m
AIR QUALITY CRITERIA
FOR
HYDROCARBONS
U. S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Environmental Health Service
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AIR QUALITY CRITERIA
FOR
HYDROCARBONS
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Environmental Health Service
National Air Pollution Control Administration
Washington, D.C.
March 1970
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402 - Price $1.25
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National Air Pollution Control Administration Publication No. AP-64
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PREFACE
Air quality criteria tell us what science has
thus far been able to measure of the obvious
as well as the insidious effects of air pollution
on man and his environment. Such criteria
provide the most realistic basis that we pres-
ently have for determining to what point pol-
lution levels must be reduced if we are to pro-
tect the public health and welfare.
The criteria we can issue at the present
time do not tell us all that we would like to
know; but taking all of man's previous ex-
perience in evaluating environmental hazards
as a guide, we can conclude that improved
knowledge will show that there are identifi-
able health and welfare hazards associated
with air pollution levels that were previously
thought to be innocuous. As our scientific
knowledge grows, air quality criteria will have
to be reviewed and, in all probability, revised.
The Congress has made it clear, however, that
we are expected, without delay, to make the
most effective use of the knowledge we now
have.
The 1967 amendments to the Clean Air
Act require that the Secretary of Health, Edu-
cation, and Welfare ". . . from time to time,
but as soon as practicable, develop and issue
to the States such criteria of air quality as in
his judgment may be requisite for the protec-
tion of the public health and welfare . . . Such
criteria shall. . . reflect the latest scientific
knowledge useful in indicating the kind and
extent of all identifiable effects on health and
welfare which may be expected from the pres-
ence of an air pollution agent ..."
Under the Act, the issuance of air quality
criteria is a vital step in a program designed to
assist the States in taking responsible tech-
nological, social, and political action to pro-
tect the public from the adverse effects of air
pollution.
Briefly, the Act calls for the Secretary of
Health, Education, and Welfare to define the
broad atmospheric areas of the Nation in
which climate, meteorology, and topography,
all of which influence the capacity of air to
dilute and disperse pollution, are generally
homogeneous.
Further, the Act requires the Secretary to
define those geographical regions in the coun-
try where air pollution is a problem—whether
interstate or intrastate. These air quality con-
trol regions will be designated on the basis of
meteorological, social, and political factors
which suggest that a group of communities
should be treated as a unit for setting limita-
tions on concentrations of atmospheric pol-
lutants. Concurrently, the Secretary is re-
quired to issue air quality criteria for those
pollutants he believes may be harmful to
health or welfare, and to publish related infor-
mation on the techniques which can be em-
ployed to control the sources of those pol-
lutants.
Once these steps have been taken for any
region, and for any pollutant or combination
of pollutants, then the State or States respon-
sible for the designated region are on notice
to develop ambient air quality standards ap-
plicable to the region for the pollutants in-
volved, and to develop plans of action for im-
plementing the standards.
The Department of Health, Education, and
Welfare will review, evaluate, and approve
these standards and plans and, once they are
approved, the States will be expected to take
action to control pollution sources in the
manner outlined in their plans.
At the direction of the Secretary, the Na-
tional Air Pollution Control Administration
has established appropriate programs to carry
out the several Federal responsibilities speci-
fied in the legislation. Previously, on February
in
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1 1, 1969, air quality criteria and control tech-
niques information were published for sulfur
oxides and particulate matter.
This publication, Air Quality Criteria for
Hydrocarbons, is the result of extensive and
dedicated effort on the part of many per-
sons—so many that it is not practical to name
each of them.
In accordance with the Clean Air Act, a
National Air Quality Criteria Advisory Com-
mittee was established, having a membership
broadly representative of industry, universi-
ties, conservation interests, and all levels of
government. The committee provided invalu-
able advice on policies and procedures under
which to issue criteria, and provided major
assistance in drafting this document.
With the help of the committee, expert
consultants were retained to draft portions of
this document, while other segments were
drafted by staff members of the National Air
Pollution Control Administration. After the
initial drafting, there followed a sequence of
review and revision by the committee, as well
as by individual reviewers specially selected
for their competence and expertise in the
many fields of science and technology related
to the problems of atmospheric pollution by
hydrocarbons. These efforts, without which
this document could not have been completed
successfully, are acknowledged individually
on the following pages.
As also required by the 1967 amendments
to the Clean Air Act, appropriate Federal de-
partments and agencies, also listed on the fol-
lowing pages, were consulted prior to issuing
this criteria document. A Federal consultation
committee, comprising members designated
by the heads of 17 departments and agencies,
reviewed the document, and met with staff
personnel of the National Air Pollution Con-
trol Administration to discuss their com-
ments.
This Administration is pleased to acknowl-
edge the efforts of each of the persons specifi-
cally named, as well as the many not named
who have contributed to the publication of
this volume. In the last analysis, however, the
National Air Pollution Control Administra-
tion is responsible for its content.
JOHN T. MIDDLETON
Commissioner
National Air Pollution
Control Administration
IV
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NATIONAL AIR QUALITY CRITERIA ADVISORY COMMITTEE
Chairman
Dr. Delbert S. Barth, Director
Bureau of Criteria and Standards
National Air Pollution Control Administration
Dr. Herman R. Amberg*
Manager, Manufacturing Services Dept.
Central Research Division
Crown Zellerbach Corp.
Camas, Washington
Dr. Nyle C. Brady*
Director, Agricultural Experiment Station
Cornell University
Ithaca, New York
Dr. Seymour Calvert
Dean
School of Engineering
University of California at Riverside
Riverside, California
Dr. Adrian Ramond Chamberlain
Vice President
Colorado State University
Fort Collins, Colorado
Mr. James P. Garvey*
President and Director
Bituminous Coal Research, Inc.
Monroeville, Pennsylvania
Dr. David M. Gates
Director
Missouri Botanical Gardens
St. Louis, Missouri
Dr. Neil V. Hakala
President
Esso Research & Engineering Company
Linden, New Jersey
Dr. Ian T. Higgins
Professor, School of Public Health
The University of Michigan
Ann Arbor, Michigan
Mr. Donald A. Jensen
Director, Automotive Emissions Office
Engineering Staff
Ford Motor Company
Dearborn, Michigan
Dr. Herbert E. Klarman
Department of Environmental Medicine
and Community Health
Downstate Medical Center
State University of New York
Brooklyn, New York
Dr. Leonard T. Kurland*
Professor of Epidemiology
Mayo Graduate School of Medicine
Head, Medical Statistics
Epidemiology and Population Genetics
Section, Mayo Clinic
Rochester, Minnesota
Dr. Frederick Sargent II
Dean, College of Environmental
Sciences
University of Wisconsin at Green Bay
Green Bay, Wisconsin
Mr. William J. Stanley*
Director, Chicago Department of
Air Pollution Control
Chicago, Illinois
*Membership expired June 30, 1969
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CONTRIBUTORS AND REVIEWERS
Dr. David M. Anderson
Assistant Manager
Environmental Quality Control
Bethlehem Steel Corporation
Bethlehem, Pennsylvania
Dr. Mario C. Battigelli
Department of Medicine
School of Medicine
University of North Carolina
Chapel Hill, North Carolina
Dr. Sidney W. Benson
Department of Thermochemistry and
Chemical Kinetics
Stanford Research Institute
Stanford, California
Mr. Francis E. Blacet
Department of Chemistry
University of California at
Los Angeles
Los Angeles, California
Mr. F. W. Bowditch
Director, Emission Control
General Motors Technical Center
Warren, Michigan
Mr. Robert Bryan
Environmental Health Systems
Systems Development Corporation
Santa Monica, California
Dr. Leslie A. Chambers
Director
Institute of Environmental Health
School of Public Health
University of Texas
Houston, Texas
Dr. Robert J. Charlson
Associate Professor of Atmospheric
Chemistry
University of Washington
Seattle, Washington
Mr. C. G. Cortelyou
Coordinator
Air and Water Conservation
Mobile Oil Corporation
New York, New York
Dr. Ellis F. Darley
Air Pollution Research Center
University of California at Riverside
Riverside, California
Dr. Robert Eckhart
Director, Medical Research Division
Esso Research and Engineering Company
Linden, New Jersey
Mr. W. L. Faith
Consulting Chemical Engineer
San Marino, California
Dr. Hans L. Falk
Associate Director for Laboratory
Research
National Institute of Environmental
Health Sciences
Research Triangle Park, North Carolina
Mr. J. L. Gilliland
Ideal Cement Company
Denver, Colorado
Dr. John R. Goldsmith, Chief
Environmental Epidemiology Unit
California Department of Public Health
Berkeley, California
VI
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Dr. Bernard D. Goldstein
New York University Medical Center
Department of Medicine
School of Medicine
New York, New York
Dr. Harold H. Golz
Medical Director
American Petroleum Institute
New York, New York
Mr. C. M. Heinen, Chief Engineer
Emission Control and Chemical Development
Product Planning and Development Staff
Chrysler Corporation
Detroit, Michigan
Dr. Charles H. Hine
Clinical Professor of Occupational
and Environmental Medicine
University of California Medical School
San Francisco, California
Dr. Kenneth D. Johnson
Staff Engineer
Manufacturing Chemists' Association
Washington, D. C.
Mr. C. E. Kircher
Research Manager, Research Division
Detrex Chemical Industries, Inc.
Detroit, Michigan
Dr. Paul Kotin, Director
National Institute of Environmental
Health Sciences
Research Triangle Park, North Carolina
Mr. J. F. Kunc
Senior Research Associate, Petroleum
Staff
Esso Research and Engineering Company
Linden, New Jersey
Mr. Philip A. Leighton
Consultant, Atmospheric Chemistry
Solvang, California
Mr. Arthur Levy
Chief, Air, Water, and Solid Waste
Chemistry
Battelle Memorial Institute
Columbus, Ohio
Dr. H. N. MacFarland
Professor and Director
Centre of Research on Environmental
Quality
Faculty of Science
York University
Downsview, Ontario, Canada
Dr. Roy O. McCaldin
College of Engineering
University of Florida
Gainesville, Florida
Mr. Herbert C. McKee
Assistant Director
Department of Chemistry and
Chemical Engineering
Southwest Research Institute
Houston, Texas
Dr. George McNew
Director
Boyce Thompson Institute of Plant
Research, Inc.
Yonkers, New York
Mr. John A. Maga
Executive Officer
California Air Resources Board
Sacramento, California
Mr. W. W. Moore
Vice President
Research-Cottrell, Inc.
Bound Brook, New Jersey
Dr. Thaddeus J. Murawski
Bureau of Epidemiology
New York State Department
of Health
Albany, New York
VI)
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Dr. John N. Pattison
Professor of Environmental
Engineering
University of Cincinnati
Cincinnati, Ohio
Dr. Alexander Rihm
Assistant Commissioner
Division of Air Resources
New York State Department of Health
Albany, New York
Mr. Elmer Robinson
Chairman
Environmental Research Department
Stanford Research Institute
Arlington, Virginia
Mr. Jean J. Schueneman, Chief
Division of Air Quality Control
Environmental Health Services
Maryland Department of Health
Baltimore, Maryland
Mr. Francis Scofield
Vice President, Technical Affairs
National Paint, Varnish and Lacquer
Association, Inc.
Washington, D. C.
Dr. R. W. Scott
Coordinator for Conservation Technology
Esso Research and Engineering Company
Linden, New Jersey
Dr. Edgar Stephens
Air Pollution Research Center
University of California at Riverside
Riverside, California
Mr. Morton Sterling
Director
Detroit and Wayne County Air Pollution
Control Agencies
Detroit and Wayne County Departments
of Health
Detroit, Michigan
Professor Arthur Stern
Department of Environmental Sciences
and Engineering
The School of Public Health
University of North Carolina
Chapel Hill, North Carolina
Dr. Herbert E. Stokinger
Chief, Laboratory of Toxicology
and Pathology
Bureau of Occupational Safety
and Health
Environmental Control Administration
Cincinnati, Ohio
Dr. Raymond R. Suskind
Director, Department of
Environmental Health
College of Medicine
University of Cincinnati
Cincinnati, Ohio
Mr. Victor H. Sussman
Director
Bureau of Air Pollution Control
Pennsylvania Department of Health
Harrisburg, Pennsylvania
Dr. O. Clifton Taylor
Air Pollution Research Center
University of California at Riverside
Riverside, California
Dr. Peter O. Warner
Laboratory Supervisor
Technical Services Section
Air Pollution Control Division
Wayne County Department of Health
Mr. Lowell G. Wayne
Air Pollution Control Institute
University of Southern California
Los Angeles, California
Dr. Eugene Weaver
Product Development Group
Ford Motor Company
Detroit, Michigan
via
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Mr. Harry B. Weaver, Manager
Environmental Engineering
Automobile Manufacturers Association, Inc.
Detroit, Michigan
Mr. Leonard H. Weinstein
Program Director
Environmental Biology
Boyce Thompson Institute for Plant
Research, Inc.
Yonkers, New York
Dr. Bernard Weinstock
Manager and Senior Scientist
Fuel Sciences Department
Ford Motor Company
Dearborn, Michigan
Mr. Melvin Weisburd
Manager, Environmental Health Systems
Systems Development Corporation
Santa Monica, California
Mr. Harry J. White, Head
Department of Applied Sciences
Portland State University
Portland, Oregon
Mr. J. Wilkenfeld, Director
Environmental Health
Hooker Laboratories
New York, New York
Mr. John E. Yocum
Director, Engineering and
Technical Programs
The Travelers Research Corporation
Hartford, Connecticut
IX
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FEDERAL AGENCY LIAISON REPRESENTATIVES
Department of Agriculture
Dr. Theodore C. Byerly
Assistant Director of Science
and Education
Department of Commerce
Mr. James R. Hibbs
Advisor on Environmental Quality
Department of Defense
Mr. Thomas R. Casberg
Office of the Deputy Assistant Secretary
(Properties and Installations)
Department of Housing & Urban Development
Mr. Samuel C. Jackson
Assistant Secretary for Metropolitan
Development
Department of the Interior
Mr. Harry Perry
Mineral Resources Research Advisor
Department of Justice
Mr. Walter Kiechel, Jr.
Assistant Chief
General Litigation Section
Land and Natural Resources Division
Department of Labor
Dr. Leonard R. Linsenmayer
Deputy Director
Bureau of Labor Standards
Post Office Department
Mr. W. Norman Meyers
Chief, Utilities Division
Bureau of Research & Engineering
Department of Transportation
Mr. William H. Close
Assistant Director for Environmental Research
Office of Noise Abatement
Department of the Treasury
Mr. Gerard M. Brannon
Director
Office of Tax Analysis
Atomic Energy Commission
Dr. Martin B. Biles
Director
Division of Operational Safety
Federal Power Commission
Mr. F. Stewart Brown
Chief
Bureau of Power
General Services Administration
Mr. Thomas E. Crocker
Director
Repair and Improvement Division
Public Buildings Service
National Aeronautics and Space
Administration
Major General R. H. Curtin, USAF
(Ret.)
Director of Facilities
National Science Foundation
Dr. Eugene W. Bierly
Program Director for Meteorology
Division of Environmental Sciences
Tennessee Valley Authority
Dr. F. E. Gartrell
Assistant Director of Health
Veterans Administration
Mr. Gerald M. Hollander
Director of Architecture and Engi-
neering
Office of Construction
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TABLE OF CONTENTS
Chapter Page
LIST OF FIGURES xiv
LIST OF TABLES xiv
1. INTRODUCTION 1-1
2. NATURE, SOURCES, AND PRINCIPLES OF CONTROL OF ATMOSPHERIC
HYDROCARBON 2-1
A. INTRODUCTION 2-1
B. HYDROCARBON CLASSES 2-1
C. HYDROCARBON ATMOSPHERIC REACTIONS 2-2
1. General Discussion 2-2
2. Expected Photooxidation Products 2-5
a. Commonly Recognized Products in Photochemical Air Pollution ... 2-5
b. Products of Photooxidation of Hydrocarbons in Experimental Studies . 2-6
D. ESTIMATION OF HYDROCARBON EMISSIONS 2-10
1. Emission Levels of Hydrocarbons from Natural Sources 2-10
2. Emission Levels of Hydrocarbons from Technological Sources 2-12
a. National Emission Estimates 2-12
b. Regional Emission Estimates 2-13
3. Technological Sources of Hydrocarbons 2-13
a. Carbureted Gasoline Engines 2-14
b. Diesel Engines 2-14
c. Gas Turbines and Aircraft Jet Engines 2-15
d. Stationary Sources 2-15
4. Emission Factors 2-15
E. PRINCIPLES OF HYDROCARBON EMISSION CONTROL 2-16
1. General Principles of Control 2-16
2. Motor Vehicle Controls 2-16
a. Present Controls 2-16
b. Proposed Controls 2-16
3. Stationary Source Control 2-17
a. Evaporation Emission Controls 2-17
b. Control by Incineration 2-17
c. Control by Adsorption 2-17
d. Control by Absorption 2-17
e. Control by Condensation 2-17
f. Control by Substitution of Materials 2-17
F. SUMMARY 2-17
G. REFERENCES 2-18
3. ATMOSPHERIC LEVELS OF HYDROCARBONS AND THEIR RELATED PRO-
DUCTS 3-1
A. INTRODUCTION 3-1
B. HYDROCARBONS 3-1
1. Hydrocarbons in Ambient Air 3-2
xi
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Liiaptcr
•3 O
2. Diurnal Variation
3. Seasonal Variation
4. Community Levels • • ' '
C. SECONDARY CONTAMINANTS 3~9
1. Aldehydes 3"9
2. Aerosols 3'10
D. SUMMARY ' 3'12
E. REFERENCES 3'14
4. GENERAL STANDARDIZATION AND ANALYSIS METHODS 4-1
A. INTRODUCTION 4-1
B. CALIBRATION TECHNIQUES 4-1
1. Dynamic 4-1
2. Static 4-2
C. METHODS FOR ANALYSIS OF TOTAL HYDROCARBONS 4-2
1. Flame lonization 4-2
2. Spectrophotometric Methods 4-2
D. METHODS FOR ANALYSIS OF SPECIFIC HYDROCARBONS 4-2
1. Subtractive Columns 4-2
a. Nomenthane Hydrocarbons 4-2
b. Reactive Hydrocarbons 4-3
2. Gas Chromatography 4-3
3. Spectrometric Methods 4-3
4. Methods for Olefins 4-4
E. METHODS FOR ANALYSIS OF GASEOUS ALDEHYDES AND KETONES . . 4-4
1. General 4-4
2. Bisulfite Method 4-4
3. Other Condensation Reagents 4-4
F. SAMPLE COLLECTION AND HANDLING 4-4
G. AEROSOL MEASUREMENTS 4-5
H. SUMMARY 4-5
I. REFERENCES 4-5
5. RELATIONSHIP OF ATMOSPHERIC HYDROCARBONS TO PHOTOCHEMICAL
AIR POLLUTION LEVELS 5-1
A. INTRODUCTION AND GENERAL DISCUSSION 5-1
B. ANALYSIS OF AEROMETRIC DATA 5-2
C. SUMMARY 5-11
D. REFERENCES 5-12
6. EFFECTS OF HYDROCARBONS AND CERTAIN ALDEHYDES ON VEGETATION 6-1
A. INTRODUCTION 6-1
B. RELATIVE IMPORTANCE OF HYDROCARBON GASES IN CAUSING IN-
JURY TO VEGETATION 6-1
C. EFFECTS OF ATMOSPHERIC ALDEHYDES ON VEGETATION 6-2
D. SYMPTOMS OF EFFECTS OF ETHYLENE ON VEGETATION 6-3
E. ESTIMATES OF ECONOMIC LOSS (DAMAGE) ASSOCIATED WITH ETHYL-
ENE INJURY TO VEGETATION 6-4
F. DOSE-INJURY RELATIONSHIPS FOR VARIOUS PLANTS EXPOSED TO
ETHYLENE 6-4
xii
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Chapter page
G. NEED FOR FURTHER RESEARCH 6-7
H. SUMMARY 6-7
I. REFERENCES 6-7
7. TOXICOLOGICAL APPRAISAL OF HYDROCARBONS AND ALDEHYDES .... 7-1
A. INTRODUCTION 7-1
B. TOXICOLOGY OF HYDROCARBON COMPOUNDS 7-1
1. General Discussion 7-1
2. Aliphatic Hydrocarbons 7-1
3. Alicyclic Hydrocarbons 7-2
4. Aromatic Hydrocarbons 7-2
5. Summary 7-2
C. TOXICOLOGY OF ALDEHYDES 7-2
1. General Discussion 7-2
2. Mechanisms of Toxicity 7-7
a. Primary Irritation of the Skin, Eyes, and Respiratory Mucosa 7-7
b. Sensitization 7-7
c. Anesthesia 7-7
d. Pathological Effects 7-7
3. Formaldehyde and Acrolein 7-8
a. General Discussion 7-8
b. Formaldehyde 7-8
c. Acrolein 7-12
d. Sensory Physiology and Central Nervous System Responses 7-15
4. Acetaldehyde and Other Aldehydes 7-16
5. Summary 7-18
D. HYDROCARBON-MIXED ATMOSPHERE EXPERIMENTATION 7-18
1. Introductory Discussion 7-18
2. Changes in Pulmonary Function 7-19
3. Eye Irritation 7-20
4. Summary 7-26
a. Pulmonary Function 7-26
b. Eye Irritation 7-26
E. SUMMARY 7-27
F. REFERENCES 7-28
8. SUMMARY AND CONCLUSIONS 8-1
A. INTRODUCTION 8-1
B. SOURCES, NATURE, AND PRINCIPLES OF CONTROL OF ATMOSPHERIC
HYDROCARBONS 8-1
C. ATMOSPHERIC LEVELS OF HYDROCARBONS AND THEIR RELATED
PRODUCTS 8-1
D. SAMPLING AND STANDARDIZATION METHODS FOR MEASUREMENT OF
HYDROCARBONS 8-2
E. RELATIONSHIP OF ATMOSPHERIC HYDROCARBONS TO PHOTO-
CHEMICAL AIR POLLUTION LEVELS 8-2
F. EFFECTS OF HYDROCARBONS AND CERTAIN ALDEHYDES ON VEGETA-
TION 8-3
xin
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Chapter
G. TOXICOLOGICAL APPRAISAL OF HYDROCARBONS AND ALDEHYDES . • 8-3
H. CONCLUSIONS 8-4
I. RESUME 8-5
APPENDIX A-l
SUBJECT INDEX M
LIST OF FIGURES
Figure PaSe
3-1. Concentration Ratios for Nomethane Hydrocarbons/Methane in Los Angeles (213
hours during October and November, 1964) and Cincinnati (574 hours during
September 1964), with 655 jug/m3 (Ippm) Methane Deducted to Correct for Esti-
mated Background Biospheric Concentration 3-1
3-2. Nonmethane Hydrocarbons by Flame lonization Analyzer, Averaged by Hour of
Day Over Several Months for Various Cities 3-4
3-3. Nonmethane Hydrocarbons by Flame lonization Analyzer Averaged by Hour of
Day for Three Los Angeles County Sites, October 1966 through February 1967. . 3-5
3-4 Average Concentrations of Several Pollutants, Azusa and Downtown Los Angeles,
September Through November, 1967 3-11
3-5. Hourly Aldehyde Concentrations at Two Los Angeles Sites, October 22, 1968. .. 3-13
5-1. Maximum Daily Oxidant as a Function of Early Morning Total Hydrocarbons,
1966-1968 for CAMP Stations; May through October 1967 for Los Angeles. ... 5-7
5-2. Maximum Daily Oxidant as a Function of Early Morning Total Hydrocarbons,
Denver, 1966-1968 5-8
5-3. Maximum Daily Oxidant as a Function of Early Morning Nonmethane Hydro-
carbons, 1966-1968 for CAMP Stations; May through October 1967 for Los Angeles. 5-9
54. Location of Selected Los Angeles County Air Monitoring Stations 5-10
5-5. Upper Limit of Maximum Daily Oxidant at Three Los Angeles County Stations,
May through October 1967 5.}]
7-1. Regression Curve of the Effect of Atmospheric Concentrations of Total Aldehyde
on Panel Eye Irritation 7.3
7-2. Regression Curve of the Effect of Atmospheric Concentrations of Formaldehyde
on Panel Eye Irritation 7.4
7-3. Effects of Varying Concentrations of Propylene and Nitric Oxide on Eye Irritation. 7-23
74. Average Reported Eye Irritation Intensities of 12 Subjects During Photooxidations
with Ethylene and Propylene, Related to Observed Formaldehyde Concentrations. 7-25
LIST OF TABLES
Table page
1-1. Factors to be Considered in Developing Air Quality Criteria 1_2
2-1. Hydrocarbon Concentrations in Morning and Afternoon Ambient Air Samples,
Riverside, California, Fall 1968 2-3
2-2. Hydrocarbon Concentrations of Irradiated and Nonirradiated Synthetic Atmos-
pheres Containing Diluted Automobile Exhaust Gases 2-4
2-3. Ozone Levels Generated in Photooxidation of Various Hydrocarbons with Ox-
ides of Nitrogen 2-8
2-4. Yields of Carbonyl Compounds in Experimental Photooxidation of Hydro-
carbons with Oxides of Nitrogen 2-9
xiv
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Table Page
2-5. Yields of Peroxyacyl Nitrates and Alkyl Nitrates Observed in Photooxidation of
Various Olefins and Alkylbenzenes 2-10
2-6. Estimates of Hydrocarbon Emissions by Source Category 2-12
2-7. Summary of Hydrocarbon Emissions from 22 Metropolitan Areas in the United
States, 1967-1968 2-13
2-8. Percent of Total Area Hydrocarbon Emissions by Source Category, 22 Metro-
politan Areas in United States 2-14
3-1. Some Hydrocarbons Identified in Ambient Air 3-2
3-2. Average Atmospheric Light Hydrocarbon Concentrations, by Hour, Los Angeles,
September through November, 1967 3-6
3-3. Mean of Daily Maximum Hourly Average Total Hydrocarbon Concentrations (as
ppm methane), 17 California Cities, 1968-1969 3-7
3-4. Average Hydrocarbon Composition,218 Ambient Air Samples, Los Angeles, 1965 3-8
3-5. Average and Highest Concentration Measured for Various Aromatic Hydrocar-
bons in Los Angeles, 26 days, September through November, 1966 3-9
3-6. Comparison of Results from Ultraviolet Irradiation of Ambient Air Samples . . 3-10
3-7. Range of Yearly Maximum 1-Hour Average Concentrations of Aldehydes and
Formaldehyde, Los Angeles County Stations, 1951 through 1957 ........ 3-12
3-8. Average Aldehyde Concentrations by Hour in Los Angeles, September 25
through November 15, 1961 3_12
3-9. Comparison of Composition of Suspended Particulate Air Samples from Five
United States Cities 3_13
6-1. Relative Concentrations of Several Unsaturated Hydrocarbons that Produce Bio-
logical Response Similar to that Produced by Ethylene g_2
6-2. Dosage-Response Relationships of Various Plants to Ethylene 5.5
7-1. Toxicity of Saturated Aliphatic Hydrocarbons (through Octane) 7.3
7-2. Toxicity of Unsaturated Aliphatic Hydrocarbons 7.4
7-3. Comparative Effects of Single Exposure to 61.8 mg/m^ (18,000 ppm) Cyclo-
hexane Vapor in Air 7.5
7-4. Comparative Effects of Chronic Exposure to Cyclohexane Vapor in Air 7.5
7-5. Comparative Effects of Chronic Exposure to Methylcyclohexane Vapor in Air . 7.5
7-6. Comparative Effects of Acute and Chronic Exposure to Aromatic Hydrocarbon
Vapors in Air 7.5
7-7. Reported Sensory Responses of Man to Formaldehyde Vapors 7.9
7-8. Survival Time of Mice Exposed to 15,375 jug/m^ (12.5 ppm) Formaldehyde in
Presence of Aerosols 7-11
7-9. Reported Sensory Responses of Man to Acrolein Vapors 7-13
7-10. Survival Time of Mice Exposed to 16,150 ng/m^ (6 ppm) Acrolein in Presence
of Aerosols 7-14
7-11. Air Quality Standards for Formaldehyde 7-14
7-12. Air Quality Standards for Acrolein 7-14
7-13. Animal Toxicity of Inhaled Aldehydes 7-17
7-14. Toxicity of Aldehydes to Humans 7-17
7-15. Comparison of the Effects of Irradiated Exhaust with those of Nonirradiated
Exhaust on Pulmonary Function Parameters 7-20
7-16. Eye Irritation Potency of Various Hydrocarbons in Irradiated Synthetic
Atmospheres 7-25
xv
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AIR QUALITY CRITERIA FOR HYDROCARBONS
CHAPTER 1.
INTRODUCTION
Pursuant to authority delegated to the
Commissioner of the National Air Pollution
Control Administration, Air Quality Criteria
for Hydrocarbons is issued in accordance with
Section 107(b) of the Clear Air Act (42
U.S.C. 1857-18571).
Air quality criteria are an expression of the
scientific knowledge of the relationship be-
tween various concentrations of pollutants in
the air and their adverse effects on man and
his environment. They are issued to assist the
States in developing air quality standards. Air
quality criteria are descriptive; that is, they
describe the effects that have been observed
to occur when the ambient air level of a pol-
lutant has reached or exceeded specific figures
for a specific time period. In developing cri-
teria, many factors have to be considered. The
chemical and physical characteristics of the
pollutants and the techniques available for
measuring these characteristics must be con-
sidered, along with exposure time and condi-
tions of the environment.
The criteria must consider the contribution
of all such variables to the effects of air pollu-
tion on human health, agriculture, materials,
visibility, and climate. Further, the individual
characteristics of the receptor must be taken
into account. Table 1-1 is a listing of the
major factors that need to be considered in
developing criteria.
Air quality standards are prescriptive. They
prescribe pollutant exposures that a political
jurisdiction determines should not be ex-
ceeded in a specified geographic area, and are
used as one of several factors in designing
legally enforceable pollutant emission stand-
ards.
This document focuses on gas-phase hydro-
carbons and certain of their oxidation prod-
ucts, particularly aldehydes, that are associ-
ated with the manifestations of photo-
chemical air pollution. Particulate hydrocar-
bons, and more specifically polynuclear
hydrocarbons, are not treated in this docu-
ment; these compounds will be considered at
a later date in a separate set of air quality
criteria. It is important to recognize that the
criteria for hydrocarbons rest almost entirely
on their role as precursors of other com-
pounds formed in the atmospheric photo-
chemical system and not upon the direct
effects of the hydrocarbons themselves. It is
for this reason that several of these reaction
products are discussed in this document. A
companion document, AP-63, Air Quality Cri-
teria for Photochemical Oxidants, covers the
effects of a class of photochemical reaction
products not treated in this document.
This publication reviews the chemical and
physical characteristics of hydrocarbons and
their degradation products, especially alde-
hydes, and considers the basic analytical
methods used for measuring the atmospheric
content of these compounds. A brief review
of the sources of hydrocarbons and principles
of their control is included. The chemistry of
hydrocarbon reactions in the atmosphere is
briefly reviewed. The direct effects of hydro-
carbons, essentially limited to vegetation
damage from ethylene, are discussed. Toxico-
logical data on hydrocarbons and aldehydes
are also included.
The National Air Pollution Control Admin-
istration is currently advocating the use of the
metric system to express atmospheric concen-
trations of air pollutants, e.g., micrograms per
cubic meter (jug/m^). In most instances, gase-
ous pollutants have hitherto been reported on
a volume ratio basis, i.e., parts per million
1-1
-------
Table 1-1. FACTORS TO BE CONSIDERED IN
DEVELOPING AIR QUALITY CRITERIA3
Properties of pollution
Concentration
Chemical composition
Adsorbed gases
Coexisting pollutants
Physical state of pollutant
Solid
Liquid
Gaseous
Kinetics of formation
Residence time
Measurement methods
Flame ionization
Spectroscopic
Gas chromatographic
Chemical
Exposure parameters
Duration
Concomitant conditions, such as
Temperature
Pressure
Humidity
Characteristics of receptor
Physical characteristics
Individual susceptibility
State of health
Rate and site of transfer to receptor
Responses
Effects on health (diagnosable effects, latent
effects, and effects predisposing the organism
to disease)
Human health
Animal health
Plant health
Effects on human comfort
Soiling
Other objectionable surface deposition
Effects on atmospheric properties
Effects on radiation and temperature
aAdapted from S. Calvert's statement for air quality
criteria hearings held by the Subcommittee on Air
and Water Pollution of the U.S. Senate Committee on
Public Works, July 30, 1968. Published in "Hearings
before the Subcommittee on Air and Water Pollution
of the Committee on Public Works, United States
Senate (Air Pollution 1968, Part 1)."
(ppm). Conversion from volume (PPm) to
mass (jug/m^) units requires a knowledge ot
the gas density at the temperature and pres-
sure of measurement, since gas density vanes
with changes in these two parameters. In this
document, 25° C (77° F) has been taken as
standard temperature and 760 mm Hg (atmos-
pheric pressure at sea level) as standard pres-
sure. It should be borne in mind that almost
all data for the atmospheric hydrocarbons
under discussion were originally recorded as
ppm.
In general, the terminology employed
follows usage recommended in the publica-
tion style guide of the American Chemical
Society. An appendix to the document
includes an explanation of the procedure for
converting volume (ppm) to mass (jug/m^)
units.
The literature has generally been reviewed
through October 1969. This document is not
intended as a complete literature review and
does not cite every published article on the
material covered herein. A particular effort
was made, however, to relate hydrocarbons to
the manifestations of photochemical air pollu-
tion. This document summarizes the current
scientific knowledge on the role of hydro-
carbons with respect to photochemical air
pollution and points out the major defi-
ciencies in that knowledge and the need for
future research.
The technological and economic aspects of
air pollution control are considered in com-
panion volumes to criteria documents. The
techniques for control of hydrocarbons, as
well as the cost of applying these techniques,
are described in two separate documents:
AP-66, Control Techniques for Carbon
Monoxide, Nitrogen Oxide, and Hydrocarbon
Emissions from Mobile Sources, and AP -68,
Control Techniques for Hydrocarbon and
Organic Solvent Emissions from Stationary
Sources.
1-2
-------
CHAPTER 2.
NATURE, SOURCES, AND PRINCIPLES OF CONTROL OF
ATMOSPHERIC HYDROCARBONS
A. INTRODUCTION
The class of hydrocarbons covered in this
document are those which exist in the atmos-
phere in the gas phase. Many of these com-
pounds may enter into atmospheric photo-
chemical reaction processes leading to the
products and manifestations associated with
photochemical air pollution. Excluded are
hydrocarbons and other organics associated
only with suspended particles in the atmos-
phere. Even with this restriction, a large
number of compounds are involved.
It is significant that most of the principal
effects are caused not by hydrocarbons direct-
ly, but by compounds derived from the
atmospheric reactions of hydrocarbons and
their derivatives with other substances.
An appraisal, therefore, of the effects of
atmospheric hydrocarbon pollution must be
made in relation to the manifestations of pho-
tochemical air pollution. Aspects that must be
considered include photochemical reactions,
the influence of solar irradiation, and mete-
orological factors relating to the transport and
diffusion of air pollutants.
In this chapter, information is presented on
hydrocarbon sources and emissions, and on
principles of emission control. This informa-
tion is intended to provide a basic under-
standing of the nature and importance of
sources of hydrocarbons from the standpoint
of appraising their contribution to the atmos-
pheric photochemical system. A detailed
treatment of technological and economic
factors relating to control is not intended; this
function is provided by separate documents,
AP-66, Control Techniques for Carbon
Monoxide, Nitrogen Oxide, and Hydrocarbon
Emissions from Mobile Sources, and AP-68,
Control Techniques for Hydrocarbon and
Organic Solvent Emissions from Stationary
Sources.
B. HYDROCARBON CLASSES
Hydrocarbons are compounds whose mol-
ecules consist of atoms of hydrogen and
carbon only. All compounds of carbon,
except the oxides of carbon, the carbides, and
the carbonates, are organic compounds.
Hydrocarbons, therefore, are organic com-
pounds, as are many other carbon compounds
having additional elements such as oxygen,
nitrogen, and chlorine. The hydrocarbons of
concern in this document are those gas-phase
hydrocarbons which may be encountered in
urban atmospheres; of special interest are
those hydrocarbons emitted into the atmos-
phere as contaminants by technological
sources.
The volatility of hydrocarbons is ap-
proximately determined by their carbon
number. Hydrocarbons with a carbon number
(that is, number of carbon atoms in each mol-
ecule) greater than about 12 are generally not
sufficiently abundant to reach troublesome
atmospheric concentrations in the gas phase;
however, many of these higher hydrocarbons,
as particles or in association with particulate
matter, are important air contaminants in
another context and will be treated in future
air quality criteria. Hydrocarbons having a
carbon number of 1 to 4 are gaseous at
ordinary temperatures, whereas those with a
carbon number of 5 or more are liquids or
solids in the pure state. (Liquid mixtures of
hydrocarbons, such as gasoline, may include
some proportion of compounds which, in the
pure state, would be either gases or solids.)
2-1
-------
Hydrocarbons fall into three classes, which
are defined in terms of their general molecular
structure: acyclic, alicyclic, and aromatic.
Acyclic hydrocarbons are those whose carbon
atoms are arranged in chains only, with or
without branching chains, but without rings.
Aromatic hydrocarbons are all those whose
atoms are arranged in benzene rings, that is,
six-membered carbon rings with only one ad-
ditional atom (of hydrogen or carbon)
attached to each atom in the ring. Alicyclic
hydrocarbons are all those having rings other
than benzene rings. A subsidiary classification
often used is that of saturated versus unsat-
urated hydrocarbons. A saturated hydro-
carbon is one with each of its carbon atoms
boned to four other atoms; an unsaturated
hydrocarbon with two or more carbon atoms
is bonded to less than four other atoms. Sat-
urated aliphatic hydrocarbons all correspond
to the empirical formula CnH2n+2> where n is
the carbon number. Saturated alicyclics with
one ring have the formula CnH2n; those with
two rings have the formula CnH2n_2, and so
on.
Detailed discussions of hydrocarbon clas-
ses, their properties, and their nomenclature
may be found in textbooks on organic chem-
istry.
C. HYDROCARBON ATMOSPHERIC
REACTIONS
1. General Discussion
Reactions of hydrocarbons in the urban
atmosphere are important because they give
rise to secondary contaminants and reaction
intermediates that cause nearly all the detri-
mental effects of hydrocarbon air pollution.
The chemistry of these reactions and their
products is not fully known, but existing
knowledge is sufficient to explain the most
important features of the observed behavior
of photochemical air pollution. In a practical
sense, adequate prediction of the real effects
of controlling hydrocarbon emissions depends
on applying both the available knowledge and
the relevant scientific principles concerning
these reactions.
Hydrocarbons become involved in ':ne
photochemical air pollution complex not be-
cause of their exposure to sunlight, but
because of their reactions with oxygen atoms,
excited-oxygen and ozone molecules, and free
radicals generated by the action of sunlight on
other components in the atmosphere, most
particularly nitrogen dioxide. Sunlight alone
has no appreciable effect on hydrocarbons in
the air; in the absence of such highly reactive
matter, hydrocarbons would not be involved
in photochemical air pollution.
The speed with which the photochemical
air pollution is developed can be related
directly to the rates at which the hydrocarbon
molecules are attacked by the reactive species
and is indicated by the rate of consumption,
i.e., the rate of decrease in concentration of
hydrocarbons. Thus, in principal, if the rate
of consumption of hydrocarbons can be
predicted, an expected rate of development of
photochemical air pollution can be deduced.
As a consequence of the different reac-
tivities of individual hydrocarbons, it is im-
possible to predict accurately the rate of con-
sumption of hydrocarbons in photochemical
air pollution reactions unless the detailed
composition of the hydrocarbon component
of the air is known or can be estimated.
Knowledge of the total concentration of
hydrocarbons is insufficient, since two atmos-
pheres having the same total hydrocarbon
measurement may contain individual hydro-
carbons of very different reactivity and thus
exhibit very different rates of hydrocarbon
consumption and photochemical air pollution
development.
The total rate of hydrocarbon consumption
is the sum of the rates of consumption of all
the individual hydrocarbons. Since the indi-
vidual hydrocarbons have different reac-
tivities, some are consumed much more
rapidly than others, and their concentrations
change correspondingly faster. Thus the com-
position of the hydrocarbon component of air
after an extended period of exposure to
sunlight is quite different from the pre-
exposure composition. Stephens and Burleson1
compared the hydrocarbon composition of an
-------
air sample collected in well-aged photo-
chemical air pollution in Riverside, California,
with that of early morning samples in the
same vicinity. They found the more reactive
components to be reduced by more than 90
percent relative to some of the less reactive
compounds,1 as shown in Table 2-1. Earlier,
Neligan analyzed samples of synthetic atmos-
pheres containing diluted automobile exhaust
gases before and after simulated sunlight irra-
diation in the laboratory with similar results,2
as shown in Table 2-2.
