedlar and Teflon are often used for sample collection
and storage, but these materials result in some hydrocarbon losses and some
contamination by bag emissions. Tedlar bags have been shown to be adequate
for the storage of paraffinic and olefinic hydrocarbons (0.0 to 0.3 ppm C) for
up to 191 hours. Aromatic hydrocarbons showed a 5 to 15 percent decay over
62
this period. Storage of zero hydrocarbon air in Tedlar bags for 4 hours,
however, resulted in production of up to 40 ppb C. Longer storage—24 to 48
hours—resulted in acetaldehyde and acetone in excess of that level. Irradia-
rn
tion prior to use increases emissions from Tedlar bags. When zero air was
CO
stored, in another study, in 5 mil Teflon bags, contamination of 1 ppm C
occurred after 72 hours. The major contaminants of samples stored in Teflon
have been identified as C2~C. fluorinated hydrocarbons. Pre-irradiation for
12 hours and vacuum heating reduce contamination from Teflon outgassing but
also reduce bag life. Untreated 2 mil Teflon produces no contamination by
6-12
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HCT6 JOB A 2-19-80
^2~^4 f 1uon'nate£l hydrocarbons but does produce fluorinated aromatics with
time.63
Stainless steel canisters have also been used in collection and storage
of air samples for subsequent GC analysis. While they do not produce outgassing,
canisters must be thoroughly cleaned after storage of each sample to prevent
cross-contamination. Cleaning, however, often results in rust. Contamination
from stainless steel canisters appears to be less severe than from Teflon or
Tedlar bags. Because of the bulk, weight, and need for cleaning, canisters
64
have not been favored as storage vessels by researchers in the field.
Despite these sample handling and storage problems, gas chromatography
can be an accurate method of analysis of individual hydrocarbons. Data presented
later in this section, for example, were obtained by deploying mobile laboratories
outfitted with gas chromatographs so that samples could be analyzed soon after
they were obtained. Care was taken in these studies to identify any chromatogram
peak artifacts so that they could be assigned to bag emissions rather than
ambient air compounds. Furthermore, analysis of hydrocarbon mixtures in
ambient air must be performed by GC if the contributions of those mixtures and
their individual components to photochemical oxidant formation are to be
determined, and if relative contributions of various souces are to be evaluated.
Thus, for these and other applications in which compositional analysis is
required, GC techniques must be used. Likewise, for short-term studies, such
as may be required to provide data for use in a model or to validate a model
over a short but intensive period of data collection, GC may not be too
expensive and time-consuming but may, in fact, prove to be the method of
choice.
6-13
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HCT6 JOB A 2-19-80
6.3 SOURCES AND EMISSIONS OF HYDROCARBONS
6.3.1 General
Data on sources and emissions of hydrocarbons that appeared in the 1970
criteria document were for 1968. The most recent compilation of emissions
data, prepared by EPA, covers 1977 but also includes summaries of data for
1970 through 1977. The data appearing in the 1970 document, as well as the
more recent data, are not specific for hydrocarbons but include emissions of
all volatile organic compounds (VOC). Consequently, most manmade emissions
reported in this section will be referred to as VOC. Generally, emissions of
methane, ethane, methyl chloroform, and Freon 112 are considered to have
53
negligible photochemical reactivity and are not included. For many stationary
fuel combustion sources, however, sufficient information is not available to
permit exclusion of these compounds, and current emission factors that include
methane and ethane have been used to estimate these emissions. Highway vehicle
emissions are reported as nonmethane hydrocarbons to which an estimated value
r-j cf.
for methane has been added. '
A summary of national emission estimates for VOC for 1970 through 1977 is
presented in Table 6-2, and emissions of VOC by source category for 1977 are
presented in Table 6-3. It is clear from Table 6-3 that transportation is a
major source of emissions. Other major sources of VOC emissions are industrial
processes and miscellaneous sources. Within these two categories, chemical
manufacturing (listed as chemicals), industrial organic solvent use, and
miscellaneous organic solvent use (domestic and commercial) together total 9.1
x 10 MT/yr, nearly the total of VOC emissions produced by highway vehicles
(9.9 x 106 MT/yr).
A very rough estimate of the percentage of VOC which are actually hydrocarbons
may be obtained from Table 6-3 by assuming that emissions from chemical manufacturing
6-14
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HCT6 JOB A 2-19-80
TABLE 6-2. SUMMARY OF NATIONAL ESTIMATES
OF VOLATILE ORGANIC EMISSIONS, 1970-197767
(106 MT/yr)
YEAR VOC
1970 29.5
1971 29.1
1972 29.6
1973 29.7
1974 28.6
1975 26.9
1976 28.7
1977 28.3
6-15
-------
HCT6 JOB A 2-19-80
TABLE 6-3. NATIONAL ESTIMATES OF
VOLATILE ORGANIC EMISSIONS, 1977,
BY SOURCE CATEGORY67
(106 MT/yr)
Source category
Transportation
Highway vehicles
Nonhighway vehicles
Stationary fuel combustion
Electric utilities
industrial
Residential, commercial,
and institutional
Industrial processes
Chemicals
Petroleum refining
Metals
Mineral products
Oil and gas production
and marketing
Industrial organic
solvent use
Other processes
Solid waste
Miscellaneous
Forest wildfires
Agricultural burning
Coal refuse burning
Structural fires
Miscellaneous organic
solvent use
VOC
11.5
(9.9)
(1.6)
1.5
(0.1)
(1.3)
(0.1)
10.1
(2.7)
(1.1)
(0.1)
(0.1)
(3.1)
(2.7)
(0.3)
0.7
4.6
(0.7)
(0.1)
(o)a
(0)
(3.7)
28.3
% of Total
41
5
36
2
16
100
Zero indicates emissions <50,000 MT/yr.
6-16
-------
HCT6 JOB A 2-19-80
and from industrial and miscellaneous organic solvent use are 100 percent
non-hydrocarbon VOC. While thus assumption is not wholly accurate, it is also
true that exceptions to it are more than likely offset by non-hydrocarbon VOC
emissions such as oxygenated or possibly even halogenated HC from highway
vehicles, stationary source fuel combustion, oil and gas production and marketing,
and miscellaneous combustion sources.
Evaporative VOC emissions result primarily from the transportation and
storage of crude oil and volatile petroleum products such as gasoline and
distillate fuel oil, and from the use of organic solvents for surface coating,
degreasing, and other applications. Evaporative emissions have shown a steady
increase over the years because of increased demands for motor vehicle fuels
co
and organic solvents. As the result of industrial growth, industrial process
emissions have increased by about 17 percent. This increase has been offset
by decreases in emissions from other categories. Emissions from highway
vehicles have decreased as a result of Federally mandated motor vehicle emission
controls, implemented under the Federal Motor Vehicle Control Program for
meeting requirements of Title II provisions of the Clean Air Act. This decrease
of about 7 percent from 1970 through 1977 occurred in spite of an estimated 30
percent increase in motor vehicle travel during that period. Less solid waste
was burned during that time, resulting in fewer emissions. Emissions from
miscellaneous organic solvent use decreased as water-based emulsified asphalts
were introduced in place of paving asphalts liquefied with petroleum distillates
that evaporate when the asphalt cures. Overall, emissions of VOC decreased
slightly from 1970 through 1977.
Emissions of VOC are not uniformly distributed throughout the United
States. Figures 6-1 and 6-2, which are population density and VOC emission
6-17
-------
01
I
s
FT-»
/ * f«35sri5S5;i~"*~'°"~"pj'»:
•-:^$&$&:?*:??:?:?;i
> 10.00P
900 -1.000
600 • 900
200 - 600
Figure 6-1. Density of population in U.S. in 1975 by state, no. people/mi.2 b9-
-------
r
•*"*- / ; ^^^-f: :m
rJ r*i=i ; *'•++:'•:•:•:•:•: :::i<
\ I •p^rT.-^Ktsssrt.r.v.T'.-.T::.^*:-:-:-:-:-:-:-:-:- ••:•:•:
1 / r^S^S^Si^^jS^^ *"^
Figure 6-2. Density of total nonmethane hydrocarbon emissions in U.S. in 1975 by state, tons/mi.2
-------
HCT6 JOB A 2-19-80
density maps prepared from 1975 data, ' are presented to illustrate graphi-
cally the correspondence between population and pollution. The areas with the
greatest population and greatest VOC emission densities are (1) the northeast
corridor extending from Washington, D.C., to Boston; (2) certain industrial
states (Illinois, Indiana, Ohio, Pennsylvania, and New York); and (3) states
along the Gulf Coast. Maps showing VOC emission densities by county rather
than state have better resolution. These show that high emission densities
also exist in the Los Angeles and San Diego, California, areas; and in portions
of Texas and the Gulf Coast states.
6.3.2 Natural Sources and Emissions
The estimates for VOC presented in the previous section included some
natural VOC emissions, those given off by forest wildfires. Other natural
sources of hydrocarbons (not VOC) have already been described in Section 5.
The 1970 document cited Koyama's estimate of natural methane emissions of
14 8
2.7 x 10 g/yr (3 x 10 tons/yr). That estimate did not include methane
emissions generated in swamps and tropical areas, and thus can be considered a
conservative estimate. Robinson and Robbins added production from swamps
and humid tropical areas to Koyama's estimate for an estimated natural pro-,
14 9
duction of methane of 14.5 x 10 g/yr (1.6 x 10 tons/yr). Assuming a methane
emission rate per unit of land area that is half the world average—a reasonable
assumption, given our temperate climate—natural methane emissions in the
United States would be about 5 x 10 tons/year. Though its role in photo-
chemical smog systems is under renewed investigation, methane is still con-
sidered to play little, if any, role in the photochemical formation of oxidants
and other smog components.
6-20
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HCT6 JOB A 2-19-80
Of somewhat more importance than methane relative to photochemical smog
are the natural emissions of terpenes and isoprene from vegetation, since both
can act as scavengers of ozone and, under different conditions, can help
53 19
generate ozone. Rasmussen and Went estimated a global production rate for
volatile organics from vegetation of about 438 x 106 tons/yr. More recent
work by Zimmerman, done since publication of the 1970 criteria document,
estimated net worldwide emissions of all natural hydrocarbons, methane plus
8 72
vegetational, at 8.3 x 10 tons/yr. Zimmerman derived an estimate of isoprene
13 6
plus terpene emissions of 6.5 x 10 g/yr in the United States (70 x 10
73
tons/yr). The complexity of the factors involved, coupled with some methodo-
logical uncertainties, makes this estimate somewhat less than firm, but it
appears to be the best estimate available for emissions from vegetation. The
distribution of terpene and isoprene emissions is not as uniform in the
United States as the methane emissions, based on background concentrations of
methane measured at various sites. Zimmerman's emission inventory indicates
that 43 percent of the total natural HC emissions occur during the summer
months (June, July, and August); and that 45 percent of the annual emissions
occur in the southern United States, and that isoprene constitutes 34 percent
of this portion. At the NMHC/NO ratios occurring in rural areas, neither
/\
terpenes nor isoprene appear to contribute to ozone production. Rather, at
those ratios, they act as scavengers of ozone through ozonolysis of the double
bonds in the compounds.
6.3.3 Manmade Sources and Emissions
Several comprehensive descriptions of manmade sources and emissions of
VOC are available. '' EPA has published and periodically updates detailed,
comprehenstve data on VOC emission rates in Compilation of Emission Factors
6-21
-------
HCT6 JOB A 2-19-80
(AP-42), but because that document presents emission rates for source categories
and subcategories in terms of total VOC rather than species of VOC or HC, the
~7 QK
information given here was derived from another EPA document and from
Vapor-Phase Organic Pollutants, published by the National Academy of Sciences.
6.3.3.1 Stationary Source Emissions—The material presented in this section
was taken directly from or derived from Volatile Organic Compound (VOC) Species
Data Manual. a report prepared for EPA in 1978. The manual summarizes and
documents the available information on species of VOC emitted from stationary
and mobile sources in a format usable by those preparing emission inventories
for photochemical models. Most of the information in the manual was obtained
from material prepared for the California Air Resources Board or from reports
supplied by EPA. Individual references will not be cited in the summary
presented here.
The information summarized here was chosen to represent the kinds of
emissions and sources characteristic of the major stationary source categories
presented in Table 6-3: (1) stationary fuel combustion, (2) industrial
processes, (3) solid waste disposal, and (4) miscellaneous sources.
Sources of stationary fuel combustion include both external combustion
sources and internal combustion engines. The major fuels burned by external
combustion sources are coal, oil, and natural gas. External combustion units
include utility, industrial, commercial, and institutional boilers; commercial
and domestic combustion units; process heaters; furnaces; kilns; etc. If
units are properly operated and maintained, emissions from these sources are
small. For example, a 1000 megawatt power plant is estimated to emit 100 to
75
200 tons per year of volatile organic compounds. This low concentration of
organics in source effluents makes their analysis difficult and readily accounts
6-22
-------
HUb JOB A 2-19-80
for the fact that newer information, '4 based on newer and more sophisti-
cated technologies, may disagree with emission rates and species presented in
the NAS document, which were based on 1968 data. Table 6-4A presents a
profile of the VOC emitted from external combustion sources, categorized by
fuel burned.
Internal combustion engines are used in applications similar to those
employing external combustion units. Internal combustion engines may be
turbines or reciprocating engines, and may be fueled by the usual fossil fuels
such as diesel, oil, or natural gas. They are used in electrial power
generation, in gas pipeline pump and compressor drives, and in various in-
dustrial processes. The majority of gas turbines are used in electrical
generation for continuous, peaking, or stand-by power. Table 6-4B tabulates
emissions of VOC from internal combustion engines used in electrical power
generation and in industrial processes. Note the differing emission profiles
for larger versus smaller (30 hp) reciprocating engines. Smaller engines also
have higher emission rates (emissions per unit of fuel burned) than larger
engines, though the profiles presented here do not include comparisons of
emission rates.
The manufacture of chemicals and chemical-based products contributes
about 27 percent of the total VOC emissions attributable to industrial processes
(Table 6-3). Emissions from the manufacture of one chemical and two chemical-
based products are shown in Table 6-4C. As demonstrated in this table and
from comparison of this table with the preceding tables, emissions from chemical
manufacturing show wide qualitative variations. No one organic compound or
group of compounds dominates emissions.
6-23
-------
HCT6 JOB A 2-19-80
TABLE 6-4A. EMISSIONS OF VOLATILE ORGANIC COMPOUNDS FROM
STATIONARY EXTERNAL COMBUSTION SOURCES74
(wt%)
Compound
emitted
Methane
Formaldehyde
Ethane
Ethyl ene
Acetylene
Acetone
Propane
Propylene
rr Butane
Isobutane
n-Pentane
Isomers of pentane
n-Hexane
Isomers of hexane
jv- Heptane
Isomers of heptane
ri-Octane
Isomers of octane
Cyclohexane
Benzene
Toluene
Residual Distillate
Oil Oil
11.0
42.0 48.7
-
-
-
28.0
1.2
-
14.0 12.2
4.1
4.7
5.5
5.0 10.8
5.2
0.3
2.6
-
4.7
-
-
-
Fuel
Natural Refinery
Oil Oil
56.0 7.6
8.0 7.6
20.9
-
-
-
4.0 18.9
17.5
9.0 23.1
4.4
6.0
9.0
-
1.0
-
-
-
-
1.0
4.0
2.0
CokeO^en
Gas
82.8
-
2.5
11.7
0.8
-
-
0.3
-
-
-
-
-
-
-
-
-
-
-
1.9
-
6-24
-------
HCT6 JOB A 2-19-80
TABLE 6-4B. EMISSIONS OF VOLATILE ORGANIC COMPOUNDS FROM
STATIONARY SOURCE INTERNAL COMBUSTION ENGINES74
(wt %)
Compound
emi tted
Methane
Formaldehyde
Ethane
Ethyl ene
Acetylene
Propane
Propylene
n- Butane
Isobutane
Butene
1,3-Butadiene
Benzene
Electrical generation
Natural Diesel,
gas, turbine recip.
70.0 11.6
30.0
2.8
28.7
11.3
_
17.3
-
-
13.4
7.0
7.9
Dist.
Oil , recip.
11.6
-
2.8
28.7
11.3
-
17.3
-
-
13.4
7.0
7.9
Industrial
Natural
Gas, recip.
76.0
1.0
10.0
1.0
-
10.0
-
1.0
1.0
-
-
-
Natural gas,
Recip. , 30 hp
93.5
-
2.6
2.5
0.9
0.4
0.1
-
-
-
-
-
6-25
-------
HCT6 JOB A 2-19-80
TABLE 6-4C. EMISSIONS OF VOLATILE ORGANIC COMPOUNDS
FROM MANUFACTURE OF SELECTED CHEMICALS/PRODUCTS
(wt %)
Compound
emitted
Varnish
Phthalic
anhydride
Printing
inks
Methane - 80.0
Methyl alcohol - - 5.0
Ethane - 0.4
Ethyl alcohol , - - 2.5
Acetone 38.7 8.6 5.5
Glycol ether 3.0
Acetylene - 4.4
Propane - 11.7
Isopropyl alcohol - - 38.0
Methyl ethyl ketone 41.6 - 5.0
Propylene - 3.1
n-Butane - 36.1
Isobutane - 0.4
n-Butyl alcohol - - "3.0
n-Butyl acetate - - 4.0
Methyl isobutyl ketone 16.7
Isomers of pentane - 22.6
n-Hexane - 21.4
Cyclohexane - 11.3 5.0
Ethyl benzene - - 3.0
Isomers of diethyl benzene - - 3.5
Mineral spirits (paraffins) - - 25.5
Composite emissions from chemical wastes.
6-26
-------
HUb JUB A 2-19-80
In the case of varnish manufacture, cooking and thinning operations are
the major sources of VOC emissions. Incineration and catalytic oxidation have
been used to control VOC from varnish-making; 99 percent control is possible
with incineration. Uncontrolled emissions of VOC are about 185 kg/MT of
product, but controlled emissions are about 1.85 kg/MT.
Phthalic anhydride is produced by the vapor-phase oxidation of naph-
thalene or o-xylene with excess air or catalysis. Reactor and condenser
effluents are the main sources of VOC emissions, but other, minor sources
are present. The emissions profile in Table 6-4C for phthalic anhydride
production is a composite of all sources.
Printing inks consist of a fine dispersion of pigments or dyes in a
vehicle that consists of a drying oil with or without resins and added driers
or thinners. The preparation of the vehicle, by heating, is the largest
source of VOC from ink manufacturing. Composite controlled emissions from
ink manufacturing, reduced by about 90 percent of uncontrolled by means of
scrubbers or condensers followed by an afterburner, are about 21 kg/MT of
product.
Though the disposal of solid wastes contributes only 2 to 3 percent of
all VOC emissions in the United States, Table 6-4D, a profile of VOC from
sanitary landfills, is included here as an indication of the kinds of
emissions that are given off from solid wastes. The use of sanitary land-
fills is a long-accepted method for the disposal of residential and in-
dustrial wastes, most of which consist of refuse, domestic garbage, and inert
construction materials. Waste is generally layered, compacted, and covered
by thin layers of silt. Consequently, anaerobiosis occurs, resulting in the
6-27
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HCT6 JOB A 2-19-80
TABLE 6-4D. EMISSIONS OF VOLATILE ORGANIC COMPOUNDS
FROM SANITARY LANDFILLS
Compound
emitted Wt %
Methane 98.6
Ethane 0.1
Perch!oroethylene 0.3
Propane 0.1
n-Butane 0.2
Isobutane 0.1
n-Pentane 0.1
Cyclopentane 0.2
Terpenes 0.1
Toluene 0.1
Isomers of xylene 0.1
6-28
-------
HCT6 JOB A 2-19-80
generation of appreciable amounts of methane-rich gas. Methane and carbon
dioxide together constitute about 99 percent of gaseous emissions from
landfills.
Next to emissions from highway vehicles, miscellaneous use of organic
solvents contributes the largest percentage of total VOC emissions in the
United States, 13 percent. Three examples of area source emissions of VOC in
this category are presented in Tables 6-4E through 6-4G. Domestic solvents
are those found in products used around the house, garage, or yard. Emissions
of VOC from domestic chemicals or chemical-based products result from the
vaporization of low-boiling-point solvents in the product, the quantity and
species depending on the product. Composite estimates of the percentage by
weight of organic species emitted from domestic solvents are given in Table
6-4E; they were calculated on the basis of annual sales of products containing
these solvents. Organic emissions from domestic chemical use are estimated at
1.1 tons/1000 people/yr.
Pesticides are commonly available in the form of liquids, aerosols, or
powders and are applied by spraying, or dusting, or both. The VOC emitted
from pesticide use arise from vaporization of the pesticide itself or from the
solvent(s) used as the pesticide vehicle. Table 6-4F presents a profile of
VOC emissions resulting from the domestic and commercial use of pesticides.
Total VOC emissions from pesticide use have been estimated at 9 tons/100,000
people/yr.
Table 6-4G presents a profile of VOC emissions resulting from the use of
architectural coatings, which are those paints and other coatings applied to
stationary surfaces such as pavements and curbs, and structures and their
6-29
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HCT6 JOB A 2-19-80
TABLE 6-4E. EMISSIONS OF VOLATILE ORGANIC COMPOUNDS
FROM GENERAL USE OF DOMESTIC SOLVENTS a
Compound Wt %
Formaldehyde 0.6
Ethyl alcohol 36.9
Acetone 1.4
Glycol ether 8.3
Propylene glycol 3.2
Isopropyl alcohol 38.5
Isobutane 5.3
n-Butyl acetate 1.3
Naphtha 4.5
Estimated at 1.1 tons/1000 people/yr. Many common domestic products contain
solvents: furniture polish, shoe polish, shaving soap, perfumes, cosmetics,
shampoo, hair spray, hand lotion, rubbing alcohol, nail polish remover, etc.
6-30
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HCT6 JOB A 2-19-80
TABLE 6-4F. EMISSIONS OF VOLATILE ORGANIC COMPOUNDS FROM DOMESTIC
AND COMMERCIAL USE OF PESTICIDES3'74
Compound Wt %
Methylene bromide 10.0
Propane 1.8
n-Butane 4.4
Isobutane 1.4
n-Pentane 3.2
Isomers of pentane 3.1
n-Hexane 3.7
Isomers of hexane 8.1
C7 cycloparaffins 15.4
Cg cycloparaffins 1.6
Mineral spirits (paraffins) 15.0
Benzene 12.3
Toluene 5.0
Isomers of xylene 15.0
Estimated at 9 tons/100,000 people/yr.
6-31
-------
HCT6 JOB A 2-19-80
TABLE 6-4G. EMISSIONS OF VOLATILE ORGANIC COMPOUNDS FROM THE
USE OF ARCHITECTURAL SURFACE COATINGS3'74
Compound Wt %
Acetone 3.2
Methyl alcohol 3.9
Ethyl alcohol 0.6
Ethylene glycol 0.6
2-Ethoxyethyl acetate 1.3
Dimethylformamide 0.5
Isopropyl alcohol 16.4
Methyl ethyl ketone 5.6
Propylene glycol 0.8
n-Butyl alcohol 1.6
n-Butyl acetate 2.5
Isobutyl alcohol 0.6
Isobutyl acetate 1.5
Methyl n-butyl ketone 0.7
Methyl isobutyl ketone 0.6
Isobutyl isobutyrate 6.1
n-Hexane 20.7
Cyclohexane 20.7
Toluene 5.2
Isomers of xylene 2.6
Ethylbenzene 4.3
Estimated at 3.5 tons/1000 people/yr, but since estimates were
derived from Southern California, which is subject to control of
solvent vapors (SCAQMD Rule 442, formerly Rule 66), this estimate
is probably low.
6-32
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HCT6 JOB A 2-19-80
appurtenances. Industrial coatings are excluded from this table. When paints
and other coatings are applied, the solvents in the coating materials must
evaporate so that the coating can form a film or barrier. The evaporation of
these solvents, along with that of the solvents used to thin coatings or to
clean up, generate emissions that represent a significant area source of VOC
emissions. Emissions of VOC from the use of paints and other coatings in
Southern California were estimated to be 3.5 tons/1000 people in 1976.
Because solvent emissions are controlled in California (Rule 442, formerly Rule
66), this estimate is probably low relative to the rest of the country.
