REPORT FOR CONSULTATION ON THE
PHOENIX-TUCSON
INTRASTATE AIR QUALITY CONTROL REGION
(ARIZONA)
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Consumer Protection and Environmental Health Service
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REPORT FOR CONSULTATION ON THE
PHOENIX-TUCSON
INTRASTATE AIR QUALITY CONTROL REGION
(ARIZONA)
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
PUBLIC HEALTH SERVICE
CONSUMER PROTECTION AND ENVIRONMENTAL HEALTH SERVICE
NATIONAL AIR POLLUTION CONTROL ADMINISTRATION
SEPTEMBER 1969
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TABLE OF CONTENTS
PREFACE. . . .
. . . . . . . . .
.........
INTRODUCTION
.......
......
EVALUATION OF ENGINEERING FACTORS
......
. . . . . . . . .
EVALUATION OF URBAN FACTORS .
. . . . . . . . . . .
THE PROPOSED REGION. . . . . .
. . . . . . . . . .
DISCUSSION OF PROPOSAL. . . .
. . . .
APPENDIX A . . . . . . . . . .
......
. . . . . . . . . .
1
1
10
27
43
45
50
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i
PREFACE
The Secretary, Department of Health, Education, and Welfare, is
directed by the Clean Air Act, as amended, to designate "a,ir quality
control regions" as an initial step toward the adoption of regional-
air quality standards and the establishment of plans to implement
those standards.
In addition to listing the major factors to be
considered in the development of region boundaries, the Act stipu-
lates that the designation of a region shall be preceded by consul-
tation with appropriate State and local authorities.
The National Air Pollution Control Administration, DHEW, has
conducted a study of southern Arizona, including the Phoenix and
Tucson metropolitan areaA.
The results of the study are presented
in this document.
The Region* boundaries recommended in this
report reflect a consideration of all available and pertinent data;
however, the boundaries remain subject to revision suggested by
consultation with State and local authorities.
This report is
intended to serve as a background document for the formal
consultation.
The Administration is appreciative of assistance received
either directly during the course of this study, or during previous
activities in the State of Arizona, from the Arizona State
* For the purpose of this report, the word "region", when capi-
talized, will refer to the proposed Phoenix-Tucson Intrastate Air
Quality Control Region (Arizona). When not capitalized, unless
otherwise noted, it will refer to air quality control regions in
general.
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ii
Department of Health, the Maricopa County Health Department, and
the Pima County Air Pollution Control District.
Useful. data was
also supplied by the Arizona State EmploYment Service Division and
the Unemployment Compensation Division of the Employment Security
Commission of Arizona, the Arizona State Economic Planning and
Development Department, tpe Tucson Department of Community Deve10p-
m~nt, _and the Pima C.ounty Planning Department.
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1
INTRODUCTION
"For the purpose of establishing ambient air
quality standards pursuant to section lOS, and for
administrative and other purposes, th~ Secretary,
,after consultat~on with appropriate State and local
authorities shall, to the extent feasible, within
is months after the date of enactment of the Air
Quality Act of 1967 designate air quality control
regions based on jurisdictional boundaries, urban-
industrial concentration, and other factors including
atmospheric areas necessary to provide adequate ~-
p1ementation of air quality standards. The Secretary
may from time to time thereafter, as he determines
I
necessary to protect the public health and welfare
and after consultation with appropriate State and
local authorities, revise the designation of such
regions and designate additional air quality control
regions. The Secretary sh~ll immediately notify the
Governor or Governors of the affected State or
States of such designation."
Section 107(a) (2), Clean Air Act as Amended.
THE CLEAN AIR ACT
Air pollution in most of the Nation's urban areas is a
regional problem.
This regional problem demands a regional solu-
tion, consisting of coordinated planning, data gathering, standard
setting and enforcement.
.
Yet, with few exceptions, such coordi-
,
nated efforts are notably absent among ~he Nation's urban complexes.
Beginning with the ~ec.tion quo,ted abo~e, in which the
'.
Secretary is required to designate air quality control regions,. the
Clean Air Act, as amended, presents an approach to air pollution
control involving coordinated efforts by Federal, State, and local
governments, as shown in Figure 1~
~fter th~ Secretary has (1) des-
I
ignated regions,
(2) published. air quality criteria, and
(3)
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HEW DESIGNATES
AI R QUALITY
CONTROL REGIONS.
HEW DEVELOPS AND
PUBLISHES AIR
QUALITY CRITERIA
BASED ON SCIENTIFIC
EVIDENCE OF AIR
POLLUTION EFFECTS.