The rate of consumption of each of the
individual hydrocarbons in the sum of the
rates of the various reactions by which it is
consumed. Rates of these reactions depend in
principle upon the concentrations of the in-
dividual hydrocarbon and the attacking
species, and can be estimated (within reason-
able limits) by established methods of
theoretical chemical kinetics. A detailed treat-
ment of the prediction of gas-phase reaction
rates is provided by Benson,3 who developed
methods of estimating rate parameters for
many types of reactions involving carbon
compounds, including hydrocarbons. These
methods have been tested and found sur-
prisingly accurate in a substantial number of
reactions for which experimental observations
were available. Utilizing these or similar
techniques, it should be possible in the near
future to develop accurate and scientifically
well-based means of accounting for the
detailed chemical behavior of hydrocarbon
Table 2-1. HYDROCARBON CONCENTRATIONS IN MORNING AND
AFTERNOON AMBIENT AIR SAMPLES,
RIVERSIDE, CALIFORNIA, FALL 19681
Hydrocarbon
Methane
Ethane
Propane
Acetylene
Ethylene
Propylene
Methyl acetylene
1 ,3-Butadiene
1-Butene
Isobutene
trans-2-Eutene
cw-2-Butene
2-Methyl-l-butene
Cyclopentene (with 2-Methyl-l ,
3-butadiene)
trans-2-Pentene
2-Methyl-2-butene
Isobutane
Butane
Isopentane
Pentane (with 3-methyl-l-butene)
Cyclopentane
2,2-Dimethyl butane (with 1-pentene)
2,3-Dimethyl butane
2-Methyl pentane (with cw-2-pentene)
3-Methyl pentane
Hexane
Concentration, ppm
7:30 a.m. , PST 4:10 p.m. , PST
Sept. 24, 1968 Oct. 24, 1968
2.355 2.530
0.0636 0.0722
0.0188 0.0499
0.0770 0.0420
0.0656 0.0179
0.0192 0.0013
0.0026 0.0012
0.0036 0.0003
0.0026 0.0003
0.0052 0.0020
0.0014 <0.0002
0.0014 <0.0002
0.0024 0.0004
0.0044 0.0008
0.0024 <0.0002
0.0026 <0.0002
0.0080 0.0197
0.0276 0.0620
0.0392 0.0412
0.0224 0.0214
0.0032 0.0024
0.0016 0.0009
0.0038 0.0019
0.0124 0.0096
0.0084 0.0061
0.0090 0.0083
2-3
-------
Table 2-2. HYDROCARBON CONCENTRATIONS OF IRRADIATED AND
NONIRRADIATED SYNTHETIC ATMOSPHERES CONTAINING
DILUTED AUTOMOBILE EXHAUST GASES2
Diluted -nonirradiated
Sample No.
Fuel, bromine No.
Exhaust to chamber
dilution ratio
Components
Paraffins
Propane
2-Me-Propane
w-Butane
2-Me-Butane
fl-Pentane
2-Me-Pentane
2,3-Me2-Butane
n-Hexane
2,4-Me2-Pentane
2-Me-Hexane
3-Me2-Hexane
2,3-Me2-Pentane
2,2,4-Me3-Pentane
Total
Olefins
Propene
2-Me-l-Propene
1-Butene
trans-2-Butene
cw-2-Butene
1-Pentene
2-Me-l-Butene
cw-2-Pentene
2-Me-2-Butene
4-Me-l-Pentene
1-Hexene
2-Me-l-Pentene
trans-2-Hexene
ctt-3-Hexene
cw-2-Hexene
Cyclopentene
Total
Acetylenes
Acetylene
Me-Acetylene
Total
Diolefins
Propadiene
1 ,3-Butadiene
Total
1
20
1-500
2
30
1-500
3
30
1-250
4
20
1-250
Diluted-irradiated
1A
20
1-500
2A
30
1-500
3A
30
1-250
4A
20
1-250
Concentration, ppm
0.03
0.02
0.14
0.07
0.03
0.05
0.02
0.01
0.37
0.11
0.04
0.02
0.005
0.02
0.01
0.01
0.03
0.005
0.005
0.26
0.45
0.02
0.47
0.02
0.02
0.03
0.01
0.13
0.10
0.04
0.05
0.02
0.02
0.01
0.01
0.03
0.45
0.13
0.06
0.01
0.01
0.005
0.03
0.02
0.06
0.005
0.02
0.005
0.01
0.01
0.38
0.62
0.02
0.64
_
0.04
0.04
0.02
0.03
0.28
0.19
0.07
0.10
0.02
0.05
0.03
0.05
0.03
0.87
0.29
0.12
0.03
0.01
0.01
0.03
0.02
0.10
-
0.02
0.04
0.02
0.01
0.70
1.32
0.04
1.36
0.06
0.06
0.04
0.02
0.24
0.14
0.04
0.12
0.05
0.02
0.01
0.05
0.03
0.76
0.27
0.09
0.02
0.01
0.005
0.02
0.01
0.05
0.01
0.01
0.005
0.01
0.51
0.93
0.03
0.96
0.04
0.04
0.04
0.02
0.15
0.08
0.03
0.06
0.02
0.40
0.04
0.01
0.005
0.01
0.005
0.01
0.08
0.43
0.005
0.44
0.005
0.01
0.02
0.02
0.12
0.08
0.03
0.05
0.02
0.02
.
0.03
0.39
0.04
0.01
0.01
0.005
0.07
0.55
0.01
0.56
_
0.05
0.02
0.22
0.13
0.05
0.08
0.02
0.02
0.01
0.07
0.05
0.72
0.11
0.03
0.03
-
0.01
0.005
0.01
_
—
0.20
1.04
0.03
1.07
0.01
0.01
0.03
0.02
0.19
0.11
0.04
0.09
0.02
0.02
0.01
0.03
0.02
0.58
0.11
0.02
0.02
_
0.005
-
0.16
0.79
0.02
0.81
0.01
0.01
2-4
-------
Table 2-2 (Continued). HYDROCARBON CONCENTRATIONS OF IRRADIATED AND
NONIRRADIATED SYNTHETIC ATMOSPHERES CONTAINING
DILUTED AUTOMOBILE EXHAUST GASES2
Diluted -nonirradiated
Sample No.
Components
Aroma tics
Benzene
Toluene
Total
1
2
3
4
Diluted -irradiated
1A
2A
3A
4A
Concentration, ppm
0
0
0
05
07
12
0.07
0.14
0.21
0.18
0.34
0.52
0
0
0
.14
.19
.33
0.06
0.09
0.15
0.08
0.16
0.24
0.12
0.22
0.34
0
0
0
11
19
30
Unresolved compounds
Ethanea
Ethylene
2,2-Me2-Butane
trans-2-Pentene
4-Me-2-Pentene
3-Me-Pentane
Total
Cyclics
Cyclopentane
Me-Cyclopentane
Cyclohexane
Total
Total hydrocarbons
recovered
0.32
0.02
0.03
0.37
0.01
0.01
1.62
0.33
0.03
0.02
0.38
0.01
0.02
0.01
0.04
2.14
0.93
0.03
0.04
1.00
0.02
0.04
0.06
4.57
0.69
0.02
0.05
0.76
0.02
0.03
0.05
3.41
0.34 0.32 0.69
0.005 0.005 0.01
0.02 0.02 0.03
0.37 0.35 0.73
0.01
0.01
1.46
0.005
0.01
0.02
0.04
1.65
0.01
0.02
0.01
0.04
3.11
0.58
0.01
0.04
0.63
0.01
0.01
0.02
2.51
aNot detectable, but may be present in small quantities.
gases in urban atmospheres. This will include
the prediction of rates of development of sec-
ondary contaminants as well as rates of con-
sumption of the various hydrocarbon species
in the air. First steps in this direction have
already been indicated by Wayne and Ernest4
with the development of a computer sim-
ulation model for the kinetics of photo-
oxidation of propylene.
2. Expected Photooxidation Products
The ultimate products of photooxidation
of hydrocarbons in urban air, if a captured
parcel of air were to be irradiated by sunlight
for a long enough time, would probably be
carbon dioxide and water vapor. From the
standpoint of ordinary urban atmospheres,
these products are of no interest because,
aside from their abundance in the natural
global atmosphere, no air parcel remains in
the urban atmosphere long enough for its
hydrocarbons to be fully oxidized. The
products of concern in photochemical air pol-
lution are all intermediate products of the
complex, i.e., all are capable of further reac-
tion and degradation. They differ in that
some react only very slowly and therefore ac-
cumulate to appreciable concentrations only
if formed at appreciable rates, whereas others
react rapidly and are therefore efficiently
scavenged, even though their rates of forma-
tion may be high. In the following paragraphs,
the confirmed and expected (intermediate)
products of the photochemical complex are
discussed, beginning with those having the
longest lives and highest concentrations.
a. Commonly Recognized Products in
Photochemical Air Pollution
(1) Ozone.—Best known of the compounds
generated in photochemical air pollution is
ozone (03), a highly reactive and toxic form
of oxygen. Because this substance is one of
the group of secondary contaminants known
2-5
-------
as photochemical oxidants, it is discussed in
greater detail in the companion document,
AP-63, Air Quality Criteria for Photochemical
Oxidants. It is important to observe, however,
that ozone plays a significant role in the
degradation of hydrocarbons, especially the
olefinic hydrocarbons. Further, it must be
noted that the level and composition of the
hydrocarbons in the urban atmosphere, in
conjunction with levels of oxides of nitrogen
and meteorological factors (including sun-
shine), determine the concentrations and
dosages of ozone that will be reached in
photochemical episodes, as they do those of
all the secondary contaminants.
(2) Nitrogen Dioxide.-Nitrogen dioxide in
photochemical smog is generated primarily by
the photooxidation of nitric oxide, which is
facilitated by the free radicals generated by
photolysis of aldehydes and other secondary
contaminants, as well as by the reactions of
hydrocarbons with oxygen atoms and other
chemical species. This substance will be dis-
cussed in a forthcoming air quality criteria
document dealing with nitrogen oxides.
(3) Aldehydes.-Aldehydes are major
products in the photooxidation of hydro-
carbons and in the individual reactions of
hydrocarbons with ozone, oxygen atoms, or
free radicals. They are dissociated by the
ultraviolet fraction of sunlight with the
production of alkyl radicals, formyl radicals,
and hydrogen atoms. Because the chemical
bond between the hydrogen atom and the
carbonyl group is weaker than most carbon-
hydrogen bonds in hydrocarbon molecules,
aldehydes are relatively more susceptible to
hydrogen abstraction reactions, which yield
acyl radicals or alkyl radicals and carbon
monoxide, according to the equations:
CH3CHO + RO-» CH3CO + ROM (2-1)
CH3CO + M -> CH3 + CO + M (2-2)
In urban air, however, the photolysis and all
other aldehyde-consuming reactions such as
(2-1) are not collectively rapid enough to
prevent their accumulation to levels as high as
2-6
about 0.2 ppm in photochemical air pol-
lution.5
Specific aldehydes found in urban air are
formaldehyde (HCHO) and acrolein
(CH2CHCHO). Formaldehyde usually ac-
counts for about 50 percent of the estimated
total aldehydes in polluted air, and acrolein
for perhaps 5 percent.6'7 The chemical identi-
ty of the remaining aldehydes in urban air is
unknown, but higher aliphatic aldehydes such
as acetaldehyde (CH3CHO) are probably
present.
(4) Peroxyacyl Nitrates.-Peroxyacyl
nitrates, R(CO)OONO2 are in the main proba-
bly products of the reaction of peroxyacyl
radicals with nitrogen dioxide, as in equation
(2-3),
R(CO)OO + NO2 = R(CO)OONO2
(2-3)
although other reactions, such as acylate
radicals with nitrogen trioxide, as in equation
(2-4), are not completely excluded.
R(CO)O + NO3 = R(CO)OONO2
(2-4)
These compounds are among the products of
photochemical air pollution that oxidize
certain standard reducing agents and are dis-
cussed in AP-63, Air Quality Criteria for
Photochemical Oxidants. It should be noted
that the most abundant member of the class,
peroxyacetyl nitrate (frequently abbreviated
PAN) is the only one usually detected in
atmospheric samples, although smaller
amounts of higher homologues are probably
present.
PAN may absorb ultraviolet light from the
sun, with probable production of free
radicals. The specific products of the primary
step are not known.
b. Products of Photooxidation of Hydro-
carbons in Experimental Studies
Laboratory irradiations of synthetic atmos-
pheres provide valuable information in
understanding the photochemistry of polluted
air because they facilitate the study of rates
-------
and products of reaction of individual hydro-
carbons or of mixtures with carefully control-
led composition. Further, they can be used to
determine quantitatively the relations be-
tween reaction rates or product yields and
such environmental factors as light intensity,
temperature, humidity, and initial reactant
concentrations. In many such studies the
initial concentrations employed have been
larger than those usually found in urban
atmospheres, but still small enough to give a
reasonably good indication of the relations to
be expected under conditions of the ambient
atmosphere.
The many studies on irradiated synthetic
atmospheres containing hydrocarbons and
oxides of nitrogen were thoroughly reviewed
by Altshuller and Bufalini in 1965.8 From
that review and reports of subsequent
studies, 9'l ° it appears that the carbon atoms
of photooxidized hydrocarbons can be well
accounted for in terms of aldehydes, ketones,
carbon monoxide, carbon dioxide, alkyl
nitrates, and peroxyacyl nitrates, except that
acceptable carbon balances have not been
achieved for the photooxidation of aromatic
hydrocarbons.
The chemical behavior of irradiated atmos-
pheres containing auto exhaust has been
shown to resemble rather closely that of
photooxidized mixtures of hydrocarbons and
nitric oxide. Ozone and peroxyacyl nitrates
are formed, but do not accumulate until nitric
oxide is nearly consumed, whereas the alde-
hydes are produced from the beginning of the
irradiation and are always found as major
products.
(1) Ozone.—Appreciable ozone concentra-
tions have been observed to result from
photooxidation (with nitric oxide or nitrogen
dioxide) of many olefins, paraffins (not in-
cluding methane), and alkylbenzenes. At con-
centrations of 3 ppm hydrocarbons and 1,230
Mg/m^ (1 ppm) nitrogen oxide, Schuck and
Doyle11 measured ozone levels between 200
and 1,960 jug/m3 (0.1 and 1 ppm) for 25
hydrocarbons, as listed in Table 2-3. At the
selected levels of initial concentrations, most
of the olefins tested yielded more than 980
Mg/m^ (0.5 ppm), while most of the paraffins
yielded less than that amount. At other levels
of initial concentrations, there can be little
doubt that different results would be obtain-
ed. Altshuller9 et al. have shown, for
example, that in experiments with 3,460
jug/m^ (2 ppm) propylene the optimum nitric
oxide level for ozone production is about
1,230 Mg/m3 (1 ppm), which yields 2,160
3 (1.1 ppm) ozone; while, for 6,870
^ (3 ppm) butane, the optimum nitric
oxide level is about 125 Mg/rn^ (0.1 ppm),
which yields about 1,760 Mg/m3 (0.9 ppm)
ozone.
A simple relation that would permit the
prediction of ozone yields, either absolute or
relative, from initial concentrations in irra-
diation experiments has not yet been dis-
covered. There does appear to be a practical
limit to the concentration of ozone that can
be generated in this way; regardless of what
hydrocarbon or mixture of hydrocarbons
serves as the substrate for photooxidation and
regardless of what initial concentrations or
light intensities have been provided, no
chamber irradiation has yet produced ozone
in excess of 2,940 Mg/m3 (1-5 ppm), and a
few have reached 1,960 Mg/m3 (1-0 ppm). In
urban atmospheres, a level of 1,960 Mg/m
(1.0 ppm) has not yet been recorded.
(2) Nitrogen dioxide — All irradiation
chamber photooxidations in which nitric ox-
ide is introduced as a reactant show con-
version of nitric oxide to nitrogen dioxide at
rates dependent on the reactant levels and the
hydrocarbon reactivity as well as such exper-
imental variables as light intensity and tem-
perature. Ordinarily the nitrogen dioxide con-
centration reaches a maximum and then
declines somewhat less rapidly than it had
previously risen. The time required for
nitrogen dioxide concentration to reach this
maximum is always less than the time re-
quired for ozone to reach a maximum. Some
examples are seen in Table 2-3. The degree of
conversion (i.e., the ratio of highest observed
nitrogen dioxide concentration to the initial
2-7
-------
Table 2-3. OZONE LEVELS GENERATED IN PHOTOOXIDATIONa
OF VARIOUS HYDROCARBONS WITH OXIDES OF NITROGEN* 1
Hydrocarbon
Isobutene
2-Methyl-l ,3-butadiene
trans-2-Butene
3-Heptene
2-Ethyl-l-butene
1 ,3-Pentadiene
Propylene
1,3-Butadiene
2,3-Dimethyl-l, 3-butadiene
2,3-Dimethyl-2-butene
1-Pentene
1-Butene
cu-2-Butene
2,4,4-Trimethyl-2-pentene
1,5-Hexadiene
2-Methylpentane
1 ,5-Cyclooctadiene
Cyclohexene
2-Methylheptane
2-Methyl-2-butene
2,2,4-Trimethylpentane
3-Methylpentane
1,2-Butadiene
Cyclohexane
Pentane
Methane
Ozone level, ppm
1.00
0.80
0.73
0.72
0.72
0.70
0.68
0.65
0.65
0.64
0.62
0.58
0.55
0.55
0.52
0.50
0.48
0.45
0.45
0.45
0.26
0.22
0.20
0.20
0.18
0.0
Time, min
28
45
35
60
80
45
75
45
45
70
45
45
35
50
85
170
65
35
180
38
80
100
60
80
100
aHydrocarbon concentration (initial) 3 ppm; oxide of nitrogen (NO
or NO2, initial) 1 ppm.
total of both oxides) is often near 100 per-
cent, especially in systems in which the reac-
tions are rapid, as with some of the more
reactive olefins and a nitric oxide concentra-
tions near the optimum for ozone production.
(3) Aldehydes and ketones — In all irra-
diation chamber experiments in which
products have been appropriately analyzed,
carbonyl compounds have been found among
the major products. Table 2-4 shows yields of
these compounds for a number of initial
hydrocarbons, as tabulated by Altshuller and
Bufalini.8 The yields are shown in relation to
initial concentrations in the irradiation cham-
ber; therefore, yields relative to hydrocarbons
reacted would be greater than those shown
(although perhaps, in some cases, no much
greater).
Formaldehyde can be seen (from Table
2-4) to be the most important carbonyl
2-8
product identified from many of these com-
pounds, forming half or more of the total for
each of the 1-alkenes. Acetaldehyde is im-
portant as a product from propylene, cis- and
^rafts-2-butenes, and 2-methyl-2-butene, but
not from ethylene, isobutene, or
1,3-pentadiene and 2-methyl-l,3 pentadiene;
acetone, from isobutene, 2-methyl-2-butene,
and 2,3-dimethyl-2-butene. For the olefins
cited, the results are consistent with the view
that a large fraction of the hydrocarbon mol-
ecules that react yield products typical of
their reaction with ozone. It appears, how-
ever, that some of the formaldehyde ultimate-
ly produced may result from the further reac-
tions of other intermediate species in the
system, including higher aldehydes.
With alkybenzenes, the yield of carbonyl
compounds is smaller,12 ranging from 0.1 to
-------
Table 2-4. YIELDS OF CARBONYL COMPOUNDS IN EXPERIMENTAL PHOTOOXIDATION
OF HYDROCARBONS WITH OXIDES OF NITROGENS
Hydrocarbon
Ethylene
Propylene
1-Butene
Isobutene
trans-2-butene
cw-2-butene
1 ,3-Butadiene
1-Pentene
2-Methyl-2-butene
1,3-Pentadiene
2-M ethyl- 1 ,3-Pentadiene
cz>3-hexene
2,3-Dimethyl-2-butene
Cyclohexene
2,3-Dimethyl-l ,3-butadiene
3-Heptene
Toluene
p-Xylene
o-Xylene
m-Xylene
1 ,3,5-Trimethylbenzene
1 ,2,4,5-Tetramethylbenzene
Moles/mole of initial hydrocarbon
Formaldehyde
0.35a, 0-45b
0.32C, 0.45d
0.40a, 0.45e
0.45a, 0.4f
0.7a, 0.6b
0.3-0.45d, 0.6e,
0.6f, 0.5-0.78
0.35f, 0.35h
0.6a, 0.6e,0.5f
0.55a
0.5a,0.3e
0.65a
0.55a
0.25a
0.4e
0.65a
0.8a
0.1 5a
0.1 5k
0.1 5k
Acetaldehyde
<0.01C
0.4a,0.15-0.2e
0.01e
1.40a, 1.5f,
0.9-1. 2h
0.9a, 0.8-1. Od
~0.01e
0.75a, 0.4-0.56
Acrolein
0.55a, 0.251,
0.2e
0.3 5a
0.4a
•
Acetone
0.03-0.056
0.6a, 0.5d
0.68, 0.25-0.46
~0.02e
0.45a, 0.3-0.46
1.25a, 0.8-0.98,
1.4J
Total or other
aldehydes
0.9a,0.5f
1.0b, 0.98
0.4a
1.3a
0.9a
1.0b, 0.9-1. Od
0.9-1.08
1.3a
1.2a
O.llk
0.26b
0.22b
0.25b, 0.3k
0.6b, 0.3k, 0.41
0.45b
aSchuck and Doyle.11
bStephens and Scott.12
c Altshuller and Cohen.13
dStephens14 et al.
eSchuck15etal.
fSigsby16etal.
Sstephens.17
"Tuesday.18
i Altshuller and Bufalini.8
JBufalini and Altshuller.19
kLeighton.20
Vrbaski and Cvetanovic.
0.3 relative to the hydrocarbon reacted.
Again, most of the carbonyl product is
formaldehyde, with smaller amounts of
acetaldehyde reported.
Paraffins also yield carbonyl compounds
upon photooxidation. Using 3 ppm of hydro-
carbon with 0.6 ppm of nitrogen oxides (ni-
trogen oxide composition not specified),
Altshuller9 et al. have found formaldehyde,
acetaldehyde, propionaldehyde, butanone
(methyl ethyl ketone), and a component
which may have been acetone; butyraldehyde,
or both. Alkanes tested in this study were
butane, isopentane, 2-methylpentane,
3-methylhexane, 2,4-dimethylhexane,
«-nonane, and methylcyclohexane. About 70
percent of isopentane consumed could be ac-
counted for as carbonyl products.
(4) Organic nitrates and nitrites - Of the
nitrogen-containing organics produced in irra-
diation studies, peroxyacetyl nitrate is clearly
the most common and most abundant. Table
2-9
-------
2-5 shows maximum yields of PAN and alkyl
nitrates in irradiation studies with various
olefins and alkylbenzenes. Yields of PAN
were less than 0.25 mole per mole of initial
hydrocarbon, with the exception of trans
-2-butene and 2,3-dimethyl-2-butene, for
which some yields larger than 0.5 were found.
Yields of alkylnitrates were uniformly 0.25 or
less.
On photooxidation of alkanes (butane,
isopentane, 2-methylpentane, 3-methyl-
hexane, 2,4-dimethylhexane, «-nonane, and
methylcyclohexane), yields of peroxyacetyl
nitrate and of alkyl nitrates were about 1 per-
cent or less of the initial hydrocarbon con-
centration, which was usually 3 ppm in these
tests.9 Individual alkyl nitrates identified
were methyl nitrate, ethyl nitrate, propyl ni-
trate, and isopropyl nitrate. Very small
amounts of alkyl nitrites have been reported
as products in chamber irradiations,15 and ni-
tromethane has been found in experiments
with reduced oxygen concentrations.1 8
(5) Minor products - Small yields of
epoxides, alcohols, esters, and peroxides have
been reported.8 Carbon monoxide is some-
times formed in appreciable yields11'18 (0-2
to 0.4, relative to initial hydrocarbon), and
carbon dioxide has been found in yields up to
0.25, with 2-butene as the substrate.18 These
products probably have been formed in
various experiments in which they were not
detected, either because the necessary analysis
was not done or because the concentrations
were below the limits of detection of tech-
niques applied.
D. ESTIMATION OF HYDROCARBON
EMISSIONS
1. Emission Levels of Hydrocarbons from
Natural Sources
The presence of natural hydrocarbons in
the atmosphere, particularly methane, only
recently has been established by measure-
ment.24 Although most of these hydro-
carbons arise from biological sources, small
and highly localized quantities of methane
and a few other lower-molecular-weight
hydrocarbons are attributable to geothermal
areas, coal fields, and natural gas and petro-
leum fields, and natural fires.
Table 2-5. YIELDS OF PEROXYACYL NITRATES AND
ALKYL NITRATES OBSERVED IN PHOTOOXIDATION
OF VARIOUS OLEFINS AND ALKYLBENZENESS
2-10
Hydrocarbon
Ethylene
Propylene
1-Butene
Isobutene
trans-2-Butene
cw-2-Butene
cw-3-Hexene
fran.y-3-Hexene
2,3-Dimethyl-2-butene
p-Kylene
o-Xylene
m-Xylene
1 ,3,5-Trimethylbenzene
1 ,2,4,5-Tetramethylbenzene
Highest
PAN
0
0.25
0.11
0.23
0.51
0.16
0.16
0.20
0.69
0.08
0.08
0.11
0.16
0.14
yield, relative to initial hydrocarbon
Alkyl nitrate
0.10
0.15
0.12
0.12
0.14
0.25
0.15
aStephens and Scott.12
bTuesday.22
cStephens.17
"Kopczynski.2^
-------
Various estimates have been made of the
contributions of these natural sources to
hydrocarbons in the atmosphere. Koyama has
estimated the production rate of methane to
be about 3 x 10^ tons per year.25 Of this
amount, the greatest quantity arises from the
decomposition of organic matter at the
earth's surface. Ehhalt26 and Robinson and
Robbins,2 7 however, conclude that this is a
very conservative estimate, since methane
generated in swampy and tropical areas was
not included.
Volatile terpenes and isoprene constitute a
separate class of hydrocarbons for which
worldwide natural emission rates have been
estimated. Rasmussen and Went28 have
estimated the rate of production of such com-
pounds to be about 4.4 x 10^ tons per year.
Hazes associated with vegetation in many
areas of the world, such as the blue haze of
the Appalachian Mountain region, have been
ascribed to photochemical aerosol formation
caused by these substances.
From these estimates, it appears that
production of methane from natural sources
is roughly equivalent on a weight basis to that
of the higher-molecular-weight volatile
organics. There is a great difference, however,
in their natural background levels, which
implies a related difference in the lifetimes of
these materials in their global cycles.
There is substantial agreement on the
natural background concentration of methane
in the atmosphere based upon different
methods of measurement and the locations of
such measurements. Junge2 9 indicates that
the worldwide range is 0.8 to 1.1 mg/m^ (1.2
to 1.5 ppm). This is seen both in optical
measurements such as reported by Fink30 et
al. and Goldberg and Muller,31 and in
measurements made by gas chromatography.
From samples taken in nonurban atmos-
pheres, Stephens and Burleson32 report
methane values averaging 0.93 mg/m^ (1.39
ppm) over a southern California mountain
area during desert winds; they reported simi-
lar values for Hawaii. Ethane, ethylene, and
acetylene were found at 0.003 ppm or less.
Cavanagh3 3 et al. found a mean methane con-
centration of 1.1 mg/m^ (1.6 ppm) with
butane at 0.14 mg/m^ (0.06 ppm) at Point
Barrow, Alaska, whereas Swinnerton34 et al.,
during an oceanographic cruise between
Washington, D. C., and Puerto Rico, reported
a mean methane concentration of 0.83
mg/m^ (1.25 ppm). Furthermore, these latter
authors found that the methane content of
ocean water was in equilibrium with that
found in the atmosphere.
The lowest hydrocarbon concentrations
measured in urban atmospheres are in the
same range as the values previously reported
for methane in nonurban areas. Data on urban
hydrocarbon concentrations were obtained
from special gas chromatographic measure-
ments by Altshuller3 s > 36 et al., and from
total hydrocarbon measurements by flame
ionization analyzers from the National Air
Surveillance Network, the State of California
SCAN network, and the Los Angeles County
Air Pollution Control District.
Few measurements of low-molecular-
weight hydrocarbons other than methane
have been made in nonurban areas, and no
accurate statement can be given as to ranges
of concentrations for those compounds.
Butane concentrations measured at Point Bar-
row, Alaska, by Cavanaugh33 et al., and
ethane, ethene, and acetylene concentrations
measured in southern California mountain
areas by Stepehns and Burleson3 2 were two
to three orders of magnitude lower than con-
centrations of methane.
Higher-molecular-weight hydrocarbon and
other volatile organic compound concentra-
tions have been estimated by Rasmussen and
Went2 8 on the basis of sensitive gas chroma-
tographic measurements of alpha- and beta-
pinene. Pinene content averaged about 0.01
ppm.
Using his own methane production figures
and a total instantaneous mass of 4.3 x 10^
g in the atmosphere, Koyama25 calculated an
atmospheric average life of 20 years for
methane. Ehhalt26 and Robinson and
Robbins27 consider this an overestimate and
suggest that an average life of only a few
years is more likely. In contrast with the
2-11
-------
estimated life of methane, the lifetime of
higher-molecular-weight natural hydrocarbons
may be on the order of days to months.
The principal implications of the reported
information on abundance of hydrocarbons
from natural sources would appear to relate
to atmospheric sampling. Since methane is
photochemically nonreactive and the other
hydrocarbons from natural sources are too
low in concentration to be of concern in
urban areas, the relatively high concentration
of methane as compared to other hydro-
carbons of photochemical significance from
technological sources makes the use of analyt-
ical methods which are specific for methane
of critical importance.
In summary, it appears that in nonurban
air, background levels of methane are ordi-
a.
narily in the range of 0.7 to 1.0 mg/m3 (1-0
to 1.5 ppm), whereas other hydrocarbons, in-
cluding various terpenes, are each present at
levels less than 0.1 ppm.
2. Emission Levels of Hydrocarbons
from Technological Sources
National Emisison Estimates
Total nationwide emissions of hydro-
carbons and related organic compounds to the
atmosphere for the year 1968, according to
U. S. Public Health Service estimates, amount-
ed to approximately 32 x 10" tons.37 Table
2-6 shows the distribution of this total by
major source categories, including percent of
relative contribution. Motor vehicles (49 per-
cent), industrial processes (14 percent), and
solvent usage (10 percent) constitute by far
the most significant sources. According to
Table 2-6. ESTIMATES OF HYDROCARBON EMISSIONS37
BY SOURCE CATEGORY, 1968^
Source
Transportation
Motor vehicles
Gasoline
Diesel
Aircraft
Railroads
Vessels
Nonhighway use, motor fuels
Fuel combustion-stationary
Coal
Fuel oil
Natural gas
Wood
Industrial processes
Solid waste disposal
Miscellaneous
Forest fires
Structural fires
Coal refuse
Organic solvent evaporation
Gasoline marketing
Agricultural burning
Total
Hydrocarbon emissions,
1 06 tons/yr
16.6
0.7
4.6
1.6
8.5
32 0
15.6
0.3
0.3
0.1
0.3
0.2
0.1
Negligible
0.4
2.2
0.1
0.2
3.1
1.2
1.7
15.2
0.4
Percent of total
emissions
51.9
2.2
14.4
5.0
26.5
100.0
48.7
1.0
1.0
0.2
1.0
0.7
0.3
Negligible
1.2
6.9
0.2
0.6
9.7
3.8
5.3
47.5
1.2
aThese emission estimates are subject to revision as more refined information becomes
available.
2-12
-------
Mason38 et al., who reported similar informa-
tion for the year 1966, approximately 63 per-
cent of the total hydrocarbon emissions arise
from urban areas.
b. Regional Emission Estimates
Hydrocarbon emission estimates have been
made for 22 major metropolitan areas in the
United States.38 Although information is still
quite fragmentary, emissions by area range
from 0.05 to 1.3 million tons per year. Table
2-7 shows this information for each of the
available areas.
Perhaps of greater significance are the data
given in Table 2-8, which provides estimates
of the percent of contribution by source
catetory to total hydrocarbon emissions in
the 22 metropolitan areas included in the
study referred to previously. The most signif-
icant finding was that while transportation
sources accounted for a higher proportion of
total hydrocarbon emissions in these metro-
politan areas than in the Nation as a whole,
the range was extremely wide: 37 to 99 per-
cent.
3. Technological Sources of Hydrocarbons
Hydrocarbon pollutants originate primarily
from the inefficient combustion of fuels,
particularly the more volatile fuels, such as
gasoline, and from the use of hydrocarbons as
process raw materials, such as solvents. The
sources of hydrocarbons generally are treated
in terms of mobile and stationary sources be-
cause of the differing control strategies re-
quired for each in terms of the engineering,
technological, economic, and legal factors
that must be taken into account. Mobile
sources are chiefly gasoline-powered vehicles,
but also include other types of vehicles, in-
cluding aircraft. Stationary sources primarily
Table 2-7. SUMMARY OF HYDROCARBON EMISSIONS FROM
22 METROPOLITAN AREAS IN THE UNITED STATES,
1967-196837
Location3
Los Angeles
Philadelphia
San Francisco
Detroit
Washington, D. C.
Boston
Pittsburgh
St. Louis
Hartford
Dallas
Seattle
Houston
Milwaukee
Cincinnati
Buffalo
Kansas City
Providence
Indianapolis
San Antonio
Dayton
Louisville
Birmingham
Population
7,100,000
5,500,000
4,500,000
4,090,000
2,700,000
2,700,000
2,520,000
2,410,000
2,290,000
2,187,000
2,010,000
2,000,000
1,730,000
1,660,000
1,300,000
1,230,000
1,200,000
1,050,000
982,000
880,000
840,000
750,000
Area,
mi ^
41,000
4,590
7,000
2,680
2,270
1,280
3,050
4,500
2,650
8,000
15,000
7,800
2,630
2,620
1,470
3,200
1,000
3,080
7,320
2,310
1,390
1,120
Emissions,
103 tons/yr
1,270
470
790
480
310
87
95
330
120
143
170
292
83
55
130
230
54
74
71
64
46
64
aDefined on the basis of Standard Metropolitan Statistical Areas; these may include
substantial areas which are rural in nature and thus of low population density.
2-13
-------
Table 2-8. PERCENT OF TOTAL AREA HYDROCARBON
EMISSIONS BY SOURCE CATEGORY,
22 METROPOLITAN AREAS IN UNITED STATES38
Source category
Transportation
Average
Range
Motor vehicles
Average
Fuel combustion
Average
Range
Power plants
Average
Industrial
Average
Domestic
Average
Process losses
Average
Range
Refuse disposal
Average
Range
Percent of total area hydrocarbon emissions
70.2
37-99a
66.9
2.8
0- 18
0.1
2.2
0.5
19.9
1 -63
7.1
0.4 - 26
aMore recent estimates indicate that the maximum percent of
total area hydrocarbon emissions in the transportation category is
somewhat less than 99.
include petroleum and petrochemical opera-
tions and solvent usage, with some contribu-
tion from waste burning.
a. Carbureted Gasoline Engines
Carbureted gasoline internal combustion
engines (i.e., conventional automobile
engines) emit air pollutants from four
sources: engine exhaust, crankcase blowby,
carburetor, and fuel tank. According to a
survey conducted on a large number of un-
controlled automobiles, about 60 percent of
the unburned hydrocarbons comes from the
engine exhaust; another 20 percent of un-
burned hydrocarbons escapes from crankcase
blowby; and an additional 10 percent each
results from the evaporation of gasoline from
the carburetor and from the fuel tank.39
Literally hundreds of different hydrocarbons
are emitted, primarily in trace quantities.40
These emissions include organic acids, olefins,
and carbonyl compounds.
2-14
The quantity and reactivity (or photo-
chemical potential) of the unburned hydro-
carbons, as well as the quantity of nitric ocide
and carbon monoxide emitted from the auto-
mobile exhaust, depend on the engine opera-
tion mode41 (e.g., idle, acceleration, cruising,
deceleration), the engine parameters42 (e.g.,
compression ratio, spark advance, air-fuel
ratio), and the fuel composition.43
b. Diesel Engines
The emission from diesel exhaust differs
from that of carbureted gasoline engines,
mainly because carbureted gasoline engines, in
general, operate with a deficiency of com-
bustion air, whereas the diesel engine normal-
ly operates with a substantial excess of com-
bustion air and with a substantially higher
compression ratio.
The emission of urburned hydrocarbons
from diesel exhaust is substantially lower than
that from gasoline engines. The higher emis-
sion of aldehydes (including formaldehyde),
-------
however, may be partially responsible for the
distinctive diesel exhaust odor.44- 4S Air pol-
lution from crankcase blowby is negligible
with diesel engines, since the diesel compress-
es only air instead of an air and fuel
mixture.41 Practically no air pollution results
from evaporation from the fuel system be-
cause the volatility of diesel fuel is very low.
c. Gas Turbines and A ircraft
Jet Engines
The combustion process in gas turbines and
aircraft jet engines differ from that in gasoline
and diesel engines mainly in that it occurs at
constant pressure (continuous process), low
compression ratio, and with a very large
excess of combustion air. In general, the ex-
haust emission is low in unburned hydro-
carbons.4 6 The main source of pollution from
gas turbines and aircraft jet engines is the ex-
haust. Pollution resulting from evaporation
from the fuel tank is minimal because fuels
with low volatility are generally used.
d. Stationary Sources
The major stationary sources of hydro-
carbons in the United States are the produc-
tion, processing, storage, and transfer of
petroleum products (principally gasoline), and
the loss of organic solvents. Relatively smaller
quantities arise from the combustion of fuels
and refuse.46
Potential sources of hydrocarbon emissions
in petroleum production and processing in-
clude: oil field and refinery leakage, gasoline
storage tanks, gasoline loading facilities, air
blowing of asphalt, blow-down systems,
catalyst regenerators, processing vessels,
flares, compressors, pumps, vacuum jets,
waste effluent handling equipment, and
turnaround operations.
Gasoline distribution and marketing
systems emit hydrocarbon vapors from tank
truck loading racks, service station tank filling
operations, and automobile tank filling opera-
tions.
Organic solvents are derived mainly, but
not exclusively, from petroleum. They are
used in many kinds of operations. Chemical,
drug, and pharamceutical manufacturing
plants can emit organics from those opera-
tions involving the use of organic solvents.
Rubber and plastic product manufacturing
often involves the use of organic solvent-based
adhesives and other solvents that lead to
organic emissions. Paints, varnishes, lacquers,
undercoatings, etc., are composed of 40 to 80
percent organic solvents that evaporate during
or after the application of the coating. De-
greasing of manufactured metal items can
cause significant organic emissions. Vapor-
phase degreasing with trichlorethylene (a
hydrocarbon derivative) is the most widely
used method, but spray degreasing with other
solvents is also used. Dry cleaning of clothing
utilizes organic solvents and contributes to
emissions. The processes by which solvents
and solvent-containing materials (e.g., paints
and lacquers) are manufactured are also
potential sources.
Metallurgical coke plants emit varying
amounts of hydrocarbons, depending on the
type of furnace, operating methods, main-
tenance practices used, and other factors.
Fuel-burning equipment of all types can emit
organics when improperly adjusted, in-
adequately maintained, or incorrectly oper-
ated. Waste disposal by burning can cause
hydrocarbon emissions from incomplete com-
bustion. Open burning of refuse is the greatest
offender in this category, and inefficient in-
cinerators may also contribute as a source.
Miscellaneous sources of organic gases from
biological materials include industries em-
ploying fermentation, food processing,
organic fertilizer processing, wood distillation,
and soap manufacturing.
4. Emission Factors
An adequate emission inventory will define
the magnitude, frequency, duration, and
relative contribution of emissions. For a
regional emission inventory, a detailed
analysis of all sources of interest would be
desirable. It is often necessary, however, to
estimate emissions from sources for which
detailed data are unavailable. Estimates are
arrived at by the use of emission factors,
which are based on sampling data, material
2-15
-------
balances, and engineering appraisals of sources
similar to those in question.