Finally, profiles are given in Table 6-4H of VOC emissions given off by
forest fires and from the open burning of agricultural and landscape wastes
such as spent field crops, weeds, prunings, etc. Ground-level open burning is
affected by many variables, including wind, ambient temperature, composition
and moisture content of the wastes, and compactness of the burning refuse.
Likewise, emissions differ according to burning pattern, i.e., head fires or
back fires. Actual emission rates are difficult to calculate because of the
important influence of these variables and none are presented here.
This survey of VOC species and weight percent of species emitted demon-
strates the diversity of compounds arising from various types of sources. It
also serves to corroborate the estimate made earlier in this section that as
much as 30 percent or more of VOC emissions may be non-hydrocarbons.
6.3.3.2 Mobile Source Emissions—Though VOC emissions from highway vehicles
decreased about 7 percent from 1970 through 1977 (Section 6.2.1), motor
vehicles remain the largest single category of contributors to atmospheric HC
burdens, and are the most influential widespread source of VOC emissions in
general and of hydrocarbon emissions in particular. Stationary sources have a
6-33
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HCT6 JOB A 2-19-80
TABLE 6-4H. EMISSIONS OF VOLATILE ORGANIC COMPOUNDS FROM FOREST FIRES
AND FROM OPEN BURNING OF AGRICULTURAL/LANDSCAPE WASTES
(wt%)
Compound
emitted
Methane
Ethane
Ethyl ene
Acetylene
Methyl acetylene
Propane
Propylene
n-Butane
Isobutane
Butene
Isomers of butene
1,3-Butadiene
3-Methyl-l-butene
n-Pentane
Isoroers of pentane
1-Pentene
Isomers of pentene
n-Hexane
n- Heptane
n-Octane
Unidentified HCs
Forest fires
9.8
10.5
19.1
8.4
0.4
0.4
3.9
0.2
0.1
-
0.8
0.5
0.2
-
0.2
-
-
-
-
-
44.6
Agricultural /landscape
burning
-
-
19.4
1.9
-
1.9
-
1.9
1.9
5.9
-
-
-
1.9
-
11.8
11.8
13.9
13.9
13.8
_
6-34
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HCT6 JOB A 2-19-80
major impact in most urban areas, and in some urban areas, such as Houston and
Chicago, they may have greater impact than mobile sources. Nevertheless, HC
emissions from light-duty gasoline vehicles come the closest to being
ubiquitous and consistent in composition of any hydrocarbon mixtures from any
major sources. This section is limited mainly to a discussion of hydrocarbon
and oxygenated hydrocarbon emissions from diesel- and gasoline-powered
automobiles, since they are the most important mobile sources of gas-phase
hydrocarbons. According to EPA data, shown in Table 6-5, highway vehicles
account for 86 to 87 percent of all VOC emissions; and aircraft, railroads,
marine vessels, and other non-highway vehicles together account for 13 to
14 percent.
TABLE 6-5. NATIONWIDE ESTIMATES OF VOC
EMISSIONS FROM TRANSPORTATION SOURCES, 1970 THROUGH 197767
Year
1970
1971
1972
1973
1974
1975
1976
1977
Total VOC
emissions, 10
12.2
12.2
12.5
12.3
11.5
11.3
11.6
11.5
Highway VOC,
MT/yr 106 MT/yr
10.6
10.6
10.9
10.7
10.0
9.8
10.0
9.9
% of
total
86.9
86.9
87.2
87.0
87.0
86.7
86.2
86.1
Nonhighway
VOC, 106 MT/yr
1.6
1.6
1.6
1.6
1.5
1.5
1.6
1.6
% of
total
13.1
13.1
12.8
13.0
13.0
13.3
13.8
13.9
6-35
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HCT6 JOB A 2-19-80
The 1976 NAS document on vapor-phase organic pollutants states that
gasoline-powered vehicles account for about 99 percent of all vehicular hydro-
carbon emissions. While this estimate is probably high now because of a
growing trend toward use of diesel engines, it is still true that most cars
and light-duty trucks are gasoline-powered.
As noted in Section 5.3, there are potentially four sources of volatile
hydrocarbons and other organic compounds from gasoline-powered vehicles:
crankcase blowby emissions, carburetor evaporative emissions, fuel tank
evaporative emissions, and exhaust emissions. Diesel vehicles emit volatile
hydrocarbons and other organic compounds almost exclusively from the exhaust;
evaporative emissions are practically nonexistent because of low fuel
volatility.77'78
Sources of vehicle emissions have come under increasing control since
1963 when the introduction of positive crankcase ventilation systems virtually
eliminated blowby emissions from gasoline-powered vehicles. The introduction
of absorption-regeneration systems in 1970, which reduce evaporative emissions
by about 30 percent in new vehicles, has resulted in a decline since that time
21 79
in atmospheric emissions from carburetor and fuel tank evaporation. '
Likewise, exhaust HC emissions have been reduced by about 90 percent in new
vehicles since 1968 by means of a variety of engine modifications, including,
most recently (about 1975), catalytic oxidation systems. The actual reduction
in HC emissions effected by these control systems is less than the percentages
cited above because of the inevitable deterioration of these control devices.
Nevertheless, with the implementation of these emission controls in highway
vehicles, emissions from mobile sources have been reduced in spite of con-
tinuing increases in motor vehicle travel. As cars are replaced, both current
control systems and more advanced controls anticipated for the future are
6-36
-------
HCT6 JOB A 2-19-80
expected to reduce HC emissions from motor vehicles further, at least up
through the mid-to-late 1980s. However, it is projected that the automobile
will continue to be a significant source of air pollution, partly because of
80
the expected continued concentration of automobiles in congested urban areas.
For new cars equipped with catalytic oxidation systems, evaporative
emissions account for nearly 60 percent of hydrocarbon and other VOC emissions;
CO
and exhaust emissions account for the rest. Deterioration of exhaust control
systems results in a change in those proportions with time so that emissions
from the two sources are more nearly equal for a car having 4 to 5 years of
road life. Evaporative emissions can still be expected at that time, however,
to contribute the major fraction of vehicle hydrocarbon emissions.
Because of the major contribution of evaporative emissions, it is worth-
while to look at the composition of gasoline and of gasoline vapor. Gasoline
normally contains more than 200 hydrocarbon compounds, mainly in the C^ to Cg
range. Alkanes and aromatics generally constitute the largest fraction, but
olefins and naphthenes are also present. Final gasoline composition is the
result of the mixture of about six blending stocks. The highest octane blending
components in gasoline are aromatics and branched-chain paraffins. Different
gasoline blends are required for different climatic regions of the United States.
A summary of gasoline composition data, for a composite blend that is representative
81
of U.S. consumption, is given in Table 6-6. The average composition of
gasoline vapor, determined from weighted averages of gasoline blending stocks
80
and vapor pressures of respective compounds, is shown in Table 6-7.
Evaporative emissions from automobiles, plus evaporative losses from
gasoline marketing and storage, result in the presence of gasoline vapor
components in all urban atmospheres. Evaporative emissions consist of the
6-37
-------
HCT5/H
TABLE 6-6. SUMMARY DATA ON GASOLINE
COMPOSITION, REPORTED AS WEIGHT PERCENT
81
Hydrocarbon
Paraffins
Isobutane OC/i)
n-butane (nC.)
Isopentane (^5)
n-pentane ("^5)
Dimethyl butanes (C,.;
Methyl pentanes (C;)
n-hexane
Dimethyl pentanes
Methyl hexanes
Trimethyl pentanes
n- heptane
Hi methyl hexanes
Methyl ethyl pentanes
Dimethyl hexanes
Trimethyl hexanes
n- octane
Naphthenes
Methyl cycl opentane
Cyclohexane
Methyl cycl ohexane
Other saturates
Olefins
Methyl butene
Pentene
Methyl pentene
Other olefins
Aromatics
Benzene
Toluene
Ethyl benzene
Xylenes
Propyl benzene
Methyl ethyl benzenes
Trimethyl benzene
Other aromatics
Total
Saturates
Olefins
Aromatics
Morris and
Dishart3
0.7
4.8
8.5
3.4
2.0
4.6
2.0
2.4
5.9
11.1
1.2
1.3
1.4
1.3
1.4
1.3
2.0
0.9
1.2
7.5
2.5
0.8
0.8
7.5
0.9
6.5
1.3
8.8
1.4
2.8
7.1
5.2
62
11
27
Myers
et al.
7.0
9.3
4.5
1.4
6.2
3.3
1.4
6.3
8.5
2.0
2.9
1.8
1.0
2.5
0.8
1.5
2.5
1.5
5.9
1.3
5.9
1.5
1.7
Maynard and
Sanders
4.3
10.2
5.8
2.0
6.0
1.5
1.9
3.2
9.4
2.0
2.0
0.4
0.4
0.6
0.2
0.3
1.3
1.6
1.1
3.5
0.8
12.2
1.7
7.3
0.3
1.6
2.3
2.3
62
9
29
Cited in Reference 81.
6-38
-------
HCT6 JOB A 2-19-80
TABLE 6-7. AVERAGE GASOLINE VAPOR COMPOSITION81
Mean volume
Compound percent
Alkanes
Propane 0.8
ri-butane 38.1
Isobutane 5.2
Isopentane 22.9
rv-Pentane 7.0
Cyclopentane 0.7
Dimethyl butane 0.7
Methylpentanes 3.6
rrHexane 1.5
Methylcyclopentane 1.3
Dimethylpentanes 1.1
Trimethylpentanes 0.5
Alkenes
Isobutylene 1.1
Methylbutenes 2.8
Aromatics
Benzene 0.7
Toluene 1.8
Xylene 0.5
lighter components of gasoline, primarily C^ and C^ hydrocarbons. The exact
composition of the emissions depends on the composition of the gasoline, on
the temperature it reaches (in carburetor, fuel tank, storage tank; during
delivery), and the degree of "weathering," that is, prior evaporation.
Analyses from several studies indicate that the light paraffins and light
olefins constitute about 70 percent of carburetor emissions and about 90
percent of fuel-tank emissions. Isopentane and n-butane were by far the
predominant hydrocarbons, making up about 50 percent of the total. Despite
variations in gasoline composition, these two paraffins account for the major
portion of all gasoline evaporation losses.
6-39
-------
HCT6 JOB A 2-19-80
Exhaust emissions from gasoline-fueled vehicles typically contain fuel
components and low-molecular-weight hydrocarbons that are not present in the
fuel. These low-molecular-weight hydrocarbons include methane, ethane, ethylene,
acetylene, propylene, the C. olefins, and sometimes propadiene and methyl-
acetylene. The fuel components include hydrocarbons with carbon numbers
higher than butane (C.). The predominant hydrocarbons in auto exhaust, as
reported in three separate studies, appear in Table 6-8. As this table
shows, the low-molecular-weight hydrocarbons—methane, ethylene, acetylene,
and propylene--are high on each list. Toluene and isopentane seem to be the
major fuel components.
Extensive studies have been conducted on the effect of gasoline composition
on exhaust composition. Dishart and coworkers concluded that ethylene is
formed from saturates and olefins—propylene and butene primarily from saturates,
and diolefins primarily from olefins—and that additional amounts of toluene,
benzene, and xylenes are formed from higher aromatics and additional 2-methyl
QO—O>l QC
-2-butene from higher saturates. Doe!ling et al. concluded that
gasoline composition had no effect on the total concentration of hydrocarbons
in exhaust, but that the percentages of paraffins, olefins, and aromatics in
86
exhaust were correlated with fuel composition. Neligan et al. concluded
that fuel olefinic exhaust emission is proportional to the olefin content of
the fuel, but that the nature and concentration of the light, cracked products
are independent of the olefin content of the fuel.
The use of catalytic converters has had a pronounced effect not only on
the amount of hydrocarbons emitted from cars but also on the kinds. In general,
oxidation catalysts have resulted in an increase in the percentage of paraffins,
6-40
-------
HCT6 JOB A 2-19-80
TABLE 6-8. PREDOMINANT HYDROCARBONS ,n
IN EXHAUST EMISSIONS FROM GASOLINE-FUELED AUTOS10
Hydrocarbon
Methane .
Ethyl ene .
Acetylene.
Propylene
n-Butane
Isopentane
Toluene.
Benzene
ji-Pentane
m- + pj-Xvlene
1-Butene
Ethane0
2-Methylpentane
n-Hexane
Isooctane
All others
Fraction
62-Car
survey
16.7
14.5
14.1
6.3
5.3
3.7
3.1
2.4
2.5
1.9
1.8
1.8
1.5
1.2
1.0
22.2
of total
15-Fuel
study82
18
17
12
7
4
4
5
—
—
"3C
—
--
--
30
HC, vol %
Engine-variable
study3'88
13.8
19.0
7.8
9.1
2.3
2.4
7.9
--
—
2-5,.
6.0C
2.3
—
—
--
26.9
.Variables were air:fuel ratio and spark timing.
Combustion products.
Includes isobutylene.
6-41
-------
HCT6 JOB A 2-19-80
especially methane; and a decrease in percentage of olefins and acetylene.
Typically, exhaust from a catalyst-equipped automobile contains about 62
percent paraffins, 17 percent aromatics, 18 percent olefins, and 3 percent
acetylene; as compared with 40, 24, 26, and 11 percent, respectively, for
automobiles without exhaust emission converters. The methane levels generally
on on
range from about 10 to 30 percent. ' A study by Jackson produced the
emission data for uncontrolled and catalyst-equipped cars presented in
91
Table 6-9. Jackson evaluated the emissions by six scales used to indicate
potential photochemical reactivity of hydrocarbons. All six showed that
catalyst-equipped cars produced exhaust hydrocarbon mixtures that were less
reactive than those from non-catalyst cars. The reductions in photochemical
reactivity per gram ranged from about 10 to 35 percent. Thus, catalytic
converters have not only reduced total hydrocarbon emissions but have also
91
reduced the oxidant-forming potential of those emissions.
Exhaust gases from gasoline-fueled autos contain organic compounds besides
hydrocarbons, such as aldehydes, ketones, alcohols, ethers, esters, acids, and
phenols. The concentration in exhaust of these oxygenates is about one-tenth
that of the total hydrocarbon concentration. Aldehydes are generally believed
to be the most important class of oxygenates. Formaldehyde is by far the
predominant aldehyde, constituting about 60 to 70 percent of the total (by
volume); acetaldehyde is next, at about 10 percent; and propionaldehyde,
acrolein (acrylic aldehyde), benzaldehyde, and the tolualdehydes are all found
in appreciable amounts. As might be expected, the compositon of the gasoline
burned influences the composition of the aldehydes formed.
6-42
-------
HCT5 JOB B 11-5-79
TABLE 6-9. SUMMARY OF EXHAUST EMISSION DATA
FOR UNCONTROLLED AND CATALYST-EQUIPPED
GASOLINE-FUELED CARS BY MODEL YEAR91
No. of Calif. Cars
No. of Fed. Cars
Mi 1 eage
1970 1972 1973
1 - 3
3600 42105 19802
Carbon, % of
1974 1975
8 9
9162 16075
total hydrocarbon
1976
2
3218
1977
9859
Nonreactive hydrocarbons
Acetylene
Methane
Benzene
Ethane
Propane
Nonreactive total
Reactive hydrocarbons
Ethyl ene
Toluene
Xylenes
Propy 1 ene
Trimethylpentanes
n-Bentane
T-Pentane
Butenes
Methyl pentanes
n-Pentane
Ethyl benzene
i- Butane
Other hydrocarbons
Reactive total
Hydrocarbon classes
Paraffins
Olefins
Acetylene
Aromatics
7.
6.
6.
1.
0.
21.
10.
11.
9.
8.
2.
1.
4.
6.
2.
0.
1.
0.
19.
78.
23.
32.
7.
36.
4
2
4
2
1
4
1
7
7
0
1
6
4
0
0
6
7
8
8
6
9
0
4
7
10.
6.
3.
0.
0.
21.
15.
11.
2.
9.
3.
7.
5.
2.
1.
2.
0.
2.
15.
78.
34.
31.
10.
23.
7
3
8
9
0
7
5
4
3
6
0
0
2
3
2
1
6
3
6
3
5
1
7
7
7.8
4.9
3.4
1.0
0.1
17.1
12.8
9.1
4.1
6.3
5.5
2.0
4.5
2.9
2.9
1.4
1.1
0.8
29.7
82.9
36.8
25.7
7.8
29.7
Hydrocarbon
Molar-based reactivity
NO 2 formation rate
Altshuller
Methane exclusion
Dimitriades
7.
4.
4.
1.
0.
18.
12.
7.
7.
6.
4.
4.
3.
4.
2.
1.
1.
0.
25.
81.
33.
25.
7.
33.
7
7
9
0
1
4
4
5
7
1
0
7
6
0
0
3
7
6
6
6
2
8
7
3
reactivity
2.5
11.3
3.7
2.6
0.3
20.4
7.4
6.5
5.9
3.1
5.4
5.3
5.4
2.5
3.0
2.1
1.4
1.0
29.6
79.6
52.9
16.4
2.5
28.2
3.
9.
4.
3.
0.
21.
7.
7.
7.
3.
5.
3.
4.
4.
3.
2.
1.
0.
27.
78.
46.
17.
3.
33.
6
8
8
0
3
6
2
2
3
9
0
9
5
2
2
1
9
8
2
4
4
0
6
0
0.3
28.0
1.6
4.5
0.3
34.7
7.8
7.7
2.0
1.5
15.6
7.2
5.9
0.4
1.5
0.3
0.6
0.3
14.0
65.3
74.3
9.9
0.3
15.6
per gram
scales
0.
0.
0.
0.
0542
0571
0167
1612
0.
0.
0.
0.
0511
0556
0190
1773
0.0467
0.0499
0.0166
0.1548
0.
0.
0.
0.
0485
0518
0165
1560
0.0366
0.0162
0.0132
0.1210
0.
0.
0.
0.
0380
0892
0139
1232
0.0222
0.0234
0.0109
0.1078
6-43
-------
HCT5 JOB B 11-5-79
TABLE 6-9 (continued).
No. of Calif. Cars
No. of Fed. Cars
Mileage
1970 1972
1
3600 42105
1973
3
19802
1974
1
8
9162
1975
~T~
9
16075
1976
2
3218
1977
4
9859
Carbon, % of total hydrocarbon
Carbon-based reactivity scales
Methane exclusion 0.9380 0.9370 0.9510 0.9530 0.8870 0.9020 0.7200
Cal. Air Res. Bd. 0.4808 0.4469 0.4160 0.4215 0.3300 0.3443 0.2456
Relative reactivity per gram (nonconverter car average = 100.0)
Molar-based reactivity scales
N0? formation race 111.3 104.9 95.9 99.5 75.2 78.0 45.6
Altshuller 109.8 106.9 96.0 99.6 69.6 75.4 45.0
Methane exclusion 100.0 113.8 99.4 98.3 79.0 83.2 65.3
Dimitriades 101.3 112.5 98.2 99.0 76.8 78.2 58.4
Carbon-based reactivity scales
Methane exclusion 98.7 98.6 100.1 100.3 93.4 94.3 75.8
Cal. Air Res. Bd. 112.8 104.8 97.6 98.9 77.4 30.7 57.6
6-44
-------
HCT6 JOB A 2-19-80
Gasoline composition and catalytic converters are but two of many factors
that influence the composition of exhaust gases from cars. Other factors
include driving patterns, ambient temperature and humidity, and individual
automobile characteristics such as make, model year, age, engine size, air:fuel
ratio, and spark timing. In addition, fuel additives can alter the exhaust
hydrocarbon emissions. Of particular interest is the effect of lead additives.
The use of tetraethyl lead (TEL) as a gasoline antiknock agent tends to increase
exhaust hydrocarbon emissions directly and also indirectly, by promoting the
buildup of engine deposits. According to one study, TEL directly increases
hydrocarbon emissions by about 5 percent; the indirect effect, from accumula-
92
tion of deposits, results in an additional 7 percent. The composition of
go
exhaust hydrocarbons is not affected by TEL.
Just as the use of lead additives affects exhaust hydrocarbon emissions,
so does their non-use; again, indirectly. To achieve the same octane and
antiknock properties found in leaded gasoline, refineries must process more of
the lower octane blending stocks such as light, straight-run gasoline; hydro-
cracked gasoline; and thermally cracked gasoline. These processes primarily
involve conversion of naphthenes to aromatics and normal paraffins to
Q-l
isoparaffins. In actual practice, gasolines of all grades generally have
lower octane ratings now than in previous years. While aromatics in all
gasolines, leaded as well as unleaded, have gradually increased over a period
of years, the aromatic content of unleaded gasoline has not increased commensurately
with the removal of lead; that is, the aromatic content is not high enough to
94
attain the combined octane and antiknock properties of leaded gasoline.
Nevertheless, the increases in aromatic content that have occurred, along with
6-45
-------
HCT6 JOB A 2-19-80
possible future increases, are expected to affect the hydrocarbon composition
of exhaust emissions. Benzene is considered the most toxic component of the
aromatic fraction of gasoline vapor. Toluene, xylenes, and other alkylated
benzene derivatives are more toxic than benzene in acute exposures but less
$1
toxic in chronic exposures; they are also much less volatile than benzene.
On the other hand, benzene has low reactivity in atmospheric photochemical
processes, whereas primary and secondary monoalkyl benzenes are highly
reactive and tertiary monoalkyl benzenes and tolualdehyde are moderately
7 53
reactive. Benzaldehyde, like benzene, is of low reactivity. ' The effects
of increased gasoline aromaticity on aromatic aldehyde emission rates from
95
non-catalyst-controlled vehicles are shown in Table 6-10. Increased
aromaticity also produces increased amounts of phenols in exhaust emissions in
uncontrolled cars and, with as much as 46 percent aromatic fuels, in
catalyst-equipped cars as well. The effects of increased aromaticity on
ambient air concentrations of aromatics appear to be negligible to date, as
discussed in Section 6.4.
TABLE 6-10. INCREASE IN AROMATIC ALDEHYDE EMISSION RATES FOR
NON-CATALYST GASOLINE CARS WITH INCREASE IN FUEL AROMATICITY95
Fuel
Unleaded premium
Leaded premium
Leaded regular
Aromatics,
mole %
46.6
30.8
27.3
Total aldehydes,
ppm
65
72
69
Aromatic
aldehydes,
ppm
13.6
6.1
5.8
6-46
-------
HCT6 JOB A 2-19-80
Precipitated by the energy crisis, an additional development that may
affect exhaust emissions of hydrocarbons from cars is the possibility of using
methanol or gasoline-methanol (gasohol) mixtures as fuel. A study by Bernhardt
97
and Lee showed that organic emissions from a methanol-fueled car contain
only a small percentage of hydrocarbons, mainly methane, ethane, and ethylene.
Emissions of methanol and total aldehydes, however, using the same engine with
the same compression ratio, are significantly higher with methanol than with
gasoline. Total aldehydes in the exhaust are about twice as high with methanol
as with gasoline. The total aldehydes can be reduced substantially, however,
by increasing the compression ratio or by adding water to the pure ethanol.
The overall emission rates for hydrocarbons, as determined by hot FID corrected
97
by a factor obtained from GC analysis, were as shown in Table 6-11. (Using
the Federal emission test cycle, the vehicle tested emitted 4.5 g/mi from
gasoline and 2.5 g/mi from pure methanol. The vehicle would not have met the
97
1975 Federal emission standard for HC of 1.5 g/mi.)
TABLE 6-11. TOTAL HYDROCARBON EMISSION RATES (ECE TEST CYCLE) FOR Q7
CAR FUELED WITH GASOLINE, METHANOL, OR A 15% METHANOL-85% GASOLINE MIXTURE1"
Fuel
Gasoline
Methanol
15% methanol -
85% gasoline
Test
Cold start
Hot start
Cold start
Hot start
Cold start
Hot start
HC emissions,
g/test
9.8
7.9
12.0
5.7
8.3
6.5
HC emissions,
emissions from
100
100
122
72
85
82
% of HC
gasoline
6-47
-------
HCT6 JOB A 2-19-80
Diesel emissions are almost exclusively exhaust emissions. The gas-phase
hydrocarbon fraction of diesel exhaust is complex and shows a bimodal distribu-
tion by carbon number. The fraction consists of light, cracked hydrocarbons
... *,,., . . . u-ur 77,98-100
and of heavy fuel-like components ranging up to as high as C4Q.
Except for methane, the light, cracked hydrocarbons are mainly olefins.
