EPA-450/3-76-028b
December 1976
OPEN SPACE
AS AN
AIR RESOURCE
MANAGEMENT MEASURE
VOLUME II: DESIGN CRITERIA
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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EPA-450/3-76-028b
OPEN SPACE
AS AN
AIR RESOURCE
MANAGEMENT MEASURE
VOLUME II: DESIGN CRITERIA
by
R.S. DeSanto, R.A. Glaser, W.P. McMillen,
K.A. MacGregor, and J.A. Miller
COMSIS Corporation
972 New London Turnpike
ClaBlonbury, Connecticut 06033
Contract No. 6842-2350
EPA Project Officer: Thomas McCurdy
Prepared for
ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
December 1976
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This report is issued by the Environmental Protection Agency to report
technical data of interest to a limited number of readers. Copies are
available free of charge to Federal employees, current contractors and
grantees, and nonprofit organizations - in limited quantities - from the
Library Services Office (MD35), Research Triangle Park, North Carolina
27711; or, for a fee, from the National Technical Information Service,
5285 Port Royal Road, Springfield, Virginia 22161.
This report was furnished to the Environmental Protection Agency by
COMSIS Corporation, Glastonbury, Connecticut 06033, in fulfillment
of Contract No. 68-02-2350. The contents of this report are reproduced
herein as received from COMSIS Corporation. The opinions, findings,
and conclusions expressed are those of the author and not necessarily
those of the Environmental Protection Agency. Mention of company or
product names is not to be considered as an endorsement by the Environ-
mental Protection Agency.
Publication No. EPA-450/3-76-028b
11
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ACKNOWLEDGEMENTS
We wish to thank Mr. Thomas McCurdy, the E.P.A. project officer for this study,
whose assistance and advice was most valuable and greatly appreciated.
STAFFING
Dr. Robert S. DeSanto was project manager and principal investigator for this
study at COMSIS CORPORATION - Environmental Services. Mr. Richard A. Glaser,
of David A. Crane and Partners, provided interpretations of the literature from
the point of view of the landscape architect. He also provided all illustrative
material with the exception of the electron micrographs which were provided by
Dr. William H. Smith of the Yale University School of Forestry and Environmental
Studies. Mr. William P. McMillen and Mr. Kenneth A. MacGregor of COMSIS CORPORATION
assisted in all aspects of this study providing engineering and planning overviews
and writing much of the text. Dr. Joseph A. Miller, Head Librarian at Yale
University School of Forestry and Environmental Studies, executed all library
services and guided the numerous processing operations required for document delivery.
Ms. Dana Pumphrey of COMSIS CORPORATION assisted at all levels in the preparation
of the report. Her help was broad and very important.
Mrs. Joy Maxfield typed the manuscript entirely alone. Her accuracy and her
stamina were important to us and to our successful completion of this Volume.
We are grateful to her for her support.
iii
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•TABLE OF CONTENTS
Chapter Title Page
LIST OF FIGURES v
LIST OF TABLES viii
I INTRODUCTION, APPROACH AND SUMMARY OF RESULTS 1-1
A. INTRODUCTION AND ORGANIZATION OF THE REPORT .... 1-1
B. SUMMARY OF THE RESULTS 1-4
II HIGHWAY BUFFER AND RELATED OPEN SPACE II-1
A. POLLUTANT IDENTIFICATION II-1
1. Source Emissions II-1
2. Transport Mechanisms . . . . * II-5
3. Atmospheric Diffusion 11-10
B. LITERATURE SEARCH FINDINGS 11-18
C. POTENTIAL DESIGN ALTERNATIVES 11-42
1. Summary of Literature Search Findings 11-42
2. Design Configurations 11-54
III REGIONAL OPEN SPACE III-l
A. POLLUTANT IDENTIFICATION III-l
1. Source Emissions III-3
2. Pollutant Removal 111-12
B. LITERATURE SEARCH FINDINGS Ill-17
C. LAND USE/GREEN BELT ORGANIZATION 111-22
D. CONVERSION OF LEAF AREA TO GROUND AREA AND
WEIGHTED SINK FACTORS 111-28
IV GLOSSARY IV-1
V BIBLIOGRAPHY V-l
VI APPENDIX VI-1
A. HIGHWAY DIFFUSION MODELS VI-1
B. SENSITIVE SPECIES LIST VI-20
C. CALCULATION OF LEAF AREAS FOR SELECTED TREES .... VI-46
D. HOLLAND STACK RISE EQUATION VI-52
iv
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TABLE OF FIGURES
Figure Title Page
1-1 SCANNING ELECTRON MICROGRAPH OF THE ADAXIAL SURFACE
OF A LONDON PLANETREE LEAF... 1-5
1-2 SCANNING ELECTRON MICROGRAPH OF AGGREGATE PARTICLES ON
THE ADAXIAL SURFACE OF A LONDON PLANTREE LEAF 1-6
1-3 SCANNING ELECTRON MICROGRAPH OF A TRICHOME ON THE
ADAXIAL SURFACE OF A LONDON PLANETREE LEAF... ... 1-7
1-4 SCANNING ELECTRON MICROGRAPH OF AGGREGATE PARTICLE
BLOCKING A STOMATE OF A LONDON PLANETREE LEAF 1-8
1-5 SCANNING ELECTRON MICROGRAPH OF SUB-MICROMETER PARTICLES
ON THE SURFACE OF A LONDON PLANETREE LEAF
TRICHOME... 1-9
1-6 SCANNING ELECTRON MICROGRAPH OF POLLEN AND FUNGI ON THE
ADAXIAL SURFACE OF A LONDON PLANETREE LEAF... ... I-10
II-1 THE INFLUENCE OF WIND SPEED ON GROUND LEVEL POLLUTANT
CONCENTRATIONS II-6
I1-2 SOIL LEVEL OF LEAD QUEEN'S PARK AND SOIL LEVEL OF
CADMIUM QUEEN'S PARK II-8
II-3 LEAD CONTAMINATION OF WHITE PINE TWIGS PLUS NEEDLES
SAMPLED FROM TREES GROWING AT VARYING DISTANCES FROM
INTERSTATE 95, CONNECTICUT... II-9
I1-4 COORDINATE SYSTEM SHOWING GAUSSIAN DISTRIBUTIONS IN THE
HORIZONTAL AND VERTICAL 11-11
IT-5 HORIZONTAL DISPERSION COEFFICIENT AS A FUNCTION OF
DOWNWIND DISTANCE FROM THE SOURCE 11-14
I1-6 VERTICAL DISPERSION COEFFICIENT AS A FUNCTION OF DOWNWIND
DISTANCE FROM THE SOURCE 11-15
II-7 ALTERNATE SOLUTION CALIFORNIA LINE SOURCE CROSSWIND
MODEL FOR CARBON MONOXIDE CONCENTRATIONS 11-17
I1-8 THE SHELTER PROVIDED BY A 16-METRE-HIGH SHELTERBELT
OF DECIDUOUS TREES IN SUMMER AND WINTER 11-33
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TABLE OF FIGURES (CONTINUED)
Table Tltlfe Page
II-9 DESIGN PARAMETERS OF BUFFERS FOR SOUND ATTENUATION. . . . 11-41
11-10 DENSITY OF BUFFER RELATED TO REDUCTION OF WIND VELOCITY . 11-46
11-11 EXTENT OF INFLUENCE OF WINDBREAK AND SHELTERBELT PLANTINGS 11-49
11-12 FORM OF BUFFER IS RELATED TO REDUCTION OF WIND VELOCITY . 11-50
11-13 INCREASED DIVERSITY WITHJN EDGE CONDITION MAXIMIZES
SINK POTENTIAL 11-51
11-14 CREATION OF THERMAL CHIMNEYS FOR VENTILATION OF
FORESTS AND BUFFERS 11-51
II-15 CO CONCENTRATIONS ADJACENT TO ROADS 11-52
11-16 INCREASING BUFFER EDGES 11-55
11-17 INCREASING BUFFER VENTILATION 11-55
11-18 CHEVRON HEDGEROW 11-56
11-19 PARALLEL HEDGEROW 11-56
11-20 MULTIPLE HEDGEROW 11-57
11-21 MANAGED NATURAL BUFFER 11-57
11-22 VENTILATING ROADWAY CUTS 11-58
11-23 RECREATION FACILITY SETBACK 11-58
11-24 PLANTING EXISTING MEDIANS . . 11-59
III-l SCHEMATIC REPRESENTATION OF THE CHEMICAL PROCESSES
INVOLVING ENVIRONMENTAL SULFUR... III-3
III-2 SECTION ALONG 79TH STREET, MANHATTAN ISLAND 111-19
III-3 WEDGES 111-20
III-4 GREENBELTS 111-20
III-5 STREET TREE PLANTINGS ARE ENCOURAGED AS PART OF REGIONAL
PLANTING AND BUFFER PROGRAM 111-21
vi
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•TABLE OF FIGURES (CONTINUED)
Table Title Page
III-6 DISTANCE OF MAXIMUM CONCENTRATION AND MAXIMUM XU/Q AS A
STABILITY AND EFFECTIVE HEIGHT OF EMISSION 111-25
III-7 TWO DIMENSIONAL RELATIONSHIPS BETWEEN SOURCE, SINK, AND
RECEPTOR LOCATIONS 111-26
III-8 IDEALIZED POINT SOURCE BUFFERS WITHOUT REGARD TO LAND
CONSTRAINTS 111-27
III-9 IDEALIZED POINT SOURCE BUFFER WITH LAND CONSTRAINTS. . . 111-27
vli
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LIST OF TABLES
Table Title Page
II-l KEY TO STABILITY CATEGORIES 11-13
II-2 PLANTS KNOWN FOR THEIR CAPACITY TO RETAIN DUSTS 11-22
II-3 NUMBER OF KERNELS IN ONE CM3 11-25
11-4 PROCESS OF SULFUR ABSORPTION BY PLANTS 11-30
I1-5 ECOLOGICAL CHARACTERISTICS OF COMMERCIAL FORESTS AS
CONTRASTED WITH PROTECTIVE GREENBELT VEGETATION .... 11-36
III-l SUMMARY OF SOURCES AND ANNUAL EMISSIONS OF ATMOSPHERIC
POLLUTANTS III-2
III-2 ESTIMATED CARBON MONOXIDE EMISSION SOURCES IN THE
UNITED STATES IN 1970 III-6
III-3 KEY TO STABILITY CATEGORIES 111-24
III-4 WEIGHTED SINK AND EMISSION FACTORS FOR AVERAGE SOIL AND
AVERAGE VEGETATION... 111-30,31
III-5 SPECIES RELATIONSHIP OF GROUND AREA COVERED TO PLANT
SURFACE AREA 111-32
III-6 SELECTED TREES AS POLLUTION SINKS 111-32,33
VI-1 PLANT SPECIES SENSITIVITY LISTS
FLUORINE VI-22
VI-2 PLANT SPECIES SENSITIVITY LISTS
GENERAL POLLUTION VI-26
VI-3 PLANT SPECIES SENSITIVITY LISTS
HYDROGEN CHLORIDE VI-33
VI-4 PLANT SPECIES SENSITIVITY LISTS
NITROGEN DIOXIDE VI-35
VI-5 PLANT SPECIES SENSITIVITY LISTS
OZONE VI-37
viil
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LIST OF TABLES (CONTINUED)
Table Title Page
VI-6 PLANT SPECIES SENSITIVITY LISTS
PAN VI-40
VI-7 PLANT SPECIES SENSITIVITY LISTS
PARTICULATES-SMOKE VI-41
VI-8 PLANT SPECIES SENSITIVITY LISTS
SULFUR DIOXIDE VI-42
VI-9 DATA CHARTS OF THE TREE SPECIES USED IN THE MODEL
HECTARE VI-50
ix
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I. INTRODUCTION. APPROACH AND SUMMARY OF RESULTS
A. INTRODUCTION AND ORGANIZATION OF THE REPORT
The work undertaken in this project has resulted in the preparation
of three separate report volumes and one Appendix Volume. Taken together,
they cite and attempt to interpret all of the pertinent and accessible literature
from the United States of America, and elsewhere, relating to the potential use of
open space as a practical means to mitigate air pollution.
Volume II, this Volume, is entitled Design Criteria and presents the essence of
this study in the form of a workbook. It reviews the primary biological and design
features which are crucial to the effective utilization of open space to mi-
tigate air pollution. It presents generalized schemes for the design and
location of buffer strips and other forms of open space and also illustrates
air pollution mitigation by open space by identifying the mathematical pro-
cedures necessary in order to permit the incorporation of the appropriate sink
factors into four generally used carbon monoxide diffusion models.
Since this project concerns an investigation into the real and potential
use of open space, a rather abstract and loosely used phrase, the following
definition is given as the frame upon which our work is placed. Open space is
an area with a natural cover of soil, water, and plants, where there are usually
minimal human activities, and where there are legal restrictions that limit
the development of facilities or structures. In a limited sense, open space may
be thought of as parks. However, they may also be Resource Open Spaces where the land
or water is devoted to some form of non-structural production activity. A forest,
range-lands, and water storage lakes or rivers, are examples. Flood control and
drainage lands, lands used as waste disposal areas or borrow pits, wildlife refuges,
or lands reserved for future urban development, are all examples of Utility Open
Spaces. Another major category may be called Green Open Spaces where recreation,
or relatively non-structural uses, are sought and where the natural vegetation
tends to dominate the landscape. Examples include; national park areas, urban
parks, buffers, and the associated greenbelts or green wedges, which may be
interspersed with urban development. A fourth major category consists of Corridor
Open Spaces where space is allocated for the movement of people and material from
one point to another. Examples include, rights-of-way such as highways and streets,
or canals and railroads, and the areas associated with the terminals and/or
interchanges associated with those rights-of-way.
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These, and other categories of open space are more fully described in
the literature. DeChiara and Koppelman (1975) include the above definitions and
others which may be useful should the reader seek detailed information from the
point of view of urban planning and design. However, as explored in this project,
open space is limited to those categories defined above.
Open space, in its natural state or manipulated state, can have a varied
and far reaching effect on regional air quality. It has been well documented in
Volume I of this report that open spaces particularly when planted, as bare soil,
or as water bodies, can act as sinks for important air pollutants. Through the
natural process of adsorption, absorption,impingement,and deposition, pollutants
generated by urban land uses can be entrapped by these areas. From a planning
point of view, open space has been used as a buffering device to contain the expansion
of urban development and its attendant generation of air pollution. The characterization
of open space as land upon which there is minimal human activity makes' the phase an
antonym to urban type development. The extent and location of such open space has
varied effects on regional air quality. For example, the use of an open space
adjacent to a transportation artery (i.e a roadway,) reduces the ambient levels
of automobile generated pollutants. Vegetation in the path of air, laddened
with particulates, can serve to filter out some of the particulates. This capability
can reduce concentrations of particulates which would otherwise impact area residents.
The use and design of open space areas on a micro-scale can mitigate pollution
transport characteristics. Through the break-up of tunnel or canyon effects,
vegetation canopies can encourage air current eddying and thus can cause mixing
and the sedimentation of particulates.
The atmosphere should be looked upon as a finite sink for pollutants. It
has a limit which we can try and set as an "acceptable" concentration of pollutants.
By reducing the density of urban development through the use of open space, the
loadings are reduced in a region.
The possible negative effect of open space includes the natural emission
factors characteristic of particular plant species. The generation of hydrocarbons
by plants produce photochemical oxidants. Depending upon the amount of plant materials,
the hydrocarbons emitted can intensify or create oxldant problems. The use of
1-2
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open space within a comprehensive land use plan can also have negative effects
on overall air quality if the entire community infrastructure is not evaluated.
For example, if large tracts of open spaces cause an increase in vehicular travel,
the associated generation of transportation related pollutants is Increased.
In addition, some open space uses are marked air polluters. For example, open pit
mining and agricultural activities, such as plowing, can significantly increase
the particulate loadings in the ambient air.
The knowledge obtained from the investigation of open space as an air
quality maintenance strategy should be used to re-evaluate the concept of the
atmosphere as a sink. Historically, our view has been to dilute the pollutants
with the atmosphere. However, vetetation and open space can be utilized as a sink
or filtering device. It would be efficient to concentrate polluting emissions and
direct them through an appropriate open space so that they can be filtered. This
seems contrary to present day thinking. However, systems planning, value engineering
and resource recovery are also relatively new concepts gaining in their acceptance.
It is hoped that the information in this report may help make open space an air quality
management technique somewhat better understood than was previously the case. It
should be actively implemented as an additional strategy available for environmental
management.
Volume I is entitled Sink Factors and presents the data collected from
the manual and computerized literature searches. Most of the information presented
in the other volumes was derived from the data contained in Volume I. There-
fore, much cross referencing is made. Volume I contains tables of sink and
emission factors which were developed based on the collected data, and it also
contains tables of pollution sensitive and pollution resistant plant species derived
from the surveyed literature. The separate Appendix Volume for Volume I presents
abstracts of the pertinent literature. It was decided to include as many abstracts
as possible in order that our work might find as broad a utilization as possible
by future researchers.
Volume III is entitled Demonstration Plan and applies our findings in
a hypothetical manner to a test city, St. Louis, Missouri. This demonstration
plan includes a cost/effectiveness analysis of the combined open space/AQMA
plan with that analysis based on the best available data which we were able to
secure. It provides the reader with a realistic application and evaluation
of using open space as a practical part of the AQMA plan strategy.
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B. SUMMARY OF THE RESULTS
Of approximately eight thousand references examined, about two thousand
were used because they were directly or indirectly relevant to
determining the sink and emission factors of those pollutants under study.
Information was collected on: 1) Ammonia, 2) Carbon monoxide, 3) Chlorine,
4) Fluorine, 5) Hydrocarbons, 6) Nitrogen oxides, 7) Ozone, 8) Perbxyacetylnitrate
(FAN), 8) Particulates, and 9) Sulfur dioxide. Sink and emission factors are
reported from the literature and, where possible, the average factor is calculated
based on a subjective evaluation of the data.
As a result of this study, it is clear that there are very little data
available that quantitatively evaluate the function of water bodies as a sink
and/or source of air pollutants. Most of the data we reviewed dealt with soil and
vegetation relative to sinks and emissions and therefore, the imbalance of data
causes this report to make only very general statements concerning the importance of
water as a factor in open space mitigation of air pollution. Future research should
focus on this area for both qualitative and quantitative analyses.
The present literature is most clear in its conclusion that open space,
vegetation in particular, is a filter for all manner of partlculates. In
fact, the air-pollution-mitigating-capacity of open space is graphically so
clear that this Summary of Results has been extended to include the following
series of electromicrographs prepared by the Yale University Laboratory of
Dr. William H. Smith, a co-author of Volume I - Sink Factors.
Particles are intercepted by vegetation,and the literature also
reports absorption of various air polluting gases. These are summarized in
Volume I and their conclusions are applied in this Volume. Soil, as a sink for
carbon rronoxide, is the most effective element of open space in removing
noxious gas, as reported in the literature.
With these two simple and well documented findings, it is clear that
open space, carefully placed, can effectively function to filter particulates and
carbon monoxide from the air. Furthermore, it can be demonstrated from the
literature that open space also functions to mitigate numerous other pollutants.
The use and predicted mitigation by open space as an air resource management
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II. HIGHWAY BUFFER AND RELATED OPEN SPACE
This section of the study is concerned with the control of pollutants from
a highway source. It introduces the concept of using highway buffer strips to absorb
pollutants transported to the edge of a highway. Initially, a review of pollutants
emitted from motor vehicles is presented followed by discussions on transport
methodology and diffusion modeling. Next, sink factors are presented for various
highway related pollutants. Finally, the literature is reviewed on buffer strips
and design alternations.
The section was written to allow the user to initially predict the type and
amount of pollutants that will be present adjacent to highways and highway
corridors. Following this predictive methodology, one can determine the amount
and type of buffer strips that would best absorb these pollutants.
It should be noted that the concepts presented in this chapter are not
based on an exact science and should be used only as planning guidance*. The
sink factors and design alternatives that are presented are based solely on a
review of the literature. More practical research is needed on the effective-
ness of using these concepts. In addition, before making detailed predictions of
the concentrations of pollutants near highways, Jihe user should consult with
other publications to determine the best model to use for the actual case with
which he is involved.
A. POLLUTANT IDENTIFICATION
1. Source Emissions.
Before developing design concepts for highway buffer strips, it
is necessary to review the type and quantities of pollutants that are emitted from
a motor vehicle. Air is polluted as a result of combustion and the majority of
transportation systems today use the combustion of fossil fuels as their main source
of energy. Carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen (N0x)
are the three major air pollutants released by motor vehicles. It has been
estimated that motor vehicles represent 98% of the sources for CO, 50% of the sources
for NO and 60% of the sources for HC (Willis ,'et al.,|1973).
II-1
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In addition to the above, motor vehicles emit a small percentage
of two other pollutants usually considered in air pollution problems; sulfur oxides
(SO ) and total suspended particulates (TSP). SO is usually considered more of
X X
a regional problem associated with individual point sources and it will be discussed
in Section III of this study. Although transportation sources are not responsible
for any significant portion of TSP emissions, their contribution,especially lead,
should and can be considered in designing buffer strips for highway corridors.
Wolsko, et al., (1972) present a description of the fuel combustion process
and how pollutants are formed. The majority of emissions come from gasoline
powered motor vehicles. When gasoline is mixed with air in proper proportions, a
combustible mixture is formed. Because the combustion process is not complete, by-
products are formed which are considered pollutants. This situation is character-
istic of any combustion process using fossil fuels (electrical generating stations,
space heating, transportation).
Fuel Combustion Equation for Gasoline
Gasoline . Air Combustion _g^ Combustion Products + Pollutants
(HC)m w^tv/ ^^» C02 + H20 + H9 + CO + NO
* = many types
The above equation depicts that carbon dioxide (CO.,) , water vapor
(H20), free hydrogen (HO, oxygen (02) and nitrogen (N2) make up the
bulk of the products of combustion, but carbon monoxide, oxides of nitrogen (NO,
N0_) and unburned hydrocarbons (HC) are also produced. More than 200 unburned
hydrogens (HC) have been detected in vehicle exhaust. (Note: The above equation
is representative of the fuel combustion process and does not necessarily balance
in a chemical sense).
The amount of each of the pollutants emitted on a highway is dependent
on the number of vehicles using the highway as well as the relative efficiency
of each automobile's emission system. Because of the many different types of
vehicles and their different ages and degrees of operating efficiency, emissions
vary widely from vehicle to vehicle,:-. In addition to differences in vehicle
emission characteristics, the operating cycle is also an important determinant
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of pollutant emissions from transportation sources. Speed, cold starts, acceleration,
starts and stops,are factors of the vehicle operating cycle that effect emissions.
The Environmental Protection Agency has published factors which
represent the weighted emissions for a standard distribution of vehicles. Using
emission factors for each vehicle, it is possible to quantify the total pollutants
being emitted along a highway corridor. The necessary data and procedures used to
calculate emission factors for motor vehicles are contained in "Supplement No. 5
for Compilation of Air Pollutant Emission Factors" (U.S. EPA, 1975).
In order to determine the total emissions for a given time period,
multiply the emission factor obtained from Supplement No. 5 by the total number
of vehicles for that same period.
The amount of particulates emitted from a highway source Is more
difficult to quantify than the gaseous pollutants. Most of the particulate matter
comes from two sources: the first being the salts formed in the exhaust and the
second being rubber particles from tires and asbestos particles from brake linings.
In addition to these sources, the turbulence in the air from a moving vehicle causes
dirt particles on the side of the road to be disturbed and emitted into the air.
The particulate from automobiles that has been-given most attention
is lead. To reduce quantities of lead being emitted, all new cars are made
to use lead free gas thereby eliminating the source of the problem. However, it
will take years before all older vehicles are phased out and only lead free
automobiles are allowed on the highway.
Lead is one of the principal particulates emitted by motor vehicles.
Specific estimates of the amount of lead annually introduced to the atmosphere via
gasoline combustion includes 98% (National Academy of Sciences, 1972) and 95%
(Ewing and Pearson, 1974). Atmospheric, terrestrial and aquatic environments
immediately adjacent to roadways are contaminated with lead by motor vehicles
combusting leaded gasoline. No controversy surrounds this observation.
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Most of the gasoline for vehicles sold prior to 1975 in the United
States contains alkyl lead compounds to improve the antiknock quality of the fuel.
The amount of lead in gasolines prior to 1975 (in the form of lead alky Is) varied
from 2 to 4 g/gal. The average lead content is approximately 2.5 g/gal.
(Ewing and Pearson, 1974).
Not all the lead combusted in automobile engines is released into
the atmosphere. Hirschler and Gilbertl( 1984)1, concluded that 25% of the lead
combusted may be held in exhaust system deposits or removed during changes of
lubricating oil and oil filters. These investigators further found that the
percentage of lead burned in the engine, which is discharged to the atmosphere,
varies with driving speed, driving conditions, vehicle age and fuel employed
among others. Over many thousands of miles of driving it is generally assumed
that approximately 70-80% of the combusted lead will eventually be released
to the atmosphere. Assuming average and approximate conditions, automobiles
prior to 1975 may release 130 mg of lead per mile per car (81 mg Pb/km) into the
roadside environment (Smith, 1975).
2.5gPb/gal x 0.80 emission n ., _. , ...
" ?,.—7; ;—; = O.U g. Pb/mile
15 miles/gal.
An average lead emission rate for production vehicles at 108 mg.
of lead per mile has been given by Cantwell, etal., (1972). A more conservative
average emission rate of 40 mg. of lead per mile has been presented by Haar (1972).
To determine the amount of lead emitted from vehicles along a highway
corridor it is suggested that one use 130 mg. Pb/mile and apply this emission
rate to the percentage of vehicles using the highway corridor that were manufactured
prior to 1975. After 1975, all vehicles are using no-lead gas and thereby, no
lead salts are being emitted. The age distribution of vehicles in a particular
state is usually available from the local motor vehicle department.
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2. Transport Mechanisms.
The concentration of pollutants at a roadway edge (the receptor)
depends on more than just the quantity of pollutants emitted at the source.
The atmosphere is the agent that transports and dispenses pollutants between
sources and receptors and thus its state helps to determine the concentration
of pollutants observed at the receptor location. The following paragraphs
have been adapted from Epstein, et al. (1974) and are used to briefly review
the phenomena of transport mechanisms for gaseous pollutants (CO, HC, NO) from
A
a highway source.
In general,,three parameters are used to describe atmosphere
transport and dispersion;processes. These are wind speed, wind direction and
atmospheric stability. For a ground level pollutant (the general case for
a highway) the concentration of pollutants downwind from a highway source is
inversely proportional to wind speed. This phenomenon is illustrated in
Figure II-1.
Wind direction ±s perhaps the most important atmospheric
condition influencing the concentration at a given receptor location. For a
given wind direction,nearly all the pollutant transport and dispersion will be
downwind.
Atmospheric stability is a measure of the turbulent structure of
the atmosphere. Epstein explains that "it may be defined in terms of the
atmospheric temperature profile where ambient temperature is a function of
height above ground level. When the temperature decreases rapidly with height,
vertical motions in the atmosphere are enhanced, and the atmosphere is called
unstable. ...When the temperature does not decrease rapidly with height,
vertical motions are neither enhanced nor repressed and the stability is
described as neutral... When the temperature decreases very little, remains
the same, or increases with increasing height, the atmosphere is called stable."
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FIGURE II-l
THE INFLUENCE OF WIND SPEED ON GROUND LEVEL POLLUTANT CONCENTRATIONS
Height
Wind
Direction
Distance Downwind
/
14.4
-Kilometers +•
•S r-
L_
Kilo
-7.2—*
Kilometers
.Volume of air
containing the
pollution emitted
In one hour
Wind Speed •
4 Meten/Second
Volume of air
containing
the pollution emitted
in one hour
Wind Speed- 2 Motors / Second
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An unstable atmosphere is the best type for dispersing pollutants.
A neutral atmosphere allows dispersion of pollutants in the horizontal direction,
but not as rapidly in the vertical direction. A stable atmosphere is the worst
for air pollutant dispersion as it suppresses the upward movement of rising air.
It essentially forms a lid beneath which pollutants can freely disperse horizontally
but not vertically.
The available literature on the transport of lead reveals that it
is slightly affected by prevailing winds and that most of this contaminant is
contained in the particulate fraction of materials generated by the traffic.
The distance that the lead particles will be transported depends on size of the
particle and the atmospheric conditions prevalent during the time period.
Hirschler and Gilbert (1964),suggest that one-half to two-thirds of the lead
exhausted in city type driving was in particles 5y in diameter or less.
Only 4 to 12% of the exhaust lead was lu or less. Under cruise conditions
and at constant speed, Mueller, ec al. ,(1963), found that 62 to 80% of the particulate
lead exhausted was less than 2y in diameter. Of these small particles, 68%
were less than 0.3vi.
The roadside environment receives lead particles of all size
classes, the large ones by sedimentation and the smaller ones by impaction,
precipitation and inhalation. Determining the amount of lead at various distances
from a highway source is reflected in literature concerning the lead content
of soils and vegetation near the highway. Hutchinson, (1971), has developed experimental
data illustrating the soil level of lead adjacent to Queen's Park (Figure II-2).
Smith (1971), has studied lead contamination of white pine twigs in Connecticut
(Figure II-3), and concluded that the lead content drops drastically as the perpendicular
distance from the roadway increases. This conclusion is supported by numerous
studies, the finest being that of Daines, et al.,(1970), and Shuck ancTLocke (1970).
Between 30 and 150m perpendicular distance from the highways in the above
studies, the atmospheric lead rate per 30m was 32%and 23% respectively. In the
Daines et al., (1970),study, the lead content of the air decreased 50% between
3 and 46m from the highway. At 533 m perpendicular distance, 50% of the lead
containing particles greater than 6.5jj settle out of the air. Little
surface deposition, however, of the less than 3.5y diameter particles occurred
in this zone.
II-7
-------
FIGURE II-2
SOIL LEVEL OF LEAD IN QUEENfs PARK AND SOIL
LEVEL OF CADMIUM IN QUEEN's PARK
600
Soil Depth
• 0-1/2 inches
• 2-3 inches
5-6 inches
6 8 10 12 14 16 18 20 22 24 26 28 30
DISTANCE FROM ROAD (METERS)
II-8
-------
FIGURE II-3
LliAD CONTAMINATION OF WHITE PINE TWIGS PLUS NEEDLES (GROWTH OF PREVIOUS YEAR)
SAMPLED FROM TREES GROWING AT VARYING DISTANCES NORTH AND SOUTH OF INTERSTATE
95 IN CONNECTICUT. SAMPLES TOWARD THE ROAD WERE COLLECTED FROM THE TREE BRANCH
CLOSEST TO THE HIGHWAY WHILE SAMPLES AWAY FROM THE ROAD WERE COLLECTED FROM THE
OPPOSITE SIDE OF THE TREE, FARTHEST FROM THE HIGHWAY.