HEW PREPARES
AND PUBLISHES
REPORTS ON
AVAILABLE CONTROL
TECHNIQUES
Figure 1.
STATES INDICATE
THEIR INTENT
TO SET STANDARDS. (PUBLIC
HEARINGS)
STATES SET
AI R QUALITY
STANDARDS
FOR THE AIR
QUALITY CONTROL
REGIONS.
STATES SUBMIT
STANDARDS FOR
HEW REVIEW.
N
STATES ESTABLISH
COMPREHENSIVE PLANS
FOR IMPLEMENTING
AIR QUALITY
STANDARDS.
STATES SUBMIT
IMPLEMENTATION PLANS
FOR HEW REVIEW.
STATES ACTi"O CONTROL
AIR POLLUTION IN ACCORDANCE
WITH AIR QUALITY STANDARDS
AND PLANS FOR IMPLEMENTATION.
Flow Diagram for Action to Control Air Pollution
on a Regional Basis, under the Clean Air Act
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3
published corresponding documents on control technology and associ-
ated costs, the Governor(s) of the State(s) must file with the
Secretary within 90 days a letter of intent, indicating that the
State(s) will adopt, within 180 days, ambient air quality standards
for the pollutants covered by the published criteria and control
technology documents, and establish within an additional 180 days,
plans for the implementation, maintenance, and enforcement of those
standards
in the designated air quality control region.
The new Federal legislation provides for a regional attack on
air pollution and, at the same time, allows latitude in the form
which regional efforts may take.
While the Secretary reserves ap-
prova1 authority, the States involved in a designated region assume
the responsibility for developing standards and an implementation
plan which includes administrative procedures for abatement and con-
tro1.
For regions which extend across jurisdictional boundaries,
informal cooperative arrangements may be adequate in some cases.
In some cases, too, more formal arrangements, such as interstate
compacts, may be selected to insure compatible standards and proper
enforcement among the jurisdictions.
The objective in each instance
will be to provide effective mechanisms for control on a regional
basis.
PROCEDURE FOR DESIGNATION OF REGIONS
Figure 2 illustrates the procedures used by the National Air
Pollution Control Administration for designating air quality control
regions.
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ENGINEERING EVALUATION
. EMISSIONS INVENTORY
. TOPOG RAPHY
~ -
. METEOROLOGY
. AI R QUALITY ANALYSIS
EXISTING AIR QUALITY DATA
DIFFUSION MODEL OUTPUT
~ !7
PRELIMINARY CONSULTATION FORMAL
~ WITH STATE AND ...
DELINEATION -p '" DESIGNATION BY
OF REGIONS LOCAL OFFICIALS SECR ET ARY-H EW
URBAN FACTORS EVALUATION ;~}.
. JURISDICTIONAL BOUNDARIES
.
. URBAN-INDUSTRIAL CONCENTRATIONS
. COOPERATIVE REGIONAL ARRANGEMENTS
-
. PATTERNS AND RATES OF GROWTH
. EXISTING STATE AND LOCAL AIR POLLUTION
CONTROL PROGRAMS & LEGISLATION
~
Figure 2. FLOW DIAGRAM FOR THE DESIGNATION OF AIR QUALITY CONTROL REGIONS.
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5
A preliminary delineation of the region is developed by bring-
ing together two essentially separate studies -- the "Evaluation of
Engineering Factors," and the "Evaluation of Urban Factors."
The "Evaluation of Engineeriltg Factors" considers pollutant
source locations and the geographic extent of significant pollutant
concentrations in the ambient air.
An inventory of air pollutant
emissions determines the geographic location and quantities of the
various pollutants emitted from the sources in a region.
Major
quantities of pollution are emitted by automobiles and industry, and
from refuse disposal operations, power generation, and space heating.
The subsequent effect of the pollution emitted into the atmosphere
is determined by measuring ambient air quality.
The air quality
analysis presented in this report is divided into two major segments.
The first part deals with the topography and meteorology of the area
and measured air quality.
This section deals with the topographical
influences on local meteorological conditions and the subsequent
meteorological effect on air quality.
The second part of the ana1y-
sis describes the results of the diffusion model applied to the
metropolitan Phoenix and Tucson area in order to predict air quality.
Some of the limitations of the model are also described.
In addi-
tion, basic conclusions drawn from the model results, as they relate
to the size of the proposed Region, are outlined.
The "Evaluation of Urban Factors" encompasses all considera-
tions of a nonengineering nature.
This evaluation consists of a
review of existing governmental jurisdiLtions, current air pollution
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6
legislation and control programs, demographic data, current urbaniza-
tion, and projected patterns of urbanization.