Ethylene, acetylene, and propylene are the predominant light hydrocarbons,
with smaller amounts of C. olefins and even smaller amounts of Cr and Cg
olefins.77 Researchers at EPA100 have found that the C1Q-C40 organics are
dominated by unburned fuel and lubricant components. Some of the organics in
this range are particle-bound and some are gas-phase. The distribution of
diesel exhaust hydrocarbons according to molecular weight is shown in Figure
6-3. The exhaust hydrocarbons in the C, to C,Q range result from the combus-
tion process, cracking from higher-molecular-weight organics. Those emitted
in the C,Q to C.Q range result mainly from unburned fuel in the C-.Q to C^c
range and from lubricant in the C-,,- to C.Q range. Partial combustion and
rearrangement compounds occur in this range also. For comparison, the
distribution of hydrocarbons, by molecular weight, in diesel fuel and lubricant
is shown in Figure 6-4. Fuel specifications for No.20 diesel fuel call for
66.2 percent paraffins, 1.3 percent olefins, and 32.5 percent aromatics.
Emission rates for low-molecular-weight hydrocarbons in exhaust of two diesel
vehicles, obtained with the 1975 Federal Test Procedure (FTP), are shown in
Table 6-12.101
Low-molecular-weight aldehydes have also been found in diesel exhaust by
many workers. Formaldehyde has been reported most often, followed by acrolein.
6-48
-------
LU
O
<
I
CQ
<
S!
LU
cc
•S6.88 0 PARTICLE BOUND OLDSMOBILE DIESEL
TOTAL HYDROCARBON - 0.456 g/mi
PARTICLE BOUND - 0.181 g/mi
HYDROCARBON
(*|5.90
NISSAN DIESEL
TOTAL HYDROCARBON - 0.351 g/mi
PARTICLE BOUND - 0.058 g/mi
HYDROCARBON
r*5.78
TURBO-CHARGED RABBIT DIESEL
TOTAL HYDROCARBON - 0.295 g/mi
PARTICLE BOUND - 0.050 g/mi
HYDROCARBON
Irfr
246 8101214161820222426283032343638404244
CARBON NUMBER
Figure 6-3. Distribution of diesel hydrocarbon exhaust emissions, by
molecular weight, between gas-phase and paniculate forms.
6-49
-------
HI
o
CO
NO. 20 DIESEL FUEL
LUBRICANT
10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44
CARBON NUMBER
Figure 6-4. The distribution of hydrocarbons in diesel fuel and
lubricant according to molecular weight.100
6-50
-------
HCT6 JOB A 2-19-80
TABLE 6-12. EMISSION RATES FOR HYDROCARBONS
IN EXHAUST FROM TWO DIESEL VEHICLES101
(g/mi)
Compound
Methane
Ethane
Propane
Acetylene
Benzene
Ethyl ene
Propyl ene
Total nonreactive HC
Nonreactive HC,
% of total HC
Methane, % of
total HC
Total HC (hot
1975
Peugeot
0.0121
0.0021
0.0010
0.0120
0.0092
0.0413
0.0137
0.0364
12.0
4.0
0.304
1973
Nissan
0.0135
0.0009
~0
0.0129
0.0073
0.0280
0.0094
0.0346
14.0
5.5
0.247
FID analysis)
6-51
-------
HCT6 JOB A 2-19-80
102
Vogh measured the following aldehydes in one diesel exhaust sample: formal-
dehyde (18.3 ppm); acetaldehyde (3.2 ppm); acrolein, acetone, propionaldehyde,
and isobutyraldehyde (2.9 ppm); n-butyraldehyde (0.3 ppm); crotonaldehyde and
valeraldehyde (0.4 ppm); hexanaldehyde (0.2 ppm); and benzaldehyde (0.2 ppm).
Data obtained by Braddock and Gabele
emissions on fuel. These data are presented in Table 6-13.
showed the dependence of diesel aldehyde
101
TABLE 6-13. ALDEHYDE EMISSIONS FROM DIESEL VEHICLES
OPERATING ON FIVE DIFFERENT FUELS, 1975 FTP101
(mg/mi)
Test fuel and number (n) of tests
Compound
Formaldehyde
Acetaldehyde
Propionaldehyde
+ acrolein
Crotonaldehyde
Hexanaldehyde
Benzaldehyde
Total aldehydes
Total HC (hot FID)
% Aldehydes
Jet A
(n=7)
21.9
7.5
5.4
0.5
0.3
0.9
36.3
344
10.6%
Local no. 1
(n=7)
16.9
7.4
6.2
~0
0.5
7.8
38.9
304
12.8%
Nat'l avg. no.
2 (n=4)
48.2
11.9
8.7
0.6
0.4
0.8
60.1
471
12.8%
No. 2-D
n=7
40.8
8.2
5.5
~0
0.1
1.4
55.9
489
11.4%
Nissan no. 2
n=5
25.4
10.8
4.7
6.4
~0
0.3
47.6
334
14.2%
•I no
In a study of catalyst-controlled diesel engines, Marshall et al. found
that all four of the noble metal catalytic converters tested effected 10 to 50
6-52
-------
HCT6 JOB A 2-19-80
percent reductions in peak emission rates of hydrocarbons. Detailed examina-
tion by gas-liquid chromatography indicated that the catalysts tended to
oxidize preferentially the unsaturated hydrocarbons. The remaining
high-molecular-weight hydrocarbons were, as a result, predominately the
saturated compounds. Because peak emission rates of aldehydes occurred at
light load (low exhaust temperature), the catalysts had little influence on
peak emission rates. Average emission rates, however, were reduced
substantially.
Since diesels emit hydrocarbons almost exclusively from the exhaust, and
gasoline-powered cars emit both exhaust and evaporative emissions, diesels
emit fewer net gas-phase hydrocarbons. Diesel exhaust from uncontrolled
vehicles can, however, contain higher concentrations of gas-phase hydrocarbons
104
than the exhaust of catalyst-equipped gasoline-fueled vehicles. While the
net production of exhaust HC emissions is important from the health standpoint,
the contribution of the kind of hydrocarbons emitted from diesels to the
formation of photochemical smog products is also important. Spicer and Levy
critically reviewed the nature and photochemical smog reactivity of diesel
engine exhaust organic components. Although an enumeration of the assumptions
made and reactivity scales employed is beyond the scope of this paper, a
summary of their findings on the reactivity of the two exhaust organic
105
fractions is presented in Table 6-14. Though a direct comparison of
gasoline and diesel exhaust emissions is difficult because different test
cycles are used, these data and those of Landen and Perez indicate that the
calculated reactivity of diesel exhaust, on a ppm emission basis, is fairly
low relative to gasoline exhaust.
6-53
-------
HCT6 JOB A 2-19-80
TABLE 6-14. SUMMARY OF REACTIVITY OF DIESEL EXHAUST
HYDROCARBON EMISSIONS AND PERCENTAGE CONTRIBUTIONS,^
OF LOWER-MOLECULAR-WEIGHT HYDROCARBONS AND ALDEHYDES^
Gas-phase
HC fraction
C -C
4 L5
r -r
ul L22
Aldehydes
Total HC
Concentration
ppm
38.7
70.0
32.2
102.2
%
38
69
31
100
N02a
90.1
180.3
193.2
373.5
Reactivity index units
°33
223.4
483.0
460.4
943.4
E.I.a
38.1
98.0
119.3
217.3
Aerosol3
36.6
314.0
32.2
346.2
Percentage contribution
of total
Aldehydes,
% of total
55
46
50
108
46
95
39
122
12
10
NOp photooxidation reactivity; ozone-forming potential; potential for forming
components causing eye irritation; and aerosol-forming potential.
Because transportation sources in general, and highway vehicles in particular,
are major contributors to hydrocarbons in ambient air, emissions from these
sources strongly influence the composition of hydrocarbon mixtures in urban
atmospheres. Table 6-15 summarizes emission characteristics of gasoline-fueled,
methanol-fueled, and diesel autos, since changes in patterns of fuel use or in
the percentage of diesel versus internal combustion engines in operation will
result in qualitative as well as quantitative changes in hydrocarbons emitted
from mobile sources.
6-54
-------
HCT6 JOB A 2-19-80
TABLE 6-15. SUMMARY OF EMISSION CHARACTERISTICS FOR GASOLINE-FUELED,
DIESEL, AND METHANOL-FUELED AUTOS
Auto, control device
or fuel
Emission characteristics
Gasoline-fueled,
uncontrolled
Gasoline-fueled,
catalytic con-
verters
Diesels
Methanol-fueled
Lead additives
gasoline
in
1. Exhaust emissions about 40% paraffins; 24%
aromatics; 26% olefins; 11% acetylene.
2. Main components of exhaust emissions; methane,
ethane, acetylene, ethylene, propylene, C. olefins,
toluene, benzene, n-butane, n-pentane, isopentane,
xylene; aldehydes and some organic acids, ketones,
phenols.
3. Evaporative emissions: 70% of carburetor emissions
are light paraffins and olefins; 90% of fuel-tank
emissi0;is are light paraffins and olefins.
1. Exhaust emissions: about 62% paraffins, 17% aromatics,
18% olefins; 3% acetylene. Methane is about 10-30%
of exhaust emissions.
2. Catalysts preferentially oxidize unsaturated HC.
3. Lower reactivity per gram HC emissions than from un-
controlled gasoline-fueled.
4. Lower net HC emissions than from uncontrolled gas-
oline-fueled.
1. Almost exclusively exhaust emissions.
2. Emissions: light, cracked HC, mainly methane,
ethylene, acetylene, propylene; also aldehydes
(C-j-Cgx, including acrolein), and acetone.
3. Lower reactivity per gram HC emissions than from
gasoline-fueled.
4. Lower net HC emissions than from gasoline-fueled.
5. Higher carbonyl emissions (aldehydes, ketones).
1. Higher cold-start HC emissions than from gasoline-
fueled.
2. Significantly lower hot-start HC emissions than
from gasoline-fueled.
3. Exhaust emissions: mainly methane, ethane, ethylene.
4. Significantly higher methanol and aldehyde emission
than gasoline-fueled (aldehydes reduced by increasing
compression ratio or adding water to methanol).
1. Presence of TEL increased HC emissions.
2. Absence of TEL (or TML) necessitates higher
aromaticity of gasoline to achieve higher
octane ratings.
6-55
-------
HCT6 JOB A 2-19-80
6.4 AMBIENT AIR CONCENTRATIONS
Ambient air monitoring for hydrocarbons is not required under EPA regulations
for purposes of enforcing the HC NAAQS.5 The monitoring of hydrocarbons that
is conducted by the states is for the purpose of controlling oxidant levels.
Thus, states have measured ambient air levels of HC primarily to obtain data
that can be used as imput to the respective models used to determine the
percentage reductions in HC emissions that are needed to attain and maintain
the NAAQS for ozone. Hydrocarbons in ambient air are also measured by the
states and by EPA for other purposes, including: (1) to verify models; (2) to
determine the effectiveness of control strategies; (3) to study oxidant transport
phenomena; and (4) to obtain empirical data to verify reaction mechanisms and
kinetics.
Since routine monitoring has not been required, most of the data available
have been obtained from field studies conducted by EPA, alone or in conjunction
with state and local control agencies or contractors. Most of the data presented
in this section were obtained by the Environmental Sciences Research Laboratory
(ESRL), ORD, EPA, Research Triangle Park; or by its contractors and grantees.
In many instances these data have not yet been published. In other instances,
data from the open literature are available and have been presented. Some of
the data given here are 24-hour averages of total NMHC, calculated from 2-hour
or 3-hour averages obtained during diurnal studies. Some are "instantaneous"
concentrations measured in grab samples that are taken over a period of 5 to
10 minutes. Some of the data describe concentrations of individual hydrocarbons,
some classes of hydrocarbons, and some total nonmethane hydrocarbons. These
data are presented in these various forms partly because they are available
only in these forms and partly in order (1) to compare them with data that
6-56
-------
HCT6 JOB A 2-19-80
appeared In the 1970 criteria document; (2) to compare ranges in ambient air
levels with levels used in clinical and toxicological studies and with levels
found in occupational exposures; (3) to compare profiles—qualitative and
quantitative—of hydrocarbon mixtures in ambient air from one city to another;
and (4) to compare profiles of ambient air hydrocarbon mixtures with auto
exhaust and with gasoline vapor.
One quite important point must be noted at this juncture since it relates
to comparisons between ambient air HC concentrations and exposure levels
reported in occupational, clinical, or toxicologic studies. Most of the
ambient air data reported in this section have been calculated in terms of ppm
or ppb carbon (C), largely because the calibration gas used for most FID
measurements is methane, CH,, which contains one carbon atom per molecule and
because mixtures cannot be expressed in terms of compound concentration. Data
reported by physicians and toxicologists are generally expressed as ppm or ppb
compound. Atmospheric concentrations are expressed as ppm C or ppb C by
multiplying the concentration of the compound by the number of carbon atoms in
the compound. An example at this point may serve to clarify the difference.
Pentane contains five carbons. A concentration of 20 ppb compound of pentane
is equivalent to a concentration of 100 ppb C, since the compound concentration
is multiplied by the number of carbons in the compound.
qc
In a recently published compendium, Graedel has documented the detection
in ambient air of more than 1000 organic compounds. Five sources account for
the bulk (in terms of number of entries) of the detected, identified substances:
gasoline-powered vehicles, diesel vehicles, tobacco smoke, turbines, and
vegetation. Ambient air concentrations for gas-phase hydrocarbons as reported
36
in this monograph are summarized in Table 6-15. These data do not include
6-57
-------
HCT6 JOB A 2-19-80
TABLE 6-15A. AMBIENT AIR CONCENTRATIONS OF HYDROCARBONS
REPORTED BY GRAEDEL3
Concentration range, ppb
Compound (unless specified)
ALKANES
Methane 1.3-4.0 ppm
Ethane 0.05-95
Propane 12-94
Butane 0.01-182
Isobutane 0.06-35
2,3-Dimethylbutane 3.8
Pentane 0.023-64
Isopentane 0.1-101
2-Methylpentane 5-12
3-Methylpentane 3-11
2,2-Dimethylpentane 1-2
2,3-Dimethylpentane 2
2,4 Dimethylpentane 0.3-13
2,2,4-Trimethylpentane 17
Hexane 4-27
2-Methylhexane 10-28
3-Methylhexane 10
Heptane 0.2-34
2-Methylheptane 3.4
Octane 0.04-3.4
Nonane 0.1-9.0
Decane 1.0-11.2
Undecane 0.95-8.8
Dodecane 1.3-5.1
Hexadecane 0.16-1.0
ALKENES AND ALKYNES
Acetylene - 0.2-227
Ethene 0.7-700
Propene 1-52
Propadiene 2-4
Propyne 1-6
1-Butene 1-6
2-Methyl-1-butene 1-19
Isobutene 1-6
1,3-Butadiene 1-9
Isoprene 0.2-2.9
cjs-2-Butene 1-11
trans-2-Butene 1-3
6-58
-------
HCT6 JOB A 2-19-80
TABLE 6-15A(continued)
Concentration range, ppb
Compound (unless specified)
2-Methyl-2-butene 2-18
1-Pentene 1-12
4-Methyl-l-pentene 1-3
c_^s-2-Pentene 2-6
trans-2-Pentene 2-4
2,4-Dimethyl-2-pentene 3-10
1-Hexene 3
cis-2-Hexene 4-8
TERRENES
crPinene 0.93-1.20
B-Pinene 0.14-0.40
Myrcene 0.74-1.0
Limonene 0.06-5.7
ALICYCLICS
Cyclopentane 2-14
Cyclopentene 2-6
Cyclohexane 3-6
Methylcyclohexane 3-7
c_ij>-1,2-Dimethyl cyclohexane 3
AROMATICS (BENZENE AND DERIVATIVES)
Benzene 0.025-57
Toluene 0.005-129
o-Xylene 0.5-33
m-Xylene 1-61
p_-Xylene 1-25
1,2,3-Trimethylbenzene 1-2
1,2,4-Trimethylbenzene 3-15.3
1,3,5-Trimethyl benzene 1.3-11
1,2,3,5-Tetramethylbenzene 1.3-5.3
1,2,4,5-Tetramethylbenzene 1.5-3.9
Ethylbenzene 0.1-22
o-Ethyltoluene 0.7-2.6
m-Ethyl toluene 1.1-13
p-Ethyltoluene 1.1-13
Ethyl dimethyl benzene 0.74-2
Styrene 1.5-5
n-Propylbenzene 1-6
Cumene 1-12
p_-Cymene 0.12-2
s^c-Butylbenzene 4-15
tert-Buty1 benzene 2-6
— OC
compiled from Graedel.
6-59
-------
HCT6 JOB A 2-19-80
the unpublished EPA data presented later in this section, but are the result
of a comprehensive survey of the open literature.
Many of the published detailed studies of organic compounds in the urban
atmosphere were conducted in the 1960s. Results of those studies were summarized
2
and discussed in the 1970 criteria document for hydrocarbons. Published data
on total levels of organic compounds in urban atmospheres from 1970 through
the present are relatively abundant, but most of these data suffer from consider-
able measurement error because they were obtained by FID instrumentation
(Section 5.2). Nevertheless, FID measurements constitute the most comprehensive
published data base on NMHC levels in ambient air. Some statistics derived
from FID-measured NMHC are shown for 1967 through 1972 for six cities in
Table 6-16.107
Because the Los Angeles, California, area has population and traffic
density patterns, meteorological characteristics, and emission sources that
are uniquely conducive to photochemical oxidant formation, NMHC concentrations
have been measured there for many years and these measurements make up the
best long-term hydrocarbon data base available. For comparison with earlier
data from Los Angeles that were reported in the 1970 criteria document, more
recent data from the Los Angles area of the California South Coast Air Basin
are reported here. Trends in concentrations of total NMHC for Los Angeles for
1963 through 1972 are shown graphically in Figure 6-5, based on data reported
108
by Trijonis et al. In a separate study of trends in Los Angeles, Mayrsohn
and Crabtree looked at long-term changes in concentrations of three "tracer"
hydrocarbons—acetylene, propane, and isopentane. These three hydrocarbons
are uniquely associated with known sources and thus can serve as tracers that
indicate the contributions of those sources to total NMHC concentrations.
6-60
-------
TABLE 6-16. FREQUENCY DISTRIBUTIONS FOft 6-TO-9-a.«. NONHETHANE HYDROCARBON CONCENTRATIONS AT CAMP SITES, 1967-1972
(PP-C)
,99
Site
Denver, Colo.
(060680002A10)
Washington, D.C.
(090020002A10)
Chicago, 111.
(141220002A10)
1 Phi 1 aHalnhi A Da
• rill lautflpilla, ra.
M (397140002A10)
Cincinnati, Ohio
St. Louis, Mo.
(264280002A10)
Year
6<
68?
O«f^.
70b
71b
72
66b
68?
69
70b
&
68b
69b
70b
71b
66b
67b
68?
69b
70?
71?
72b
68?
69h
70?
71°
72b
68b±
69b
70D
71b
72D
Nutter
of
saaples
29
161
219
231
178
282
250
244
231
267
279
187
146
300
220
269
260
154
192
264
234
59
109
188
99
104
238
198
292
232
314
235
Percent! lea
Min.
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
OA
* u
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
10
0.0
0.2
0.0
0.0
0.3
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.1
0.0
0.0
0.0
OA
. u
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.1
0.1
0.0
0.0
0.0
0.0
0.0
20
0.3
0.4
0.1
0.2
0.6
0.4
0.1
0.1
0.0
0.0
0.0
0.0
0.2
0.1
0.0
0.2
03
. J
0.1
0.0
0.1
0.1
0.0
0.0
0.0
0.0
0.0
0.2
0.2
0.0
0.1
0.0
0.0
0.0
30
0.4
0.6
0.3
0.3
0.7
0.5
0.2
0.1
0.0
0.0
0.0
0.0
0.4
0.3
0.0
0.3
Oc
.3
0.2
0.1
0.2
0.2
0.1
0.1
0.1
0.2
0.0
0.3
0.3
0.2
0.2
0.1
0.0
0.0
40
0.6
0.8
0.5
0.5
0.9
0.7
0.3
0.3
0.0
0.0
0.1
0.1
0.6
0.5
0.0
0.4
Of
.O
0.3
0.2
0.3
0.3
0.2
0.3
0.2
0.2
0.0
0.4
0.3
0.4
0.3
0.2
0.0
0.1
50
0.9
1.0
0.7
0.6
1.1
0.9
0.4
0.4
0.0
0.0
0.1
0.1
0.8
0.7
0.0
0.5
01
. /
0.5
0.3
0.5
0.4
0.2
0.4
0.3
0.4
0.0
0.5
0.4
0.6
0.4
0.3
0.1
0.2
60
1.1
1.1
0.8
0.8
1.3
1.1
0.5
0.5
0.1
0.1
0.2
0.3
1.0
0.8
0.2.
0.6
OA
. O
0.6
0.5
0.6
0.6
0.4
0.4
0.4
0.4
0.0
0.6
0.4
0.8
0.5
0.4
0.2
0.2
70
1.8
1.4
1.0
1.0
1.5
1.3
0.6
0.6
0.3
0.3
0.3
0.5
1.1
1.1
0.5
0.8
0.8
0.6
0.7
0.7
0.4
0.6
0.6
0.5
0.0
0.7
0.5
0.9
0.7
0.6
0.3
0.3
80
2.3
1.7
1.3
1.1
1.8
1.6
0.7
0.8
0.3
0.5
0.5
0.6
1.4
1.4
0.8
1.0
1.1
0.9
0.9
1.0
0.6
0.7
0.8
0.7
0.1
0.9
0.7
1.1
1.0
0.7
0.4
0.4
90
2.7
2.7
1.7
1.6
2.4
2.0
1.0
1.1
0.5
0.8
0.8
1.1
1.8
1.8
1.4
1.4
1.6
1.6
1.3
1.3
0.9
1.1
1.4
1.1
0.4
1.1
1.0
1.6
1.4
1.1
0.7
0.7
Max.
5.2
5.3
4.9
5.9
5.7
3.9
1.8
2.6
2.3
2.0
3.3
2.0
2.8
3.6
4.1
2.7
5.9
3.7
3.7
2.3
3.0
2.4
3.4
3.1
2.3
2.0
3.4
4.4
3.4
2.9
2.5
1.8
Arithmetic
Mean
1.3
1.2
0.8
0.8
1.3
1.0
0.5
0.5
0.2
0.3
0.3
0.4
0.8
0.8
0.5
0.6
On
. 3
0.7
0.6
0.6
0.5
0.4
0.5
0.5
0.5
0.1
0.6
0.5
0.7
0.5
0.4
0.2
0.3
Std
dev.
1.2
1.0
0.8
0.7
0.9
0.7
0.3
0.4
0.2
0.3
0.3
0.4
0.6
0.7
0.7
0.5
07
. /
0.7
0.7
0.5
0.4
0.4
0.4
0.6
0.5
0.3
0.4
0.4
0.7
0.5
0.4
0.3
0.2
Geometric
Std
Mean dev.
0.74
0.87
0.50
0.52
0.99
0.74
0.35
0.35
0.16
0.19
0.20
0.25
0.64
0.54
0.25
0.46
OKA
. D"t
0.42
0.34
0.42
0.37
0.27
0.31
0.31
0.32
0.23
0.45
0.40
0.44
0.37
0.31
0.19
0.21
3.69
3.62
3.26
2.96
2.29
2.73
2.56
2.73
2.27
2.62
2.64
2.82
2.58
2.99
3.20
2.58
9 70
£ . / W
3.11
3.17
2.74
2.90
2.74
3.02
3.18
2.79
2.22
2.37
2.09
3.25
2.83
2.72
2.54
2.42
'Concentrations greater than or equal to specified value in indicated percentage of samples.
Yearly standard exceeded.
-------
So
T~IIIIII
O MAX. HOURLY AVERAGES • ALL DAYS OF YEAR
D MAX. HOURLY AVERAGES - JULY, AUG.. SEPT.
A 6-TO-9 A.M. AVERAGES - JULY, AUG., SEPT.