E
d
o.
250
ZOO
150
(£
O
in
ui
_j
O
UJ
UI
z
•f
Ui
o
> 50
100
25°
z
o
t-
z
o
o
o
<
UJ
200
I5O
IOO
50
NORTH OF ROAD
•o—o- SAMPLES TOWARD ROAD
-•-—»• SAMPLES AWAY FROM ROAD
•o o o
-*L r=-0.56
SOUTH OF ROAD
j_
00,
. ~~T
••
• '••••
r=-0.57
= -0.33
•
5 10 15 2O 25 30
TREE DISTANCE FROM ROAD (METERS)
II-9
-------
In addition to distance from the road, numerous other factors
influence the lead content of the atmospheric compartment of the roadway
environment. Some of the important factors include traffic volume, proximity
Lo other roads, prevailing winds, turbulence, season of the year and time of
day. Urban atmospheres over streets may differ significantly from rural atmos-
pheres over roadways. Edwards (1974),has suggested that the canyons formed
by multiple story buildings may restrict ventilation and cause high increases
in atmospheric lead.
The effect of traffic density is limited to a relatively narrow
zone (76m) along busy highways according to the data of Daines et al., (1970).
Numerous studies have shown if the prevailing wind direction is perpendicular
to the highway, greater amounts of lead will be distributed to the lee side
of the road. In seasonal studies, conducted in various United States locations,
the fall months consistently exhibit the highest air lead levels. The increasing
fall concentrations are generally ascribed to favorable wind patterns and
atmospheric mixing occurring at this time of year. Diurnal variations in
atmospheric lead burden close to the road generally follow the peak traffic
volumes of early morning and late afternoon.
Without further refinement, no exact relationship can be constructed
for the amount of lead in the atmosphere versus the perpendicular distance
from the highway. However it can be safely concluded that the majority of the
lead particles are deposited by some method close to the highway (50m ±). The
lighter particles (< 3.5y) travel a further distance from the highway source
and generally would tend to accumulate on the leeward side of the highway.
3. Atmospheric Diffusion.
The preceding two sections have described the quantities of
polLutants emitted from a motor vehicle and the transport mechanisms that
influence their dispersion from the source to receptor location. There are
numerous mathematical models that simulate the dispersion of CO from a highway
source. These models are generally classified into the following categories:
Gaussian statistical, box, particle-in-cell, and mass conservation. This section
will describe the Gaussian model and its adaption to a highway line source for the
prediction of CO.
11-10
-------
The Gaussian plume dispersion model has achieved considerable
popularity among people attempting to describe the role of atmosphere dispersion.
The model is an adaption of the normal distribution curve as a predictive tool
to describe the concentration of gaseous pollutants at given distances from
a source. The model was originally suggested for use by Pasquill(1961) and
modified by Gifford (1961).
The concentration (x) of gas or aerosols (particles less than about
20 v diameter) at x,y,z from a continuous source with an effective emission
height, H, is given by equation 1 and the coordinate system used in the equation
is illustrated in Figure TI-4.
FIGURE II-A
COORDINATE SYSTEM SHOWING GAUSSIAN DISTRIBUTIONS
IN THE HORIZONTAL AND VERTICAL
(1)
11-11
-------
The following assumptions are made in equation (1):
(1) The plume spread has a Gaussian distribution in both
the horizontal and vertical planes, with standard
deviations of plume concentration distribution in the
horizontal and vertical of ay and oz, respectively.
(2) The mean wind speed affecting the plume is p.
(3) The uniform emission rate of pollutants is Q.
(4) Total reflection of the plume takes place at the earth's
surface.
Any consistent set of units may be used. The most common is:
x (g nf3)
Q (g sec )
y (g sec )
oy,oz, H,x,y, and z (m)
For concentrations calculated at ground level, i.e. z=Q, the
equation becomes:
x (x,y,0;H) = ^r^T exp
(2)
[-•Hi-)1]
Where the concentration is to be calculated along the center line
of the plume (y=0), the equation is simplified to:
IT
§— -exp I — -i-f^Y 1
-------
The values of oy and oz in the previous equations have produced the
major areas of investigation. Turner (1972), developed a procedure to relate
oy and oz to stability classes which is in turn estimated from wind speed at a
height of about 10 meters and, during the day, the incoming solar radiation or
during the night, the cloud cover. Stability classes are given in TableH-l-
TABLE II-1
KEY TO STABILITY CATEGORIES
Day
Surface Wind — ; — - — —
Speed (at 10 m). lncomin* Solar Radiallon
m sec~»
< 2
2-3
3-5
5-6
> 6
Strong
A
A-B
B
C
C
Moderate
A-B
B
B-C
C-D
D
Slight
B
C
C
D
D
Night
Thinly Overcast
or
^4/8 Low Cloud
E
D
D
D
^3/8
Cloud
F
E
D
D
The neutral class, D, should be assumed for overcast conditions during
day or night.
SOURCE: (TURNER, 1972)
Having determined the stability classes, one can estimate ay and oz
as a function of downwind distances from the source, x, using Figures II-5 and II-6.
The Gaussian plume dispersion model can be applied to a continous
line source, such as a highway. Federal Highway Administration (1972) suggests
that equation (5 )be used to predict downwind ground level concentrations for at
grade highways and crosswind conditions:
c
sin-0-
where:
Q = source strength, grains/meter-second
K = empirical constant = 4.24
p = wind speed, m/sec
•6- = wind angle with respect to road
oz = vertical dispersion parameter, meters
11-13
-------
FIGURE I1-5
HORIZONTAL DISPERSION COEFFICIENT AS A FUNCTION
OF DOWNWIND DISTANCE FROM THE SOURCE
10,000
1 10
DISTANCE DOWNWIND, km
11-14
-------
FIGURE H-6
VERTICAL DISPERSION COEFFICIENT AS A FUNCTION
OF DOWNWIND DISTANCE FROM THE SOURCE
1,000
E
r~
b
1 10
DISTANCE DOWNWIND, km
11-15
-------
Using a technique developed by Noll, et al., (1975) equation (5) can
be solved for CO using a nomograph (Figure II-7). Starting at the left axis,
there are six meteorology scales labeled A-F and marked off in a wind speed scale
in meters/second. These meteorology scales reflect allowable wind speed ranges
for each stability class as outlined in Table II- 1. To the right of the meteorology
lines are next found a scale labeled jj 0z, m2/sec and then x, normal distance from
the road, meters. Connecting any distance on the x-axis with the desired stability-
wind speed combination yields the product y oz on the intermediate axis.
The next axis is labeled, $, the wind angle with respect to the
road. This axis represents sin , and a line connecting the previously obtained
_ 2
M oz, through the appropriate value for $ (yields the product y oz sin <|>, m /sec
on the next axis.)
Having now evaluated the denominator in equation (5), it is now left
to evaluate the line source strength, Q, gms/m-sec.
Q = (VPH) (EF) (1.73 (10.7)) (6)
where:
VPH = Traffic volume, veh/hr
EF = emission factor, gms/veh-m
3
Q = pollutant concentration, gms/m
The emission factor (EF) is obtained from "Supplement No. 5 for
Compliance of Air Pollution Emission Factors", (U.S. EPA, 1975).
However, concentration in parts per million (ppm), by volume is
required. Assuming ideal gas behavior, yields at 25 C for CO:
ppm CO = (875) (S^2) (7)
ppm CO = 1.51 (10-4) (8)
oz v sin$ '
Equation 8 is solved graphically by the last four lines of the
nomograph in Figure II-7. Connecting the previously described value
of {I oz sin<|> with a value of emission factor yields an intermediate value on the
pivot line. Alignment of this pivot point with a value for traffic volume
and extending to the final line yields the desired result, ppm CO,
11-16
-------
FIGURE H-7
ALTERNATE SOLUTION CALIFORNIA LINE SOURCE CROSSWIND
MODEL FOR CARBON MONOXIDE CONCENTRATIONS
M
C <
ft
A
3
2
1
9
4
3~
'
2
•
1)
[" . 1 8
U 0) _
_
a es o> -e- o
13 CL O
7
1
e
9
E
4
• 3
0
•2
C
•
.
1
9
4
3
F
3
,
s ;
' 2 '
1
1
H*1 •
0 v» C
190 *> 0» i- *g
"
l
0
^~ «
C.
(U
'so
40
30
20
. 10
i 8
: 6 1
' 4 !
1 3
2
* 1
•
,
t
,
•
.
.
.
.
O.
0.
rlOO
80
' 60
40
•30
20
10.
e.
6.
• 4.
3.
2.
1.0
.BO
• .60
.40
.30
.20
0.1
.08
.06
.04
.03
.02
0.01
stability wind
speed, u-m/sec
11-17
-------
B. LITERATURE SEARCH FINDINGS
This section of Literature Search Findings is composed of those key
points which were extracted from the greenbelt literature utilized to derive the
landscape architectual information in this Volume. These papers represent a
relatively small fraction of the literature obtained for the entire project. An
overview of the main body of information about vegetation as sinks and emissions
may be gained by referring to the approximately two thousand abstracts appearing
in the bibliography of Volume I. The majority of the papers cited in that
bibliography were located and read. Those papers that were potentially valuable
for the purposes of the landscape architect were then selected. The landscape
architect team member decided which were most relevant and most important in his
conceptualization of effective greenbelts. Additional papers were sought which
augmented the Volume I bibliography. The key bibliography used for this
Volume is presented here.
Where possible, the exact words of the various authors are quoted in order
to insure accuracy. In other instances, the author's words were paraphrased, but
most of the information appears without interpretation. These papers are presented
as generally representative of a larger literature and they are interpreted in the
following order:
1) The value of forests in removing particulates
2) Plant mechanisms for absorbing and adsorbing pollutants.
3) Organization of plantings.
4) Maximizing buffer edges to increase sink potential.
5) Ventilation of buffers and woodlots to increase sink potential.
6) Importance of local adaptation of plants to local site conditions.
7) Ecological approach to roadside treatment.
8) Size of buffers.
9) Safety factors as design.
10) The sound absorbing qualities of buffers.
11) Idealized plant material.
11-18
-------
1. The value of forests in removing particulates.
It has been frequently stated that plants, in general, forests
especially, are excellent agents for reducing ambient air pollutant levels.
Excellent discussions of the functions of forests which produce
this phenomenon are found in Keller (1971) :
An essential factor for environmental protection, on
the other hand, is the filtering action of the forest
on dust-shaped air pollution. The most favorable effect
in this respect is from loosely structured, step-like
forest stands, as can be deducted from Nageli's
investigation of windbreak sectors (1943), dense forest
stands deflect the wind upwards which also leads to
precipitation of dust due to turbulence for irregular
trre roof tops. Loosely structured forests, on the
other hand,let the wind penetrate and brake it, thereby
permitting the dust particles to sedimentate. In
addition, it is well known that particles up to 80y can
on impact even adhere to vertically located surfaces of
leaves and the like. Forest air is, therefore, especially
devoid of dust with the exception of blossom time when
noticeable amounts of pollen are discharged into the air.
The filtering action of the forest regarding dust can
manifest itself even in soil scientific studies. In
this way, in the lee of an area of industrial concentration
where enormous amounts of soft coal, rich in ash, were
burnt ,the pH value of the humus layer in pine forests
to a distance of about 30km was increased because the
tops filtered out alkaline fly ash.
According to Warren (1973), the best deciduous trees for reduction
of particulates (according to Russian literature) - are lilac, maple,poplar.
Conifers are best for all year filtering - apparently they may remove 34% of the
submicroscopic particles compared to 19% removed by deciduous trees.
Bach (1972), further suggests that the best genera for adsorbing
particulates are:
Lilac (Syringa) 2.33 g/mj
Maple (Acer) 1.11 g/m.
Linden (Tilia) 0.61 g/m.
Poplar (Populus) 0.26 g/m
Also good: sugar maple, sycamore and white ash.
11-19
-------
According to Geiger (1950), studies have demonstrated that the
reduction of wind velocity by forests and shelterbelts is proportional to tree
height; one can expect a 10% reduction in wind speed within a distance equal to
three times the tree height on the windward side and twenty times the tree
height on the leeward side. Dense plantings, however, seem to reduce this effect
due to the turbulance that they create. (See Figure II- 11).
Other studies on the characteristics of pp.iticulate distribution
within a forest indicate that temperature differential within and above the
forest canopy can provide convection currents which move the air (and the pollutants)
Fritschen and Edmonds (date unknown) found:
Inversions in the crown during the daytime and above
the crown at night trapped the particles within the stem
space. Particles released below the inversion were trapped
until they reached a thermal chimney (i.e.; less dense
vegetation where solar heating had penetrated to the forest
floor) where they escaped above the forest.
Hagevik (1974) refers to:
A study by A.L. Page, et al. examined lead concentrations
in 27 varieties of vegetation along highways. They
found a direct relation between lead content in the plants
and distance from the roadway, although the relationship
was most significant at distances less than 150 meters
from the highway. Lead content was also found to be
influenced by prevailing winds.
Although Warren (1973) feels that this can be reduced by the
planting of hedgerows which essentially reduce the velocity of the air to a point
where the heavy metal precipitates. In one study cited, a dense hedgerow was
responsible for an approximate 40% decline in the lead content behind it.
The World Meterorological Organization (1964) indicated that:
...the measurements of Woodruff & Zingg (1955) with systems
of four belts in the wind tunnel show no accumulative
effects but an increased degree of turbulence in the air
flow after passing the first belt. This indicated that when
several parallel belts are planted the interval between
them should not increase but should be the same.
It follows then that increased spacing between parallel hedgerows will
create increased turbulence and therefore increase the amount of CO and particulates
removed.
11-20
-------
2. Plant mechanisms for absorbing and adsorbing pollutants.
To understand the functions of the plants to reduce various
pollutants, their mechanisms and responses to various pollutants must be understood.
a. Particulates
Smith and Dochinger (1975) state:
Much of the understanding of the mechanics of deposition
of particles on natural surfaces has been gleaned from
studies with particles in the size range l-50\i m and is
reviewed in the excellent papers of Chamberlain (1967)
and Ingold (1971). Basically.participates are deposited on
natural surfaces by three processes: sedimentation under the
influence of gravity, impaction under the influence of
eddy currents and deposition under the influence of per-
cipitation. Sedimentation usually results in the deposition
of particles on the upper surfaces of plant parts and is
most important with large particles. Sedimentation velocity
varies with particle density, shape and other factors.
Impaction occurs when air flows past an obstacle and the
airstream divides, but particles in the air tend to
continue straight due to their momentum and strike the
obstacle. The efficiency of collection via impactation
increases with decreasing diameter of the collecting obstacle
and increasing diameter of the particle. Chamberlain
(1967), suggested that impaction is the principal means of
deposition if; 1) particle size is of the order of tens
of microns or greater, 2) obstacle size is of the order of
centimeters or less, 3) approach velocity is of the order
of meters per second or more and 4) the collecting surface
is wet, sticky, hairy or otherwise retentive. Ingold (1971),
presented data indicating that leaf petioles are consid-
erably more efficient particulate impacters than either twigs
(stems) or the leaf lamina. For particles of dimensions
l-5jj impaction is not efficient and interception by fine
hairs on vegetation is possibly the most efficient retentive
mechanism. The efficiency of washout of particles by
rain is high for particles approximately 20-30y m in size.
The capturing efficiency of raindrops falls off very sharply
for particles of 5\i m or less. Particulate removal by
stomatal uptake has been suggested (Jordan 1975), but is
of unclear significance. The latter process would probably
involve small (< lym dia) particles.
Heichel and Hankin (1976) found that the pattern of lead accumulation
on twigs is unrelated to the pattern or quantity of precipitations falling on a site.
It appears that these particles are less easily dislodged from the rough surfaces
of twigs than from the waxy, smooth surfaces of needles or leaves.
Wylie and Bell (1973) concluded that the major deposition of lead
particles along roadways occurs within the first 25 meters(m) away from the road edge.
11-21
-------
Berindan (1969) remarks:
The property of leaves to retain dust is a function of
the roughness of their surface. Table III indicates some
of the species for which the retention has been tested.
This ability is much less in winter. To ensure continuous
action, the species in Table III must be combined with
Coniferae; yet, considering that the latter are highly
sensitive, this combination is no longer effective in
cases of mixtures of dusts with SO., for example."
"Some air pollution studies have focused on the third
aspect of dust retention by plants which is the action
of swirl of suction, in view of their property for
directing pollutants from top to bottom at the level of
the respiratory tract. This type of draught is made up
behind any barrier which is high enough to hinder the
main direction of the wind (22, 39, 56) (Fig. 7).* It
is also thought that by using this property, it is possible
for dusts carried by the wind behind strips to be drained
at the level of the land. In cases of thick clumps,
however, the reverse result may be obtained: the current
brings the dusts on the targets that are to be protected.
TABLE H-2
PLANTS KNOWN FOR THEIR CAPACITY TO RETAIN DUSTS
(Modified from Berindan,- 1969)
Plant Units of
Species Dust Removal
Abies 30
Picca 30
Pinus 30
Ulmus '7.3
Syringa 2.9
Betula 2.5
Tilia 2.4
Acer platanoides 1.9
Populus 1
Platanus
Fraxinus
Morus -
(Original units in gr/rn.c)
Smith and Dochinger (1975) observed:
Trees may be especially efficient filters of airborne
particles because of their large size, high surface to volume
ratio of foliage, and frequently hairy or rough leaf,
twig or bark surfaces.
* Number 22 refers to Halitsky (1962); number 39 refers to Moses (1964); and
number 56 refers to Warren Spring Laboratory (1966). Figure 7 can be located on
page 15 of Berindan (1969).
11-22
-------
Numerous investigations, reviewed by White & Turner (1970),
have indicated that trees catch airborne nutrient particles.
These authors found that their mixed deciduous forest was
capable of annually removing 125 kilogram/hectare (kg/ha)
sodium, 6 kg/ha potassium, 4 kg/ha calcium, 16 kg/ha
magnesium and 0.1 kg/ha phospherous from the atmosphere.
Degree of leaf hairiness was inversely correlated with
particle retention. Apparently the small droplets employed
had insufficinet inertia to penetrate the stable boundary
layer created by the hairy leaves. Small diameter
branches were more efficient particle collectors than
large diameter branches in all species examined.
Monteith (1975) states:
Once particles are at rest on a surface, surface
tension and other forces hold them, and the drag of the
wind is reduced by the viscous sub-layer, so they are not
easily disturbed.
Warcen (1973), says that concentration of particulates is reduced
by 40 - 50% within the first 65' - 85' of forest adjacent to the edge.
Smith and Dochinger (1975) comment:
Many investigators, for example, Raynor et al. (1966),
have shown that the concentration of particles carried by
an air mass through a woodland decreases rapidly from
the edge.
Keller (1971) mentions:
The powerful filter action of the forest in regards to
dust makes itself felt most impressively, however, in
reports of figures (Handbuch der Staubtechnik, Handbook of
Dust Technology, 1955, by Meldau) according to which
1 Hectare (ha) of spruce forest can fix 32 tons, beech
forest even 68 tons of dust until the filtering capacity
has been exhausted. This means that in an extreme case
the forest could fix several times the weight of its tops;
however, these figures should be regarded as very maximum,
in a way, as the potential dust collecting capacity of
the forest.
Podgorow (1967) states:
...considerable quantities of dust are deposited on
1m of the region which is adjacent to the city. Plantings
growing in the vicinity of the city (500 - 1,900m) retain
80.1% of the precipitation/surface of ground dust. From
this quantity up to 40.2% can be attributed to the
pine needles. Our investigations thus showed that the
pine is a good retainer of dust. It is, therefore,
necessary to include them in the plantings of parks and
wooded areas which are close to industrial centers.
11-23
-------
Haupt and Flemming (1973) investigated the efficiency with which dust
is filtered out of the air by forests. It is dependent upon the leaf and needle
surfaces and their species specific collecting capacity. It was observed that coal
dust deposition was less during calm and wet periods and more during turbulent and
dry periods. For example, dust deposition during April was 207 times greater than
in July. In addition, rates of deposition at any one time were virtually the same
whether the collecting surface was vertical or horizontal.
Lampadius (1963) determined that spruce stands on 1 hectare(ha) absorb
67-114 kg of sulfate which reduces the S02 content of the air by 18-40 grams.
Similarly, a ha spruce stand absorbs 32 tons of dust, pine absorbs 36.4 tons and
beech absorbs 68 tons, but no time span is mentioned in this comparative study.
Relative to pollen, Zinke (1967) found that dispersion into a forest
is reduced by interception in the canopy. That filter may remove 30% of the pollen
grams compared to the concentration in the air over an adjacent open field.
Raynor et al. (1966) concluded that pollen grains are removed from
forest air more rapidly at low wind speeds than at higher speeds. Impaction seems
important in the first 10 meters of travel into a forest and along the upper canopy
surface. Decreased wind speed within the forest allows pollen and other aerosols
to settle out by gravitation.
Neuberger et al. (1967) studied concentrations of ragweed pollen
within a dense coniferous forest. They found that 80% was removed within the
first 100 meters of trees. The efficiency of Aitken nuclei removal by coniferous
material averaged 34% while deciduous material averaged 19%.
Weisser (1961) investigated dust contents of forests. One hectare
plots of spruce can contain approximately 32 tons of dust, Scotch pine, 35.4 tons,
and beech, 45 tons. The average dust settling on a 100 meter square (m2) plot
ranges between 3,000 grams per month near a fossil fuel power plant, 1,072 grams
per month in a city, and 340 grams per month in a large urban park.
Smith and Dochinger (1975) point out that under controlled wind
tunnel conditions, the deposition of particulates on rough, pubescent sunflower
leaves was 10 times greater than on smooth.waxy, tulip poplar leaves.
Bernatzky (1968) states:
The air in a city is impregnated with a large number of
kernels which become the nuclei about which such matter
as exhaust gases and radioactive substances gather;
eventually they will get into the respiratory organs where
they will work havoc. (The kernels which we refer to are
particles of pollution of a size measuring from one
millionth to one five thousandth of a millimeter.)
11-24
-------
TABLE II-3
NUMBER OF KERNELS IN ONE CM"
Big cities
Small towns
Country places
Coastal areas
Mountains:
500-1000m
1000-2000m
above 2000m
Ocean
Average
147,000
34,300
9,500
9,500
6,000
2,130
950
940
Max.
of average
379,000
114,000
66,500
33,000
36,000
9,830
5,830
4,680
Min.
ge
49,100
5,900
1,050
1,560
1,390
450
160
840
(A.
Absolute
Maximum
4,000,000
400,000
336,000
150,000
155,000
37,000
27,000
39,800
Landsberg)
Average values of air pollution have been found by Reifferscheldt
in Germany shortly after the end of the war to be
Kernels
Dust particles
Big cities
200,000
270
Country
8,000 per cm3
7-10
Air pollution varies according to hours of the day and
to the seasons of the year as well as to the height
above ground. We may distinguish three levels:
Just above ground
Roof level (domestic heating)
Level of factory chimineys
This means that high blocks of flats which are much
higher than other houses might easily reach their upper
storeys into zones that are polluted to a far greater
extent and where the amount of pollution is continually
kept on a certain level by the factory chimneys as well
as the smoke from the houses. The content of kernels and
dust particles leads to the formation of a dust dome which
is responsible for ultraviolet (U-V) poorness and dimness
of sunlight (loss of 20%) in the cities.
The higher the buildings of a city, the more they do
to counteract the natural flow of air. To overcome
friction, energy is used up. the draught action slows
down and thus an air cushion is formed above the city.
Oncoming air currents have to rise above this cushion and
the result is poor ventilation of the city.
11-25
-------
Smith and Dochinger (1975) comment:
The annual mean concentrations of suspended particulate
matter in the United States urban areas range from
60 micrograms/cubicmeters (mg/m3) to 200 ug/m^. The maximum
24 hour average concentration is usually approximately
three times the annual mean. Urban areas generally have
higher particulate loads in the winter than in the summer
(Spirtas and Levin, 1971).
b. Carbon Monoxide (CO)
Carbon monoxide is one of the primary pollutants produced by
automobiles. Studies have shown that the most effective receptor for CO are
soil microorganisms which apparently metabolize the gas.
Summarizing the findings of a recent study by the General
Electric Company on the dispersion characteristics of carbon monoxide cited by
Hagevik (1974) it was found that CO exhibits exponential decay with distance as
long as the path of the pollution is not obstructed. Also,the concentration
of CO at the level of the automobile exhausts is inversely related to traffic
speed. As the speed of the traffic increases, the concentration of CO decreases
due to the increased efficiency of the vehicles and the increased turbulence.
Although the distance required for the removal or decay of CO has been studied,
the impact of turbulance and canyon effect on the dispersion of the gas is not
clear. Also, the shape and size of surrounding buildings appears to have an effect
on dispersion irrespective of wind velocity. The General Electric study indicates
that peak values occur at impermeable walls, and the magnitude of CO concentrations
are related to traffic volumes on each side of the highway. The example of an
open roadway cut is given the maximum concentration occurs at the two walls and
the minimum concentration occurs at the center of the roadway. In an example
where there is a wall (or cut) along one side of the road and an open area on
the opposite side, the maximum concentration occured along the wall; where both
sides of the road are open to ventilation, the maximum concentration occurs in the
center of the roadway and decreases in both directions. (See Figure 11-15).
H.E. Heggestad is cited by Hagevik (1974) as indicating that soil,
apart from vegetation, is important in removing pollutants from the atmosphere,
especially gas such as CO and ethylene which are not absorbed by green plants.
Apparently, it is fungal microflora which are the primary absorbers of CO. The
soil is also a sink for hydrocarbons, a major automotive pollutant.
Inman and Ingersoll (1971) found that non-sterile potting soil
reduced CO concentrations in a chamber from 120 parts per million (ppm) to zero
within a three hour period. When sterilized, the soil removed no CO. Furthermore,
soil absorption of CO was apparently dependent upon high organic matter content and
low pH.
11-26
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ti. Ozone (03)
Aldaz (1969) reported that bare, dry soil removes about 75%
more ozone than when it is moist while the opposite is true when vegetation is
present. Relative to water bodies, it was reported that ozone is removed from
the atmosphere about 15 times faster over land areas than over sea water.
In 1970 Fesler reported that tobacco plants were generally most
sensitive to ozone concentrations coincident with low nitrogen fertilization levels
(60 Ibs./acre), and high levels least sensitive was found for plants treated with
an intermediate level of nitrogen fertilization (120 Ibs. N/acre).
Babich and Stotzky (1974) concluded that the removal of ozone
from the atmosphere by soil is directly dependent upon the moisture content and
surface texture of the soil. Soil compaction and increasing moisture content both
decrease exposed soil surfaces and porosity and therefore, decrease the sink
capacity of that soil relative to ozone removal. They also feel that the removal
process is essentially a physical and chemical process with soil micro-organisms
possibly serving as additional active decomposers of ozone.
Smith and Dochinger (1975) report that herbaceous species
absorb more ozone than do woody species and that as an example the deposition
velocity determined for a petunia species was about 9 times greater than an oak
species.
Turner et aj..(1974) investigated the dispersion and absorption
of ozone as it passes through forested areas. They found a 10% decrease in
concentration as the ozone containing air passed through about thirty meters of
forest.
Davis (1975) calculated that an average shade tree contains
4,300 square feet of leaf area and that if one assumes an average 8 hour 03
concentration of 0.17 ppm, and an 03 diffusion resistance of 0.33 min/cm,
about 27% of the ambient 03 would be removed if the air passed into the canopy
at a speed of less than 0.1 miles per hour.
Braun (1974) found that the penetration of solutions under
natural conditions occurs mainly through the cuticle and not tnrough the stomata.
Therefore, foliar uptake is significantly affected by the chemical composition of
the cuticle of each species as well as by the mobility and solubility of the
pollutant in question.
Smith and Dochinger (1975) also point out that herbaceous species
absorb more ozone than do woody species.
Bennett and Hill.(date unknown) determined that under
favorable growing conditions, air pollutants tend to be taken up by vegetation
in the exposed and upper portions of dense canopies.
11-97
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d. Sulfur Dioxide (S02)
Sulfur dioxide is a gas produced primarily by the burning of
fossil fuels, it is generally considered an industrial pollutant rather than
associated with vehicular traffic. It is believed that S02 (and other water
soluble gases) pass into the plants through the stonata and go into solution within
the plant itself.
The following studies cited by Smith and Dochinger (1975)
illustrate these processes.
Speeding (1969) investigated the uptake of S02 by
barley leaves and found a 6-fold increase in average
deposition velocity with open stomata compared to closed
ones. In related work, Rich and Associates (1970)
reported that uptake of ozone (03) by bean was regulated
by the same factors that control the exchange of water
vapor between leaves and the atmosphere. This conclusion
is also supported by Thorne and Hanson (1972). Once
inside the leaf gases probably become dissolved in water.
Hill (1971) compared the rates of uptake of pollutants by
alfalfa with the water solubility of the pollutants.
Fluorides had the highest water solubility and uptake.
As the rates of uptake of pollutants decreased, their water
solubility was also reduced. Any factor that affects the
stomata influences the uptake rate of gaseous pollutants.
Some of the environmental factors that are important in
the action of stomata are light, humidity, temperature,
wind, and the available supply of soil water.
Atmospheric pollutants themselves are also reported to have
an effect on stomatal activity. Majernik and Mansfield (1970)
and Unsworth et al. (1972) reported that SO2 caused stomata
to open faster in the light, to achieve a greater aperature,
and to close more slowly in darkness. All of these would allow
for the absorption of more S(>2.
Berindan (1969) describes the process in the following excerpt:
As regards the action of green spaces on gaseous
pollutants, it is much less known since research aiming
at determining it has been more restricted and more
recent..."
So far the retention of sulphurous gas, fluorine,hydrogen
sulphide, and nitrogen oxides has been established. Or
all of these mechanisms of action, S02 is very well known,
its diagram is shown on Table II-4. This table explains the
absorption process of sulphur by plants, wherein it can
pile up to a given level, which once exceeded, entails the
deterioration of the plant.