E. PRINCIPLES OF HYDROCARBON
EMISSION CONTROL
1. General Principles of Control
The control of hydrocarbon vapors from
technological sources rests upon several basic
principles. These include: (1) optimization of
combustion processes, (2) recovery by mass
transfer principles, (3) restriction of evapora-
tive loss, and (4) substitution of process
materials and fuels with other having different
chemical or physical properties. The applica-
tion of these principles depends upon whether
emissions arise from product storage and
transfer, industrial processes, or combustion.
Vehicular sources involve a complex mixing
of both evaporative and combustion losses.
2. Motor Vehicle Controls
a. Present Controls
(1) Crankcase emission controls—Es-
sentially 100 percent control of crankcase
emissions may be achieved by closing off
the normal crankcase vents and returning the
gases through appropriate piping to the intake
manifold. In essence, these gases then dilute
the combustion air and are recycled through
the combustion process.
(2) Exhaust emission controls — In sys-
tems presently in use, the reduction of hydro-
carbons in exhaust gases is accomplished by
one of two general approaches. The first
involves the injection of controlled amounts
of additional combustion air at the cylinder
exhaust ports in order to oxidize the un-
burned or partially burned hydrocarbons in
the oxygen deficient exhaust gases.
The second and most widely used approach
to exhaust gas hydrocarbon control is preven-
tive in nature. It involves a series of integrated
engine and engine accessory modifications
designed to improve overall combustion ef-
ficiency (not to be confused with energy uti-
lization efficiency). The major elements in-
volved in the engine modification approach
2-16
include: (1) leaner air-to-fuel ratios, (2) im-
proved air-fuel mixing, (3) a more uniform
air-fuel mixture distribution, (4) a more
precise fuel metering, and (5) improved
cylinder combustion conditions.
(3) Evaporative emission controls-
Evaporation controls consists of a means
for conducting the fuel vapors to either the
crankcase or an activated charcoal canister. In
the first case, the vapors are merely held in
the air space, whereas in the latter, the
charcoal actually adsorbs them. The gasoline
collected is eventually returned to the induc-
tion system for burning in the engine, with
the precaution that this be done when it will
not interfere with air-fuel mixtures and thus
increase exhaust emissions.
b. Proposed Controls
Most restrictive motor vehicle emission
controls for hydrocarbons will require the ap-
plication of control techniques beyond those
now in use. First steps might include direct
and catalytic exhaust reactors, more drastic
engine modification, and fuel alteration.
In the latter approach, volatility would be
reduced and less reactive hydrocarbons would
be substituted for certain of the components
(principally olefins) now commonly present.
This type of hydrocarbon control is most
effective in reducing evaporative losses and
becomes less important where mechanical
evaporative controls are used.
In addition to the hydrocarbon control
now thought possible with the present four-
cycle, spark-ignited, gasoline-fueled, internal
combustion engine, other types of motive
power have been advanced and publicized.
These have sometimes been described as "low
emission" systems and include the gas
turbine, electric drive, the steam engine, the
Stirling engine, and the stratified charge
engine. Other suggestions involve the
complete substitution of liquefied petroleum
gases or, as a special case, liquefied natural gas
for gasoline.
Additional proposals for the reduction of
hydrocarbon emissions from vehicular sources
-------
include measures other than the use of
specific vehicular emission standards. These
include: (1) substitution, in part, of public
transportation for private motor vehicles; (2)
improved road design and traffic control
systems, to enable reduction of high-emission
stop-and-go driving; and (3) restriction of the
use of private vehicles by regulation or by
economic incentive.
3. Stationary Source Control
Control principles used for stationary
sources of hydrocarbons and related organic
substances include: (1) evaporation preven-
tion (including vapor recovery), (2) incinera-
tion, (3) adsorption, (4) absorption, (5)
condensation, and (6) substitution of less
volatile and less photochemically reactive
materials in solvents for cleaning and surface
coating use. A brief description of the
principles involved for each follows.
a. Evaporation Emission Controls
The direct control of hydrocarbon
evaporation involves, as a general principle,
minimizing liquid-air contact. The major op-
portunities for this control measure are in the
storage and transfer of materials. When such
direct control is not possible, vapor recovery
systems, which physically move excess vapors
to a control unit, may be used. These systems
are normally used only with hydrocarbons of
rather high vapor pressure.
b. Control by Incineration
The control of hydrocarbon emissions by
combustion eliminates product recovery, but
by-product heat may sometimes be utilized. It
is used only if the products of combustion are
innocuous. A successful combustion control
process requires adequate heat input, good
mixing, and sufficient residence time. Less
than optimum conditions may result in only
partial combustion.
c. Control by Adsorption
Adsorption is a physical process whereby
gas molecules are held on solid surfaces.
Certain solids, such as activated alumina, silica
gel, and activated carbon, have these proper-
ties to the extent that they have practical ap-
plications. Adsorbents are for the most part
selective in their properties. Polar adsorbents
preferentially adsorb water, whereas nonpolar
adsorbents are selective for most organic sub-
stances. For this reason, activated carbon, a
nonpolar adsorbent, is most commonly used
to control organic emissions.
d. Con trol by A bsorp tion
Absorption is the process by which gases or
vapors are collected in a relatively nonvolatile
liquid absorbent. To be effective, the ab-
sorbent should have the capability of holding
relatively large quantities of the solute gas at
normal temperatures. Because organic ab-
sorbents have relatively low capacities, this
approach to hydrocarbon control is limited.
e. Control by Condensation
Condensation is the process by which
vapors are converted from gases to liquid by
cooling. This technique is most suitable for
high concentrations of hydrocarbons since
substantial quantities of a vapor may coexist
with its liquid phase even at the lowest tem-
perature practically obtainable. Condensation
for air pollution control is generally used as a
pretreatment to reduce the load on a more
efficient process such as adsorption or in-
cineration.
/ Control by Substitution of Materials
The substitution of photochemically non-
reactive materials as a stationary source con-
trol measure has been largely limited to
solvents used in degreasing operations, in
surface coatings, and in printing inks. In some
cases, satisfactory reformulation of products
with nonreactive solvents has been difficult,
and in other cases the increased costs are
greater than those for control equipment.
F. SUMMARY
The hydrocarbons of interest in this
document are those that may be encountered
in the gas phase in urban atmospheres. In this
context, hydrocarbons having a carbon
number greater than about 12 are generally
not encountered in the atmosphere in suf-
ficiently high gaseous concentrations to be of
concern.
2-17
-------
Most natural sources of hydrocarbon emis-
sions are biological in nature. A conservative
estimate made for the worldwide natural
production rate of methane is 3 x 10° tons
per year. A similar estimate of 4.4 x 108 tons
per year was made for volatile terpenes and
isoprenes. Hydrocarbon background con-
centration estimates have been made by
several authors using a variety of techniques.
It appears that nonurban air contains from
0.7 to 1.0 mg/m3 (1.0 to 1.5 ppm) methane
and less than 0.1 ppm each of other hydro-
carbons.
Total nationwide technological emissions
of hydrocarbons and related organic com-
pounds for the year 1968 were estimated to
be 32 x lO^ tons. Transportation, the largest
source category, accounted for 52 percent of
this estimate. The miscellaneous source
category, principally organic solvent evapora-
tion, was the second largest and represented
27 percent of the total emissions. Industrial
processes (14 percent) was third; solid waste
disposal (5 percent) was fourth; and fuel com-
bustion in stationary sources (2 percent) was
fifth.
Local emissions for 22 metropolitan areas
were estimated to range from about 0.05 to
1.3 million tons per year. Transportation
sources accounted for 37 to 99 percent of
local emissions, and process losses accounted
for 1 to 63 percent. Hydrocarbon emissions,
therefore, originate primarily from the inef-
ficient combustion of volatile fuels and from
their use as process raw materials.
Uncontrolled conventional automobile en-
gines are capable of emitting hydrocarbons by
four means: engine exhaust, crankcase
blowby, carburetor evaporation, and fuel tank
evaporation.
The control of hydrocarbon emissions rests
upon the basic principles of: (1) combustion
process optimization, (2) recovery by mass
transfer, (3) restriction of evaporative loss,
and (4) process material and fuel substitution.
The first three principles are all applied with
varying degrees of success in the control of
automobile emissions.
2-18
Specific control measures that may be ap-
plied to stationary sources include: (1)
evaporation prevention, (2) incineration, (3)
adsorption, (4) absorption, (5) condensation,
and (6) substitution.
G. REFERENCES
1. Stephens, E.R. and F.R. Burleson. Distribution
or Light Hydrocarbons in Ambient Air. Present-
ed at the 62nd Annual Meeting of the Air Pol-
lution Control Association. New York. June
22-26, 1969.
2. Neligan, R.E. Hydrocarbons in the Los Angeles
Atmosphere. Arch. Environ. Health. 5:581-591,
December 1962.
3. Benson, S.W. Thermochemical Kinetics. New
York, John Wiley & Sons, Inc., 1968. 223 p.
4. Wayne, L.G. and T.E. Ernest. Photochemical
Smog, Simulated by Computer. Presented - at
62nd Annual Meeting of the Air Pollution Con-
trol Association. New York. June 22-26, 1969.
5. Scott, W.E. and L.R. Reckner. Atmospheric
Reaction Studies in the Los Angeles Basin.
Progress Report. November 15, 1968 to January
15, 1969. Scott Research Laboratory. APRAC
Project CAPA 7-68. 1969.
6. Altshuller, A.P. and S.P. McPherson. Spectropho-
tometric Analysis of Aldehydes in the Los
Angeles Atmosphere. J. Air Pollution Control
Asosc. 13:109-111, March 1963.
7. Renzetti, N.A. and R.J. Bryan. Atmospheric
Sampling for Aldehydes and Eye Irritation in Los
Angeles Smog — 1960. J. Air Pollution Control
Assoc. 77:421-424, 427, September 1961.
8. Altshuller, A.P. and J.J. Bufalini. Photochemical
Aspects of Air Pollution: A Review. Photochem.
Photobiol. 4(2):97-146, March 1965.
9. Altshuller, A.P. et al. Photochemical Reactivities
of N-Butane and Other Paraffinic Hydrocarbons.
J. Air Pollution Control Assoc. 79:787-790,
October 1969.
10. Altshuller, A.P. et al. Photochemical Reactivities
of Paraffinic Hydrocarbon-Nitrogen Oxide
Mixtures Upon Addition of Propylene or
Toluene. J. Air Pollution Control Assoc.
79:791-794, October 1969.
11. Schuck, E.A. and G.J. Doyle. Photooxidation of
Hydrocarbons in Mixtures Containing Oxides of
Nitrogen and Sulfur Dioxide. Air Pollution
Foundation. San Marino, Calif. Report Number
29. October 1959. 104 p.
12. Stephens, E.R. and W.E. Scott. Relative Reac-
tivity of Various Hydrocarbons in Polluted
Atmospheres. Proc. Amer. Petrol. Inst.
42:665-670, 1962.
-------
13. Altshuller, A.P. and I.R. Cohen. Presented at the
145th National Meeting of the American
Chemical Society. New York. September 1963.
14. Stephens, E.R. et al. Photochemical Reaction
Products in Air Pollution. Int. J. Air Water Pol-
lution. 4(1/2):79-100, June 1961.
15. Schuck, E.A., G.J. Doyle, and J. Endow. Photo-
chemistry of Polluted Atmospheres. Stanford
Research Institute. July 1960.
16. Sigsby, J.E. et al. Presented at the 145th
National Meeting of the American Chemical
Society. New York. September 1963.
17. Stephens, E.R. The Photochemical Olefin —
Nitrogen Oxides Reaction. In: Chemical Reac-
tions in the Lower and Upper Atmosphere. New
York, Interscience Publishers, 1961, p. 51-69.
18. Tuesday, C.S. The Atmospheric Photooxidation
of Trans-Butene-2 and Nitric Oxide. In: Chemical
Reactions in the Lower and Upper Atmosphere.
New York, Interscience Publishers, 1961, p.
15-49
19. Bufalini, J. J. and A. P. Altshuller. Presented at
the 145th National Meeting of the American
Chemical Society, Division of Water and Waste
Chemistry. New York. September 1963.
20. Leighton, P.A. Photochemistry of Air Pollution.
New York, Academic Press, 1961, 300 p.
21. Vrbaski, T. and R.J. Cvetanovic. Relative Rates
of Reaction of Ozone with Olefins in the Vapor
Phase. Can. J. Chem. 55:1053-1062, July 1960.
22. Tuesday, C.S. The Atmospheric Photooxidation
of Olefins — The Effect of Nitrogen Oxides.
Arch. Environ. Health. 7(2):188-201, August
1963.
23. Kopczynski, S.L. Photooxidation of Alkylben-
zene-Nitrogen Dioxide Mixtures in Air. Int. J. Air
Water Pollution. 8:107-120, February 1964.
24. Migeotte, M.V. Spectroscopic Evidence of
Methane in the Earth's Atmosphere. Phys. Rev.
75(5):519-520, March 1, 1948.
25. Koyama, T. Gaseous Metabolism in Lake Sed-
iments and Paddy Soils and Production of
Atmospheric Methane and Hydrogen. J.
Geophys. Res. 65(13):3971-3983, July 1, 1963.
26. Ehhalt, D.H. Methane in the Atmosphere. J. Air
Pollution Control Assoc. 77:518-519, August
1967.
27. Robinson, E. and R.C. Robbins. Sources,
Abundance, and Fate of Gaseous Atmospheric
Pollutants. Stanford Research Institute. February
1968. (Report prepared for American Petroleum
Institute, New York, New York).
28. Rasmussen, R.A. and F.W. Went. Volatile
Organic Material of Plant Origin in the Atmos-
phere. Proc. Nat. Acad. Sci. U.S. 55:215-220,
January 1965.
29. Junge, C.E. Air Chemistry and Radioactivity.
International Geophysical Series, Van Mieghem,
J. (ed.), Vol. 4, New York, Academic Press,
1963.382 p.
30. Fink, U., D.H. Rank, and T.A. Wiggins. Abun-
dance of Methane in the Earth's Atmosphere. J.
Opt. Soc. Amer. 54:472-474, April 1964.
31. Goldberg, L. and E.A. Muller. The Vertical Dis-
tribution of Nitrous Oxide and Methane in the
Earth's Atmosphere. J. Opt. Soc. Amer.
43:1033-1036, November 1953.
32. Stephens, E.R. and F.R. Burleson. Distribution
of Light Hydrocarbons in Ambient Air. Present-
ed at the 62nd Annual Meeting of the Air Pol-
lution Control Association. New York. June
22-26, 1969.
33. Cavanagh, L.A., C.F. Schadt, and E. Robinson.
Atmospheric Hydrocarbon and Carbon Monox-
ide Measurements at Point Barrow, Alaska.
Environ. Sci. Technol. 5:251-257, March 1969.
34. Swinnerton, J.W., V. J. Linnenbom, and C.H.
Cheek. Distribution of Methane and Carbon
Monoxide Between the Atmosphere and Natural
Waters. Environ. Sci. Technol. 5:836-838,
September 1969.
35. Altshuller, A.P. and T.A. Bellar. Gas Chroma-
tographic Analysis of Hydrocarbons in the Los
Angeles Atmosphere J. Air Pollution Control
Assoc. 75:81-87, February 1963.
36. Altshuller, A.P. et al. Continuous Monitoring of
Methane and Other Hydrocarbons in Urban
Atmospheres. J. Air Pollution Control Assoc.
76:87-91, February 1966.
37. National Air Pollution Control Administration,
Reference Book of Nationwide Emissions. U.S.
DHEW, PHS, CPEHS, NAPCA. Durham, N.C.
38. Mason, D.V. et al. Sources and Air Pollutant
Emission Patterns in Major Metropolitan Areas.
Presented at the 62nd Annual Meeting of the Air
Pollution Control Association. New York. June
22-26, 1969.
39. Data Provided by the National Air Pollution Con-
trol Administration, Bureau of Criteria and
Standards, NIAPEC, Durham, North Carolina.
40. Grant, E.P. Auto Emissions. Motor Vehicle Pol-
lution Control Board Bulletin. 6(4):3, 1967.
41. Motor Vehicles, Air Pollution, and Health. A
Report of the Surgeon General to the U. S.
Congress in Compliance with Public Law 69-498,
the Schenck Act. U. S. Dept. of Health,
Education, and Welfare, Public Health Service,
Division of Air Pollution. Washington, D.C., U.S.
Government Printing Office. House Document
No. 489, 87th Congress, 2d Session. 1962. 459 p.
42. McReynolds, L.A., H.E. Alquist, and D.B.
Wimmer. Hydrocarbon Emissions and Reactivity
as Functions of Fuel and Engine Variables (SAE
Paper No. 650525). S. A. E. Transactions.
74:902-911, 1966.
2-19
-------
43. Neligan, R.E., P.P. Mader, and L.A. Chambers. 45. Vogh, J.W. Nature of Odor Components in Diesel
Exhaust Composition in Relation to Fuel Com- Exhaust. J. Air Pollution Control Assoc.
position. J. Air Pollution Control Assoc. 79(10):773-777, October 1969.
11:178-186, April 1961. 46. Duprey, R.L. Compilation of Air Pollutant Emis-
44. Wetmiller, R.S. and L.E. Endsley, Jr. Effect of sion Factors. National Center for Air Pollution
Diesel Fuel on Exhaust Smoke and Odor. S. A. Control. Durham, N. C. PHS Publication Number
E. Transactions. 50(11):509-520, December 999-AP-42. 1968. 67 p.
1942.
2-20
-------
CHAPTER 3.
ATMOSPHERIC LEVELS OF HYDROCARBONS AND THEIR
RELATED PRODUCTS
A. INTRODUCTION
In the examination of atmospheric hydro-
carbon concentrations in relation to photo-
chemical air pollution, several factors must be
considered. First, as discussed in Chapter 2,
there is an enormous variation in the tend-
ency for different hydrocarbons to enter into
the photochemical air pollution reaction se-
quence. For example, methane is virtuallly
inert. Second, the simpler and less laborious
atmospheric hydrocarbon detection methods
are likely to respond most strongly to
methane and other alkanes. Third, methane is
often more abundant than all other hydro-
carbons combined. There is, in fact, apparent-
ly a "geophysical" minimum level of
methane, present worldwide, of about 0.7 to
1.0 mg/m3 (1.0 to 1.5 ppm).1-3 It is im-
portant, then, in assessing photochemical air
pollution to be able to discriminate between
methane and other more reactive hydro-
carbons. Unfortunately, this type of analysis
is expensive and time-consuming, so that such
data are not abundant. They are available,
nevertheless, and in this section such observa-
tions are discussed.
B. HYDROCARBONS
Although on occasion all other hydro-
carbon concentrations drop to unmeasurably
low levels, methane does not. Numerous
measurements suggest a worldwide minimum
methane concentration of about 0.7 to 1.0
mg/m3 (1.0 to 1.5 ppm).3 In inhabited areas,
methane levels are often much higher; values
of 4 mg/m3 (6 ppm) or more have been ob-
served.4
Yearly averages of monthly maximum
1-hour average total hydrocarbon concentra-
tions recorded at stations that are part of the
Continuous Air Monitoring Projects (CAMP)
network ranged, for the years 1962 through
1967, from 8 to 17 ppm (as carbon).5
Ratios of nonmethane hydrocarbons (as
carbon) to methane have been estimated for
urban areas, after subtracting 1 ppm from
methane values to allow for estimated bio-
genie background levels.4 The nonmethane/
methane hydrocarbon ratios for several weeks
averaged 0.6 in Cincinnati and 1.9 in Los
Angeles, although methane values were similar
(Figure 3-1). The higher Los Angeles ratios
3.0
2.5
I 2.0
<-
<*5 1-0
Z X
a:'
i- i
o
(J
' 0.6
0.5
0.4
0.3
0.2
0.15
LOS ANGELES
12
6
-u.m.
12
nle
6
-p.m.
12
LOCAL TIME
Figure 3-1. Concentration ratios for non-
methane hydrocarbons/methane in Los
Angeles (213 hours during October and
November, 1964) and Cincinnati (574 hours
during September 1964), with 655 ug/m3 (1
ppm) methane deducted to correct for esti-
mated background biospheric concentration.4
3-1
-------
may possibly result from local differences in
traffic density and solvent losses.
1. Hydrocarbons in Ambient Air
Table 3-1 lists the individual hydrocarbons
detected in samples of urban air by gas
chromatographic analysis in several investiga-
tions.6"8 Of the 56 compounds detected, 17
were alkanes, 23 alkenes (including two
alkadienes), 2 were alkynes, 10 aromatics, 3
cycloalkanes, and 1 was a cycloalkene. The
length of this list is limited only by the sensi-
tivity of the analytical methods, and it is
certain that many additional hydrocarbon
compounds are actually present in urban air.
Especially at the higher carbon numbers, the
complexity of the chromatographic records
becomes so great that the effort to interpret
them in terms of individual compounds may
be insufficiently rewarding. The listing in
Table 3-1 of compounds with carbon numbers
of 7 and higher must be considered as only a
partial list.
Table 3-1. SOME HYDROCARBONS IDENTIFIED IN AMBIENT AIR
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
Class
Alkane
Alkane
Alkene
Alkyne
Alkane
Alkene
Alkene
Alkyne
Alkane
Alkane
Alkene
Alkene
Alkene
Alkene
Alkene
Alkane
Alkane
Alkene
Alkene
Alkene
Alkene
Alkene
Alkene
Alkene
Cycloalkane
Cycloalkene
Alkane
Alkane
Alkane
Alkane
Alkane
Alkene
Alkene
Alkene
Alkene
Alkene
Alkene
Alkene
Compound
Methane
Ethane
Ethylene
Acetylene
Propane
Propylene
Propadiene
Methylacetylene
Butane
Isobutane
1-Butene
cw-2-Butene
trans-l-Butene
Isobutene
1 ,3-Butadiene
Pentane
Isopentane
1-Pentene
cw-2-Pentene
trans-2-Pentene
2-Methyl-l-butene
2-Methyl-2-butene
3-Methyl-l-butene
2-Methyl-l,3-butadiene
Cyclopentane
Cyclopentene
Hexane
2-Methylpentane
3-Methylpentane
2,2-Dimethylbutane
2,3-Dimethylbutane
1-Hexene
cu-2-Hexene
fran.y-2-Hexene
cw-3-Hexene
trans-3-Hexene
2-Methyl-l-pentene
4-Methyl-l-pentene
Reference
7
6,7
6,7
6,7
6,7
6-8
7
7
6,7
6,7
6,7
6-8
6-8
6-8
6-8
6-8
6-8
6-8
6-8
6
6-8
6-8
6
6
6,7
6,7
6,7
6,7
6,7
6,7
6,7
7
7
7
7
7
7
7
3-2
-------
Table 3-1 (Continued). SOME HYDROCARBONS IDENTIFIED IN AMBIENT AIR
Carbon
number
6
6
6
6
7
7
7
7
7
8
9
10
Class
Alkene
Aromatic
Cycloalkane
Cycloakane
Alkane
Alkane
Alkane
Alkane
Aromatic
Alkane
Aromatic
Aromatic
Aromatic
Compound
4-Methyl-2-pentene
Benzene
Cyclohexane
Methylcyclopentane
2-Methylhexane
3-Methylhexane
2 ,3 -Dimethy Ipentane
2 ,4-Dimethylpentane
Toluene
2 ,2 ,4-Trimethylpentane
o-Xylene
m-Xylene
p-Xylene
m-Ethyltoluene
p-Ethyltoluene
1 ,2,4-Trimethylbenzene
1 ,3,5-Trimethylbenzene
sec-Butylbenzene
Reference
7
7
7
7
7
7
7
7
*7 o
1,0
1
8
8
8
8
8
8
8
8
All the hydrocarbons above carbon number
4 listed in Table 3-1 are found in gasoline.9
These and the lower alkenes and acetylenes
are also found in automobile exhaust gases.
The lower alkanes (methane, ethane, and
propane) occur in only trace amounts in auto
exhaust gases, but are ordinary constituents
of natural gas. Stephens and Burleson have
reported that the hydrocarbon composition
of their samples resembled that of auto ex-
haust gases with an addition of natural gas
and gasoline vapor.6 However, samples taken
in industrial areas and from near the smoke
plume from a brush fire have shown distinc-
tive differences in composition, which should
reasonably be attributed to these particular
recognized sources. Special studies such as
these can be very useful in identifying the im-
portance of various sources as contributors to
the pollution of air by hydrocarbons.
2. Diurnal Variation
In Figures 3-2 and 3-3 are shown diurnal
patterns for nonmethane hydrocarbons in sev-
eral cities, averaged over several months.5'10
In most of these the maximum concentra-
tions at 6:00 to 8:00 a.m. are mainly
due to the morning commuter traffic rush.
The morning peak is clearest in Denver and
Los Angeles, where the automobile is especial-
ly important as a means of transportation.
Even within a large metropolitan area there
may be considerable variation. In Figure 3-3
are shown average diurnal patterns for non-
methane hydrocarbons at three locations in
Los Angeles County. There are considerable
differences among the three patterns, al-
though the morning maxima are still evident
in all. In Table 3-2 the diurnal patterns are
given for the €2 to €4 hydrocarbons and
isopentane, showing the hour-by-hour varia-
tions as averaged over some weeks in the Los
Angeles smog season. All species listed reach a
maximum in the morning, then decline
through the midday.11
3. Seasonal Variation
Necessary data are not now available for
the assessment of seasonal or annual varia-
tions in nonmethane hydrocarbon levels. In
most instances, total hydrocarbons consist
mostly of methane (inert photochemically).
Total hydrocarbon concentrations are tabu-
lated for 17 California cities in Table 3-3.l 2 It
is noteworthy that 14 of these cities show
highest hydrocarbon concentrations (averages
3-3
-------
1.5
1.0
0.5
1.5
CHICAGO
(MAY THROUGH AUGUST AND OCTOBER, 1968)
I I I I I I I I I
U
°-
1.0
§ 0.5
U
Q
>- 2.0
< 1.5
LLJ
i 1.0
O
z
0.5
1
ST. LOUIS
"'x.^
II
1
1 1
(MAY THROUGH JULY, SEPTEMBER, AND OCTOBER, 1968)
I I I I I I I I I
I I I T
i r
DENVER
(JANUARY THROUGH MARCH, MAY, SEPTEMBER, AND OCTOBER, 1968)
—J I ^ I ^ ^ I I I I I
0.5
0
1
I
WASHINGTOh
(JANUAR
I
2
I I
J.DX,^*
• ""^ • — -.*. . —
Y THROUGH APRIL AND AU
I I I
6 12
I I I
GUST THROUGH OCTOBER, 1968)
II II
6 12
LOCAL TIME
Figure 3-2. Nonmethane hydrocarbons by flame ionization analyzer, averaged
by hour of day over several months for various cities.5
of maximum hourly averages) in October or
November. This is presumably a consequence
of the generally similar meteorological condi-
tions along the California Coast. Cities in
other parts of the country would be expected
to show other patterns, dependent on their
particular meteorology.
4. Community Levels
Since routine air monitoring methods do
not yet exist for measuring individual hydro-
3-4
carbons other than methane, special studies
have been required to establish existing levels
of individual hydrocarbons. For the most part
these studies have involved gas chromato-
graphic analysis of periodic samples, by tech-
niques discussed in Chapter 4.
In Table 3-4 concentrations of many indi-
vidual hydrocarbons as averaged from more
than 200 samples from the Los Angeles
atmosphere10 are tabulated. The great pre-
dominance of methane is noteworthy. Even
-------
3.0
2.0
1.0
U
Q.
CL
i i i r
WEST LOS ANGELES
I I I T
I I
V
1
I I I I I
I I
. 3.0
2
O
CO
U
O
UJ
2
I-
LU
O
2
I I T
LOS ANGELES
I I T
A
2.0
1.0
I I
I I
1.0
I I
PASADENA
I I
I V
N._
12
6
a.m.
12
> <
6
p.m
12
LOCAL TIME
Figure 3-3. Nonmethane hydrocarbons by flame ionization analyzer averaged by
hour of day for three Los Angeles county sites, October 1966 through February
1967 .'10
3-5
-------
Table 3-2. AVERAGE ATMOSPHERIC LIGHT HYDROCARBON CONCENTRATIONS,
BY HOUR, LOS ANGELES, SEPTEMBER THROUGH NOVEMBER, 196?U
Local
time
No. of
days
averaged
Hydrocarbon, ppm C
Ethane
Downtown Los Angeles (DOLA)
5:00 a.m.
6:00 a.m.
7:00 a.m.
8:00 a.m.
9:00 a.m.
10:00 a.m.
11:00 a.m.
Noon
1:00 p.m.
2:00 p.m.
3:00 p.m.
4:00 p.m.
27
28
28
31
15
33
12
32
16
38
16
34
0.140
0.140
0.151
0.145
0.107
0.126
0.094
0.106
0.076
0.094
0.090
0.075
East San Gabriel Valley (Azusa)
5:00 a.m.
6:00 a.m.
7:00 a.m.
8:00 a.m.
9:00 a.m.
10:00 a.m.
11:00 a.m.
Noon
1:00 p.m.
2:00 p.m.
3:00 p.m.
4:00 p.m.
32
33
30
32
18
32
18
30
16
42
16
37
0.143
0.128
0.180
0.118
0.093
0.086
0.090
0.089
0.111
0.097
0.092
0.079
Ethylene
0.031
0.049
0.122
0.102
0.063
0.067
0.039
0.039
0.020
0.026
0.026
0.036
0.029
0.017
0.030
0.037
0.031
0.024
0.021
0.015
0.016
0.018
0.020
0.021
Acetylene
0.077
0.112
0.234
0.212
0.141
0.152
0.106
0.101
0.068
0.074
0.079
0.095
0.060
0.065
0.103
0.101
0.079
0.069
0.057
0.050
0.066
0.064
0.065
0.058
Propane
0.113
0.113
0.125
0.126
0.098
0.118
0.080
0.108
0.078
0.097
0.101
0.081
0.087
0.076
0.102
0.084
0.065
0.066
0.062
0.058
0.067
0.075
0.075
0.076
Propylene
0.025
0.036
0.064
0.054
0.032
0.038
0.025
0.020
0.013
0.017
0.016
0.024
0.013
0.015
0.024
0.020
0.015
0.019
0.011
0.010
0.018
0.017
0.015
0.014
Isobutane
0.053
0.061
0.074
0.075
0.063
0.064
0.048
0.063
0.044
0.057
0.050
0.046
0.036
0.031
0.041
0.044
0.036
0.040
0.037
0.040
0.046
0.050
0.081
0.041
H-Butane
0.176
0.200
0.300
0.304
0.209
0.260
0.180
0.200
0.149
0.156
0.132
0.139
0.101
0.098
0.136
0.149
0.114
0.132
0.107
0.098
0.121
0.121
0.175
0.122
Butylenes
0.032
0.034
0.056
0.049
0.028
0.034
0.021
0.015
0.014
0.019
0.020
0.021
0.014
0.012
0.018
0.018
0.015
0.015
0.010
0.009
0.017
0.018
0.015
0.014
Isopentane
0.177
0.224
0.335
0.346
0.249
0.303
0.200
0.199
0.162
0.155
0.144
0.141
0.104
0.103
0.144
0.160
0.114
0.136
0.101
0.093
0.111
0.117
0.125
0.123
on a carbon atom basis, methane constitutes
about half the total hydrocarbon. In the re-
mainder, the staturated hydrocarbons (rela-
tively unreactive photochemically) are pre-
dominant. These samples were generally taken
just before or during the morning traffic rush.
The proportion of aromatic to aliphatic
hydrocarbons and some of the proportions
among the aromatics have been studied.13
Table 3-5 shows, again for Los Angeles,
averages for concentrations of aromatics ob-
served in the atmosphere over several weeks
sampling.
There has been little comparison of hydro-
carbon concentrations from various geograph-
ical locations. The study of Altshuller4 et al.
compared methane and nonmethane hydro-
carbons in Cincinnati and Los Angeles (see
Figure 3-1). Stephens and Burleson6 have de-
termined the hydrocarbon compositions for a
number of air samples from widely scattered
3-6
locations: Hawaii, Denver, New York, and
Monterey-Salinas (California), as well as
Riverside in Southern California. There are
apparently substantial differences in the pro-
portions of individual hydrocarbons present,
which may sometimes, but not always, be re-
lated to known differences in source contribu-
tions and extent of atmospheric reaction.
Laboratory work shows that in the photo-
chemical reaction system the rates of disap-
pearance or reaction of various hydrocarbons
differ widely. These differences may be re-
lated to some extent to structure: olefins and
most aromatics are reactive; higher alkanes are
not very reactive; and benzene, acetylene, and
lower alkanes are virtually inert.14 In the
atmosphere these differences have been
harder to observe. Since the general effects of
meteorological dilution and continuing source
emission obscure the effects of reaction,
Stephens and Burleson15 studied the changes
-------
Table 3-3. MEAN OF DAILY MAXIMUM HOURLY AVERAGE TOTAL
HYDROCARBON CONCENTRATIONS (as ppm methane), 17 CALIFORNIA CITIES, 1968-196912
San Francisco Bay Area
Richmond
San Rafael
San Francisco
Redwood City
San Jose
Central Valley
Fresno
Bakersfield
Sacramento
Stockton
Central Coast
Salinas
Monterey
Southern California
Los Angeles (downtown)
Azusa
Anaheim
Riverside
San Bernardino
San Diego
1968
>v
June
5
4
5
N.A.
4
3
7
4
3
3
3
4
4
4
5
4
3
July
6
4
4
12
4
3
7
4
4
2
2
5
4
5
5
5
N.A.
Aug.
4
5
N.A.b
14
4
3
8
5
4
3
3
4
5
5
7
5
4
Sept.
6
6
5
16a
6
4
10a
5
5
3
3
5
5
6
6
6a
5
Oct.
9a
13a
7a
13
8a
6a
10a
10a
6a
3
4a
6
6a
8
7
6a
7
Nov.
8
10
6
11
8a
5
9
7
4
4a
4a
7a
5
10a
7
6a
7
Dec.
9a
9
6
9
7
5
10a
7
5
4a
4a
7a
5
10a
8
6a
9a
1969
>v
Jan.
8
6
5
7
7
4
7
6
4
3
4a
6
4
7
7
5
7
Feb.
8
6
5
6
5
4
8
5
3
3
4a
4
4
7
9a
N.A.
6
Mar.
7
8
5
7
6
5
7
7
5
3
3
5
5
7
8
6a
6
Apr.
6
6
5
5
6
3
6
4
4
2
3
4
5
5
4
5
5
May
4
6
4
5
5
3
6
4
4
N.A.
3
3
5
3
4
4
3
aHighest mean concentration for 12-month period.
bN.A. = Not available.
in concentrations in trappped atmospheric
samples, artifically irradiated, and found that
reactivities were much as expected from
laboratory findings. Table 3-6 displays these
results.
In another attempt to relate atmospheric
hydrocarbon concentrations to other photo-
chemical air pollution effects, Gordon1' et al.
examined the diurnal patterns of several
pollutants recorded in the Fall of 1967 at two
California sampling sites, downtown Los
Angeles and Azusa. The measurements taken
were segregated according to the maximum
daily oxidant concentration. The high oxidant
(HiOx) category included those days on which
the maximum oxidant level was above
590 Mg/m^ (0.30 ppm) at either station. The
low oxidant (LoOx) category included those
days when neither station reached an oxidant
maximum as high as 390 jug/m-^ (0.20 ppm).
Some of the results of this study are shown in
Figure 3-4. Acetylene, €2 to €4 olefins, and
carbon monoxide (curves a, b, and c) all peak
at around 8:00 a.m. at both sites on "HiOx"
days, and decline rapidly thereafter. Since
acetylene and carbon monoxide are known to
be very unreactive photochemically, their
decrease during the day is attributable to
ventilation and a decrease in emissions.
The similar shape for the olefin curve sug-
gests that olefin depletion by reaction is not
more important than by other mechanisms.
Some of the curves for alkanes (e and f) and
oxides of nitrogen (d) peak later and decline
much more slowly. This suggests that there is
further production of these components from
3-7
-------
Table 3-4. AVERAGE HYDROCARBON COMPOSITION,
218 AMBIENT AIR SAMPLES,
LOS ANGELES, 196510
Compound
Methane
Ethane
Propane
Isobutane
n-Butane
Isopentane
rc-Pentane
2,2-Dimethylbutane
2-Methylpentane
2,3-Dimethylbutane
Cyclopentane
3-Methylpentane
n-Hexane
Total alkanes (excluding methane)
Ethylene
Prop en e
1-Butane + Isobutylene
fran,y-2-Butene
cw-2-Butene
1-Pentene
2-Methy 1-1 -Bute ne
trans-2-Pentene
cw-2-Pentene
2-Methyl-2-Butene
Propadiene
1,3-Butadiene
Total alkenes
Acetylene
Methylacetylene
Total acetylene
Benzene
Toluene
Total aroma tics
Total
Concentration
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
different sources than those emitting acety-
lene and CO (mainly auto exhausts). Curve g
shows oxidation development peaking hours
later than other components, as expected for
a reaction product. Oxidant levels for Azusa
are always equal to or greater than those at
downtown Los Angeles, even in morning
hours, although primary pollutant levels of
3-8
hydrocarbons and oxides of nitrogen are
higher at downtown Los Angeles until well
after noon. This shows the complexity of the
reaction system.
These curves also illustrate an apparent
anomaly examined by Neligan7 and by
Stephens and Burleson.6 In qualitative terms
auto exhaust, gasoline evaporation, and nat-
-------
Table 3-5. AVERAGE AND HIGHEST CONCENTRATION MEASURED13
FOR VARIOUS AROMATIC HYDROCARBONS IN LOS ANGELES,
26 DAYS, SEPTEMBER THROUGH NOVEMBER, 1966
Aromatic hydrocarbon
Benzene
Toluene
Ethylbenzene
p-Xylene
m-Xylene
o-Xylene
!-Propylbenzene
n-Propylbenzene
3- and 4-Ethyltoluene
1,3,5-Trimethylbenzene
1,2,4-Trimethylbenzene, and
z'-Butyl- and sec-Butylbenzene
te/7-Butylbenzene
Total aromatics
Average
concentration,
ppm
0.015
0.037
0.006
0.006
0.016
0.008
0.003
0.002
0.008
0.003
0.009
0.002
0.106
Highest measured
concentration,
ppm
0.057
0.129
0.022
0.025
0.061
0.033
0.012
0.006
0.027
0.011
0.030
0.006
0.330
ural gas sources are adequate to explain ob-
served hydrocarbon components. Quantia-
tively, however, there are more light alkanes
present, especially propane, than can be
explained by the analysis of samples from
these sources. There may be an additional
source not yet identified, or the samples used
for analysis may not be sufficiently represen-
tative.
C. SECONDARY CONTAMINANTS
The photochemical interaction of organic
materials in the atmosphere with oxides of
nitrogen, leads to numerous products, includ-
ing oxidants such as ozone, carbonyl com-
pounds, and peroxyacyl nitrates. The oxi-
dants are discussed fully in a separate criteria
document, and will therefore only be referred
to here as required in the discussion of other
aspects of hydrocarbon behavior.
1. Aldehydes
Of all the principal reaction products
formed in the atmosphere by photochemical
processes, the aldehydes are among the most
poorly quantified. By far most of the avail-
able data are from Los Angeles, where for the
period 1951 through 1957 aldehydes were
regularly measured by manual techniques.16
Total aldehydes was determined by the bisul-
fite procedure17 and reported as formalde-
hyde; formaldehyde was determined by the
chromotrophic acid procedure.18 Table 3-7
shows the range of yearly maximum 1-hour
average concentrations obtained over this
7-year period. Typical maximum concentra-
tions were nearer the low end of the range,
although insufficient data are available to give
a complete characterization.
A study in Los Angeles County during the
period July to November of 1960 provided
additional data on total aldehydes, formalde-
hyde, and acrolein.19 Total aldehydes ranged
up to 0.36 ppm for a 10-minute sample, but
formaldehyde did not exceed 130 jug/m^
(0.10 ppm). Typical aldehyde concentrations
were near 0.10 ppm on many days. The maxi-
mum acrolein value was 25.2 jug/m (0.011
ppm), with most values being less than half
that amount.