1963 1964 1965 1966 196? 1968 1969 1970 1971 1972
YEAR
Figure 6-5. Nonmethane hydrocarbon trends in Los Angeles, 1963
through 1972.108
6-62
-------
HCT6 JOB A 2-19-80
Acetylene is a good indicator of automobile exhaust because no other significant
sources of this HC are known. Isopentane is a major component of both automobile
exhaust and of gasoline. Propane, present only in trace amounts in gasoline
and auto exhaust, is a major component of natural gas.108a All three of these
compounds have relatively long residence times in the atmosphere and therefore
serve as good indicators of the actual quantities in the ambient air of auto
exhaust, gasoline vapor, and natural gas, respectively. Table 6-R shows
the 1967 through 1977 concentrations of acetylene, propane, and isopentane at
two sites in the Los Angeles area. Mayrsohn et al. measured individual
NMHC species and total NMHC at four sites in the Los Angeles area during the
smog season (June through September) in 1975. Monitoring was not done con-
currently at these Long Beach, El Monte, Azusa, and Upland sites, so that
direct comparison of data are not possible. However, the data are useful for
indicating the NMHC composition at the respective sites as well as the total
NMHC concentrations. These data are presented for C~ through C-.-, NMHC and for
total NMHC in Table 6-S. Although descriptions are not given in this
section of the specific methodologies employed in obtaining GC measurements of
ambient air samples presented, special note is made on Table 6-S of the methods
used since they differ from the methods used by ESRL, EPA. Mayrsohn et al.
measured HC up through C,g, whereas ESRL researchers do not commonly attempt
to separate or quantify compounds greater than C.Q because chromatograms often
show peaks resulting from column breakdown products that occur at the retention
times and temperatures at which compounds >C-,Q are resolved. c The miniscule
amounts of >C,2 compounds also complicates their separation, identification,
and quantification. The individual concentrations shown in Table 6-S are for
Cp through C11 only, but the total NMHC concentrations include the Cp through
C-.Q compounds.
6-63
-------
HCT6 JOB A 2-19-80
TABLE 6-R. TRENDS IN 6-TO-9 a.m. CONCENTRATIONS OF INDICATOR HYDROCARBONS AT
TWO SITES IN THE CALIFORNIA SOUTH COAST AIR BASIN, 1967 THROUGH 1977108a
(ppb C)
Acetylene
Year
1967
1968
1969
1870
1971
1972
1973
1974
1975
1976
1977
Azusa
90
-
75
64
-
-
37
51
46
40
33
DO LA"
186
153
124
119
-
-
84
95
-
99
86
Propane
Azusa
87
-
113
91
-
-
56
71
63
53
56
DO LA
121
102
151
147
-
-
92
102
-
92
104
Isopentane
Azusa
136
-
126
105
-
-
91
107
113
88
79
DO LA
302
280
214
245
-
-
169
175
-
185
154
aDOLA = downtown Los Angeles.
6-64
-------
HCT6 JOB A 2-19-80
TABLE 6-S. MAXIMUM AND AVERAGE 6-TQ-9 a.m.
NONMETHANE HYDROCARBON CONCENTRATIONS3 AT FOUR
SITES IN CALIFORNIA SOUTH COAST AIR,BASIN,
JUNE THROUGH SEPTEMBER 19751UOD
(ppb C)
Compound
Ethane
Ethyl ene
Acetylene
Propane
Propylene
All ene
Isobutane
Butane
Butene-1
Butene-2
Isopentane
Pentane
Pentenes
C6
C7
C8
C9
C10
CU
I NMHC
i c2-cu
Long
Avg.
56
26
22
72
10
1
36
83
3
7
86
49
2
2
94
80
66
84
48
921
889
Beach
Max.
170
71
63
279
48
4
111
340
10
19
306
179
21
21
394
257
174
342
224
3216
3084
El Monte
Avg.
114
60
72
101
30
4
52
111
8
24
171
87
25
167
284
271
200
256
198
2396
2232
Max.
239
118
159
212
69
7
176
250
16
57
397
196
93
426
785
762
463
828
896
6137
5601
Azusa
Avg.
77
40
46
63
20
2
31
71
5
15
113
55
5
129
202
231
184
294
229
2079
1811
Max.
122
64
78
135
33
4
65
143
10
29
233
110
30
282
344
444
1375
2149
2933
19425
7418
Upland
Avg.
51
40
43
48
14
2
30
88
4
8
91
47
2
128
169
157
111
202
145
1493
1378
Max.
100
108
88
97
20
4
70
262
9
16
188
94
11
502
441
503
547
1597
967
5666
5156
aEthane through pentane separated on Durapat phenylisocyanate porasil-c
column. Pentane through xylene separated and quantified by means of SE-30
column. Xylene (Cft) through C18 adsorbed on graphitized carbon black,
desorbed, and separated and quantified by means of an OV-101 column.
GC calibrated with known concentrations of individual components.
6-65
-------
HCT6 JOB A 2-19-80
Total NMHC data are available for St. Louis from special field studies
conducted in 1972 and 1973 by the Environmental Sciences Research Laboratory
(ESRL). St. Louis, next to Los Angeles, probably is the most-studied city in
the United States with respect to air pollution in general and oxidant and its
precursors in particular. St. Louis is representative of an urban area having
better ventilation characteristics than Los Angeles. Consequently, the ambient
air levels of NMHC in St. Louis are considerably lower than those observed in
the Los Angeles area. Like Los Angeles, however, the hydrocarbon composition
109
in St. Louis is dominated by automotive-related sources. Total NMHC data
are presented in Tables 6-17 and 6-18 for one urban site in 1972 and for one
urban site in 1973. These are concentrations in 2-hour samples collected over
24-hours for 6 and 4 days, respectively.
During the 1972 ESRL field study, individual hydrocarbon measurements
by gas chromatography (GC) were made at the St. Louis University urban site.
Representative data are presented in Table 6-19. These are 24-hour average
hydrocarbon concentrations calculated from twelve 2-hour sample measurements
on September 13, 1972. Inspection of Table 6-19 easily verifies that methane
concentrations far exceed the concentrations of all other hydrocarbons combined.
As the table footnote indicates, the value for ethylene is erroneous as the
result of contamination from a nearby ozone chemiluminescence monitor.
Consequently, the total NMHC concentration is undoubtedly erroneously high.
Conspicuous by its absence from this table, benzene is not quantitatively
determined by the GC method employed in these and many of the other individual
hydrocarbon measurements obtained by ESRL that are reported in this section. (The
GC method used by ESRL involves separation of lower-molecular weight aliphatics
and alicyclics on one column and higher-molecular-weight aliphatics and alicyclics
6-66
-------
HCT5 JOB F 11-5-79
TABLE 6-17. TOTAL NONMETHANE HYDROCARBON CONCENTRATIONS IN 2-hour
SAMPLES MEASURED BY GAS CHROMATOGRAPHY AT URBAN SITE IN ST. LOUIS
FOR 6 DAYS, SEPTEMBER 13-25, 1972a'b
(ppm C)
Sampling
period
11.00 p.m. -1.00 a.m.
1.00 a.m. -3. 00 a.m.
3.00 a.m. -5. 00 a.m.
5.00 a.m. -7. 00 a.m.
7.00 a.m. -9. 00 a.m.
9.00 a.m. -11. 00 a.m.
11.00 a.m.- 1.00 a.m.
1.00 p.m.- 3.00 a.m.
3.00 p.m.- 5.00 p.m.
5.00 p.m.- 7.00 p.m.
7.00 p.m.- 9.00 p.m.
9.00 p.m. -11. 00 p.m.
Range of
values
0.416 to 3.847
0.478 to 4.056
0.402 to 3.937
0.486 to 5.491
0.431 to 6.585
0.433 to 4.750
0.405 to 3.184
0.263 to 3.450
0.352 to 2.194
0.384 to 1.854
0.247 to 1.728
0.242 to 1.912
Average
(6 days)
1.663
1.466
1.244
2.031
2.125
1.681
1.311
1.172
1.080
0.903
0.938
1.043
aSt. Louis University site.
bSummed from measurements of individual hydrocarbons; ethylene values are
excessively high because of contamination, while benzene measurements are
absent. Total NMHC, because of erroneously high ethylene data, are
accordingly high.
6-67
-------
HCT5 JOB F 11-5-79
TABLE 6-18. TOTAL NONMETHANE HYDROCARBON CONCENTRATIONS IN 2-hour
SAMPLES MEASURED BY GAS CHROMATOGRAPHY AT URBAN SITE IN ST. LOUIS
FOR 4 DAYS, JUNE 21-JULY 8,19?3a'b
(ppm C)
Sampling
period
Midnight-2:00 a.m.
2:00-4:00 a.m.
4:00-6:00 a.m.
6:00-8:00 a.m.
8:00-10:00 a.m.
10:00-Noon
Noon-2:00 p.m.
2:00-4:00 p.m.
4:00-6:00 p.m.
6:00-8:00 p.m.
8:00-10:00 p.m.
10:00 p.m. -Midnight
Range of
values
0.467 to 0.858
0.270 to 0.842
0.199 to 1.112
0.341 to 0.860
0.465 to 1.567
0.350 to 1.013
0.297 to 1.014
0.512 to 0.972
0.391 to 1.090
0.235 to 0.645
0.384 to 0.644
0.514 to 0.639
Average
(6 days)
0.643
0.636
0.635
0.559
0.974
0.727
0.636
0.685
0.641
0.393
0.454
0.572
aCAMP site.
Summed from measurements of individual hydrocarbons. Ethylene values
within normal range; benzene measurements are absent.
6-68
-------
HCT6 JOB A 2-19-80
TABLE 6-19. 24-hour AVERAGE HYDROCARBON
CONCENTRATIONS MEASURED BY GAS CHROMATOGRAPHY
AT URBAN SITE IN ST. LOUIS, SEPTEMBER 13, 1972a'b'
(ppb C)
Compound 24-hr avg. concn.
Methane
Ethane
Ethyl ene
Propane
Acetylene
Iso-butane
n-Butane
Propylene
Propadiene
Neopentane
Iso-pentane
1-Butene + Iso-Butylene
trans-Butene-2 + Methyl acetylene
cls-Butene-2
1,3-Butadiene
n- Pentane
Pentene-1
2-Methylbutene-l
t-Pentene-2
cis-Pentene-2
2-Methylbutene-2
Cyclopentane +
2-Methylpentane
3-Methylpentane
4-Methy 1 pentene-2
Hexane
Hexene-1
2,2-Dimethylpentane
2, 4-Dimethyl pentane
2-Methylpentane
cis-2-Hexene
3,3-Dimethylpentane
Cyclohexane
3-Methyl hexane
2 ,3-Dimethyl pentane
3- Methyl hexane
l-cis-3-Dimethylcyclopentane
2,2, 4-Tri methyl pentane
n- Heptane
Rethy 1 cycl ohexane
Toluene
5473.8
27.3
2212. 5C
24.0
24.8
14.0
57.1
6.4
N.D.d
N.D.
70.8
8.2
4.8
1.4
1.1
26.4
2.1
3.2
5.3
1.6
5.8
36.0
11.2
0.0
13.8
N.D.
0.7
6.6
9.1
0.0
N.D.
N.D.
7.9
8.8
10.1
1.6
11.6
5.4
1.5
61.1
6-69
-------
HCT6 JOB A 2-19-80
TABLE 6-19 (continued)
Compound 24-hr avg. concn.
n-Nonane
Ethyl benzene
g-Xylene
m-Xylene
o-Xylene
5.2
9.0
7.8
24.3
11.1
Isopropylbenzene N.D.
+ styrene
n-Decane 13.0
n-Propylbenzene 2.9
m + p-Ethyl benzene 6.9
1,3,5-Trimethylbenzene 3.0
tert-Buty1 benzene 1.6
+ o-Ethyl toluene
sec-Butyl benzene 15.7
+ 1,2,4-Trimethylbenzene
Unknown 3.6
1,2,3-Trimethyl benzene 3.6
n-Butylbenzene + p_-Di ethyl benzene 3.6
I NMHC
I NMHC - ethyl ene
I Paraffins6
I Olefins7
I Aromatics9
2793.5
581
362.1
64.7
154.2
St. Louis University site.
Gas chromatograph calibrated by standards of individual compounds.
Ethylene concentration not valid; contamination by nearby ozone monitoring
system is indicated when the ethylene/acetylene ratio exceeds about 3.
dNot detected.
eAlicyclics counted with paraffins.
Acetylene counted with olefins.
^C unknown counted with aromatics.
6-70
-------
HCT6 JOB A 2-19-80
and the aromatics on a second column. The retention time for benzene is too
long on the first column, so that column breakdown products and the diffuse
nature of the peak prevent the quantitative measurement of benzene. The
separation characteristics and a too rapid elution time for benzene also
preclude quantitative measurement on the second column. Measurements of
benzene concentrations obtained by other GC methods will be presented separately.)
In a 1974 field study, ESRL obtained total NMHC and individual hydrocarbon
data at a rural site in Ohio. The sampling sites for this study were selected
as rural ground-level locations downwind of major metropolitan complexes.
Although geographically a rural area (Wilmington; McConnelsville; and Wooster,
Ohio), this area was found to be affected, as suspected, by transport of
polluted urban air masses. Hydrocarbon composition was also found to be
influenced by local HC point sources in surrounding communities. Nevertheless,
data collected in the Ohio study are probably representative of many such
109
rural areas across the United States. The distribution of total NMHC
concentrations (in ppb C) by number of samples is shown in Figure 6-6 for
Wilmington and McConnelsville (the latter is located about 100 miles east-
northeast of Wilmington).
Individual hydrocarbon concentrations at the Wilmington site were measured
by gas chromatography. These data, consisting of 24-hour average concentrations
calculated from ten 2-hour and four 1-hour samples, are presented in Table
6-20. Note that the ethylene concentration is quite low. This is significant
for a semi-agricultural area, since ethylene is a known phytotoxicant. The
low level reflects the relatively light traffic density, since ethylene is
emitted mainly in auto exhaust. These same data are presented in Table 6-21
by time of day for total hydrocarbons, hydrocarbon classes, and selected oxygenates.
6-71
-------
0.
2
c/»
u.
O
IT
OVI
25
20
10
5
0
\
—
m
1
////:
1
1 | — IMORNING SAMPLES
I 1 700- 900 _
W77A EVENING SAMPLES
fc222ia 1700-1900
1
~1 n r
i
M
—
1
0 100 200 300
WILMINGTON, OHIO
0 100 200 300
MCCONNELSVILLE, OHIO
TOTAL NONMETHANE HYDROCARBON CONCENTRATION. ppbC
Figure 6-6. Sum of nonmethane hydrocarbon concentrations versus
number of samples for two ground sites used in the 1974 Midwest
Oxidant Transport Study.110
6-72
-------
HCT6 JOB A 2-19-80
Data representative of a major suburban area were obtained by ESRL in the
greater Boston area during the Northeast oxidant transport study in 1975. The
individual hydrocarbon data are presented in Table 6-22 as 24-hour average
concentrations, in ppb C, that were calculated from twelve 3-hour samples.
Middleton and Medfield are suburban towns in the greater Boston area, and
Chickatawbut Hill is an Audubon Society preserve located about 10 miles south
of Boston.
Data from one final urban area are presented. Houston, Texas, is a good
example of an urban area whose atmospheric hydrocarbon burdens are influenced
by both automotive and industrial emissions. Houston has a high density of
petroleum production and refining activities as well as other major chemical
and petrochemical industrial activities. In addition, the shipping channel
from Houston to Galveston (another petroleum/industrial city) is responsible
for emissions (ship and possibly fugitive emissions from petroleum and other
cargo) that influence the ambient air of Houston. The Houston area has a
greater number of hydrocarbon-polluting industries than St. Louis or Boston;
and certainly more than the rural area represented by Wilmington and McConnels-
109
ville, Ohio, even though local influences there included a refinery.
Consequently, the Houston area is expected to have a higher proportional
contribution from industrial hydrocarbons than would be found in St. Louis or
109
Boston. The data presented for Boston were obtained at sites 10 to 15
miles north and south, respectively, of central Boston. The qualitative
composition is expected to be similar to that in the central city; the concen-
109
trations, however, are lower as a result of dilution. It is also quite
possible that the most highly reactive hydrocarbons may have been consumed by
the time concentrations were measured 10 to 15 miles out, given the time
required for dispersion and transport.
6-73
-------
HCT6 JOB A 2-19-80
TABLE 6-20. 24-HOUR AVERAGE INDIVIDUAL HYDROCARBON MEASUREMENTS AT
WILMINGTON, OHIO, July 18, 1974, DETERMINED BY GAS CHROMATOGRAPHY
(ppb C)
Compound
Ethane
Ethyl ene
Propane
Acetylene
Isobutane
n-Butane
Propylene
Isobutylene
trans-Butene-2
cis-Butene-2
Butadiene- 1,3
Isopentane
n-Pentane
Pentene-1
2-Methylbutene-l
trans-Pentene-2
cis-Pentene-2
2-Methylbutene-2
Cyclopentane
2-Methylpentane
3-Methylpentane
4-Methylpentene-2
rr Hexane
Hexene-1
trans-Hexene-3
2,4-Dimethylpentane
Methyl cyclopentane
3 , 3-Di methyl pentane
Cyclohexane
2-Methyl hexane
2 , 3-Dimethyl pentane
3-Methyl hexane
1-ci s-3-Dimethyl cycl opentane
2, 2, 4-TH methyl pentane
n-Heptane
Methyl cycl o hexane
Benzene
Toluene
Nonane
Ethyl benzene
p/-Xylene
Concn.
range
7.4 - 13.9
1.1 - 5.1
3.6 - 10.7
1.6 - 9.2
1.5 - 7.6
3.1 - 14.7
0.3 - 1.5
0.3 - 2.0
0.8 - 1.7
N.D.
N.D.- 0.7
2.5 - 21.4
1.2 - 8.1
N.D.
N.D.
N.D.
N.D.
N.D.
0.4 - 5.7
0.9 - 4.1
0.7 - 2.8
N.D.- 0.3
0.8 - 5.1
N.D.- 3.2
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
0.8 - 4.5
1.0 - 6.8
1.9 - 5.8
0.3 - 2.3
0.3 - 4.8
24- hr
average concn.
9.9
2.9
6.6
5.4
3.9
8.0
0.7
0.8
1.2
-
0.1
8.8
3.7
-
-
-
_
-
1.6
2.2
1.4
0.0
2.1
0.2
-
-
-
-
-
-
-
-
••
-
-
2.3
3.5
3.2
0.6
0.9
6-74
-------
HCT6 JOB A 2-19-80
TABLE 6-20 (continued)
Compound
Concn.
range
24- hr
average concn.
m-Xylene
0-Xylene
n-Decane
n-Propylbenzene
m,£-Ethyl toluene
1,3,5-Trimethyl benzene
o-Ethyl toluene
1,2,4-Trimethylbenzene
Unknowns
Methane, ppm
Total NMHCD
Acetaldehyde
Propionaldehyde
Acetone
N.D.-
0.2 -
0.7 -
0.2 -
N.D.-
N.D.-
N.D.
0.3 -
1.0
6.1
2.0
1.2
0.8
1.0
2.2
0.5 - 10.2
1.48 - 2.43
42.3 -223.5
1.3 - 7.5
N.D.- 11.4
3.0 - 20.7
0.6
1.6
1.2
0.3
0.4
0.1
0.8
5.4
1.6
101.6
4.4
2.6
8.5
*N.D. = not detected.
Includes aldehydes, acetone, and unknowns.
6-75
-------
HCT6 JOB A 2-19-80
TABLE 6-21. CONCENTRATIONS OF TOTAL NONMETHANE HYDROCARBONS,
METHANE, AND SELECTED OXYGENATES IN ELEVEN 2-hour AND TWO 1-hour
SAMPLES TAKEN OVER 24 hours, JULY 18, 1974, WILMINGTON, OHIO
Compound/class, ppb C
Time Methane
Midnight-2:00 a.m.
2:00-4:00 a.m.
4:00-6:00 a.m.
6:00-8:00 a.m.
8:00-10:00 a.m.
10:00 a.m. -Noon
Noon-2:00 p.m.
2:00-3:00 p.m.
3:00-4:00 p.m.
4:00-5:00 p.m.
5:00-6:00 p.m.
6:00-8:00 p.m.
8:00-10:00 p.m.
10:00 p.m. -Midnight
1500
1520
1520
1590
1590
1520
1520
1480
1600
2430
1500
1530
2200
1730
NMHCa
71.7
42.3
55.4
65.6
66.0
52.7
128.1
149.0
149.7
223.5
150.5
104.3
84.5
78.5
IPb
31.8
24.5
31.8
36.5
40.9
34.1
78.5
91.0
90.7
161.6
93.0
59.3
61.5
59.1
I0b
3.3
2.9
4.1
5.5
7.0
3.4
5.5
6.3
5.3
10.3
6.3
4.5
7.1
7.4
IAb
20.9
5.9
7.1
8.6
9.2
6.8
10.0
12.6
14.7
14.5
19.2
14.8
6.0
5.2
Unknowns
9.0
2.2
4.0
2.8
1.9
3.2
10.2
9.7
7.8
7.3
9.6
6.9
0.5
0.5
Aldehydes
1.9
1.8
4.1
5.3
3.2
2.2
8.5
10.2
10.5
18.7
11.8
7.4
6.0
6.3
Acetone
4.8
5.0
4.3
6.9
3.8
3.0
15.4
19.2
20.7
11.1
10.6
11.4
3.4
N.D.
^Includes aldehydes, acetone, and unknowns.
IP = total paraffins; 10 = total olefins; IA = total aromatics.
6-76
-------
HCT5/D
TABLE 6-22. 24-hour AVERAGE INDIVIDUAL HYDROCARBON
CONCENTRATIONS MEASURED BY GAS
CHROMATOGRAPHY, BOSTON AREA, 1975
(ppb C)
MiddletorL, 8/11/75
Avg.
Ethane
9.
7
Ethyl ene Contain.0
Propane
Acetylene
Isobutane
n-Butane
Propylene
Isobutylene
trans-Butene-2
cis-Butene-2+Butadi ene
Tsopentane
n-Pentane
Pentene-1
2-Methylbutene-l
trans-Pentene-2
cis-Pentene-2
2-Methylbutene-2
Acetaldehyde
Cyclopentane
2-Methylpentane
3-Methylpentane
4-Methylpentene
n-Hexane
Hexene-1
Unknown
trans-Hexene-3
2,4-DiMethylpentane
Cyclopentane
cis-Hexene-2
Unknown
Propionaldehyde
Acetone
3,3-Dimethylpentane
Cyclohexane
2-Methyl hexane
2,3-Dimethylpentane
3-Methyl hexane
Unknown
l-c-3-Dimethyl cyclo-
pentane
2, 2, 4-Trimethyl cyclo-
pentane
l-t-3-Di methyl cyclo-
pentane
""Heptane
Methyl cyclohexane
Unknown
11.
10.
9.
22.
3.
3.
1.
I.
25.
14.
0.
0.
N.
N.
0.
(6.
6.
10.
6.
N.
6.
N.
0.
0.
0.
4.
0.
N.
(N.
(6.
N.
0.
3.
1.
3.
I.
0.
3.
0.
2.
1.
—
9
7
9
4
6
5
0
8
6
3
6
8
D.
D.
6
6)
0
3
3
D.
6
D.
5
3
9
6
1
D.
D.)
8)
D.
8
2
8
3
6
8
0
3
8
9
•-
Range
7.3
- 12.1
Contain. d
6.9
7.5
5.8
14.6
2.0
1.3
0.2
0.8
15.7
9.0
0.3
0.3
N.D
N.D
N.D
(3.5
N.D
N.D
3.9
N.D
3.9
N.D
N.D
0.2
0.2
2.8
N.D
N.D
(N.
(1.
N.D
0.2
1.3
0.4
1.5
N.D
N.D
1.8
N.D
0.9
N.D
—
- 17.4
- 17.6
- 13.1
- 32.4
- 6.8
- 6.8
- 2.2
- 2.7
- 39.3
- 22.5
- 1.3
- 1.5
t
.
! - 1.5
- 8.9)
. - 9.3
. - 16.3
- 10.7
.
- 10.8
s
. - 0.8
- 0.7
- 1.9
- 6.2
. - 0.4
. - 0.2
D.)
7 - 12.6)
.
- 1.3
- 5.4
- 3.4
- 6.3
. - 12.1
. - 1.5
- 5.1
. - 0.6
- 4.7
. - 7.3
Medfield^ 8/21/75 Chickatawbut,
Avg.
3.9
Range
2.0 -
5,2
Contain. Contain.
9.0
5.7
4.1
10.3
2.3
2.4
1.2
1.0
15.1
10.5
0.5
0.7
1.0
0.4
0.9
(2.0)
5.2
6.1
3.9
0.1
4.2
0.2
0.4
0.4
0.9
3.1
0.4
0.1
(0.3)
(2.0)
N.D.