11-28
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Blum (1965) in a review of the literature found that a mature
beech stand served to filter S02 from the air in the vicinity of a smeltery.
This beech stand protected an adjacent, enclosed stand of spruce which died in
response to removal of the beech trees.
Davis (1975) reported that the use of fertilizers can increase
the resistance of plants to S02 damage, but that they do not necessarily relate
to the rate of S02 uptake by this vegetation.
Murphy et pi. (1975) determined that the diurnal pattern of
S02 uptake by plants reflect changing sun light patterns and temperature as they
affect stomatal functioning and S02 solubility. Seasonal changes in day length
and leaf area are key variables and the formation of dew and the vegetation can
form a very sizable sink for the transient absorption of SC^.
e. Gases - General & Miscellaneous
Smith & Dochinger (1975)
In the case of gaseous pollutants, much of the evidence
comes from controlled environmental studies with non-woody
species. We do not have adequate information to document the
ability of trees to remove "meaningful" quantities of
pollutants from actual urban atmospheres. Trees have yet to
be shown to be capable of reducing a particular air
contaminant below a significant threshold of effect for any
urban area.
The primary method of vegetative removal of gases from
the atmosphere is via uptake through the stomates. Minor
methods by which plants remove gaseous pollutants from the
atmosphere may include uptake by plant surface microflora,
uptake through bark pores and absorption of gases to the
surfaces of plant parts.
The processes of transpiration and photosynthesis require
that plants exchange gases with the ambient atmosphere
through leaf, branch and stem pores. Contaminant gases
present in the atmosphere in the vicinity of a plant may be
absorbed when the stomates of lenticels are open.
Shclterbelts and windbreaks have traditionally been used to
alter microclimate in various ways, primarily by slowing down wind speed and reducing
evapotranspiration.
World Meteological Organization (1964) cites:
....in Canada, after experiments at the Soil Research
Laboratory, Dora. Exper. Sta., Swift Current, Saskatchewan,
as by Matjakin (1952) and Panfilov in the U.S.S.R. (1937).
According to these two an impermeable belt of woodland
hardly lets the wind through at all Immediately behind the
wind is almost completely calm and when it returns to earth
in the lee it is very turbulent. A belt of medium permiability
with numerous small holes distributed evenly over the entire
belt acts as a sieve, preventing turbulence to a large
extent.
11-29
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TABLE 11-4
PROCESS OF SULFUR ABSORPTION BY PLANTS
so2
sterna tes
SO-
sulphites—fr absorption and transformation
in sulphates (the decrease by
30 times of the toxicity as a
DEPOSITS of sulphites
gradual increase
.result of the slow process of oxidation)
localized chronic lesions
closed opened
-darkness -heavy light
-increased relative humidity
-humidity reserve
-moderate temperature
incomplete metabolism
in organic sulphur
-------
Thus, by using plant materials to break up the winds, a great amount
of exposure of the air currents to the leaf surfaces occurs. This results not only in
slowing down the wind and allowing particulates to settle out but enables the gaseous
pollutants to be taken up by the leaves. Furthermore, the turbulance created by
the air passing through the shelter belt forces the air current down toward the
ground where CO can become engaged by soil microorganisms.
Turner et al. (1974) investigated the dispersion and absorption
of 03 as it passes through forested areas. They found a 10% decrease in
concentration as the 03 containing air passed through about thirty meters of
pores.
Davis (1975) calculated that an average shade tree contains
4,300 square feet of leaf area and that if one assumes an average 8 hour 03 concen-
tration of 0.17 parts per million (ppm), and on 03 diffusion resistance of 0.33 m
minute per centimeter (min/cm), about 27% of the ambient 63 would be removed if
this air passed into the canopy at a speed of less than 0.1 miles per hour.
Makarov and Dokuchayev (1970) found that there is a considerable
variation in the liberation of nitrogen dioxide (N02> during the growing season.
Reduced generation rates are associated with treatments which suppress miceobial
metabolism.
3. Organization of plantings
Factors effecting the efficiency and functioning of buffers are
similar to windbreaks and shelterbelts. In both cases the importance of
breaking up and slowing down air currents is essential.
World Meterological Organization (1964)states:
Windbreaks and shelterbelts alter 'the air flow primarily
according to strength, direction, and degree of turbulence.
We can for the moment forget whether a windbreak be artificial
or of natural growth. Effective protection and the
influence on the windy area are not directly dependent on
this.
The deciding factor for wind reduction with shelterbelts
is the belts*s density permeability.
Immediately behind very dense belts wind reduction is
at its greatest; with increased permeability it becomes
less. At wind minimum, wind reduction is also a function
of permeability, called "covering degree" by Tanaka (1956).
With dense belts the position of greatest wind reduction is
very close to the belt; yet it is furthest away when the
belt is of medium density. According to George (1960)
maximum wind reduction occurs immediately in the lee of a belt
of 10 rows, shifting to 2.4 x H with 5 to 7 - row belts.
Similarly the distance behind belts where wind reductions
are still at least 20% is greatest behind belts of medium
density and least for very dense and very loose belts.
11-31
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The different density belts show different curves of wind
speed on their leeward side. So it is not permissible to
judge the sheltering effect of belts, as Den uyl did (1936)
only on measurements taken at small distances. From the curves
it can be concluded that where wind reduction extending far
behind the belts is required, more than sharp reduction,
high belts of medium density are the best (Naegeli, 1946;
van der Linde, 1958). The smaller extent of wind reduction
with dense belts is a consequence of the stronger displacement
flow and the greater power of recovery that this gives
the surface wind. The wind recovers speed behind denser
belts more quickly than it was reduced.
Blenk & Trienes (1955) also studied the effect of different
shapes of belt with four impermeable models 30 millimeters (mm)
high in the wind tunnel. One of them was 1 mm wide, the
other three 15 mm, of which one was right-angular in cross-
section, with sharp edges; the other two were rounded off
in different degrees. The model most rounded off on the top
edge had the least extent of wind reduction; the one with
less had a little greater extent, and the best proved to be
the sharp-edged sheet 1 mm wide. (See Figure II- 12).
In the Russian terminology a permeable belt is a wood
plantation with large gaps running right through.
These belts in the U.S.S.R. mostly have bare, 1 to 2 inch
thick trunks without undergrowth or stunted threes.
With such belts eddies would be prevented particularly
near the surface by the wind penetrating the lower parts.
A permeability of 40 to 50% can be obtained by various
sizes and shapes of opening. According to Naegeli (1946),
Nffkkentved (1938), Konstantinov (1950), many small
openings are especially effective. Blenk and Trienes (1955)
compared three strips 30 mm high with a permeability of
50%, but with different sizes of opening, in the wind tunnel.
The wind distribution behind those with openings of 2 and 5 mm
diameter was almost equal. The strips with openings of 8 nun
reduced wind for a considerably shorter distance.
In the open, where the degree of permeability is hard to
estimate, van der Linde (1958) classes well cared for leafy
blackthorn or yew hedges as dense, counting belts of Lombardy
poplar among those of medium density. Eucalyptus makes
equally good belts of medium density in warm, semi-arid areas,
but according to Duncan (1950) belts of "thin cottonwood"
20 m high belong to the very loose and least effective.
Shelterbelts of deciduous trees vary in density with the
season. According to Flensborg and N^kkentved (1940)
the seasonal differences with loose belts in Denmark were
slight; in the autumn dense belts assume the character of
medium, and medium that of loose. The protective effect
of leafless belts is not to be neglected, however. Figure II-8
shows the wind conditions at a belt of medium density 16m
high with and without foliage (Naegeli, 1946).
11-32
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FIGURE II-8
THE SHELTER PROVIDED BY A 16-METRE-HIGH SHELTERBELT OF
DECIDUOUS TREES IN SUMMER AND WINTER (NAEGELI, 1946)
wsw
WSW - Wind
Summer
Winter
ENE -Wind
Winter
According to Jensen (1954) and N^kkentved (1938) leafless
belts generally gave 60% of the shelter with folage. In
northwest Germany, Franken & Kaps (1957) found about 50%
less wind reduction at three, four and seven belts when
without leaves. Similar evaluations were made by von
Eimern (1957) at a two row belt of maple 12m high with
undergrowth.
Berindan (1969) states:
...some guiding concepts may be defined for the planting
of green spaces for sanitary protection:
a) The necessity of a correlation between the type and
the concentration of the pollutant and the degree of resistance
of plants;
b) The necessity, in some countries, of checking, through
research and experimentation the findings on the resistance of
plants, since the uncontrolled inplementation of the findings
could lead to erroneous or inefficient solutions;
c) For each situation, the degree of toxicity of the
pollutant or the mixture of pollutants must be known in
order to select species which have adequate specific resistance;
d) In so far as the height of the plantings are concerned,
in the first place, it must be recommended to plant trees, shrubs
and/or to plant some turfs only to supplement their retention
capacity. In the last analysis, flowers are used for
decorating roads. The same applies to fruit trees, provided
however that they are resistant and are not exposed to
accumulation of toxics, otherwise planting them will be useless,
costly and sometimes even dangerous;
11-33
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e) Aerated structure plantings, obtained by grouping
curtains or rows of trees can better retain dust or even
gaseous pollutants, than compact clumps, due to the filtering
action of the former. To this end, the form and composition
of cross sections of green barriers, function of the effects
desired and resulting from the draughts generated are to be
closely studied;
f) It is necessary to place dust collecting plants by order
of capacity: those that retain large particles are to be placed
close to the source; and further off, those which stick to
the smallest particles.
4. Maximizing buffer edges to increase sink potential
It is clear that the most diverse and most important part of forests
(and buffers) for the purposes of reducing pollutants is the area within the buffer,
adjacent to the edge. Warren (1973) previously cited, indicates that the most effec-
tive and efficient zone for this purpose lies within 65 - 85 feet of the edge.
This is due to the greater diversity of plant materials within this area. Generally
the canopy occurs at all elevations not only at the top as it is further into the
forest interior (See Figure II- 13).
Obviously in the design of effective buffers, techniques to Increase the
edges are of great importance. This is true not only for newly planted installations
but for existing forests and woodlots as well.
5. Ventilation of buffers and woodlots to increase sink potential
As previously indicated, thermal chimneys within a forest can
increase deposition of particulates and absorption of gases by increasing ventilation,
and exposing pollution laden air to leaf surfaces high in the interior canopies. Such
a phenomenon can be built into buffers or existing forest areas by the creation of
openings in the interior forest canopy. (See Figure 11-14).
6. Importance of local adaptation of plants to local site conditions
World Meteorological Organization (1964)states:
As the extent of the protective effect of belts is
proportional to their height, it is often (in the U.S.S.R.
for example) considered an advantage to plant belts which
reach a maximum height dependant on soil and climate, for
which purpose the types of tree and bush particular to
that landscape are selected.
Width and shape of belts are not always decided from the
aspect of best wind reduction; forestry also plays a
large part. Because of maintenance, care and their possible
use for other purposes, wider belts of more than 5 -10m
are preferred in many climates. In such belts part of the
wood can be used elsewhere without appreciable harming
the wind reducing effect, and they are often.'capable of
reducing themselves; filling gaps left by dead wood with new
growth. In any case they seldom leave such large gaps that
harmful nozzle effects evolve...
11-34
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Smith and Dochinger (1975) state:
1. Trees selected or bred to provide this amenity function
must be tolerant of acute, adverse influences or air pollution.
Clearly if the tree is severely damaged or killed by one or
an interaction of contaminants utility as a sink will
be short-lived. In addition to air pollution tolerance,
suitable tree varieties should be capable of withstanding other
urban stresses, such as poor soil aeration and drought, nutrient
deficiencies and microclimate extremes. A suitable variety
should be able to grow vigorously. Vigorous growth will
require maximum stomatal aperture and ensure maximum uptake
of gaseous pollutants.
2. Coniferous species retaining their foliage year round
may appropriately be favored over deciduous species. The
atmospheric burden of both particulates and gases is generally
higher in the winter than in the summer for most urban areas.
It is important, therefore, to have maximum plant surface
available for absorption and adsorption during winter months.
Since the time of persistence of foliage of evergreens is
longer than deciduous foliage, the opportunity for pollutant
removal is correspondingly longer. The morphology of coniferous
foliage (for example; pine, spruce, fir) results in a high
surface to volume ratio which may be instrumental in more
efficient removal rates.
3. Since petioles are especially efficient particle receptors,
species with long petioles (for example; ash, aspen, maple)
may be favored.
4. Surface hairiness on plant parts (leaves, twigs, petioles,
buds), may be especially effective for retention of particles.
Those species processing these hairs(for example; oak,birch,
sumac) should be considered.
5. Species with small diameter branches and twigs should be
selected or bred over species with large diameter branches
or twigs as the former are more efficient particle collectors.
6. Since gases are removed from the atmosphere primarily by
the stomates, species should be selected or bred with maximum
stomatal capacity for absorption. This ability may be related
to absolute stornate number per unit of leaf surface, size of
stomatal capacity number per unit of leaf surface, size of
stomatal aperature and length of time the stomates are open.
7. Species should be selected or bred that have maximum
resistance to stomatal closure occasioned by environmental
variables such as moisture availability, temperature, wind,
light intensity and air pollution.
8. Selection and breeding should consider one relative ability
of tree species to utilize pollutant gases as partial sources
for required nutrients.
11-35
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7. Ecological approach to roadside treatment.
Using natural succession as a basis for roadside management.
resulting in increased sink potential, reduced maintanence costs.
Odum (1971)
TABLE II-5
ECOLOGICAL CHARACTERISTICS OF COMMERCIAL FORESTS AS
CONTRASTED WITH PROTECTIVE GREEN BELT VEGETATION
Features
Species diversity
Age structure
Annual growth increment
Stratification
Mineral cycles
Selection pressure
Maintenance costs (re-
planting, fertiliza-
tion, pest control,
thinning, etc.)
Stability (resistance to
outside perturbations
such as storms, pest
outbreaks, etc.)
Overall function
Commercial Forest
Low (usually monoculture)
Even-aged
High
One-layered (mostly
canopy trees)
More open (losses from
leaching and run off)
For rapidly growing, sun-
adapted species (often
softwoods)
High (requires "manage-
ment")
Low
Production of '-rket-
able products
Green Belt Vegetation
High (mixed species)
Multi-aged
Low
Multi-layered (under-
story, and ground
cover well developed)
More closed (retention
and recycling within
stand)
For slower-growing,
shade tolerant spe-
cies (more hardwoods)
Low (self-maintaining)
High
Protection of the qual-
ity of man's envi-
ronment
Use of mixed plantings - mixed canopy trees, and shrubs - deciduous
and evergreen to increase sink potential, screening headlights of oncoir'.ng cars,
reducing maintanence costs, protecting wildlife, etc.
11-36
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Rich (1972) comments:
Many species of roadside trees suffer moderate to severe
injury from sodium chloride applied to the highways in
winter to prevent ice formation and to aid in snow and ice
removal. Trees within 30 feet of the edge of the highway are
affected most frequently and most severely..." Canadian
hemlock, balsam fir, white and red pine, and sugar and red
maple, basswood and American elm are among the most sensitive.
Tolerant species include: red oak,white oak, white ash, black
locust, quaking aspen, black cherry, black birch, grey birch,
paper birch, yellow birch, Norway maple and red cedar.
Odum (1971) states:
The first and most important consideration in planning and
managing the urban greenbelt, then is diversity.
Too often tree plantings in urban and suburban areas end up
as even-aged monocultures with no provision for understory
young trees that could replace the old ones as they die
or become diseased.
A second important ecological consideration involves careful
selection of species and varieties that are naturally disease
resistant, and adapted to soil, water, light, topographic
and other conditions of the microhabitat. When trees are
planted outside of their preferred habitat (bottomland trees
planted on dry uplands, or vice versa, for example)
a lot of maintenance (watering, fertilizing, etc.) may be
required.
Also, the metabolic cost of adapting to the suboptimum
condition makes the tree vulnerable to disease or drought.
Williston (1971) comments:
Trees will lower right of way maintenance costs. Grasses
need to be periodically fertilized to maintain good cover
on roadbanks; trees do not, and yet they control erosion
well. Trees eliminate the need for weed control and for
maintenance mowing, which can cost $10. or more per acre
per year. (Costs are 1971 - add 10%/year).
Odum (1971) states:
Shrubs in the buffers are important.
1. Shrubs, and leafmold they produce, enhance soil
moisture, encourage useful soil decomposer organisms, and
help in self-fertilization of nutrient recycling.
11-37
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2. Shrubs, especially evergreen ones, are very effective
noise barriers. Robinette (1969), for example, points out
that a band of dense shrubs backed by several rows of
trees along a highway or street can reduce noise of traffic
or garbage collection ten-fold. In such a case sound is
not only absorbed by twigs and foliage of shrubs, but it is
reflected upward (away from hearer) by trees. Trees alone
would have very little value in noise abatement at close
range. Since noise pollution is rapidly becoming critical,
it could well be that plantings structured to mimic a
multi-layered natural forest could be more valuable for noise
abatement than for any other purpose.
3. Shrubs and other understory vegetation are absolutely
essential for songbird populations. I think we will all
agree that pleasant sights and sounds of songbirds are a
desirable point of the urban landscape. Among desirable
birds only the robin thrives in habitats containing the
only tall trees and grass or other ground cover. Most
songbirds (mockingbirds, brown thrashers, thrushes, towhees,
song sparrow, etc.) require shrubs or understory vegetation
for nesting and escape shelter. Contrary to most people's
ideas very few songbirds nest high in trees. In a study of
bird nesting heights,Preston and Norris (1947) found that
80% of bird nests were between 3 and 18 feet above ground
with the median height being 7 feet. For more about the
dependency of songbirds on the understory see Odum and Davis
(1969).
8. Size of buffers.
Warren (1973) feels that greenbelts should be a minimum of 100 to
120m. wide and should channel the wind to provide a maximum dispersion for the
gaseous pollutants. The width must depend on the pollutants and local conditions
and could range up to 2,000 feet.
Buffers adjacent to highways should be planted with trees and shrubs
as close to the highway as safely possible. Also, forested or planted medians
should be provided. They should be at least 15-30m. wide and average 10-20m. tall.
Hagevik (1974) states:
Peter Rydell and Gretchen Schwarz cite a Russian study
which concludes1that the concentration of pollution decreases
by about half over 500 meters of planted land1. I.A. Singer
also notes a 75% reduction in dust particle count over a 600
foot wide strip of open space.
11-38
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Frank Cross determined the size requirements for a buffer
zone to protect citrls groves from fluoride emitted from
a phosphate plant gypsum pond. Based upon a standard where
75 parts per million of fluoride in citrus leaves was considered
to be evidence of pollution a one half mile buffer strip was
established around the pond to alleviate the fluoride effect.
In another case, Cross defined a zone for suspended particles
emitted from a dolomite processing plant, and concluded that
to reduce the adverse impact of settling particles upon
nearby residents, a buffer of 1,500 feet radius around the
plant site would be required. A third study by Cross inves-
tigated the buffer width needed to restrict ambient air
particulate concentrations from a hot mix asphalt plant to
100 micrograms per cubic meter. Results indicated that a
buffer zone of one mile radius reduced particulate concentration
to the determined level.
Bernatzky (1968) in West Germany feels that to reduce gases the
stands need to be 5 times deeper than their height on the windward side and 25
times deeper than their width on the leeward.
Corn (1968) comments:
Numerous studies have found that particulate dispersion
is directly related to the source and receptor. It is
difficult, however, to establish a specific distance as a
guideline for buffer width, since dispersion depends upon
factors other than distance alone.
The acutal direction of transport is determined by large
scale circulation in the atmosphere as well as by the local
influences of breezes, the surface features of a specific area,
heat sources (such as the higher temperature observed over
urban areas) and air masses of differing densities."
9. Safety factors as design considerations.
Williston (1971) states:
Planting areas must be carefully selected lest they
interfere with the drivers' safety. Trees growing to a
diameter breast height(d.b.h.) of at least 4 inches or
larger should be planted 30 feet or more from the edge of
the pavement, smaller trees at least 20 feet. Care must
be taken that as the trees grow they do not form a tunnel,
causing drivers to crowd the centerline. On cut sections,
plan at least 6 to 8 feet up the slope from the edge of the
ditch and do not plant fills.
Screening headlight glare by planting trees on the median
strip is most needed on level ground.
11-39
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According to Everett (1974) there is a very real danger in exercising
in areas of heavy traffic. Many cyclists ride along crowded roads and joggers
running along arterials are common. Also many other types of active recreation
facility are initially located along roads which are later improved to accommodate
high volumes of traffic.
Studies indicated that levels of pollutants in air along such corridors
may be as much as 10 times higher than ambient pollution. Heavy exercise in these
zones can cause particulates and other harmful pollutants such as lead, and asbestos
can be pulled deep into the lungs and deposited there. Also, as a greater volume
of gaseous pollutants are pulled over the particulates, the possiblity of synergistic
reactions is increased.
Buffer strips intended to be used in conjunction with active recreation
areas should separate such facilities from heavily traveled roads with heavy planting.
Although no specific dimensions have been identified for this purpose, Warren (1973)
indicated that 40-50% of concentration of particulates is removed by the first 65 -
80 feet of forest. An 80 foot minimum would probably be reasonable.
10. Sound absorbing qualities of buffers.
It has been adequately shown that plant materials acting as
buffers can effectively absorb sound. Hagevik states that, generally, intensities
greater than 120 d 6(A) may cause pain to the human ear and that physical damage
may result at 160 d B(A) especially if the exposure is prolonged.
There apparently are conflicting opinions as to the importance of
the sound frequency (cycles per second or o.p.s.) but Embelton (1963) suggests
that attenuation is independent of frequency tange of 200 - 2000 c.p.s. for
all tree types including deciduous trees in full leaf. Gerhard Reethof (1972)
indicates that trees 40-50 feet tall planted in a buffer 100' wide can reduce
noise by 5-8 dB. His data supported Embleton's conclusions.
Reethof (1972) states:
...other studies point out the difficulty in making
definitive statements concerning the value of trees in
reducing noise. For instance, assuming that noise reduction
in the 300 - 800 c.p.s. range is desirable and that a
25 d B(A) reduction is required, based upon Embelton's
data, a dense, coniferous growth, approximately 400 feet wide
would be needed; data compiled by F.M. Weiner and
D.N. Keast (1959) indicate that a 1,900 foot wide belt
would be necessary for the same reduction.
Hagevik (1974) cites two recommendations of Cook and Haverbeke (1971)
which indicates the possibility of reducing noise levels to 5-15 dB. Specifically,
for high speed vehicular noise, they recommend planting a 65 - 100 foot wide belt
of shrubs and trees with the edge of the belt within 50 - 80 feet of the middle
of the traffic lane nearest the buffer. Trees in the center of the buffer should
be at least 45 feet high.
11-40
-------
FIGURE I1-9
DESIGN PARAMETERS OF BUFFERS
FOR SOUND ATTENUATION
- AFTER COOK AND HAVERBEKE,(1971)
(£Road
20-50' 20-50'
For moderate speed traffic
<£ Road
50-80' 65-100'
For high speed traffic
In cases where the traffic speed is moderate, the belts need only
be 20 - 50 feet wide with shrubs along the edge. This should be placed 20 - 50
feet from the middle of the nearest lane of traffic. The shrubs should be 6 - 8
feet tall with trees being 15 - 30 feet high. See Illustration II-9.
The characteristics of plantings upon which sound attenuation is
dependent are height, density, and width. Hagevik cites a study by Peter Durk
which indicates that a 50 meter(m) wide buffer or park can result in a 20 - 30 dB
reduction of noise level. Odum (1971) also references the use of vegetation as
a buffer for noise (See page 11-37).
11-41
-------
C. POTENTIAL DESIGN ALTERNATIVES
After reviewing the available literature, certain guidelines for
establishing and maintaining healthy, efficient greenbelts become evident.
Examples of the authors' recommendations and data may be located in the Liter-
ature Search Findings section and also, Sections III and IV of Volume I.
The information for creating greenbelts that are efficient sinks of airborne
contaminants is summarized below and this material is the basis for the
design alternatives of highway buffers.
Summary of Literature Search Findings:
1. Evaluation of the environment -La necessary before selecting or
breeding plant species that will compose the greenbelt which functions in the
improvement of air quality.
Two factors which dictate plant growth are climate and soil. The
degree of the protective effect of greenbelts is dependent on the amount of
growth which is expressed by the vegetation, particularly in terms of height.
Vegetative buffers which attain maximum height asre generally mare efficient
in the role of sinks for air pollutants. Since climate and soil greatly influence
whether vigorous growth will occur, both of these elements of the environment
should be analyzed before determining the most suitable woody plants for a
greenbelt. Plant species that are unable to adapt adequately to both the
climate and soil will not sufficiently remove airborne pollutants.
Poor soil conditions will cause harmful stresses on even the most
tolerant plant species. To alleviate the primary detrimental effects produced
by poor soil in terms of plant growth is to relieve any deficiencies in water
or nutrients and also, to provide proper aeration of the soil. By taking
such measures, the general health of the vegetation may improve and the plants
may be capable of more than merely existing; active growth may actually occur.
Vigorous growth requires maximum stomatal aperture which ensures optimum uptake
of atmospheric pollutants.
However, the energy expended in improving the soil will not
produce satisfactory results if the plants are not growing in their preferred
habitats. Plants surviving in a suboptimum environment will not significantly
11-42
-------
participate in the removal of air pollutants. Also, the metabolic cost of
adapting to less than favorable conditions may cause the plants to become more
susceptible to disease and drought.
2. Selection or "breeding of plant species that can withstand the adverse
effects of the air pollutants that are present in their potential habitats is
essential to contribute to the health of the greenbelt.
A woody plant that is extremely sensitive to one or a combination
of pollutants will be a poor sink due to irreversible damage and even death
of that particular plant. The degree of resistance of plants is correlated with
the type and the concentration of the pollutant. The Plant Species Sensitivity
List, which is located in Volume I and also, in Volume II, this Volume, as
Appendix B, provides lists of plant species which are either relatively tolerant
or sensitive to some of the primary types of air pollutants: fluorine, hydrogen
chloride, nitrogen dioxide, ozone, PAN, particulates - smoke, sulfur dioxide.
Since vegetation is usually exposed to a combination of pollutants instead
of a single pollutant, lists of relatively resistant and sensitive plants
for general pollution also have been developed.
3. Removal rates of air pollutants by vegetation and soil types
should be considered in attempting to increase the efficiency of roadside
forests and buffers as air pollutant sinks.
General estimates of the removal and emission rates of air pollutants
by vegetation and soil types are given in Volume I. These values are arranged
in tables headed by the pollutants ammonia, carbon monoxide, fluorine,
hydrocarbons, nitrogen oxides, ozone, PAN, particulates, lead, and sulfur dioxide.
By reading the literature about air pollution and natural elements and extracting
the pertinent information from the research papers, the data was carefully
evaluated and limitations of the presently available information were observed.
11-43
-------
These limitations of the literature are discussed in the introduction of Section III
in Volume I. Therefore, it is essential to recognize that the removal and emission
rates are general estimations which are based on information that is very limited.
However, the tables provide some guidelines for mitigating air
pollution problems by the utilization of soil and vegetation. A utility factor of
1,2 or 3 was assigned to each given value. The utility factor of 1 means that
the research team attempted to measure field conditions and the methods for
obtaining the data seemed appropriate. Results that were less applicable to the
tables were given utility factors of 2 and the least applicable data was designated
as being 3.
Table III-ll on page 111-40 of Volume I is a summary table which
was developed by selectively averaging the sink and emission factors for each
pollutant. The purpose of this table was to find figures which roughly approximate
the data obtained from the reviewed publications.
The tables of the section on Sink and Emission Factors for Natural
Elements are tools for landscape design in terms of natural removal of air pollution.
By referring to these tables and the Plant Species Sensitivity List, the effectiveness
of a particular natural element for removing a specific pollutant may be estimated.
Also, Table III-ll of Volume I, which provides very rough estimates for absorbing
and emitting specific pollutants by vegetation and soil, displays much larger
concepts of the effectiveness of natural elements in removing airborne contaminates.
4. Plants that have certain morphological characteristics are
relatively more efficient particle and gas receptors.
In addition to selecting or breeding tree and shrub species that
are relatively resistant to the types and concentrations of air pollutants present
in their potential habitats, the morphological aspects of these species should
also be considered. Certain physical characteristics that are especially
efficient pollutant receptors have been identified in the literature, particularly
11-44
-------
in Smith and Dochinger (1975). These characteristics are listed below
and species with several of the features should be selected or bred over
species that lack most of the advantageous characteristics.
a. Petioles are effective in the retention of particles and
there is a correlation between the length and the collection.'capacity of the
petiole.
b. Surface hairiness on leaves, twigs, petioles, etc. trap
the particles more readily than the plant parts that are smooth in texture.
c. Generally, more particulates are deposited on small
diameter branches and twigs as compared to large diameter branches and twigs.
d. Maximum stomatal capacity for absorption is a significant
characteristic in plants potentially used in greenbelts since the primary
mechanisms for removal of gaseous pollutants are by stomatal processes.
e. Species having maximum resistance to stomatal closure
caused by environmental variables are preferred for removal of airborne pollutants
than species in which stomatal closure occurs due to slight changes in temperature,
moisture, light, or air pollution.
f. Plants that more readily metabolize substances extracted
from the atmosphere may be considerably more suitable for greenbelts than
plants that lack the capacity to utilize contaminated air as a partial source
for essential nutrients.
5. Multi-layered stratification is a characteristic of an efficient
roadside forest for absorption and adsorption of air pollutants.
A stratified forest, formed by developing the understory and
ground cover as well as the upper tree layer, is a more effective receptor of
air contaminants than an unstratified forest. However, if the strata of a
forest, particularly at the edge, grow to such an extent that dense overlapping
results, this "natural wall" may drastically hinder the passage of the wind through
the forest and the exposure of the air pollutants to the vegetation is reduced.
Therefore, the degree of effectiveness of a forest in removing air pollutants
is partially dependent on the permeability of that forest. As the diagram on the next
page illustrates, moderate permeability is the most favorable condition of a forest
11-45
-------
since more vegetative surface area comes in contact with the flow of air than
in a forest of maximum permeability and also, less wind deflection occurs than
in a forest of minimum permeability.
FIGURE II-10
DENSITY OF BUFFER RELATED TO REDUCTION OF WIND VELOCITY
impermeable
moderate
permeability
maximum
permeability
6 There are other advantages of maintaining a multi-layered forest
in addition to improving air quality.