Diurnal variations in aldehydes are ap-
parent for analytical data obtained in Los
Angeles from September to November,
1961.20 These data are shown in Table 3-8.
The concentrations show an early rise, a
broad plateau or maximum through most of
the day, and a decrease in the afternoon. Data
3-9
-------
Table 3-6. COMPARISON OF RESULTS FROM ULTRAVIOLET
IRRADIATION OF AMBIENT AIR SAMPLESlS
Compounds
Ethane
Ethene
Propane
Propene
Propane
Propene
Isobutane
n-butane
Acetylene
1-butene
Isobutene
trans-2-butene
Isopentane
cw-2-butene
n-pentanea
1,3- butadiene
Methyl acetylene
2,2-dimethyl butane
1-pentene
2-methyl butene-1
trans-2-pentene
2,3-dimethyl butane
2-methyl pentane''
3-methyl pentanec
Cyclopentane
n-hexane
Cyclopentene
Concentration, ppm
12/22/65
Ohr
0.0385
0.1342
0.0174
0.0354
0.0216
0.0484
0.0252
0.1190
0.3105
0.0064
0.0118
0.0060
0.0936
0.0045
0.0600
0.0090
0.0095
0.0023
0.0050
0.0089
0.0055
0.0013
0.0340
0.0347
0.0060
0.0250
—
24 hr
0.0384
0.0320
0.0152
0.0014
0.0172
0.0020
0.0172
0.0785
0.2620
0.0005
0.0007
0.0
0.0464
0.0
0.0300
0.0
0.0050
0.0017
0.0
0.0
0.0
0.0010
0.0140
0.0088
0.0029
0.0094
—
re-
remaining
0.0995
0.0238
0.0875
0.0040
0.0796
0.0041
0.0684
0.0660
0.0846
0.0078
0.0059
0.0
0.0495
0.0
0.0500
0.0
0.0526
0.0740
0.0
0.0
0.0
0.0770
0.0412
0.0253
0.0484
0.0375
—
3/3/66
Ohr
0.0376
0.0512
0.0146
0.0156
0.0130
0.0134
0.0074
0.0448
0.0696
0.0022
0.0040
0.0014
0.0276
0.0010
0.0186
0.0024
0.0020
0.0006
0.0010
0.0020
0.0016
0.0012
0.0084
0.0088
0.0014
0.0072
0.0024
24 hr
0.0352
0.0126
0.0114
0.0014
0.0104
0.0006
0.0048
0.0272
0.0568
0.0004
0.0004
0.0
0.0136
0.0
0.0058
0.0
0.0012
0.0004
0.0
0.0
0.0
0.0010
0.0036
0.0022
0.0010
0.0034
0.0
%
remaining
0.0937
0.0246
0.0782
0.0090
0.0800
0.0045
0.0650
0.0607
0.0816
0.0181
0.0100
0.0
0.0493
0.0
0.0312
0.0
0.0600
0.0666
0.0
0.0
0.0
0.0832
0.0429
0.0275
0.0275
0.0473
0.0
aContains 3-methyl butene-1.
"Contains cw-2-pentene.
cContains 2-methyl butene-2.
from a 1968 study at two sites east of down-
town Los Angeles are shown in Figure 3-5 for
a single day.21 In this work it is apparent that
formaldehyde contributes the bulk of the al-
iphatic aldehyde concentration, whereas the
acrolein concentration is less than one-tenth
that of formaldehyde.
In these few available studies of ambient
levels of aldehydes, the ratio of formaldehyde
to total aldehydes showed no consistent val-
ue, ranging from about 10 percent in one
study19 to 90 percent in another.21 This in-
consistency may be attributable in part to the
use of different methods for analyzing alde-
hydes.
3-10
2. Aerosols
Cities in the United State with a population
greater than 400,000 have an average at-
mospheric particulate-burden2 2 of about 120
Mg/nA Characteristics of atmospheric particu-
lates are described in AP-49, Air Quality Cri-
teria for Particulate Matter.2 2 Some particu-
late matter is organic and some inorganic. The
national average content of suspended partic-
ulates from 1960 through 1965 was 6.5 per-
cent benzene-solubles; the total organic
content might be several times this, depending
on its geographical origin. Some specific com-
parisons for selected cities are shown in Table
3-9. Total suspended particulates for the cities
-------
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Q.
Q.
-£
O
1-
<
a
1-
z
LU
(J
Z
o
u
UJ
0
<
a:
UJ
>
<
ia
16
14
12
10
0.4
0.3
0.2
0.1
Q
0.20
0.16
0.12
0.08
0.04
1 A ' ' ' '
- ; \
Ij^^V b. CARBON MONOXIDE
/-•A^ S2&
/,' """"*••« \ DOLA-^"'!
1 1 1 1 1 1
- 1 1 1 1 1 1
/ *— -\ d. OXIDES OF
— / V NITROGEN
y \ 3
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Table 3-7. RANGE OF YEARLY MAXIMUM
1-HOUR AVERAGE CONCENTRATIONS OF
ALDEHYDES AND FORMALDEHYDE,
LOS ANGELES COUNTY STATIONS,
1951 THROUGH 19S716
Year
1951
1952
1953
1954
1955
1956
1957
Concentration range, ppm
Formaldehyde
0.05-0.12
Total aldehydes
0.26 - 0.67
0.20-0.27
0.25- 1.20
0.39-0.80
0.47- 1.28
0.51 1.30
0.27-0.47
shown are comparable, but the amounts of
benzene- solubles and of nitrates are highest
in Los Angeles, whereas New York has the
highest sulfate levels. The Los Angeles loading
is produced largely from automobile exhaust
with only moderate amounts produced by the
consumption of heavy fuel oil (and no coal);
in New York much sulfur-containing coal was
burned during the period covered.
In Los Angeles, the nitrate content of par-
ticulate matter is strikingly higher than in the
other cities. There is reason to suspect that
this is due to the photooxidation of oxides of
nitrogen in the photochemical reaction se-
quence. The benzene-soluble particulate con-
centration also is higher in Los Angeles than
in any other of 60 standard metropolitan sta-
tistical areas of the United States, although
Los Angeles ranks only twelfth in total con-
centrations of particulate matter. This
suggests that organic aerosol material, photo-
chemically generated, may be quantitatively
significant in the Los Angeles atmosphere.
It has been suggested that sulfur dioxide
may be oxidized to sulfates more rapidly in
the presence of photochemical oxidants than
otherwise. Without further study of emission
variables, the available information can yield
no evidence on this point.
D. SUMMARY
Air quality within a metropolitan region,
on a statistical basis, shows gradients asso-
ciated with prevailing patterns of wind move-
ment. For primary pollutants, the greatest
concentrations are to be found, on the
average, in the near vicinity of the most pro-
lific sources of emissions. For the secondary
contaminants of the photochemical air poll-
ution complex, the same generalization does
not hold. Maximum concentrations of such
Table 3-8. AVERAGE ALDEHYDE CONCENTRATIONS BY HOUR IN LOS ANGELES,20
SEPTEMBER 25 THROUGH NOVEMBER 15, 1961
Sampling
time
7:00 a.m.
8:00 a.m.
9:00 a.m.
10:00 a.m.
11:00 a.m.
Noon
1:00 p.m.
2:00 p.m.
3:00 p.m.
4:00 p.m.
Formaldehyde
Number of
days
7
18
21
28
27
23
25
27
25
15
Average
concentration, ppm
0.041
0.043
0.045
0.044
0.051
0.044
0.041
0.034
0.026
0.019
Acrolein
Number of
days
2
3
3
5
5
3
7
5
4
5
Average
concentration, ppm
0.007
0.009
0.009
0.008
0.008
0.005
0.008
0.007
0.004
0.004
3-12
-------
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5 0.12
Q
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<
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< LO °-06
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£ °-1°
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^ 0.06
Qi
O 0.04
LL
0.02
e
I I I I I
— ^x^*. HUNTINGTON —
^^ \
.^^ % i A r\ i\
- / X\\
/* » »
/ /'.A
i * •* * i\
— si •** **»* ~~
— / **..** ALIPHATIC —
/ X1** ~"~ ALDEHYDES
"" 4* — —
•^** • — -FORMALDEHYDE
L • *
+ EL MONTE
_ A
/— —i
_ \
"~ x^^ K*""~ ~
> . ~
- » *
^ ^« • • i^^*
~ %i* i i i i ~
> 12 e
u.uia
0.016
0.014
0.012
E
0.010 £
K
0.008 g
0.006 i-
<
0.004 ^
0.002 ^
U
0 Z
O
0.014 U
0.012 -
UJ
0.010 ^
0.008 u
0.006 <
0.004
0.002
-p.m.
LOCAL TIME
Figure 3-5. Hourly aldehyde concentrations
at two Los Angeles sites, October 22,
1968.21
Table 3-9. COMPARISON OF COMPOSITION OF SUSPENDED PARTICIPATE
AIR SAMPLES FROM FIVE UNITED STATES CITIES22
Component
Total suspended
particulates
Benzene-soluble
organics, (% of
total particulates)
Nitrates
Sulfates
Year
1961
through
1965
1961
through
1965
1962
1963
1964
1962
1963
1964
O
Geometric mean concentration, Aig/rrr
Los Angeles
146
15.5
(10.6)
8.7
8.3
N.A.
12.9
6.9
N.A.
Denver
147
11.7
(8.0)
1.4
1.9
2.0
2.2
3.6
3.0
Chicago
177
9.5
(5.4)
N.A.a
1.1
2.0
N.A.
15.2
16.7
New York
135
10.1
(7.5)
N.A.
2.3
1.8
N.A.
25.0
28.7
Wash.
104
9.4
(9.0)
1.2
2.1
1.7
11.0
13.1
8.0
aN.A. = not available.
3-13
-------
photochemical products as aldehydes,
nitrogen dioxide, peroxyacyl nitrates, and
especially ozone, are very likely to be dis-
placed by 10 or 20 miles from the areas in
which the effective primary contaminants
were emitted, and residual effects will be ob-
served even farther downwind.
Yearly averages of monthly maximum
1-hour average hydrocarbon concentrations,
including methane, recorded continuously in
various stations of the CAMP network, have
reached 8 to 17 ppm (as carbon), but at least
half of this amount is probably the unreactive
methane component in all cases. Thus concen-
trations of 10 ppm (as carbon) or less of non-
methane hydrocarbons can give rise to ob-
served concentrations of secondary photo-
chemical contaminants in urban atmospheres.
In a series of 200 samples taken in one
urban location, average concentrations of the
most abundant hydrocarbons were as follows
(in ppm as carbon): methane, 3.22; toluene,
0.37; «-butane, 0.26; /-pentane, 0.21; ethane,
0.20; benzene, 0.19; /7-pentane, 0.18;
propane, 0.15; ethylene, 0.12. Among classes
of hydrocarbons, the alkanes predominate,
even if methane is excluded. They are fol-
lowed by the aromatics, olefins, acetylene,
and alicyclics.
The diurnal variation of hydrocarbon con-
centrations resembles that of carbon mon-
oxide (at stations in the Los Angeles area) in
having a pronounced maximum, which ap-
pears usually between 6:00 and 8:00 a.m.
PST. It is not, however, parallel to the diurnal
variation of secondary contaminants, particu-
larly ozone, which typically show a pro-
nounced maximum in the afternoon. This dif-
ference in behavior is characteristic of the
photochemical air pollution complex.
Observed concentrations of photochemical
oxidants are reviewed in detail in the com-
panion document, AP-63, Air Quality Criteria
for Photochemical Oxidants. For nonoxidant
photochemical secondary contaminants, avail-
able information is limited to results of spe-
cial studies on aldehydes in the Los Angeles
area. These show that yearly maximum
1-hour average total aldehyde concentrations
range from 0.20 to 1.30 ppm and that the
analogous formaldehyde concentrations range
from 60 to 150 Mg/m3 (0.05 to 0.12 ppm).
Hourly average acrolein concentrations range
from 10 to 270 Mg/m3 (0.004 to 0.010 ppm)
in various other studies. The ratio of formal-
dehyde to the total aldehyde index has been
reported at from about 10 percent to about
90 percent. Much of the variation is undoubt-
edly caused by the use of different analytical
methods in the different investigations.
E. REFERENCES
1. Cavanagh, L. A., C. F. Schadt, and E. Robinson.
Atmospheric Hydrocarbon and Carbon
Monoxide Measurements at Point Barrow,
Alaska. Environ. Sci. Technol. 3:251-257, March
1969.
2. Ehhalt, D. H. Methane in the Atmosphere. J. Air
Pollution Control Assoc. 17: 518-519, August
1967.
3. Swinnerton, J. W., V. J. Linnenbom, and C. H.
Cheek. Distribution of Methane and Carbon
Monoxide Between the Atmosphere and Natural
Waters. Environ. Sci. Technol. 5:836-838, Sep-
tember 1969.
4. Altshulller, A. P. et al. Continuous Monitoring of
Methane and Other Hydrocarbons in Urban At-
mospheres. J. Air Pollution Control Assoc.
1 6:87-91, February 1966.
5. 1962-1967 Summary of Monthly Means and
Maximums of Pollutant Concentrations, Continu-
ous Air Monitoring Projects, National Air Surveil-
lance Networks. U.S.DHEW, PHS, NAPCA. Pub.
No. APTD 69-1, April 1969.
6. Stephens, E. R. and F. R. Burleson. Distribution
of Light Hydrocarbons in Ambient Air. Pre-
sented at 62nd Annual Meeting of the Air Pollu-
tion Control Association. New York. June 22-26,
1969.
7. Neligan, R. E. Hydrocarbons in the Los Angeles
Atmosphere. Arch. Environ. Health. .5:581-591,
December 1962.
8. Altshuller, A. P. et al. A Technique for Measuring
Photochemical Reactions in Atmospheric Sam-
ples, Science. (Submitted for publication.)
9. Los Angeles County Air Pollution Control Dis-
trict. A Study of Low Visibilities in the Los An-
geles Basin, 1950-1961. Air Quality Report No.
53, 1964.
10. Laboratory Data, 1966-1967. Los Angeles
County Air Pollution Control District.
11. Gordon, R. J., M. Mayrsohn, and R. M. Ingels.
C^- GS Hydrocarbons in the Los Angeles Atmos-
3-14
-------
phere. Environ. Sci. Technol. 2:1117-1120, De-
cember 1968.
12. California Air Quality Data, 1968-1969. Cali-
fornia Air Resources Board.
13. Lonneman, W. A., T. A. Bellar and A. P. Alt-
shuller. Aromatic Hydrocarbons in the At-
mosphere of the Los Angeles Basin. Environ. Sci.
Technol. 2:1017-1020, November 1968.
14. Altshuller, A. P. and J. J. Bufalini. Photo-
chemical Aspects of Air Pollution: A Review.
Photochem. Photobiol. 4(2):97-146, March
1965.
15. Stephens, E. R. and F. R. Burleson. Analysis of
the Atmosphere for Light Hydrocarbons. J. Air
Pollution Control Assoc. 77:147-153, March
1967.
16. Dickinson, J. E. Air Quality of Los Angeles
County. Los Angeles County Air Pollution Con-
trol District. Los Angeles, Calif. Technical Prog-
ress Report, Vol. II. February 1961.
17. Laboratory Methods: Aldehydes. Los Angeles
County Air Pollution Control District. California.
Method 5-46. 1958.
18. Laboratory Methods: Formaldehyde. Los An-
geles County Air Pollution Control District. Cal-
ifornia. Method 8-53. 1958.
19. Renzetti, N. A. and R. J. Bryan. Atmospheric
Sampling for Aldehydes and Eye Irritation in Los
Angeles Smog-1960. J. Air Pollution Control
Assoc. 11:421-424. 427, September 1961.
20. Altshuller, A. P. and S. P. McPherson, Spectro-
photometric Analysis of Aldehydes in the Los
Angeles Atmosphere. JAPCA 1 J(3): 109-111,
1963.
21. Atmospheric Reaction Studies in the Los Angeles
Basin — Vol. I. Scott Research Laboratories, Inc.
for Coordinating Research Council, Inc. NAPCA
Contract No. CPA 22-69-19. 1969.
22. Air Quality Criteria for Particulate Matter. U.S.
DHEW, PHS, EHS, National Air Pollution C
ontrol Administration. Washington, D. C. Publi-
cation Number AP-49. 1969.
3-15
-------
CHAPTER 4.
GENERAL STANDARDIZATION AND ANALYSIS METHODS
A. INTRODUCTION
For most common gaseous air pollutants,
the analyst must develop a specific analytical
method for one or at most a few related spe-
cies.1'3 Thus for many pollutants both simple
manual and complex instrumental methods
are available. This is not the case with hydro-
carbons, for the complexity of the mixture of
the compounds that may be present demands
more sophisticated instrumentation and tech-
niques for measurement.
One instrumental technique can measure
the total hydrocarbon concentration of the
atmosphere. The value of the data obtained
is severely limited, however, because the
high background level of naturally occurring
methane obscures the variation in levels of
reactive hydrocarbon species, which, because
they may participate in photochemical reac-
tions, are usually of principal interest. While
simple attempts to eliminate the methane in-
fluence have had some success, only specific
analysis provides the data needed to delineate
properly and fully the nature of atmospheric
photochemistry and to evaluate the relative
contributions of various sources.
B. CALIBRATION TECHNIQUES
1. Dynamic
Calibration at regular intervals is required
for all analytical methods. It may be dynamic
or static. Dynamic calibration involves passing
known, realistic concentrations of the pol-
lutant in air into the system as if it were an
actual sample. This technique may be fairly
difficult because of the very low concentra-
tions of some pollutants and the reactivity or
condensability of others.
Standard calibration gases in high-pressure
steel cylinders are most commonly used to
calibrate hydrocarbon analyzers. The gas is
diluted in the cylinder to the desired concen-
tration and then fed directly to the analyzer.
Common hydrocarbons diluted to atmos-
pheric concentration ranges are available com-
mercially. Commercial mixtures should
always be checked against a reference stand-
ard; or, if this is not possible, they should at
least be checked by an independently cali-
brated hydrocarbon analyzer.
Various gas dilution systems have been de-
scribed. A fairly simple method recently
developed utilizes permeation tubes; this
method is suitable for pollutants that can be
condensed at moderate pressures in plastic
tubes. The pollutant will effuse through the
walls of a tube made of a specific plastic at a
rate dependent upon tube surface area and
temperature. To generate a known dynamic
concentration, air is passed at a known rate
over the permeation tube in a thermostated
vessel. The tube may be calibrated gravi-
metrically if it is held at constant tempera-
ture, and the permeation rate remains con-
stant as long as the tube contains appreciable
liquid.
Another dynamic calibration technique in-
volves the addition of a measured amount of
pollutant to a known fixed volume of air in a
large vessel. The addition may be made by
syringe injection or by crushing a weighed
glass ampoule containing the pollutant. If the
vessel is rigid, it must be large relative to the
amount of sample to be withdrawn. Bags
made of plastics, which have the advantage of
collapsing as the sample is withdrawn, may
also be used. Bags must be made of an inert
material to avoid changes in concentration
through absorption or reaction with the walls
of the bag.
4-1
-------
Only dynamic calibration tests the integ-
ritiy of intake lines, flow-measuring devices,
filters, pumps, and other components of the
analyzer that may contaminate or alter the
sample before it reaches the sensor.
2. Static
In static calibration, a standard solution of
the pollutant, a substance that will generate
the pollutant, or the final reaction product
may be used. Static calibration is useful for
preliminary standardization of a method and
for the adjustment of photometric sensors,
but the only adequate calibration is by
dynamic techniques.
C. METHODS FOR ANALYSIS OF
TOTAL HYDROCARBONS
1. Flame lonization
Originally developed as a detector for gas
chromatography, the flame ionization tech-
nique (FID) was later adapted for total hydro-
carbon analysis. In the technique, a sensitive
electrometer detects the increase in ion inten-
sity 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 approxi-
mately in proportion to the number of organi-
cally bound carbon atoms in the sample. The
FID is essentially a carbon atom counter, but
its response to carbon atoms in different com-
pounds is nonlinear. As a result, FID data are
usually expressed as the calibration gas
used: for example, parts per million of carbon
as methane. Carbon atoms bound to oxygen,
nitrogen, or halogens give reduced or no re-
sponse. 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 instrument also responds to
hydrocarbon derivatives approximately ac-
cording to the proportion of carbon atoms
bound to carbon or hydrogen.
The response of the FID is rapid and, with
careful calibration, is sensitive to a fraction of
a ppm carbon as methane. The variations in
response to various hydrocarbons and deriva-
4-2
tives must be accounted for in data evalua-
o
tion. Practically all continuous hydrocarbon
analyzers in use today utilize the flame ioniza-
tion detector as the sensing element. The
flame ionization hydrocarbon analyzer is gen-
erally accepted by the National Air Pollution
Control Administration at the present time as
the method of reference for the determina-
tion of total hydrocarbons.
2. Spectrophotometric Methods
Spectrophotometric methods are usually
applied to samples concentrated by freeze-
out or other techniques. The principal prob-
lem encountered with their use is one of cali-
bration. In many cases hexane is chosen as a
calibration compound to represent the whole
hydrocarbon class. In infrared Spectrophoto-
metric methods, the reading is made at about
3.4 minus, which is the carbon-hydrogen
bond stretch wavelength. At this wavelength,
more weight is given to saturated hydro-
carbons, which are rich in carbon-hydrogen
bonds, than to unsaturates. The absorbance at
other infrared wavelengths can be read and
correction made for certain principal compo-
nents, such as methane, acetylene, and ethyl-
ene.1"3
Nondispersive infrared Spectrophotometric
instruments have similar limitations. Because
instrument sensitivity is low, atmospheric
analysis without freeze-out requires very long
cell path lengths.1'3
D. METHODS FOR ANALYSIS OF
SPECIFIC HYDROCARBONS
1. Subtractive Columns
a. Nonmethane Hydrocarbons
In typical polluted air samples the principal
hydrocarbon component, methane, is usually
more abundant than all other hydrocarbons
combined. Methane, however, is inert in pho-
tochemical reactions. It is therefore desirable
to measure methane separately to permit an
estimation by difference of the nonmethane
hydrocarbons.9 In one technique, a carbon
column is treated with methane until it
"breaks through," that is, until no more
-------
methane is absorbed, although other hydro-
carbons are still retained.1 ° This column be-
comes a "methane only" analyzer when it is
used to absorb nonmethane hydrocarbons
before analysis of the sample by a flame
ionization analyzer. If the methane analyzer is
run in parallel or in alternation with a conven-
tional total hydrocarbon analyzer, methane
and total hydrocarbons are measured and, by
difference, the nonmethane hydrocarbon con-
centration may be calculated. Thus a some-
what better approximation of the reactive
fraction is provided.11 >12
b. Reactive Hydrocarbons
Fractionation of organic compound con-
taminants can be useful when it results in
separate determinations of classes of com-
pounds having significantly different reactivi-
ties in the photochemical air pollution com-
plex. Such a system, described by Klosterman
and Sigsby,1 3 permits separate determination
of three groups: (1) olefins and acetylenes,
both aliphatic and alicyclic as well as, presum-
ably, aromatic; (2) aromatics excluding ben-
zene; and (3) other hydrocarbons, including
benzene. The members of the first group are
scrubbed from a sample stream by a column
containing firebrick supporting mercuric sul-
fate; those of the second group are removed
by palladium sulfate. The first column also
removes alcohols, ketones, and organic acids;
the second is effective in scrubbing aldehydes,
ethers, and esters. Though at present it is only
used in the analysis of automobile exhausts,
the system shows promise for use in
conjunction with other hydrocarbon ana-
lyzers, including flame ionization and gas
chromatographic units, in giving a complete
definition of the nature of hydrocarbon pollu-
tion.
2. Gas Chromatography
Gas chromatography (GC) is the only avail-
able method for specific atmospheric hydro-
carbon analysis.12'14 With flame ionization
detection, it is sensitive in the ppb range.
Through the judicious choice of columns and
temperatures, almost any desired separation
of components can be effected.
Very little data except those from California
are available on ambient levels of individual
hydrocarbons, and none are available on a
tinuous basis. Two factors tended to produce
this situation: GC data are in a form most
tedious to reduce to meaningful information;
and, until recently, automation of data reduc-
tion was not possible and the manpower need-
ed to process the volume of raw data
manually was not available.
Qualitative identification of the many over-
lapping peaks is difficult. An unknown can be
identified, however, by comparing the chro-
matogram with that of reference compounds
run under the same operating conditions, or
by attaching a qualitative detector such as an
infrared or mass spectrometer to the GC out-
put. Both approaches require highly trained
personnel.
For type separations using GC, subtractive
columns may be used before or after the unit.
Examples are mercuric perchlorate 'and silver
sulfate — sulfuric acid columns, which are
used to remove unsaturates and pass
paraffins. The use of subtractive columns
simplifies an analysis in which individual com-
ponents of different hydrocarbon types over-
lap or interface in the chromatogram.
3. Spectrometric Methods
Both infrared and mass spectrometric
methods are capable of considerable discrimi-
nation among hydrocarbons, but the low
sensitivity required for ambient air monitor-
ing often necessitates a freeze;out or concen-
tration step. The operation and maintenance
of either instrument is demanding and expen-
sive, and data reduction is complicated. Infra-
red spectra may be used to determine the
proportions of various olefin types, various
aliphatic carbon-hydrogen types (primary,
secondary or tertiary), and some aromatic
types.15 The mass spectrometer can differen-
tiate paraffin, olefin plus naphthene, and aro-
matic groups; in restricted narrow fractions it
may permit analysis for individual compo-
nents.16'17
4-3
-------
4. Methods for Olefins
A number of methods for olefin determina-
tion by colorimetric or coulometric tech-
niques are available. The colorimetric reagents
include phosphomolybdate18 p-dimethyl-
aminobenzaldehyde in sulfuric acid.19 A
coulometric analyzer based on the reaction of
olefins with bromine was used successfully in
several studies.20
E. METHODS FOR ANALYSIS OF GASE-
OUS ALDEHYDES AND KETONES
1. General
Limitations of methodology allow measure-
ment of only a few specific oxygenated organ-
ics. Except for one formaldehyde proce-
dure,2 ! there are no automated measurement
methods for these contaminants. Only manual
colorimetric procedures employing bubblers
for sampling are available. The methods used
for measurement of carbonyls (aldehydes and
ketones) are mostly based on condensation
reactions.22 There is no single method that
reliably measures total carbonyls or alde-
hydes. Sampling of oxygenates is difficult
because of their water solubility and their
ready condensation or adsorption in the sys-
tem.
2. Bisulfite Method
The bisulfite aqueous reagent23 forms
moderately stable complexes with lower-
molecular-weight aldehydes and methyl ke-
tones.24 Heavier aldehydes are too insoluble
for complex formation, and most ketones
form unstable complexes. After complex for-
mation, the excess reagent is destroyed and
the complex is broken up. The released bisul-
fite is analyzed by iodimetry. This method is
only moderately sensitive. Bisulfite reagent is
also used as a collection absorber for other
methods because the carbonyls are readily lib-
erated by acidification of the complex.
3. Other Condensation Reagents
Among the condensation reagents that will
react with carbonyl compounds1'3 are:
cyanide, hydroxylamine, phenylhydrazine,
2,4-dinitrophenylhydrazine, Schiffs re-
agent,2 * 2-hydrazinobenzothiazole,
44
3-methyl-2-benzothiazole hydrazone (MBTH),
and chromotropic acid.25 The Schiffs re-
agent and chromotropic acid methods can re-
sult in good precision and sensitivity for
formaldehyde measurement when used with
current analytical procedures. The MBTH
method is good for aliphatic aldehydes (in-
cluding formaldehydes), but purity of the
MBTH is a constant problem. Since it reacts
with both aldehydes and ketones,26-28
2,4-dinitrophenylhydrazine is one of the more
general carbonyl reagents used.29 Color-
imetric determinations with 2,4-dinitro-
phenlhydrazine are complicated by shifts in
wavelength with type of carbonyl compound;
gravimetric analyses with 2,4-dinitrophenyl-
hydrazine are lengthy and too insensitive for
atmospheric work.
Formaldehyde, generally found to be the
predominant carbonyl compound in the
atmosphere, is very water soluble and in most
derivatives is not typical of aldehydes as a
class. For this reason it is often desirable to
use a procedure specific for formaldehyde
(such as the chromotropic acid meth-
od),25'30 and then determine total aldehydes
or carbonyls by another method, attempting
to allow for the amount of formaldehydes
found independently.
The unsaturated aldehyde, acrolein, has
also received special attention because, like
formaldehyde, it is a known lacrimator
found in measurable concentration in photo-
chemically polluted air. The method used
most commonly is colorimetric and employs a
4-hexylresorcinol reagent, which is specific
and sensitive.31
The chromotropic acid method for alde-
hydes and the MBTH method for total alde-
hydes and ketones are the most widely used
methods and are recommended by the
National Air Pollution Control Administra-
tion as the reference methods for analysis of
these compounds.
F. SAMPLE COLLECTION AND
HANDLING
Samples for hydrocarbon measurement
must occasionally be collected in the field and
-------
returned to a central laboratory for analysis.
The manner in which they are transported
must be chosen so as to prevent deterioration
in storage and transit. Evacuated glass vessels
or inert plastic bags are sometimes used for
the collection of grab samples.32
For condensable pollutants, a freeze-out
technique may be used. The air is passed
through a trap immersed in a cold bath (ice
or liquid air) suitable for condensing the
materials of interest. Sometimes the trap is
packed with an inert solid absorbent. Later
the trap is connected to the detector and
warmed up to volatilize the sample. In this
method, the normally large quantities of
water vapor in air also condense. The water
can cometimes be removed by a drying agent
if the pollutant of interest is not also affected
as a result. In most instances, these grab sam-
ples can be analyzed by the techniques de-
scribed above.
G. AEROSOL MEASUREMENTS
The participate material observed in photo-
chemical air pollution (in addition to that
portion of solid particulates found even in the
absence of a photochemical reaction system)
is partially liquid in character. In a sample the
moisture and other evaporable liquid gen-
erally present make weight and volume esti-
mates difficult and dependent on the recent
sample history. Prolonged passage of sample
air over the aerosol may evaporate part of the
colllected material. The weight of a collected
photochemical aerosol also depends on the
relative humidity to which it has been ex-
posed between time of collection and weigh-
ing.33 The extent to which gaseous photo-
chemical reaction products condense to liquid
and perhaps solid materials, or condense onto
solid particulate material, is very uncertain.
Thus aerosol collection, separation by part-
icle size, and characterization are difficult.
Most of the conventional collection methods
are suitable for solid particulates, but have
very uncertain effects on liquid aerosols.
Methods based on light scattering do not
affect the particles appreciably, but are hard
to relate to known particulate sizes and den-
sities. The reader is referred to AP-49, Air
Quality Criteria for Particulate Matter3 4 for a
detailed discussion of aerosol sampling and
analysis techniques.
H. SUMMARY
With a few exceptions, atmospheric hydro-
carbon measurements are made with contin-
uous, relatively complex instruments. Increas-
ing demands for detailed data on specific
compounds will reinforce this trend.
Continuous analysis instrumentation de-
mands dynamic calibration techniques. Stand-
ard gases for this purpose are commercially
available, may be generaged by permeation
tubes or dilution systems, or may be prepared
in large containers.
Flame ionization analyzers are sensitive,
reliable, and suitable for the continuous meas-
urement of total hydrocarbons. They are gen-
erally accepted as the method of choice by
the National Air Pollution Control Adminis-
tration. They fail, however, to give the spe-
cific detailed information required for a
thorough understanding of the atmospheric
photochemical problem. Attempts to further
define the hydrocarbon mixture by using pre-
treatment columns to measure only methane
or various reactive classes have met with some
success in limited application.
Spectrometric techniques both for total
and specific analyses are complex and gen-
erally insensitive; they require sample concen-
tration steps or long path lengths.
Gas chromatrographic analysis provides the
requisite sensitivity and specificity for the
quantitation of individual hydrocarbons. Dif-
ficulties in qualitative analysis and data hand-
ling have limited the application of GC to
short-term studies for the most part, and no
continuous data are available.
Carbonyl compounds, specifically alde-
hydes and ketones, can be measured by sev-
eral manual colorimetric techniques, but few
actual data are available.
I. REFERENCES
1. Hendrickson, E. R. Air Sampling and Quantity
Measurements. In: Air Pollution, Stern, A. C.
4-5
-------
(ed.), Vol. II, 2d ed. New York, Academic Press,
1968. p. 3-52.
2. Katz, M. Analysis of Inorganic Gaseous Pollu-
tants. In: Air Pollution, Stern, A. C. (ed.), Vol.
II, 2d ed. New York, Academic Press, 1968. p.
53-114.
3. Lodge, J. P. Production of Controlled Test
Atmospheres. In: Air Pollution, Stern, A. C.
(ed.), Vol. II, 2d ed. New York, Academic Press,
1968, p. 465-483.
4. Lodge, J. P., Jr. et al. The Use of Hypodermic
Needles as Critical Orifices in Sampling. J. Air
Pollution Control Assoc. 76:197-200, April
1966.
5. Thomas, M. D. and R. E. Amtower. Gas Dilution
Apparatus for Preparing Reproducible Dynamic
Gas Mixtures in Any Desired Concentration and
Complexity. J. Air Pollution Control Assoc.
76:618-623, November 1966.
6. O'Keefe, A. E. and G. C. Ortman. Primary Stand-
ards for Trace Gas Analysis. Anal. Chem.
55:760-763, May 1966.
7. Andreatch, A. J. and R. Feinland. Continuous
Trace Hydrocarbon Analysis by Flame loniza-
tion. Anal. Chem. 52:1021-1024, July 1960.
8. Bruderreck, H., W. Schneider, and I. Halasz.
Quantitative Gas Chromatographic Analysis of
Hydrocarbons with Capillary Columns and Flame
lonization Detector. Anal. Chem. 56:461-473,
March 1964.
9. Altshuller, A. P. An Evaluation of Techniques for
the Determination of the Photochemical Reactiv-
ity of Organic Emissions. J. Air Pollution Control
Assoc. 16: 257-260, May 1966.
10. Ortman, G. C. Monitoring Methane in Atmos-
phere with a Flame lonization Detector. Anal.
Chem. 55:644-646, April 1966.
11. Altshuller, A. P. et al. Continuous Monitoring of
Methane and Other Hydrocarbons in Urban
Atmospheres. J. Air Pollution Control Assoc.
16:87-91, February 1966.
12. Altshuller, A. P. Atmospheric Analysis by Gas
Chromatography. In: Advances in Chromato-
graphy, Giddings, J. C. and R. A. Keller (eds.),
Vol. 5. New York, Marcel Dekker, Inc., 1968. p.
229-262.
13. Klosterman, D. L. and J. E. Sigsby, Jr. Applica-
tion of Subtractive Techniques to the Analysis of
Automotive Exhaust. Environ. Sci. Technol.
1:309-314, April 1967.
14. Pierce, L. B. and P. K. Mueller. Analysis of
Atmospheric Hydrocarbons by Gas Chromato-
graphy. Presented at the 10th Conference on
Methods in Air Pollution and Industrial Hygiene
Studies. San Francisco. February 19-21, 1969.
15. Mader, P. P. et al. Determination of Small
Amounts of Hydrocarbons in the Atmosphere.
Anal. Chem 24:1899-1902, December 1952.
4-6
16. Shepard, M. et al. Isolation, Identification and
Estimation of Gaseous Pollutants in Air. Anal.
Chem. 25:1431-1440, October 1951.
17. Weaver, E. R. et al. Interpretation of Mass
Spectra of Condensates from Urban Atmos-
pheres. J. Res. Nat. Bur. Stand. 59(6):383404,
December 1957.
18. MacPhee, R. D. Use of Molybdates for Estimat-
ing Amounts of Olefinic-Type Hydrocarbons in
the Air. Anal. Chem. 26:221-225, January 1954.
19. Altshuller, A. P. and S. F. Sleva. Spectrophoto-
metric Determination of Olefins. Anal. Chem.
55:1413-1420, September 1961.
20. Nicksie, S. W. and R. E. Rostenbach. Instru-
mentation for Olefin Analysis at Ambient Con-
centrations. J. Air Pollution Control Assoc.
77:417-420, September 1961.
21. Lyles, G. R., F. B. Dowling, and V. J. Blachard.
Quantitative Determination of Formaldehyde in
the Parts per Hundred Million Concentration
Level. J. Air Pollution Control Assoc.
75:106-108, March 1965.
22. Altshuller, A. P. et al. Analysis of Aliphatic Alde-
hydes in Source Effluents and in the Atmos-
phere. Anal. Chim. Acta. 25(2): 101-117, August
1961.
23. Laboratory Methods: Aldehydes. Los Angeles
County Air Pollution Control District. California.
Method 5-46. 1958.
24. Wilson, K. W. Fixation of Atmospheric Carbonyl
Compounds by Sodium Bisulfite. Anal. Chem.
50:1127-1129, June 1958.
25. Altshuller, A. P., D. L. Miller, and S. F. Sleva.
Determination of Formaldehyde in Gas Mixtures
by the Chromotropic Acid Method. Anal. Chem.
55:621-625, April 1961.
26. Sawicki, W. et al. The 3-Methyl-2-Benzothiazo-
lone Hydrazone Test. Sensitive New Methods for
the Detection, Rapid Estimation, and Determina-
tion of Aliphatic Aldehydes. Anal. Chem.
55:93-96, June 1961.
27. Altshuller, A. P. and L. J. Leng. Application of
the 3-Methyl-2-Benzothiazolone Hydrazone
Method for Atmospheric Analysis of Aliphatic
Aldehydes. Anal. Chem. 55:1541-1542, Septem-
ber 1963.
28. Hauser, T. R. and R. L. Cummins. Increasing
Sensitivity of 3-Methyl-2- Benzothiazolone
Hydrazone Test for Analysis of Aliphatic
Aldehydes in Air. Anal. Chem. 56:679-681,
March 1964.
29. Jones, L. A., J. C. Holmes, and R. B. Seligman.
Spectrophotometric studies of Some 2,4-Dini-
trophenylhydrazones. Anal. Chem. 25:191-198,
February 1956.
30. Laboratory Methods: Formaladehyde. Los
Angeles County Air Pollution Control District.
California. Method 8-53. 1958.
-------
31. Cohen, I. R. and A. P. Altshuller. A New Spec- 33. Lundgren, D. A. and D. W. Cooper. Effect of
trophotometric Method for the Determination of Humidity on Light-Scattering Methods of Meas-
Acrolein in Combustion Gases and in the Atmos- uring Particle Concentration. J. Air Pollution
phere. Anal. Chem. 33:726-133, May 1961. Control Assoc. 19: 243-247, April 1969.
32. Schuette, F. Plastic Bags for Collection of Gas 34. Air Quality Criteria for Particulate Matter. Na-
Samples. Atmos. Environ. 1: 515-519, July tional Air Pollution Control Administration.
1967. Washington, D.C. Publication Number AP-49.
1969.
4-7
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CHAPTER 5.
RELATIONSHIP OF ATMOSPHERIC HYDROCARBONS TO
PHOTOCHEMICAL AIR POLLUTION LEVELS
A. INTRODUCTION AND GENERAL
DISCUSSION
As discussed in detail in the companion
document, AP-63, Air Quality Criteria for
Photochemical Oxidants, health effects (in-
cluding eye irritation), vegetation damage,
material damage, and visibility reduction have
all been associated with the products that re-
sult from the interaction of hydrocarbons
within the nitrogen dioxide atmospheric pho-
tolytic cycle. The major objective of this chap-
ter is to delineate the quantitative relation-
ships existing between hydrocarbon concen-
trations and their photooxidation products,
and thus to relate hydrocarbon concentra-
tions to the effects of photochemical air pol-
lution. In one sense this objective has been
accomplished in considerable detail in the lab-
oratory, as is described in AP-63. Yet for a
variety of reasons, these laboratory results
cannot be quantitatively extrapolated to am-
bient atmospheres. Because of experimental
limitations, most laboratory results relate to
hydrocarbon and nitrogen oxide concentra-
tions that are somewhat higher than those ob-
served in ambient atmospheres. An additional
factor of importance is that detailed analyti-
cal procedures used in laboratory experimen-
tation have not been readily available for rou-
tine air monitoring. Thus, until recently, ntost
air monitoring systems have had to rely on a
total hydrocarbon measurement that con-
tained a sizeable fraction of photochemically
nonreactive compounds. Without additional
information as to the composition of this
total hydrocarbon mixture or, more impor-
tant, its compositional variability in the at-
mosphere, it is difficult to appraise the sig-
nificance of any apparent relationship in the
atmosphere between total hydrocarbon con-
centrations and photochemical effects. Since
1966, however, several of the CAMP stations
have been routinely measuring methane as
well as total hydrocarbons. This is a relatively
important advance since methane, a photo-
chemically inactive hydrocarbon, is known to
comprise 50 percent or more of the total
hydrocarbon measurement.