0.6
2.8
1.4
2.8
0.1
0.4
2.3
0.3
1.9
2.8
1.6
1.6 -
2.1 -
1.6 -
3.4 -
0.6 -
1.4 -
0.5 -
0.5 -
5.6 -
2.8 -
0.2 -
0.3 -
N.D.
N.D.
N.D.
N.D.
1.3 -
2.2 -
1.4 -
N.D.
1.6 -
N.D.
N.D.
N.D.
N.D.
1.4 -
N.D.
N.D.
(N.D.
(N.D.
N.D.
0.3 -
1.1 -
0.7 -
1.0 -
N.D.
N.D.
0.5 -
N.D.
0.9 -
1.6 -
N.D.
21.6
10.1
6.7
15.8
5.4
4.0
1.7
1.9
24.1
28.7
0.9
1.5
- 3.1
- 1.7
- 2.0
- 4.0
8.2
11.2
6.4
- 0.3
6.9
- 0.6
- 0.9
- 0.8
- 1.8
5.2
- 0.9
- 0.4
- 1.3)
- 9.2)
1.0
4.8
2.2
4.7
- 0.6
- 1.4
4.8
- 1.0
• 3.2
• 4.5
- 11.1
Avg.
2.
5.
2.
3.
2.
6.
1.
1.
0.
0.
8.
4.
0.
0.
N.
N.
0.
(2.
5.
3.
2.
0.
3.
0.
0.
0.
0.
2.
N.
N.
N.
2.
N.
0.
2.
1.
2.
0.
2.
0.
2.
2.
— -
9
2
7
9
8
2
8
8
7
7
2
3
2
2
D.
D.
1
4)
4
8
6
0
5
0
1
1
2
4
D.
D.
D.
0
D.
6
1
0
2
5
0
5
0
1
•—
8/21/75
Range
2.0
1.2
1.2
0.9
0.8
1.8
0.4
0.6
0.6.
N.Db
2.8
1.5
N.D.
N.D.
N.D.
N.D.
N.D.
1.2
1.1
1.9
0.7
N.D.
1.0
N.D.
N.D.
N.D.
N.D.
1.0
N.D.
N.D.
N.D.
1.1
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
---
- 4.2
- 6.8
- 4.2
- 6.9
- 6.0
- 12.3
- 2.8
- 4.0
- 0.9
. - 1.3
- 13.8
- 6.4
- 0.4
- 0.6
- 0.8
- 3.8
- 11.5
- 5.7
- 4.2
- 0.2
- 9.1
- 0.3
- 0.4
- 0.3
- 0.6
- 5.1
-' 3.8
- 1.8
- 4.0
- 1.8
- 4.2
- 2.1
- 3.0
- 1.3
- 4.4
- 4.9
6-77
-------
HCT5/D
TABLE 6-22 (continued)
Middleton, MA
Avg.
Toluene
Unknown
Unknown
Unknown
n-Nonane
Unknown
Unknown
Unknown
Unknown
Ethyl benzene
p_-Xylene
m-Xylene
Unknown
crPinene
o-Xylene
n-Decane
Tsopropy 1 benzene
Unknown
p-Pinene
Unknown
rrPropyl benzene
m,£, -Ethyl toluene
Unknown
Unknown
A-Carene
1,3, 5-Tri methyl benzene
0- Ethyl toluene
1,2,4-Trimethylbenzene
Unknown (Undecane?)
D-Limonene
26.
1.
N.
N.
2.
0.
0.
0.
0.
7.
6.
21.
0.
N.
13.
3.
5.
1.
N.
N.
1.
6.
0.
N.
N.
1.
1.
7.
1.
N.
5
5
D.
D.
8
9
2
1
2
2
8
5
0
D.
2
9
8
5
D.
D.
8
7
7
D.
D.
5
4
3
4
D.
Range
N.D.
N.D.
N.D.
N.D.
0.3
N.D.
N.D.
N.D.
N.D.
2.5
2.3
7.2
N.D.
N.D.
4.9
0.9
1.1
N.D.
N.D.
N.D.
• N.D.
3.0
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
- 44.8
- 6.5
- 6.3
- 2.9
- 0.6
- 1.0
- 0.4
- 23.3
- 19.4
- 66.4
- 0.4
- 30.2
- 7.8
- 23.8
- 4.1
- 4.7
- 19.3
- 3.1
- 3.8
- 2.9
- 12.5
- 8.3
Medfield. MA Chickatawbut Hill, MA
Avg.
21.
0.
N.
N.
0.
—
0.
0.
5.
6.
14.
N.
N.
6.
1.
2.
0.
N.
N.
0.
3.
N.
N.
N.
0.
0.
5.
--
4
2
D.
D.
9
-
1
6
8
6
4
D.
D.
5
7
0
6
D.
D.
8
4
D.
D.
D.
9
8
7
-
Range
7.9
N.D.
N.D.
N.D.
0.2
—
N.D.
N.D.
3.2
3.2
N.D.
N.D.
N.D.
4.8
0.5
0.5
N.D.
N.D.
N.D.
N.D.
1.0
N.D.
N.D.
N.D.
N.D.
N.D.
2.0
—
- 43.6
- 0.8
- 2.2
- 0.5
- 5.0
-8.7
- 17.0
- 24.2
- 9.6
- 4.4
- 3.5
- 2.1
- 1.6
- 6.4
- 1.6
- 1.4
- 8.6
Avg.
18.3
0.7
N.D.
N.D.
1.1
1.8
3.7
2.2
N.D.
N.D.
3.1
0.8
0.8
0.2
0.6
2.0
—
—
—
0.3
0.3
4.1
3.7
Range
8.3
0.2
N.D.
N.D.
N.D.
0.6
0.4
N.D.
N.D.
N.D.
1.6
N.D.
N.D.
N.D.
N.D.
0.6
—
—
—
N.D.
N.D.
2.5
N.D.
- 41.3
- 1.6
- 3.3
- 3.1
- 8.5
- 6.3
- 4.4
- 1.1
- 1.7
- 1.0
- 1.1
- 2.6
- 0.6
- 0.7
- 5.4
- 9.2
HC sampler located adjacent to ozone chemiluminescence monitor that employed
ethylene; data contaminated.
5N.D. Not detected
6-78
-------
HCT6 JOB A 2-19-80
The Houston data presented here were obtained at numerous sites in and
around the city. A complete analysis of the available data has not yet been
made. However, the ranges in total NMHC from day to day and from site to site
demonstrate both the effects of local meteorology and the effects of unique
local point sources (versus the more homogeneous emissions of auto exhaust and
fuel evaporation). Variations with time of day demonstrate the effects of
ventilation characteristics in respective urban areas. The data for both.St.
Louis and Houston show that during the 6-to-9 a.m. period hydrocarbon concen-
trations can be as much as ten times greater than the concentrations during
the l-to-4 p.m. period, even though there is no variation with time of the
source emission rates.
Data presented in Table 6-23 demonstrate the diurnal variations in total
NMHC (measured by FID) at one site in Houston in 1976. The data show the
average concentration and the concentration range for samples measured hourly
over 24 hours for 23 days. The concentration during the 6-to-9 a.m. period is
about three times higher than that of the l-to-4 p.m. period.
Additional hydrocarbon data for Houston have been acquired by ESRL in an
extensive field study conducted by EPA in conjunction with local and state air
pollution agencies. More recent data are still being reduced and prepared for
publication. Data for 1973 and 1974 portions of the Houston study are presented
in Tables 6-24 and 6-25. Concentrations of the three major classes of hydro-
carbons in air samples collected at 19 different sites, in three separate
112
phases of the study, are shown in Table 6-24. Paraffins include the alicyclics
for purposes of this tabulation. Detailed gas chromatographic analyses of
hydrocarbons in samples collected at three representative sites in Houston in
112
1973 are presented in Table 6-25. Site 1 is located in the midwestern
6-79
-------
HCT6 JOB A 2-19-80
TABLE 6-23. TOTAL NONMETHANE HYDROCARBON
CONCENTRATIONS IN HOUSTON BY TIME OF DAY FOR 23 DAYS,
JULY 3-25, 1976 (DETERMINED BY FID)111
(ppm C)
Time of day
1:00 a.m.
2:00
3:00
4:00
5:00
6:00
7:00
8:00
9:00
10:00
11:00
Noon
1:00 p.m.
2:00
3:00
4:00
5:00
6:00
7:00
8:00
9:00
10:00
11:00
Midnight
Concn.
range
0.1 -
0.1 -
0.1 -
0.1 -
0.1 -
0.0 -
0.2 -
0.2 -
0.2 -
0.2 -
0.0 -
0.1 -
0.1 -
0.1 -
0.1 -
0.1 -
0.1 -
0.1 -
0.1 -
0.1 -
0.3 -
0.2 -
0.2 -
0.2 -
1.6
1.4
1.6
2.1
1.6
2.9
1.9
1.7
1.5
0.9
1.3
0.7
0.7
0.8
0.6
0.6
0.9
1.3
1.3
2.0
1.9
2.4
1.3
1.3
Avg. concn.
0.6
0.6
0.6
0.7
0.7
0.8
1.0
1.0
0.7
0.5
0.4
0.4
0.3
0.3
0.3
0.3
0.4
0.5
0.6
0.6
0.7
0.8
0.6
0.6
6-80
-------
HCT6 JOB A 2-19-80
TABLE 6-24. CONCENTRATIONS OF HYDROCARBONS
BY CLASS IN AIR SAMPLES COLLECTED AT 19 SITES3 IN HOUSTON, 1973
AND 1974 (DETERMINED BY GAS CHROMATOGRAPHY]
(ppb C)
,112
Date
September
1973
January
1974
Apri 1
1974
Sites
7 (HOI,
H04, H06
7 (H12,
H15, H16
5 (H21,
H23, H24
H03,
, H07, H08, H09)
H13, H14,
, H17, HIS)
H22,
, H25)
Class
Paraffinsb
Olefins
Aromatics
Total
Paraffins
Olefins
Aromatics
Total
Paraffins
Olefins
Aromatics
Total
Avg.
concn.
298.8
79.6
179.1
557.5
3315.8
533.1
904.4
4753.3
470.9
136.4
143.0
75O
% of
total
53.6
14.3
32.1
100.0
69.8
11.2
19.0
100.0
62.8
18.2
19.0
looTo
Sampling sites in traffic tunnels were excluded from this tabulation in order
to obtain averages more representative of Houston ambient air.
3Paraffins include the alicyclics in this tabulation.
6-81
-------
HCT5/E 11-5-79
TABLE 6-25. CONCENTRATIONS OF INDIVIDUAL HYDROCARBONS IN AIR
SAMPLES COLLECTED IN HOUSTON ON SEPTEMBER 11,
(ppb C)
Compound
Ethane
Ethyl ene
Propane
Acetylene
Isobutane
n-Butane
P ropy! ene
Isobutylene
trans-2-Butene
cis-2-Butene
1,3-Butadiene
Isopentane
n- Pentane
1-Pentene
2 Methyl -1-butene
trans-2-Pentene
cis-2-Pentene
2 Methyl -2-butene
Acetaldehyde
Cyclopentane
Isoprene
2-Methylpentane
3-Methylpentane
4 Methyl -2- Pentene
n- Hexane
1-Hexene
Unknown
trans-3-Hexene
2,4 Dimethyl pentane
Methyl cyclopentane
cis-2-Hexene
Unknown
Propionaldehyde
Acetone
3,3 Dimethyl pentane
Cyclohexane
2-Methyl hexane
2,3 Dimethyl pentane
3-Methyl hexane
Site la
35.1
174.7
28.0
41.9
41.5
111.3
22.5
20.8
4.1
2.5
4.1
117.8
58.5
4.8
7.1
9.4
11.4
7.9
—
—
—
52.3
21.8
0.0
30.4
0.0
0.0
7.2
12.7
0.0
8.0
15.3
22.5
22.9
l-cis-3- Dimethylcyclopentane
2,2,4 Trimethyl pentane
It3 Dimethylcyclopentane
n-Heptane
32.0
—
16.2
Site 2a
24.8
30.8
22.7
8.8
21.4
38.0
7.3
8.4
4.0
1.0
2.8
42.1
20.8
1.7
1.8
2.9
7.8
3.1
—
—
— _
21.7
7.3
0.0
14.3
0.0
0.0
5.0
10.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
—
0.0
Site 3a
21.7
24.5
19.0
20.7
11.4
29.2
9.6
11.6
4.0
0.0
4.0
33.5
20.0
1.3
1.1
2.2
1.3
1.8
—
—
—
19.8
8.5
0.0
8.5
0.0
0.0
2.1
4.7
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
—
0.0
Avg.
concn.
27.2
76.7
23.2
23.8
24.8
59.5
13.2
13.6
4.0
1.2
3.6
64.5
33.1
2.6
3.3
4.8
6.8
4.3
— -
—
—
31.3
12.5
0
17.7
0
0
—
4.8
9.2
—
0
—
—
2.7
0
5.1
7.5
7.6
0.0
10.7
—
5.4
6-82
-------
HCT5/E 11-5-79
Table 6-25 (Continued)
Compound
Methyl cyclohexane
Toluene
n-Nonane
Ethyl benzene
£-Xylene
m-Xylene
o-Xylene
Tsopropyl benzene
n-Decane
n-Propyl benzene
g- Ethyl toluene
m- Ethyl toluene
1,3,5 Trimethyl benzene
o- Ethyl toluene
1, 2, 4-Trimethyl benzene
Unknown
1,2,3 Trimethyl benzene
n-Butyl benzene +
|-Di ethyl benzene
m-Di ethyl benzene
Unknown
Methane, ppm
Site 1
16.8
132.0
19.9
19.8
20.0
86.1
75.1
13.5
20.4
3.8
15.5
___
15.5
5.7
182.9
36.6
0.0
0.0
0.0
0.0
2.01
Site 2
0.0
35.6
6.4
6.7
5.0
13.0
8.8
7.3
10.1
4.5
10.9
---
0.0
9.6
31.8
—
2.3
0.0
0.0
0.0
1.77
Site 3
0.0
44.2
7.8
5.3
5.3
21.0
8.4
—
8.7
1.3
5.8
__-
2.6
1.5
6.8
10.1
0.0
0.0
0.0
0.0
1.75
Avg.
concn.
5.6
70.6
11.4
10.6
10.1
40.0
30.8
10.4
13.1
3.2
10.7
___
6.0
5.6
73.8
23.4
0.8
0
___
0
0
1.84 ppm
See text for site information.
6-83
-------
HCT6 JOB A 2-19-80
sector of the city and is representative of the influence of auto exhaust.
The site is the farthest of the three from the Houston shipping lanes and is
112
the closest of the three sites to a major traffic artery. The influence of
auto emissions is clearly discernible in the concentrations and proportions of
ethylene, acetylene, isopentane, 2- and 3-methylpentane, toluene, and the
xylenes; all of these are considered to be among the predominating hydrocarbons
in auto exhaust. Sites 2 and 3 are in the northeast and southeast sectors
of Houston, respectively; they are much closer to the shipping lanes than site
1 and are not close to any major traffic arteries.
More recent data are available from a study conducted by EPA in Houston
in September through December 1978 to investigate visibility and photochemical
ozone problems in that area. a One important aspect of the study was to
obtain data on the hydrocarbon composition of ambient air at various locations
in the Houston area for subsequent use in a sophisticated photochemical model
for ozone. The 1978 investigation of air quality in the Houston area consisted
of two individual but complementary studies, the Houston Aerosol Characterization
Study (HACS) and the Houston Ozone Modeling Study (HOMS), both of which were
the result of a Congressional mandate. The data reported here were collected
as part of HOMS.
Grab samples were collected and analyzed by gas chromatography. A total
of 109 peaks were seen on the chromatograms, of which unidentified peaks
represented 8 to 12 percent of the total NMHC concentration. These unknown
compounds may have resulted from sample contamination by outgassing of the
sample container, but that is uncertain. The problem is more likely to have
affected the sum of unknown aromatics than of paraffins or olefins. It is
possible, since a three-column GC procedure was used, that one or more unknown
6-84
-------
HCT6 JOB A 2-19-80
compounds may have been resolved by more than one column, and thus may have
been counted twice in the total NMHC concentration. For these reasons, plus
the relatively low percentage contribution of the unknowns to the total concen-
tration, the unknowns were excluded from the total NMHC concentration. Only
identified compounds are included in the data reported here. Table 6-Y shows
the average percentage composition of paraffins, olefin, and aromatics observed
at nine HOMS sites. It also includes, for comparison, similar information
obtained from two sites in St. Louis in 1972 and 1977.
The results from Houston agree reasonably well with those from St. Louis.
Likewise, comparison of these Houston data with those presented in Table 6-24,
which were obtained in 1973 and 1974, shows good agreement between the composite
averages of the earlier data and the 1978 data from individual sites. It
should be noted that Table 6-Y reports only the average composition observed.
The composition not only varies from site to site, as shown by these averages,
but also fluctuates day to day at each site. The standard deviation reported
in Table 6-Y gives an indication of the day-to-day fluctuations that occur.
The largest variations are seen in the olefin and aromatic percentages.
Variations in the more abundant paraffins are smaller. Overall, the largest
variations were seen at sites near industrial areas, where emission patterns
are expected to be more variable. The ratio of NMHC to NO at the respective
}\
sites is included in Table 6-Y and compared with limited data from St. Louis
(1977). The data from Houston agree with the limited data from St. Louis
except for Houston site 12, which is a site in a "boundary" area located close
to Galveston Bay.
The effects of meteorology on hydrocarbon concentrations are demonstrated
in Table 6-Z, which shows the effects of wind direction on site 03, an urban
monitoring site.
6-85
-------
HCT6 JOB A 2-19-80
TABLE 6-Y. AVERAGE PERCENTAGE COMPOSITION OF HYDROCARBONS IN
AMBIENT AIR AT SELECTED SITES IN HOUSTON (1978) AND ST. LOUIS
(1972 AND 1977), 6 TO 9 A.M. PERIOD1123
Site
HOMS
02
03
05
06
10
12
15
17
20
ST.
1972
1977
Type of
Site
Industrial
Urban
Suburban
Suburban
Industrial
Boundary
Boundary
Suburban
Boundary
LOUIS
Paraffins
63.0 ± 10.9
60.0 ±4.6
65.2 ± 5.7
59.2 ± 4.7
55.8 ± 11.0
66.8 ± 6.8
66.2 ± 3.5
70.2 ± 12.4
68.1 ± 7.7
62.0
64.0
Olefins
16.1 ± 5.0
13.5 ± 1.3
11.1 ±3.2
13.9 ± 2.7
21.4 ± 9.1
14.2 ±3.8
10.3 ±1.4
12.4 ± 5.8
10.0 ± 6.5
11.3
10.7
Aromatics
17.8 ± 6.7
23.3 ±4.1
21.1 ±3.2
23.3 ± 2.0
20.6 ± 8.7
16.7 ± 6.3
20.7 ± 2.8
16.5 ± 12.0
19.2 ± 4.4
22.7
24.4
NMHC:
NOx
15.9 ± 16.6
--
11.9 ±6.1
—
10.5 ±1.6
39.3 ± 13.0
14.9 ± 9.0
15.1 ± 8.4
17.0
a '
Between suburban and rural, outside the northern perimeter of Houston.
6-86
-------
HCT6 JOB A 2-19-80
TABLE 6-Z. EFFECT OF WIND DIRECTION ON HYDROCARBON
COMPOSITION AT SITE 03
(ppb C)
CDT
0600-0900
1300-1600
0600-0900
1300-1600
Total
NMHC
concn.
September
1205.6
(49)a
694.7
(40)
September
1005.3
(60)
504.7
(48)
Paraffins
18-20, Prevail
708.5
(40)
377.3
(35)
25-27, Prevail
557.9
(50)
293.9
(40)
Olefins
ing winds
194.5
(60)
117.3
(45)
ing winds
166.7
(67)
72.7
(64)
Aromatics
90° - 104°
302.6
(64)
200.1
(45)
0° - 60°
280.7
(68)
139.0
(57)
Percentage of emissions attributable to vehicular emissions
is given in parentheses.
6-87
-------
HCT6 JOB A 2-19-80
When the winds were from nonindustrial areas, north to northeast, a
higher percentage of the NMHC concentration could be attributed to vehicular
tailpipe sources. When the prevailing winds shifted and were from the eai;t
and southeast, two effects were observed: (1) the percentage tailpipe emissions
decreased; and (2) the total NMHC concentrations increased for both the morning
and afternoon time periods. a
Ethylene concentrations are of particular interest since the 1970 criteria
p
document reviewed the phytotoxic effects of this compound. Concentrations of
ethylene are reported for several cities, including Houston, in conjunction
with discussion of its phytotoxic properties in the section on welfare effects
(Section 6.7).
As noted earlier in this section, benzene concentration data are sparse
among the data obtained from field studies directed toward precursor/oxidant
relationships. Since it is considered photochemically nonreactive, and since
sampling and measuring it call for specialized techniques, benzene was not
measured routinely in the special studies drawn upon in this section.
(The data for Wilmington, Ohio, are an exception and do include benzene because
of the GC columns used in that particular study.) Some published data are
available, however, that indicate the range of concentrations found in urban
air.
In the Wilmington, Ohio, study by ESRL, cited earlier, benzene concentra-
tions ranged from 0.8 ppb to 4.5 ppb over 24 hours (July 18, 1974), with an
average of 2.3 ppb. Toluene concentrations measured at the same time ranged
from 1.0 ppb to 6.8 ppb, with an average of 3.5 ppb. Benzene concentrations
in Toronto, Canada, were reported in 1973 by Pilar and Graydon to average 13
113
ppb C, with a maximum of 98 ppb C. Variations in benzene concentrations
with the location of sampling sites were linked with traffic patterns by these
6-88
-------
HCT6 JOB A 2-19-80
authors, who also concluded that automobiles accounted for virtually all
1 -i q
benzene contamination and most of the toluene contamination. They attribu-
ted the relatively high toluene/benzene ratio in Toronto to the direct evapora-
-i -1 q
tion of gasoline, rather than to auto exhaust emissions alone. Toluene/benzene
ratios in auto emissions were found in 1966 to range from 1:1 to 2.8:1, with
an overall average of 1.8:1. A study in Los Angeles in 1968 showed
toluene/benzene ratios there of 1.4:1 to 4:1, with an average of 2.5:1.
The ratios in Toronto ranged from 1.5:1 to 4:1, for an average of 2.4:1, which
is close to results from Los Angeles. The toluene/benzene ratio from Wilmington,
Ohio, is 1.5:1. Disparities between auto exhaust ratios and ambient air
ratios may indicate other souces of toluene (or benzene) such as gasoline
evaporation or solvent losses. Concentrations of ambient air in Riverside,
115a
California (1973), were reported to range from 7 to 8 ppb C.
West German researchers determined the effect of reducing the lead
content in gasoline, with necessary concomitant increases in aromaticity, on
ambient air levels of benzene and toluene. Lead in gasoline was reduced in
West Germany from 0.40 g/liter to 0.15 g/liter on January 1, 1976. Data from
sixty 15-minute air samples taken in 1975, before the reduction, showed a
3
concentration range for benzene of 7 to 171 ug/m (2.3 to 57 ppb C), with a
3
mean of 16 ppb C; and a range for toluene of 9 to 355 ug/m (2 to 95 ppb C),
with a mean of 100 ug/m (27 ppb C). A series of three studies conducted in
1976 after the reduction in lead content produced the data shown in Table 6-26.
The conclusion reached was that increases in aromatics in gasoline did not, in
the 6 months immediately following the reduction in lead content, result in
higher toluene or benzene levels in ambient air. It should be noted in
6-89
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HCT6 JOB A 2-19-80
TABLE 6-26. MEAN VALUES AND RANGES IN AROMATIC
HYDROCARBON CONCENTRATIONS INVEST GERMANY, JULY 1976
116
Compound
Benzene
Toluene
No.
samples
25
12
29
25
12
29
Sampling
time, min.
30
15
5
30
15
5
Range
24 to 84a
28 to 54
17 to 144
57 to 171
60 to 111
40 to 328
Mean
46
43
55
101
93
113
Ratio of
means
101/46 =2.2
93/43 =2.2
113/55 =2.0
aTo convert ug/m to ppm, divide by 3175 for benzene and 3780 for toluene.