Trees are considered to be efficient filters of airborne pollutants
because of their large dimensions. Some trees are capable of growing to sub-
stantial heights which increases the protective effect of greenbelts. Another
important aspect of most trees in terms of the uptake of pollutants is their
high surface area to volume ratio.
Although the large dimensions of trees provide greater vegetative
surface for absorption and adsorption than other life forms, a forest with a
poorly developed understory is less efficient in the removal of pollutants
than a stratified forest. Therefore, developing the understory (primarily by
opening the tree canopy which will stimulate the growth of the lower plants or
by planting shade tolerant species) will increase the effectiveness of the forest.
Also, a stratified forest is valuable in the abatement of noise.
Sound may either be absorbed by the twigs and foliage of shrubs or reflected
upward by trees. A forest composed of primarily mature trees located near a
source of noise pollution, such as adjacent to a highway, is incapable of trans-
ferring the sound upward, away from the hearer.
In addition to their role in noise abatement, shrubs can improve
the habitat. The leaf matter produced by shrubs as well as trees enhances soil
moisture and maintains the populations of the soil decomposer organisms which
are essential components of nutrient recycling. Also, wildlife require shrubs
11-46
-------
and other understory plants for shelter and food. Many songbirds utilize the
understory vegetation for nesting and protection from predators.
7. The use of mixed plantings for reducing levels of pollution should
ecrtf'nly include trees and shrubs which contain deciduous and coniferous plants.
To ensure continuous filtering action, conifers should be planted
with the deciduous trees. Compared to deciduous woody plants, conifers possess
a longer time of foliage retention which provides a correspondingly greater
opportunity for pollutant removal. Another morphological characteristic of
conifers that promotes the removal of air pollutants is the high surface area
to volume ratio. Both the persistent foliage and the consistently -high surface
to volume ratio of conifers become increasingly important in urban areas, and
possibly along highways, as the winter progresses. Urban areas generally have
higher concentrations of atmospheric particulates and gases in the winter as
compared to the ambient pollutant concentrations of the summer.
Although conifers may be preferred over deciduous species in terms
of absorption and adsorption of pollutants, coniferous species are generally
more vulnerable to the adverse effects of atmospheric pollutants than most
deciduous trees due to the greater concentrations of pollutants in the foliage
of the conifers. Since deciduous trees lose their leaves after the termination
of each growing season, the pollutants have less time to accumulate in the living
deciduous leaves as opposed to coniferous foliage. In other words, deciduous
species have a more rapid mechanism for the disposal of lethal levels of pollutants
in their foliage than conifers. That is seasonal leaf senescence.
As a result, mixed plantings of deciduous and coniferous species
are recommended since the deciduous trees will protect the conifers by extracting
a substantial amount of airborne contaminants present in an area which will
Jower the pollutant load in the vicinity of the conifers.
11-47
-------
8. A high number of plant species with varying ages is important for
developing healthy, efficient greenbelts.
Many urban plantings are even-aged monocultures in which regeneration
is negligible. Since understory young trees are virtually absent, the older,
mature trees as they die or become diseased cannot be replaced. Also, in these
situations of extremely low plant diversity, the dominant tree species is
more susceptible to disease. Two recommendations for improving such urban greenbelts
are to increase the diversity index, especially for tree species, and to maintain
representatives of all age groups.
9. Moderate density is the optimum density for the removal of air
pollutants.
Moderate density is achieved when more surface area of the vegetation
is exposed to the flow of air through a greenbelt than in a low density condition
and when less deflection of the wind occurs than in a high density condition.
10. There are numerous factors influencing the determination of the minimum
width of greenbelts necessary for maximum dispersion of atmospheric pollutants.
The minimum width of a particular greenbelt which causes maximum
dispersion of air pollutants is dependent on numerous factors in addition to that
of the distance from the source to the receptor. The large scale circulation
of the atmosphere determines the general direction of pollutant transport and
deviations may be caused by local breezes, topographical features of a specific area,
varying densities of air masses, etc.'
Warren (1973) estimates that the minimum width of greenbelts is
100 to 120 meters in which maximum dispersion of airborne pollutants results.
11. The speed of the wind passing through or over a greenbelt may be
influenced by the dimensions and density of that particular greenbelt.
Decreasing the wind speed by natural barriers allows the ambient
substances to settle out onto the vegetation and soil by gravitation. The
extent of wind disruption resulting in the deposition of particulates is partly
dependent on the height, shape, and permeability of forests and buffers.
11-48
-------
The reduction of wind velocity by a greenbelt is correlated to tree
height. According to Geiger (1950), the wind speed is reduced 10% within a
distance equal to three times the tree height on the windward side and twenty
times the tree height on the leeward side. The diagram that follows may
illustrate this phenomenon more clearly.
FIGURE II-ll
EXTENT OF INFLUENCE OF WINDBREAK AND SHELTERBELT PLANTINGS
windward
3h
leeward
20h
WIND
Area of Wind Shadow
V=Velocity
h=Unit of Length
Wind reduction occurs in the lee of greenbelts regardless of the
degree of permeability; however, the location of the area of greatest wind
reduction is a function of permeability. Immediately behind a dense greenbelt
is the area of greatest wind reduction whereas the position of greatest wind
reduction is further away from the boundary of a greenbelt of medium density.
The extent of wind reduction caused by greenbelts of medium density
is greater than that caused by dense greenbelts. Also, a natural barrier of
medium permeability with openings distributed evenly throughout the greenbelt
prevents turbulence in the lee to a larger extent than an impermeable forest or
buffer does.
Blenk and Trienes (1955)created models of impermeable plant belts which
varied in shape. The rounded model that was devoid of any sharp edges was the
least efficient in wind reduction whereas the model that exerted the greatest
effect in wind reduction was right-angular in cross section. The diagram on the
following page displays three of the models and their differing degrees of wind reduction.
11-49
-------
Buffers which are permeable to wind are more efficient in reducing wind velocity
than those buffers which are not as permeable.
FIGURE H-12
FORM OF BUFFER IS RELATED TO REDUCTION OF WIND VELOCITY.
maximum
reduction
moderate
reduction
least
reduction
In conclusion, during the process of developing plant belts, there
should be some consideration of the conditions influencing wind reduction. The
dimensions and permeability of a greenbelt are factors that cause disruption of
the air flow which may lower the velocity to such an extent that pollutants filter
out of the air onto the vegetation and soil surface.
12. Increasing the sink potentials of roadside forests and buffers
can be accomplished by expanding the length and increasing the diversity of the
edge.
According to Warren (1973), the initial 65 to 85 feet from the edge
of a forest can reduce the concentration of particulates by as much as 50%. By
increasing the diversity and thereby, increasing the density of the plant species
within the first 65 to 85 feet of the greenbelt, the rate of removal of airborne
particulates by vegetation composing the edge can be enhanced. The following
diagram shows the relative efficiency of the first 65 to 85 feet of a forest
for depositing particulates.
Another method for increasing the sink potential of buffers or
roadside forests is by clearing to create additional edge. (Figure 11-16 on page 11-55
of the Design Alternatives demonstrates a pattern for clearing the vegetation
to increase the length of edge).
11-50
-------
FIGURE 11-13
INCREASED DIVERSITY WITHIN EDGE CONDITION MAXIMIZES SINK POTENTIAL
Line
or Source
Pollution
65-85 L particulates reduced
maximum
efficiency
40-50%
13. Thermal chimneys within the forest aid -in increasing air circulation
which causes more exposure of polluted air to the upper leaf surfaces in the
interior canopies.
The installation of thermal chimneys in the forest will allow the
airborne particles trapped below the forest canopy to become dispersed in the
crowns of the trees since the openings in the canopy will promote the movement
of air that will escape above the forest. The diagram below illustrates how a
thermal chimney can increase the ventilation of a forest.
FIGURE II-14
CREATION OF THERMAL CHIMNEYS FOR
VENTILATION OF FORESTS AND BUFFERS
clear cut
11-51
-------
14. Poor ventilation along highways may be caused by steep banks or
dense buffers and this adverse condition aan be partially removed by alleviating
the effect of the natural and artificial barriers.
Steep roadside banks promote localized areas of high carbon monoxide
concentrations, especially in areas of high traffic volumes. If the flow of air
containing carbon monoxide is not obstructed, the amount of carbon monoxide
fallout corresponds to increasing distance from the highway. The dispersion
characteristics of carbon monoxide in situations in which the highway is
bordered on each side by steep banks are that the maximum concentrations occur
in the vicinity of the impermeable walls and the minimum concentrations of
carbon monoxide are found at the center of the highway. The peak values of
carbon monoxide also occur along the wall in a situation where there is a
barrier along one side of the roadway and an open space area on the opposite
side. If the sides of the road are open to ventilation, the center of
the highway will have the highest content of carbon monoxide while the
concentration of carbon monoxide will decrease in both directions. The
diagram below displays the three dispersion patterns of carbon monoxide due to
the presence or absence of barriers adjacent to the highway.
FIGURE H-15
CO CONCENTRATIONS ADJACENT TO ROADS
««
increasing concentration of CO
increasing 44 ^ ^ decreasing
concentration concentration
decreasing concentration
11-52
-------
Also, Figure 11-22 on page 11-58 of the Design Alternatives shows a
method for increasing ventilation of a roadway originally bordered by steep banks.
In some instances, dense buffers may hinder adequate ventilation
and high concentrations of carbon monoxide may occur. By cutting through the
vegetation, the carbon monoxide concentration values will be reduced due to
the increased dispersion of this pollutant caused by more ventilation. The
technique of increasing buffer ventilation is illustrated in Figure 11-17 on page 11-55
of the Design Alternatives.
15. Safety measures that should be included in tine design of greeribelts
near highuays or in urban areas.
The minimum distance from the edge of the pavement for safely
planting trees growing to a diameter breast height (d.b.h.) of 4 inches or larger
is 30 feet and for smaller trees is 20 feet.
Persons vigorously exercising near areas of high traffic volumes
may be jeopardizing their health. To avoid some of the potentially dangerous
effects, it is recommended to establish a buffer which separates areas of high
traffic volumes from active recreation sites. This buffer should be at least
65 to 80 feet wide since the percentage of particulate removal as indicated
by Warren (1973) is 40 to 50%. Figure 11-23 of the Design Alternatives on page II-5g
shows the protection of a recreational facility by the use of a buffer that
is at least 65 feet wide.
Width is not by any means the only consideration for developing
a vegetative barrier that effectively shields actively exercising individuals
from the potential dangers of air contaminants emitted by motor vehicles. The
buffer should be high enough to hinder the prevailing winds coming from the
polluting source. Also, a barrier of high density may cause an adverse effect
since the wind will be unable to sufficiently penetrate the thick clumps of
vegetation and the deflected current may bring the harmful pollutants in contact
with the people that are to be protected.
11-53
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2. Design Configurations.
The preceding text was a summary primarily concerning the methods for
increasing the sink potential of greenbelts. The information can also be found
in the Literature Search Findings of Volume II, the Plant Species Sensitivity
List in the appendix of Volume II, and the Sink and Emission Factors for Natural
Elements of Volume I. This material provided the guidelines for developing the
design alternatives which follow.
Each of the designs illustrate ways for increasing the removal rate
of atmospheric pollutants by vegetation resulting in the improvement of air
quality. Some of the designs for enhancing the sink potential of natural
elements involve compiling plants into hedgerows and the most effective
arrangement of these hedgerows depends on the direction of the prevailing
wind, location of the polluting source, variations in topography, etc. By
correctly placing the hedgerows, the wind may be disrupted to such an extent
that the airborne particulates settle out onto the vegetation and soil.
In situations where the dense buffers along highways cause inadequate
ventilation to such a point that high localized accumulations of carbon
monoxide occur, one of the solutions is to divide the vegetation into hedgerows.
The design on page 11-55 (Figur,e II-17)shows that gaps in the dense vegetation will
channel the polluted air away from the highway. Also, by cutting through the
thick vegetation, the edge length will be increased.
Another method for enhancing the edge effect is demonstrated in Figure II-16
on page IT-55 which involves cutting gaps at least 65 feet back from the original
edge of the buffer. The additional edge will increase the deposition of
pollutants by the greenbelt.
The rest of the designs range from improving the sink capacity of a
grassy median to ensuring the adequate protection of individuals vigorously
exercising in the vicinity of a heavily traveled highway. All of the designs
have at least one common characteristic which is increasing the efficiency of
highway buffers in extracting harmful air pollutants emitted by motor vehicles.
11-54
-------
Increasing
Buffer
Edges
In cases where buffers or road-
side forest cover exist, the
sink potential of the vegeta-
tion can be increased by
clearing to create additional
edges. As the first 65 to 85
feet of forest is the most
valuable as a receptor for
pollutants, this technique will
greatly increase the efficiency
of the existing buffer,
especially for the removal of
particulates.
Section
65' min.
FIGURE 11-16
Plan
Increasing
Buffer
Ventilation
Dense buffers along high volume
arterials can create high con-
centrations of CO (as shown in
Figure 11-15. To reduce CO con-
centration, cuts through the
vegetation will allow ventila-
tion of the roadway and dis-
persion of CO. This technique
also provides increased forest
edge thus aiding in the removal
of particulates as well as
soluble gases.
Section
FIGURE II-
11-55
Ran
-------
Chevron
Hedgerow
The alignment of discontinuous
hedgerows in a chevron pattern
will provide a large area of
leaf surface contact for adsorp-
tion of particulates and absorp-
tion of soluble gases. The gaps
between the plantings provide
adequate ventiliation for CO
dispersion. The belts should be
oriented at a 45 degree angle
to the road; in the direction
of the prevailing winds. A 30'
safety setback should be main-
tained .
Wind
FIGURE 11-18
Plan
Parallel
Hedgerow
In situations where existing
woodlots or buffers are para-
llel to the road and relatively
perpendicular to the prevailing
winds, the placement of a dis-
continuous hedgerow windward
of the edge of vegetation, as
shown, will increase wind tur-
bulence and decrease wind speed
thereby causing particulates to
drop out. The polluted air is
forced closer to the soil sur-
face where CO can be metabo-
lised by soil organisms. The
increased exposure of leaf
surfaces further reduces par-
ticulates and allows for the
absorption of soluble gases.
Openings in the hedgerows are
located at intervals to limit
the buildup of CO. A 30' safety
setback should be maintained.
Section
FIGURE 11-19
Plan
11-56
-------
Multiple
Hedgerow
In areas of sloping terrain or
where roads are located on fill,
an arrangement of multiple
hedgerows, parallel to the road
and perpendicular to the pre-
vailing winds are recommended.
This arrangement provides a
maximum disruption of the wind
which results in the deposition
of particulates as well as
maximum exposure of polluted
air to leaf and soil surface
which reduces CO and soluble
gases. The increased spacing
between rows will increase
turbulence thereby decreasing
particulates.
Section
FIGURE 11-20
Plan
Managed
Natural
Buffer
Management of rights of way
along roads to stimulate
natural plant succession to
occur is a useful technique
for providing buffers. The
development of old fields and
forests, or woodlot conditions,
will provide increased pollu-
tant sink potential by first
reducing wind speed through
increased turbulence and by
exposure of leaf and twig sur-
face for adsorption of par-
ticulates and absorption of
soluble gases.
Section
8' Manage as as
old field forest
FIGURE 11-21 Plan
11-57
-------
Ventilating
Roadway
Cuts
Steep roadside cuts become areas
of high concentrations of CO,
particularly in areas of high
traffic volume (as illustrated
in Figure 11-15). Cutting
back steep banks to more
shallow slopes provides better
air ventilation to reduce CO
levels. Covering the exposed
banks with legumes (such as
crown vetch) provides soil
stability as well as increased
sink potential. It also may
improve the visual quality of
the road experience.
•original
grade
Section
FIGURE 11-22
Plan
Recreation
Facility
Setback
Foot or
Because of the potential dangers
of vigorous exercise adjacent
to high traffic volumes, it is
recommended that active recre-
ation facilities be located at
least 65 feet behind the buffer
edge.
Section
* bike
path
FIGURE 11-23
11-58
-------
Planting
Existing
Medians
Roads with medians now planted
in maintained grass could
greatly reduce the level of
pollution by installing a
moderately dense mixed planting
of trees and shrubs, both ever-
green and deciduous. This
would also reduce headlight
glare and ambient noise levels.
Section
FIGURE 11-24
Plan
11-59
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JTI. REGIONAL OPEN SPACE
This section of the study is concerned with the regional control of
pollutants. Initially, a review of pollutants from both natural and anthropo-
genic sources is presented including sulfur compounds, nitrogen compounds,
carbon monoxide, organic gases (eg. hydrocarbons), asbestos, lead and fluorocarbons.
Next, removal processes are discussed to illustrate how regional pollutants
interact with the environment. Finally, the literature is reviewed on using
open spaces to reduce regional pollutants and several planning concepts are
presented.
A. POLLUTANT IDENTIFICATION
Regional scale air pollution problems are generally associated with point
sources of pollutants. However, there are numerous natural sources of air
pollutants that can be the major cause or that can contribute to regional pollution
problems. Ultimately, all air pollutants are from natural sources. However most
problems occur when the natural compound is transformed by man into an air
polluting compound. As an example, the major source of air polluting sulfur is
hydrogen sulfide (H_S) which, in itself, is not injurous. However, tUS is rapidly
oxidized to sulfur dioxide (S02>, sulfur trioxide (SOO, and sulfuric acid (H_SO,)
which are all considered air pollutants. In the combustion process, S0_ is
produced from elemental sulfur. It is also important to recognize that while sulfur
in the form of SCL may be considered an air pollutant in industrial areas, crops of
various kinds are dependent upon atmospheric sources for a large proportion of
their sulfur needs.
Table 1II-1 is a summary of the annual emissions of various atmospheric
pollutants. Careful attention should be directed to the proportion of natural
emissions by the anthropogenic sources.
III-l
-------
TABLE III-l
SUMMARY OF SOURCES & ANNUAL EMISSIONS
OF ATMOSPHERIC POLLUTANTS
POLLUTANT
so2
H S
£,
N20
NO
N0_
2
NH
CO
°i
J
non-
reactive
hydrocar-
bons
reactive
hydrocar-
bons
asbestos
MAJOR SOURCE
ANTHROPOGENIC NATURAL
combustion of coal
and oil
chemical processes;
sewage treatment
none
combustion
combustion
coal burning;
fertilizer; waste
treatment
auto exhaust;
and other
combustion
processes
none
auto exhaust;
combustion of
oil
auto exhaust;
combustion of
oil
insulation,
i shipbuilding,
lead
f Luorocar-
bons
brake linings
auto exhaust,
combustion of
coal, refuse &
sludge incener-
ation
aluminum, fertili-
zer, fuel combus-
tion, steel indus-
tries
volcanoes
volcanoes ;
biological decay
biological decay
bacterial action
in soil; photo-
dissociation of
NO and N02
bacterial action
in soil; oxidation
of NO
biological decay
oxidation of methane;
photodissociation
of CO ; forest fires;
oceans
tropospheric reactions
and transport from
stratosphere
biological processes
in swamps
biological processes
in forests
mining
mining
ESTIMATED EMISSION KILOGRAM
ANTHROPOGENIC NATURAL
65 x 109
3 x 109
none
53 x 109
combined with
N07
4 x 109
360 x 109
70 x 109
27 x 109
(?)
143 x 106
(?)
2 x 109
100 x 109
590 x 109
768 x 109
170 x 10^
3000 x 109
(?)
(?)
300 x 109
175 x 109
(?)
(?)
(?)
SOURCE: Rasmussen, et al, 1974
m_2 (Adapted by COMSIS CORP. 1976)
-------
1. Source Emissions.
a. Sulfur Compounds
The element sulfur (S) occurs in a variety of stable compounds
that are derived from both the natural environment and from air pollution sources.
Among the more common compounds are: hydrogen sulfide (H.S), sulfur dioxide (SO.),
sulfur trioxide (SO.) and sufuric acid (H.SO,). H.S has not, in itself, been
considered a pollutant. However, it oxidizes rapidly to S0_ and further to SO. and
H2SO,. This chemical reaction is represented in Figure III-l (Kellogg, et al.,
1972).
FIGURE III-l
SCHEMATIC REPRESENTATION OF THE CHEMICAL PROCESSES INVOLVING
ENVIRONMENTAL SULFUR, WITH INDICATIONS OF THE MEAN LIFETIME
OF EACH COMPOUND IN THE LOWER ATMOSPHERE
(hours or days;
Anaerobic bacteria *(aster'" solutlonl
in soil, marshes, «
and tidal flats 3
XSO/
Robinson & Robbins, (1968), have suggested that on an annual basis,
220 x 10 tons of sulfur are discharged into the atmosphere with about one third
coming from air pollution sources, mostly in the form of SO., and the rest from
natural processes. Kellogg, et al., (1972), estimated that man is contributing
about one half as much as nature, but that by AD 2000 he will be contributing about
III-3
-------
as much, and in the Northern Atmosphere alone he will more than match the
natural generation rate.
Most of the S being emitted by natural sources is in the form of
H-S. It is estimated that H_S represents one half of the total sulfur now being
6
released to the atmosphere, 100 x 10 tons (Robinson & Robbins, 1968), The primary
sources for this natural emission are decaying vegetation in swamps, bogs and
other land areas. Estimates of the annual emissions from natural sources vary.
9
Erikson, (1960), suggests decaying vegetation is the source of 112 x 10 kg H_S
9 L
per year. Robinson & Robbins, (1968), estimate 70 x 10 kg per year.
The oceans have also been suggested as a source of H_S. Erikson,
*• c
(1960), speculated that the annual H?S emission from the oceans is 202 x 10 tons.
*• e.
Robinson & Robbins, (1968), suggest that it generates 10 tons. Kellogg, et al.,
(1972), dispute both these figures saying that undoubtedly some H-S is liberated
from tidal flats, but probably very little is emitted from the open ocean. Active
volcanoes are another source of H«S, however, no estimates are known of the amount
of H S emitted. Only small quantities of H^S are emitted from anthropogenic sources.
Most of the SO. and SO, compounds in the air are from anthropogenic
sources and their contribution to pollution problems can be linked with industrial
growth. A good example of this is illustrated by the fact that in 1940 there was
9
an estimated 78 x 10 kg/yr of SO. emitted on a global basis (Katz, 1956).
Robinson & Robbins, (1968), in Rasmussen et al., (1974), estimated anthropogenic
9
activity in 1968 as the source of 146 x 10 kg SO- each year, 70% of which they
estimated was due to the combustion of coal, 16% from the combustion of petroleum
products, primarily residual fuel oil. The remaining emissions resulted from
refining operation ( 4%) and non-ferrous smelting ( 10%). Kellogg et al.,(1972),
9
believes an estimate of about 100 x 10 kg SO- per year would be reasonable for
the same period.
In terms of regional areas, Prince and Russ, (1972), have estimated that
_2
S0_ emissions in Britain have increased from 9.1 to 11.4 mg km from 1950 to 1970,
—2
an increase of 2.3 mg km" in 20 years. On the same basis, they estimated emissions
_2
in the United States were approaching 2 mg km in 1970 and are expected to reach
_2
3.3 mg km by 1980 if the fossil fuel becomes available and no steps are taken to
reduce emissions.
III-4
-------
Most of the natural sources of SO- is from volcanic activity. Kellogg,
et al.,(1972), estimated that the quantity released by volcanoes is about 1.5 x 109
kg/yr. Stoiber and Jepsen (1973), estimated annual volcanic emissions of S00 to be
9 a
15 x 10 kg. Rasmussen, et al., (1974), determined an average to be 2.0 x 10 kg/yr.
b. Carbon Monoxide
Carbon monoxide (CO), is the most abundant and widely distributed air
pollutant found in the atmosphere. CO emissions generally exceed that of all other
pollutants combined (excluding carbon dioxide CO.) particularly in urban atmospheres.
Practically all of the CO formed is due to man's technology with more than 90%
of the total CO emitted from combustion of fossil fuels being derived from motor vehicle
emissions (Jaffe, 1973).
Rasmussen,et al., (1974), has written an excellent review of
natural and anthropogenic sources of CO. The following is a synopsis of that
material.
By far the largest single anthropogenic source of CO is motor vehicle
exhaust. Jaffe (1973), estimated that of a total anthropogenic CO emission
9 9
source in the United States in 1970 of 132.6 x 10 kg, 96.9 x 10 kg resulted from
the burning of gasoline by motor vehicles alone. Other significant contributions
9
to this man-made CO burden are from solid waste disposal (6.5 x 10 kg), industrial
9 9
process loss (10.3 x 10 kg) and agricultural burning (12.5 x 10 kg). On a global
9
basis, for 1970 Jaffe(1973), estimated CO emissions to be approximately 360 x 10 kg.
(See Figure III-2).
The most widely recognized natural source of CO is forest fires
9
which have been estimated as releasing 11 x 10 kg CO into the atmosphere each year
(Robinson & Robbins, 1968). Minor amounts of CO have been found to be released
from volcanoes and marshes (Flury and Zernik, 1931). CO can also be formed
during electrical storms (White, 1932), and by the photo dissociation of C0?
in the upper atmosphere (Bates and Witherspoon, 1952). Calvert, et al.,(1972) has
suggested the photo dissociation of fonneldehyde as a possible source of CO
and recently, Swinnerton, et al.,(1971) found CO to be present in rain water in
high concentrations.
II1-5
-------
TABLE IH-2
ESTIMATED CARBON MONOXIDE EMISSION SOURCES
IN THE UKITED STATES IN 1970
Enissions,
Source Category 10' "erne ton*
Han-Kade Sources
Fuel coabustion in stationary sources 0.7
Steam and electrical 0-1
Industrial 0.1
Commercial and institution*! ".2
fcesidential 0.1
Transportation, mobile sources J0ff.fi
Motor vehicles, gasoline 8b.9
Motor vehicles, diesel 0-7
Railroads 0-1
Kaiercrafl !-J
Aircraft 2-7
Oihei nonhighway use • •*
Solid waste disposal *•*
Municipal incineration 0.3
On-site incineration "•*
Open burning *•!
Conical burning *••
Industrial process losses J0-3
Miscellaneous **•*
Structural fires 0.2
Coal refuse burning 0-3
Agricultural burning 12.S
Preicribed burning '-^
Total all ean-oadc categories 732.fi
Matural Sourcei
Forest fires (wild) Z.J
Source: Jeffe, 1973
The ocean was first suggested as a major source of CO by Swinnerton,
9
et al.,(1970), who estimated that it can produce up to 220 x 10 kg each year.
Robinson o Moser,(1971) suggested that plants could indirectly be the source of
q
about 54 x 10 kg CO by the oxidation of released terpenes. Finally, McConnell,
o
et al.,(1971), suggested that approximately 900 x 10 kg CO are produced each
year by the oxidation of methane.
Rasmussen,et al., (1974), also points.out that Stevens et al.,O972)
believes that natural sources of CO could yield about 10 times more CO than
all anthropogenic sources in the northern hemisphere. Using that conclusion they
9
estimate the total CO natural emissions to be 3000 kg x 10 per year.
On a regional basis, the emissions from anthropogenic sources far
exceed any natural sources. The concentration of this pollutant is well corelated
with can's activity and predominantly with the flow of vehicles on urban streets.
III-6
-------
c. Nitrogen Oxides
The photochemical smog reaction involving nitrogen oxides, hydrocarbons
and sunlight was identified in the early 1950s as the basic mechanism for the
characteristic air pollution problem found in Los Angeles. Since that time photo-
chemical smog has been identified as a significant air pollution factor in a
number of large urban areas and has focused attention on the role of nitrogen
oxides in urban air pollution (Robinson & Moser, 1971).
The main source of N.O is believed to be the result of bacterial
decomposition of other nitrogen compounds in the soil. On a global basis,
the quantity of N_0 and NO produced naturally has been estimated as 786 x 10
tons by Robinson & Moser, (1971). Goody & Walshaw, (1953) estimated
12
a global NO production rate of about 100 x 10 kg/year and Robinson & Robbins
(1968) suggested that soils produce about 59.2 x 10 kg N20 each year by biological
action; and of this about 55.4 x 1010 kg (35.3 x 1010kg NjO-N) are reabsorbed by
the soil and about 3.8 x 1010 kg N20 (2.4 x 1010 kg N^-N) travels up to the
stratosphere where it is destroyed. Schutz et al., (1970), cited in Rasmussen, et al.,
(1974) showed a flux of NjO in the order of 10~8 g NjO/m2 sec, a level which, if
maintained globally, would necessitate on N?0 cycle of about 70 years.
Nitrogen (N) is one of the most abundant elements constituting
78% of our atmosphere. There are a number of compounds of nitrogen, but only 2
are considered pollutants - nitric oxide (NO) and nitrogen dioxide (N0_). Most
other compounds are from anthropogenic sources. Another compound, nitrous oxide
(N?0), is predominantly from natural sources; however it oxidizes to NO compounds
» X
and therefore should be considered in air pollution calculations. In pollution
estimates, the NO and NO. are usually considered together and expressed as NO-.
It is estimated that natural emission of nitrogen as N_0 are approximately 15
9 9
times greater than pollutant emissions (768 x 10 kg NO. vs. 53 x 10 kg NO.,
Robinson & Robbins, 1970).
Production rates of N0 and N02 by soils are much more difficult to
predict. McConnell (1973) in Rasmussen, et al.,(1974) recently summarized a
few of the problems involved in appraising the amount of nitrogen oxides generated
by soil. He contends that the soil source is small compared to that produced as
a result of the gas phase oxidation of atmospheric ammonia (NH ) by oxides of
nitrogen. He believes this source produces 7 x 1010 kg NO^N/year. He offers
alternative reaction sequences for NH3 in the atmosphere. One reaction sequence
provides a constant source of NO, the other a sink. If the later occurs in the
atmosphere an additional source of NO must be found in order to account for the
amount of NO known to be in the atmosphere. In this case, McConnell concedes
III-7
-------
that the soil might actually constitute a significant source of NO , generations
11 x
above 10 kg/year.
Estimation of the anthropogenic emissions of NO and NO are lumped
together as emission data which rarely distinguishes between the two forms. Robinson
and Moser, (1971), estimated that annual production is about 53 x 10 kg with 31%
of the total due to coal combustions and 41% due to petroleum production and the
combustion of petroleum products. Within the petroleum class, combustion of gasoline
and residual fuel oil are the major contributors of NOj. For the coal combustion
category, power generation and industrial users account for most of the NO.
emissions. Robinson and Robbins (1970), suggest using the same anthropogenic
9 Q
emission rate of 53. x 10 kg of NO but convert it to 16 x 10 kg NO -N.