Wherever possible in this chapter, an at-
tempt has been made to correlate photochem-
ical products with the nonmethane hydrocar-
bon concentrations. In lieu of such nonme-
thane data, as is the case in the Los Angeles
area, an approximate correction for methane
was used based on the determined ratio of
total hydrocarbon to methane. It must be kept
in mind that even the measurement of non-
methane hydrocarbons is not as specific as the
photochemistry demands. Thus the propor-
tion of photochemically active hydrocarbons
in this nonmethane hydrocarbon total is sub-
ject to change on a long-term basis, because
the methods of hydrocarbon control have dif-
fering efficiencies for individual hydrocar-
bons. Such effects will eventually, over a per-
iod of years, change the relative composition
of the ambient hydrocarbon mixture. It is
possible, for example, to use control methods
that are more efficient for nonreactive hydro-
carbons. Thus, the amount of reduction in the
photochemically reactive fraction will be less
than that indicated by the nonmethane
hydrocarbon measurement. The opposite ef-
fect is also possible, since a control method
may be chosen that is more efficient for the
photochemically reactive hydrocarbons. In
this discussion, the relationship that is devel-
oped between nonmethane hydrocarbons and
5-1
-------
oxidant levels must be recognized as subject
to change due to changes in the relative pro-
portions of photochemically reactive hydro-
carbons in ambient air. On the other hand,
such a change in the composition of the am-
bient hydrocarbons will necessarily be slow;
several years may pass before these variations
can be demonstrated. More specific methods
for measuring the photochemically reactive
fraction of atmospheric hydrocarbons are
under development and may soon be available
for monitoring purposes.
Most of the available information concern-
ing the photochemical system has been dis-
covered by laboratory investigation of simu-
lated atmospheres. As previously discussed in
AP-63, Air Quality Criteria for Photochemical
Oxidants, it has not been apparent how such
results are to be extrapolated to ambient at-
mospheres. Recent improvements in tech-
niques, however, are permitting experimental
simulation of hydrocarbon - oxides of nitro-
gen mixtures that are characteristic of the
concentrations found in ambient atmos-
pheres; therefore, less extrapolation is being
required. Thus, the findings of a study
conducted by the Bureau of Mines for the
National Air Pollution Control Admin-
istration will soon be published and will
present the results of simulated-atmosphere
studies using diluted automobile exhaust in
which the total hydrocarbon concentration
varied from 0.1 to 5 ppm C. The oxides of
nitrogen concentration in these studies varied
from 0.08 to 0.27 ppm. Simulated-sunlight ir-
radiation of these mixtures under static condi-
tions indicates that an hourly average con-
centration of 0.1 ppm oxidant can be
achieved when the total hydrocarbon value is
in the range of 0.1 to 0.4 ppm C. These
results represent the closest simulation of
ambient atmospheres to date. While certain
unknowns still exist relative to extrapolation
of such laboratory data, it is of interest to
note the similarity of these results with those
subsequently shown to be associated with
ambient atmospheres at certain CAMP
stations.
There are several principles based on lab-
oratory experimentation that are applicable
to the analysis of ambient air data. Although
the reactions are complex and incompletely
understood, the products of photochemical
reactions and their effects are relatively well
delineated. Each hydrocarbon capable of in-
teracting within the NC>2 photolytic cycle leads
to predictable and invariable products. The
most common hydrocarbon products of pho-
tochemical reactions are aldehydes and ke-
tones. Among the minor products, the most
important in terms of effects are the peroxy-
acyl nitrates and the peroxybenzoyl nitrates.
Certain of these products are known to con-
tribute to specific effects associated with pho-
tochemical air pollution. Aldehydes, notably
formaldehyde and acrolein, and the peroxy-
nitrates are associated with eye irritation.
Similarly, ozone and the peroxynitrates may
be associated with health effects, vegetation
damage, or damage to materials.
Perhaps the least understood effect is that
of visibility reduction resulting from the pres-
ence of photochemically formed atmospheric
aerosols. It is known, however, that certain
aromatic hydrocarbons interacting within the
NC>2 photolytic cycle lead to the formation
of such aerosols. Furthermore, and perhaps of
more importance, it is known that some as-
pect of the photochemical complex leads to
the rapid oxidation of sulfur dioxide to form
sulfuric acid aerosols.
B. ANALYSIS OF AEROMETRIC DATA
Prior studies of air monitoring data have
largely been limited to the application of cor-
relation analyses and to the attempted use of
empirical relationships. Good correlation has
beftn demonstrated between oxidant concen-
trations and reported eye irritation1 and
measured visiblity reduction.2 These results
are surprising in a sense, since on a day-to-day
basis, the correlations are rather poor. The ob-
served relationships do illustrate certain char-
acteristics of air monitoring data that are of
prime importance and utility in studying at-
mospheric data. Perhaps the most important
characteristic is that the observed correlations
5-2
-------
are largely a function of the dominating influ-
ence of meteorological variables relating to
dispersion and dilution. A second important
characteristic is that the correlation between
oxidant concentrations and additional mani-
festations of photochemical smog is generally
good because the oxidants, the eye irritants,
and the visibility-reducing aerosols are all
products of, and thus dependent variables in,
one set of photochemical reactions. The third
characteristic is the additional dominating in-
fluence of the macro-meteorological factors
on the concentrations of both precursors and
products. As yet there is no model with which
the relationship among emissions, their ambi-
ent air concentrations, and their photochemi-
cal products can be delineated.
In the absence of such a model, rather lim-
ited attempts have been made to establish em-
pirical relationships. From the practical view-
point of control, an empirical relationship
that delineates the relationship between ambi-
ent hydrocarbon levels and subsequent oxi-
dant levels would be quite adequate, since the
established correlation between oxidant con-
centrations and both eye irritation and visibil-
ity reduction means that a clear definition of
the hydrocarbon-oxidant relationship also es-
tablishes a relationship between hydrocarbons
and eye irritation and hydrocarbons and visi-
bility reduction.
The closest approach, albeit undefinitive,
to establishing the required relationship has
been achieved by directly comparing the rela-
tionship between early morning total hydro-
carbon concentrations with the subsequent
maximum daily oxidant concentration. There
are three problems associated with this ap-
proach. The first problem is that until recent-
ly insufficient evidence was available to show
that measurements of total hydrocarbons and
the photo chemically reactive hydrocarbon
fraction could be related. As previously indi-
cated, this problem has been partially solved
by measuring both total hydrocarbons and
methane at certain of the CAMP stations.
Evaluating data from only the 6:00 to 9:00
a.m. period reveals several relationships. In
Philadelphia, for example, the ratio of non-
methane hydrocarbons to total hydrocarbons
on the 71 days investigated in the 1966 to
1968 period was 0.3 ± 0.1. In Washington,
D.C., for 78 days during the same time period.
this ratio was 0.2 ± 0.1. In Denver, a study of
32 days during the 1967 and 1968 period
yielded a ratio of 0.4 ±0.1. During a portion
of 1968, NAPCA measured nonmethane and
total hydrocarbons in downtown Los Angeles.
In this study during the 6:00 to 9:00 a.m.
period for 38 days, the hourly values were
determined. The average ratio of nonmethane
to total hydrocarbon was 0.50, with a range
of 0.43 to 0.54. These Los Angeles ratios are
partially a function of time of the day and
day of the week. A review of these findings
indicates that it is possible in certain cases to
use these ratios to approximate the non-
methane hydrocarbon concentration. Never-
theless, a direct measurement is less subject to
error. Wherever possible in this discussion, di-
rectly measured nonmethane hydrocarbon
values have been used. In the initial develop-
ment of the relationship between hydrocar-
bon and oxidant concentrations, however, it
has been necessary to use the uncorrected
total hydrocarbon values, since such measure-
ments comprise the bulk of available data.
For the Los Angeles station, no nonmethane
data are available. Thus, where data from this
station are used on a nonmethane basis, they
have been corrected by use of the independ-
ently determined ratio. In any event, the Los
Angeles data do not affect the direct determi-
nation of the association between hydrocar-
bon and oxidant levels discussed later in this
chapter. The Los Angeles data are useful pri-
marily because they demonstrate locational
independence of the hydrocarbon-oxidant re-
lationship, they illustrate the predominance
of macro-meteorological variables, they de-
lineate the limit of oxidant concentrations re-
sulting from certain hydrocarbon concentra-
tions, and they show the air quality relation-
ship that exists between widely separated sta-
tions within a given metropolitan area.
A second problem is the implied assump-
tion inherent in comparing early morning
5-3
-------
hydrocarbon levels with the maximum oxi-
dant concentrations occurring several hours
later. The implication is that the measurement
of air quality at a specific point is a good
quantification of the air quality of the air
mass covering large segments of the metro-
politan area. The results of correlation anal-
yses and the dominance of macro-meteor-
ological factors would tend to support such
an implication. Yet, fortunately, one need not
rely on such supposition, since this question is
directly amenable to investigation. A study of
data from several stations within a given area
is necessary, and such data for the Los An-
geles area have been examined. Examination
of data from June 1962 to June 1963 shows
that there generally exists a very close and
definable relationship between oxidant values
measured at various points over a 600-square-
mile area.3 The correlation between air qual-
ity measurements at various stations within
this area exhibited a standard deviation of less
than 10 percent.
Again it seems quite clear that the macro-
meteorological variables are dominant influ-
ences on the ambient air quality and, there-
fore, account for the close correlation be-
tween ambient concentrations at widely sepa-
rated points within a metropolitan area. Fur-
ther examination of these Los Angeles data
indicates that changes in human activities
could account for as much as 20 percent of
the variation in hydrocarbon levels and result-
ant oxidant levels on a day-to-day basis. The
total range in hydrocarbon and oxidant con-
centrations, however, varies up to 200 per-
cent, again illustrating the importance of
meteorological variables on hydrocarbon and
oxidant levels. This direct examination of the
air quality of a metropolitan air mass supports
the concept that early morning hydrocarbon
levels measured at a single point are propor-
tional to the hydrocarbon levels responsible
for oxidant concentrations observed at the
same single point later in the day. .
A third problem relates to the choice of
early morning hydrocarbon concentrations in
preference to, for example, the concentration
found at the time of peak oxidant levels. Re-
54
flection shows that examination of the 6:00
to 9:00 a.m. time period constitutes the most
conservative approach; and, in addition, it is
most consistent with current knowledge of
the reactions involved. It is considered con-
servative, since this time period usually corre-
sponds to the peak hydrocarbon concentra-
tions (see Chapter 3, Figures 3-2 and 3-3)
prior to the development of the peak oxidant
level. Thus, adoption of any other hydrocar-
bon concentration would lead to an associa-
tion of even lower hydrocarbon values with
the peak oxidant level than those herein dem-
onstrated. This 6:00 to 9:00 a.m. technique is
consistent with knowledge of the facts, i.e.,
that the measured hydrocarbon during this
period must contain that fraction of photo-
chemically reactive compounds that contrib-
ute most to the oxidant peak. Comparison of
peak oxidant concentrations with the hydro-
carbon levels at the time of this oxidant peak
is of dubious value, since it is known from
atmospheric analysis that most of the photo-
chemically reactive hydrocarbons have disap-
peared from the mixture by this time. Varia-
tions in the chosen time period have also been
taken into consideration.
Changes in human activities on weekends
frequently shift the time of peak hydrocarbon
concentration by an hour or more; but if the
measurements were extended to cover the
6:00 to 10:00 a.m. period for the entire
week, the overall result would be an associa-
tion of slightly lower hydrocarbon values with
a given oxidant concentration. Alternately,
only that hour when the peak hydrocarbon
concentration occurs might be chosen. This,
however, has additional problems that are less
consistent with facts. Such a choice ignores
the fact that it is not a single hour's emissions
that contribute the photochemically reactive
compounds. It, likewise, ignores the fact that
a peak in the 6:00 to 7:00 a.m. period will
contribute much less to the subsequent maxi-
mum oxidant concentration than an 8:00 to
9:00 a.m. peak. It has also been considered
that the 3-hour period chosen should be shift-
ed, wherever applicable on weekends, to con-
form to the hydrocarbon peak. Such a system
-------
has associated problems, however, since any
time beyond 9:00 a.m. is definitely entering
the period in which the photochemically reac-
tive hydrocarbons are disappearing. Addition-
ally, and more important, is the fact that even
when such a system is adopted, it does not
yield significantly different results over those
obtained by using only the 6:00 to 9:00 a.m.
period. It is obvious that because of the domi-
nance of the meteorological factors, a rela-
tionship between hydrocarbon and oxidant
values will be obtained almost regardless of
what hydrocarbon values are chosen. Yet, the
known facts must not be ignored, and on this
basis, the 6:00 to 9:00 a.m. average hydrocar-
bon concentration appears most realistic and
practical for the purpose of establishing a rela-
tionship between ambient hydrocarbon and
oxidant concentrations.
Demonstrating that a relationship between
early morning hydrocarbons and maximum
daily oxidant can be expected still leaves that
relationship to be defined. There is more in-
terest in the limits of such a relationship than
in mean values. Specificially, it is desirable to
know the maximum oxidant concentration
that can be associated in ambient atmospheres
with a given hydrocarbon concentration. De-
lineation of this upper limit can be ap-
proached in several ways, but the simplest
way, without making additional assumptions,
is to examine all available individual days.4 In
such an examination, the only restriction that
must be observed is that the data for each day
be examined for validity and that the limita-
tions of measurement techniques be taken
into account. This latter item applies mainly
to the oxidant measurement. The instruments
in common use were designed to measure oxi-
dant in the 0 to 1,960 Mg/m^ (0-1 ppm) concen-
tration range. Therefore, the meaning of oxi-
dant values below approximately 135 Mg/m^
(0.07 ppm) becomes questionable. In this
treatment of data, the examination has been
restricted to oxidant values greater than 135
Mg/m^ (0.07ppm). Reflection shows that this
restriction will have no effect on the results,
since maximum rather than minimum effects
are being sought. It is apparent that the lower
limit in all cases will be near zero, since the
data include days of no sunshine.
In order to make use of the largest possible
number of days, the first examination is based
on total hydrocarbon values (Figure 5-1). A
total of 326 applicable days was available dur-
ing the 1966 through 1968 time period in
Denver, Cincinnati, Philadelphia, and Wash-
ington, and during the May through October
1967 period at the downtown Los Angeles
station. The downtown Los Angeles data were
used here, since the location of the station
more nearly corresponds to that of the CAMP
stations, i.e., it is centrally located in a metro-
politan area. When these maximum daily oxi-
dant values are plotted as a function of early
morning hydrocarbon concentration, the re-
sult is as shown in Figure 5-1. The most strik-
ing feature of this relationship is that, appar-
ently, an upper limit exists of the maximum
daily oxidant concentration as a function of
hydrocarbon concentration. Furthermore, the
data in Figure 5-1 suggest that the oxidant-
hydrocarbon relationship is largely inde-
pendent of metropolitan area. Several points
relative to the results illustrated in Figure 5-1
require discussion. For example, it becomes
obvious why a large number of days must be
considered. With only a small number of data
points available, a scatter diagram with no
clear indication of the upper limit line would
be obtained. Even with 326 days of available
data, it can be noted that delineation of the
upper limit above 3 ppm hydrocarbon be-
comes difficult. A second point to be consid-
ered is the suggested independence of this
upper limit of metropolitan geographic area.
Considering that meteorological factors are
dominating the relationship and that the mag-
nitude of meteorological factors affecting dis-
persion and dilution varies widely between
metropolitan areas, one would not expect
such an independence. A closer examination
of Figure 5-1 yields additional detail regarding
this subject. For example, it will be noted
that above a hydrocarbon level of 3 ppm C,
the Los Angeles data, and to a lesser extent
the Denver data, dominate the relationship.
Extending this observation, it is noted that
5-5
-------
the Los Angeles data contribute very few
points below 3 ppm C hydrocarbon. This is to
be expected, since the meteorological factors
restricting dilution and dispersion are more in-
tense in the Los Angeles region. Thus, al-
though imprecisely defined in Figure 5-1,
there must exist an ordering of metropolitan
areas in terms of maximum possible oxidant
values that is essentially dictated by the mix-
ing and dispersion factors. This ordering of
areas can, of course, be affected by hydrocar-
bon emission rates on a unit-area basis. Differ-
ences in such rates in the central portions of
large metropolitan areas, however, are not
likely to be great. A check on such emission
rates yields a value of approximately 3 tons
per square mile per day for both Washington,
D.C., and Los Angeles.
The single major feature not yet discussed
in relation to Figure 5-1 is the influence of
sunlight intensity. Examination of the data
points in the vicinity of the upper limit line
shows such data to be almost exclusively con-
fined to the June through August period
when sunlight intensities in the United States
are at their highest and are essentially inde-
pendent of latitude. While latitude during
these months has little contribution, altitude
does. Thus at Denver, which is at 5,000 feet
elevation, one might expect a 10 to 15 per-
cent increase in sunlight intensity over that
observed at sea level.5 On the other hand, lab-
oratory experimentation indicates that inten-
sity changes of this magnitude have more of
an effect on rates of reactions than on ulti-
mate concentrations of products. In reality,
the changes in ground level incident sunlight
intensity caused by the polluted atmosphere
itself can be much greater than the 10 to 15
percent change produced by a change in alti-
tude. Studies conducted in the Los Angeles
area during October 1965 indicate a 50 per-
cent drop in incident solar radiation at ground
level over that observed at a 5,000-foot eleva-
tion.6 If only 15 percent of this change is at-
tributed to altitude, then 35 percent must be
attributed to absorption within the polluted
air mass. In any event, the data in Figure 5-1
do not indicate any unusual characteristic of
the Denver data.
In examining Figure 5-1, it is difficult to
see the relationship for a single station. A
search of the available data indicates the
Denver station has the most applicable points.
These data for 126 days are shown in Figure
5-2. The only point to note in relation to
these data is the already predicted tendency
for the plot to deteriorate into a scatter dia-
gram with indefinite delineation of the upper
limit on oxidant as the number of data points
is decreased.
As indicated previously, it is possible to
apply, in an approximate manner, the deter-
mined ratio of nonmethane hydrocarbon to
total hydrocarbons to the data in Figures 5-1
and 5-2. Because these ratios are variable,
however, it is better to use the nonmethane
values whenever possible. These nonmethane
values are obtained by subtracting the
methane concentration from the total hydro-
carbon concentration. Since both measured
concentrations have a precision of ± 0.1 ppm
C, their difference, i.e., nonmethane hydro-
carbons, has doubtful significance when it is
less than 0.3 ppm C. In the 1966 to 1968
period, there were 125 days of valid data at
Washington, Philadelphia, and Denver when
the oxidant concentration was greater than
135 Mg/m^ (0.07 ppm) and the nonmethane
hydrocarbon concentration was greater than
or equal to 200 ng/m^ (0.3 ppm C).
These points are shown in Figure 5-3. Also
plotted are the upper limit data points from
Los Angeles data that have been corrected,
since no directly determined nonmethane
values were available, by use of the previously
determined ratio. Little can be said concern-
ing the relative ranking of cities, since only 18
days were available from Denver as compared
to 56 from Philadelphia and 51 from Washing-
ton.
The data of most interest in Figure 5-3 are
those in the vicinity of 200 jug/m3 (0.1 ppm)
maximum hourly oxidant concentration. It is
quite apparent that the 6:00 to 9:00 a.m.
early morning nonmethane hydrocarbon value
5-6
-------
0.25
E
Q.
0.
^ 0.20
Q
X
O
LU
0
o:
UJ
< 0.15
OL
ID
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X
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n
D DENVER
• CINCINNATI
A LOS ANGELES S
,*"' A
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X* ^
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O PHILADELPHIA .S A
A WASHINGTON S <
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/'a D AOAAADADADA AA •DA««^
326 DAYS OF DATA; COINCIDENT
POINTS NOT PLOTTED
iD«0 ««A A
6-9 a.m. AVERAGE TOTAL HYDROCARBON
CONCENTRATION, ppm C
Figure 5-1. Maximum daily oxidant as a function of early morning total hydrocarbons, 1966-1968
for CAMP stations; May through October 1967 for Los Angeles.
must be below 200 jug/m3 (0.3 ppm C) if the
maximum 1-hour average oxidant concentra-
tion is to be kept below 200 Mg/m3 (0.1
ppm.). It will be noted that this is a conser-
vative approach that depends on direct exami-
nation of the data rather than extrapolation.
Obviously extrapolation would yield a lower
hydrocarbon value, but such extrapolation
cannot be justified.
It will be recalled that data from the Los
Angeles downtown station were used because
the location more nearly corresponded to the
location of the CAMP sites. Previous investiga-
tions, however, have clearly demonstrated
5-7
-------
0.30
0.25
0.20
X
o
LU
O
<
a:
LU
> 0.15
•<
a:
o
o
X
0.10
x
<
0.05
A A A
A A *
» A A A A A A
/ A 4A*AA
A A AA A*
AAA A
AAA A»A
* *
A A*» AAAAA*A*A A AA A*A
A AA A
6-9 a.m. AVERAGE TOTAL HYDROCARBON
CONCENTRATION, ppm C
Figure 5-2. Maximum daily oxidant as a function of early morning total hydrocarbons, Denver,
1966-1968.
that this particular Los Angeles site does not,
on the average, experience the highest oxidant
values in this metropolitan area.3 It is ap-
propriate at this point to further explore this
Los Angeles phenomenon, since the same
facts probably apply to the CAMP sites and
thus have implication for the value of non-
methane hydrocarbon that can be associated
with 200 Mg/m (0-1 PPm) maximum 1-hour
average oxidant concentration. The relative
location of selected Los Angeles air moni-
toring stations is shown in Figure 54. The
average wind direction is northeasterly, which
is fortunate because data from three stations
in line with this wind direction are available.
These stations, as shown in Figure 54, are
5-8
-------
0.30)
0.25'
a
a.
x
o
UJ
o
0.20
QL
O
X
0.15
0.10
X
<
0.05
LOS ANGELES*
LOS ANGELES .^* DENVER
WASHINGTON* ^f —
• ^ * LOS ANGELES
,«^A A PHILADELPHIA
.^ LOS ANGELES
PHILADELPHIA*
PHILADELPHIA
WASHINGTON S
WASHINGTON/
A A A A A A A
A A A A
•I
WASHINGTON 4.
, A A* A A AA A
A A A A A A A/
A* . i A AA 4i *A A* A*
A A* A A AAA
AA AA /A JAA * * A* A AA
0.5
1.0
1.5
2.0
2.5
6-9 a.m. AVERAGE NONMETHANE HYDROCARBON
CONCENTRATION, ppm C
Figure 5-3. Maximum daily oxidant as a function of early morning nonmethane hydrocarbons,
1966-1968 for CAMP Stations; May through October 1967 for Los Angeles.
located in downtown Los Angeles, at the
University of Southern California (USC)
Medical School, and at Pasadena. This ar-
rangement of stations thus permits examina-
tion of the contribution to oxidant values
from upwind sources. Using the May through
October data for 1967, the upper limit line of
oxidant concentration for these three stations
was determined. When these data are plotted
on one graph, the result is as shown in Figure
5-5. The results demonstrate that the more
restrictive the vertical dispersion factors, as
evidenced by higher hydrocarbons and maxi-
mum oxidants, the greater the contribution to
oxidant levels from upwind sources. The
greatest pollutant transfer is, as expected,
5-9
-------
BURBANK
HOLLYWOOD
FREEWAY
PASADENA
(ELEVATION
800 feet)
AZUSA
WEST
LOS ANGELES
DSC MEDICAL CENTER
DOWNTOWN
LOS ANGELES
INGLEWOOD
AVALON VILLAGE
LONG BEACH
(ELEVATION
0 feet)
12
24
36
Scale of mi les
Figure 5-4. Location of selected Los Angeles County air monitoring stations.
from downtown Los Angeles to the USC
Medical Center, a distance of only 3 miles. In
contrast, much less transfer occurs between
the USC Medical Center and the Pasadena
station, a distance of 10 miles. It is noted that
as the curves in Figure 5-5 are extrapolated to
200 Mg/m3 (0.1 ppm) oxidant, the contri-
5-10
bution of upwind sources tends toward a
minimum. Since most of the relationships in
Figures 5-3 and 5-5 are a function of mete-
orological variables, it appears that dispersion
rates become greater at the lower hydro-
carbon values. Thus, at oxidant concentra-
tions of 200 Mg/m3 (0.1 ppm), the
-------
0.40
6-9 a.m. AVERAGE TOTAL HYDROCARBON
CONCENTRATION, ppm C
Figure 5-5. Upper limit of maximum daily
oxidant at three Los Angeles County stations,
May through October 1967.
contributions from sources more than 3 miles
distant appear to be counterbalanced by high
dispersion rates. The air mass at the CAMP
sites studied would appear to have much
higher dispersion rates than the Los Angeles
atmosphere. Therefore, upwind oxidant con-
tributions may also be minimal at these sites.
This latter concept is based on analogy, how-
ever, and not on known facts. A more defini-
tive evaluation of this phenomenon in the
CAMP cities must await evaluation of the
results from multi-station sites in those cities.
Based on the observed association, it
should be possible to estimate by city the
percent of the time the maximum oxidant
potential is attained. Again, however, the
available data severely limit such estimations.
Combined data for Washington, Denver, and
Philadelphia for the 125 days shown in Figure
5-3 indicate that when the oxidant concentra-
tion was equal to or greater than 135 jug/m^
(0.07 ppm) and the nonmethane hydrocarbon
concentration was equal to or greater than 0.3
ppm, the maximum oxidant potential was
achieved about 8 percent of the time. Since
Figure 5-3 contains only about 11 percent of
all days for these cities for a 3-year period, it
follows that for all days in the 3-year period
the maximum oxidant potential was achieved
on less than 1 percent of the days.
C. SUMMARY
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 max-
imum daily oxidant levels must be approach-
ed empirically. The empirical approach
adopted is a comparison of 6:00 to 9:00 a.m.
average hydrocarbon values with hourly max-
imum oxidant values attained later in the day.
This approach has validity only because of the
dominating influence of the macro-mete-
orological 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 guaran-
tees 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 maxi-
mum values of attainable oxidant are a direct
function of the early morning hydrocarbon
concentration. This upper limit of the maxi-
mum daily oxidant concentration is depen-
5-11
-------
dent on the metropolitan geographical area
only to the extent that differences in meteo-
rological 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.
In defining this oxidant upper limit, all
available data relating directly measured non-
methane hydrocarbon values to maximum
daily oxidant concentrations have been used.
Direct observation of this limit in the vicinity
of 200 Aig/m3 (0.1 ppm) daily maximum
1-hour average oxidant concentrations shows
that in order to keep the oxidant below this
value, the 6:00 to 9:00 a.m. average non-
methane hydrocarbon concentration must be
less than 200 ^g/m3 (0.3 ppm C). This maxi-
mum oxidant concentration potential may be
expected to occur on about 1 percent of the
days.
Oxidants. Publication No. AP-63. Raleigh, North
Carolina, 1970.
2. Renzetti, N.A. and V. Gobran. Studies of Eye
Irritation Due to Los Angeles Smog 1954-1956.
Air Pollution Foundation Report No. 29. San
Marino, California. July 1957.
3. Schuck, E.A., J.N. Pitts, and J.K.S. Wan.
Relationships Between Certain Meteorological
Factors and Photochemical Smog. Air and Water
Pollut. Int. J., 10:689-711, 1966.
4. Schuck, E.A. et al. Relationship of Hydrocarbons
to Oxidants in Ambient Atmospheres. Accepted
for publication in J. Air Pollution Control Assoc.
20(5), May 1970.
5. U.S. Department of Commerce, Environmental
Science Services Administration. Climatological
Data. Volume 18, No. 7. Asheville, North
Carolina. July 1967.
D. REFERENCES
1. U.S. Department of Health, Education, and
Welfare, National Air Pollution Control Admin-
istration. Air Quality Criteria for Photochemical
6. U.S. Department of Health, Education, and
Welfare, National Air Pollution Control Admin-
istration. Pilot Study of Ultraviolet Radiation in
Los Angeles, October 1965. Publication No.
999-AP-38. Cincinnati, Ohio. 1967.
5-12
-------
CHAPTER 6.
EFFECTS OF HYDROCARBONS AND
CERTAIN ALDEHYDES ON VEGETATION
A. INTRODUCTION
Ethylene is one of the major petrochem-
icals in the United States as well as a major
product of auto exhaust; and it appears to be
the gaseous hydrocarbon presenting the
greatest hazard to vegetation. Ethylene is a
significant phytotoxicant, and it contributes
to the formation of photochemical air pol-
lution.
Around the turn of the century, plant
physiologists and commercial greenhouse
operators noted that illuminating gas escaping
in greenhouses caused malformations of
certain plants and injuries to flowers.1'3 Of
the hydrocarbons tested, only ethylene
produced injury at the relatively low con-
centrations associated with such leaks. Later,
ethylene attributed to illuminating gas leaks
was found to injure orchid blossoms.4
Ethylene from various sources has been re-
ported to be responsible for considerable
losses of flowers in California5 and of cotton
in Texas.6 Research has demonstrated that
ethylene is produced naturally within tissues
of plants and serves as a hormone in regulat-
ing growth, development, and the other proc-
esses such as the ripening of fruit. Consider-
able investigation has been done in this area,
and the subject has recently been re-
viewed.7'9 Thus, ethylene is unique in being
both an endogenous plant-growth regulator
and a serious phytotoxic air pollutant. As in-
dicated by Crocker,1 ethylene has long been
recognized as a growth modifier rather than a
highly lethal gas that can readily kill tissue. As
early as 1913, Knight and Crocker10 sug-
gested that ethylene, and perhaps other
carbon-containing gases, be considered phyto-
toxic.
Photochemical reactions with certain
olefins in the atmosphere are known to
produce phytotoxic secondary products, but
there is no evidence that the olefins per se
cause an added or reduced response of plants
to these secondary reaction products.11
Although ethylene has the unique role of
both an endogenous plant hormone as well as
an exogenous phytotoxicant, the principal
concern here is with the latter function. The
extensive literature on the former role is
covered in detail by Burg,7 Hansen,8 and
Pratt and Goeschl.9
B. RELATIVE IMPORTANCE OF HYDRO
CARBON GASES IN CAUSING INJURY
TO VEGETATION
Because ethylene is both a phytotoxic
atmospheric pollutant and a growth regulator,
the comparative activity of other hydro-
carbons in each of these areas is of interest.
Crocker12'13 et al. found that exposure to
115 Mg/m^ (0.1 ppm) ethylene for a given
time produced epinasty in sensitive plants.
The relative concentrations of acetylene,
propylene, and 1-butene that produce the
same degree of response as ethylene are given
in Table 6-1. In this table, the activity of
ethylene is defined as 1 with respect to the
other hydrocarbons tested. Methane, ethane,
propane, butane, 1,3-butadiene, and benzene
ring compounds had no effect.
Zimmerman14 studied growth inhibition of
tobacco by ethylene, propylene, acetylene,
and 1-butene and found no effects from
1-butene at the highest level used. Burg and
Burg15 found that concentrations of 115
Mg/m^ (0.1 ppm) ethylene inhibited elonga-
tion in peas. They compared the relative ef-
fectiveness of propylene, acetylene, 1 -butene,
6-1
-------
Table 6-1. RELATIVE CONCENTRATIONS OF SEVERAL UNSATURATED
HYDROCARBONS THAT PRODUCE BIOLOGICAL RESPONSE
SIMILAR TO THAT PRODUCED BY ETHYLENE 16
Compound
Ethylene
Propylene
Acetylene
1-Butene
1,3-Butadiene
Abscission
1
60
1,250
100,000+
100,000+
Inhibition of growth
Pea stem3
1
100
2,800
270,000
5,000,000
Tobaccob
1
100
100
2,000
--
Epinastyc
1
500
500
500,000
--
Reference 15.
bReference 14.
cReference 12.
and 1,3-butadiene on the same response.
Methane, czs-2-butene, trans-2-butene, and
isobutene were inactive.
Abeles and Gahagan16 found that 115
Mg/m3 (0.1 ppm) ethylene produced about
one-half maximum abscission. This response
was then studied using propylene, acetylene,
1-butene, and 1,3-butadiene. As shown in
Table 6-1, these authors tabulated their
results along with others12,14,15 ^o snow the
relative concentrations of five hydrocarbons
that would produce similar activity.
Heck and Pires1 7 fumigated a number of
plants with 10, 100, and 1,000 ppm of 11
hydrocarbons for periods of from 1 to 3
weeks and noted various responses of the test
plants. Only ethylene, acetylene, and
propylene had adverse effects. The activity of
the three gases has been rated16 in the order
noted in Table 6-1. Acetylene and propylene
were considerably less effective than ethylene.
Methane, ethane, propane, butane, 1-butene,
1, 3-butadiene, isobutane, and isobutene were
inactive.
From the reports cited, ethylene is the only
hydrocarbon that should have adverse effects
on vegetation at ambient concentrations of 1
ppm or less. The hydrocarbon gases most
nearly approaching the activity of ethylene
are acetylene and propylene, but concentra-
tions of at least 60 to 500 times that of ethyl-
ene are required to produce adverse effects.
Stephens and Burleson18 and Stephens19 et
al. have reported that ambient concentrations
6-2
of ethylene in congested urban areas were 25
to 150 Mg/m3 (0.02 to 0.13 ppm), and pro-
pylene concentrations were considerably
lower, 5 to 50 Mg/m3 (0.003 to 0.03 ppm).
Ethylene concentrations are, therefore, within
the range that will produce harmful effects on
vegetation.
C. EFFECTS OF ATMOSPHERIC ALDE
HYDES ON VEGETATION
Aldehydes are a major reactant product of
the photochemical complex and, as such, have
been of some interest to investigators study-
ing the effects of air pollutants on vegetation.
Haagen-Smit20 et al. reported abnormal
injury to several sensitive plant species after
exposure to fairly high concentrations of
several aldehydes, but concluded that injury
seen on natural vegetation was not caused by
aldehydes. Stephens21 et al. reported injury
to plants from irradiated propionaldehyde but
no injury from irradiated ds-2-butene plus
ozone where acetaldehyde was a major
product. Hindawi and Altshuller22 and
Altshuller1 [ et al. reported injury to sensitive
plants after exposure to irradiated propio-
nalaldehyde with and without added nitrogen
dioxide, although traces of nitrogen dioxide
were present even when not added. They re-
ported no injury after similar exposures to
formaldehyde, even though oxidant levels
with both aldehydes were sufficiently high to
produce plant injury.
Brennan23 et al. reported injury to
-------
petunias that correlated well with total atmos-
pheric aldehyde levels (including ketones),
even when oxidant levels were low. This work
has been criticized because of the analytical
procedure used and laboratory reports on irra-
diated formaldehyde-nitrogen dioxide mix-
tures.2 2
Results to date suggest that atmospheric al-
dehydes per se are not important phytotox-
icants, but that products from the irradiation
of propionalaldehyde and higher-molecular-
weight saturated aldehydes in the presence of
nitrogen oxides may cause injury to plants.
D. SYMPTOMS OF EFFECTS OF
ETHYLENE ON VEGETATION
Ethylene enters plant leaves during the
course of the normal gas exchange required
for growth. For this reason, the site of the
primary response is in the leaves. In some
cases, petals and sepals of flowers may be af-
fected, but these are actually modified leaves.
Responses may range from the death of plant
parts to very subtle changes within the leaf
cells that can be detected only by complex
biochemical and histological methods.
Effects may be described in three broad
categories: (1) acute, identified by tissue
collapse and death (necrosis) of leaf parts and
usually accompanied by rapid change in leaf
color; (2) chronic, identified by the slow
development of mild or severe symptoms over
a long period, such as chlorosis without death
of cells; and (3) growth suppression and/or
alternation, identified by a change in the
normal growth pattern of the plant, without
obvious symptoms on the leaves.24-25
Premature leaf fall (abscission) may occur
following chronic injury or may be found
with no noticeable leaf injury.
The drying of the orchid sepals is the only
acute symptom associated with exposure of
plants to ethylene.
Chronic injury is often nondescript and
usuallly appears as an early senescence of
sensitive tissue. It cannot be used to distin-
guish the effects of ethylene from other pol-
lutants or from injury caused by other factors
such as disease, insects, nutritional disorders,
or climatic conditions.
A variety of growth abnormalities have
been associated with the exposure of plants to
ethylene. In 1901, Neljubow notes, illumina-
ting gas containing about 1,145 Mg/m^ (1
ppm) ethylene caused retarded elongation, an
oblique growth toward the horizontal, and a
radial swelling or thickening of the stem in
seedling plants.1'9'13 These three responses
were later termed the "triple response" by
Knight and Crocker.26 They suggested that
these responses be used to detect the presence
of ethylene.
Harvey3 noted that illuminating gas caused
leaves of castor bean to grow in a downward
direction and suggested that this epinastic
response could also be used to detect ethylene
because the plant responded to as little as 115
jug/m^ (0.1 ppm). Doubt2 also reported
epinastic growth, as well as leaf abscission, in
a variety of plants. Subsequently, the effects
of illuminating gas on a variety of plants were
studied, and the responses were consistently
associated with ethylene.27-30
Abscission and loss of apical dominance,
which results in a spreading vine-like growth
instead of an upright plant, have been re-
ported.1-24 Since complaints of epinasty by
commercial growers are uncommon, there is
no evidence that epinasty per se seriously af-
fects the health of plants.
Ethylene causes color changes in leaves and
flowers and death of flower parts. These
responses are in contrast to the effects of
other phytotoxic pollutants that normally
cause rather characteristic markings on af-
fected plant leaves. Most of the reports of
adverse effects from ethylene involve flower
crops grown in greenhouses.1'31 The first
extensive injury to a field-grown crop was a
1957 report on cotton by Hall6 et al.
Growth suppression may occur when plants
are exposed to dosages of ethylene less than
those that cause chronic injury or growth
abnormalities. Experiments using carefully
controlled air are required to demonstrate this
effect, since it is virtually impossible to detect
under field conditions. In most cases., growth
suppression can be explained on the basis of
6-3
-------
the effect of the pollutants on biochemical
and physiological systems of the plant.32"34
Perhaps the most characteristic symptoms
of ethylene injury are the drying of orchid
sepals, the closing of carnation flowers
(sleepiness), and the shattering of snapdragon
petals. Thus, acute symptons caused by other
pollutants can not be confused with
symptoms caused by ethylene. Chronic
symptoms characteristic of natural senes-
cence, however, may be confused with ethyl-
ene injury and with certain chronic symptoms
associated with sulfur dioxide, ozone, PAN,
and several other common pollutants. Ac-
cordingly, these effects could not be related
to a specific pollutant.
As noted by Brandt and Heck,24 other
factors may produce effects that could be
confused with ethylene. Wilting of leaves due
to water stress, bacterial wilts, or root rots
resembles epinasty. These factors, as well as
nutritional imbalance and early senescence,
cause leaf chlorosis. The latter factors could
cause premature abscission of leaves and
flowers.
E. ESTIMATES OF ECONOMIC LOSS
(DAMAGE) ASSOCIATED WITH
ETHYLENE INJURY TO
VEGETATION
The scattered information that exists on
economic losses due to ethylene relates
mostly to flower crops. Hall6 et al. reported
that the yield of cotton was meager within 1
mile of an industrial source, but the decline in
monetary value of the crop was not assessed.
Darley4 et al. reported that during 1959 the
combined damages incurred by three orchid
growers in Northern California amounted to
$70,000. James35'36 surveyed losses in the
San Francisco Bay area. Data supplied up to
1964 by several cooperating orchid growers
indicated an annual loss ranging from $60,000
to $100,000. Reduction in profit suffered by
carnation growers in 1963 was estimated at
$700,000. A value for snapdragon losses was
not given, but they were quite severe.
Although information is not available for
other parts of the country, it can be assumed
64
that comparable losses with respect to flower
crops could occur in those urban areas where
elevated levels of ethylene occur.
For purposes of using plants to assess losses
from ethylene pollution, the best indicators at
present are orchids and possibly carnations
and snapdragons. Brandt and Heck24 have
suggested the additional use of cowpea and
cotton because of their relatively high sensi-
tivity.
F. DOSE-INJURY RELATIONSHIPS FOR
VARIOUS PLANTS EXPOSED TO
ETHYLENE
In early investigations, dose-injury relation-
ships for vegetation were studied with il-
luminating gas and/or ethylene. When
comparative tests were made, the concentra-
tion of ethylene in the illuminating gas was
approximated for parallel experiments with
ethylene alone. These experiments were
conducted in chambers without air exchange,
and concentrations in many experiments
ranged from over 1,145 mg/m3 (1,000 ppm)
to less than 1,145 jug/m3 (1 ppm). Modern
analytical techniques were not available, but
many early investigators produced valid
results and, as noted by Abeles and
Gahagan,16 some of these results compare
favorably with later work. More recent studies
on ethylene have been performed in chambers
with dynamic airflow systems and better
analytical methods. Concentrations approach-
ing 1,145 mg/m3 (1,000 ppm) have been
used, but most experiments have utilized
lower levels. In general, only the lowest
concentrations of the exposure range are
considered in discussing the experimental
results in this section.