6-90
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HCT6 JOB A 2-19-80
this context that there is evidence of the hydro-dealkylation of toluene
during combustion of gasoline, resulting in a higher proportion of benzene in
94
auto exhaust than in the fuel.
The NAS document on ozone and other photochemical oxidants depicted
graphically the similarities and differences between the hydrocarbon profiles
of urban air in the nation as a whole and in the nation with California excluded;
and the profiles in auto exhaust and in gasoline. That graph, somewhat modified,
is presented (Figure 6-7) to facilitate the same comparison.9
6.5 HYDROCARBON-OZONE RELATIONSHIP
The chemical relationship between precursor hydrocarbons and ozone and
other photochemical oxidants was summarized in Section 5.1 and updated in
Section 6.1. Early efforts to quantify the relationship of hydrocarbons and
oxidants were summarized in Section 5.5. That section included a brief review
of the aerometric data base and of the underlying assumptions that were used
to derive the Appendix J model for relating NMHC emissions to oxidant air
quality via NMHC ambient air concentrations. The relationship between hydrocarbons
and photochemical oxidants was perceived in 1971, when the existing hydrocarbon
standard and the Appendix J model were promulgated, to be such that the
attainment and maintenance of a given level of ambient air NMHC (an NAAQS)
would ensure the attainment and maintenance of the 1971 photochemical oxidant
standard. The empirical data that formed the basis of the "envelope curve,"
or "upper-limit curve," used to derive the 1971 NAAQS for hydrocarbons, and
also used to derive the Appendix J model, did not depict an absolute relationship
between hydrocarbon ambient air concentrations and resulting oxidant concentrations.
Rather, the upper-limit curve was thought to demonstrate that maximum oxidant
concentrations in ambient air were primarily a function of 6:00 to 9:00 a.m.
6-91
-------
NO. CARBON ATOMS
1
n-ALKANES
BRANCHED
ALKANES
CYCLIC
ACETYLENICS
ALKYL-
BENZENES
POLYNUCLEAR
AI ALKENES
A2 ALKENES
A4 ALKENES
DIOLEFINS
ryri ic
OLEFINS
STYRENE,
INDENE,
TERPENES
5 10 15 2C
y| I I I I I I I I
m//w//M%%ffmM
Z^^M
mmmzmm
Wmw$mm
:-v •.:•:•;.: ivivXyXv:!
///////////////////////////A
w/////mm
;*/Xv//A
1
W/////////////////M
\--:--:^:-v:--:<-:--:-v:---:\
Y/////////////A
' //A
W/yff7/7/
W////////M.
:•:•:-:•:•;••.:-:•:-:•:•:•:-:•:•;-:•:•:•:•:•:• c-:-:-i
•/.•.•.-.•.-.;.-.;.;.;.;.;.;.;.-.;.|.|.\|.^ [•:';• j
y,,//(ffff\ ^ ^
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yM\ ^
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•
w/<
'////
'flmYi
'7A
II 1 i i 1 1 1 | 1 1 1 1
5 10 15 21
CARBON NUMBER
E%%3 GASOLINE
f:;:;S::3 EXHAUST
L:':i:i;iJ (GASOLINE-'
FUELED)
URBAN AIR
IURBAN AIR
'EXCLUDING
CALIFORNIA
Figure 6-7. Occurrence of gas-phase hydrocarbons, by carbon number, in
gasoline, exhaust, and urban ambient air. 9
6-92
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HCT6 JOB A 2-19-80
concentrations of NMHC in ambient air. Thus, when the oxidant standard was
set at 0.08 ppm maximum 1-hour average, not to be exceeded more than once per
year, the NAAQS for hydrocarbons was set at 0.24 ppm C, the level shown by the
upper-limit curve to be the level that would ensure the production of no more
than 0.08 ppm of ambient air oxidant (maximum 1-hour average).
On its promulgation of a new standard for ozone in February 1979, EPA
determined that the Appendix J model "no longer represents an acceptable
analytical relationship between hydrocarbons and ozone. Appendix J is, therefore,
being deleted. EPA will now allow states to use any of four analytical techniques
to determine the amount of hydrocarbon reduction necessary to demonstrate
attainment of the national ozone air quality standards:..." In taking this
regulatory action, EPA has made it clear that the "upper-limit curve," which
formed the empirical basis for the Appendis J method, does not adequately
describe the relationship between emissions of NMHC and ambient air concentrations
of NMHC, and between ambient air concentrations of NMHC and ambient air con-
centrations of ozone and other photochemical oxidants.
The replacement of the Appendix J method and the setting of the new
standard for ozone at 0.12 ppm maximum 1-hour average, not to be exceeded more
than once per year, both impact strongly on the existing NAAQS for hydrocarbons.
The second question posed at the beginning of this issue paper must be answered,
at least in a general way, in order to provide an adequate basis for a subsequent
regulatory decision on the NAAQS for hydrocarbons. That question is: According
to present knowledge, can the attainment and maintenance of a uniform, nationwide
concentration of NMHC in ambient air ensure the attainment and maintenance of
the ozone NAAQS? In answering that question, this section (1) surveys the
6-93
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HCT6 JOB A 2-19-80
factors that affect the hydrocarbon-ozone relationship; and (2) briefly
discusses the models promulgated by EPA for use in determining reductions
needed in precursor hydrocarbon emissions in order to attain and maintain the
NAAQS for ozone.
The fact that the original NAAQS was promulgated as a control strategy
for the attainment and maintenance of an oxidant standard rather than an ozone
standard does not impact on this question and will not be addressed here. The
rationale for promulgation in 1979 of an ozone standard rather than an oxidant
standard and the use of hydrocarbon emission reductions as appropriate and
effective strategy for the control of ozone and other photochemical oxidants
have been fully explained and documented in Air Qua!ity Criteria for Ozone and
Other Photochemical Oxidants and in the notice of rulemaking on ozone.
6.5.1 Factors Affecting the Hydrocarbon-Ozone Relationship
As summarized in Sections 5.1 and 6.1, the presence of ozone in ambient
air results largely from a series of multiple, complex photochemical reactions
between nitrogen oxides and numerous organic compounds, including hydrocarbons.
In the absence of appreciable amounts of organic compounds, resulting levels
of ozone remain low as the result of establishment of chemical equilibrium
among ozone, nitric oxide, and nitrogen dioxide. In the presence of appreciable
amounts of organic compounds, this equilibrium is disturbed and larger amounts
of ozone are produced. ' The basic chemistry involved was summarized in
simplified form in Sections 5.1 and 6.1. A basic understanding of the chemical
relationships among hydrocarbons, nitrogen oxides, and ozone is a prerequisite
for the development of techniques that relate precursor emissions to ozone
concentrations in ambient air. Three relatively recent documents have
6-94
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HCT6 JOB A 2-19-80
presented thorough discussions of the chemical relationships between ozone and
7~9
its precursors. All three also discussed the meteorologic and geographic
factors that affect the photochemical formation of ozone, and two of the three
reviewed the approaches used to describe quantitatively those relationships
7 Q
for various predictive applications. ' The relative importance of the
respective factors—chemical, meteorologic, and geographic—that influence the
formation of ozone was evaluated in the cited documents and will not be
covered here.
The simple enumeration given in Table 6-X of the main factors that affect
the NMHC-ozone relationship produces a recognition of the complexity of that
relationship that is heightened by the realization that these factors are all
interactive. Examination of the number and kind of factors that affect ozone
production reveals that the relationship between ambient air concentrations of
hydrocarbons and those of ozone cannot, in a given locality much less
nationwide, be described by a simple proportionality; that is, hydrocarbon
ambient air concentrations are not constant vis-a-vis ozone concentrations.
Emissions of NMHC and NO and background, or starting, ambient air concentrations,
/\
as well as the ratio of NMHC to NO , differ from place to place, from city to
city. Likewise, the spatial and temporal distribution of these sources of
differing strengths varies from city to city.
In addition to those basic chemical factors that affect the photochemical
formation of ozone, meteorological factors play an important role. The
dependence of ozone concentrations on NO and hydrocarbons (and other
J\
organics) can be dominated by meteorological conditions. Some of the
meteorological variables, such as sunlight intensity and its spectral
6-95
-------
HCT6 JOB A 2-19-80
TABLE 6-X. SOME FACTORS THAT AFFECT THE
PHOTOCHEMICAL FORMATION OF OZONE FROM PRECURSORS
Chemical factors
NMHC and NO emissions (starting reactants)
Rates/source strength
Spatial variations (location, point, source)
Temporal variations (diurnal, seasonal, year-to-year)
Species of NMHC or NO emitted
Reaction rates
Reactivities
Molecular weights/diffusion rates
Stoichiometry (main and side reactions)
Ratio of NMHC/NO ; ratio of N02/N0
Presence of other reactants (inducting oxygenated HC)
Presence of background levels of NMHC and NO
Presence of scavengers/sinks
Meteorological factors
Advection
Mixing heights
Turbulent diffusion
Frequency/duration of inversions
Prevailing winds
Direction
Speed
Humidity
Temperature
Sunlight intensity
Diurnal
Seasonal
Wavelength distribution
Geographi c/topographi c
Longitude
Latitude
Altitude
Terrain
Ventilation characteristics
Sinks
6-96
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HCT6 JOB A 2-19-80
%
distribution, directly influence the rates of the ozone-forming photochemical
reactions, thereby influencing equilibria among reactants.117 Geographic
location influences photochemical reactions inasmuch as sunlight intensity
varies with latitude. Temperature, the net product of geographic and meteoro-
logic factors, directly influences photochemical reactions; summer temperatures
are conducive to ozone formation throughout at least the contiguous United States.
A number of meteorologic and climatic factors other than temperature and
sunlight intensity exert major influences on the atmospheric formation of
ozone. For example, mixing height and its diurnal variations determine the
extent to which local emissions disperse and the extent to which transported
ozone and its precursors are likely to affect local ozone concentrations.
Atmospheric mixing inhibits the accumulation of precursors and the photochemical
formation of ozone and other oxidants. The interaction of locally emitted HC
and NO with transported pollutants is influenced also by prevailing wind
/\
speeds and wind trajectories. Geographic factors that affect the hydrocarbon-
ozone relationship are chiefly those that affect the meteorology of an area,
such as variations in insolation with latitude. Geography and topography are
the main factors in phenomena such as the Seabreeze-landbreeze patterns observed
in the South Coast Air Basin of California. Topographic influences such as
mountains, canyons, and valleys are responsible for unique ventilation patterns
that can serve to reduce ozone levels in some areas and to increase them in
118
other areas.
The factors listed in Table 6-X and surveyed here are not all-inclusive,
but they are representative of the complex influences that affect the
hydrocarbon-ozone relationship such that the reductions in hydrocarbon
emissions needed to attain the NAAQS for ozone will differ from city to city,
from season to season, and from year to year.
6-97
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HCT6 JOB A 2-19-80
One factor listed in Table 6-X, the differing reactivities of individual
hydrocarbons, is worthy of detailed discussion inasmuch as it bears upon the
question of whether measurements of ambient air concentrations of total NMHC
have utility in the determination of needed reductions in hydrocarbon emissions.
The fact that organic substances, including hydrocarbons, differ widely
in their respective reactivities is significant for understanding atmospheric
photochemical oxidation processes. This variation in reactivity is also
significant because it introduces selective organic compound control as a
possible refinement of the practice of controlling all organics to the same
extent, irrespective of their reactivity. Variations in reactivity are particu-
larly important conceptually with respect to an ambient air standard for
hydrocarbons.
That individual hydrocarbon species participate to differing degrees in
the formation of ozone and other secondary products (aldehydes, ketones,
organic aerosols, etc.) was acknowledged in the 1970 criteria document for
hydrocarbons:
As a consequence of the differing reactivities of individual
hydrocarbons, it is impossible to predict accurately the rate of
consumption of hydrocarbons in photochemical air pollution unless
the detailed composition of the hydrocarbon component is known or
can be estimated. Knowledge of the total concentration of hydrocarbons
is insufficient, since two atmospheres having the same total hydrocarbon
measurement may contain individual hydrocarbons of very different
reactivity and thus exhibit very different rates of hydrocarbon
consumption and photochemical air pollution development.
Conceptually, then, a national ambient air quality standard for hydrocarbons
is of limited value in controlling photochemical oxidant levels in ambient
air, even if ambient air concentrations of total NMHC could be shown to bear a
constant relation to ozone air quality. The measurement of total hydrocarbon
mass in ambient air does not describe the potential of that atmospheric loading
6-98
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HCT6 JOB A 2-19-80
of hydrocarbons for producing ozone or other secondary smog components.
Because of the differing reactivities of individual hydrocarbons, ambient air
measurements of total NMHC may have limited utility for predicting the impact
of hydrocarbon emissions on photochemical oxidant levels, although day-to-day
variations in the composition of the hydrocarbon mix within a given city, at a
given site, are likely to be much less than the differences that exist between
cities.
Reactivity data on hydrocarbons have been obtained from smog chamber
studies in which a given hydrocarbon or hydrocarbon mixture is mixed with
clean air, NO, and f^ at prescribed concentrations and irradiated with artifi-
7 53
cial sunlight. ' Experimental conditions for such measurements are, to the
extent feasible and practical, similar to the conditions typically present in
polluted ambient atmospheres. Thus, the reactant concentrations, the intensity
and spectral distribution of the radiation, the temperature, and often the
relative humidity are comparable to actual summer atmospheric conditions.
Because residence time and irradiation time in the atmosphere are prolonged in
situations in which the hydrocarbons are transported from the source area,
separate hydrocarbon reactivity data must be obtained for simulations of
transported air masses. Most available reactivity data are applicable only to
urban situations in which the hydrocarbons react for a few hours and cause
7 53
oxidant pollution in the vicinity of their sources. '
Reactivity data applicable to urban situations were compiled by
Altshuller and are presented in terms of a reactivity classification in Table
119
6-27. As this table indicates, not all hydrocarbons are equally reactive
6-99
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HCT6 JOB A 2-19-80
Table 6-27. COMPARISON OF REACTIVITIES OF DIFFERENT TYPES OF ORGANICS
119
o
o
Reactivity with respect
Substances of
subclass
C,-C3 paraffins
Acetylene
Benzene
C.+ paraffins9
Toluene (and other
monoal kyl benzenes)
Ethyl ene
1-alkenes
Diolefins
Dial kyl- and trialkyl-
benzenes
Internally double-
bonded olefins
Aliphatic aldehydes
Ozone or
oxidant
0
0
0
0-4
4
6
6-10
6-8
6-10
5-10
5-10
Peroxy-
acyl-
nitrate
0
0
0
Ob
NDC
0
4-6
0-2
5-10
8-10
+e
Formal-
dehyde
0
0
0
Ob
2
6
7-10
8-10
2-4
4-6
+e
to designated effects,
Aerosol
0
0
0
0
2
1-2
4-8
10
+e
6-10
NDC
Eye
irrita-
tion
0
0
0
Ob
4
5
4-8
10
4-8
4-8
+e
0 to 10 scale
Plant Overall
damage reactivity
0
0
0
0
0-3
+b
6-8
Ob
5-10
10
+e
0
0
0
1
3
4
7
6
6
8
--
^Averaged over straight-chain and branched-chain paraffins.
Very small yields or effects may occur after long irradiations.
j experimental data avaialble.
Includes measurements on propylene through 1-hexene, 3-ethyl-l-butene and 2,4,4-trimethyl-l-l-pentene.
eEffect noted experimentally, but data insufficient to quantify.
-------
HCT6 JOB A 2-19-80
in the formation of the respective smog components or effects of smog. Note
also that aldehydes, which are both primary and secondary pollutants, are as
reactive as many of the hydrocarbons in the production of ozone. Results of
systematic studies conducted by five groups of researchers* were used by EPA
in classifying organics into the three reactivity classes shown in Table
6-28. While this table does not give numerical ratings for the respective
organics, it does illustrate the differing reactivities of individual hydrocarbon
and other organic species. Furthermore, it demonstrates the differences in
reactivity that exist, though not always systematically, between compounds as
a result of structural characteristics, including degree and kind of substitution.
For example, benzene shows low reactivity, but its substituted primary monoalkyl,
toluene, shows high reactivity. Likewise, methanol shows low reactivity, and
ethanol is moderately reactive; but 2-ethoxy-ethanol is highly reactive.
Partially halogenated paraffins show low reactivity, but partially halogenated
olefins demonstrate high reactivity.
These differences in reactivity can be useful in permitting selective or
preferential emission control as part of control strategies if the photochemical
behavior of a mixture of organic pollutants is consistent with—and can be
predicted from—the behavior of the individual components. Overall results
of smog chamber studies tend to support the view that the behavior of the
mixture can be predicted from the behavior of the components. The main effects,
however, of controlling highly reactive species to a greater degree than
moderately or slowly reactive species are: (1) a delay in production of a
daily oxidant maximum; and (2) a reduction in the peak oxidant concentrations
as a result of increased time for dispersion. The consequences of "carryover"
*Japanese Environment Agency; Bureau of Mines, U.S. Dept. of Interior; General
Motors Corp.; Battelle Memorial Institute Laboratories-Columbus; and Shell
6-101
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HCT6 JOB A 2-19-80
TABLE 6-28. CLASSIFICATION OF ORGANICS WITH RESPECT TO OXIDANT-RELATED
REACTIVITY IN URBAN ATMOSPHERES7
Class I
(Low reactivity)
Class II
(Moderate reactivity)
Class III
(High reactivity)
C-j-C^ paraffins3
Acetylene3
Benzene
Benzaldehyde
Acetone
Methanol
Isopropanol
Tert-alkyl alcohols3
Methyl acetate
Methyl benzoate
Ethyl amines
N, N-dimethyl
formamide
Perhalogenated
hydrocarbons
Partially halogenated
paraffi ns
Mono, dichlorobenzenes
Methyl ethyl ketone
Tert-monoalkyl benzenes
Cyclic ketones
Tolualdehydes
Tert-alkyl acetates
2-Nitropropane
C.+ paraffins, cyclo-
paraffins
Ethanol
Prim, sec C2 alkyl
N, N-dimethyl acetamidec
n-alkyl C5+-ketones
Prim-, sec-, monoalkyl
benzenes
Dialkyl benzenes
Styrene
N-Methyl pyrrolidone
Partially halogenated
olefins
Aliphatic olefins
Tri-, tetra-alkyl
benzene
Methyl styrene
Branched alkyl ketones
Unsaturated ketones
Aliphatic aldehydes
Diacetone alcohol
Ethers3
2-Ethoxy-ethano1
Currently classified as not photochemically reactive under Los Angeles
County Rule 66 and similar regulations.
6-102
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HCT6 JOB A 2-19-80
of organic pollutants to the second day, coupled with transport processes, are
under intensive investigation. As yet, few data are available on the reactivities
of aged emissions during second-day irradiations. The greater part of unreacted
organic precursors will escape the photochemical process during the first
solar day and will be transported downwind where, if sufficient NO is present
yk
on the second day, ozone will be produced from the NO and organic precursors.
}\
The few reactivity data available for "transport" situations indicate that
under transport conditions the effective range of reactivities is narrower
than for the urban situation.
6.5.2 Models for Determining Hydrocarbon Emission Reductions
In the years following the 1971 promulgation of the Appendix J method,
experience has corroborated the theoretical deficiencies of that method. The
Agency has now officially recognized the deficiencies of the Appendix J method
by replacing it with other models for determining the HC emission reductions
needed to attain the ozone NAAQS. The revisions to 40 CFR, Part 51, that
accompanied the notice of promulgation of the new ozone standard in February
1979 stated that:
...Appendix J is being replaced by four analytical techniques. States
must use one of the four techniques to determine the amount of hydro-
carbon reductions necessary to demonstrate attainment of the national
ozone standard. The four techniques include: (1) Photochemical dis-
persion models, (2) Empirical Kinetics Modeling Approach (EKMA), (3)
Empirical and Statistical Models, and (4) Proportional Rollback. (40
CFR, Partn51, "Preparation, Adoption, and Submittal of Implementation
Plans")120
These four techniques prescribed by EPA have as their chief objective the
determination of reductions needed in hydrocarbon emissions to attain the
ozone NAAQS.
6-103
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HCT6 JOB A 2-19-80
The promulgation of these four models as required options to be used by
the states resulted from the efforts of an EPA working group that was formed
in 1975 to investigate the viability of alternatives to the Appendix J method.
Suggestions made as a result of working group sessions were reviewed periodically
by a group of experts outside of EPA. The conclusion reached as a result of
these efforts is that it is not possible to recommend a single approach for
all applications. The variety of applications, complexity of individual
situations, and differences in data availability and resources all preclude
use of a single procedure nationwide. EPA is presently preparing additional
information on models for use by the States in preparing revisions to State
121
Implementation Plans for attainment and maintenance of the ozone standard.
The four models prescribed as alternatives to the Appendix J method are
described briefly below.
1. Photochemical Dispersion Models. These are air quality simulation models
and are based on the most accurate available physical and chemical principles
120
underlying the formation of ozone. Photochemical dispersion models have
the greatest potential for evaluating the effectiveness of oxidant control
strategies mainly because (1) the model permits spatial and temporal resolution
and (2) it can relate precursor emissions directly to ambient air ozone concen-
trations via atmospheric dispersion equations and chemical mechanisms. Data
requirements for these models may be extensive, however.
2. Empirical Kinetics Modeling Approach (EKMA). This model represents a
simpler alternative to the photochemical dispersion models. It includes the
use of a kinetic model that represents a detailed sequence, derived from smog
chamber data, of the chemical reactions that occur when a mixture of propylene,
n-butane, and NO is irradiated. While retaining some of the vigorous
6-104
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HCT6 JOB A 2-19-80
treatment of chemical and physical principles that is characteristic of photo-
chemical dispersion models, it does not require the extensive input data
1 on
needed for those models.
There are two variations of EKMA. The first involves the use of city-
specific ozone isopleths. The second involves the use of a standard set of
isopleths in which fixed assumptions have been made about sunlight intensity,
atmospheric dilution rate, reactivity of emissions, and diurnal emission
patterns. The city-specific approach is preferable because (1) it can be used
to evaluate a wider variety of control measures, including measures that are
initiated concurrently; and (2) it employs locally unique assumptions about
atmospheric dilution rate, sunlight intensity, and diurnal emission patterns.
The second advantage is not as crucial as it might appear, however, and using
the standard isopleths has the advantage that fewer input data are needed and
a computer is not needed.
EKMA makes use of a kinetics model to express maximum afternoon ozone
concentration as a function of morning ambient air levels of nonmethane hydro-
carbons (NMHC) and NO . EKMA is empirical in that it requires the use of
observed second-highest hourly ozone concentrations and morning NMHC/NO
ratios to estimate control requirements.
3. Empirical and Statistical Models. These models are derived from observed
120
relationships between ozone and other variables. Two features of empirical-
statistical models are central. First, any one statistical relationship is
site-specific. Second, the use of these models is most appropriately limited
to applications involving moderate changes from the base control state, since
the imposition of drastic changes could appreciably alter the functional
relationship that was derived from data observed during the base set of control
conditions.
6-105
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HCT6 JOB A 2-19-80
4. Proportional or Linear Rollback. Linear rollback assumes a linear relation-
121
ship between hydrocarbon emissions and ambient air concentrations of ozone.
Other proportional rollback models embody the principle that reductions in
emissions are reflected by improvements in air quality, as shown by a curved
line or a complex surface that expresses some proportionality relationship.
Rollback models work best if the geographic and temporal distribution of
emission sources is not changed. The linear rollback model has two chief
advantages: (1) it uses aggregated emissions data and (2) it is mathema-
tically simple. It has two chief disadvantages: (1) ideally, it should be
applied only to pollutants that do not undergo chemical transformations in the
atmosphere; and (2) it does not take into account the dependence of NMHC-ozone
relationships on the initial or base period NMHC/NO ratio. Linear rollback
/\
is less data-intensive than EKMA and is a possible alternative for estimating
upper and lower bounds on control requirements for hydrocarbon and other
organic precursors.
A limitation of these and other available techniques is that most of
these models have received little validation. All of the above techniques,
including photochemical dispersion models, must employ simplifications to keep
them from being intractable. The accuracy of methods incorporating such
simplifications can be determined or at least estimated by verification studies
that compare model results with observed data. There are few locations,
however, in which the data base is presently adequate for the verification of
117
analytical methods relating precursors and oxidants.