Although the natural sources of nitrogen compounds are greater
than the anthropogenic sources, the anthropogenic sources are concentrated in
industrial sections and thus their contribution is more significant in a±T pollu-
tion problems. There is more than one reason for the build-up of NO in urban
areas. First, the soil serves as the main sink for NO and in urban areas the
X
anthropogenic sources of NO usually exceed the capacity of the soil to absorb
NO . Secondly, although the soil releases great quantities of N00, the release
x Z
occurs at the ground surface thus the same soil can serve as a sink in a dynamic
equilibrium.
Most of the anthropogenic sources of NO. are released 20-50 meters
in the air. Because a soil - gas interface is necessary, the soil has less of
a chance to serve as a sink for NO. released at height. Therefore, NO. remains
in the air for a longer period and can contribute to the photochemical smog
problem. It is recognized that if the NO- were released at the ground level
there would be higher concentrations; however the soil could then better serve
as a sink and absorb more of the NO..
d. Organic gases (hydrocarbons)
This group of gases represents a major factor contributing to air
pollution. It includes all classes of hydrocarbons including those
formed when some of the hydrogen of original compound is replaced by other
III-8
-------
substituent groups including nitrogen, sulfur or oxygen (Rasmussen, et al., 1974).
There are two classifications of organic gases, reactive and non-reactive.
In areas where photochemical air pollution is a serious problem, a major concern
is with the olefins and other reactive hydrocarbons rather than with the total
organic emissions. Using factors derived by the Bay Area Air Pollution
Control District in San Francisco, Robinson & Moser, (1971) estimated that
approximately one-third of the total hydrocarbon emissions are classed as reactive,
or about 27 x 106 tons out of the 88 x 10 total tons of organic materials. The
major natural source of reactive hydrocarbons is decaying vegetation and plant
metabolic processes.
Since the analytical work of F.W. Went in 1960, an increasing base of informa-
tion has been developing related to the emissions of air polluting hydrocarbons
by vegetation. Particular focus has been made on the presence of aromatic
ethers, and some unsaturated material which generally is found in air and is
among the prime determinants of our perception of the 'freshness* of the air
(Turk and D'Angio, 1962).
The primary volatile organic compounds emitted are the monoterpenes which
contain ten carbon atoms and include a-pinene, B-pinene, and limonene and the
hemiterpene isoprene which contains five carbon atoms (Rasmussen, 1970, 1972).
Other naturally occurring hydrocarbons include Camphene,6-phellandrene,
1, 8-Cineal, Camphor, P-Cymena, Terpinene and A3-Carene. In effect, these
substances serve as tracers for a larger group of lower molecular weight
organics which provide material available for reaction with ozone to generate
smog through the photochemical reaction of these chemicals.
It has been estimated that 1.7 x 108 tons of volatile hydrocarbons
are generated each year by all of the vegetation of the earth as compared with
0.27 x 108 tons of reactive hydrocarbons generated from anthropogenic sources
(Eschenroeder, 1974). However, natural emissions from vegetation, because of
the low emission densities involved, are not believed to be present in
sufficiently high ambient concentrations to result in significant quantities
of photochemical oxidants—especially in comparison with ozone levels resulting
from anthropogenic precursors.
A cursory examination of the literature reveals that the synthesis of
aromatic carbon compounds by plants is an integral part of their cellular
III-9
-------
activities. It is logical to anticipate the release of these biosynthetic
products in proportion to the potential metabolic activity of the plant
species under consideration (Beytia, et.al., 1969). Certain species are far
more efficient hydrocarbon generators than others and variations may even be found
between clonal variations of the same species (Gerhold and Plank, 1970; Rodwan
and Ellis, 1975).
On the other hand, a single species of plant may show marked fluctuation
in the generation of hydrocarbons in apparent physiological response to a very
wide array of environmental alterations. These alterations include, at a
minimum, injury such as from elevated ozone levels (Craker, 1971) or insect
attack (Shain and Hillis, 1972). Other alterations include temperature,
humidity, nutrient level and any other factor contributing to the cellular
environment of the plant under study (DeSanto, personal communication).
There are numerous pollutant sources of reactive hydrocarbons.
On a global basis, Robinson and Myers,(1971), have estimated an emission rate of
88 x 10 tons per year. Of this total, 66% is from petroleum usuage, 34 x 10
tons from gasoline usage, 6.3 x 10 tons from refinery uperections; 7.8 x 10
tons by transfer losses; petroleum evaporation, and 10 x 10 tons from solvent
usage. Other sources of hydrocarbons include incineration and coal combustion.
e. Other pollutants
There are numerous other pollutants emitted by both natural
and anthropogenic sources including asbestos, lead and flourocarbons. Most of
the sources of these pollutants can be considered minor when compared to the
pollutants previously discussed. A brief description of each pollutant is contained
below.
1) Asbestos
Asbestos is a generic term covering several fibrous silicate
minerals that are found in almost every country in the world. These minerals
are classified into two groups: (1) Serpentine - chrysotile and (2) Amphiboles
encompassing actinolite, amosite, anthophyllite, crocidolite and tremolite.
Chrysotile - the fibrous form of serpentine, the so called white asbestos -
is the most widely used type of the mineral, constituting more than 90% of the
III-10
-------
world's production. Within the second group, anthophyllite, amusite, and crocidolite
are of commercial importance (Hammons and Huff, 1974).
Hammons and Huff, (1974), have reported that in the last 60 years
global use of asbestos has increased more than. 100 fold-from 30,000 tons to four
million tons. The same authors stated that asbestos is used in more than 3,000
products - cement, textiles, yarns and cords, boards and papers, sealing and packing
materials, plastics, thermal insulants and fire proofing and friction material for
brake linings and many other devices.
Anthropogenic sources of asbestos are mostly industrial that use it
as part of their final product. These include ship building, insulation, construction,
iron foundries, pharmaceutical and brake lining industries. Natural sources of
asbestos include mineral production, weathering of mineral outcrops, and
release during farming of asbestos - containing soil. No information could be
found on quantities of asbestos being emitted on either a global or regional level.
2) Lead
Lead is a heavy metal that is naturally present in small amounts
in soil, rocks, surface waters and the atmosphere. Due to its unique properties,
it has been an element widely used by man. This utility has resulted in greatly
elevated lead concentrations in certain ecosystems.
The primary source of lead in urban areas is the combustion of
gasoline containing lead additives. Specific estimates of the amount of lead annually
introduced to the atmosphere via gasoline consumption includes 98% (National
Academy, of Science. 1972), and 952, {Ewing and Pearson, 1974). Approximately 136 x
10 kg of lead were released in automotive exhausts in 1970 ( U.S. Bureau of Mines,
1971). Since 1970 no-lead and low-lead gasolines have become increasingly available
and in 1974 all new cars in the United States were required to use no-lead gasoline.
Other sources of lead include coal combustion, refuse and sludge incineration, burning
or attrition of lead-painted surfaces and industrial processes.
Lead is a naturally occurring element and therefore small amounts
are present in the environment from non-anthropogenic sources. In studies to
determine the impact of lead from highways on vegetation it has been reported that
III-ll
-------
the background lead content of twigs and foliage of shrubs and decidous trees
is generally within the range of 1-4 pg/g dry weight of tissue (Smith, 1975).
Other studies have reported that the lead content of the upper
soil horizons of unmineralized and uncontaminated areas is approximately 10-20 vg/g,
dry weight (Smith, 1975). These statistics indicate the amount of lead occurring
naturally in the environment.
3) Fluorocarbons
Atmospheric fluorides may be placed into four major categories;
gaseous, particulate, soluble and insoluble. The major form of fluorine is
hydrogen flouride (HF) and is given off by aluminum, steel and fertilizer processing
industries. Coal and shale contain up to 120 - 550 ppm fluorine respectively
(Crossley, 1944), and during the combustion process a proportion of this is
released as hydro fluoric acid, silicon tetra fluoride and as a form associated
with particulate matter (Davison, et al., 1973).
2. Pollutant Removal.
There are numerous mechanisms for removing air pollutants from the
atmosphere by natural phenomena. A review of these mechanisms was performed by
Rasmussen, et al., 1974, which was based on work by Robinson and Robbins, 1968, and
Hidy, 1973. The important mechanisms include:
(1) Precipitation scavenging in which the pollutant is removed
by two modes. The first is "rainout" which involves the absorption of gases and
aerosols by clouds. The second is "washout" which involves both gas absorption and
particle capture by falling rain drops;
(2) Chemical reactions in the atmosphere, including the stratosphere,
which produce either aerosols or oxidized products such as carbon dioxide and water
vapor.
(3) Dry deposition which involves absorption by aerosols and subse-
quent deposition on the earth's surface; and
(4) Absorption by various substances at the earth's surface including
vegetation, soil and water bodies.
111-12
-------
The remainder of this section will discuss how each of these
processes affects the removal of each of the previously mentioned atmospheric
pollutants. Particular attention will be given to those processes that contribute
to the removal of pollutants using open space measures.
a. Sulfur Compounds
S07 is very soluble in water and very reactive either photochemically
or catalytically in dilute concentrations in the atmosphere. Accordingly, the main
processes for the removal of SO, from the atmosphere are: (1) precipitation scavenging
(2) chemical conversion and (3) absorption by soil, water, rock and plants.
In precipitation scavenging, the S02 will undergo a series of
reactions, some catalytic, to ultimately form HjSO^ drops or a sulfate salt. In
the chemical conversion processes, dry S0« in the daytime under low humidity condition,
will react with N02 and hydrocarbons in the transformation of S02 to form a H2SO^
aerosol. At night and under high humidity a process involving the absorption of SO.
by alkaline water droplets and a reaction to form SO, within the drop is a well-documented
process and can occur at an appreciable rate which removes S0_ from the atmosphere
(Robinson and Robbins, 1968).
In terms of open space measures, SO. can be absorbed from the
atmosphere directly by vegetation, soil, rocks and water. This technique can be
thought of separately or in combination with dry deposition and precipitation
scavenging. Vegetation needs elemental sulfur for metabolic processes and much of
that sulfur can be obtained from S02 especially in areas where the soil is sulfur
deficient. Soils readily absorb SO although the removal process is not fully
understood. Smith, et al., 1973, suggests that S02 absorbed is oxidized to
sulfate which may then be subject to leaching and uptake by plants. Thus the
soil can remain a renewable sink for SOj. Limestone rocks react with H-SO, to
form gypsum, thus serving as a sink for SO.. Table 111-10 of Volume I of this study is
a synopsis of sink factors for SO-.
111-13
-------
b. Carbon Monoxide
For all practical purposes carbon monoxide is insoluble in water.
Therefore, the processes of washout and rainout are insignificant in removing it
from the air. Gas-phase reactions in the troposphere serve as chemical sinks for
CO. In these reactions, CO interacts with the hydroxyl radical to form C02
(Rasmussen, et al., 1974). However, there is much debate about this removal process
as well as its technical accuracy. It is believed that most of the CO that enters
the stratosphere is destroyed (Pressman, et al., 1970).
Soil, and vegetation to a lesser degree, serve as sinks for CO
and thus can be utilized in mitigation techniques. Based on laboratory results, it
has been proven that soil can act as a significant sink for CO. There are two
schools of thought on the subject; Inman and Ingersoll, 1971, believe that the CO
is removed by biological activity while Smith, et al., 1973, using sterilized soil
in their laboratory concluded that soil could act as a sink by a definitely non-
biological pathway. It is evident from the literature that practical research
is needed to determine the ability of in situ soils to serve as a sink for CO.
Vegetation can reduce CO from the atmosphere but not as effectively as soil. The
results of the ability of both to serve as a sink are summarized in Table III-2
of Volume I.
c. Nitrogen Compounds
Of the major nitrogen compounds, N.O is slightly soluble in water
and under normal troposphere conditions, is chemically inert. Therefore there are
no significant removal processes. NO is rather insoluble in water and is either
oxidized to NO™ or photolyzed to N~ in the atmosphere. The N02 is then removed
primarily by precipitation in the form of nitric acid (HNO.j). It can also be
removed by vegetation and soils. The main removal mechanisms for NO and NO^ are
precipitation scavenging, chemical reactions and absorption by plants and soil.
111-14
-------
The main removal mechanism for NO is precipitation. There is
X
no disagreement with this conclusion. However, there are many theories as to the
exact chemical reactions involved. With hydrolysis, the outcome is the same and
the nitric acid formed by the reaction of NO with rain is absorbed onto hygroscopic
particles or it reacts with atmospheric ammonia to form nitrate salt aerosols
(Rasmussen, et al., 1974).
NO can also be removed by chemical reactions in the atmosphere.
A
The primary reaction is its oxidation by ozone to form N02< It can also be
photolyzed to form N which can then react with other NO molecules to.form N . N0_
can also react with ozone to form N0_ or with the hydroxyl to form nitric acid.
In polluted atmospheres, NO and NO. react with SO. and hydrocarbons
to form aerosols. The most important aerosols formed is atomic oxygen which is
free to react with molecular oxygen to form ozone.
In terms of open space techniques for air pollution mitigation,
vegetation and soil can serve as a sink for NO and N0_. There is no valid evidence
of the exact methodology by which vegetation absorbs N02, but from laboratory work
it is evident that it serves as a sink for both NO and NO-. Soil has long been considered
a natural emission for N20, but recently it has been discovered that it also can
absorb NO and N0_. It is believed that the N0_ absorbed will ultimately be oxidized
to nitrate (Nelson and Bremner, 1970). The nitrates eventually decompose'and result
in the production of N0?. NO. is also produced from the absorption of NO from the
atmosphere, but the reaction is almost instantaneous. However, certain alkaline
earth cations can retard this NO- production Sundareson, et al., 1967, found that
alkaline earth zeolites readily absorb NO and release it as NO and HNO_. Much
' x 3
research is needed on the exact mechanisms involved in the use of soil as a sink
for NO and especially on the rule of organic material in the soils to halt or
J\
hinder the production of NO-
f, m
d. Organic Gases (Hydrocarbons)
Reactive hydrocarbons are completely insoluble in water and there-
fore cannot be removed by washout or precipitation. The main removal mechanism is
chemical reaction where some of the gases are transformed in the troposphere to
other gases. For instance, methane has been shown to react with the hydroxyl ion
to form CO (Rasmussen, et al., 1974).
111-15
-------
In terms of open space techniques, there have been recent
laboratory experiments that show that vegetation may be a sink for hydrocarbons
and that soil may use them in bacteriological processes. It is also suggested
that vegetation may serve to retard the natural release of hydrocarbons to the
atmosphere. For instance, tree canopies may prevent sunlight from filtering to
a roadway edge where the light would otherwise cause the reactive hydrocarbons to
form smog. This is a theoretical possibility but the principal is sound.
e. Other Pollutants
There are numerous papers that discuss the capacity of vegetation
and soil to act as sinks for numerous particulates including asbestos, lead and
fluorine (inits particulate form). The photographs in the introduction to this
volume illustrate this phenomenon.
Lead is introduced into the atmospheric compartment of the
roadside environment from exhaust emissions and then transferred to the soil, plant
or animal compartment, via sedimentation, impaction, precipitation or inhalation.
The roadside environment receives lead particles of all classes, the larger ones
by sedimentation and the smaller ones by the latter three processes (Smith, 1975).
Sedimentation and precipitation (washout and washoff) act to
deposit lead particles, primarily in the relatively soluble halide form, on the
soil surface in the roadside environment. Once the lead enters the soil surface,
it is speculated that it may react with soil anions, or with some soil organic
or clay complex (Singer and Hanson, 1969 in Smith, 1975). These reactions would
indicate that the lead is insoluble in the soil and thus preclude its rapid
mobility and restricts plant or microbial uptake.
Lead may also react with sulfuric acid in the atmosphere to
form lead sulfate (Pb SO,). This reaction could also occur at the soil-atmosphere
interface. Reaction with the sulfate anion may occur in the soil in contact with
ground water (Skogorbee, 1974 in Smith, 1975).
111-16
-------
Vegetation has been proved (see especially Smith, 1975) to be
an effective agent to adsorb lead particulates in the atmosphere. It is accumulated
by the vegetative component of roadside ecosystems from both the atmospheric and
soil compartments. Contamination of above ground plant parts from the atmospheric
compartment may be via gravity settling, impaction (kinetic capture/ or precipitation)
Contamination from the atmospheric compartment is also generally considered to
be topical (superficial) in nature and largely susceptible to removal by washing
(National Academy, 1972 in Smith, 1975).
We found no literature on removal of asbestos from the atmosphere.
However, it can be speculated that in the particulate form, it can be removed
from the atmosphere in the same manner as lead. Reaction in the soil compartment
has not been studied so no conclusions can be made relating to this agent serving
as a sink.
There is some evidence that vegetation can serve as a sink for
fluorine. The results indicate that fluorine from the air can be adsorbed to the
surface of leaves (in its particulate form) as well as accumulated internally
(in its gaseous form) and that fluorine in leaves can be translocated outward to
the surface as well as upward to the tips. Fluorine remains in a soluble form in
plant leaves and maintains the chemical properties of free, inorganic fluorine.
The solubility and mobility of fluorine and the ease of removal from plant tissue
indicate that irreversible binding to cellular components does not occur
(Jacobson, et al., 1966).
B. LITERATURE SEARCH FINDINGS
While there are a number of articles on town planning and buffers
to control air qulaity, relatively little work has been done to quantify these
planning proposals. The criteria developed for highway buffers are also applicable
to larger (i.e. regional) open space systems. Essentially,the purpose of both is
similar and the differences are generally those of scale and proximity to
pollutant source.
111-17
-------
Berindan (1969) states:
Numerous authors recommend, at present, the necessity
of a zone which separates air polluting industries from
other urban sectors. This zone is compulsorily provided for
in the management plans of towns of certain countries.
The idea of planting this zone is to increase its protective
efficiency and, consequently, to reduce its surface area,
an essential advantage in view of the crisis of urban areas
which has become generalized in our time.
An example of such a town in the U.S.S.R. is Volgograd, a new town
proposed by Milijutin, considered to be one of the best examples of urban zoning.
The plan of the town locates residential, industrial, railroad access, and park
land in linear bands perpendicular to the prevailing wind and separates industrial
and transportation corridors from residential areas with wide bands of "planted
protection zones."
1. Urban parks play an important role in the reduction of pollutant levels.
Sherman (1972) comments:
Dr. Davidson studied the atmospheric concentration of
sulphur dioxide (S0_) in mid-Manhattan, going from the
Hudson River to the East River along 79th Street downwind.
Remember that this is a single component of the air pollution
load, but an important one associated with the burning of coal
and oil. The significant feature of this study is the
dramatic drop in the S02 level created by the presence of
Central Park in mid-Manhattan. There are no belching stacks
in the park, so being pollution-free itself, it provides
an important, perhaps indispensable, dilution of the rest
of the community's air pollution load. See Figure III-2.
Bach (1972) states:
For Hyde Park, a recreation area of only one square
mile in size in the center of London, an average reduction
in the smoke concentration of 27% was found.
Stanley Tankel (1963) advocates the use of green wedges as opposed to
greenbelts due primarily to the in flexibility of the greenbelt concept in response to
urban growth. Green wedges, radiating from the urban center, can grow with the
demand for urban development. Also, they can respond to regional transportation
systems and provide access to regional open space. See Figure III-3.
111-18
-------
FIGURE III-2
SECTION ALONG 79th STREET, MANHATTAN ISLAND
(AFTER SHERMAN, 1972)
'§
b 2-
CO
!40% dilution of S<
at Central Park
Hudson
River
WEST
Central Park
East
River
EAST
There are apparently no established minimum widths for such wedges. They
are generally dependant upon local physiographic features such as river valleys,
escarpments, flood plains, etc. However, in Hagevik (1974).literature is cited
which observes that a 75% reduction of dust particles occurred within a 600 foot
wide greenbelt. Hagevik also cites a study concluding that the concentration of
pollutants is decreased by half as they pass over 1500 feet of planted land.
Work was also reported which demonstrated that the pollutants from a
phosphorous plant required a buffer of 2540 feet in order to protect a citrus grove
from fluoride. In another study, it was determined that suspended particles
from a dolomite plant required a buffer of 1500 feet in order to minimize impact.
111-19
-------
Wedges
Primary open space:
available natural
features; i.e.
valleys
FIGURE III-3
WEDGES
rivers.
Secondary open space:
transportation related
FIGURE III-4
GREENBELTS
Greenbelts
To contain growth and
separate land use
functions.
111-20
-------
FIGURE III-5
STREET TREE PLANTINGS ARE ENCOURAGED AS
PART OF REGIONAL PLANTING AND BUFFER PROGRAM
Tt was also proposed that a buffer one mile wide be used around a hot mix asphalt
plant in order to minimize particulate pollution.
Such guidelines imply that a great amount of land be used for the
regional buffer systems. If the minimum width for such sinks is established between
600 feet and one mile, depending upon the pollutant source and local conditions
and opportunities many hundreds of square miles would be involved.
system.
However, there are opportunities for other land uses within the buffer
Aside from its function as a pollution sink, the following are all compatible:
2.
.Recreation/Parks
.Cemetaries/Memorial Parks
.Education/Agriculture
.Wildlife Protection
.Protection of Natural Resources
(flood plains, steep slopes, archeological sites,
historic sites, etc.)
.Sanitary Landfill
.Spray Effluent Fields
Planning design criteria for regional buffer systems resulting
from overall consideration of the literature.
a. Radial wedge system based upon natural land features as primary
wedges and planted buffers along major transportation radials augmenting the
system.
111-21
-------
b. Size of wedges determined by local conditions including pollutant
sources and prevailing winds. Minimum width to be set at 600 - 5,000 feet.
Hagevik (1974) feels:
...that the economics of providing buffer zones
to improve environmental quality do not justify locating
them in the most densely populated urban areas. However,
several practical approaches to providing additional
sink potential to a region inlcude:
(1) Thinning existing forest areas to increase turbulance and
increase leaf surface area. Creating openings in dense canopies in order to provide
thermal chimineys and increase exposure of pollution laden air to leaf surface.
Clear cutting edges of existing forests to provide additional edge areas.
(2) Urban street tree programs in order to reduce ambient
pollutant levels. According to Geiger (1950).streets with trees had 1000 - 3000
dust particles/litre; streets without trees had 10,000 - 12,000 dust particles/litre.
Commonly, in areas where street trees are doing poorly, such
as on many city streets, the plants are allowed to die and are not replaced.
Instead, additional trees should be planted to reduce the pollutant burden on the
existing trees by providing adequate leaf surface area to bring pollutant levels
down to a level that can be tolerated by the trees.
C. LAND USE/GREENBELT ORGANIZATION
The literature search findings indicates that the use of greenbelts in
urban areas can have multiple benefits. Planners and engineers have, to date,
recognized the positive contributions of soil retention, physical separations
between non-compatible land uses, climatology, etc. It is now evident that
greenbelts can contribute to the air cleansing process or urban pollutants.
111-22
-------
The land use planning process has utilized many techniques in order
to prepare plans which best serve the interests of the community. Deciding on the
amount of acreage and the location of lands to be used for residences, commercial
establishments and industries, is a fairly straight forward process. Open space
has usually been assigned to serve a recreational need, buffers between different
land uses, or it has been identified as land that does not or is not expected to
experience developmental pressures.
Now that it is recognized that vegetative plantings within a buffer
area can trap particulates and remove other pollutants, the open space land use
takes on an increased level of importance. Within current planning processes,
sufficient quantities of land are reserved to serve population and development
pressures. Ideally, such lands are located in a manner which best serves the
interest of the community, e.g. industrial areas near transportation and utility
arteries; commercial plots near residential centers, etc. Planners can reserve
grecnbelt open space lands using comparable planning design criteria. The particular
technique that would be utilized requires considerable investigation to allow
planners to rationally quantify required areas for greenbelts and to locate them
so that they tend to balance urban pollutant loadings.
Planning design in the previous section calls for urban tree programs
to reduce ambient pollutant levels. Such programs have usually been haphazardly
undertaken based upon vague civic Interest. It should be considered that
rights-of-way along streets systems be put into an active use by being planted.
Such rights-of-way have been used for utility line placement and access, sidewalks,
etc. Street plantings for pollution control should be inventoried and planned
for just as any other land use.
The planning design criteria also calls for the use of radial
wedges to be utilized in consort with major transportation arms and natural land
features. The planners should now look to reserving such lands and, more
specifically, assign a value to them that is comparable with that normally
associated with some of the more dominant land uses.
The value of open space and greenbelts take on added dimension when
land use planners specifically identify their use as air pollution sinks.
Preservation of open space can significantly contribute to the maintenance of air
quality which elevates the value of open space above the historically associated
benefits of aesthetics and recreation.
111-23
-------
The objectives of this strategy is to locate an open space area within
the influence area associated with maximum ground level air pollutants generated
from existing stationary sources. The information required in order to establish
these areas includes:
a. The effective height of the emission source (H)
b. The percentage distribution of 'wind directions experienced at
the given point source of pollution over a period of time (wind rose showing
prevailing wind direction).
c. The Stability Class of the atmosphere - the degree of turbulence
that is experienced during the hours of operation of the source of pollution.
The coordinate system in the Figure II-4 is used in the analysis
of air pollution dispersion. The point identified as (x, 0, 0) is located where
the maximum concentration of pollutants occurs most of the time.given the
prevailing winds and the dominant stability class.
In order to determine point (x,0,0) the following must be known:
a. Effective stack height obtained from area air pollution central
agencies or calculated using the Holland stack rise equation as defined in Appendix D.
b. Prevailing wind direction obtained from area meteorology stations
of published reports.
c. The dominant stability classes obtained from area meteorology
stations are determined from the following table:
TABLE III-3
KEY TO STABILITY CATEGORIES
Surface W,nd
Speed (at 10 m), lncominS Solar Radiation Thinly Overcast
m sec-1
< 2
2-3
3-5
5-6
> 6
Strong
A
A-B
B
C
C
Moderate
A-B
B
B-C
C-D
D
Slight
B
C
C
D
D
Ul
^4/8 Low Cloud
E
D
D
D
— J/8
Cloud
F
E
D
0
The neutral class, 0. should be assumed for overcast conditions during
day or night.
One may start the analysis by selecting the prevailing wind direction
and stability class for the period of time during which the source usually operates.
With these inputs, Figure 111-6, may be used in order to determine x Max (x,0,0).
111-24
-------
FIGURK IH-6
DISTANCE OF MAXIMUM CONCENTRATION ANb MAXIMUM xu/Q AS A FUNCTION OF
STABILITY (CURVES) AND EFFECTIVE HEIGHT (METERS) OF EMISSION (NUMBERS)
111-25
-------
The point x Max merely provides a centroid of pollutant concentrations.
Naturally, the pollutants spread downwind and in a crosswind direction around
this point. The task of designing the actual buffer involves many inputs. As a
starting point, an idealized configuration is as shown in Figure III-7.
FIGURE III-7
TWO DIMENTIONAL RELATIONSHIPS BETWEEN SOURCE,
SINK, AND RECEPTOR LOCATIONS
source
receptor
Under ideal circumstances, theta (•&) should represent a sweep
angle of predominating winds for the site. Where consistent winds are encountered,
will be smaller than where the winds are less limited in their directions.
The land use planner would need to locate all point sources and determine
x Max for each case. The position of sensitive land uses relative to the point
sources, would be plotted and the buffer configuration ideally expanded to shield
the receptor.
If available open space were not at a premium in an urban area, the
logical buffer design would be a series of concentric belts, each with an inside
radius equal to the particular x Max, around each point source.
111-26
-------
FIGURE III-8
IDEALIZED POINT SOURCE BUFFERS WITHOUT
REGARD TO LAND CONSTRAINTS
This seems hardly ever feasible. Therefore, we end up with configurations
such as shown in Figure III-9 where the open space is designed as arcs.
FIGURE III-9
IDEALIZED POINT SOURCE BUFFER WITH LAND CONSTRAINTS
»
I
*
source
4
b
*
a
*
c
The estimation of horizontal dispersion of the pollutants is necessary
in order to determine the arc length of the buffer. The Gaussian dispersion in a
y axis helps determine this arc length of the greenbelt as do variations in prevailing
wind directions (6-). Finally, the space available for placing these buffers will
determine final configurations.
Planning the location of greenbelts can only be done within the
context of the comprehensive land use planning process. The input variables are
of such a magnitude that no generalization can be made other than those outlined
in the foregoing procedures.
111-27
-------
D. CONVERSION OF LEAF AREA TO GROUND AREA AND WEIGHTED SINK FACTORS
The sink and emission factors for soil are reported in this project
relative to the surface area of the soil as a unit of measure. Therefore, the
relative removal rate or the emission rate for soil is reported as micrograms/
square meter/hour. The removal rate or the emission rate, reported for various
types of vegetation is also given in units of micrograms/square meter/hour. However,
in the case of vegetation, square meters refers to the surface area of the leaves
and not the ground area over which the vegetation grows. Therefore, in order to
estimate the gross removal rate, or emission for an open space, it is necessary
to convert to square meters the canopy area (that is, the ground area shaded by the
covering vegetation) to leaf surface area. This requires that one knows the height
and canopy diameter of each species of tree growing on the site. It also requires
knowledge of the relationship between the particular species of vegetation involved
and its leaf area at various stages in its life history. We used the following
process in making required adjustments which allow us to draw general conclusions
from the available literature. In addition to determining the relationship
between canopy area and leaf area, it is also necessary to determine average removal
and emission rate for various general types of vegetation. This is important because
the literature does not contain much specific information about more than a few
species of plants. Taken together then, determination of a typical leaf surface
area for an open space, in combination with a typical removal or emission rate
for the same area, will allow us to estimate the rate of removal for certain
specified pollutants. Table III-ll,entitled SUMMARY OF SINK AND EMISSION FACTORS
FOR NATURAL ELEMENTS , appeared in Volume I and it has been used here as the basis
for a further modification, adapting it more directly to an integrated use in
conjunction with estimation of leaf surface areas. That Summary Table is based
upon selective averaging of the sink and emission factors for each pollutant under
consideration. It was meant as a first rough approximation of the broadest inter-
pretation of the reviewed literature and must be utilized with that caution in mind.
It reflects the factors associated with both deciduous and coniferous trees as well
as shrubs and various ground covers treated by the literature. Therefore, in order
to make the summary table more applicable to an evaluation of woody plants in open
spaces, it was determined to modify the Summary Table slightly in the following way.