Because a carnation grower complained
that the flowers in his greenhouse did not
open normally, or once open would close
again, Crocker and Knight27 investigated this
phenomenon and found that ethylene in il-
luminating gas was responsible. A 3-day expo-
sure to 115 Mg/m3 (0.1 ppm) ethylene
prevented the flowers from opening, and a
12-hour exposure to 575 jug/m3 (0.5 ppm)
caused flowers to close. Darley4 et al. re-
ported that the minimum exposure required
-------
to close the flowers was 115 Mg/m3 (0.1 ppm)
for 6 hours.
Zimmerman29'30 et al. and Crocker12-1 3
et al. have exposed a number of plants for
various periods of time. Epinasty occurred on
the sensitive plants after a 3-hour exposure to
3,435 Mg/m3 (3 ppm) and after a 24-hour
exposure to about 345 Mg/m3 (0.3 ppm).
Exposure to as little as 1.15 Mg/m3 (0.001
ppm) for 20 hours caused epinasty on African
marigold, the most sensitive species studied. A
5-day exposure to 1,145 Mg/m3 (1 ppm)
produced yellowing along the veins of rose
leaves. Of some 202 species tested, 44 percent
reacted adversely to ethylene. Long exposure
periods were required for abscission of plant
parts. Rose leaf abscission began after expo-
sure to 350 Mg/m3 (0.3 ppm) for 120 hours,
while 11,450 Mg/m3 (10 ppm) induced the
same response in 24 hours.
Barley4 et al. found that 115 Mg/m3 (0.1
ppm) for several hours induced dropping of
the flower buds on tomato and pepper plants.
Hitchcock28 et al. reported that all
varieties of several species in the lily family
were retarded in growth when exposed for 7
days to about 855 Mg/m3 (0.75 ppm) ethyl-
ene contained in illuminating gas. Crocker1
later reported 25 to 50 percent growth in-
hibition of four species exposed to 115 Mg/m3
(0.1 ppm) ethylene for 4 weeks.
Davidson5 found that when a concentra-
tion of 115 jug/m3 (0.1 ppm) ethylene was
exceeded for 8 hours, injury to Cattleya
orchids (dry sepal) was usually more severe
than that normally occurring in greenhouses.
At 575 to 1,145 Mg/m3 (0.5 to 1 ppm) for 20
hours, buds remained closed and the tissues
collapsed within 2 to 4 days. Dry sepal injury
occurred at a concentration of 45 Mg/m3
(0.04 ppm) for 8 hours and 25 Mg/m3 (0.02
ppm) for 24 hours. The lowest exposure at
which injury occurred was 6 Mg/m3 (0.005
ppm) for 24 hours.
Darley4 et al. found that the minimum
ethylene concentrations for injury to orchids
at 1-, 6-, and 24-hour exposures to be 345,
57.5, and 11.5 Mg/m3 (0.3, 0.05, and 0.01
ppm), respectively. They also fumigated
snapdragons and found that exposure to 575
Mg/m3 (0.5 ppm) for 1 hour caused the petals
to fall from the flowers.
Heck and Pires37 exposed 89 species of
horticultural and agronomic crops to the
relatively high concentrations of 2,290,
5,750, and 11,450 Mg/m3 (2, 5, and 10 ppm)
ethylene for 10 days. Based on the severity of
a variety of symptons, they categorized the
plants according to six broad groups. Plants
typical of the six groups, from the most sensi-
tive to the least sensitive, were cowpea, cot-
ton, squash, soybean, radish, and grasses,
respectively. The most marked responses ex-
hibited by cowpea were epinasty, chlorosis,
and death of the older leaves. These symp-
toms later extended to the younger leaves,
and death of plants was common. Squash
leaves were chlorotic and necrotic, with
evidence of growth inhibition, but the plants
were not killed. There was no injury to soy-
bean, but growth was retarded. Grasses were
not injured and the principal effect observed
was the reduction of leaf elongation. Twenty-
two of the species flowered during the ex-
posure; floral injury developed on all of them
and was quite severe on 18.
The only occurrence of ethylene injury to
field grown crops was reported by Hall6 et al.
on cotton in Texas in 1957. Fields of cotton
in the vicinity of a polyethylene manufac-
turing plant were severely affected, those
within 1 mile giving negligible yield due to
abscission of the fiber-bearing squares. Lateral
buds were stimulated, which resulted in a
prostrate, vine-like growth rather than a
normal, upright plant. Concentrations of
ethylene about the source ranged from 45 to
3,435 Mg/m3 (0.04 to 3 ppm). Injury occur-
red in the areas with the higher concentra-
tions. In controlled experiments under static
conditions, defoliation occurred in 48 to 72
hours with 11,450 to 114,500 Mg/m3 (10 to
100 ppm).
Heck38 et al. conducted detailed fumiga-
tion experiments on cotton, wherein plants
were exposed to 690 Mg/m3 (0.6 ppm) for
various periods up to 3 months. Though the
6-5
-------
plants were seriously affected, the field
symptoms noted in the previously reported
study were not duplicated, especially the
prostrate growth habit. Among the more
significant responses after 1 month were an
approximate 50 percent reduction in plant
height and leaf size, an increase in leaf abscis-
sion, an increase in the number of nodes, and
an abscission of squares. Leaf chlorosis was
not pronounced, but leaves were badly curled
and developed a granular texture on their
surfaces.
A summarization of the dose-response data
is given in Table 6-2. Listings of plants
Table 6-2. DOSAGE-RESPONSE RELATIONSHIPS OF VARIOUS
PLANTS TO ETHYLENE
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)
Epinasty
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
Dosage
Concentration,
Aig/m3
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
8hr
120hr
24 hr
1 hr
1 month
1 day
5 days
1 0 days
8hr
8hr
24 hr
24 hi
1 hr
6hr
24 hr
20 hr
24 hr
3hr
1 0 days
3 days
20 hr
6hr
12hr
1 mo
Not stated
7 days
1 0 days
Not stated
Reference
Hall6 et al.
Heck38 etal.
Darley^ et al.
Zimmerman3 0 et al.
Darley^ et al.
Heck38 etal.
Heck and Fires"
Zimmerman3^ et al.
Heck and Fires"
Davidson-*
Darley^ et al.
Crocker^ 2 et al.
Zimmerman™ et al.
Heck and Fires37
Crocker and Knight2 '
Davidson 5
Darley4 et al.
Crocker and Knight27
Heck38 etal.
Hall6 et al.
Hitchcock28 et al.
Heck and Fires3 7
Hall6 et al.
-------
according to sensitivity can be found in
several references.12,13,24,29,30,37
G. NEED FOR FURTHER RESEARCH
There appears to be sufficient evidence
available to confirm the belief that ethylene is
the only hydrocarbon that affects vegetation
at known ambient concentrations. • To
produce comparable effects, the concentra-
tions required of the other active gases,
acetylene and propylene, are at least'100
times that of ethylene.
The range of plant responses induced by
ethylene is known and has been confirmed by
many investigators. Since the principal effect
at reported ambient concentrations is on
plant growth, more information is needed
concerning the long-term economic effects of
concentrations less than 345 jug/m^ (0.3 ppm)
on a wide variety of greenhouse and field
crops. Heck and Pires37 have examined a
large number of crops exposed to ethylene,
but the concentrations were relatively high
and the exposure to ethylene was for only 10
days. Heck38 et al. observed a significant
reduction in the growth of cotton at 690
Mg/in^ (0.6 ppm) over a period of 1 to 3
months, but were able to examine only the
one species. These results indicate the
direction that continued research should take.
The possible synergistic action of ethylene
in combination with other pollutants,
particularly those occurring in the photo-
chemical complex, should be investigated.
Heck39 observed no synergistic effect on
several species; however, Menser and Heg-
gestad40 reported that a mixture of ozone
and sulfur dioxide caused injury to tobacco
when the same concentrations acting alone
had no effect. Consequently, research in this
area is also needed.
H. SUMMARY
Hydrocarbons were first recognized as
phytotoxic air pollutants about the turn of
the century as a result of complaints of injury
to greenhouse plants from illuminating gas.
Ethylene was shown to be the injurious com-
ponent. 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 photo-
chemical reaction complex. Research on
several unsaturated and saturated hydro-
carbons proved that only ethylene had
adverse effects at known ambient concentra-
tions. It is noteworthy that the activity of
acetylene and propylene resemble more
closely that of ethylene than do other similar
gases, but 60 to 500 times the concentration
is needed for comparable effects.
In the absence of any other symptom, the
principal effect of ethylene is to inhibit
growth of plants. Unfortunately, this effect
does not characterize ethylene because other
pollutants at sublethal dosages, as well as
some diseases and environmental factors, may
also inhibit growth.
Epinasty of leaves and abscission of leaves,
flower buds, and flowers are somewhat more
typical of the effects of ethylene, but the
same effects may be associated with nutrition-
al imbalance, disease, or early senescence.
Perhaps the most characteristic effects are the
dry sepal wilt of orchids and the closing of
carnation flowers. Injury to sensitive plants
has been reported after exposure to ethylene
concentrations of 1.15 to 575 jug/m-^ (0.001
to 0.5 ppm) for an 8- to 24-hour time period.
Economic loss has not been widely
documented except among flower growers in
California, where damage to orchids and
carnations has been assessed at about
$800,000 annually. More research needs to be
done on economic losses sustained in field
and greenhouse crops from long exposures to
very low concentrations of ethylene.
I. REFERENCES
1. Crocker, W. Growth of Plants. New York,
Reinhold Publishing Corp., 1948. 459 p.
2. Doubt, S. L. The Response of Plants to Il-
luminating Gas. Botan. Gaz. 63(3) 209-224,
March 1917.
3. Harvey, E. M. The Castor Bean Plant and Labora-
tory Air. Botan. Gaz. 56(5): 439-442, November
1913.
4. Darley, E. F. et al. Plant Damage by Pollution
Derived from Automobiles. Arch. Environ.
Health, 6:761-770, March 1963.
6-7
-------
5. Davidson, O. W. Effects of Ethylene on Orchid
Flowers. Proc. Amer. Soc. Hort. Sci. 55:440-446,
May 1949.
6. Hall, W. C. et al. Ethylene Production by the
Cotton Plant and Its Effects Under Experimental
and Field Conditions. Physiol. Plant.
(Copenhagen). 70(2):306-317, 1957.
7. Burg, S. P. The Physiology of Ethylene Forma-
tion, In: Ann Rev. Plant Physiol., Machlis, L.
(ed.), Vol. 13. Palo Alto, Calif., Annual Reviews,
Inc., 1962. p. 265-302.
8. Hansen, E. Postharvest Physiology of Fruits. In:
Ann Rev. Plant Physiol., Machlis, L. (ed.), Vol.
17. Palo Alto, Calif., Annual Reviews, Inc., 1966.
p. 459-480.
9. Pratt, H. K. and J. D. Goeschl. Physiological
Roles of Ethylene in Plants. In: Ann. Rev. Plant
Physiol., Machlis, L. (ed.), Vol. 20. Palo Alto,
Calif., Annual Reviews, Inc., 1969. p. 541-584.
10. Knight, L. I. and W. Crocker. Toxicity of Smoke.
Botan. Gaz. 55: 337-371, May 1913.
11. Altshuller, A. P. et al. Products and Biological
Effects from Irradiation of Nitrogen Oxides with
Hydrocarbons or Aldehydes under Dynamic
Conditions. Int. Jour. Air Wat. Poll. 70:81-98,
1966.
12. Crocker, W., A. E. Hitchcock, and P. W. Zimmer-
man. Similarities in the Effects of Ethylene and
the Plant Auxins. Contributions from Boyce
Thompson Institute. 7(3):231-248, July-
September 1935.
13. Crocker, W., P. W. Zimmerman, and A. E.
Hitchcock. Ethylene-Induced Epinasty of Leaves
and the Relation of Gravity to It. Contributions
from Boyce Thompson Institute. 4(2): 177-218,
June 1932.
14. Zimmerman, P. W. Anaesthetic Properties of
Carbon Monoxide and Other Gases in Relation to
Plants, Insects, and Centipedes. Contributions
from Boyce Thompson Institute. 7(2): 147-155,
April-June 1935.
15. Burg, S. P. and E. A. Burg. Molecular Require-
ments for the Biological Activity of Ethylene.
Plant Physiol. 42:144-152, January 1967.
16. Abeles, F. B. and H. E. Gahagan, III. Abscission:
The Role of Ethylene, Ethylene Analogues,
Carbon Dioxide, and Oxygen. Plant Physiol.
43:1255-1258, August 1968.
17. Heck, W. W. and E. G. Pires. Growth of Plants
Fumigated with Saturated and Unsaturated
Hydrocarbon Gases and Their Derivatives. Texas
Agri. Exp. Sta. Misc. Publ. No. 603. 1962. 12 pp.
18. Stephens, E. R. and F. R. Burleson. Analysis of
the Atmosphere for Light Hydrocarbons. J. Air
Pollution Control Assoc. 77:147-153, March
1967.
19. Stephens, E. R., E. F. Darley, and F. R. Burleson.
Sources and Reactivity of Light Hydrocarbons in
6-8
Ambient Air. Proc. Div. Refining, Amer. Petrol.
Inst. 47: 466-483, 1967.
20. Haagen-Smit, A. J. et al. Investigation on Injury
to Plants from Air Pollution in the Los Angeles
Area. Plant Physiol. 27:18-34, 1952.
21. Stephens, E. R. et al. Photochemical Reaction
Products in Air Pollution. Int. Jour. Air Wat.
Poll. 4: 79-100, 1961.
22. Hindawi, I. J., and A. P. Altshuller. Plant Damage
Caused by Irradiation of Aldehydes. Science.
746:540-542, 1964.
23. Brennan, E. G., I. A. Leone, and R. H. Daines.
Atmospheric Aldehydes Related to Petunia Leaf
Damage. Science. 74^:818-819, 1964.
24. Brandt, C. S. and W. W. Heck. Effects of Air
Pollutants on Vegetation. In: Air Pollution,
Stern, A. C. (ed.), Vol. I, 2d ed. New York,
Academic Press, 1968. p. 401-443.
25. Thomas, M. D. Gas Damage to Plants. Ann. Rev.
Plant Physiol. 2:293-322, 1951.
26. Knight, L. I. and W. Crocker., Toxicity of
Smoke. Bot. Gaz. 55:337-371, 1913.
27. Crocker, W. and L. I. Knight. Effect of Il-
luminating Gas and Ethylene Upon Flowering
Carnations. Botan. Gaz. 4<5(4):259-276, October
1908.
28. Hitchcock, A. E., W. Crocker, and P. W. Zimmer-
man. Effect of Illuminating Gas on the Lily,
Narcissus, Tulip, and Hyacinth. Contributions
from Boyce Thompson Institute. 4(2): 155-176,
June 1932.
29. Zimmerman, P. W., A. E. Hitchcock, and W.
Crocker. The Response of Plants to Illuminating
Gas. Proc. Amer. Soc. Hort. Sci. 27:53-56, De-
cember 1930.
30. Zimmerman, P. W., A. E. Hitchcock, and W.
Crocker. The Effect of Ethylene and Illuminating
Gas on Roses. Contributions from Boyce
Thompson Institute. 3(3): 459-481, September
1931.
31. Hasek, R. F., H. A. James, and R. H. Sciaroni.
Ethylene-Its Effects on Flower Crops. Florists'
Rev. 744(3721 ):21, 65-68, 79-82, March 27,
1969; 144 (3722): 16-17, 53-56, April 3, 1969.
32. Darley, E. F. and J. T. Middleton. Problems of
Air Pollution in Plant Pathology. Ann. Rev.
Phytopathology. 4: 103-118, 1966.
33. McCune, D. C. et al. Concept of Hidden Injury in
Plants. In: Agriculture and the Quality of Our
Environment, Brady, N.C., (ed.), 33-44. Amer.
Assoc. Adv. Sci., 1967.
34. Taylor, O. C. and F. M. Eaton. Suppression of
Plant Growth by Nitrogen Dioxide. Plant
Physiol. 47:132-135, 1966.
35. James, H. A. Flower Damage—A Case Study. San
Francisco Bay Area Air Pollution Control
District. California Information Bulletin Number
8-63. 1963.
-------
36. James, H. A. Commercial Crop Losses in the Bay
Area Attributed to Air Pollution. San Francisco
Bay Area Air Pollution Control District. Cali-
fornia. 1964.
37. Heck, W. W. and E. G. Pires. Effect of Ethylene
on Horticultural and Agronomic Crops. Texas
Agri. Exp. Sta. Misc. Publ. Number MP-613.
1962. p. 3-12.
38. Heck, W. W., E. G. Pires, and W. C. Hall. The
Effects of a Low Ethylene Concentration on the
Growth of Cotton, J. Air Pollution Control
Assoc. 77:549-556, December 1961.
39. Heck, W. W. Plant Injury Induced by Photochem-
ical Reaction Products of Propylene-Nitrogen
Dioxide Mixtures. Jour. Air Poll. Control. Assoc.
14:255-261, 1964.
40. Menser, H. A. and H. E. Heggestad. Ozone and
Sulfur Dioxide Synergism: Injury to Tobacco
Plants. Science. 75J(3734):424-425, July 22,
1966.
6-9
-------
CHAPTER 7.
TOXICOLOGICAL APPRAISAL OF HYDROCARBONS AND ALDEHYDES
A. INTRODUCTION
Studies of atmospheric chemistry have
shown that hydrocarbons enter into and
promote the formation of photochemical air
pollution, and thus contribute to the develop-
ment of eye irritation and other associated
manifestations. In the description of the
effects of these atmospheric hydrocarbons, it
is insufficient to regard the reported effects of
each hydrocarbon compound alone; the dis-
cussion must include due consideration of the
potential of these compounds under certain
atmospheric conditions to form more hazard-
ous derivatives.
Many gaseous hydrocarbons in the atmos-
phere are intimately involved in the formation
of formaldehyde and other aldehydes,
ketones, peroxyacetyl nitrate (PAN), and
other oxidants, primarily through atmos-
pheric photochemical reactions. Because the
formation of aldehydes in photochemical air
pollution is so closely related to the presence
of hydrocarbons, a review of the toxicological
effects attributed to aldehydes is included
here.
Although concentrations of aldehydes —
especially formaldehyde and acrolein — and
PAN encountered in ambient air are not likely
to produce severe health effects, they un-
doubtedly contribute to the eye irritation ex-
perienced in photochemical air pollution.1-2
Because the presence of gaseous hydro-
carbons in ambient air can lead to the forma-
tion of the eye irritants as a result of photo-
chemical reactions, a discussion of the rele-
vant toxicological studies of eye irritation is
also included in this chapter.
The present state of knowledge does not
demonstrate any direct effects of the gaseous
hydrocarbons in the ambient air on pop-
ulations, although many of the effects at-
tributed to photochemical oxidants are in-
directly related to ambient levels of these
hydrocarbons. Thus the effects of hydro-
carbons in the ambient air on groups of
people living or working in a community or
area cannot be directly assessed in epidemio-
logical studies.
B. TOXICOLOGY OF HYDROCARBON
COMPOUNDS
1. General Discussion
Experimental hydrocarbon toxicology is
fraught with difficulties not found in the
study of the toxicology of other groups of
compounds. Hydrocarbons in the presence of
nitric oxide (or nitrogen dioxide) and ultra-
violet irradiation (sunlight) react to form
various toxic compounds. The toxicity of
hydrocarbons may be of lesser importance
than the toxicity of their reaction products.
Hydrocarbons, at concentrations found in
ambient air, have rarely been observed to have
direct physiological effects on humans or
animals, although effects have been noted at
higher levels. Concentrations well above those
in the atmosphere have been used in most of
the studies discussed below. The results are
included here only as a guide to orient the
reader in developing a perspective on the
photochemical air pollution complex.
2. Aliphatic Hydrocarbonss
In general, members of the aliphatic hydro-
carbon series are biologically and biochemical-
ly inert, i.e., they produce no detectable
functional or subclinical alterations.3 The
lower members, with the exception of
methane and ethane, are gases that tend to
7-1
-------
have anesthetic properties; this is particularly
true of the unsaturated (olefin) compounds.
Ethylene, propylene, and acetylene have all
been used as anesthetics, and available
evidence indicates that these gases are rapidly
eliminated from the lungs in the unchanged
state. These hydrocarbons must usually be
present in relatively high concentrations
before noticeable effects are produced, as is
illustrated in Tables 7-1 and 7-2.
3. Alicyclic Hydrocarbons
Toxicologically, the alicyclic hydrocarbons
resemble their open-chain relatives, the
aliphatic hydrocarbons. In general, they are
anesthetics and central nervous system depres-
sants with a relatively low order of toxicity.
They do not tend to accumulate in body tis-
sues; thus cumulative toxicity from repeated
exposure to low atmospheric concentrations
is improbable. An overwhelming acute
exposure resulting in prolonged unconscious-
ness, anoxia, and convulsions may result in
central nervous system sequelae and has been
described only following exposure to volatile
aliphatic hydrocarbons.5
Laboratory experiments5 concerning the
toxicity of cyclohexane and methylcyclo-
hexane are summarized in Tables 7-3, 7-4, and
7-5.
4. Aromatic Hydrocarbons
Members of the class of aromatic hydro-
carbons are biochemically active. The vapors
are much more irritating to the mucous mem-
branes than equivalent concentrations of the
aliphatic or alicyclic hydrocarbons, and
systemic injury can result from their inhala-
tion. Table 7-6 summarizes the effects of
acute and chronic exposure to the aromatic
hydrocarbons on the laboratory animal and
man. Hematological abnormalities have also
been associated with the aromatic hydro-
carbons.6 The chronic effects of inhaling
benzene over a prolonged period of time may
be important in the industrial use of this
chemical, and anemia and leukopenia are
often associated with chronic benzene
poisoning. Greenburg7 did complete blood
studies on 102 workmen exposed to benzene
7-2
in the rotogravure industry. A positive
diagnosis of chronic benzene poisoning,
varying in severity, was made in 74 men. In
this group were men with clinical benzene
poisoning whose blood studies were normal,
and also men with serious blood abnormalities
in the complete absence of signs or symptoms
of benzene poisoning. Signs and symptoms
may include headache, dizziness, fatigue, loss
of appetite, irritability, nervousness, and nose-
bleed or other hemorrhagic manifestations.
Toluene, on the other hand, is a more
powerful narcotic and is more acutely toxic
than benzene, although it does not have the
hematological effects attributed to benzene.8
It appears that the acute toxicity of the
xylenes is even greater than that of benzene
or toluene.6
5. Summary
Experimental data obtained from animal
and human research indicate that:
1. The aliphatic and alicyclic hydrocarbons
are generally biochemically inert, though not
biologically inert. These compounds are only
somewhat reactive at concentrations hundreds
to thousands of times above those levels
found in the atmosphere. No effects have
been reported at levels below 500 ppm.
2. The aromatic hydrocarbons are biochem-
ically and biologically active. The vapors are
much more irritating to the mucous mem-
branes than equivalent concentrations of the
aliphatic or alicyclic groups. Systemic injury
can result from the inhalation of vapors of the
aromatic compounds, and hematological ab-
normalities are especially associated with
chronic benzene inhalation. No effects, how-
ever, have been reported at levels below 25
ppm.
C. TOXICOLOGY OF ALDEHYDES
1. General Discussion
Although aldehydes are widely used in
industrial situations, and despite the potential
of aldehydes as air pollutants, comprehensive
studies of the toxicological effects on human
and animals exposed to these compounds are
lacking. There have been almost no long-term
-------
Table 7-1. TOXICITY OF SATURATED ALIPHATIC HYDROCARBONS (THROUGH OCTANE)4
Hydrocarbon
Methane
Ch4
Ethane
c2He
Propane
C3»8
Butane
C4H10
Pentane
C5H12
Hexane
C6H14
Heptane
7H16
Octane
C8H18
Concentration, ppm
100,000
No
effect
No irri-
tation
noticed
Dizziness
in a few min.
Narcosis
in 5-60
minutes
50,000
No
effect
40,000
Convul-
sions
and
death
30,000
Narcosis
20,000
Odor not
detected
Convul-
sions,
death
in 30-
60 min
15,000
Narcosis
in 30-
60 min
10,000
No symp-
toms
after
brief
exposure
Drowsi-
ness in
10 min
Narcosis
in 30-
90 min
5,000
Odor not
detectable
Odor read-
ily detect-
able;
No irrita-
tion or
symptoms in
10 min
Dizziness,
giddiness,
in 10 min
In 4 min:
marked ver-
tigo, hilar-
ity, incoor-
di nation
In 15 min:
uncontrolled
hilarity
or stupor
2,000
No symp-
toms in
10 min
Slight
vertigo
in 4
min
1,000
TLV3
500
TLVa
TLVa
TLVa
0
aTLV - threshold limit value.
-------
Table 7-2. TOXICITY OF UNSATURATED ALIPHATIC HYDROCARBONS4
Hydrocarbon
Ethylene
Propylene
1-Butene
1 ,3-Butadiene
2-Methyl-l,3-
butadiene
Acetylene
Concentration, ppm
350,000
Uncon-
scious-
ness in
in 5
min.
300,000
Inco-
ordina-
tion
200,000
Marked
intoxi-
cation
100,000
Slight in-
toxicat-
ing ef-
fect on
man
50,000
40,000
20,000
8,000
Irritation
of eye
and upper
respiratory
tract in man
5,500
MPLa
5,000
MPLa
4,000
MPLa
MPLa
MPLa
1,000
TLVb
aMPL - maximum permissible limit in workroom air.
bTLV - threshold limit value.
-------
Table 7-3. COMPARATIVE EFFECTS OF SINGLE EXPOSURE TO
61.8 mg/m3 (18,000 ppm) CYCLOHEXANE VAPOR IN AIR5
Animal
Mouse
Guinea pig
Rabbit
Cat
Time to produce effect, min
Trembling
5
Slight
6
—
Disturbed
equilibrium
15
—
15
11
Complete
recumbency
25
—
30
18-25
Table 7-4. COMPARATIVE EFFECTS OF CHRONIC EXPOSURE TO
CYCLOHEXANE VAPOR IN AIR5
Animal
Rabbit
Rabbit
Monkey
Rabbit
Rabbit
Concentration
ppm
434
786
1,243
3,330
7,400-
18,500
mg/m3
1,491
2,710
4,270
11,439
25,419-
63,548
Daily
exposure,
hr
8
6
6
6
6
Exposure,
days
130
50
50
50
10
Effects
No effect
Minor microscopic
changes in kidneys
and liver
No effect
No fatalities or signs
of injury
Some fatalities
Table 7-5. COMPARATIVE EFFECTS OF CHRONIC EXPOSURE
TO METHYLCYCLOHEXANE VAPOR IN AIR5
Animal
Rabbit
Rabbit
Rabbit
Rabbit
Rabbit
Rabbit
Rabbit
Concentration,
ppm
241
1,162
2,800
3,300
5,600
7,300
10,000
mg/m
996
4,659
11,228
13,233
22,456
29,273
40,100
Daily
exposure,
hr
24
24
24
5
6
6
6
Exposure,
days
70
70
70
70
28
14
14
Effects
No effect
No effect
No effect
Minor evidence of
kidney and liver in-
jury
No fatalities; lethargy
in 50%
25% fatalities
100% fatalities
7-5
-------
Table 7-6. COMPARATIVE EFFECTS OF ACUTE AND CHRONIC EXPOSURE TO
AROMATIC HYDROCARBON VAPORS IN AIR6
Compound
Benzene
Toluene
Styrene
Xylene
Subject
Man
Man
Mice
Man
Mice
Mice
Man
Mice
Rats
Man
Man
Man
Man
Man
Man
Man
Mice
Mice
Mice
Rat
Man
Guinea
Pig
Rat
Rabbit
Guinea
Pig
Guinea
pig&
rat
Guinea
pig&
rat
Guinea
pig&
rat
Mice
Man
Rat &
rabbit
Concentration,
ppm
25
100
370
3,000
4,700
7,400
7,500
14,100
17,800
20,000
50-100
200
300
400
600
600
2,700
6,700
9,500
13,500
100
650
1,300
1,300
1,300
2,500
5,000
10,000
174
200
690
mg/m3
80
319
1,180
9,570
14,993
23,606
23,925
44,979
56,782
63,800
188-377
753
1,130
1,506
2,259
2,259
10,166
25,226
35,768
50,828
418
2,714
5,428
5,428
5,428
10,438
20,875
41,750
755
868
2,995
Daily
exposure,
hr
Acute
Acute
Acute
Acute
Acute
Acute
Acute
Acute
Acute
Acute
Acute
8
8
8
3
8
Acute
Acute
Acute
Acute
Acute
8
8
8
8
8
1
1/2-1
Acute
Acute
8
Exposure,
days
1
1
1
1
1
180
180
180
180
1
1
1
130
Effect
Threshold limit value (TLV)
Mucous membrane irritation
Threshold for affecting the central
nervous system
Endurable for 1/2-1 hour
Prostration
LC50
Dangerous after 1/2-1 hour
LC100
LC100
Fatal after 5-10 minutes
No effect
Mild fatigue, weakness, confusion,
skin parethesias
Symptoms more pronounced
Also: mental confusion
Also: nausea, headache, dizziness
Also: loss of coordination, staggering
gait, pupils dilated
Prostration
LC50
LC100
LC100
Threshold limit value (TLV)
No effect
Eye & nasal irritation only
Eye & nasal irritation only
10% deaths
Some fatalities; varying degree of
weakness, stupor, incoordination,
tremor, unconsciousness (in 10 hrs.)
Unconsciousness in 1 hour
Unconsciousness in 10 minutes;
deaths in 30-60 minutes
Threshold for affecting central
nervous system
Threshold limit value (TLV)
No hematological effects
7-6
-------
Table 7-6 (continued). COMPARATIVE EFFECTS OF ACUTE AND CHRONIC EXPOSURE TO
AROMATIC HYDROCARBON VAPORS IN AIR6
Compound
Subject
Rabbit
Mice
Mice
Mice
Rat
Concentration,
ppm
1,150
4,699
9,200
12,650
17,250
mg/m
4,991
20,394
39,928
54,901
74,865
Daily
exposure,
hr
8
Acute
Acute
Acute
Acute
Exposure,
days
55
Effect
Decreased leukocytes & red blood
cells; increased platelets
Prostration
LC100
LC100
studies in experimental animals, and much of
the available information on the toxicity of
aldehydes pertains either to the effects from
single, acute exposures of animals, or to
industrial exposures to high concentrations
rather than to levels of aldehydes as they oc-
cur in the ambient air. Aldehydes, however,
are among the contributors to the eye irrita-
tion observed during photochemical smog.
2. Mechanisms of Toxicity
The general and parenteral toxicities of the
aldehydes appear to be related primarily to
their irritant properties. Reports from occupa-
tional exposures have failed to indicate the
presence of serious cumulative effects,
although primary irritant reactions and
contact dermatitis are occasionally seen. Four
basic types of effects of aldehydes are re-
ported: primary irritation, sensitization,
anethesia, and pathological effects.
a. Primary Irritation of the Skin, Eyes,
and Respiratory Mucosa
The principal effect of low concentrations
of aldehydes on humans and animals is
primary irritation of the mucous membranes
of the eyes and the upper respiratory tract,
particularly the nose and throat, as well as
irritation of the skin. Animal studies indicate
that high concentrations can also injure the
lungs and other organs of the body. The ir-
ritant properties are well documented, being
possessed in varying degrees by nearly all of
the aldehydes, although the unsaturated
(olefinic) and the halogenated aldehydes
generally cause more noticeable irritation
than saturated aldehydes, while aromatic and
heterocyclic aldehydes generally cause less ir-
ritation than saturated aldehydes.9'10 The
irritant effect decreases with increasing mole-
cular weight (within a given aldehyde series),
and thus decreases with increasing chain
length.10'11 The lower aldehydes act chiefly
on the eyes and upper respiratory tract, while
the higher, less soluble aldehydes, tend to
penetrate more deeply into the respiratory
tract and may affect the lungs.12
b. Sensitization
Certain aldehydes have been reported to
cause allergic reaction. Animals or humans
who respond either to concentrations of alde-
hydes lower than established thresholds or to
concentrations that ordinarily do not affect
others are said to be sensitized. Direct sensiti-
zation of the skin or respiratory tract to alde-
hyde vapors is uncommon, and asthmatic-like
symptoms are very rarely caused by inhala-
tion of aldehydes.10
c. Anethesia
Most aldehydes posses anesthetic proper-
ties,1 °'12 •r 3 the degree of activity decreasing
with increasing molecular weight in each alde-
hyde group. The quantities of aldehydes that
can be tolerated by inhalation, however, are
so rapidly metabolized that no anesthetic
symptoms occur.
d. Pathological Effects
The principal pathological changes found in
animals exposed to high concentrations of
aldehyde vapors are those of damage to the
respiratory tract and pulmonary edema.
7-7
-------
Multiple hemorrhages and alveolar exudates
may occur, although these effects are
ordinarily not observed during experimental
aldehyde intoxication. High dosages of com-
pounds such as formal and furfural have been
reported to cause various changes in the liver,
kidneys, and central nervous system, but
there has been no confirmation of this type of
action in human industrial exposures. In fact,
the aldehydes as a group invoke only a weak
response in the experimental animal or in
man. Alveolar thickening, minor areas of
pulmonary consolidation, minimal parenchy-
mal lung damage, and only rare evidence of
residual damage have been reported following
aldehyde inhalation, although a decrease in
the muco-ciliary activity of the tracheobron-
chial tree is noted at low concentrations.
Acute pathological changes or definitive
cumulative organic damage to tissues other
than those that may be associated with
primary irritation or sensitization are only
rarely noted.10 The fact that aldehdyes are
readily metabolized in the body14 probably
accounts for this lack of cumulative damage.
3. Formaldehyde and Acrolein
a. General Discussion
In the field of air pollution, major interest
centers on two specific aldehydes, formalde-
hyde and acrolein. Their effects on humans
are known, and their concentrations are gen-
erally higher than those of other aldehydes
present in the atmosphere. In addition, some
reports suggest that they contribute to the
odor15"19 as well as the eye irritation com-
monly experienced in photochemical air pol-
lution. The concentrations of these two com-
pounds have been shown to correlate with the
intensity of odor of diesel exhaust and the
intensity of eye irritation during natural and
chemically produced air pollution.15,17,19
The eye irritation potential of aldehydes is
further discussed in Section D.3 of this
chapter.
b. Formaldehyde
(1) Human studies - The principal effect
of formaldehyde vapor on humans appears to
be irritation of the mucous membranes of the
7-8
eyes, nose, and other portions of the upper
respiratory tract, 10,12,20-23 although skin
irritation can also occur. Repeated exposures
may result in chronic irritation of these
organs12-20 as well as inflammation of the
eyelids.20 Symptoms that have been observed
from nonfatal exposures to formaldehyde in-
clude lacrimation, sneezing, coughing,
dyspnea, a feeling of suffocation, rapid pulse,
headache, weakness, and fluctuations in body
temperature. Reported responses of man to
formaldehyde are summarized in Table 7-7.
Several reports indicate that irritation of the
eyes and upper respiratory tract can first be
detected at formaldehyde levels of 12 to
1,230 jug/m3 (0.01 to 1.0 ppm).1.10,24,26-28
Although there are variances as to the exact
irritant and odor thresholds, it should be
noted that researchers tend to be in agree-
ment that these values may be well below
1,230 ,ug/m3 (1 ppm) of formaldehyde vapor.
Variables involved in the experiments, which
include the measurement of a subjective re-
sponse, individual differences in sensitivity,
previous exposures, the nature of the synthe-
tic atmospheres, and the apparatus utilized,
can easily result in multiple values for the
same measurement. Fortunately, there has
been an attempt to minimize the number of
variables in an effort to consistently replicate
experimental results as demonstrated in the
reports of experimental exposures to formal-
dehyde or acrolein.
On the other hand, according to Fassett,10
no discomfort is noted until concentrations of
2,460 to 3,690 Mg/m3 (2 to 3 ppm) are
reached, at which time a very mild tingling
sensation may be detected in the eyes, nose,
and posterior pharynx. Since some tolerance
occurs, repeated 8-hour exposures to 2,460 to
3,690 Mg/m3 are possible. At 4,920 to 6,150
jug/m3 (4 to 5 ppm), the discomfort increases
rapidly, with mild lacrimation occurring in
most people.10 This level may be tolerated
fairly well for periods of 10 to 30 minutes by
some, but not all people; longer exposures to
this level are unpleasant. Elkins32 reported
complaints of eye irritation from acclimatized
-------
Table 7-7. REPORTED SENSORY RESPONSES OF MAN TO
FORMALDEHYDE VAPORS
Concentration,
/Jg/m3
70
80
98
410-
1,110
615
1,230
2,460 -
3,690
4,920 -
6,150
6,150
12,300
24,600
24,600
24,600
ppm
0.060
0.065
0.08
0.33-
0.9
0.5-
1.0
2.0-
3.0
4.0-
5.0
5.0
10.0
20.0
20.0
20.0
Exposure
time
—
—
—
—
—
8hr
10-30min
Few min
15-30 sec
30 sec
1-2 min
Response
Odor threshold (Russian
literature)
Chronaximetric response
threshold
Cortical reflex threshold
Irritant threshold
Odor threshold
Tolerable; mild irritation
of eyes, nose, and pos-
terior pharynx
Intolerable to most
people; mild lacrima-
tion; very unpleasant
Severe irritation to
throat
Profuse lacrimation
Lacrimation
Irritation of nose and
throat
Sneezing
Reference
Melekhina24- 2S
Melekhina24'25
Melekhina24' 2S
Bourne26
Roth27
-Morrill28
Stern29
Fassett10
Fassett10
Fassett10
Walker20' 30
Fassett10
Barnes31
Barnes31
Barnes31
aThis table excludes several studies of eye irritation, which are discussed in Section D.3 of
this chapter.
persons when the maximal concentration was
from 6,150 to 7,380 Mg/m3 (5 to 6 ppm),
although eye irritation was noted in unac-
climatized persons upon exposure to much
lower levels. At a concentration of 12,300 to
24,600 Mg/m3 (10 to 20 ppm), breathing
becomes difficult, coughing occurs, and burn-
ing of the nose and throat becomes more
severe, and extensive irritation of the trachea
is evident.10 On exposure to clean air, lacri-
mation subsides promptly, but nasal and
respiratory irritation may persist for an hour
or more. The concentration at which serious
inflammation of the bronchi and upper respi-
ratory tract would occur is not known, but
inhalation of high concentrations has caused
laryngitis, bronchitis, and broncho-
pneumonia.20 Based on the above findings, it
has been estimated that exposure to 61,500
to 123,000 jug/™3 (50 to 100 ppm) for 5 to
10 minutes might be expected to cause
serious injury.1 °
(2) Industrial exposures — Some additional
observations on formaldehyde toxicology
have been gathered from occupational expo-
sures. Harris3 3 studied 25 men engaged in the
manufacture of urea-formaldehdye and
phenolformaldehyde resins. Exposures varied
from 5 to 18 years, and, as a general rule, the
concentrations were well below 12,300 /xg/m3
(10 ppm). Dermatitis was found in only four
of the men. In another group of about 150 to
200 men engaged in the manufacture of urea-
formaldehyde resins, glues, molding powders,
7-9
-------
etc., Harris33 was able to uncover three
distinct lesions. Some workers developed a
sudden eczematious reaction of the face, neck,
scrotum, flexor surfaces of the arms, and eye-
lids, which in some instances appeared only a
few days after commencing work. Another
eczematous type of reaction that only ap-
peared after years of exposure started in the
digital areas of the back of the hands, wrists,
forearms, and parts of the body exposed to
friction from clothing. A third type of
reaction included a combination of the first
two types. Many other descriptions of formal-
dehyde dermatitis have appeared in the liter-
ature, but these have generally been related to
situations wherein there was direct contact
with either liquid solutions, solid materials, or
resins containing free formaldehyde; hence
these exposures are not analagous to air pol-
lution situations.
According to Fassett,10 skin sensitization
from exposures to formaldehyde vapors is
very rare; furthermore, no cases of authentic
pulmonary sensitization have occurred.
Individuals who have already developed an
eczematous skin sensitization, however, may
subsequently have a skin reaction upon ex-
posure to formaldehyde vapors. All fatal
poisonings attributed to formaldehyde have
resulted from ingestion.21
In 1969, the American Conference of
Government Industrial Hygienists set the
8-hour threshold limit value (TLV) at 6,150
Mg/m3 (5 ppm) and the American Industrial
Hygiene Association recommended that
ambinet levels of formaldehyde should not
exceed 125 ng/m^ (0.1 ppm).34'36
(3) Animal studies — Irritation of the eyes,
respiratory tract, and skin also occurred
during animal experimentation. Higher con-
centrations, long exposure periods, and post-
mortem examinations, however, have resulted
in information that would have been unavail-
able if studies had been limited to human
volunteers.