Each of these models has its own characteristic limitations and uncertain-
ties, many of which have not been included here but which are given in detail
in other documents. ' ' ' The uncertainties in each model are questions
6-106
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HCT6 JOB A 2-19-80
more of degree than of direction. With respect to limitations, however, it
should be noted that:
models that relate oxidant to ambient concentrations [of
precursors] rather than to emissions [of precursors] are
subject to the same validity limitation as the Appendix J
method, namely, that the model does not directly relate
air quality to precursors. Instead, the direct relationship.,
is between oxidant and the atmospheric dispersion factor. '
However, in spite of limitations inherent to each of the models briefly described
here, they appear to have fewer shortcomings and uncertainties than the Appendix J
method. All of the methods indicate that substantial reductions in organic
precursors are needed to reduce ozone levels appreciably. Therefore, the four
techniques prescribed by EPA can be regarded as approximations that will be
useful in estimating hydrocarbon emission control requirements.
120
The Federal Register issuance that promulgated these four techniques
took note of criticisms of the techniques, pointing out that reviewers and
commentators have cited various shortcomings. Among the shortcomings listed
is the fact that the respective models produce different results. EPA acknow-
ledged in that issuance "that the various techniques do produce different
results since different assumptions and different data bases are required for
each specific model. Also, EPA agrees that control strategies should be based
120
on the most effective models."
Present information indicates, then, that no one model can be used in all
urban areas in the United States for all applications. Thus, present knowledge
militates against the concept that attainment of a uniform level of NMHC
throughout the country is conceptually sound, from the scientific standpoint,
as a means of attaining the ozone NAAQS. This is demonstrated (1) in the
complexity and variability of the factors that influence the photochemical
6-107
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HCT6 JOB A 2-19-80
formation of ozone; (2) in the fact that no one model can be successfully'
applied to all situations in all urban areas, coupled with the fact that
different models give different results; and (3) the fact that models relating
NMHC concentrations, rather than NMHC emissions, to oxidant concentrations
really relate those oxidant concentrations to the atmospheric dispersion
factor.
6.6 HEALTH EFFECTS
Since promulgation of the hydrocarbon standards in 1971 the direct
and indirect effects of hydrocarbons on public health and welfare have
been extensively reviewed by EPA in a technical report (1972) entitled,
124
Hydrocarbon Pollutant System Study. and by the National Academy of
Science in a monograph (1976) entitled, Vapor-Phase Organic Pollutants.
IOC
In 1977, NIOSH published a criteria document addressing alkanes (C5-C8).
Most recently (1978), the Office of Air Quality Planning and Standards
81
published a document entitled, Assessment of Gasoline Toxicity. This
document reviews the various hydrocarbons present in gasoline either as
individual compounds, as classes, or collectively as a group of mixed
hydrocarbons.
A review of the literature since 1970 reveals once again that
hydrocarbons, per se, do not present a significant health hazard in the
atmosphere at the present detectable levels. They should be controlled or
restricted on the basis of their contribution to photochemical smog and
the resultant adverse effects of the smog products. To properly defend
this position it seems appropriate to present an up-to-date toxicological
evaluation of the hydrocarbon literature addressing each chemical family
individually. Components that represent major health hazards are identified
6-108
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HCT6 JOB A 2-19-80
and their toxicities discussed. Because of its objective, this toxicity
assessment reviews only the effects associated with environmental exposure to
hydrocarbons, either as mixtures (e.g., gasoline; solvents) or as individual
compounds, by inhalation.
6.6.1 Aliphatic Hydrocarbons
This class of straight chain or branched hydrocarbons includes the alkanes
(saturated), the alkenes (unsaturated, double bond) and the a!kynes (unsaturated,
triple bond). A number of alkanes (methane, ethane, propane, butane), alkenes
(ethylene, propylene) and a single alkyne (acetylene) constitute a group of
inert gases and vapors collectively known as "simple asphyxiants." These
hydrocarbons, when present in high concentrations in air, act as simple
asphyxiants without other significant physiological effects. Any systemic
effects that may be observed are thought to be secondary due to the oxygen-
replacing capabilities of these gases and/or vapor at extremely high con-
centrations. No threshold limit values (TLV) have been established for these
"inert" substances by the American Conference of Governmental Industrial
Hygienists (1978 listing). A TLV is not recommended for each simple asphyxiant
because the limiting factor is the available oxygen. The minimum oxygen content
should be 18 percent by volume under normal atmospheric pressure (equivalent
to a partial pressure, pCL of 135mm Hg). Atmospheres deficient in oxygen do
not provide adequate warning and most simple asphyxiants are odorless.
The recent use of isobutane, butane, and propane as substitutes for
fluorocarbons in aerosol products raises the question of the potential of
127
these gases to injure humans. Aviado et al. addressed this question in a
monograph entitled, Non-Fluorinated Propel!ants and Solvents for Aerosols. In
this monograph the literature was thoroughly reviewed in an attempt to
6-109
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HCT6 JOB A 2-19-80
determine whether the mixture of three hydrocarbons (80.4 mol % isobutane, 25
mol % butane; 17.1 mol % propane) is more toxic than each of the individual
components. The threshold effective concentration (TEC, based on myocardial
and hemodynamic responses) for the hydrocarbon mixture (A-46) was 1.9 percent
by volume of air (19,000 ppm) compared to propane (TEC 3.3 percent), isobutane,
(TEC 2.0 percent) and n-butane (TEC 0.5 percent). The propellant mixture A-46
possesses the same pharmacologic effect as other hydrocarbons studied and does
not enhance the individual effects of isobutane, butane, and propane. The
primary preference of isobutane over fluorocarbons as a predominate component
of aerosol propellant mixtures is the increased threshold level required for
eliciting cardiac arrhythmia.
In general, the simple asphyxiants can be tolerated in high concentrations
in inspired air without producing significant physiological effects; however,
128
Reinhardt et al. reported that "aerosol sniffing" of these simple asphyxiants
in some cases has sensitized the heart, to the extent that small quantities of
epinephrine may lead to ventricular fibrillation and ultimately death through
cardiac arrest.
Generally, alkanes from pentane (Cr) through octane (Cg) show increasingly
strong narcotic properties. With the exception of respiratory irritation and
central nervous system (CMS) depression manifested acutely upon exposure to
high vapor concentrations, the Cg through Cg aliphatic hydrocarbons were
regarded as relatively innocuous. Since exposure to only one alkane is
infrequent, NIOSH has recommended a time-weighted average concentration of 350
mg/m as the occupational limit for pentane, hexane, heptane, octane, and
total alkanes (mixtures). On a volume/volume (v/v) basis, these concentrations
are equal to about 120 ppm pentane, 100 ppm hexane, 85 ppm heptane, and 75 ppm
6-110
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HCT6 JOB A 2-19-80
octane. NIOSH also recommends a ceiling limit (MAC) of 1800 mg/m3 either
singly or mixtures for 15 minutes (about 610 ppm pentane, 500 ppm hexane, 440
ppm heptane and 385 ppm octane). The recommended standard is based on the
conclusion that acute intoxication by these alkanes involves a transient
central nervous system depression and that chronic intoxication may involve a
1?5
more persistent effect, polyneuropathy. Polyneuropathy has usually been
attributed to n-hexane, but occupational exposures to n-hexane alone have not
been described, and the recommended standard is based on the belief that this
neuropathy can be caused by other alkanes and their isomers as well. Should
sufficient evidence be developed that this is not the case, the TLV limit of
350 mg/m of total alkanes recommended by NIOSH might be considered for upward
revision in the case of those alkanes and/or isomers not causing chronic
neurological disorders.
The effects of alkane (Cr-Cg) vapor exposure on humans and animals are
lot;
illustrated in Tables 6-29 and 6-30, respectively.
No studies were found to suggest that any of the volatile aliphatic
hydrocarbons are related to carcinogenic, mutagenic, or teratogenic effects in
humans or experimental animals; nor is there any reason to suspect that they
will be found to produce such effects because these compounds are not chemically
related to substances known to have carcinogenic, mutagenic or teratogenic
effects. On the basis of limited bioassays, both alkanes and alkenes have
been classified as noncarcinogens. Although some of the long-chain (C,» or
greater) aliphatic hydrocarbons have been implicated as cocarcinogens or
tumor-promoters, based on mouse skin experiments, the straight-chain
hydrocarbons above octane (Cg) are not sufficiently volatile to warrant serious
consideration as vapor hazards at room temperature. In 1976 the American
Conference of Governmental Industrial Hygienists (ACGIH) TLV committee imposed
6-111
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HCT6 JOB A 2-19-80
Table 6-29. EFFECTS OF ALKANE VAPOR EXPOSURE ON HUMANS
125
Hexane
Hexane
Hexane
Hexane
Hexane
Heptane
Exposure
Concentration
Al kane
Pentane
Hexane
Hexane
Subjects
3-6 men and
women
3-6 men and
women
6 men and
women
and duration
Up to 5000 ppm
10 min
5000 ppm
10 min
2500-1000 ppm
10-12 hr/d
Effects
No symptons
Marked vertigo,
Drowsiness in 0.
appetite in some
giddiness
5 hr, fatigue,
, paresthesia
loss of
in distal
93 men and
women
3-6 men and
women
3 women
11 men and
women
4 men and
women
3-6 men and
women
2500-500 ppm
2000 ppm
10 min
1300-650 ppm
8-10 hr/d
2-10 months
1000-500 ppm
3-6 months
not available
5000 ppm
15 min
extremities
Sensory impairment in distal portion of
extremities, muscle weakness in 13, cold
sensation of extremities in some, blurred
vision, headache, easy fatigability, anorexia,
weight loss at onset of polyneuropathy,
muscular atrophy, demyelination and axorial
degeneration of peripheral nerves.
No symptoms
Headache, burning sensation of face, ab-
dominal cramps, numbness, paresthesia,
weakness of distal extremities, bilateral
foot and wrist drop, absence of Achilles
tendon reflexes, fibrillation potentials,
decreased conduction time in motor and sensory
nerves, denervation-type injury of muscles,
numerous neurophathologic changes.
Fatigue, anorexia, paresthesia in distal
extremities, muscular atrophy
Peripheral neurophathy, reduced motor and
sensory nerve conduction velocities, knee-
jerk and Achilles tendon reflexes absent,
muscular atrophy, diminished sensations of heat
and touch, pathologic abnormalities in muscles
and nerves.
Marked vertigo, incoordination, hilarity
for 30 min.
6-112
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HCT6 JOB A 2-19-80
Table 6-29. (continued)
A1 kane
Heptane
Heptane
Heptane
Heptane
Heptane
Octane
Subjects
3-6 men and
women
3-6 men and
women
3-6 men and
women
3-6 men and
women
3-6 men and
Exposure
Concentration
and duration
5000 ppm
7 min
5000 ppm
4 min
3500 ppm
4 min
2000 ppm
4 min
1000 ppm
6 min
No
Effects
Marked vertigo, incoordi nation of space,
hilarity in some
Marked vertigo, inability to walk straight,
hilarity
Moderate vertigo
Slight vertigo
Slight vertigo
Data Available
6-113
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HCT6 JOB A 2-19-80
Table 6-30. EFFECTS OF ALKANE VAPOR EXPOSURE ON ANIMALS
125
Al kane
Pentane
Pentane
Pentane
Pentane
Pentane
Pentane
Pentane
Hexane
Hexane
Hexane
Hexane
Hexane
Species No.
Mice 1
Mice 4
Mice 1
Mice
Mice 1
Mice 4
Mice 4
Mice 1
Mice 1
Mice 1
Mice
Mice
Exposure
concentration
and duration
129,200 ppm
37 min
128,000 ppm
5 min
108,800 ppm
26 min
102,000-
68,000 ppm
2 hr.
91,800 ppm
66 min
64,000 ppm
5 min
32,000 ppm
5 min
64,000 ppm
5 min
51,120 ppm
9 min
42,600 ppm
127 min
42,600-
34,080 ppm
2 hr
39,920 ppm
127 min
Effects
Decreased respiration rate, loss of reflexes,
death by 37 min of exposure
Irritation, deep anesthesia, respiratory
arrest in 1 mouse by 4.75 min of exposure.
Lying down by weakened reflexes
Lying down
Temporary lying down
Irritation, anesthesia during recovery
period
Anesthesia during recovery period
Irregular respiratory pattern, respiratory
arrest by 2.5 - 4.5 min
Death after spasms, no narcosis
Loss of reflexes, death
Death
Death
6-114
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HCT6 JOB A 2-19-80
Table 6-30. (continued)
A1 kane
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
Heptane
Heptane
Heptane
Species
Mice
Mice
Mice
Mice
Mice
Mice
Mice
Mice
Mice
Mice
Mice
Mice
No.
1
4
4
7
6
19
6
4
4
Exposure
concentration
and duration
34,080 ppm
123 min
32,000 ppm
5 min
28,400 ppm
2 hr
16,000 ppm
5 min
8000 ppm
5 min
1000-2000 ppm
6 d/wk, 1 yr
500 ppm
6 d/wk, 1 yr
250-2000 ppm
6 d/wk, 1 yr
250 ppm
6 d/wk, 1 yr
64,000 ppm
5 min
32,000 ppm
5 min
18,300 ppm
2 hr.
Effects
Light narcosis
Deep anesthesia
Lying down
No anesthesia
No anesthesia
Marked abnormal posture and muscular atrophy
and degeneration; in electromyographic tests,
fibrillation at rest, complex NMU voltage and
high amplitude NMU voltage during movement, and
weakened interference waves during strong
contractions; increased electrical reaction
time; reversal of flexorextensor chronaxy
rati o
Abnormal posture and muscular atrophy
Higher strength-duration curve with increased
concentrations
Slightly abnormal posture and muscular atrophy;
in electromyographic tests, some fibrillation
at rest
Respiratory arrest in 3 mice by 3.75 min of
exposure
Irregular respiratory pattern
Death in 2 hr
6-115
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HCT6 JOB A 2-19-80
Table 6-30. (continued)
Alkane
Heptane
Heptane
Heptane
Octane
Octane
Octane
Octane
Octane
Octane
Octane
Octane
Species No.
Mice 4
Mice
Cats
(decere-
brated)
Mice 4
Mice 4
Mice 1
Mice
Mice
Mice
Mice
Mice
Exposure
concentration
and duration
16,000 ppm
5 min
9760 ppm
2 hr
24,400-
6100 ppm
5 min
32,000 ppm
5 min
16,000 ppm
5 min
12,840 ppm
185
10,700 ppm
2 hr
8560 ppm
55 min
7490 ppm
2 hr
6634 ppm
1 yr
5350 ppm
48 min
Effects
No anesthesia
Lying down
Decreased blood pressure during exposure
return to normal during recovery period;
increased respiration, then decreased
Respiratory arrest in 4 mice by 4 min of
Respiratory arrest in 1 during recovery
Decreased respiration rate, death by fol
day
Loss of reflexes
Narcosis
Lying down
Lying down
No narcosis
, rapid
initial
exposure
period
1 owi ng
6-116
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DHCT6 JOB A 2-19-80
a limit of 200 ppm on nonane based on analogy with other members of this
series and not on actual data. In 1978, Carpenter et al.129 established a no
ill-effect level for nonane at 590 ppm based on extensive rat inhalation studies.
This work was in good agreement with work by Nau et al.130 in 1966. Nonane
concentrations commonly found in the ambient air range between 0.0001 and 0.0009
ppm relative to acceptable workplace exposure levels of 200 ppm (TLV). In
view of the low volatility of nonane and its analogy with other aliphatic
hydrocarbons, it would appear that this Cg aliphatic hydrocarbon poses no danger
to human health at these ambient levels.
6.6.2 Alicyclic Hydrocarbons
lexicologically, the alicyclic compounds, as a class, resemble the pre-
viously discussed aliphatic hydrocarbons in that they act as general anesthetics
and central nervous system depressants with a relatively low order of acute
toxicity. The alicyclic compounds (naphthenes), which are present in modern
gasolines and gasoline vapors in relatively low concentrations compared to
other hydrocarbon components, have not been indicated as hematopoietic toxicants.
These compounds are rapidly metabolized and eliminated in the urine in the
form of conjugated glucuronides and sulfates, thus eliminating the chance of
increased body burden upon repeated exposure to low atmospheric concentrations.
In general the chronic exposure studies involving animals were very deficient
with respect to a dose-response relationship. No occupational or epidemiological
evidence was found to indicate that naphthenes have any systemic effects.
Unlike the aliphatic hydrocarbons, the degree of toxicity of the alicyclic
hydrocarbons does not correlate with structural characteristics (e.g., number
of carbon atoms, degree of unsaturation and amount of branching, etc.).
6-117
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DHCT6 JOB A 2-19-80
Naphthene vapors at very high concentrations cause irritation of the
mucous membrane, with the saturated hydrocarbons generally causing less
irritation than the corresponding unsaturated ones. No studies were found
regarding the carcinogenic, mutagenic, or teratogenic potential of any alicyclic
hydrocarbons.
6.6.3 Aromatic Hydrocarbons
The primary route of exposure to benzene is by vapor inhalation. High
concentrations of benzene, like most organic solvents, can cause depressidn of
the central nervous system. Symptoms are acute narcosis, accompanied by
drowsiness, vertigo, nausea, unconsciousness, and death. The effects of acute
benzene narcosis are usually completely reversible unless the initial severity
of exposure causes pathologic changes. Acute poisoning by high concentrations
of toluene is uncommon but, like benzene, both toluene and xylene can produce
effects on the central nervous system.
The health effects of chronic benzene exposure have been addressed in
three recent reviews. Benzene exposure by inhalation and other routes
is strongly implicated in three pathological conditions; namely, leukemia,
pancytopenia, and chromosomal aberrations. The most severe long-term hazard
is to the hematopoietic system. Hematopoietic anomalies can affect a number
of blood parameters, including erythrocyte count, hemoglobin, mean corpuscular
volume of red blood cells, platelet counts, and leukocyte counts. Reportedly,
hematologic abnormalities have developed in humans as a result of repeated
exposure to benzene concentrations ranging down to 105 ppm and 60 ppm. '
l ^fi
According to Pagnatto's data, suggestive but inconclusive hematologic
changes were noted from exposure to benzene concentrations as low as 20 to 25
ppm in rubber coating plants.
6-118
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OHCT6 JOB A 2-19-80
It is now generally agreed that benzene can cause various forms of leukemia
1 ^ft
which can arise with or without a previous history of aplastic anemia.
Knowledge of the carcinogenic potential of benzene has been primarily through
the experience of human occupational exposure. The exposure data in these
studies do not allow a scientific derivation of a dose-response curve. Most
studies in which exposure levels were determined involved doses in the range
of 100 to 500 ppm, though in some the benzene concentrations were lower.
Currently there is no convincing evidence that benzene causes neoplasias,
including leukemia, in animals. In animal studies, the most consistent
physiological response to benzene has been leukopenia. ' '
The incidence of benzene-induced chromosomal aberrations in peripheral
blood lymphocytes and bone marrow has received considerable attention.
Available data from studies in which measurements ranged from 25 to 150 ppm
strongly suggest that chromosome breakage and rearrangement can result from
chronic exposure to benzene; in at least one study, significant effects were
noted at 2 to 3 ppm (time-weighted average). A dose-response relationship has
not been demonstrated for benzene-induced chromosome aberrations; however,
this may result from variations in individual susceptibility.
NIOSH, in recognition of accumulated clinical and epidemiological evidence
to the effect that benzene is leukemogenic and a probable cause of other
severe systemic toxicity, has recommended a much more stringent standard for
141
occupational exposure to benzene. Since it is not currently possible to
establish a safe level of exposure to a carcinogen, NIOSH recommends that :
exposure to benzene be kept as low as possible. The proposed occupational
standard of a maximum of 1 ppm benzene for 60 minutes is expected to material-
ly reduce the risk of benzene-induced leukemia from that incurred at the
present acceptable ceiling of 25 ppm.
6-119
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DHCT6 JOB A 2-19-80
In addition, EPA has addressed the effects of benzene exposure in a
health document entitled Assessment of Health Effects of Benzene Germane
1 ^"-^
to Low Level Exposure. In combination with an exposure assessment document
"I A O
tntitlod Assessment of Human Exposures to Atmospheric Benzene, the Cancer
Assessment Croup of EPA, using a linear non-threshold model, estimated the
leukemic risk at 90 cases per year upon exposure of the general population to
ambient atmospheric benzene levels (1 ppb). This amounts to between 0.23 and
1.62 percent of the total leukemia deaths in the United States, based upon
1D73 vi .a! statistics.
Toluene (methyl benzene), xylenes (dimethyl benzenes), and trimethyl-
benzenes are generally much less toxic and volatile than benzene. The primary
and most hazardous route of exposure to toluene in the workplace is via inhala-
tion. At equilibrium the body retains approximately 50 percent of the inhaled
toluene, 20 percent of which is excreted unchanged by the lungs while the
remainder is metabolized via the liver to benzoic acid. The majority of
benzoic acid (80 percent) is conjugated with glycine and excreted as hippuric
acid in the urine. The remaining 20 percent of benzoic acid is conjugated
with glucuronic acid in the urine as the glucuronide.
Today there is general agreement in the literature that toluene, unlike
benzens, does not affect the hematopoietic system. The myelotoxic effects
previously attributed to toluene from early studies are presently judged by
updated investigations to be the result of concurrent exposure to benzene as a
contaminant. These updated investigations involve both experimental and
occupational inhalation exposure to pure toluene.
Effects from toluene have also been reported for other organs; namely,
the nervous system, liver, kidney, heart, mucous membrane, immune system, and
6-120
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DHCT6 JOB A 2-19-80
the skin. Like many of the early investigations of the effects of toluene on
the hematopoietic system, the reported effects for some of these organs (liver,
kidney, heart, peripheral nervous system) are inconsistent and may be attributed
to impure toluene and/or inaccurate exposure data. The most sensitive indicators
of toluene exposure are a number of symptoms in the central nervous system and
in the psychomotor functions. The effects of toluene, however, on the central
nervous system are not specific for this aromatic hydrocarbon but typify the
responses to other hydrocarbons.
The majority of reported effects have been observed at high exposure
levels. Very few observations have been made at exposure levels of 0 to 375
2
mg/m (0 to 100 ppm). There are no reports on the dose response relationship
over an 8-hour workday at these concentration levels. The present threshold
limit value for toluene has been established at 100 ppm. A detailed review of
the literature regarding the health effects of toluene has been reported by
NIOSH and, most recently, by Scandinavian scientists.
No data are available on actual occupational or environmental exposures
to xylenes that warrant their consideration as important environmental health
hazards. The current xylene standard of 100 ppm was designed primarily to
protect workers against the irritating and narcotizing properties of xylene.
6-6.4 Hydrocarbon Mixtures—Gasoline
Inhalation toxicity data based upon human exposure of gasoline vapors are
very limited. Inhalation of extremely high concentrations of gasoline vapor
can cause narcosis, coma, and sudden death. Death upon acute exposure to
gasoline fumes is generally attributed to severe central nervous system
6-121
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DHCT6 JOB A 2-19-80
depression terminating in respiratory paralysis. Gasoline vapors can sensitize
the myocardium to the extent that small quantities of epinephrine may precipitate
ventricular fibrillation. This may explain the type of sudden deaths observed
in cased of accidental gasoline exposure, since the edema observed in
these individuals upon autopsy did not appear severe enough to be fatal. This
is a reasonable explanation in view of the fact that Chenoweth showed that
both gasoline and numerous constituents of gasoline are known to induce
149
ventricular fibrillation in the presence of epinephrine.
Acute inhalation exposures to milder concentrations of gasoline vapor are
usually characterized by nonspecific anesthetic or narcotic effects. Symptoms
such as headache, vertigo, blurred vision, ataxia, tinnitus, nausea, anorexia,
and muscular weakness are not uncommon. Early studies by Drinker et al. ,
demonstrated only slight irritation to the eyes, nose, and throat after Human
exposure to gasoline for 1 hour. Slight dizziness accompanied the eye irrita-
tion at 2600 ppm, while at 10,000 ppm marked intoxication was experienced
after 4 to 5 minutes. More recently, a study by Davis et al. revealed no
manifestations of intoxication in humans exposed to any of three different
unleaded gasolines for 30 minutes at concentrations of 200, 500, and 1000 ppm.
The only significant effect reported was eye irritation at the 1000 ppm level.
The effects of gasoline vapor on humans are summarized in Table 6-31. Little
definitive animal experimentation has been reported to date which has assessed
43
the acute toxicity of commonly used gasolines. Machle furnished the only
acute toxicity data with respect to animals exposed to gasoline. He reported
that gasoline vapor exposures in excess of 10,000 ppm rapidly caused death in
most experimental animal species.