111-28
-------
The average value for vegetation or soil serving as a sink for each of the
pollutants, was taken directly from the Table. The detailed tables of emission
and sink factors, which also appear in Volume I, Section III, were reviewed and
where specific or general averages were available relating to the specific
pollutants, these figures were also considered in creating a new average sink rate
as shown on Table III-4 in this Volume. The end result is that based on the
available literature,the average sink or emission rates are weighted toward the
vegetation or soil which we would most likely expect to find in an open space
project in St. Louis, Missouri. This project area is further defined
in Volume III of this report.
In order to estimate the sink capacity of some representative vegetation,
it is necessary to relate total leaf area to canopy diameter. This relationship
can be made for several representative trees based upon information provided by
Rich (1970) and Monteith (1976). They have reported ratios of the surface area of
certain trees to their height and canopy diameters. The logic of our approach
to this analysis, and the use of Leaf Area Indexes, is detailed in Appendix C of
this Volume. Here, the conclusion of that interpretation has been used to create
Table III-5.
111-29
-------
TABLE III-4
WEIGHTED SINK AND EMISSION FACTORS FOR AVERAGE SOIL AND
AVERAGE VEGETATION BASED ON DATA REPORTED IN VOLUME I
POLLUTANT
ECOSYSTEM ELEMENT
REMOVAL RATE
REFERENCE
CARBON MONOXIDE
Vegetation
Vol.1 (Table III-11)
Average Unspecified
Weighted Average
2.5 x 10 yg m
2.75 x 103 yg m"
3 -2-1
2.6 x 10 yg m hr
1 rBidwell & Fraser, 1972
'1 \Ziegler, 1975
Soil
Vol. I (Table III-11)Average
Forest soil - Charlton
Forest/field soil
Columbia, Mo.
Mt. Olive, Miss.
Weighted Average
2.0 x 104 yg m 2hr l
2.2 x 104 yg nf^r'1
8.0 x 10 yg m^hr"1
3.82 x 104 yg m~2hr~L
1.52 x 10 yg m~ hr~
4 -2-1
1.9 x 10 yg m hr
rHeichel,1973a
LHeichel,1973b
Heichel,1973b
Ingersoll, 1972
Ingersoll, 1972
NITROGEN OXIDES
Vegetation
Vol. 1 (Table III- 11) Average 2 x 1C3 yg nf
Unspecified
Unspecified
Weighted Average
7.42 x 1Q yg nhr"
3 -2 -1
4.09 x 10 yg m hr
3 -2 —1
2.3 x 10 yg m hr
Heggestad, 1972
Dochinger, 1974
Soil
Vol. 1 (Table 111-11) Aver age 2.0 x 102 yg
OZONE
Vegetation
Vol. 1 (Table III-11)Average
white oak
white oak
sugar maple
sugar maple
Ohio buckeye
Ohio buckeye
sweet gum
sweet gum
8.0 x 10 yg nfr"
6.35 x 104 yg m'^r"1
1.32 x 105 yg nf^r'1
3.71 x 10 ug m hr
8.63 x 104 yg nf^r'1
3.62 x 104 yg nf^r""1
9.27 x 104 ug m"2^"1
Townsend, 1974
Townsend, 1974
Townsend, 1974
Townsend, 1974
Townsend, 1974
Townsend, 1974
Townsend, 1974
2.78 x 10 ug m 'hr
4 -2-1
8.54 x 10 ug m hr Townsend, 1974
111-30
-------
POLLUTANT
ECOSYSTEM ELEMENT
REMOVAL RATE
REFERENCE
OZONE (cont.)
Vegetation
red maple
red maple
white ash
white ash
Weighted Average
2.72 x 10 yg
5.55 x 10* yg
2.39 x 104 yg
5.62 x 104 yg
6.2 x 104 yg n
Townsend, 1974
Townsend, 1974
Townsend, 1974
Townsend, 1974
Soil
Vol. 1(Table I11-11)Average
Q -2-1
1.0 x 10 yg m hr
PAN
PARTICULATES
Vegetation
Vol.(Table III-11)Average
Vegetation
Vol. 1 (Table III-11)Average
hardwood canopy
conifer canopy
chestnut
tuliptree
Weighted Average
, _ . /-Jenson, 1973
1.2 x 10 yg m hr j^Hill, 1971
4.0 x 10 yg nT
1.79 x 103 yg nf
6.28 x 103 yg n
2.74 x 103 yg m'
3.0 x 102 yg m'
2.5 x 103 yg m'
Dochinger, 1972
Dochinger, 1972
Chasseraud,1958
Wedding,et al.,1975
SULFUR DIOXIDE
Vegetation
Vol. 1 (Table III-11)Average
forest(unspecified)
vegetation (unspecified)
vegetation (unspecified)
Weighted Average
5.0 x 10 yg nfr"
3.33 x 103 yg m'^r"1
1.47 x 104 yg tn'^r"1
] .45 x 10 yg m hr
4.1 x 104 yg n^hr"1
Davis, 1975
Dochinger, 1974
Jensen, 1973
Soil
Vol. 1 (Table III-11)Average
oolitic limestone
acid soil (unspecified)
Weighted Average
1.15 x 10 yg
1.68 x 105 yg
1.15 x 107 yg
7.7 x 106 yg n
Spedding, 1969
Bohn, 1972
111-31
-------
TABLE III-5
SPECIES RELATIONSHIP OF GROUND AREA COVERED TO PLANT SURFACE AREA
SPECIES
HEIGHT
GROUND AREA COVERED
PLANT AREA
Maple
(Acer plantano-ides)
Oak
(Quercus robur)
Poplar
(Populus tremula)
Linden
(Tilia cordate)
Birch
(Be tula vevrufiosa)
Pine
(Pinus sp.)
6m
6m
6m
5m
5m
3m
7
7
7
4
4
1
. 1m
. 1m
. 1m
.5m2
.5m
.8m
36.8m2
36.1m2
52.5m2
23.0m2
27.2m2
4.2m2
Having weighted sink factors and a relationship of total leaf area to ground area,
we can develop the following table:
TABLE III-6
SELECTED TREES AS POLLUTION ' SINKS
ug/hr
TYP ftons/vr)
One maple tree (6 m high)
sulfur dioxide
participates
carbon monoxide
nitrogen oxides
ozone
PAN
One oak tree (6 m high)
sulfur dioxide
particulates
carbon monoxide
nitrogen oxides
ozone
PAN
1.5 x 19*
9.4 x 10*
9.6 x 1CK
8.5 x lo£
2.3 x 10°
4.4 x 10
1.5 x lOJj
9.0 x 10J
9.4 x lo£
8.3 x HT
2.2 x 10°
4.3 x 10^
1.0 x 10~2
9.0 x 10~7
9.0 x 10"?
8.0 x 10";
2.0 x 10 ,
«£L
4.0 x 10 *
1.0 x 10"?
9.0 x 10~£
9.0 x 10~^
8.0 x 10,
2.0 x 10 7
— /*
4.0 x 10
111-32
-------
TABLE III-6(cont)
*Conversion of pg/hr to tons/yr.
pg/hr x gm/106PB x lb/453.59 gm
x T/2000 Ibs x 24 hrs/day
x 365 days/yr = T/yr
ug/hr
TYP (tons/yr)
One poplar tree (6m high)
sulfur dioxide
particulates
carbon monoxide
nitrogen oxides
ozone
PAN
One linden tree (5 m high)
sulfur dioxide
particulates
carbon monoxide
nitrogen oxides
ozone
PAN
One birch tree (5 m high)
surfur dioxide
particulates
carbon monoxide
nitrogen oxides
ozone
PAN
One pine tree (3m high)
sulfur dioxide
particulates
carbon monoxide
nitrogen oxides
ozone
PAN
2.2 x 10^
1.3 x 103
1.4 x 103
1.2 x 10£
3.3 x 10
6.3 x 10
9.4 x 10^
5.8 x 107
6.0 x 10?
/i
5.3 x 107
1.4 x 10°
2.8 x 10
1.1 x 10?
6.8 x 107
7.1 x 10,
6.3 x 10^
1.7 x lo£
3.3 x 10
1.7 x HTJ
1.1 x 10J
1.1 x 107.
9.7 x 105
2.6 x 10-
5.0 x 10J
2.0 x 10"
i.o x io~;r
1.0 x 10 ^
1.0 x 10~2
3.0 x 10"
6.0 x \0
9.0 x 10"^
6.0 x 10 ~7
^£l
6.0 x 10 7
5.0 x 10~2
1.0 x 10~
3.0 x 10
1.0 x 10"
7.0 x 10 7
7.0 x 10~7
mm/I
6.0 x 10_2
2.0 x 10~,
3.0 x 10
2.0 x 10~,
1.0 x 10~*
1.0 x 10"^
9.0 x 10"
3.0 x 10"
5.0 x 10"3
111-33
-------
GLOSSARY
IV-1
-------
AIR POLLUTION - Contamination of the air by liquids, solids and/or gases at
unexceprably high levels (except water in its several phases) or in unnatural,
anthropogenic forms. Typical natural contaminants are salt particles from
the oceans or dust and gases from active volcanoes. Typical anthropogenic pollutants
are waste smokes and gases formed by industrial, municipal, household, and
automotive combustion processes.
BUFFER - Used here to mean land used to separate one land usage from another.
Especially relating to open space used to insulate one land use from a contiguous
land use.
CONIFEROUS - Refering to cone bearing trees. Generally, evergreen needle-leaved
vegetation.
D.B.H. - diameter breast height - The diameter of the trunk of a tree measured at
approximately 4.5 feet above the ground.
DECIDUOUS - Refering to those plants which shed their leaves seasonally. Generally,
plants other than evergreens.
GLABROUS - Smooth, without fuzz or hair.
GREENBELT - In this report, an open space land use within, or around, urban growth
and separating one land use from another. Usually, an open space band at least
a few hundred feet wide and of variable length.
LENTICLES - Corky spots on young bark, corresponding in function to stomata on
leaves (i.e. relating to gas exchange).
LEAF LAMINA - The flattened body of a leaf. A leaf consists of a stem (stalk or
petiole) and a lamina.
OPEN SPACE - In this report, a park or natural area unoccupied by formal structures
and generally unspoiled and permitting the natural processes of animal and plant growth.
PARTICIPATES - Minute and separate particles which may be viable (e.g.. pollen,
bacteria, viruses, protozoans, etc.) or non-viable, (e.g. mineral dust, metals, etc.)
and which are readily transported. Generally, sizes of particulates range between
0.0005 and 500 micrometers in diameter.
PHOTOSYNTHESIS - The process by which green plants convert water and carbon dioxide
into sugars and oxygen.
PETIOLE - The stem of a leaf.
SHELTER BELT - A linear planting of shrubs and trees generally parallel to
agricultural fields to protect them from winds (i.e. a windbreak).
STOMATES-(vernacular; sing, stoma; pi. stomata) - A microscopic opening generally
on the lower surface of leaves, through which there is a gaseous interchange
between the atmosphere and the interior of the leaf.
TRANSPIRATION - The movement of water from the internal circulation of a plant
through its surfaces (such as the leaves) into the atmosphere as water vapor.
IV-2
-------
BIBLIOGRAPHY
V-l
-------
Aldaz, L. 1969; "Flux measurements of atmospheric ozone over land and water."
J. Geophys. Res.. 74(28);6943-6946.
American Horticultural Society. Transit Planting: A Manual. Urban Mass Transportation
Administration, U.S. Dept. of Transportation. Urban Mass Transportation Demonstration,
Project //UA-06-0006. (No date).
Babich, H., and G. Stotzky. 1974. "Air pollution and microbial ecology." Critical
Rev. Environ. Control, 4(3);353-421.
Bach, Wilfred. 1972- "Planning and air pollution control." In: Atmospheric
Pollution. McGraw-Hill, New York, pp. 116-130.
Bates, D.R., and A.E. Witherspoon. 1952. "The photochemistry of some minor
constituents of the earth's atmosphere." Mon. Notic. Roy. Astron. Soc., 112;
101-124.
Bennett, J.H., and A.C. Hill. "Interaction of gaseous air pollutants with
canopies of vegetation." Agricultural Environmental Quality Institute, NE
Region Agricultural Research Service, USDA, Md., 45pp.(No date).
Berindan, Cornelia 1969- "Interrelationship between air pollution and green spaces
as criteria for protecting industrial cities." Pollution Atmospherique. 11(43);
143-153.
Bernatzky, A. 1968- "Protection plantings for air purification and improvement
of environmental conditions." Tree J., ,2:37-42.
Bernatzky, A., "Climatic influence of the greens and city planning." Garden
and Landscape Architect, pp. 29-33. (No date).
Beytia, E., P. Valenzuela, and 0. Cori. 1969. "Terpene biosynthesis: formation
of Nerol, Geraniol, and other prenols by an enzyme system from Pinus radiata
seedlings." Arch. Biochem. Biophys.. 129:346-356.
Bidwell, R.G.S., and D.E. Fraser. 1972. "Carbon monoxide uptake and metabolism
by leaves." Can. J. Botany. 50(7); 1435-1439.
Blenk, H., and H. Trienes. 1955. "Windschutz. darstellung der strdmungen."
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U.S. Bureau of Mines. 1971. Minerals Handbook. U.S. Govt. Printing Office,
Washington, D.C. (No pages).
U.S. Environmental Protection Agency. 1970. "Workbook of atmospheric dispersion
estimates." Research Triangle Park, North Carolina.
U.S. Environmental Protection Agency. 1973. "Compilation of Air Pollutant
Emission Factor." Research Triangle Park, North Carolina.
V-12
-------
U.S. Environmental Protection Agency. 1975. Supplement #5 for compilation of air
pollution emission factors. Office of Air and Waste Management, Research
Triangle Park, North Carolina, 2nd edition, approx. 200 pp.
University of Mass., U.S.D.A. Forest Service, and Mass. Dept. of Natural Resources.
1970. A symposium on trees and forests in an urbanizing environment, U. of
Mass., 168 pp.
Unsworth, M.H., P.V. Biscoe, and H.R. Pinckney. 1972. "Stomatal responses to sulphur
dioxide." Nature. 239;458-459.
van der Linde, R.J. 1958. "Het probleem van houtopstanden in net cultuurlandschap."
(The problem of shelterbelts in cultivated areas). Centrum voor landbouwkundige
documentatie, No. 21., 44 pp.
van Eimern, J. 1957. "Uber die Veranderlichkeit der Windschutzwirkung einer
Doppelbaumreihe bei verschiedenen meteorol. Bedingungen. "(On the variability
of shelter effect of a double-tree row at different meteorol. conditions).
Berichte Deutsch. Wetterdienst, 5(32), 21pp.
van Eimern, J., R.Karchon, L.A. Razumova, and G.W. Robertson. 1964. "Windbreaks
and shelterbelts." Secretariat of the World Meteorological Organization,
Geneva, Technical Note No. 59, 188 pp.
Voorhees, Alan M. and Associates, Inc. 1971. A guide for Reducing Air Pollution
through Urban Planning, pp. 2-35. (No publisher).
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Warren, J.L. 1973. "Green space for air pollution control." North Carolina
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The Curwen Press, London. (Number of pages unknown).
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Went, F.W. 1960. "Blue hazes in the atmosphere." Nature, 187(4738);641-643.
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V-13
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Oxford, England, pp. 137-161.
V-14
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APPENDIX A
HIGHWAY DIFFUSION MODELS
VI
-------
I. INTRODUCTION
The purpose of Appendix A is to investigate the possibilities of incorporating
vegetation sink factors for air pollutants into four(4) atmospheric dispersion models
that predict carbon monoxide (CO) concentrations from highway sources. These models
include 1) the EPA HIWAY model,2) the California Line Source Model,3) the SRI Street
Canyon model and, 4)Emp 1, an emperical model.
These models are reviewed by Noll et al.(1975), and a discussion of each
follows,
A. EPA MODEL
The EPA HIWAY computer program serves to estimate nonreactive air pollutant
concentrations downwind from a highway line source of some specified finite length.
Concentration is calculated not as the result of a continuous line source as such, but
rather by the approximation of the line source by a finite number of evenly spaced
continuous point sources of strength equal to the total line source strength divided
by the number of sources used to simulate the line.
The model itself considers each lane of traffic as an individual line
source. Thus, traffic estimates for each lane are required. Total concentration
is calculated using superposition, i.e., concentrations from the separate line
sources are additive.
Because of the physical significance of mechanical mixing above the
roadway, some initial values of vertical and horizontal dispersion parameters must
be assumed to allow the plume to conform to the actual plume shape encountered. To
accomplish this, the point sources are displaced by some virtual distance to the rear
such that sigma z and sigma y have an initial value at roadside.
With the exception of receptors directly on the highway or within
the cut, the model is applicable for any wind direction, highway orientation, and
receptor location. The model was developed for situations where horizontal wind flow
occurs. The model cannot consider complex terrain or large obstructions to the flow
such as buildings or large trees.
VI-1
-------
The EPA HIWAY model simulates a highway with a finite number of point sources
and calculates the downwind concentration from each point using the Gaussian point
source diffusion equation. The total contribution of all points Is calculated by
a numerical integration of the Gaussian point source equation over a finite length.
The coordinates of the end points source equation over a finite length. The coordinates
of the end points of a line source of length L, representing a single lane, extending
from point A to B (see Figure VI-1) are R., S , and RR, SB- The direction of the
line source from A to B is 3. The coordinates R, S of any point alcng the line at the
arbitrary distance I from point A are given by:
R = R + I Sin 8
S = SA + £ cos B (2)
Given a receptor at R. , S, , the downwind distance, x, and the crosswind
, y, of the receptor from the point R, S for any wind direction 9 Is given by
S = SA + £ cos B
distance, y, of the receptor
x = (S - Sk) cos 0 + (R - Rk) sin 9 (3)
y = (S = Sk) sin 9 - (R - Rk) cos 9
Since R and S are functions of £, x and y are. also functions of SL. The concentration,
X from the line source is then given by:
/
(5)
where for stable conditions or if the mixing height is greater or equal to 5000 meters:
VI-2
-------
FIGURE VI-1
LINE SOURCE AND RECEPTOR RELATIONSHIPS
FOR EPA HIWAY MODEL
NORTH
WIND
RECEPTOR
(
(RB,SB)
EAST
SOURCE: (Noll, et al., 1975)
VI-3
-------
!
2iro o exp
y z
~-i~M
_ 2 I',/
7
s
r^
exp
exp
lfz-»-Hl V ,fiv
- ^ -r-l f (6)
where H = height of the road above ground level, m
z = height of the receptor above ground level, m
a & a = horizontal and vertical dispersion parameters,
' respectively, m.
In unstable or neutral conditions, if a is greater than 1.6 times the mixing height,
Z
L, the distribution below the mixing height is uniform with height regardless of
source or receptor height provided both are less than the mixing height:
(7)
In the above equations, a and a are evaluated for the given stability class
y z
and the distance x + b for a and x + a for a . A and b are the virtual distances
required to produce the initial a and a respectively.
The value of the integral (Eq. 5) is approximated by use of the trapezoidal
rule. Let A2, = L/N. Then the trapezoidal approximation gives:
X =
N-l
(8)
where f. is evaluated from the appropriate Equation 6 or 7 for Si + iAfc. x and y
are functions of £.
For a given initial choice of the interval length, A£, the calculation is
then successively repeated with twice the number of intervals, that is, with At/2,
M/4..., until the concentration estimates converge to within 2 percent of the previous
estimate. This value then represnets the true value of the integral.
VI-4
-------
The above evaluation of the Integral is repeated for each lane of traffic
and the resulting concentrations summed to represent the total concentration from
the highway segment.
B. CALIFORNIA MODEL
The California model calculates pollutant concentrations generated by
motor vehicles within a microscale highway corridor. The mathematical model, which
is based on the Gaussian infinite line source diffusion equation, calculates hourly
concentrations of pollutants within a turbulent mixing cell above the highway as
well as at receptor points at given distances downwind.
In the crosswind case, the mixing cell concentration is determined by the
wind speed and pollutant emission rate of the vehicles. Dispersion downwind is
dependent on the atmospheric stability classification. In the parallel wind case,
the California model accumulates pollutants within the mixing cell to account for
downwind buildup. Pollutants are then dispersed latterally at a rate dominated by
stability class. The computerized model is capable of estimating pollutant concentrations
where the winds are either parallel or at an angle to the highway alignment and where
the highway section may be at grade, elevated or in a cut.
The California model uses separate equations for calculating pollutant
concentrations under crosswind and parallel wind conditions. The most general form
of the crosswind equation has the form of the Gaussian line source equation:
2 K az Us1n *
exp - ( + exp -
(9)
where C = concentration of pollutant gm/m
Q = emission source gm/sec-m
= wind speed m/sec (1 mph = 0.447 m/aec)
K = empirical coefficient = 4.24
ij> = angle of wind with respect to highway alignment
a z = vertical dispersion parameter, in meters
H = height of highway above surrounding terrain, in meters
z = height of receptor above surrounding ground surface, in meters
VI-5
-------
For the parallel wind case, the California model accounts for a buildup
of pollution concentration within the mixing cell. The estimated concentrations
within the mechanical mixing cell for aprallel winds, where the ratio of 30.5/W is
less than or equal to one, can be determined from the following equation:
C- A & 1 30.6 (10)
U * w
where C = concentration of pollutant (gm/m3) within the mechanical mixing
cell
= wind speed (m/sec)
K = empirical coefficient 4.24
W = width of roadway from edge of shoulder to edge of shoulder,
in meters
A = downwind concentration ratio for parallel winds (accumulation
term) is defined as C K W .
Q 30.5
30.5 = the initial width (meters) of the highway used for the finite
element of area in developing the model for parallel winds
Q = source emission strength (gm/sec)
For parallel winds, the source emission strength (Q) is calculated using
the following equation:
Q = {emission factor} x {vehicles/hour} x {5.26 x 10~ } (11)
Where the numerical constant is a factor to convert units of the product (vph)
(gm/mi) to gm/sec for a length of highway of 100 feet.
To estimate the ground level pollutant concentration at a distance away
from the highway (when the wind is parallel to the alignment) the following equation
is used.
exp - j- (=5-
(12)
VI-6
-------
where ppm = concentration of CO at the highway within the mechanical mixing
me , ,
cell
Y = normal distance in meters from receptor to near edge of highway
shoulder
o ,o = horizontal and vertical dispersion parameters in meters. These
y Z values are obtained from empirical data depending on the receptor's
normal distance (Y) from the highway and on the stability class.
The California model reduces to two simpler equations when one solves for
at-grade cases. For mixing cell concentrations with crosswinds, equation (9) reduces
to:
Cmc = * .Q , grams/cubic meter (13)
K, 1 11 sin 4p
where Q = source strength, grams /meter-second
K = empirical constant = 4.24
y - wind speed, m/sec
<() = wind angle with respect to road (90° for winds perpendicular to the road)
For downwind ground level receptors and at grade highways for crosswinds, equation
(13) reduces to:
K a zy sin (j»
where az = vertical dispersion parameter, meters
C. MAJOR DIFFERENCES IN THE MODELS
The major differences in the two models are outlined
California's model uses a Gaussian line source equation while EPA uses
an integrated point source equation. As a result, the California model requires
separate equations for predicting under crosswind and parallel wind conditions while
EPA's model needs only one equation. The California model uses a wind angle of
12.5° with respect to the road as the boundary separating the two regions within
which different equations are used. As a result, a discontinuity occurs at 12.5
between the concentrations predicted by the two equations.
VI- 7
-------
EPA's HIWAY model requires separate traffic and emission data for each
lane of the highway. Downwind concentrations are calculated by superimposing the
separate pollutant contributions of each traffic lane. California's model uses the
total traffic volume and emission rate for all lanes combined, assuming that all
emissions are initially dispersed from a uniform "mixing cell" extending from road
shoulder to shoulder (for medians <30 ft.).
Initial dispersion of pollutants at the roadside edge is handled differently
in the two models. The EPA model uses a virtual source correction providing an
initial a =1.5 meters. The California model assumes a "mixing cell" with initial
z
az = k meters. (See Figure VI-2).
Downwind dispersion is described by the empirical dispersion coefficients,
a and a . Both models use different dispersion coefficients.
y z
D. MODEL ASSUMPTIONS
The following basic assumptions are common to both models.
1) The mass of pollutants is conserved throughout the downwind length
of the plume. No material is lost by reaction or by sedimentation.
2) The ground surface, when encountered, is a perfect plume reflector.
3) There exists no wind shear in the vertical direction. The wind velocity
used should be representative of the average wind velocity between ± sigmaz from
the plume centerline in the vertical sense.
4) Dispersion occurs only by turbulent diffusion which varys according
to Pasquill's atmospheric stability categories.
5) Atmospheric stability is constant within the mixing layer containing
both sources and receptor.
6) There exists no mixing of material in the x axis (i.e., longitudinal
mixing).
7) Emissions are from continuous sources.
8) The dispersion parameters sigma and sigma are good for modeling
y z
atmospheric dispersion over flat, grassy terrain with no significant aerodynamic
roughness nor any artifical vertical instability induced by heat island effects
associated with urban areas.
VI-8
-------
FIGURE VI-2
DISPERSION FROM VIRTUAL IMAGE (EPA MODEL)
AND MIXING CELL (CALIFORNIA MODEL).
Virtual
Image
of
Plume
EPA Model
Htxlng Cell
/=A
(00 OCA
yEEz^E^
Plume
California Model
SOURCE: Noll, et al., (1975)
VI-9
-------
E. SRI STREET CANYON SUBMODEL
Stanford Research Institute's (SRI) Street Canyon Submodel was determined
from an experiment conducted by Stanford Research Institute in San Jose, California
in 1971 to estimate the dispersion of vehicular carbon monoxide emissions within a
city street canyon. For this work air motion within the canyon was believed to be a
single-helical circulation. As shown in Figure VI-3, this helical air circulation
gives substantially higher concentrations to receptors on the leeward side (right
side of the figure) than on the windward side (left side of the figure) because of the
reverse flow component across the street, near the surface. This model assumes that
the measured concentration, C, at the receptor is derived from two components. One
components is contributed from a background concentration, C.. , in the air entering
the canyon from above, and the other concentration component, AC, is supplied from
locally generated vehicular pollutant emissions, Q, in the street.Hence, we have
C = Cfek + AC (15)
This model calculates the concentration component fron the vehicular
emissions at a given receptor location by three different equations. Different
equations are used depending on whether the wind directions are parallel or crosswind
with respect to the road angle and whether receptor locations are on the leeward or
windward side of a canyon.
1. Leeward Case.
A leeward case equation is employed to calculate concentrations,
AC, from local vehicular emission for crosswinds (wind directions greater than 30
with respect to the road) and the receptor side of the highway where reverse air
movements within the canyon transports vehicular emissions directly to the receptor.
This equation can be represented by a simple box model form.
ACL = Q/UgY (16)
VI-10
-------
FIGURE VI-3
SRI STREET CANYON DESCRIPTION
Canyor
Walls
Windward
Side
Mean Wind
Leeward
Side
Canyon
Walls
where
U
s
Y =
SOURCE: (Noll et al., 1975)
concentration component from the vehicular emissions
for a receptor on the leeward side of the highway
rate of vehicular pollutant emissions
mean wind speed near the street
depth of mixing volume
The leeward case model was then determined by SRI to be as follows:
K x Q
where
where
Q
U
(U + 0.5) x (X2
LQ)
(17)
rate of vehicular pollutant emissions in the street (gm/ (m-sec)).
rooftop wind speed (m/sec.), 0.5 m/sec. is due to the influence
of the vehicles forward motion. Therefore, U of the box
model - k!(U + .5). s
horizontal distance from the receptor to the center of the nearest
lane (m) .
vertical distance from the road to the receptor (m) .
VI-11
-------
where L = two meters, the dimension where vehicular emission was assumed
completely mixed. Therefore, the depth of mixing volume (Y)
from a box model . kz((x2 + Z2)% +
2. Windard Case.
A windward case equation is for crosswind directions and for receptors
located on the windward side. Similar to the previous leeward case, a box model concept
was also used for fomulation of this equation, where the depth of mixing volume is
considered to be constrained by the canyon's size.
AC = K x Q (H - Z) (18)
W x (U + .5) " X H
where AC = vehicular emissions concentration component for receptors
on the highway's windward side.
W = width of canyon (m).
H = average building height or depth of depressed highway (m).
3. Parallel Case.
A parallel case equation was determined for wind directions within
- 30° of the highway angle and for prediction of concentrations at receptor locations
on either highway side. This equation predicts parallel wind concentrations by taking
an average of the leeward and windward equation.
AC.J. = JS(ACL + ACW) (19)
where AC = the parallel wind concentration component from the vehicular
emissions.
F. EMPRICAL MODEL
As a result of the work accomplished by Noll, et al., (1975) an empirical
model was developed to predict CO concentrations from a highway source. This empirical
model, called EMP-1, was derived from simple dimensional analysis and has the form:
VI-12
-------
C a _ k Q (20)
U (X/sin 0)a
where C = concentration at ground level from an at-grade highway, ug/m
Q = pollutant emission rate, ug/m-sec
U = mean wind speed normal to the road, m/sec
X - distance from center of the road to the receptor
0 = the angle of the wind with respect to the road, degrees,
K & a = empirical coefficients
A regression analysis was performed on In (CD /Q) versus In (X/sin 0)
using 524 measurements during perpendicular and oblique wind conditions by Noll,
et al., (1975). The values obtained for the slope of the regression line a = -1.106
and the intercept k = 8.18 were used to calibrate the model. The final equation
for EMP-1 was
C 8.18Q
U (X/sin 0) 1.106
II. INCORPORATION OF SINK FACTORS IN MODELS
The following discussion and calculation are an attempt to incorporate sink factors
into the four models previously discussed. A few words of caution are needed before
presenting these ideas. First, it should be noted, that the state of the art of
using sink factors is not advanced to the point where one can confidently predict
the amount of pollution that will be adsorbed or absorbed by a given species of
vegetation. Much more research is needed in this area. Secondly, using buffer strips
near highways, changes the aerodynamics of the plume generation by the highway.
Most of the models discussed in the previous section are valid only for flat terrains
with no interference. By using buffer strips, the models themselves are not accurate.
Thirdly, once the plume enters the buffer strip area, its characteristics will change
drastically. The vegetation will create changing flow patterns as the plume travels
amongst the trees. Thermal chimney produced by gaps in the buffer strip will produce
additional changes in the plume. Therefore, it is almost impossible to predict the
exact characteristics of the plume and its interaction with the vegetation. Given the
above considerations, it is easy to conceptualize that incorporating sink factors into
mathematical algorithm to predict concentration of CO from highways is no easy task.