Murphy37 found that rat-liver alkaline
phosphatase activity was increased after an
18-hour exposure to 4,300 jug/™3 (3.5 ppm)
formaldehyde vapor. At higher concentra-
7-10
tions, injury to the lungs and other organs
may occur in addition to causing prompt and
severe irritation of the eyes and respiratory
tract. Salem and Collumbine38 exposed
groups of 50 mice, 20 guinea pigs, and 5
rabbits simultaneously to 23,400 Mg/m3 (19
ppm) formaldehyde vapor and other alde-
hydes for periods of up to 10 hours. Upon
sacrificing the animals at the end of this time,
hemorrhages and edema were found in the
lungs, and evidence of hyperemia and
perivascular edema was noted in the liver.
Skog39 exposed rats to 98,400 jug/m3 (80
ppm) formaldehyde for up to 31 minutes. In
nonlethal exposures, most rats appeared to
recover fully within 2 or 3 days. Postmortem
examination of those animals killed by the
vapors showed expanded edematous and
hemorrhagic lungs, fluid in the pleural and
peritoneal cavities, pneumonic consolidation,
distended alveoli, and ruptured alveolar septa.
The response of pulmonary function upon
exposure to formaldehyde has been studied
with normal and tracheotomized
animals.40-43 Formaldehyde inhalation has
resulted in an increased flow resistance and
tidal volume, with a decrease in the respira-
tory rate. Amdur40 noted that the results in
tracheotomized animals were similar to, but
of a greater magnitude than, those observed
with normal animals. This was attributed to
the tracheal cannula, which prevents removal
of formaldehyde by the nasal and upper air-
way routes. Davis42 noted, however, that
tracheotomized animals had elevated respira-
tory rates accompanied by decreased tidal
volumes. These findings were ascribed to the
fact that the receptors for those responses
observed in the normal animals are in the
upper airway (i.e., larynx and above), while
these same receptors are not exposed to the
irritant when the tracheal cannula is in place.
Low levels of formaldehyde can cause
cessation of ciliary activity.44'46 In one
study, exposure to 3,690 /ig/m3 (3 ppm) for
50 seconds or 615 ;ug/m3 (0.5 ppm) for 150
seconds caused cessation of the ciliary beat in
the anesthetized respiratory tract of tracheo-
tomized rats.4 5
-------
Gofmekler47 continuously exposed preg-
nant rats to 1,125 jug/m3 (0.1 ppm) or 1,020
Mg/m^ (0.83 ppm) formaldehyde vapor. The
mean duration of pregnancy was prolonged
by 14 to 15 percent as compared to pregnant
control rats, while a decrease in the number
of fetuses per female was found with the high-
er concentration. Furthermore, the exposure
to formaldehyde appeared to cause an in-
crease in the weight of the thymus, heart, kid-
neys, and adrenals in the offspring. The au-
thor concluded that this effect was apparently
a compensatory reaction to unfavorable en-
vironmental conditions. On the other hand,
the hepatic and pulmonary systems (organs
directly affected upon inhalation of formalde-
hyde) weighed less than those of control ani-
mals.
Effects caused by the inhalation of formal-
dehyde may be modified if an aerosol is also
present. La Belle48 exposed mice to a formal-
dehyde level of 15,375 jug/m3 (12.5 ppm) in
the presence of nine different aerosols, includ-
ing solids and liquids. The time for 50 percent
survival of the mice (STso) was measured,
and the results are shown in Table 7-8. Signifi-
cant increases in the death rate and in the
severity of pulmonary edema were found with
some of the aerosols. The authors suggest that
the active aerosols exerted a synergistic effect
when combined with the formaldehyde vapor.
Amdur4 i >4 9 also investigated the response
to inhalation of formaldehyde in the presence
and absence of sodium chlorid aerosols (ap-
pproximately 0.04 micron in diameter). Guin-
ea pigs were exposed to formaldehyde con-
centrations varying from approximately 86 to
57,800 jug/m3 (0.07 to 47 ppm) with and
without the presence of 10,000 Mg/m3 of so-
dium chloride aerosol. Statistically significant
increases in "respiratory work" as a result of
the exposure to aerosol were found only
when the formaldehyde concentration was
greater than 370 jug/m3 (0.3 ppm). Moreover,
when compared with the pure vapor, the for-
maldehyde-aerosol mixture significantly pro-
longed the period necessary for recovery after
Table 7-8. SURVIVAL TIME OF MICE EXPOSED TO 15,375 jug/m3 (12.5 ppm)
FORMALDEHYDE3 IN PRESENCE OF AEROSOLS48
Aerosol
Triethylene glycol
Ethylene glycol
Mineral oil
Glycerin
Sodium chloride
Dicalite
Celited
Attapulgus clay"
Santocel CFf
Aerosol
size,
microns
1.8
2.0
2.1
2.0
2.6
3.3
2.9
3.3
2.7
Aerosol
concentration,
jug/liter
2210
2920
1420
1280
2320
420
360
960
310
ST b
min
71
168
72
114
114
118
102
157
145
Significance0
++
0
++
++
+
+
++
0
0
aSTcQ was 147 minutes for mice exposed to this concentration of formaldehyde without
aerosols.
bTime for 50 percent survival of mice.
C0 = no significance, + = significant, ++ = highly significant.
dDiatomaceous earth.
eHighly absorptive clay.
f Commercial silica gel.
7-11
-------
discontinuation of the exposure. Further ex-
periments indicated that flow resistance rapid-
ly increased as the aerosol concentration was
raised from 0 to 30,0000 jug/m3. The author
concluded that sodium chloride aerosol,
which is itself inert, can potentiate the re-
sponse to formaldehyde and prolong its effect
as compared with the response to the pure
vapor. This may be due to the concentrating
effect of sodium chloride on formaldehyde,
which results in very high aldehyde concentra-
tions surrounding the small sodium chloride
aerosol.
c. Acrolein
(1) Human studies — Acrolein, like most
other unsaturated aldehydes, is much more ir-
ritating and toxic than the saturated aliphatic
aldehydes.1 ° Its vapors are highly toxic to hu-
mans and extremely irritating to the eyes and
respiratory tract.10'12'50"52 No cases of
chronic toxicity are known,1 °>5 2 '5 3 although
repeated contact with the skin may produce
chronic irritation and dermatitis. Symptoms
reported from inhalation of acrolein include
lacrimation, swelling of the eyelids, shortness
of breath, pharyngitis, laryngitis, bronchitis,
oppression in the chest, somnolence, and asth-
ma 10,23,51,53 1^ reported responses of
man to acrolein vapors are summarized in
Table 7-9.
Concentrations of acrolein as low as 675
Mg/m3 (0.25 ppm) can cause moderate irri-
tation of the eyes and nose in 5 min-
utes.52,53,57 Sim,11 Cook,58 Henderson,59
and Hines57 have reported that lacrimation
occurred within 20 seconds after exposure to
1,880 jug/m3 (0.67 ppm), and began within 5
seconds after exposure to 2,800 Mg/m3 (1.04
ppm). After 2 to 3 minutes at the latter con-
centration, eye irritation is quite noticeable,
becoming almost intolerable after 4 to 5 min-
utes. Smith5 2 and Henderson5 9 reported that
moderate eye and nasal irritation is produced
from a 5-second exposure to 14,795 jug/m3
(5.5 ppm), and that a 20-second exposure is
quite painful. Exposure to 58,640 Mg/m3
(21.8 ppm) is immediately intolerable to hu-
mans.52'59 Pulmonary edema has been re-
7-12
ported at this level,5 3 and a fatality related to
inhalation of 403,500 Mg/m3 (150 ppm) acro-
lein vapor for 10 minutes was noted by Pren-
tiss.5 1
The American Conference of Governmental
Industrial Hygienists and the AIHA recom-
mended that ambient levels of acrolein vapor
should not exceed 27 jug/m3 (0.01 ppm) in
order to prevent sensory irritation.34'35
(2) Animal studies — Smaller concentra-
tions of acrolein are needed to produce simi-
lar effects when compared to saturated alde-
hydes. The acrolein exposure time of mice for
50 percent survival (ST5Q) is 87 minutes, ap-
proximately one-half that for formaldehyde
(147 minutes), and approximately 0.005 that
for propionaldehyde. while the one-half hour
lethal concentration for 50 percent of rats ex-
posed to acrolein (LC5o) is 130 ;ug/m3 (0.05
ppm) and approximately one-sixth of that for
formaldehyde (815 Mg/m3 or 0.67 ppm).10
Mice and rats are found to react to acrolein
even at very low levels.48 Gusev60 exposed
groups of rats to 150 Mg/m3 (0.06 ppm), 510
Mg/m3 (0.19 ppm), and 1,520 jug/m3 (0.57
ppm) acrolein in air over a period of several
weeks. The rats exposed to 1,520 Mg/m3 for
24 days showed a loss of weight, changes in
conditioned reflex activity, a decrease in cho-
linesterase activity of whole blood, a fall of
coproporphyrin excretion in the urine, and an
increase in the number of luminescent leuko-
cytes in the blood. When rabbits were ex-
posed to 1,520 jug/m3 continually for 30
days, there was no apparent effect, though
increasing the level to 5,110 to 6,995 /zg/m3
(1.9 to 2.6 ppm) for 4 hours resulted in en-
zyme alterations in eye tissue.6 l '6 2 Mur-
phy37 also reported an increase in alkaline
phosphatase activity in the liver of rats ex-
posed to similar levels.
The damage to the lungs and other organs
attributed to formaldehyde in the previous
section may also be induced by acrolein.3 8 >39
Skog39 described immediate onset of severe
respiratory difficulty with evidence of pri-
mary irritation of the eyes and upper respira-
tory tract in various animals following the in-
halation of acrolein. Pulmonary edema and
-------
Table 7-9. REPORTED SENSORY RESPONSES OF MAN TO ACROLEIN VAPORS
Concentration,
Aig/m3
525-800
600
1,500
1,750
1,880
2,690
2,690
2,690
2,690
2,800
4,500
14,795
14,795
14,795
58,640
403,500
ppm
0.20-0.30
0.22
0.56
0.61
0.67
1.0
1.0
1.0
1.0
1.04
1.7
5.5
5.5
5.5
21.8
150
Exposure
time
—
—
—
—
20 sec
1 min
2 to 3 min
2 to 3 min
4 to 5 min
5 sec
3 to 4 min
5 sec
20 sec
60 sec
Immediately
10 min
Response
Odor threshold
Dark adaptation response
threshold
Respiratory rhythm and
wave amplitude re-
sponse threshold
Chronaximetric response
threshold
Lacrimation
Slight nasal irritation
Slight nasal irritation
and moderate eye
irritation
Eye and nose irritation
Moderate nasal irritation;
practically intolerable
eye irritation
Lacrimation
Profuse lacrimation
(practically intoler-
able)
Slight odor; moderate
eye and nasal irrita-
tion
Painful eye and nasal
irritation
Marked lacrimation;
vapor practically in-
tolerable
Intolerable eye and
nasal irritation
Lethal
Reference
Leonardos54
Plotnikova55
Plotnikova55
Plotnikova55
Sim11
Smith52
Smith52
Guest50
Smith52
Sim11
Smith52
Smith52
Smith52
Smith52
Smith52
Prentiss51
marked damage to bronchial epithelium were
the principal pathological lesions. Smythe63
found that a 4-hour inhalation of 21,520
Mg/m3 (8 ppm) acrolein killed one of six
rats, while Pattle64 found that 50 percent of
mice and guinea pigs had died after exposure
to 28,245 jug/m3 (10.5 ppm) for 6 hours. At
this concentration, exposure of cats for 3-1/2
hours caused respiratory irritation, salivation,
lacrimation, and mild narcosis, although the
animals returned to normal within 2 to 3
hours after the exposure.65 Lung damage,
however, was still observed in rats 6 months
after exposure to 538,000 jug/m3 (200 ppm)
acrolein for 10 minutes each week for 10
weeks.6 6
Murphy67 used levels more nearly equiva-
lent to industrial exposures in order to deter-
mine effects on respiratory function in guinea
pigs. The animals were exposed to 1,615
Mg/m3 (0.6 ppm), and the results indicated
that acrolein vapors increased the pulmonary
flow resistance and tidal volume while de-
creasing the respiratory rate. The magnitude
of these effects increased as the acrolein con-
centration was raised; and the effects were re-
versible upon return to clean air. The in-
creased flow lesistance was felt to be due to
bronchoconstriction mediated through reflex
cholinergjc stimulation.
La Belle48 exposed mice to 16,140 ;itg/m3
(6 ppm) acrolein in the presence and absence
7-13
-------
Table 7-10. SURVIVAL TIME OF MICE EXPOSED TO 16,150 /Ug/m3 (6 ppm)
ACROLEIN3 IN PRESENCE OF AEROSOLS48
Aerosol
Triethylene glycol
Ethylene glycol
Mineral oil
Glycerin
Sodium chloride
Dicalite
Celited
Attapulgus clay6
Santocel CFf
Aerosol
size,
microns,
1.8
2.0
2.1
2.0
2.6
3.3
2.9
3.3
2.7
Aerosol
concentration,
jUg/liter
380
500
240
220
390
70
60
160
50
STsob
min
73
106
69
94
71
91
99
78
65
Significance0
0
0
+
0
+
0
0
0
+
aST50 was 87 minutes for mice exposed to this concentration of acrolein without aerosols.
bTime for 50 percent survival of mice.
C0 = no significance, + = significant.
dDiatomaceous earth.
eHighly absorptive clay.
fCommercial silica gel.
Table 7-11. AIR QUALITY STANDARDS FOR FORMALDEHYDE36
Country
West Germany
Russia
Czechoslovakia
Basic standard
Concentration,
Aig/m3
36
14.4
18
ppm
0.03
0.01
0.01
Time
period,
hr
0.5
24
24
Permissible levels (<4 hr)
Concentration,
jug/m3
84
42
60
ppm
0.07
0.03
0.04
Time
period,
min
30
20
30
Table 7-12. AIR QUALITY STANDARDS FOR ACROLEIN35
Country
West Germany
Russia
Basic standard
Concentration,
Mg/m3
10
100
ppm
0.003
0.03
Time
period,
hr
0.5
24
Permissable levels (< 4 hr)
Concentration,
Mg/m3 ppm
25 0.009
300 0.11
Time
period,
min
30
20
7-14
-------
of various aerosols (see discussion in Section
C.S.b). The results are shown in Table 7-10.
where it can be seen that significant increases
in the death rate were observed in some cases.
d. Sensory Physiology and Central
Nervous System Responses
In the U.S.S.R., maximum air pollution lev-
els have been rigidly set according to the prin-
ciple " that the ambient air should not
contain odors to be imposed on the popula-
tion against its wishes. . . ,"68 Russian studies
to develop acceptable levels of formaldehyde
and acrolein in the air were conducted in the
mid-1950's with this principle as a guideline.
Limits were based on the subjective reactions
of human volunteers. The threshold* for odor
perception and mucosal irritation in these
subjects was found to be about 800 jug/m3
(0.30 ppm) for acrolein and about 70 jug/m
(0.06 ppm) for formaldehyde. The allowable
concentrations of acrolein and formaldehyde
as adopted by the Russian government in
1957 were established as 300 jug/m3 (0.11
ppm) and 42 /zg/m3 (0.03 ppm), respectively
(Tables 7-11 and 7-12), levels about one-half
the respective threshold values.3 9 >6 8
Between 1956 and 1962, Russian scientists
attempted to define the level of formaldehyde
or acrolein that could trigger specific recep-
tors of the respiratory system (including the
nose). The striking sensitivity of the respira-
tory receptors, particularly those concerned
with olfaction, to the action of minimal con-
centrations of chemical substances has long
been known. This sensitivity is partially ex-
plained by the fact that the olfactory recep-
tors of the upper respiratory tract are located
at the point where outside air is first exposed
to the internal organism, thus exerting a sen-
tinel action in this area.6 8
The varied responses to the aldehydes dis-
cussed in this section, although not strictly
within the realm of classical toxicology, are
included because the data closely relate to the
biological considerations of this review. The
practical ramifications and toxic implications
of neurophysiological responses, however,
have not been adequately explored. One must
exercise caution in the interpretation of such
data, since there have been no replicative
studies to confirm the reported neuro-
physiological responses, and information con-
cerning experimental conditions has certainly
been less than adequate.69
Alterations in optical chronaxy"1" resulting
from stimulation of the receptors in the respi-
ratory system have been used extensively in
Russia to examine the allowable limits of at-
mospheric pollutants.24'25'55'70 No change
in optical chronaxy has been noted when either
of the aldehydes was administered to volun-
teers in concentrations equal either to their
allowable limits or their threshold levels. Lev-
els of formaldehyde exceeding threshold val-
ues (i.e., concentrations greater than 70
Mg/m or 0.06 ppm) have consistently elicited
changes in the optical chronaxy, while acro-
lein concentrations twice the threshold level
(i.e., 1750 jug/m3 or 0.61 ppm) have been
necessary to initiate chronaxy changes.
Information on optical chronaxy has been
substantiated by studies based on the adapta-
tion of the eye to darkness.24'25'55'70 The
Hagel adaptometer, an instrument that meas-
ures increasing light sensitivity of the visual
organ while the subject is in darkness, was
used. Test subjects were exposed to various
concentrations of the aldehyde vapors; and
the average sensitivity to light was computed
*The term threshold concentration applies to that
vapor level just perceptible by either odor or irrita-
tion. Subthreshold implies that the level of exposure
of the particular aldehyde cannot be detected by sub-
jective evidence of either odor or irritation.
+Weak electrical current applied to the eyeball gives
rise to the sensation of a flash of light. For each sub-
ject there is a maximum intensity of stimulation
below which the sensation of light is not perceived.
The intensity threshold, expressed in units of electrical
potential (i.e., volts), is called the rheobase. For
chronaxy determination, electrical current twice the
intensity of the rheobase is used. A stimulating current
of two rheobases causes light sensation only when it
is sufficiently prolonged. This value, which is the time
threshold necessary for the appearance of light sensa-
tion, is called optical chronaxy.
7-15
-------
utilizing a curve illustrating the change of
dark adaptation with time. It was shown that
following the inhalation of air containing 600
to 650 Mg/m3 (0.22 to 0.24 ppm) acrolein, a
fall in the curve of eye sensitivity to light was
noted. Thus, acrolein concentrations not per-
ceivable by odor had an effect on the central
nervous system by eliciting reflex changes in
the functional state of the brain cortex.
Changes in eye sensitivity to light, therefore,
appear to be a more sensitive measurement of
the effect of acrolein than does odor percep-
tion or optical chronaxy. Remarkable as it
may seem, the complex nerological processes
that cause cortical stimulation are initiated
under the influence of a subjectively nonper-
ceivable odor. On the other hand, sub-
threshold and threshold levels of formalde-
hyde have consistently failed to produce
changes in dark adaptation, and it is only
when the formaldehyde level has reached 98
jug/m3 (0.08 ppm) that changes in dark adap-
tation consistently occur. Thus, both odor
perception and optical chronaxy have proved
to be more sensitive indexes of the effect of
formaldehyde than has dark adaptation.
The Russian data are concerned wholly
with the effect of the aldehydes upon the in-
terrelationship of sensory modalities and cere-
bral cortical function. The Russians have
found that odor perception is not the most
sensitive index of acrolein concentrations, as
acrolein is detected by dark adaptation at lev-
els consistently below that perceived by odor.
It has taken twice the threshold concentration
of acrolein, however, to elicit a positive re-
sponse using the optical chronaxy method.
On the other hand, odor perception, dark
adaptation, and optical chronaxy have all
been equally sensitive in determining percep-
tible levels of formaldehdye.
The Russian results, however, do not confirm
ose noted by American researchers. Ameri-
i reports have also demonstrated that acro-
is more active and requires smaller con-
centrations to achieve the similar effects of
formaldehyde, and this remains unaccount-
able at the present time.
4. Acetaldehyde and Other Aldehydes
Acetaldehyde is almost nonirritant to man
at levels less than 90 mg/m3 (50 ppm). The
LC5Q for rats appears to be about 36,000
mg/m3 (20,000 ppm) for 30-minute expos-
ures.39 At this level, the animals rapidly be-
came excitable, but after about 15 minutes
were in a pseudoanesthetic state; survivors
usually recovered rapidly. The principal find-
ing at autopsy has been pulmonary edema.
Smythe63 found that rats survived 4 hours
after inhalation of 14,400 mg/m3 (8,000
ppm) but died from 28,800 mg/m3 (16,000
ppm); and Iwanoff65 observed that cats inhal-
ing 505 mg/m3 (280 ppm) showed no notice-
able effects even after 7 hours, though tem-
porary irritation of the air passages was
observed at 1,980 mg/m3 (1,100 ppm).
Human studies have shown that acetalde-
hyde can be readily detected at concentra-
tions well below 90 mg/m3 (50 ppm), while
some individuals can perceive it at about 45
mg/m3 (25 ppm), Silverman,71 Sim,11 and
Pattle64 have found that the majority of vol-
unteers exposed for 15 minutes to 90 mg/m3
(50 ppm) showed some signs of eye irritation,
while all subjects had red eyes and transient
conjunctivitis upon inhalation of 360 mg/m3
(200 ppm) acetaldehyde. Eye irritation and,
to a lesser extent, nose and throat irritation
appear to be the only signs reported during
industrial exposures. The American Confer-
ence of Governmental Industrial Hygienists
set the 8-hour TLV for acetaldehyde at 360
mg/m3 (200 ppm),35 although no ambient
levels were recommended.
There has been little research concerning
the toxicology of the remaining aldehyde
compounds. Fasset10 has summarized the
reported toxicity data on exposures of animals
to aldehyde (Table 7-13). It should again be
pointed out that the aldehyde concentrations
used in these experiments were far above
those encountered in ambient air.
As is the case with animal studies, very lit-
tle has been published concerning the toxi-
cological effects of aldehydes on man. Table
7-14 summarizes the data available.
7-16
-------
Table 7-13. TOXICITY OF INHALED ALDEHYDES TO RATS10
Compound
Saturated aliphatic aldehydes
Propionaldehyde
n-Butyraldehyde
Isobutyraldehyde
n-Valeraldehyde
2-Methylbutyraldehyde
Unsaturated aliphatic aldehydes
Methacrylaldehyde
(Methacrolein)
Crotonaldehyde
(/3-Methyl acrolein)
Concentration,
mg/m^
19,000
142,500
61,750
22,280
167,100
22,280
168,960
4,930
224,785
12,750
3,500
725
—
4,010
ppm
8,000
60,000
26,000
8,000
60,000
8,000
48,000
1,400
67,000
3,800
1,043
250
a
1,400
Time,
hr
4
0.3
0.5
4
0.5
4
1.2
6
0.3
6.0
6.0
4
(1 min)
0.5
Mortality
5/6
3/3
LC50
1/6
LC50
1/6
3/3
0/3
3/3
0/3
0/3
5/6
0/6
LC50
aConcentrated vapor.
Table 7-14. TOXICITY OF ALDEHYDES TO HUMANS
Compound
Crotonaldehyde
Crotonaldehyde
Propionaldehyde
Propionaldehyde
Butyraldehyde
Butyraldehyde
Isobutyraldehyde
Concentration,
mg/m^
11.7
11.5
475.0
317.3
640.5
557.0
576.5
ppm
4.1
4.0
200.0
134.0
230.0
200.0
207.0
Time,
min
10
a
a
30
30
a
30
Comments
Lacrimation after 30
seconds; no increase
during 10 min.
Highly irritant; causes
lacrimation
Almost nonirritating
Mildly irritating to
mucosal surface;
occasional comment
of odor present.
No irritation noticed
Almost nonirritating
No irritation; some
nausea
Reference
Sim11
Pattle64
Pattle64
Sim11
Sim11
Pattle64
Sim15
aNot given.
7-17
-------
5. Summary
The most characteristic and important ef-
fect of aldehydes, particularly of low-molecu-
lar-weight aldehydes in both humans and ani-
mals is the primary irritation of the eyes, up-
per respiratory tract, and skin. Aldehyde con-
centrations have been shown to correlate with
the intensity of odor of diesel exhaust and to
some extent with the intensity of eye irrita-
tion during natural and chemically produced
smogs. The effects attributable to aldehyde
inhalation, however, have been produced only
by concentrations far above the levels found
in ambient air. In fact, aldehyde levels re-
ferred to as "low" in toxicological reports are
usually much greater than concentrations rou-
tinely found in ambient air.
The observed symptoms in humans result-
ing from inhalation of "low" concentrations
of aldehydes include lacrimation, coughing,
sneezing, headache, weakness, dyspnea, laryn-
gitis, pharyngitis, bronchitis, and dermatitis.
In most cases, the general and parenteral tox-
icities of these aldehydes appear to be related
mainly to these irritant effects. The unsatu-
rated aldehydes are several times more toxic
than the corresponding aliphatic aldehydes,
and toxicity generally decreases with increas-
ing molecular weight within the unsaturated
and aliphatic aldehyde series. Sensitization
has occurred from contact with formaldehyde
solutions and other aldehydes, although sensi-
tization of the respiratory tract is produced
rarely, if at all, by inhalation of aldehydes.
The anesthetic properties of aldehydes are
generally overshadowed by their stronger irri-
tant effects. Furthermore, concentrations that
can be tolerated via inhalation can usually be
metabolized so rapidly that systemic symp-
toms do not occur.
Animal experiments have shown that alde-
hydes can affect respiratory functions, caus-
ing such effects as an increase in flow resist-
ance and tidal volume and a decrease in the
respiratory rate. Exposure of animals to high
concentrations of aldehydes (20 to 80 ppm,
depending on the compared inhaled) has been
shown to produce edema and hemorrhage in
7-18
the lungs and fluid in the pleural and peri-
toneal cavities.
Animal experiments have also indicated the
existence of possible synergistic effects be-
tween aldehydes and aerosols. Thus, acrolein
and formaldehyde in the presence of certain
inert aerosols appeared to be more toxic to
mice than the pure compounds themselves.
Formaldehyde appears to be detectable by
odor or physiological response (optical
chronaxy) at concentrations of the order of
70 to 80 Mg/m3 (0.06 to 0.065 ppm). Esti-
mates of the threshold for irritation vary over
a wide range, with values between about 12
and 1,130 Mg/m3 (0.01 to 0.9 ppm). Concen-
trations between 2,460 and 3,690 Mg/m3 (2
to 3 ppm) are unpleasant, while concentra-
tions around 5,000 Mg/m3 (4 ppm), and the
threshold for optical chronaxy (4 ppm) are
intolerable to most people after a few min-
utes.
Acrolein seems more irritating than formal-
dehyde, although published reports are at var-
iance on this point. The odor is detectable at
concentrations as low as 525 Mg/m3 (0.20
ppm), and the threshold for optical chronaxy
is reported at 1,750 Mg/m3 (0.61 ppm), much
higher than that of formaldehyde. Concentra-
tions of 2,690 ME/m3 (1 ppm) are definitely
irritating, and acrolein at a concentration of
4,580 Mg/m3 (1.7 ppm) is practically intol-
erable.
Acetaldehyde is much less irritating than
formaldehyde; its irritant threshold appears to
be near 10,000 Mg/m3 (50 ppm). No physio-
logical effects are known at levels that may be
anticipated in the atmosphere. There is little
information available on the toxicity of other
aldehyde compounds.
Additional information on the eye-irritant
potential of aldehydes, notably formaldehyde
and acrolein, is included in Section D.3 of this
chapter.
D. HYDROCARBON-MIXED ATMOSPHERE
EXPERIMENTATION
1. Introductory Discussion
It has already jeen noted that the hydro-
carbons found in the atmosphere are degraded
-------
to other atmospheric compounds during ultra-
violet irradiation. To assess the lexicological
effects of mixtures generated by this process,
researchers have exposed experimental ani-
mals to either irradiated auto exhaust, pol-
luted air, or various synthetic atmospheres, all
of which provide the milieu necessary for
hydrocarbon reactivity. It must be empha-
sized, however, that there is not always a well-
defined hydrocarbon-oxidant interrelation-
ship during these mixed atmosphere experi-
ments. Often, the primary effect is directly
related to the oxidant level, although the
hydrocarbon concentration in the synthetic
atmosphere may be directly responsible for
the oxidant concentration upon irradiation.
Thus, it is often quite difficult to define the
relative importance of either of these groups
of pollutants.
The results of several experiments relating
such mixed atmospheres to pulmonary func-
tion and to eye irritation are reviewed in this
section. Additional studies on the effects of
photochemical oxidants on pulmonary func-
tion are included in the companion docu-
ment, AP-63, Air Quality Criteria for Photo-
chemical Oxidants.
2. Changes in Pulmonary Function
Studies have been carried out to show the
effect of both ambient air and diluted auto
exhaust on pulmonary function in laboratory
animals. Murphy72 exposed guinea pigs to
irradiated and nonirradiated auto exhaust
for periods of 4 hours. Tidal vol-
ume, respiratory rate, and flow resist-
ance were measured before, during, and after
exposure. Comparison of concentrations in
irradiated and nonirradiated atmospheres of
approximately equal dilution ratios showed
the photochemical formation of aldehydes,
nitrogen dioxide, and total oxidant at the ex-
pense of nitric oxide and olefins. Flow resist-
ance and tidal volume increased while the res-
piratory rate decreased during exposure to ir-
radiated exhaust; the response to nonir-
radiated exhaust was relatively small. These
functions rapidly returned to baseline levels
following exposure. The data suggest that
components of the exhaust other than photo-
chemical reaction products play a role in the
functional changes observed. The largest re-
sponse was observed in an atmosphere con-
taining 2,950 Mg/m3 (2.4 ppm) formaldehyde,
540 Mg/m3 (0.2 ppm) acrolein, 160 Mg/m3
(0.8 ppm) ozone, and 5,075 Mg/m3 (2.7 ppm)
nitrogen dioxide. Special fumigation studies72
revealed that the effects produced could
be nearly quantitatively simulated by expos-
ing animals to 1,615 Mg/m3 (0.6 ppm) acro-
lein, while ozone alone at 1,370 Mg/m3 (0.7
ppm) produced a negligible effect on one par-
ameter (flow resistance), and on the other
two (respiratory frequency and tidal volume)
it caused responses in the opposite direction
from those observed in the irradiated exhaust
exposure.
In these experiments, the authors noted
that changes in pulmonary function were best
correlated with the aldehyde content of the
exhaust when compared with other routinely
measured agents. Even at an exhaust dilution
of 1,000:1, with hydrocarbon concentrations
well within the range reported for community
pollution levels, the same effects were detect-
able. In tests at this lower concentration, the
total oxidant level was about 785 Mg/m3 (0.4
ppm), formaldehyde was nearly 615 Mg/m3
(0.5 ppm), and the olefin content was esti-
mated to be about 900 Mg/m3.
The likelihood that oxidants were not re-
sponsible for these effects was increased to
near certainty by a comparison of the effects
of irradiated exhaust at a dilution of 1,140:1
with those of nonirradiated exhaust at a dilu-
tion ratio of 150:1. Although no oxidant was
present in the latter case, the effects of the
two conditions on the respiratory function
parameters were virtually identical, as shown
in Table 7-15. These results indicate that the
effective agents are present in raw exhaust
gases and are multiplied in quantity by the
photochemical effects of irradiation. Since
qualitatively identical pulmonary effects are
produced by acrolein and similar effects by
formaldehyde, the hypothesis that the effects
are caused by aldehydes may be entertained.
7-19
-------
Table 7-15. COMPARISON OF THE EFFECTS OF IRRADIATED EXHAUST
WITH THOSE OF NONIRRADIATED EXHAUST ON
PULMONARY FUNCTION PARAMETERS72
Air: Exhaust ratio
Effect on:
Flow resistance
Respiratory frequency
Tidal volume
Nonirradiated
150:1
+30%
-17%
+ 6%
Irradiated
1,140:1
+26%
-17%
+ 4%
360:1
+29%
-20%
+12%
150:1
+113%
33%
+ 25%
Swann73>74 also measured the flow resist-
ance in guinea pigs. The animals were located
at three stations within the los Angeles area;
at each station one group was exposed to fil-
tered air while the second was exposed to am-
bient air. Flow resistance was consistently ele-
vated in the group exposed to ambient air
when oxidant levels were sufficiently elevated
in the atmosphere. Such pollutants as nitric
oxide, carbon monoxide, and low-molecular-
weight hydrocarbons were presumably unaf-
fected by the charcoal filters, but oxidants
and some aldehydes were probably removed.
It is, therefore, impossible to decide which
components of the smoggy atmosphere were
specifically responsible for the effects ob-
served.
3. Eye Irritation
Of the compounds thus far identified in
ambient air, only formaldehyde, acrolein, and
peroxyacyl nitrates have been shown to be
eye irritants. In laboratory experiments on
the photooxidation of alkylbenzenes, peroxy-
benzoyl nitrate is formed. This substance has
been shown to be an especially potent eye
irritant75 and may, therefore, be one of the
species contributing to this manifestation in
the ambient atmosphere.
Renzetti and Bryan76 determined concen-
trations of formaldehyde, acrolein, and PAN
in photochemical smog in conjunction with
eye irritation determinations made by a quan-
tal response technique. Figure 7-1 shows the
regression line relating reported eye irritation
to total aldehyde concentrations in these air
samples, indicating a remarkably good log
plot for aldehyde concentrations between
7-20
0.035 and 0.35 ppm. Figure 7-2 shows similar
information for formaldehyde; the course of
the best-fit line is somewhat less clear than for
total aldehydes (Figure 7-1). For acrolein, the
apparent relationship was nonlinear; samples
with acrolein concentrations of more than 40
Mg/m3 (0.015 ppm) corresponded to less irri-
tating atmospheres, on the average, than those
with acrolein in the range from 8 to 40 jug/m3
(0.003 to 0.015 ppm).
Measuring eye irritation by a threshold re-
sponse method in chamber studies with irradi-
ated auto exhaust, Buchberg7 7 found a strong
correlation with formaldehyde concentration.
In a special comparison using one subject,
however, the formaldehyde threshold was
found to be 13,530 ;ug/m3 (11 ppm), while
the formaldehyde measured in the irradiated
synthetic atmosphere at the threshold was
only 1,230 jug/m3 (1 ppm). The best sets of
variables for multiple correlation were those
which included either formaldehyde concen-
trations or hydrocarbon consumption. In
these tests, initial concentrations of hydrocar-
bons ranged from 3.5 to 35 mg/m3 (1 to 10
ppm as hexane, by nondispersive infrared de-
tector), while the decrease due to reaction
was from 0.42 to 11 mg/m3 (0.12 to 2.9
ppm). Associated initial oxides of nitrogen
ranged from 0.4 to 6 ppm, and formaldehyde
generated was never more than 3,075 jug/m3
(2.5 ppm).
Studies with irradiated synthetic atmos-
pheres containing ;.uto exhaust gases were al-
so reported by Tresday78 et al. Using a sever-
ity scale for the measurement of eye irrita-
tion, they found high correlation (r = 0.80)
with formaldehyde and noted a linear relation
-------
NUMBER OF REPORTS IS IN PARENTHESIS
0.01
0.02
0.03 0.04 0.05 0.10 0.20
ALDEHYDE CONCENTRATIONS, ppm (log scale)
0.30 0.40
Figure 7-1. Regression curve of the effect of atmospheric concentrations of total aldehyde
on panel eye irritation.76
between formaldehyde accumulation and ini-
tial hydrocarbon concentration. They con-
cluded that formaldehyde concentration
might serve as a useful index of eye irritation,
even though formaldehyde was probably not
the sole agent in these atmospheres.
In these experiments, very little eye irrita-
tion was experienced, the highest average pan-
el rating being 0.6 on a scale in which 1 repre-
sented "light" eye irritation. Initial hydro-
carbon concentrations ranged from 1.1 to 9.2
mg/m3 (0.3 to 2.6 ppm as hexane, by nondis-
persive infrared detector), and oxides of nitro-
gen from 0.1 to 1.1 ppm. Formaldehyde con-
centrations were obtained up to 370 Mg/m3
(0.3 ppm), and reports of eye irritation oc-
curred with formaldehyde as low as 185
Mg/m3 (0.15 ppm).
An extensive series of irradiations of
synthetic atmospheres containing auto ex-
hausts was performed by Hamming79 et al.,
using exhaust gases generated by six fuels of
carefully defined composition. The study con-
firmed that changes in the composition of gas-
oline are reflected in changes in the composi-
tion of exhaust gases produced and in changes
in the level of eye irritation developed on irra-
diation. It was concluded that the potential of
exhaust gases for eye irritation might be
raised or lowered, but could not be eliminated
by controlling the composition of gasoline.
More specifically, there was a definite tenden-
cy for eye irritation to increase with increas-
ing fuel olefin content for fuels of equal aro-
matic content and to increase with increasing
aromatic content for fuels of equal olefin con-
tent. With fuels of equal aromatic content,
increasing fuel olefins resulted in increased
pentenes and higher olefins in the exhaust,
but had little effect on ethylene, propylene,
and butenes. Some of the observed increases
in eye irritation, therefore, must be attributed
to products of reaction of these higher olefins
in the atmosphere.
7-21
-------
40
30
20
LU
_l
<
CO
O
Of.
CL
O
h-
<
LU
O
10
a:
O
Q.
0-
I-
z
LLI
u
a:
(609)
FITTED LINE
X X**^PROVISIONAL LINE
/cxf
)(497) X
NUMBER OF REPORTS IS IN PARENTHESIS
0.01
0.02 0.03 0.04 0.05 0.10
FORMALDEHYDE CONCENTRATIONS, ppm
0.20
Figure 7-2. Regression curve of the effect of atmospheric concentrations of formaldehyde
on panel eye irritation.76
With fuels of equal olefin content, increas-
ing aromatic content decreased the produc-
tion of ethylene, propylene, butenes, and
higher olefins in automobile exhaust, but
strongly increased the production of nitric ox-
ide. Aromatic components in the exhaust
were not measured, but were presumably
higher with the more aromatic fuels. Al-
though complicated by the effect of changing
nitric oxide content, this suggests that aro-
matic hydrocarbons in the exhaust are also
effective precursors for the generation of eye
irritants. Although the relation of eye irrita-
tion to formaldehyde produced in this study
was not specifically examined, a table of peak
values of formaldehyde concentration shows
that exhaust from the high-aromatic fuel,
which had a high eye irritation potential,
nevertheless produced much less formalde-
hyde when irradiated than did exhaust from
the high-alkylate fuel, which had a low eye
irritation potential. From this it is clear that
formaldehyde concentration is not the only
determinant of eye irritation in these syn-
thetic atmospheres. Peroxybenzoyl nitrate is a
probable further contributor, especially in the
tests discussed here.
Another extensive series of irradiations of
synthetic atmospheres was performed by
Romanovsky80 et al. In one series of tests,
the hydrocarbon utilized was propylene; in
another, a mixture of ethylene, propylene,
isobutene, and gasoline was used; in a third,
auto exhaust was used. The response-delay
method was used to measure eye irritation.
Utilizing all tests regardless of the initial
hydrocarbon composition, the correlation co-
efficient for log of response time with log of
formaldehyde concentration was -0.82, indi-
cating that formaldehyde may have accounted
7-22
-------
for a large portion of the variance in eye-
irritation results. Formaldehyde levels found
in the irridated atmospheres ranged from
about 125 to 4,920 jug/m3 (0.1 to 4 ppm).
Since in these tests nitric oxide was treated as
a major independent factor, it was important
to evaluate the effects of initial hydrocarbons
and nitric oxide separately, if possible. For
this purpose, the data were fitted by curvi-
linear second- and third-degree equations with
interaction terms, by a least-squares method,
with the results shown in Figure 7-3. In this
diagram, the dashed lines enclose the points
representing initial concentrations for all the
experiments with propylene as the photo-
oxidation substrate (66 tests in all), and the
contours represent constant levels of a derived
index of eye irritation as computed from the
equation of best fit to the data.
The form of the curves in Figure 7-3 indi-
cates that for any given propylene level, maxi-
mum eye irritation should be obtained for ni-
tric oxide initial concentrations of 2,460 to
3,690 jug/m3 (2 to 3 ppm), but that the de-
gree of eye irritation encountered ought to be
determined primarily by the propylene level.