6-122
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OHCT6 JOB A 2-19-80
TABLE 6-31 HUMAN EXPERIENCE: EXPOSURE TO GASOLINE VAPORS
N5
U>
Concentration
ppm
5,000-16,000
10,000
3,000
2,600
2,000
1,000
1,000
1,000
900
550
500
300-700
160-270
Exposure time,
minutes
5 min
10 min
15 min
1 hr
1 hr
15 min
1 hr
30 min
1 hr
1 hr
1 hr
18 min
8 hr
Physiological/sensory effect
Lethal
Nose and throat irritation in 2 min; dizziness in 4
min; signs of intoxication in 4-10 min. Definite
intoxication
Dizziness, nausea
Dizziness
Dizziness, mucous membranes irritated and anesthesia
Drowsiness, dullness, numbness
Dizziness, headache, nausea
Eye irritation only
Slight dizziness, irritation of eyes, nose, and throat
Eye irritation
Eye irritation
No symptoms
Eye irritation
Reference
145
Cited in 151
Cited in 151
150
43
Cited in 151
150
151
151
150
43
Cited in 151
150
-------
DHCT6 JOB A 2-19-80
Little evidence was found on the health effects of exposure to low concen-
trations of gasoline vapor over long periods of time. Chronic gasoline toxicity
data appears to be limited to a few reports on occupational exposures and some
cases of gasoline abuse. Definitive, well-designed epidemiologic studies are
not available.
In general, the symptoms of chronic exposure to gasoline vapor are
ill-defined. They may consist of fatigue, muscular weakness, nausea, vomiting,
abdominal pain, and weight loss. Exposure is also known to have neurological
effects which include confusion, atoxia, tremor, paresthesias, neuritis and
152
paralysis of peripheral and cranial nerves.
Cases of repeated self-induced gasoline intoxication, generally involving
higher concentrations of gasoline vapor, could possibly be considered chronic
inhalation exposures. Persons engaged in the regular habit of "gasoline
sniffing" experience loss of appetite and weight, muscular weakness, and
cramps. Other effects reported to result from this practice include abnormal
EEG's and organ damage. The greatest hazard associated with chronic gasoline
inhalation is exposure to the aromatic hydrocarbons, especially benzene. As
previously noted, chronic benzene intoxication can result in severe irreversible
systemic effects such as encephalopathy, aplastic anemia, and leukemia.
Nothing was found in the literature relating chronic gasoline sniffing with
fetal pathological conditions such as liver, kidney, or bone marrow lesions.
153
McDermott and Killiany calculated a TLV for a gasoline based on the hydro-
carbon constituents present in gasoline and their respective TLV values. A
time-weighted average exposure of 300 ppm over an 8-hour period was estimated
to be reasonable along with a ceiling exposure of 1000 ppm for 15 minutes.
Included in this ACGIH "TLV for mixtures" equation was benzene because of
6-124
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DHCT6 JOB A 2-19-80
the additive effects this unique aromatic compound has in the presence of
other hydrocarbons at its former TLV level of 10 ppm.
In view of the recently promulgated (currently stayed, pending hearings)
standard reducing permissible occupational exposure limits for benzene from 10
155
to 1 ppm, Rumon reexamined the practical impact of such a standard in
relation to gasoline exposure. Gasoline TLVs were calculated using the ACGIH
method and incorporating the former benzene TLV criterion of 10 ppm, as well
as the new criterion of 1 ppm. The other constituents of gasoline used in the
calculations were estimated on actual ACGIH TLV values. The consequence of a
lowered benzene limit on a gasoline TLV is apparent from Figure 6-8. Gasoline
containing 1 percent benzene, for example, had a TLV of 300 ppm; whereas the
same gasoline, under the new benzene standard, would have a TLV of less than
150 ppm.
6.6.5 Miscellaneous Hydrocarbons
In addition to gasoline, there are many other hydrocarbon mixtures known
collectively as "solvents" that are utilized in vast quantities in the United
States. The majority of these contain more than one constituent and have
boiling ranges varying from less than 10°F to more than 100°F. In general,
the hydrocarbon constituents that make up these solvents consist of aliphatics,
benzene, alkyl-benzenes, and mono- and dicycloparaffins. The widespread usage
and accessibility of these solvents in industry under legitimate conditions
leads to potential exposure which may be further compounded by those who
intentionally inhale such mixtures for purposes of self-intoxication. Despite
the common use of hydrocarbon solvent mixtures, there is little published
information pertaining to their toxicity. Data up to 1940 have been compiled
by Von Oettingen, while information through the 1960s has been summarized
6-125
-------
300
200
a
>
o
g 100
I
I
I
2 4 6 8 10 12
PERCENT BENZENE IN GASOLINE - LIQUID PHASE
14
Figure 6-8. Calculated gasoline threshold limit value, reflecting impact of
present vs. newly promulgated TLV standard as a function of the liquid
volume percent benzene in the gasoline.155
6-126
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DHCT6 JOB A 2-19-80
by Gerarde ' and by Browning. The majority of these reports suffer
from inadequate identification of physical properties and composition of the
solvent mixtures tested. Therefore, comparison of results from the various
studies is very difficult and application of a study's findings to an immediate
solvent exposure situation are difficult.
Since 1965, investigators130'159'160 have published inhalation toxicity
data on animals that are more credible than previous work due to the advent of
more sophisticated analytical techniques, which ultimately lead to better
characterization ot the mixtures tested. To date, the most definitive reports
on inhalation toxicology of hydrocarbon mixtures have been published as a
series of seventeen articles by Carpenter et ai_129>161"176 (/\ standard
protocol was followed for 15 different solvent mixtures in evaluation of: (1)
their "no-ill-effect" level in rats and dogs, (2) LT5Q and LC5Q in rats, (3)
central nervous system effects in cats, (4) subacute toxicity in rats and
dogs; (5) respiratory irritation in mice and odor and irritation thresholds in
humans.) The suggested hygienic standards for inhalation of these various
solvents are based upon inhalation studies with rats and dogs and the sensory
response of human subjects. The composition of the hydrocarbon solvent mixtures
and the corresponding suggested hygienic standard are summarized in Table
6-32. Some solvent mixtures (e.g., kerosene) were of such low volatility (low
vapor pressure) at 25°C that lethal vapor levels could not be achieved. In
these cases, no LC5Q could be obtained, but the suggested hygienic standard
was based upon the sensory response of human subjects at the respective saturated
vapor concentrations in air at 25°C.
These studies lend additional support to the concept that the majority of
aliphatic, alicyclic, and aromatic hydrocarbons, with the exception of benzene,
appear to be relatively nontoxic, even when encountered as mixtures.
6-127
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OHCT6 JOB A 2-19-80
TABLE 6-32. SUGGESTED HYGIENIC STANDARD FOR VARIOUS HYDROCARBON SOLVENT ,
MIXTURES BASED ON INHALATION TOXICITY STUDIES OF ANIMALS AND SENSORY RESPONSE OF HUMAN SUBJECTS9
Solvents
1) Varnish maker
and painters'
naphtha
2) Stoddard
solvent
3) Rubber
<•* solvent
££ 4) Mixed xylenes
5) "60 solvent"
6) 70 solvent
7) 140 flash
aliphatic
solvent
8) 80 thinner
9) 90 thinner
Suggested
hygienic
standard,
ppn
430
200C
430
110
90
59C
37C
100
430
Constituents of hydrocarbon mixtures, % by volume
Average
LC50 rat,
ppn hrs
3,400
.
15,000
6,700
4,900
-
_
6,200
8,300
4
8
4
4
4
8
8
4
4
Paraffins
55.4
47.7
41.5
-
28.8
16.5
60.8
9.7
66.26
Cycloparaffins
Mono BT
30.3 2.4
26 11.6
53.6
-
20.6 0.8
12.6 3.1
24.5 11.2
18.7 0.2
0.61
Alkyl- Indans/
Olefins Aromatics benzenes Benzene tetralins Naphthalene
11.7 0.1 0.1
14.1 0.1 0.5
0.1 - 3.4 1.5
0.04 99.7 -
0.3 - 49.5 -
57.8 - 6.2 3.8
3.0 0.07 0.3
70.9 - 0.5 0
33 0.01 -
Toluene
-------
OHCT6 JOB A 2-19-80
TABLE 6-32. (continued)
CM
I
ro
Suggested
hygienic
standard ,
Solvents
10) Deodorized
kerosene
11) 40 thinner
12) Toluene
concentrate
13) High aromatic
solvent
14) High naphthenic
solvent
15) Naphthenic
aromatic solvent
16) n-Nonane vapor
PP«
14C
25C
480
26C
380
380
590
Constituents of hydrocarbon mixtures, % by volume
Average
LC50 rat,
ppm hrs Paraffins
8 55.2
8 35.4
8,800 4 38.69
8 0.3
960 4 29.0
960 4 24.7
3,200 4 98.4
Cycloparaffins
Mono
32.4
23.3
15.36
0.2
50.6
29.1
DT Olefins Aromatics
7.6
9.6 0.2 2.9
45.95
0.6 <0.1 89.5
19.3 - 1.1
7.9
Alkyl-
benzenes
3.1
23.6
45.89
Toluene
89.5
0.1
Toluene
34.2
Indans/
Benzene tetralins Naphthalene
0.8
0.0 5.0 2.9
0.06 -
9.2(1) 2.2
0.2
2.8(1) 1.1
unidentified components = 1.6%
^Compiled from refs. 129,161-176.
Based on Mass Spectral Analysis.
Saturated vapor concentration
in air at 25°C.
-------
DHCT6 JOB A 2-19-80
6.6.6 Health Effects Summary
Today as in 1970 there are no observed health effects associated with
volatile hydrocarbons as a class at ambient levels, however, there are health
effects reported at elevated levels for individual hydrocarbons.
Hydrocarbons, strictly speaking, are organic compounds composed of only
carbon and hydrogen. There are many other organic compounds which are loosely
referred to as hydrocarbons but in addition to carbon and hydrogen, these
compounds contain such elements as the halogens (fluorine, chlorine, bromine,
iodine) sulfur, nitrogen, oxygen, etc. Examples of the latter so-called
hydrocarbons are perch!oroethylene, ethylene dichloride, and ethylene dibromide.
The only hydrocarbons considered in our discussion were those that were volatile
and only contained carbon and hydrogen. This classification limits the carbon
number to approximately twelve and excludes the non-volatile polynuclear
aromatic hydrocarbons and the volatile substituted hydrocarbons (e.g., tetrachloro-
ethylene). The volatile hydrocarbons considered can be categorized as aliphatics,
alicyclics, and aromatics.
All three classes of hydrocarbons namely the aliphatics, alicyclics, and
aromatics are similar in that they give rise to irritation of the mucous
membrane and depression of the central nervous system. Mucous membrane
irritation is more pronounced from aromatic vapors compared to equivalent
concentrations of aliphatic and alicyclic hydrocarbons. Unlike the aliphatic
hydrocarbons, the degree of toxicity of the alicyclic hydrocarbons does not
correlate with structural character!"sites (e.g., number of carbon atoms,
degree of unsaturation and amount of branching). Aliphatic hydrocarbons
containing fewer than five carbon atoms are gases at room temperature. The
majority of these hydrocarbons, which include methane, ethane, ethylene,
6-130
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DHCT6 JOB A 2-19-80
propane, propylene, butane, and acetylene are collectively known as "simple
asphyxiants."
Some of these, especially ethylene, propylene, and acetylene, were used as
general anesthetics in the past. Any systemic effects observed at extremely
high concentrations are considered to be secondary due to the oxygen-replacing
capabilities of these gases, however, there are some reports that "aerosol
sniffing" of these simple asphyniants resulted ultimately in cardiac arrests.
To date, however, these gases are still considered harmless, physiologically
speaking, due to the fact that they are still classified as "simple asphyxiants"
by the American Conference of Government Industrial Hygienists (ACGIH) with no
assigned threshold limit values.
This is not the case with certain saturated aliphatic hydrocarbons,
namely pentane, hexane, heptane, and octane (C-5 to C-8), all of which have
been implicated as causative agents in permanent impairment of the peripheral
nervous system—namely, toxic polyneuropathy. Based upon the belief that this
neuropathy is caused by alkanes other than n-hexane, NIOSH recommended a
3
threshold limit value of 350 mg/m for total airborne C-5 to C-8 alkanes,
which may be revised upward in the case of those alkanes not causing chronic
neurological disorders. This recommended standard by NIOSH lowers the TLV
from 500 ppm for hexane, hepane, and octane for each compound to ~ 100 ppm.
Unlike the aliphatic and alicyclic hydrocarbons, aromatic hydrocarbons
have been suspected of causing hematological disorders. There is general
agreement, however, from the recent literature that these hematological
disorders which have ultimately lead to leukemia in the past, are due to
benzene alone. Knowledge of the carcinogenic potential of benzene has been
primarily gained through the experience of human occupational exposure and not
6-131
-------
DHCT6 JOB A 2-19-80
through experimental animal studies. Based upon the leukemogenic nature of
benzene and the probable cause of other severe systemic effects, NIOSH proposed
an occupational standard of 1 ppm for 1 hour compared to the present acceptable
maximum level of 25 ppm. This reduction in exposure at the workplace is expected
to materially reduce the risks of benzene-induced leukemia.
With the exception of cardiac sensitization, there is little firm evidence
that toluene exerts a specific toxic effect on any organ system in experimental
animals or in man. Early reports of toluene-induced myelotoxicity have been
discounted in that toluene was then likely contaminated by benzene. There is
firm evidence, however, that toluene may markedly alter the metabolism of
other solvents, especially if they are all oxidized by a common enzyme system
in the liver. The present threshold limit value of 100 ppm was designed to
protect workers from any CMS depressant effects, however, more recent studies
suggest that this situation may be modified by exercise.
Like other hydrocarbons, xylene causes irritation of the mucous membranes
and depression of the central nervous system. Individual isomers are apparently
similar in narcotic potency/acute potency with mixed xylene vapors. Like
toluene, the xylene-induced myelotoxicity was due to contamination with benzene.
The present TLV value of 100 ppm should protect workers against minimal irritation
and CNS depression. Many of the health effects associated with individual
hydrocarbons are likewise described for exposure to a combination of these
components which are commonly found in varying amounts in gasoline and commerical
solvents. Health effects observed upon exposure to individual hydrocarbons
and to hydrocarbon mixtures are irritation of the mucous membranes, central
nervous system depression, and neurological disorders. The majority of the
earlier studies addressing the toxicity associated with the inhalation of
6-132
-------
DHCT6 JOB A 2-19-80
solvent mixtures lacked creditability because of inadequate characterization
of the hydrocarbons present and inaccurate exposure assessments. Since 1965
more reliable data have been published due to the advent of more sophisticated
analytical techniques for characterizing mixtures. To date, the most impressive
inhalation toxicology studies are those of Carpenter from the viewpoint that
the properly designed protocol was followed for all seventeen studies and
hygienic standards were suggested based upon both human and animal data.
With the exception of benzene, it appears that aliphatics, alicyclics,
and aromatic hydrocarbons are relatively non-toxic even at fairly elevated
levels when present as individual compounds or as mixtures.
6.7 WELFARE EFFECTS
Although ethylene as an air pollutant has been reviewed earlier by a
number of workers, most of the contemporary research and concern has
centered around other components of polluted air, such as SC^, ozone (OO,
peroxyacetylnitrate, CO, fluorides, and particulates. More attention has
been focused on the other gases because, unlike ethylene, they have a direct
effect on human health and comfort and cause visible vegetation damage in the
form of ^esions and discoloration.
Ethylene arises from both natural and anthropogenic sources. The former
sources include plants (endogenous), soil, natural gas, and burning vegetation,
while anthropogenic sources include industries, greenhouses, laboratories, and
180
automobiles. In 1971 Abeles et al. estimated that the total emissions from
cars and other man-related activities in the United States is 15 million tons
annually with 93 percent due to the automobile. The contribution from vegeta-
tion was estimated to be about 20,000 tons annually or about 0.1 percent of
the total emissions. In spite of this constant production of large amounts of
6-133
-------
DHCT6 JOB A 2-19-80
ethylene, and occasional ambient measurements of ethylene in urban areas of up
to several hundred ppb, the levels in rural areas are still very low (<5 ppb).
These low levels existed prior to the introduction of emission controls on
mobile and stationary sources; consequently there are natural ways of removing
this unsaturated hydrocarbon from the ambient air. These ways include oxidation
181
by ozone, gas-phase photochemical reaction with nitrogen dioxide, and aerobic
180
microbial reactions in the soil.
Maximum concentrations of ethylene have been observed in the ambient air
of urban areas that are consistent with the increasing traffic density.
Ethylene concentrations in urban areas have ranged from < 5 ppb up to high
181a
values of 700 ppb observed by Abeles and Heggesstad in Washington, DC. In
general, these values are peak values and are not truly representative of the
majority of observations. This was well demonstrated by Hanan in Denver,
where peak values were reported as high as 180 ppb; however, the mean levels
for three different sampling stations were less than 50 ppb.
Since 1970, EPA has conducted several field studies monitoring total
nonmethane hydrocarbon and/or individual hydrocarbons. These include an urban
site at St. Louis (1972), rural sites in Ohio (1974), and special studies in
Houston (1973-1974) and the Boston area (1975). The data obtained from St.
Louis and Boston showed extremely high values of ethylene due to contamination
from nearby ozone monitoring systems. The Wilmington, Ohio, site, which is
representative of rural areas, showed ethylene levels averaging 1.44 ppb (2.88
ppb C) based on 12 samples taken every 2 hours over a 24-hour period. This is
desirable for a semi-agriculture area, since ethylene has been well established
112
as a phytotoxicant. The data presented in Table 6-33 are representative of
the concentrations of ethylene at the Houston study sampling sites. Figure
6-134
-------
DHCT6 JOB A 2-19-80
TABLE 6-33. HOUSTON STUDY ETHYLENE LEVELS112
Sampling
site code
9-11-73
HOI
H02
H03
H04
H05
H06
H07
H08
H09
1-30-74
H12
H13
H14
H15
H16
H17
HIS
4-2-74
H21
H22
H23
H24
H25
Location
Reagan Road at Euclid Road
Baytown Tunnel
Pasadena (TACB site)
Jacinto City (TACB site)
Washburn Tunnel
Industrial Drive
Channel View
Decker Road
Red Bluff
Minden and Dabney Streets
Jacinto City (TACB site)
Pasadena (TACB site)
Queens Road & Revere
Jacinto City (TACB site)
Pasadena site (TACB site)
Downtown Houston
*
Jacinto City
Industrial Drive
Jacinto Port Road
Deer Park
Pasadena
Concentration,
ppb ppb C
87.35
479.0
15.4
12.25
681.3
5.0
6.95
8.4
3.15
71.5
100.95
131.4
165.9
165.9
74.9
62.15
137.3
39.1
19.0
16.35
5.3
174.7
958.0
30.8
24.5
1362.7
10.1
13.9
16.8
6.3
143.0
201.9
262.8
331.9
331.9
149.9
124.3
274.7
78.2
38.0
32.7
10.6
6-135
-------
DHCT6 JOB A 2-19-80
112
6-9 gives the geographical location of the sampling sites. The majority of
these sites are in the ship channel area of Houston and represent the general
location of the industrial complex. The maximum concentration measured at the
various sites, with the exception of the tunnels, was 166 ppb (332 ppb C) at
site H14 and the lowest site showed a concentration of 5.0 ppb (10.6 ppb C).
The highest average levels of ethylene observed under different meteorological
conditions were for sites H12 through HIS, collected on January 30, 1974. The
average ethylene concentration was 110.4 ppb (220.8 ppb C). Since a high
pressure system was centered over the Houston area on January 30, 1974, the
nonmethane hydrocarbon (NMHC) levels measured on that day can be considered to
112
be near the maximum levels expected to occur in Houston. In view of the
ethylene contamination from adjacent ozone monitoring instruments, these
figures are probably inflated and would average out at less than 100 ppb.
In the absence of a nationwide monitoring system it is extremely difficult to
pass judgment on an appropriate mean urban level for ethylene; however, in
urban regions that have been monitored, concentrations of 25 ppb are common
181a
and 100 ppb levels are not unusual.
Generally, ethylene concentrations required to affect plants in some way,
e.g., inhibition of stem or root elongation, should exceed the threshold concen-
3 4
tration of 10 ppb. Full or maximum effect is reached at values of 10 to 10
188
ppb. Half-maximum effects are observed at 100 to 500 ppb. The effect, however,
varies greatly with the duration of exposure to a specific concentration and
with plant species.
181 c
An effective dosage term (ppb-days) was used by Piersol and Hanan to
correlate ethylene concentrations and exposure duration. They reported plant
growth inhibition induced by ethylene dosages ranging from 75 to 10,000 ppb-days.
6-136
-------
H04.H21
H13, H16
JACINTO CITY
CHANNELVIEW DRIVE
I—-
H08
H02
H24
LA PORTE
• TUNNEL SAMPLES
Figure 6-9. Geographic location of the grab sample collection sites. ^
6-137
-------
OHCT6 JOB A 2-19-80
Although the highest dosages produced the greatest growth inhibition, 70 to 80
percent of the total maximum inhibition was induced by dosages of around 100
ppb-days.
The effects of urban ethylene production on vegetation have been primarily
associated with ornamental plants grown under optimum greenhouse conditions.
The effects of ethylene on plants in the past has never been a nationwide
problem but was more severe in certain areas of the country. In 1962 California
adopted an Air Quality Standard For Ethylene, namely, 500 ppb for 1 hour; 100
ppb for 8 hours. This standard was designed to protect ornamental flowers
that are commercially produced abundantly in California, especially orchids,
which are extremely sensitive to ethylene at low levels (100 ppb for 6
hours). Ethylene levels in certain areas of California and Colorado are
aggravated by frequent inversions combined with high-density traffic. With
the introduction of the catalytic converter on all 1975 model cars and there-
after, the exhaust emissions of ethylene were decreased by a factor of two,
from ~ 12 percent to ~ 6 percent of total hydrocarbon emissions. Due to
natural sinks and the lack of good monitoring data nationwide, it is not
possible to accurately assess pre-1975 and post-1975 ethylene trends. Since
90 percent of nationwide ethylene emissions are associated with urban
transportation, it is fairly safe to say that ethylene levels have decreased
since 1975 and will continue to do so as more new model cars replace pre-1975
models. Ideally, it would be advantageous for both flower producers and
consumers to have urban ethylene concentrations approach the present rural
concentrations of 5 ppb; however, this appears to be highly impractical.
6.7.1 Welfare Effects Summary
As early as 1871, hydrocarbons were suspected of causing injury to vegeta-
tion; greenhouse plants were found to be highly susceptible. Early investigators
6-138
-------
DHCT6 JOB A 2-19-80
suspected other chemicals (e.g., CO, HCN, 02^) as the primary cause of damage;
however, later studies demonstrated that the principal cause was the gaseous
hydrocarbon, ethylene, which was found in illuminating gas and commonly used
in greenhouses. Since then research has demonstrated that ethylene is both an
endogenous plant-growth regulator and a serious phytotoxic air pollutant.
Dose-response curves have been established for ethylene damage; however, the
effect is highly dependent upon concentration, duration of exposure, and plant
species.
There are natural emission sources of this phytotoxic air pollutant;
however, man-made sources contribute by far the most, especially the internal
combustion engine. In general rural areas have ethylene levels less than
5 ppb; however, higher levels observed in urban centers are consistent with
traffic density and are highly dependent upon topography and meteorological
conditions. This is quite evident in certain areas of California (Los Angeles)
and Colorado (Denver) where traffic is dense and inversions are frequent. The
ethylene levels and the susceptibility of orchids and other ornamental flowers
to ethylene were the prime reason why the State of California adopted an Air
Quality Standard for ethylene in 1962. The impact of ethylene on welfare has
never been a nationwide problem, but in certain localities of the country,
ethylene is suspected of causing severe economic problems for individuals
involved in the production and retail sale of flowers and other crops.
With the advent of the catalytic converter on all new model cars in 1975
and thereafter, ethylene levels should begin to decrease since the internal
combustion engine is responsible for greater than 90 percent of ethylene in
the ambient air.
6-139
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HCT4/A 2-21-80
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22. Stephens, E. R. and F. R. Burleson. Distribution of light hydrocarbons
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