VI-13
-------
The methodology discussed in the remainder of this section for incorporating
sink factors into the four models is an initial attempt to perform this task. The
models should only be used for planning purposes and not to predict exact concentrations
of CO. Further research is needed to colaborate these proposed model modifications.
A. GENERAL THEORY
For the California Line Source Model, the EPA HIWAY Model, and the
Empirical Model EMP 1, there are two modifications that must be discussed. The
first modification is the determination of the portion of the plume that will enter
the buffer. The second modification is the development and incorporation of a
pollution sink factor into the highway emission rate.
To determine the portion of the plume that will be effected by the planting
of vegetation, it can be seen from the following illustration that Area A of the plume will
be unaffected where as Area B will be affected.
mixing If
cell
Area A
Area B
TOTAL AREA
4L
0 0 z
0 (62-H)
(5-4)-4L0 - JjL0 (H-4)
4L
4L
(H-4)
(6z-4)
. * ,P . u
Fraction of Pollution Entering Trees if az> H =
(H-4)
4L0 +
(oy-4)
(22)
The quantity of pollution leaving the buffer (Q2) can be determined by the
inclusion of the buffer sink factor (SLA) into that portion of the highway emission
rate (Q) that is affected by the buffer strip
VI-14
-------
4L, + !*„ (H-4)
«2-«l 4L° + ^ (T.-4) - (SLA)
2
where S = Buffer sink rate - gm/sec-m of vegetation
L = Depth of Buffer, m
A = Canopy Area Index, m^ canopy area/nr land
In other terms SLA is the quantity of pollution absorbed by a buffer,
of a specific depth (L), per length of highway. Essentially, Q2 is the quantity
of pollution remaining in the air as the air leaves the buffer strips.
B. EXAMPLE OF CALIFORNIA MODEL, EPA MODEL AND EMPIRICAL MODEL
The EPA HIWAY Model, the California Line Source Model and the Empirical
Model will be evaluated using a hypothetical 2 lane highway with a peak hour traffic
volume is 2,000 vehicles. The meteorological conditions used are a 6m/sec wind
approaching the highway 22*5° adjacent to the road with a stability classification
of D.
The buffer of trees used to demonstrate their effectiveness in removing
carbon monoxide from the atmosphere will start 10 meters from the highway shoulder
and continue to a depth of 100 meters. The receptor will be located 110 meters from
the shoulder of the highway.
For the sake of analysis, the make-up of the buffer will consist of 344
deciduous (oak, maple, poplar, birch,linden) and 700 pine trees for every hectare.
The absorptive capacity of such a planting for carbon monoxide has been determined to
be 6.328 x 10~6 gr/sec-m2 vegetation.
As the plume leaves the highway, part of the plume will escape the influence
of the buffer and the remainder of the plume will be trapped by the buffer. To
calculate the fraction of the pollution captured by the buffer, the equation (23) and
the following data will be used.
L = 10m H = 6m T_ = 7m
o z
VI-15
-------
By dividing the areas of the two trapazoidal areas between the mixing cell
and the buffer, the fraction of entrapment can be calculated.
10m x 4m + h x 10m2 x 2m _50_ _
Fraction of entrapment = i0m x 4m + J* x 10m x 3m " 55
For these specific meterological conditions, approximately 91% of the
pollution being emitted by the highway is being entrapped by the buffer.
Once part of the plume reaches the buffer, the trees start to absorb
the carbon monoxide at a hypothetical rate of SLA. For this buffer arrangement
(S) has a value of 6.328 x 10~6 gr/sec-m2. The buffer depth (L) is 100m and the
Canopy Area Index has a value of 1.5 m2/m2. Combining these three parameters yields
a value for SLA of 9.49 x 10"^ gr/m-sec.
As previously mentioned the example highway is carrying 2000 vehicles/hour
and if each car is emitting 42.8 gr/veh-km, the highway emission rate, Qi, will be
0.024 gr/m-sec. Since the Q,, SLA, and the fraction of entrapment have been calculated,
the emission rate after the buffer (0.2) can be calculated.
Q2 = .910.J - SLA (24)
Substituting previously defined values of Q]_, SLA, 0.2 can be calculated
to be:
Q2 = .91 (.024) - 9.49 x 10~4 gr/m-sec
Q- = .0209 gr/m-sec
To summarize,the following parameters have been defined for the
hypothetical situation:
U = 6m/sec QL = .024 gr/m-sec. SLA = 9.49 x 10~4 gr/m-sec
(ft = 22*5° Q2 = -0209 gr/m-sec.
1. Solution of California Line Source Model.
By determining the vertical dispersion coefficient (QZ) at .11 km normal
the road to be 13 m, the concentration of carbon monoxide for a bare road side can
to
VI-16
-------
be calculated by using equation ( 14 ) .
C =1.06 Qj (4)
>
<*>
4.24 U sin 4> az
804.
4.24 (6)(.382)(13)
If Q2 is substituted for Qj, the concentration 100m deep in the
buffer can be calculated.
C = 1.06 Q2 4
4.24 u sin <>TZ
= 1.06 (.0209)(4)
4.24 (6)(.382)(13)
As can be noted, a significant hypothetical reduction can be accomplished
by 100 meters buffer.
2. Solution of EPA HIWAY Model.
The EPA HIWAY Model was graphically solved for the proposed hypothetical
situation. The resultant concentration for an unforested highway is 4000 ugr/m3
where a forrested highway yields 3483 Mg/m3.
Similar answers could be achieved through the numerical integration
of the EPA HIWAY equations presented in Section I of this Appendix A.
3. Solution of Empirical Model.
By applying the values of Qp U and 6 to equation (21),the concentration
110 metiers (x) from non buffered highway can be calculated,
C =8.18 Qj
U (x/sln 9)1'106
C • 8.18 (.024), ._, _.. . 3
emo/.zss)1-106 ' 344 M8/m
VI-17
-------
For a buffered highway, the value of Cv is substituted for Qj which
yields,
C =8.18 Q,
„ , . L. ax 1.106
U (x/sin8)
C = 8.18(.Q209) = 39 g/m3
6(1107.283)1.106
4. Solution of SRI Street Canyon Model.
Instead of the open highway, the SRI Street Canyon Model is applicable
to a street surrounded by tall buildings. The tree configuration is also
different for this model. There will be a tree every 30 feet on each side of the
highway. If 20 ft. maples were used with a canopy area of 7.1 m2/tree, the
applicable sink rate(s) could be calculated;
S = Sink rate x canopy area/tree x I/distance between trees (25 )
S = 6.328 x 10-6_gr x 7.1 m2 x tree = 2 4fi x 1Q-6
sec mz tree 4.57m ' T-—
S6C in
The configuration of the street canyon is shown in Figure VI-2.
The dimensions of the canyon are chosen to be Z = 1m, Lo = 2m, W = 15m, X = 5m,
H = 10m. When these dimensions and the data from the previous example are entered
into equations (17 ) and ( 18) the leeward and windward concentrations can be
calculated for an unplanted street.
AC leeward = 7 Q
(U +.5)((X* + Z2)** + L0>
= 7 (.024) =
2)
AC windward = 7 Q (H-Z)
W (U+.5)H
7 (.024) (9)
1550.7 pg/tn3
VI-18
-------
The concentrations for a planted street can be determined by subtracting
S from Qjto determine a new emission rate. Subsequently the revised emission rate
Q2 equal .02399 g/m sec. By substituting this revised value into equations ( 1?)
and (18) the leeward and windward concentrations can be calculated to be:
AC leeward = 7
(U +.5)((X2 +Z*) +L0)
AC windward = 7 Q (H-Z)
W (U +.5) H
7 (.02399)(9)
(15)(6.5)(10)
VI-19
-------
APPENDIX B
SENSITIVE SPECIES LIST
VI-20
-------
The Plant Species Sensitivity Lists contained in Volume I have been duplicated and
placed in this Appendix for convenience. Both the Table and Page numbers which
appear in Volume I have been changed, where appropriate, to follow the numerical
order of this Volume. Numbers in the Reference column of this list refer to the
literature citations listed in Volume I.
VI-21
-------
TABLE VI-1
PLANT SPECIES SENSITIVITY LISTS
Fluorine
TOLERANT - Trees/Deciduous
Reference
Apple Malus sp. 733
American elm Ulrnus americana 1164, 536
American linden (Basswood) Tilia americana 1164, 536
American mountain ash Sorbus domestica 536
American sycamore Platanus occidental-is 733
Basswood (American linden) Tilia americana 1164, 536
Cornelian cherry Cornus mas 1164, 536
Cutleaf birch Betula pendula var. gracilis 536
European black alder Alnus glutinosa 536, 1164
European elder Sambucus nigra 536
European larch Larix decidua 1687
European mountain ash Sorbus aucuparia 1164, 536
European red elder Sambucus racemosa 536
Flowering dogwood Cornus florida 733
Flowering plum Prunus cerasifera 1164, 536
Hackberry Celtis sp. 733
Litte leaf linden Tilia cordata 536
Modesto ash Fraxinus velutina 1164, 536
Norway maple Acer platanoides 733
Oleaster (Russian Olive) Eleagnus angustifolia 536
Oriental cherry Prunus eerrulata 536
Pear Pyrus conmunis 1164
Russian olive (Oleaster) Eleagnus angustifolia 536
Sugar maple Acer saccharum 1164
Tree of heaven AilantTms altissima 536
Willow Salix sp. 536, 1164
White birch Betula alba 733
White mulberry Morus alba 733
TOLERANT - Trees/ Coniferous
American holly Ilex opaca 733
Austrian pine Pinus nigra 1164
Canadian hemlock (Hemlock) Tsuga canadensia 733
Eastern red cedar Juniperus virginiana 525
Hemlock (Canadian hemlock) Tsuga canadensiB 733
Juniper Juniperus sp. 1164, 536
Magnolia Magnolia sp. 733
Western hemlock Tsuga heterophylla 1687
White spruce Picea glauca 1164, 536
TOLERANT - Shrubs
Bridal wreath spirea Spirea prunifolia 1164
Currant Ribes sp. 1164
Firethorn Pyracantha sp. 1164
TOLERANT - Herbaceous
Alfalfa Medicago sativa 16
VI-22
-------
Fluorine (Con't)
TOLERANT - Herbaceous
Reference
Apricot - vine Passiflora ep. 886C
Celery Spermolepsis sp. 16
Cotton Gbssypiwn sp. 136, 16, 269
Cucumber Sicyos sp. 16
Eggplant Solarium melongena 16
Fescue Festuca elatar 890N
Geranium Geranium sp. 16
Gladiolus 886C
Grapevine Vitis sp. 886C
Kentucky bluegrass Poo. pratensis 890N
Red Fescue Festuca sp. 890N
Sweet clover Melilotus sp. 16
Tobacco Nicatiana sp. 16
INTERMEDIATE - Trees/Deciduous
Apple Malus sp. 16
Black locust Robinia pseudoacacia 1164, 536
Black walnut Juglans nigra. 536
Cut leaf birch Betula pendula var. aracilis 16
English oak QuercuB rdbor m 536
English walnut (Persian walnut) Juglana regia 1164, 536
Eugene poplar Populus canadeneis var. jugenci 1164, 536
European ash FTOxinus excelsior 1164, 536
European beech FaguB sylvatica 536
European filbert Corylua avellana 536
European hornbeam Carpinus "betulus 536
European white birch Betula pendula. 536
Green ash Fraxinus pennsylvanica lanceolata 536, 1164
Hedge maple Acer ocanpestre 536, 1164
Japanese larch Larix leptolepsis 1074
Little leaf linden Tilia cordata 1164, 536
Lombardy poplar Populue nigra var. italiea 1164, 536
Oriental cherry Primus serrulata 1164
Oriental plane tree Platanus orientalie 536
Persian walnut (English walnut) Juglans regia 1164, 536
Quaking aspen Pcpulus tremuloidea 1164, 536
Red mulberry Morus rubra 536
Serviceberry Amelanchier canadensie 1164
Silver maple Acer saecharinum 1164, 536
Smooth sumac fihus glabra 536
Spanish chestnut Castenea sativa 536
INTERMEDIATE - Trees/ Coniferous
Aborvitae Thuja sp. 536, 1164
Austrian pine Pinus nigra 525
Douglas fir Pseudotsuga menziesii 1074
English holly Hex aquifolium 1164, 536
Lodgepole pine Pinus contarta 1074
VI-2 3
-------
Fluorine (Con't)
INTERMEDIATE - Trees/ Coniferous
Reference
Noble fir Abies procera 1074
Ponderosa pine Pinus ponderosa 1074
Spruce Picea sp. 1074
Western hemlock Tsuga heterbphylla 1074
Western red cedar Juniperus scopulorum 1074
Western white pine Pinus monticola 1074
White fir Abies concolor 1074
INTERMEDIATE - Shrubs
Common lilac Syringa vulgaris 1164
Japanese yew Taxus cuspidate. 1164, 536
Rhododendron Rhododendron sp. 1164
Rose Rosa sp. 1074, 1164, 16
INTERMEDIATE - Herbaceous
Buckwheat Fagopyrum 16
Iris Iris sp. 16
SENSITIVE - Trees/Deciduous
Apricot (Flowering apricot) Primus armeniaca 536, 1&» ^&°
Box elder Acer negundo 536, 1164
Bradshaw plum Prunus domestica 'Bradshau' 536, 1164
Empress tree Paulownia tomentosa 536
Flowering apricot (Apricot) Prunus armeniaca 536, 16, 460
Hop hornbeam Carpinus betulus 765
Italian prunes Prunus sp. 269
Japanese apricot Prunus name 363
Maple Acer sp. 765
Moorhead apricot 363
Paulownia (Empress tree) Paulownia tomentosa 536
Plum Prunus sp. 16
Western larch Larix occidentalie 536
SENSITIVE - Trees/ Coniferous
Cascades fir Abies amabilis 1074
Colorado spruce Picea pungens 536,1164
Douglas fir Pseudotsuga menziesii 525, 536, 1074, 1164
1687
Eastern white pine Pinus strobus 536
Engelmann spruce Picea engelmannii 1687
Loblolly pine Pinus taeda 1164, 536
Lodgepole pine Pinus contorta 536, 525
Noble fir Abies procera 1687
Nordman's fir Abies nordmanniana 1074, 1687
Norway spruce Picea abies 1074, 1687
Ponderosa pine Pinus ponderosa 536
Scotch pine Pinus sylvestris 525, 1164, 536, 1074
VI-24
-------
Flourine (Con't)
SENSITIVE - Trees/Evergreen
Reference
Serbian spruce Pioea omorika 1074, 1687
Silver fir Abies peotinata 1687
White fir Abies ooncolor 1687
SENSITIVE - Shrubs
Blueberry Vaooiniwn sp. 1164
Common barberry Berberis vulgaris 765
Dwarf alps honeysuckle Lonicera alpigena 765
Dwarf mugo pine Pinus mugo mughus 536
St. Johnswort Hypericum maculatum 1010, 765
St. Johnswort Jupericum perforation 765
SENSITIVE - Herbaceous
Amaranthus Amaranthus retroflexus 765
Annual blue grass Poa annua 765
Catchfly Silene inflata 765
Colchis (Fall crocus) Colchicum autumale 765
Common chickweed Stellaria media 765
Corn Zea mays 16
Fall crocus (Colchis) Colchicum autumale 765
Gladiolus 990, 363, 318, 886C,
16, 136, 269
Goosefoot Chenopodiim alba 765
Goosefoot Chenopodiim murale 765
Grape Vivis vinifera 765
Iris Iris sp. 990
Mustard Sinapsis arvenis 765
Oat grass Arrhenatherum elatius 765
Orchard grass Daatylis glomerata 765
Oregan grape Vitis sp. 363
Tulip 318
VI-25
-------
J/MJLfc Vl-Z
PLANT SPECIES SENSITIVITY LISTS
General Pollution
TOLERANT - Trees/Deciduous
Alder Alnus sp.
Almond tree Prunus amygdalus
American beech (Red beech) Fagus grandifolia
Apple Malus sp.
Ash Fraxinus sp.
Balsam poplar Populus balsamifera
Birch Betula lento.
Box elder Acer negundo
Canadian poplar (Carolina poplar) Populus canadensis
Carolina poplar (Canadian poplar) Populus canadensis
Cherry Prunus sp.
Eastern poplar Populus deltoides
Elder Sarribucus sp.
Elm Ulmus sp.
European mountain ash Sorbus aucuparia
Flowering dogwood Cornus florida
Gingko (Maidenhair tree) Gingko biloba
Goat willow Salix caprea
Hawthorn Crataegus sp.
Honey locust Gleditsia triacanthos
Japanese larch Larix leptolepsis
Japanese pagoda tree Sophora japonica
Juneberry Amelcnchier sp.
Larch Larix sp.
London plane tree Platanus acerifolia
Maidenhair tree (Gingko) Gingko biloba
Oak Quercus sp.
Oleaster (Russian olive) Elaeagnus angustifolia
Ornamental apple Malus floribunda
Peach Prunus persica
Pear Pyrus communis
Plum Prunus sp.
Poplar Populus sp.
Red ash Fraxinus pennsylvanica
Red beech (American beech) Fagus grandifolia
Rcdhaw hawthorn Crataegus mollis
Russian olive (Oleaster) Elaeagnus angustifolia
Scarlet elder Sarribucus pubens
Silverberry Elaeagnus commutata.
Tree of heaven Ailanthus altissima
TOLERANT - Trees/ Coniferous
Arborvitae Thuja sp.
Austrian pine Pinus nigra
Cedar (Eastern red cedar) Juniperus virginiana
Colorado spruce Picea pungens
Eastern red cedar (Cedar) Juniperus virginiana
Eastern white pine Pinus strobus
Sitka spruce Picea sitchensis
Western red cedar Thuja plicata
Reference
39,
407
39
787
890Q,
890 J,
889 A,
886K,
890L,
890L
890L
890Q,
886N
890Q
886K,
890Q
890Q
1358
890L
889B
1976
787
1976
8900
1400
1976
1358
889A
886K,
890Q
407
809Q
407
889A,
890
39
890Q
886K,
889B,
890L
1358
1400
39
886K, 889A
8861,8900,1400
890L.890J,
8861
1501, 407
889A.890J.890Q
890J,890,889A
890Q
890J.890.889A
890L
886N
41, 787
890Q
886N, 787
890Q
889A
787
787, 890Q
-------
General Pollution (Con't)
TOLERANT - Shrubs
Reference
Alder buckthorn Rhamnus frangula 8861
Alpine currant Ribes sp. 890Q
Blueberry Vacciniion sp. 407
Common lilac Syringa vulgaris 886K
Hedgerow rose Rosa sp. 890Q
Lilac Syringa sp. 890Lf 890Q
Mentor barberry Berberis mentorensis 1501, 8861, 890Q
Spindletree Euonymus sp. 890L
Snowberry Symphoricarpos albua 890L
Sweetbriar Rosa eglantaria 890Q
Tatarian honeysuckle Lonicera tatarioa 890L
Viburnum Viburnum sp. 890Q
TOLERANT - Herbaceous
Annual bluegrass Poa annua 407
Barley Uordeum sp. 407
Bean Phaseolus 407
Benoite Geum sp. 407
Blanketflower Gaillardia sp. 1513
Cabbage Brassica napolerassiaa 407
Cauliflower 407
Chickweed Cerastium triviale 38
Chrysanthemum Chrysanthemum 407
Corn Zea mays 407
Dandelion Taraxacum platicardum 38
Day lily Hemerocallis fulva 38
Hawksbeard Crepis japanica 38
Onion AlHum japonica 38
Peas 7t0wa sp. 407
Pepper 407
Pink satin petunia Petunia ep. 797
Potatoes Solatium jarnesii 407
Radish Raphanus sp. 407
Rhubarb Rheum rhaponticwn 407
Roth Athyrium nipponicum 38
Siberian pea shrub 886K, 890
Spurge Euphorbia helioscopia 38
Spurge Euphorbia sieboldiana 38
St. Johnswort Hypericum sp. 407
Starwort Stellaria media 38
Strawberry Fragaria sp. 407
Tickseed Coreopsis tinotoria 38
Wheat Triticum aestivum 407
Woodbine Lonioera periclymenum 890Q
Wormwood Artemis vulgaris 38
INTERMEDIATE - Trees/Deciduous
Alder Alnus sp. 886C, 889A
VI-27
-------
General Pollution (Con't)
INTERMEDIATE - Trees/Deciduous
Reference
American linden (Basswood) Tilia americana 886, 733
Apple Mains sp. 1332
Apricot Prunus armeniaca 407
Ash Fraxinus bungeana 38
Ash Fraxinus longicuspis 38
Aspen (Hybrid poplar) Populus sp. 886L, 890E, 886C
Balsam poplar Populus balsamifera 890E, 886L
Basswood (American linden) Tilia americana 886, 733
Black poplar Populus nigra 890E
Box elder Acer negundo 889A
Canoe birch (White birch) Betula papyrifera 886L, 890E
Chestnut oak Quercus dentata 38
Chokecherry Prunus virginiana 733
Elder Sarribucus 886C
Elm Ulmus sp. 889A
English oak Quercus robor 886N
European larch Larix decidua 787, 886
Fig Fious carica 733
Gladbearing oak Quercus glandbearing 38, 886C
Grapefruit Citrus sp. 407
Green ash Fraxinus pennsylvanica var. lanceolata 890E
Hawthorn Crataegus 886C, 733
Hornbeam Carpinus sp. 886C
Hybrid poplar (Aspen) Populus sp. 886L, 890E, 886C
Little leaf linden Tilia oordata 886N
Lombardy poplar Populus nigra var. italica 733
Maple Acer sp. 889A
Mountain ash Sorbus americana 890E
Mulberry Morus sp. 886C
Norway maple Acer platanoides 501
Pubescent birch Betula sp. 886N
Red ash Fraxinus pennsylvanica 886N, 501, 890L
Sawtooth oak Quercus acuta 38
Silver maple Acer saccharinum 501
Tulip poplar (Yellow poplar) Liriodendron tulipifeva 501
Walnut Juglans sp. 407
White birch (Canoe birch) Betula papyrifera 886L, 890E
Willow Salix sp. 886C
Yellow poplar (Tulip poplar) Liriodendron tulipifeva 501
INTERMEDIATE - Trees/Coniferous
Arborvitae Thuja sp. 889A
Canadian hemlock Tsuga canadensis 787
Colorado spruce Picea pungens 733
Eastern white pine Pinus strobus 886N, 787
Engelmann's spruce Picea engelmanni 889A
False cypress Chameocyparis sp. 889A
Fir Abies sp. 787
Japanese red pine Pinus densiflora 38
Lodgepole pine Pinus contorta 889A
VI-28
-------
General Pollution (Con't)
INTERMEDIATE - Coniferous
Norway pine (Red pine) Pinus resinosa
Pitch pine Pinus rigida
Red pine (Norway pine) Pinus resinosa
Serbian spruce Picea omorika
Reference
886N
733
886N
889A
INTERMEDIATE - Shrubs
Common lilac Syringa Vulgaris 890J
Filbert Copylus sp. 890L
Forsythia Forsythia intermedia 733, 501
Hedgerow rose Rosa sp. 890E
Japanese barberry Berberis thunbergii 890L
Juniper Juniperus sp. 889A
Spirea Spirea sp. 733
Tatarian honeysuckle Lonicera tatarioa 501, 890J
Weigela Weigela florida 501
INTERMEDIATE - Herbaceous
Ageratum Eupatorium coelestimm 407
Bean Phaseolus sp. 407
Bluegrass Poa matsumural 38
Carnation Dianthus sp. 407
Celery Spermolepsis sp. 407
Chrysanthenum Chrysanthenum sp. 407
Common plantago Plantago major 38
Cudweed Gnaphalium multiceps 38
Daisy fleabane Erigeron strigosus 38
Endive Cichorium endivia 407
Grape Vitis vinifera 733
Groundsel Senecio nikoensis 38
Heat lettuce Lactuca sp. 407
Knotweed Polygonum virginianum 38
Lucerne Medicago sativa 407
Maidenhair Adiantwn pedatum 38
Nasturtium (Yellow cress) Nasturtium indicum 38
Oat Danthonia sp. 407
Onion Alliumsp. 407
Petunia Petunia sp. 407
Rape seed (Turnip) Brassica rapa 407
Siberian pea tree 889A, 890J, 890L
Sorrel Rwnex acetosa 38
Sudan grasses 407
Sweet coltsfoot Petasites japonioa 38
Turnip (Rape seed) Brassica rapa 407
Violet Viola sp. 38
Yellow cress (Nasturtium) Nasturtium indicum 38
Zinnias Seliopsis elegans 407
VI-29
-------
General Pollution {Con't)
SENSITIVE - Trees/Deciduous
Reference
Alder Alnus multinervis 38
Apple (Siberian crabapple) Mains baccata 886L, 311
Ash Fraxinus sp. 889A
Beech FagitS sp. 889A
Birch Betula sp. 8861, 311, 425
Black oak Quercus velutina 733
Box elder Acer negicndo 890E
Buckeye Aesculus turbinata 38
Catalpa Catalpa speciosa 311, 425
Chestnut oak Quercus prinus 733
Chokecherry Prunus virginiona 733
Elm Ulmus sp. 811, 425, 1501
Japanese maple Acer paimatwn 38, 425
Judas tree Cercis siliquastrum 1501
Larch Larix sp. 890K, 311, 38, 890E
Lichen 1490
Linden Tilia sp. 889A
Lombardy poplar Populus nigravap. italiaa 311, 425
Mahogany Melia japonica 38
Mulberry Moms microphylla 311
Oak Quercus sp. 425
Orange Citrus sp. 727
Peach Primus persica 1332, 733
Pear Pyrus comtunis 311
Pumila Arborea (Turkestan elm) Ulmts turkestanica 890E
Siberian crabapple (Apple) Malus baccata 886L, 311
Tree of heaven Ailanthus altissima 1501
Turkestan elm (Pumila arborea) Ulmus turkestanica 89°E
White oak Quercus alba 733
White poplar Populus alba 38
Wild black cherry Prunus serotina 1332
SENSITIVE - Trees/ Coniferous
Austrian pine Pinus nigra 733
Colorado spruce Picea pungens 733
Douglas fir Pseudotsuga menziesii 425, 733
Eastern white pine Pinus strobus 733, 311
Fir Abies sp. 890E» 886N> 886C»
889A
Norway spruce Picea abies 733
Ponderosa pine Pinus ponderosa 311
Scotch pine Pinus sylvestris 733, 886K, 890J,
787, 889A
Spruce Picea sp. 425> 889A» 886N»
39, 890E
VI-30
-------
General Pollution (Con't)
SENSITIVE - Shrubs
Common lilac Syringa vulgaris
Oregon holly-grape Mahonia aquifplium
Yew Taxus sp.
SENSITIVE - Herbaceous
Aconite Aconitum japonicum
Agrimony Agrimonia pilosa
Alfalfa Medicago sativa
Aster Aster bigelobii
Bachelor's button Centaurea ayanus
Barley Hordewn vulgare
Bean Phaseolus vulgaris
Bedstraw Galiwn strigoswn
Beet Beta vulgaris
Bindweed Convolvulus arvensis
Bluegrass Poo. sp.
Broccoli Brassica oleraccea
Brussel sprouts Brassica aleracea var. geimrifera
Buckwheat Fagopyrum sagittatum
Careless weed Amaranthus palmeri
Carrot Daucus carota
Catbriar Smilax racemo&a
Chickweed Stellaria media
Cinquefoil Potentilla chinensis
Clover Melilotus sp.
Clover ,frifolium\ sp.
Corn Zea mays
Cosmos Cosmos bipinnatus
Cotton Gossypium sp.
Curly clock Rumex crispus
Endive Cichorium endivia
Fleabane Erigeron canadensis
Four o'clock \Mirabilis\jalapa
Galinsoga Galinsoga parvifolia
Goosefoot Chenapodium album
Green beans Phaseolus sp.
Gypsy petunia Petunia sp.
Horsetail Equisetum arvense
Huckleberry Gaylussacia sp.
Lettuce Lactuca sativa
Lettuce, prickly Lactuca scariola
Lima bean Phaseolus limensis
Mallow Malva parvifolia
Morning glory Ipomoea purpurea
Mosses Commelina sp.
Oat Avena sativa
Okra Hibiscus esculentus
Pea Vigna sinensis
Peanut Arachis sp.
Reference
733
733
889A
38
38
727, 311
311
311
311
311
311, 407
311
886C
311
311
311, 1332
311
311
733
407
38
311
311
1332
311
311
311
311
311
311
407
407
727
797
38
733
311
311
727
311
311
1490
311
311
890K
727
V-I-31
-------
General Pollution (Con't)
SENSITIVE - Herbaceous
Reference
Pear tree 889A
Pepper bell, chili Capsicum prutescens 311
Pinto beans 727
Plantain Plantago major 311
Pumpkin Cucurbita pepo 311
Radish Raphanus sativus 311, 407
Ragweed Ambrosia artemisifolia 311
Rape seed (Turnip) Brassica rapa 311
Rhubarb Rheum rhaponticum 311
Rye Secale cereale 311
Solomon's seal Polygonatum latifolium 38
Sorrel Rumex sp. 407
Soybean Glycine max. 311, 727
Spinach Spinacia oleracea 727, 311, 407
Squash Cucurbita maxima 311
Sunflower Helianthus 311
Sweet corn 727
Sweet potato Ipamoea batatas 311
Swiss chard Beta vulgaris var. cicla 311, 407
Thistle Cirsium inconiptum 38
Tomato Lycopersicium esculentum 1332, 727
Turnip (Rape seed) Brassica rapa 311
Velvet-weed Gaura parvifolia 311
Vervain Verbena canadensis 311
Violet Viola sp. 311
Wheat Triticum sp. 311
Wild potato Solanum jamesii 727
Wood nettle Laportea bulbifera 38
Zinnia Zinnia elegans 311
VI-32-
-------
TABLE VIi3
PLANT SPECIES SENSITIVITY LISTS
Hydrogen Chloride
TOLERANT - Trees/deciduous
Birch Betula sp.
Black Cherry Prunus serotina
Cherry Prunus sp.
English walnut (Persian walnut) Juglans regia
Maple Acer sp.
Oak Quercus sp.
Oleaster (Russian olive) Eleagnus angustifolia
Pear Pyrus comrmaiis
Persian walnut (English walnut) Juglans regia
Red oak Quercus borealis
Russian olive (Oleaster) Eleagnus angustifolia
TOLERANT - Trees£oniferous
Arborvitae Thuja sp.