The fact that propylene is sufficiently reactive
to be largely consumed in these irradiations
suggests that eye irritation is cuased by for-
maldehyde or some other product showing
parallel behavior-that is, a product whose
formation is approximately proportional to
the consumption of propylene.
Multiple correlation coefficients with eye
irritation as the independent variable were
0.85 for the tests with propylene and 0.54 for
those with the olefin-gasoline mixture. Thus
the initial levels of contaminants allowed a
much better prediction of eye irritation re-
sults for the propylene system, accounting for
two-thirds of the experimental variance as
compared with only one-third for the mixed-
hydrocarbon system. At the same time, for-
maldehyde peaks could be predicted very well
(multiple correlation coefficient = 0.97) and
equally well for each system. It therefore ap-
pears that eye irritation in the mixed-hydro-
carbon system was significantly affected by
some factor not paralleling the formaldehyde
concentration. Such a factor might possibly
be peroxyacyl nitrates, which begin to accu-
l
a.
Z
o
z
HI
O
8
01
Q
X
o
1
12
f
3
77
1
14
I \
77"
f I
A l«
"i \
\ \
\ \
\ >.
x
/
1
17
\
N^
•
18
V
^-
^*«^_ .
\ \
\ » j i « \ ^^^ «•*• "T^
r
PROPYLENE CONCENTRATION; ppm
Figure 7-3. Effects of varying concentrations of propylene and nitric oxide on eye
irritation.8°
7-23
-------
mulate in photooxidation systems only after
the nitric oxide has been consumed; or it
might be some irritant not yet recoginzed.
Schuck and Doyle8 * contended that eye
irritation observed in their irradiated syn-
thetic atmospheres could be accounted for by
formaldehyde and acrolein. They compared
observed values for 24 different hydrocar-
bons, with calculated values based on assigned
contributions for unit concentrations of the
two aldehydes, with resonable agreement re-
sulting. The contributions were calculated on
the basis of tests with the individual alde-
hydes. In the evaluation tests, 3,435 jug/m
(1.5 ppm) acrolein gave an eye irritation
severity of 15 (maximum possible 24), and
4,920 Mg/m-3 (4 ppm) formaldehyde gave a
severity of 16. The compounds were therefore
assigned values of 10 and 4 (severity units per
ppm), respectively.
If these factors are applied to the aldehyde
concentrations measured in the atmosphere
by Renzetti76 (discussed above), predicted
values of the severity index are of the order of
magnitude of 0.3 for days when 50 percent of
the panelists reported eye irritation. If 50 per-
cent of the members of the panel employed
by Schuck81 reported eye irritation in a given
test, the severity index for that test would be
at least 4. Thus there appears to remain a dis-
crepancy amounting to a factor of at least 10
between the observed concentrations of for-
maldehyde and acrolein in the atmosphere
and those that would be needed, using this
formulation, to account for the observed ef-
fects.
In an attempt to explain this discrepancy,
Schuck1 et al. conducted irradiations of
synthetic atmospheres containing nitrogen
dioxide and ethylene or propylene, in con-
junction with determination of eye irritation
potential both by severity index and by re-
sponse time, as well as observations on the
blink rate of subjects exposing their eyes.
When propylene was used, the regression of
severity index against formaldehyde concen-
tration was linear, with an intercept of 3 for
zero formaldehyde. When ethylene was the
hydrocarbon, however, the relation appeared
7-24
significantly nonlinear, with values for formal-
dehydes less than 370 jug/m^ (0.3 ppm)
approaching the "pure air" average severity of
about 5 (See Figure 7-4). The investigators
interpreted these results as indicating that
formaldehyde concentrations as low as 12
Mg/m^ (0.01 ppm) could cause eye irritation.
A possibility which has been suggested to
account for the discrepancy between observed
irritation and observed concentrations of
irritants is a synergistic effect of aerosols on
gasoues eye irritants. To test this hypothesis,
Doyle82'83 measured the eye irritation ef-
fects of six olefin nitrogen oxide mixtures
irradiated with and without added sulfur
dioxide. These experiments indicated that the
aerosols formed did not increase, but on the
average decreased, the eye irritation effects
developed by the irradiation.
A series of 29 hydrocarbons, including 12
aromatic hydrocarbons, was studied in irradia-
tions of synthetic atmospheres by Heuss.7 5 It
was found that, under the conditions chosen,
the aromatic hydrocarbons produced more
eye irritation than most nonaromatic com-
pounds; in particular, styrene and j3-methyl-
styrene were more potent that any other
hydrocarbons in the list, as shown in Table
7-16. In this series, eye irritation showed no
correlation with formaldehyde. The eye irrita-
tion potency utilized by these authors is
based on a linear transformation of average
panel response time.
Further investigation revealed the presence,
in some of the systems containing aromatic
compounds, of peroxybenzoyl nitrate.7 5 This
compound was found to be a lacrimator al-
most 200 times as potent as formaldehyde; in
photooxidation of styrene, it accumulated to
a concentration of 0.4 ppm. It is, therefore,
probable that this substance caused most of
the eye irritation in some or all of these irradi-
ations of aromatic hydrocarbons. It is also
probable that the same substance is formed in
urban atmospheres and is responsible for
some of the eye irritation observed in photo-
chemical smog.
Altshuller,8 4 studying irradiated synthetic
atmospheres containing alkylbenzenes, found
-------
0 0.2 0.4 0.6 0.8
FORMALDEHYDE CONCENTRATIONS, ppm
0 0.2 0.4 0.6 0.8 10.0
FORMALDEHYDE CONCENTRATIONS, ppm
Figure 7-4. Average reported eye irritation intensities of 12 subjects during photooxidations
with ethylene and propylene, related to observed formaldehyde concentrations.''
Table 7-16. EYE IRRITATION POTENCY OF VARIOUS HYDROCARBONS
IN IRRADIATED SYNTHETIC ATMOSPHERES75
Hydrocarbon
rc-Butane
rc-Hexane
Isooctane
ferf-Butylbenzene
Benzene
Ethylene
1-Butene
Tetramethylethylene
cw-2-Butene
Isopropylbenzene
jec-Butylbenzene
2-Methyl-2-butene
fran.y-2-Butene
o-Xylene
p-Xylene
Potency3
0
0
0.9
0.9
1.0
1.0
1.3
1.4
1.6
1.6
1.8
1.9
2.3
2.3
2.5
Hydrocarbon
m-Xylene
1 ,3 ,5-Trimethylbenzene
1-Hexene
Propylene
Ethylbenzene
Toluene
«-Propylbenzene
Isobutylbenzene
«-Butylbenzene
1 ,3-Butadiene
a-Methylstyrene
Allylbenzene
|3-Methylstyrene
Styrene
Potency
2.9
3.1
3.5
3.9
4.3
5.3
5.4
5.7
6.4
6.9
7.4
8.4
8.9
8.9
"Conditions: Hydrocarbon 2 ppm, nitric oxide 1 ppm for all except styrene, a-methyl-
styrene, j3-methylstyrene, and allylbenzene (for those, hydrocarbon was 1 ppm, nitric
oxide 0.5 ppm).
7-25
-------
eye irritation panel responses of the same
magnitude as those in propylene photooxida-
tion, but mainly somewhat smaller. Toulene,
m-xylene, and 1,3,5-trimethylbenzene showed
eye irritation response greater than ethylene,
while o-xylene gave less. The same workers85
reported that eye irritation could also be
produced by irradiating synthetic atmos-
pheres containing 615 Mg/m^ (0.5 ppm) nitric
oxide and 14.3 mg/m3 (6 ppm) butane or
13.9 mg/m3 (3 ppm) 2,4-dimethylhexane. In
similar systems, 3 ppm of butane (7.1
mg/m3), isopentane (8.9 mg/m3), 2-methyl-
pentane (10.3 mg/m3), 3-methylhexane (12
mg/m3), methylcyclohexane (12 mg/m3), or
w-nonane (15.6 mg/m3) did not yield irrita-
tion significantly above that obtained with
background air. In the system with 14.3
mg/m3 (6 ppm) butane, it was noted that eye
irritation was produced even with nitric oxide
levels that were high enough to inhibit appre-
ciable accumulation of oxidants, presumably
including peroxyacyl nitrates. The authors
concluded that paraffinic hydrocarbons,
acetylene, and benzene do not contribute
appreciably to eye irritation in photochemical
air pollution.
4. Summary
a. Pulmonary Function
Pulmonary function tests are found to be
altered following the exposure of experi-
mental animals to either smog or irradiated
auto exhaust. Caution must be taken, how-
ever, on drawing conclusions from these
studies, since hydrocarbons are but one of
several type pollutants inhaled by the animals.
The following results have been previously
discussed:
1. Exposure to ambient air in Los Angeles
during episodes of photochemical smog pro-
duces a temporary increase in pulmonary
airflow resistance in guinea pigs.
2. During short-term exposure to irradi-
ated auto exhaust, the following changes in
pulmonary function may be observed in
guinea pigs: increased tidal volume, increased
minute volume, and increased flow resist-
ance,* with a decrease in the respiratory rate.
The parameters return to normal immediately
following exposure.
b. Eye Irritation
Consideration of the facts and findings
cited in the section on eye irritation may jus-
tify some conclusions as to the relation of eye
irritation to contaminant levels in photo-
chemical smog:
1. The effective eye irritants are products
of the photochemical reactions. These include,
as identified eye irritants, formaldehyde, acro-
lein, peroxyacyl nitrates, and peroxybenzoyl
nitrate.
2. The precursors of the eye irritants are
hydrocarbons (as well as other organic com-
pounds) in combination with oxides of nitro-
gen. Alkylbenzenes and olefins are more ef-
fective precursors than paraffins, benzene,
and acetylenes.
3. The secondary contaminants causing eye
irritation in the atmosphere are not known
with certainty. Although it is possible that the
compounds named above are the only irri-
tants of importance in the atmosphere, this
has not been demonstrated.
4. Concentrations of formaldehyde in
irradiated synthetic atmospheres or in am-
bient atmospheres tend to be well correlated
with observations of eye irritation. This is
especially true for series of observations in
which there is little change in the composition
of the hydrocarbon substrate. But where rela-
tive proportions of paraffins, olefins, and aro-
matics are changed, the correlation is im-
paired.
5. Eye irritation severity developing as a
result of irradiating atmospheres contami-
nated with hydrocarbons and oxides of nitro-
gen tends to reflect the concentration of
hydrocarbon prescursors more directly than
that of the oxides of nitrogen.
*When the irradiated exhaust contains 9,000 to
13,000 Mg/m3 of olefinic hydrocarbons, about 2,460
Mg/m3 (2 ppm) formaldehyde, and 540 Mg/m3 (0.2
ppm) acrolein, total expiratory flow resistance may
be doubled.
7-26
-------
6. The development of eye irritation in ir-
radiated atmospheres is not strictly parallel to
the accumulation of oxidants or ozone. Eye
irritation can be appreciable while concentra-
tions of oxidants are still negligible.
E. SUMMARY
Hydrocarbon air pollutants enter into and
promote the formation of photochemical
smog, and thus contribute to the development
of eye irritation and other manifestations.
They are intimately involved in the formation
of formaldehyde and other aldehydes and ke-
tones, and of various oxidants, including
peroxyacetyl nitrate. In developing air quality
criteria, the potential of the hydrocarbons
under certain atmospheric conditions to form
more hazardous derivatives must be discussed
also.
Experimental data resulting from the ex-
posure of animals and humans to various
hydrocarbon compounds indicate that:
1. The aliphatic and alicyclic hydrocarbons
are generally biochemically inert, though not
biologically inert, and are only reactive at
concentrations of 10^ to 103 higher than
those levels found in the ambient atmosphere.
No effects have been reported at levels below
500 ppm.
2. The aromatic hydrocarbons are biochem-
ically and biologically active. The vapors are
more irritating to the mucous membranes
than equivalent concentrations of the ali-
phatic or alicyclic groups.Systemic injury can
result from the inhalation of vapors of the
aromatic compounds; no effects, however,
have been reported at levels below 25 ppm.
Aldehydes are one of the primary contribu-
tors to the eye irritation noted during pho-
tochemical smog; and, because there is a di-
rect relationship between aldehydes and
hydrocarbons as determined through various
atmospheric reactions, a review of aldehyde
toxicology was included in this chapter. Ex-
perimental data indicate:
1. Aldehyde concentrations have been cor-
related with the intensity of eye irritation
during natural and laboratory-produced pho-
tochemical smogs. Formaldehyde appears to
be detectable by odor or physiological re-
sponse (optical chronaxy) at concentrations
in the order of 70 Mg/m3 (0.06 ppm). The
threshold for eye irritation by formaldehyde
has been estimated by various investigators to
be between 12 and 1,230 Mg/m3 (0.01 to 1.0
ppm). Acrolein can be detected by odor and
eye irritation at concentrations as low as 600
Mg/m3 (0.25 ppm), but the threshold for opti-
cal chronaxy is reported as 1,750 Mg/m3 (0.75
ppm).
2. Formaldehyde at a concentration of
2,460 jug/m3 (2 ppm) has been associated
with a doubling of the total expiratory resis-
tance of guinea pigs exposed to irradiated
atmospheres of automobile exhaust gases.
3. Acetaldehyde is much less irritating than
formaldehyde; its irritant threshold appears at
concentrations of about 10,000 Mg/m3 (50
ppm). No physiological effects are known at
levels that may be anticipated to occur in the
ambient atmosphere.
In general, the most characteristic and im-
portant effect of aldehydes for both humans
and animals is primary irritation of the eyes,
upper respiratory tract, and skin. The unsatu-
rated aldehydes are several times more toxic
than the corresponding aliphatic aldehydes;
toxicity generally decreases with increasing
molecular weight within the unsaturated and
aliphatic aldehyde series. Animal experiments
have shown that aldehydes can affect respira-
tory functions, causing such effects as an in-
crease in flow resistance and tidal volume and
a decrease in the respiratory rate. Animal ex-
periments have also indicated that acrolein
and formaldehyde, in the presence of certain
inert aerosols, appeared to be more toxic to
mice than the pure compounds themselves.
Pulmonary function and eye irritation have
also been evaluated by the exposure of experi-
mental animals and humans to various mixed
atmospheres that had the characteristic of
providing the milieu necessary for hydro-
carbon reactivity. Experimental data indicate:
1. Exposure of guinea pigs to ambient Los
Angeles air may produce a temporary increase
in pulmonary airflow resistance. Exposure of
guinea pigs to laboratory-irradated auto ex-
haust causes as increased tidal volume, minute
7-27
-------
volume, and flow resistance, with a decrease
in the respiratory rate. These parameters re-
turn to normal immediately following expos-
ure.
2. The precursors of the eye irritants are
hydrocarbons (as well as other organic com-
pounds) in combination with oxides of nitro-
gen; the alkylbenzenes and olefins are more
effective precursors than paraffins, ben/ene,
and acetylenes. The products of photo-
chemical reactions that have been identified
as effective eye irritants are formaldehyde,
acrolein, peroxyacyl nitrates, and peroxy-
benzoyl nitrate.
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24(1): 193-198, September 1942.
45. Dalhamn, T. Mucous Flow and Ciliary Activity in
Trachea of HealthyRats and Rats Exposed to
Respiratory Irritant Gases (SO2, H3N, HCHO).
Acta Physiol. Scand. (Stockholm). Suppl. 123.
56:1-161, 1956.
46. Kensler, C. J. and S. P. Battista. Chemical and
Physcial Factors Affecting Mammalian Ciliary
Activity. Amer. Rev. Resp. Dis. 95:93-102,
March 1966.
47. Gofmekler, V. A. Effect of Embryonic Develop-
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zola i formal'degiela pri ingalyatsionnom puti
vozdeistviya v eksperimente]. Hyg. Sanit.
55:327-332, January-March 1968.
48. La Belle, C.W., J.E. Long, and E. E. Christofano.
Synergistic Effects of Aerosols. Arch. Ind.
Health. 77:297-304, April 1955.
49. Amdur, M. O. The Physiological Response of
Guinea Pigs to Atmospheric Pollutants. Int. J.
Air Water Pollution. 7(3): 170-183, January
1959.
50. Guest, H. R., B. W. Kiff, and H. A. Stansbury, Jr.
Acreolein and Derivatives. In: Kirk-Othmer En-
cyclopedia of Chemical Technology Standen, A.
(ed.), Vol. 1, 2d ed. New York, Interscience Pub-
lishers, 1963. P. 255-274.
51. Prentiss, A. M. Chemicals in War. New York,
McGraw-Hill Book Co., Inc., 1937. 739 p.
52. Acrolein. Smith, C. W. (ed.). New York, John
Wiley & Sons, Inc., 1962. 273 p.
53. Properties and Essential Information for Safe
Handling and Use of Acrolein. Chemical Safety
Data Sheel SD-85. Manufacturing Chemists As-
soc., Washington, D. C. 1961.
54. Leonardos, G., D. A. Kendall, and N. J. Bernard.
Odor Threshold Determinations of 53 Odorant
Chemicals. J. Air Pollution Control Assoc.
79:91-95, February 1969.
55. Plotnikova, M. M. Acrolein as an Atmospheric
Air Pollutant. In: USSR Literature on Air Pollu-
tion and Related Occupational Diseases, Levine,
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B. S., Vol. 3. Washington, D. C., Dept. of Com-
merce, 1960. p. 188.
56. Yant, W. P. et al. Acrolein as a Warning Agent for
Detecting Leakage of Methyl Chloride from Re-
frigerators. Bureau of Mines. Washington, D. C.
Report of Investigation Number 3027. July
1930, 11 p.
57. Hine, C. H. et al. In: Proceedings of the Air Pol-
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58. Cook, W. A. Maximum Allowable Concentrations
of Industrial Atmospheric Contaminants. Ind.
Med. 74:936-946, November 1945.
59. Henderson, Y. and H. W. Haggard. Noxious Gases
and the Principles of Respiration Influencing
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60. Gusev, M. I. et al. Determination of the Daily
Average Maximum Permissible Concentration of
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srednesutochnoi predel'no dopustimoi konsten-
tratsii akroleina v atmosfernom bozdukhe]. Hyg.
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61. Mettier, S. R. et al. A Study of the Effect of Air
Pollutants on the Eye. Arch. Ind. Health. 27:1-6,
January 1960.
62. Hine, C. H. et al. Eye Irritation for Air Pollution.
J. Air Pollution Control Assoc. 10(1): 17-20, Feb-
ruary 1960.
63. Smyth, H. F., Jr. Hygienic Standards for Daily
Inhalation. Amer. Ind. Hyg. Assoc. Quart. 17
(2):129-185,June 1956.
64. Pattle, R. E. and H. Cullumbine. Toxicity of
Some Atmospheric Pollutants. Brit. Med. J.
2(4998):913-916, October 20, 1956.
65. Iwanoff, N. Experimentelle Studien Uber den
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Case und Dampfe auf den Organismus. Arch.
Hyg. Bakteriol. (Munich). 7J:338, 1911.
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Respiratoires Experimentales par Inhalation
d'Acroleine Chez le Rat]. Arch. Mai. Prof.
(Paris). 27:857-867. December 1966.
67. Murphy, S. D., D. A. Klingshirn, and C. E. Ul-
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Drugs. J. Pharmacol. Exp. Therap. 747(l):79-83,
July 1963.
68. Ryazanov, V. A. Sensory Physiology as Basis for
Air Quality Standards. The Approach Used in the
Soviet -Union. Arch. Environ. Health
5(5):480-494, November 1962.
69. Amdur, M. O. The Influence of Aerosols Upon
the Respiratory Response of Guinea Pigs to Sul-
fur Dioxide. Amer. Ind. Hyg. Assoc. Quart.
18(2): 149-155, June 1957.
7-30
70. Plotnikova, M. Basic Investigations for the Deter-
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Concentration in Atmospheric Air. In: Limits of
Allowable Concentrations of Atmospheric Pol-
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Technical Services, Washington, D. C. 1960.
71. Silverman, L., H. F. Schulte, and M. W. First.
Further Studies on Sensory Response to Certain
Industrial Solvent Vapors. J. Ind. Hyg. Toxicol.
2
-------
°4. Altshuller, A. P. et al. Chemical Aspects of the 85. Altshuller, A. P. et al. Photochemical Reactivities
Photooxidation of the Propylene - Nitrogen Ox- of N-Butane and Other Paraffinic Hydrocarbons.
ide System. Environ. Sci. Technol. 7:899-922, J. Air Pollution Control Assoc. 79:787-790, Oc-
November 1967. tober 1969.
7-31
-------
CHAPTER 8.
SUMMARY AND CONCLUSIONS
A. INTRODUCTION
This document focuses on gas-phase hydro-
carbons and certain of their oxidation
products, particularly aldehydes, that are as-
sociated with the manifestations of photo-
chemical air pollution. Particulate hydro-
carbons, and more specifically polynuclear
hydrocarbons, are not treated in this
document. It is important to recognize that
the criteria for hydrocarbons rest almost
entirely on their role as precursors of other
compounds formed in the atmospheric photo-
chemical system and not upon direct effects
of the hydrocarbons themselves. A compa-
nion document, AP-63, Air Quality Criteria
for Photochemical Oxidants, covers the
effects of a class of photochemical reaction
products not treated in this document.
B. SOURCES, NATURE, AND PRINCI-
PLES OF CONTROL OF ATMOS-
PHERIC HYDROCARBONS
Most natural sources of hydrocarbon emis-
sions are biological in nature. A conservative
estimate made for the worldwide natural
production rate of methane is 3 x 108 tons
per year. A similar estimate of 4.4 x 108 tons
per year has been made for volatile terpenes
and isoprenes. It appears that nonurban air
contains from 0.7 to 1.0 mg/m3 (1.0 to 1.5
ppm) methane and less than 0.1 ppm each of
other hydrocarbons.
Total nationwide technological emissions
of hydrocarbons and related organic com-
pounds for the year 1968 were estimated to
be 32 x 106 tons. Transportation represented
the largest source category and accounted for
52 percent of this estimate. The miscellaneous
source category—principally organic solvent
evaporation—was the second largest and repre-
sented 27 percent of the total emissions.
Industrial processes (14 percent) was third;
solid waste disposal (5 percent) was fourth;
and fuel combustion in stationary sources (2
percent) was fifth.
Local emission estimates for 22 metro-
politan areas ranged from about 0.05 to 1.3
million tons per year. Transportation sources
accounted for from 37 to 99 percent of local
emissions, and process losses accounted for
from 1 to 63 percent. Hydrocarbon emissions,
therefore, originate primarily from the inef-
ficient combustion of volatile fuels and from
their use as process raw materials.
The control of hydrocarbon emissions rests
upon the basic principles of: (1) combustion
process optimization, (2) recovery by mass
transfer principles, (3) restriction of
evaporative loss, and (4) process material and
fuel substitution. The first three principles are
all applied with varying degrees of success in
the control of automobile emissions.
C. ATMOSPHERIC LEVELS OF HYDRO-
CARBONS AND THEIR RELATED
PRODUCTS
Yearly averages of monthly maximum
1-hour average hydrocarbon concentrations
including methane, recorded continuously in
various stations of the Continuous Air Moni-
toring Projects, have reached maximum hour-
ly values of 8 to 17 ppm (as carbon), but at
least half of this amount is probably the
photo chemically unreactive methane compo-
nent in all cases.
In a series of 200 samples taken in one
urban location, average concentrations of the
most abundant hydrocarbons were as follows
8-1
-------
(in ppm as carbon): methane, 3.22; toluene,
0.37; rc-butane, 0.26; /-pentane, 0.21;
ethane, 0.20; benzene, 0.19; rc-pentane, 0.18;
propane, 0.15; and ethylene, 0.12. Among
classes of hydrocarbons, the alkanes
predominate, even if methane is excluded.
They are followed by the aromatics, olefins,
acetylenes, and alicyclics.
The diurnal variation of hydrocarbon con-
centrations resembles that of carbon monox-
ide (at stations in the Los Angeles area) in
having a pronounced maximum appearing
usually between 6:00 and 8:00 a.m.
For nonoxidant photochemical secondary
contaminants, available information is limited
to results of special studies on aldehydes in
the Los Angeles area. These show that yearly
maximum 1-hour average total aldehyde con-
centrations range from 0.20 to 1.30 ppm and
that the analogous formaldehyde concentra-
tions range from 60 to 150 Mg/m^ (0.05 to
0.12 ppm). Hourly average acrolein con-
centrations range from 10 to 270 ng/m.3
(0.004 to 0.010 ppm) in various studies. The
ratio of formaldehyde to the "total" aldehyde
index has been reported at from about 10 to
90 percent; it is likely that an appreciable part
of the variation is caused by the use of dif-
ferent analytical methods or procedures in the
different investigations.
D. SAMPLING AND STANDARDIZATION
METHODS FOR MEASUREMENT OF
HYDROCARBONS
With few exceptions, atmospheric hydro-
carbon measurements are made with relatively
complex instruments that operate continuous-
ly. Continuous instrumentation demands
dynamic calibration techniques. Standard
gases for this purpose are available or may be
generated by permeation tubes or dilution
systems, or prepared in large containers.
Flame ionization analyzers are sensitive
and reliable and are suitable for the
continuous measurement of total hydro-
carbons. They are generally accepted as the
method of choice by NAPCA. They cannot,
however, give the specific detailed informa-
tion required for a thorough understanding of
8-2
the atmospheric photochemical problem.
Attempts to further define the hydrocarbon
mixture by using pretreatment columns to
measure only methane or various reactive
classes have met with some success but
limited application.
Spectrometric techniques both for total
and specific analysis are complex and general-
ly insensitive.
Gas chromatographic analysis provides the
requisite sensitivity and specificity for the
quantitation of individual hydrocarbons. Dif-
ficulties in qualitative analysis and data hand-
ling have limited the application of GC to
short-term studies for the most part, and no
continuous data are available.
Carbonyl compounds, specifically alde-
hydes and ketones, can be measured by
several manual colorimetric techniques, but
very little actual data are available.
E. RELATIONSHIP OF ATMOSPHERIC
HYDROCARBONS TO PHOTOCHEMI-
CAL AIR POLLUTION LEVELS
The development of a model to relate
emission rates of hydrocarbons to ambient air
quality and thence 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 max-
imum daily oxidant levels has been approach-
ed empirically by a comparison of 6:00 to
9:00 a.m. average hydrocarbon values with
hourly maximum oxidant values attained later
in the day. This approach has validity only
because of the dominating influence of the
macro-meteorological variables on both the
concentrations of precursors and photochem-
ical products. Furthermore, this approach can
only yield useful information when a large
number of days are considered, thus
guaranteeing the inclusion of all possible
combinations of emission rates, mete-
orological 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 a
finite and limiting value 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 concentra-
tion. This upper limit of the maximum daily
oxidant concentration 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
concentrations.
In defining this oxidant upper limit all
available data relating directly measured non-
methane hydrocarbon concentrations to max-
imum daily oxidant concentrations have been
used. Direct observation of this limit in the
vicinity of 200 p.g/m^ (0.1 ppm) daily max-
imum 1-hour average oxidant concentration
shows that in order to keep the oxidant below
this value, the 6:00 to 9:00 a.m. average non-
methane hydrocarbon concentration must be
less than 200 /ug/m3 (0.3 ppm C). This maxi-
mum oxidant concentration potential may be
expected to occur on about 1 percent of the
days.
F. EFFECTS OF HYDROCARBONS AND
CERTAIN ALDEHYDES ON VEGETA-
TION
Hydrocarbons were first recognized as
phytotoxic air pollutants about the turn of
the century as a result of complaints of injury
to greenhouse plants from illuminating gas.
Ethylene was shown to be the injurious com-
ponent. 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 photo-
chemical smog complex. Research on several
unsaturated and saturated hydrocarbons
proved that only ethylene had adverse effects
at known ambient concentrations. Acetylene
and propylene more nearly approach the
activity of ethylene than do other similar
gases, but 60 to 500 times the concentration
is needed for comparable effects.
In the absence of any other symptom, the
principal effect of ethylene is to inhibit
growth of plants, Unfortunately, this effect
does not characterize ethylene because other
pollutants at sublethal dosages, as well as
some disease and environmental factors, will
also inhibit growth.
Epinasty of leaves and abscission of leaves,
flower buds, and flowers are somewhat more
typical of the effects of ethylene, but the
same effects may be associated with nutrition-
al imbalance, disease, or early senescence.
Perhaps the most characteristic ethylene
effects are the dry sepal wilt of orchids and
the closing of carnation flowers. Injury to
sensitive plants has been reported at ethylene
concentrations of 1.15 to 575 jug/m3 (0.001
to 0.5 ppm) during time periods of 8 to 24
hours.
G. TOXICOLOGICAL APPRAISAL OF
HYDROCARBONS AND ALDEHYDES
Hydrocarbon air pollutants enter into and
promote the formation of photochemical
smog and thus contribute to the development
of eye irritation and other manifestations.
They are intimately involved in the formation
of formaldehyde and other aldehydes and
ketones, and of various oxidants, including
peroxyacetyl nitrate. In developing air quality
criteria, there must be due consideration of
the potential of the hydrocarbons under
certain atmospheric conditions to form more
hazardous derivatives.
Experimental data resulting from the expo-
sure of animals and humans to various hydro-
carbons compounds indicate that:
1. The aliphatic and alicyclic hydro-
carbons are generally biochemically inert,
though not biologically inert, and are only
reactive at concentrations of 102 to 103
higher than those levels found in the ambient
atmosphere. No effects have been reported at
levels below 500 ppm.
8-3
-------
2. The aromatic hydrocarbons are
biochemically and biologically active. The
vapors are more irritating to the mucous
membranes than equivalent concentrations of
the aliphatic or alicyclic groups. Systemic
injury can result from the inhalation of vapors
of the aromatic compounds; no effects, how-
ever, have been reported at levels below 25
ppm.
Pulmonary function and eye irritation have
been evaluated by the exposure of exper-
imental animals and humans to various mixed
atmospheres that had the characteristic of
providing the milieu necessary for hydro-
carbon reactivity. Experimental data indicate:
1. Exposure of guinea pigs to ambient Los
Angeles photochemical smog produces a
temporary increase in pulmonary airflow
resistance. Exposure of guinea pigs to labora-
tory-irradiated auto exhaust causes an in-
creased tidal volume, minute volume, and
flow resistance, with a decrease in the
respiratory rate. These parameters return to
normal immediately following exposure.
2. The precursors of the eye irritants are
hydrocarbons (as well as other organic com-
pounds) in combination with oxides of
nitrogen; the alkylbenzenes and olefins are
more effective precursors than paraffins,
benzene, and acetylenes. The products of
photochemical reactions that have been
identified as effective eye irritants are formal-
dehyde, acrolein, peroxyacyl nitrates, and
peroxybenzoyl nitrate. In general, the most
characteristic and important effect of alde-
hydes for both humans and animals is pri-
mary irritation of the eyes, upper respira-
tory tract, and skin. The unsaturated al-
dehydes are several times more toxic than the
corresponding aliphatic aldehydes, and toxici-
ty generally decreases with increasing mol-
ecular weight within the unsaturated and
aliphatic aldehyde series. Animal experiments
have shown that aldehydes can affect respira-
tory functions, causing such effects as an in-
crease in flow resistance and tidal volume and
a decrease in the respiratory rate. Animal
8-4
populations, although many of the effects at-
tributed to photochemical smog are indirectly
related to ambient levels of these hydrocar-
bons.
Experimental data on specific aldehydes
have indicated:
1. Aldehyde concentrations have been cor-
related with the intensity of eye irritation
during natural and laboratory-produced
photochemical smog. Formaldehyde appears
to be detectable by odor or physiological
response (optical chronaxy) at concentrations
in the order of 70 /xg/m3 (0.06 ppm). The
threshold for eye irritation by formaldehyde
has been estimated by various investigators to
be between 12 and 1,230 Mg/m3 (0.0 1 to 1.0
ppm). Acrolein can be detected by both odor
and eye irritation at concentrations as low as
600 /xg/m3 (0.25 ppm), but the threshold
for optical chronaxy is reported as 1,750
Mg/m3 (0.75 ppm).
2. Formaldehyde at a concentration of
2,460 Mg/m3 (2 ppm) has been associated
with a doubling of the total expiratory resist-
ance of guinea pigs exposed to irradiated
atmospheres of automobile exhaust gases.
3. Acetaldehyde is much less irritating
than formaldehyde; its irritant threshold
appears at concentrations of about 10,000
Mg/m3 (50 ppm). No physiological effects are
known at levels that may be anticipated to
occur in the ambient atmosphere.
H. CONCLUSIONS
The conclusions that follow are derived
from a careful evaluation of the studies cited
in this document, representing the National
Air Pollution Control Administration's best
judgment of the effects that may occur when
various levels of hydrocarbons are reached in
the ambient air. Additional information from
which the conclusions were derived, and qual-
ifications that may enter into consideration of
these data, can be found in the appropriate
chapters of this document.
1. Our present state of knowledge does not
demonstrate any direct health effects of the
-------
gaseous hydrocarbons in the ambient air on
populations, although many of the effects at-
tributed to photochemical smog are indirectly
related to ambient levels of these hydrocar-
bons.
2. Injury to sensitive plants has been re-
ported in association with ethylene concentra-
tions of from 1.15 to 575 /ug/m3 (0.001 to
0.5 ppm) over a time period of 8 to 24 hours
(Chapter 6).
3. Examination of air quality data indi-
cates that an early morning (6:00 to 9:00
a.m.) concentration of 200 jug/m3 (0.3 ppm
C) nonmethane hydrocarbon can be expected
to produce a maximum hourly average oxi-
dant concentration of up to 200 jug/m3 (0.1
ppm) (Chapter 5).
I. RESUME
Studies conducted thus far of the effects of
ambient air concentrations of gaseous hydro-
carbons have not demonstrated direct adverse
effects from this class of pollution on human
health. However, it has been demonstrated
that ambient levels of photochemical oxidant,
which do have adverse effects on health, are a
direct function of gaseous hydrocarbon con-
centrations; and when promulgating air qual-
ity standards for hydrocarbons, their contri-
bution to the formation of oxidant should be
taken into account.
An analysis of 3 years of data collected in
three American cities shows that on those
several days a year when meteorological
conditions were most conducive to the forma-
tion of photochemical oxidant, nonmethane
hydrocarbon concentrations of 200 /zg/m^
(0.3 ppm C) for the 3-hour period from 6:00
to 9:00 a.m. might produce an average 1-hour
photochemical oxidant concentration of up
to 200 A
-------
APPENDIX.
CONVERSION BETWEEN VOLUME
AND MASS UNITS OF CONCENTRATION
The physical state of gaseous air pollutants
at atmospheric concentrations generally may
be described by the ideal gas law:
pv= nRT (1)
where:
p = absolute pressure of gas
v = volume of gas
n = number of moles of gas
T = absolute temperature
R = universal gas constant
The number of moles (n) may be calculated
from the weight of pollutant (w) and its
molecular weight (m) by:
w
n = —
m
(2)
Substituting equation (2) into equation (1)
and rearranging yields:
v =
wRJ
pm
(3)
Parts per million refers to the volume of
pollutant (v) per million volumes of air (V).
ppm =
106V
(4)
Substituting equation (3) into equation (4)
yields:
w
ppm= -
RT
(5)
pmlO6
Using the appropriate values for variables in
equation (5), a conversion from volume to
mass units of concentration for methane may
be derived as shown below.
T = 298°K(25°C)
p = 1 atm
m = 16 g/mole
R = 8.21 x 10'2 £-atm/mole° K
w(g) x 1Q6 Qu/g)
V(K) x lO-3 (m3/£)
8.21 x 1C'2 (£-atm/mole°K) x 298(°K)
l(atm) x 16 (g/mole) x 106
= 1.53 x ID'3 ppm
1 ppm = 655 jug/m3
In the text reference is made both to ppm
as carbon (ppm C) and to ppm as methane.
On a ppm-by-volume basis these two terms
are equivalent, since methane has only a single
carbon atom. In converting such measure-
ments from volume to mass units, therefore,
the molecular weight of methane is used.
A-l
-------
SUBJECT INDEX.
Acetaldehyde and other aldehydes,
7-16-7-18
Acrolein, 7-12-7-16
Aerometric data, analysis of 5-2—5-11
Aerosol measurements, 4-5
Aerosols, 3-10-3-12, 4-5
Air quality criteria, general discussion,
1-1-1-2
Air quality measurements, 5-1—5-12
Aldehydes, 2-6, 2-8-2-9, 3-9-3-10, 7-2-7-32
Alicyclic hydrocarbons, 7-2
Aliphatic hydrocarbons, 7-1—7-2
Analysis of gaseous aldehydes and ketones,
44
Analysis of total hydrocarbons, 4-2
Analytical methods, 4-1—4-7
Anesthesia, 7-7
Aromatic hydrocarbons, 7-2
Atmospheric reactions, 2-2—2-5
B
Bisulfite methods, 4-4
Calibration techniques, 4-1-4-2
Carbureted gasoline engines, 2-14
Classes of hydrocarbons, 2-1—2-2
Cencentrations (Atmospheric), 3-1-3-15,
6-4-6-7
Concentrations (Community levels), 3-4-3-9
Concentrations (Riverside, California), 2-3
Concentrations (Synthetic atmospheres),
2-4-2-5
Condensation reagents, 4-4
D
Denver, Colorado, air quality data, 5-6
Diesel engines, 2-14—2-15
Diurnal variation, 3-3
Dose-injury relationships for plants exposed
to ethylene, 6-4-6-7
E
Economic loss from ethylene injury to vegeta-
tion, 6-4
Effects of ethylene gas on vegetation,
6-1 -6-7
Effects of hydrocarbons and certain alde-
hydes on vegetation, 6-1—6-9
Emission controls
[See: Motor vehicle controls; Stationary
source control]
Emission estimates, national, 2-12—2-13
Emission estimates, regional, 2-13
Emission factors, 2-15—2-16
Emission levels, natural sources, 2-10—2-12
Emission levels, technological sources,
2-12-2-13
Engines
[See Carbureted gasoline engines; Diesel en-
gines; Gas turbine engines]
Ethylene, 6-1—6-7
Eye irritation, 5-2-5-3, 7-20-7-26
Flame ionization methods, 4-2
Formaldehyde, 2-8, 7-8-7-12, 7-15-7-16
Fumigation experiments, 6-5—6-7
1-1
-------
Gas chromatography, 4-3
Gas turbine engines, 2-15
Gasoline engines, 2-14
I
Internal combustion engines
[See: Carbureted gasoline engines; Diesel
engines; Gas turbine engines; Gasoline en-
gines]
K
Photochemical air pollution levels, 5-1—5-12
Pho tooxidation products, expected,
2-5-2-10,5-1-5-12
Photooxidation products, experimental,
2-6-2-10
Plant indicators (for ethylene), 6-4
Pulmonary function, 7-19—7-20
R
Reactive hydrocarbons, 4-3
Riverside, California, air pollution concentra-
tions, 2-3
Ketones, 2-8-2-9, 4-4
Los Angeles, California, air quality data,
5-3-5-11
M
Maximum daily oxidant concentrations, de-
termination of, 5-5—5-9
Macro-meteorological factors, 5-3—5-4
Measurement of aerosols, 4-5
Motor vehicle controls, 2-16—2-17
N
Nervous system, 7-30—7-36
Nitrates, peroxyacyl, 2-6
Nitrates and nitrites, organic, 2-9—2-10
Nitrogen dioxide, 2-6—2-8
Nonmethane hydrocarbons, 4-2—4-3
O
Olefin determination, 4A
Ozone, 2-5—2-7
Pathological effects of aldehydes, 7-7—7-8
Peroxyacyl nitrates, 2-6
Philadelphia, Pennsylvania, air quality data,
5-3
1-2
Sample collection and handling, 4-4—4-5
Seasonal variation, 3-3—3-4
Secondary contaminants, 3-9—3-10
Sensitization, 7-7
Sensory physiology and central nervous sys-
tem responses to formaldehyde and
acrolein, 7-15—7-16
Sources, stationary, 2-15
Sources, technological, 2-13—2-15
Spectrometric methods, 4-3
Spectrophotometric methods, 4-2
Stationary source control, 2-17
Subtractive columns, 4-2—4-3
Synthetic atmospheres, 2-4—2-5
Total hydrocarbons, 4-2
Toxicity, mechanisms of, 7-7—7-8
Toxicological appraisal of hydrocarbons and
aldehydes, 7-1-7-32
Toxicology of acrolein, 7-12-7-15; of alde-
hydes, 7-2-7-18; of alicyclic hydrocarbons,
7-2; of aliphatic hydrocarbons, 7-1-7-2; of
aromatic hydrocarbons, 7-2; of formalde-
hyde, 7-8-7-12
W
Washington, D. C., air quality data, 5-3-5-6
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