Austrian pine Pinus nigra
Balsam fir Abies balsamea
Canadian hemlock Tsuga aanadenaia
Eastern white pine Pinus strobus
Jack pine Pinus banksiona
Loblolly pine Pinus taeda
Norway spruce Picea dbies
Short leaf pine Pinus echinata
TOLERANT - Shrub
Yew Taxus sp.
TOLERANT - Herbaceous
Carrot Daunts carota
Grapevine Vitis sp.
INTERMEDIATE - Trees/Deciduous
Black Cherry Prunus serotina
Black gum Nyssa sylvatica
INTERMEDIATE - Trees/ Coniferous
Jack Pine Pinus banksiana
Short leaf pine Pinus echinata
SENSITIVE - Trees/Deciduous
Apple Mains sp.
Box Elder Acer negundo
Cherry Prunus sp.
Horsechestnut Aesculus hippoaastanum
Larch Larix sp.
Reference
536
536
886C
886C
536
536
536
536
886C
536
536
536
536, 1104
536
536
536
536
536
536
536
536
187
88 6 C
536
536
536
536
536
536
536
536
536
VI-33
-------
Hydrogen Chloride (Con't)
SENSITIVE - Trees/Deciduous
Reference
Pin oak Quercus palustris 536
Sassafras Sassafras albi&um 536
Sugar maple Acer saccharum 536
Sweetgum Liquidambar styraciflua 536
Tree of heaven Ailanthus altissima 536
VI-34
-------
TABLE vi-4
PLANT SPECIES SENSITIVITY LISTS
Nitrogen Dioxide
TOLERANT - Trees/Deciduous
Beech Fagus sp.
Gingko (Maidenhair tree) Gingko biloba
Maidenhair tree (Gingko) Gingko biloba
Oak Quercus sp.
TOLERANT - Trees/Evergreen
Austrian pine Pinus nigra
TOLERANT - Herbaceous
Cabbage Brassiaa sp.
Gladiolus
Onion Allium sp.
INTERMEDIATE - Trees/Evergreen
European larch Larix decidua
SENSITIVE - Trees/Deciduous
Apple Malus sp.
Black locust Pobinia pseudoaoaaia
European beech Fagus sylvatioa
European hornbeam Carpinus betulus
European red elder Sambucus racemosa
Gingko (Maidenhair tree) Gingko biloba
Japanese maple Acer palmatum
Large leaf linden Tilia grandiflora
Little leaf linden Tilia cordata
Maidenhair tree (Gingko) Gingko biloba
Norwary maple Acer platanoides
Pear Pyrus comnrunis
SENSITIVE - Trees/Evergreen
Austrian pine Pinus nigra
Colorado spruce Pioea pungena
Eastern white pine Pinus strobus
White spruce Picea glauoa
SENSITIVE - Shrubs
Dwarf raugo pine Pinus mugo mughus
SENSITIVE - Herbaceous
Barley Hordeum sp.
Begonia Rumex sp.
Carrot \paucus caroto.
Kidney beans Phaseolus sp.
Reference
16
16
16
16
16
16
16
16
536
536
536
536
536
536
536
536
536
536
536
536
536
536
536
536
536
536
16
16
16
16
VI-35
-------
Nitrogen Dioxide (Con't)
SENSITIVE - Herbaceous
Reference
Lettuce Lactuca sp. 1849, 16
Red clover Trifolium pretense 16
Sweat peas Lathyrus odoratus 16
Tobacco Niaotiana sp. 16
VI-36
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PLANT SPECIES SENSITIVITY LISTS
Ozone
TOLERANT - Trees/Deciduous
Reference
Acacia Acacia sp.
Alder Alnus sp. 1164
American sycamore Platanus occidentalie 1074, 1164, 990
Ash Fraxinus sp. 181
Basswood (Linden) Tilia sp. 1137
Black walnut Juglans nigra 1164, 536
English oak Quercus robor 536, 1164
European mountain ash Sorbus aucupafia 536
European white birch Betula pendula 536, 1164
Fig Ficus carica 181
Flowering dogwood Cornus florida 536, 1164
Giant sequoia Sequoia gigantea 536
Linden (Basswood) Tilia sp. 1137
Little leaf linden Tilia cordata 1164
Maidenhair tree Gingko biloba 181
Norway maple Acer platanoides 536, 1164
Plum Prunus sp. 181
Red maple Acer rubrum 536, 1164
Red oak Quercus borealis 1164
Redwood Sequoia sempervirens 536
Shingle oak Quercus imbricaria 536. 1164
Sugar maple Acer sacchanm 536, 1137
Weeping willow Salix babylonica 1164
White birch Betula papyrifera 1137
TOLERANT - Trees/ Coniferous
Arborvitae Thuja sp. 774, 1164, 536
Balsam fir Abies balsamea 1137, 536, 1164, 774
Black hills spruce Picea glauca densata 774, 1164, 536, 1137
Colorado spruce Picea pungens 1137, 536, 1164, 774
Digger pine Pinus sabiniana 536
Douglas fir Pseudotsuga menziesii 774, 1137, 536, 1164
Eastern red cedar Juniperus virginiana 181
Jack pine Pinus banksiana 1074
Norway pine (Red pine) Pinus resinosa 1137, 1164, 774, 536
Norway spruce Picea abies 1137, 774, 1164, 536
Red pine (Norway pine) Pinus resinosa 1137, 1164, 774, 536
Singleleaf pinyon pine Pinus monophylla 536
Sugar pine Pinus lambertiana 536
Torrey pine Pinus torreyana 536
Virginia pine Pinus virginiana 1074
White fir Abies concolor 774, 1164, 1137
White spruce Picea glauca 536, 1164
TOLERANT - Shrubs
Ivy Hedera sp. 181
TOLERANT - Herbaceous
Bugleweed (Carpet bugle) Ajuga sp. 181
VI-37
-------
Ozone (Con't)
TOLERANT - Herbaceous
Reference
California poppy Esahscholtzia California 181
Carpet bugle (Bugleweed) Ajuga sp. 181
Lady's slipper Cypripedium sp. 181
Leadwort Ceratostigma plwnbaginaides 181
Petunia Petunia sp. 1015, 1074
INTERMEDIATE - Trees/ Coniferous
Big cone Douglas fir Pseudotsuga macrocarpa 536
Coulter pine Pinus coulteri 536
California: Incense-cedar Libocedrus decurrens 536
White fir Abies concolor 536
SENSITIVE - Trees/Deciduous
Alder Alrcus sp. 536
American elm Ulmus americana 1164
American sycamore Platanus occidentalis 1074
Black locust Robinia pseudoacacia 1164, 536
Boxelder Acer negundo 536, 1164
California sycamore Platanus racemosa 1074
Catalpa Catalpa speciosa 1164
European larch Larix decidua 990, 1164, 1137, 536
Gambel oak Quercus gambellii 1164, 536
Green ash Fraxinus pennsylvanica lanceolata 536, 1164
Honeylocust Gleditsia triacanthos 1164, 536
Hybrid poplar Populus sp.
Japanese larch Larix leptolepsis 1164, 536, 77
Judas tree Cerois siliquastrum 536
Little leaf linden Tilia cordata 536
Mapleleaf mulberry (White mulberry) Morus alba 536
Pin oak Quercus palustris 536, 1164
Quaking aspen Populus tremuloides 536, 1164
Scarlet oak Quercus coccinea 1164, 536
Siberian crab apple Malus baccata 536, 1164
Silver maple Acer saccharinum 536, 1164
Sweetgum Liquidambar styraoiflua 1164, 536
Thornless honeylocust Gleditsia triacanthos inermis 1074
Tulip poplar (Yellow poplar) Liriodendron tulipifera 990,1164,536,1074,1137
Weeping willow Salix babylonica 536
White ash Fraxinus americana 990,1137,1074,536,1164
White mulberry (Mapleleaf mulberry) Morus alba 536
White oak Quercus alba 1164, 536, 1137
Yellow poplar (Tulip poplar) Liriodendron tulipifera 990,1164,536,1074,1137
SENSITIVE - Trees/ Coniferous
Austrian pine Pinus nigra 1164, 536, 774, 1137
VI-38
-------
Ozone (Con't)
SENSITIVE - Trees/ Coniferous
Reference
Canadian hemlock Tsuga canadensis 536, 1137
Eastern white pine Pinus strobus 536, 774, 1137, 532
990, 1164
Jack pine Pinus banksiana 774, 536, 1164
Jeffery pine Pinus jeffreyi 536
Monterey pine Pinus radiata 536
Pitch pine Pinus rigida 1164, 1135, 774, 536
Ponderosa pine Pinus ponderosa 536
Scotch pine Pinus .sylvestris 774, 536, 990
Virginia pine Pinus virginiana 536, 774, 1137
SENSITIVE - Shrubs
Bridal wreath spirea Spirea pmmifolia 1164
Camellia Cornelia sp, 2
Common lilac Syringa vulgaris 990, 1164
Common privet Ligustrum vulgare 1164
Snowberry Symphoricarpos aibus 536
SENSITIVE - Herbaceous
Aster Aster sp. 990
Sage Salvia sp. 990
Tobacco Nicotiana sp. 599
VI-39
-------
TABLE VI-6
PLANT SPECIES SENSITIVITY LISTS
Pan
TOLERANT - Trees/Deciduous
Reference
European larch Larix decidua 536
Japanese larch Larix leptolepsis 536
Sugar maple Acer saccharum 536
TOLERANT - Trees/ Coniferous
Austrian pine Pinus nigra 536
Canadian hemlock Tsuga canadensis 536
Colorado spruce Picea pungens 536
Eastern white pine Pinus strobus 536
Jack pine Pinus banksiana 536
Pitch pine Pinus rigida 536
White spruce Picea glauca 536
SENSITIVE - Trees/Deciduous
Little leaf linden Tilia cordata ^ 536
Tulip poplar (Yellow poplar) Liriodendron tulipifera 536
Yellow poplar (Tulip poplar) Liriodendron tulipifera 536
SENSITIVE - Herbaceous
Aster Aster sp. 990
Chrysanthemum Chrysanthemum sp. 990
Lettuce Laotuca sp. 1849
Petunia Petunia sp. 990
Primrose Primula sp. 990
Sage Salvia sp. 990
Snapdragon Chaenorrhinum sp. 990
VI-40
-------
TABLE VI-7
PLANT SPECIES SENSITIVITY LISTS
Particulates - Smoke
TOLERANT - Trees/Deciduous
Reference
American Elm Ulmus americana 547
European larch Larix deaidua 1604
Scarlet elder Sambuaus pubens 1390
TOLERANT - Shrub
Cranberry Vacoinium sp. 187
TOLERANT - Herbaceous
Knotweed Polygonum cilinode 1390
INTERMEDIATE - Trees/Deciduous
Alder Alnus sp. 1604
American beech (Red beech) Fagus grandifolia 1604
American hornbeam Carpinus oaroliniana 1604
Birch Betula sp. 1604
English oak Querous robor (formerly called penduaulata) 1604
Maple Acer sp. 1604
Poplar Populus sp. 1604
Raceme oak Quercus racemosa 1604
Red beech (American beech) Fagus grandifolia 1604
Red oak Quercus borealis 1604
White alder Alnus rhombifolia 1604
INTERMEDIATE - Trees/ Coniferous
Austrian Pine Pirate nigra 1604
Eastern white pine Pinus strobus 1604
Scotch pine Pinus sylvestris 1604
SENSITIVE -Trees/Deciduous
Quaking aspen Populus tremuloides 1390
Single-seeded hawthome Crataegus monogyna 1675
SENSITIVE - Trees/Coniferous
Black Spruce Picea maricna 1390
Eastern white pine Pinus strobus 1390
Fir Abies sp. 1604
Norway spruce Picea abies (exaelsa) 1604
White spruce Picea glauaa 1390
SENSITIVE - Herbaceous
Annual bluegrass Poa annua 269
VI-41
-------
TABLE VI-8
PLANT SPECIES SENSITIVITY LISTS
Sulfur Dioxide
TOLERANT - Trees/Deciduous
Reference
American sycamore Platanus occidentalis 1164
Ash Fraxinus sp. 88 6C
Basswood (Linden) Tilia sp. 369
Beech Fagus sp. 1187, 886C
Birch Betula sp. 64, 523, 1187
Black gum Nyssa sylvatica 1169, 536
Black locust ftobinia pseudoaaacia 536
Cottonwood (Eastern poplar) Populus deltoides 1164, 536
Eastern poplar (Cottonwood) Populus deltoides 1164, 536
English oak Quercus robor 1164, 536
European ash Fraxinus excelsior 369
European beech Fagus sylvatica 536
European hornbeam Carpinus betulus 536
European mountain ash Sorbus aucuparia 369
Flowering dogwood Cornus florida 1164, 536
Gingko (Maidenhair tree) Gingko biloba 1164, 369
Green ash Fraxinus pemsylvanica lanceolata 536, 1164
Hedge maple Acer campestre 536, 1164
Hornbeam Carpinus sp. 1187
Larch Larix sp. ^
Linden (Basswood) Tilia sp. 369
Maidenhair tree (Gingko) Gingko biloba 1164, 369
Mountain maple Acer spicatum i16^
Oak Quercus sp. **
Oriental plane tree Platanuo orientalis 1164
Persian walnut Juglans regia 8®^C
Pin oak Quercus palustris H64
Poplar Populus sp. 369
Red berried elder Sambucus pubescene 1074
Red maple Acer rubrum 536, 1164
Red oak Quercus borealis 1164, 44
Smooth elm Ubnus glabra 369
Sourwood Oxydendrum arboreum 369
Sugar maple Acer saccharum _ H°4
Tulip poplar (Yellow poplar) Liriodendron ftulipif&ra 16, 1164, 369
White ash Fraxinus americana ~ 138
Willow Salix sp.
Yellow poplar (Tulip poplar) Liriodendron tulipif era 16, Ho4,
TOLERANT - Trees/ Coniferous
Arborvitae Thuja occidentalis 1JJJ
Austrian pine Pinus nigra 525, 1164, 536
Canadian hemlock Tsuga canadensis
English holly Ilex aqui folium
Lawson false cypress Chamaecyparis lawsoniana
Spruce Picea sp.
Western red cedar Thuja plicata
White spruce Picea glauca
VI-42
-------
Sulfur Dioxide (Con't)
TOLERANT - Shrubs
Reference
Dwarf mugo pine Pinus mugo mughus 536
Juniper Juniperus sp. 1164, 536
TOLERANT - Herbaceous
Alfalfa Medioago sativa 886C
Corn Zea mays 16
Fringed bindweed Polygonum cilinode 1074
Galleta Hilaria jamesii 1365
Grama grass Bouteloua barbata 1365
Heliotrope Heliotropium sp. 886C
Meadow fescue Festuca elatior 136
Oats Avena sp. 88^c
Orchard grass Daatilus glomerada 136
Primrose Primula sp. 88&c
Sweetpea Lathyrus odoratus 886C
Woodwaxen 886c
INTERMEDIATE - Trees/Deciduous
Apple Malus sp. 16
Apricot Prunus armeniaca 16
Balsam poplar Populus balsamifera 116^» 536
Bigtooth aspen Populus grandidentata 116*
Norway maple Acer platanoides 1164
INTERMEDIATE - Trees/ Coniferous
Balsam fir Abies balsamea 536, 1164, 525
Douglas fir Pseudotsuga menziesii 1164, 525, 536
Lodgepole pine Pinus cantorta 536, 525
Scotch pine Pinus sylvestris 1164
Silver fir Abies pectinata 536
INTERMEDIATE - Shrubs
Rose Rosa sp. 16
INTERMEDIATE - Herbaceous
Gladiolus Jj?
Cotton Gossypitan sp. 16
Iris Iris sp. *6
SENSITIVE - Trees/Deciduous
Alder Alnus JJ5, 732
American elm Ulmus americana ^ 1164
American sycamore Platanus occidentalis 1164
Apple Malus sp.
Vl-43
-------
Sultur Dioxide
SENSITIVE - Trees/Deciduous
Reference
Aspen (Poplar) Populus sp. 732, 1187
Birch Betula sp. 1164, 1119
Blueberry elder Scaribucus coerulea 732
Canoe birch (White birch) Betula papyrifera 732
Catalpa Catalpa speoiosa 1164
Cherry Prunus sp. 732
Chokecherry Prunus virginiana 938
English walnut (Persian walnut) Juglans regia 1164
European mountain ash Sorbus auouparia 732, 1187
Horse chestnut Aesculus hippocastanum 44
Hornbeam Carpinus sp. 44
Larch Larix sp. 732, 1164
Lombardy poplar Populus nigra var. italica 1164
Maple Acer sp. 1187
Mazzard cherry Prunus avium 886C
Mountain ash Sorbus americana 1164
Mountain maple Acer spicatum 44
Narrowleaf cottonwood Populus angustifolia 1365
Pear Pyrus comnunis 1164
Persian walnut (English walnut) Juglans regia 1164
Poplar (Aspen) Populus sp. 732, 1187
Quaking aspen Populus tremuloides 1164, 119
Scarlet hawthorn Crataegus oxyacantha 990
Serviceberry Amelanchier sp. 1164
Texas mulberry Morus microphylla 1164
Utah serviceberry Amelanchier utahensis 1164
White ash Fraxinus americana 773
White birch (Canoe birch) Betula papyrifera 732
Willow Salix sp. 1164, 732
SENSITIVE - Trees/Coniferous
Black spruce Picea mariana 1164
Canadian hemlock Tsuga canadensis 1164
Douglas fir Pseudotsuga menziesii 990
Eastern white pine Pinus strobus 990, 1164, 1074,
563,732,773,119
Engelman's spruce Picea engelmannii 1164
Fir Abies sp. 119
Jack pine Pinus banksiana 1164
Mountain hemlock Tsuga mertensiana 1164
Norway pine (Red pine) Pinus resinosa 16
Ponderosa pine Pinus ponderosa 1164, 1007
Red pine (Norway pine) Pinus resinosa 16
Scotch pine Pinus sylvestris 1074, 525
Sitka spruce Picea sitchensis 732
Virginia pine Pinus virginiana 773
Western red cedar Thuja plicata 1°74
Western white pine Pinus monticola 1164
VI-44
-------
Sulfur Dioxide (Con't)
SENSITIVE - Shrubs
Reference
Mountain laurel Kalmia latifolia 1164
Ninebark Physocarpus oapitatus . 1164
Snowberry Symphoricarpos aerophilus 1365
Wild rose Rosa uoodsii 1365
SENSITIVE - Herbaceous
Alfalfa Medicago sativa 938, 732
Begonia Rumex venosus 990, 1009
Buckwheat Fagopyrum sp. 16
Celery Spermolepsis sp. 16
Cotton Gossypiwn sp. 16
Cucumber Sicyos angulatus 16
Eggplant Solarium melongena 16
Evening primrose Oenothera sp. 1365
Geranium Geranium 16
Globe mallow Sphaeralcea munroana 1365
Goosefoot Chenopodiwn ofrenonti 1365
Grape Vitis sp. 938
Hound's tongue Cynoglossim officinale 1365
Hungarian brome Bromus inpermis 136
Indian rice grass Oryzopsis hymenoides 1365
Lettuce Lactuaa sp. 1844
Locoweed Astragalus utdhensis 1365
Lucerne Medicago sativa 1007
Petunia Petunia sp. 1009
Potato Solarium -tuberosum 1007
Red clover Trifolium pratense 136
Scarlet Gilia Cilia agregata 1365
Squash Cucurbita sp. 938
Sunflower Helianthus sp. 886C
Sweet clover Melilotus sp. 732, 16
Tobacco Niootiana sp. 16
Vervain Verbena sp. 990
Violet Viola sp. 990
Wheat Tritioum aestivum 1007
VI-45
-------
APPENDIX C
CALCULATION OF LEAF AREAS FOR SELECTED TREES
VI-46
-------
A one hectare forested unit of open space ±e proposed in Volume III. It was developed
in order to estimate the amount of pollutants removed from the air by the natural
elements of such a standardized forest. The tree species composing this model
forest are red oak (Quereus robur), Norway maple (Acer platanoides"), linden (Tilia
cordata), poplar (Populus tpemula ), birch (Betula vewntcosa) and pine (Pinus sp.).
The estimated height and diameter of the canopy for each tree species at age eight
(that is, five years after planting three-year-old saplings) were used in calculating
the surface area for each tree species. The two dimensions of height, and diameter
of the canopy, for each tree species, may be found on Table VI-9.
By knowing the diameter of the canopy of a tree, the canopy area or ground area
can be calculated. For example, uncrowded red maple, six meters high, may have
a canopy diameter of three meters. Next, it is assumed that the area of a circle,
having the diameter of three meters, adequately estimates the ground area covered
by that red maple.
diameter = 3
radius = 1.5
Therefore, the area of the circle = r2 = (1.5)2 = 7.1 m2 and the estimated ground
2
area of this maple =7.1 m . The total surface area of the plant, however, is much
greater. One method for calculating that plant surface area, for a particular tree,
is to use its ground area and also, the area index of the tree. That index, is the
ratio of total plant surface area to ground area. Monteith (1976) has developed
an area index for each of the deciduous tree species used in the model hectare.
From that paper, the area index for a seven meter high maple is 5.18. However,
the height dimension for the maple growing in the model hectare is six meters.
Since the nature of an extrapolation from a seven meter tree to a six meter tree
in unknown, the area index we used is unchanged from the literature. It is assumed
that the area index for the seven meter maple may be directly used to estimate the
area index for the six meter maple. One advantage for not extrapoliating the area
index given by Monteith is that the calculations we derived can be more easily recon-
structed. Once the ground area and area index ratio for the tree is known, the plant
surface area can be computed.
VI-47
-------
ground area for maple = 7.1 m^
area index for maple = 5.18
area index = surface area/ground area
5.18 X
7.1 m^
surface area of maple = 36.8 nr
-2 i
In multiplying the weighted average sink rate (reported as ug m hr )of a pollution
by vegetation,by the surface area of a tree, the result is the amount of pollutant
removed by that tree during one hour. For instance, the surface area of a maple
as been calculated as 36.8 m2 and the weighted average sink rate for SO2
4 -2-1
by vegetation is 4.1 x 10 ug m- hr . When these two values are multiplied, the
average amount of SO^ removed by a maple tree is 1.5 x 10^ ug/hr.
One problem with this procedure for determining the amount of pollutant removed
by a tree stems from the weighted average sink rate for that pollutant. The
removal rates reported in the tables of Volume I were primarily obtained based
on studies of the rate of pollutant uptake by foliar material. That is, the
pollutant removal rates by woody tissue were usually not considered during the
measurements of pollutant removal by vegetation. As a result, the weighted average
sink rate for a specific pollutant was primarily obtained from data based on foliar
uptake,exclusive of woody tissue uptake.
The area indices reported by Monteith (1976) involve both the foliage and woody
areas of the trees. As a result, when the total surface area of a tree is calculated
by using the area index and ground area of the tree, the woody surface area is
included in the total surface area of the tree. When the latter value is multiplied
by the weighted average sink rate of the pollutant, in order to determine the
amount of pollutant removal by the tree, the calculation is generally lower than
if the surface area were all leaf. The removal rate of the pollutant by the woody
surface area is assumed to be comparable to that by foliar surface area. In truth,
the uptake rate of gaseous pollutants by the woody surface area is apparently less
efficient than the removal rate by a comparable surface area of foliage. The
opposite seems to be true when particulates are considered. However, the removal
rates for particulates by vegetation may have been primarily obtained from studies
VI-48
-------
in which the entire plant was evaluated and as a result, the weighted average sink
rate for particulates may be more accurate than the other pollutant removal rates
since both the foiliage and woody areas are considered. Therefore, when the total
surface area of a tree is multiplied by the weighted average sink rate for a
gaseous pollutant (which primarily defines the foliar uptake), the resulting amount
of pollutant removed from the air by the tree may be slightly off. However, if one
considers the ratio of the total woody area indices of the five deciduous trees used
by Monteith (1976) to the total foliar area indices of the same five species, the
amount of woody surface area to that of the foliar surface area is relatively small
(0.08:1). Because this ratio is small, any error which it may cause is felt to also
be small.
VI-49
-------
TABLE VI- 9
DATA CHARTS OF THE TREE.SPECIES USED IN THE MODEL HECTARE
Maple (Acer platanoides )
Height of the tree used in the model hectare
Diameter of the canopy of the 6.0 meter tree
Canopy area or ground area of the 6.0 meter tree
Height of the tree used in Monteith's area index
Area index of the 7.0 meter tree
Estimated plant surface area of the 6.0 meter tree
6.0m
3.0m
7.1m2
7.0m
5.18m*
36.8m2
Oak (Quercus robur}
Height of the tree used in the model hectare
Diameter of the canopy of the 6.0 meter tree
Canopy area or ground area of the 6.0 meter tree
Height of the tree used in Monteith's area index
Area index of the 6.5 meter tree
Estimated plant surface area of the 6 meter tree
6.0m
3.0m
7.1m2
6.5m
5.08m**
36.1m2
Poplar (Populus
Height of the tree used in the model hectare
Diameter of the canopy of the 6.0 meter tree
Canopy area or ground area of the 6 meter tree
Height of the tree used in Monteith's area index
Area Index of the 10.5 meter tree
Estimated plant surface area of the 6.0 meter tree
6.0m
3.0m
7.1m2
10.5m
7.4m***
52.5m2
*The area index for the 7.0 meter maple is assumed to adequately estimate the
actual area index of the 6.0 meter maple used in the model hectare.
**The area index of the 6.5 meter oak is assumed to adequately estimate the actual
area index of the 6.0 meter oak used in the model hectare.
***The area index of the 10.5 meter poplar is assumed to adequately estimate the
actual area index of the 6.0 meter poplar used in the hectare.
VI-50
-------
Linden ( Tilia cordate)
Height of the tree used in the model hectare
Diameter of the canopy of the 5.0 meter tree
Canopy area or ground area of the 5.0 meter tree
Height of the tree used in Monteith's area index
Area index of the 11.5 meter tree
Estimated plant surface area of the 5.0 meter tree
5.0ra
2.4m
4.5m2
11.5m
5.1m*
23.0m2
Birch (Betula verrueosa)
Height of the tree used in the model hectare
Diameter of the canopy of the 5.0 meter tree
Canopy area or ground area of the 5.0 meter tree
Height of the tree used in Monteith's area index
Area index of the?.6 meter tree
Estimated plant surface area of the 5.0 meter tree
Pine (pinus sp. )
Height of the tree used in the model hectare
Diameter of the canopy of the 3.0 meter tree
Canopy area or ground area of the 3.0 meter tree
Leaf area index used by Rich (1970)
Estimated woody area index
Total estimated area index
Estimated plant surface area of the 3.0 meter tree
5.0m
2.4m
4.5m2
7.6m
6.04m**
27.2m2
3.0m
1.5m
2.1m***
0.2m****
2.3m
4.2m2
*The area index of the 11.5 meter linden is assumed to adequately estimate the actual
area index of the 5.0 meter linden used in the model hectare.
**The area index of the 7.6 meter birch is assumed to adequately estimate the actual
area index of the 5.0 meter birch used In the model hectare.
*** The leaf area index used by Rich (1970) does not cite any height specification.
As a result, it is assumed that the leaf area index does adequately define the ratio
of leaf surface area to ground area of a 3.0 meter high pine.
**** The woody area index for the 3.0 meter high pine was estimated by comparing the
surface area measurements of a 12 meter high white pine which were published by
Stevens (1976). He found that the foliage surface area of the pine was 15 x lO^cm2
or 150m2 and the non-foliage or woody surface area was 15 x lO^cm2 or 15m2 (about
10% of the foliage surface area). In order to estimate the woody area index of
the 3.0 meter pine, it was assumed that the woody surface area was 10% of the leaf
surface area and this same percentage could be applied to determine the woody area
index.
VI-51
-------
APPENDIX D
HOLLAND STACK RISE EQUATION
VI-52
-------
The Holland stack rise equation is:
v d AT
AH = — - - 1.5 + 2.68 X 1(T3 p= - a
u Ls
where AH = the rise of the plume above the stack (meters)
v = stack gas velocity (m/sec)
s
d = the inside stack diameter (meters)
u = wind speed (m/sec)
p = atmospheric pressure (mb)
Ts = stack gas temperature (°K)
AT = as in equation (1) and
2.68 X 10" 3 is a constant having units of (m"1 mb )
VI-53
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1 REPORT NO
2.
3 RECIPIENT'S ACCESSION-NO.
4 TITLE AND SUBTITLE
Open Space as an Air Resource Management Measure -
Design Criteria - Volume II
5 REPORT DATE
December 1976
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
Robert S. DeSanto, Richard A. Glaser, Joseph A. Miller
William P. McMillan, Kenneth A. MacGregor.
B. PERFORMING ORGANIZATION REPORT NO.
H800-II
9 PERFORMING ORGANIZATION NAME AND ADDRESS
COMSIS CORPORATION - Environmental Services
972 New London Turnpike
Glastonbury, Connecticut 06033
10. PROGRAM ELEMENT NO.
11 CONTRACT/GRANT NO.
68-02-2350
12 SPONSORING AGENCY NAME AND ADDRESS
Strategies and Air Standards Division Office of Air
Quality Planning and Standards Environmental
Protection Agency
Research Triangle Park. North Carolina 27711
13 TYPE OF REPORT AND PERIOD COVERED
TT-lnal
14. SPONSORING AGENCY CODE
15 SUPPLEMENTARY NOTES
16 ABSTRACT
This report is a workbook which presents the primary biological and design features
which are crucial to the effective utilization of open space to mitigate air
pollution. It presents generalized schemes for the design and location of buffer
strips and other forms of open space. It also illustrates air pollution mitigation
by open space by identifying the mathematical procedures necessary in order to
permit incorporation of appropriate sink factors into four generally used carbon
monoxide diffusion models.
Directions and tables are given which may be used to estimate the air pollution
removal capacity of various types of vegetation and open space. Leaf area indices
are used in order to convert canopy areas to total leaf areas and the associated
rates of pollution filtering capacities by selected common tree species.
17
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Plants
Trees
Recreation Areas
Forests
Soils
Highways
Topographic Interactions
Air Resource Management
Open Space
Sanitary Zones
Air Pollutant Removal
Sinks
Highway Buffer Strips
Greenbelts
18 DISTRIBUTION STATEMENT
19 SECURITY CLASS (ThisReport)
Unclassified
20 SECURITY CLASS (THISpage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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