The findings of the engineering evaluation are combined with the
results of the urban factors evaluation, and an initial proposal for
the air quality control region is made.
As indicated in Figure 2,
the proposal contained in this report is submitted as a background
document for consultation with State and local officials.
After re-
viewing the official transcript of the consultation proceedings,
which provides the viewpoints of State and local officials toward
the proposal, the Secretary formally designates the region.
Formal
designation includes a notice in the Federal Register and a notifi-
cation to the Governor(s) of the State(s) affected by the
designation.
THE SIZE OF A REGION
Several objectives are important in determining how large an air
quality control region should be.
Basically, these objectives can
be divided into three separate categories.
First, a region should
be self-contained with respect to air pollution sources and recep-
tors.
In other words, a region should include most of the important
sources in the area as well as most of the people and property
affected by those sources.
In this way, all the major elements of
the regional problem will lie within one unified jurisdiction.
Unfortunately, since air pollutants can travel long distances, it is
impractical if not impossible to delineate regions which are com-
pletely self-contained.
The air over a region will usually have at
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7
least trace amo~nts of pollutants from external sources.
During
episodic conditions, such contributions from external sources may
even reach significant levels.
Conversely, air pollution generated
within a region and transported out of it can affect external recep-
tors to some degree.
It would be impractical and inefficient to
make all air quality control regions large enough to encompass these
low-level effects.
Trace effects extend over a much larger area
than that which should be the focus of air pollution control efforts.
Thus, the first objective, that a region be self-contained, becomes
a question of the relative magnitude and frequency of air pollution
problems.
The dividing line between "important influence" and
"trace effect" will be a matter of judgment.
The judgment should
be based on esti~ates of the impact a source has upon a region, and
the level of pollution to which receptors are subjected.
In this
respect, annual and seasonal data on pollutant emissions and ambient
air concentrations are a better measure of relative influence than
short-term data on episodic conditions.
The second general objective requires that region boundaries
be designed to meet not only present but also future conditions.
In other words, the region should include areas where residential
and industrial expansion are likely to create air pollution prob-
1ems in the foreseeable future.
This objective requires careful
consideration of existing metropolitan development plans, expected
population growth, and projected industrial expansion.
Such
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8
considerations should result in the designation of regions which will
contain the sources and receptors of regional air pollution for a
number of years to come.
Of course, the region boundaries need not
be permanently fixed, once desig.nated.
Boundaries should be reviewed
periodically and altered when changing conditions warrant
readjustment.
The third objective is that region boundaries should be campat-
ible with and even foster unified and cooperative governmental admin-
istration of the air resource throughout the region.
Air pollution
is a regional problem which extends across several municipal, county,
and even State boundaries.
Clearly, the collaboration of several
governmental jurisdictions is prerequisite to the solution of the
problem.
Therefore, the region should be delineated in a way which
encourages regional cooperation among the various governmental
bodies involved in air pollution control.
In this regard, the ex-
isting pattern of governmental cooperation-on the whole range of
urban problems may become an important consideration.
Certainly, the
pattern of cooperation among existing air pollution control programs
is a relevant factor.
In general, administrative considerations dic-
tate that governmental jurisdictions should not be divided. -Although
it would be impractical to preserve State jurisdictions undivided,
usually it is possible to preserve the unity of ~ounty governments
by including or excluding them in their entirety.
In certain in-
stances, the county is not an'important decision-making level of
government.
Under these circumstances, city and town boundaries are
followed in determining the region.
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9
Where any two of the above three objectives lead to incompatible
conclusions concerning region boundaries, the region selected must
represent a reasonable compromise.
A region should be determined to
satisfy the three objectives in the best way possible.
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EVALUATION OF ENGINNERING FACTORS
EMISSIONS INVENTORY
The compilation of an air pollutant emissions inventory makes
possible the correlation of pollutant emissions with specific geographic
locations.
This procedure generally results in the determination of the
"core" of an air quality control region -- that is, the area where the
bulk of the pollutant emissions occur.
In this study, the emissions
inventory results are further utilized as input data to a meteorological
diffusion model.
In this manner the spatial and temporal distribution of
the pollution emitted into the atmosphere can be systematically pre-
dicted.
For these reasons, a presentation of the emissions inventory
results serves as a logical starting point in the engineering
evaluation.
The emission inventory was conducted by the National Air POllution
Control Administration.
The following 8 counties in southern Arizona
were included in the inventory study area:
Cochise, Gila, Graham,
Greenlee, Maricopa, Pima, Pinal and Santa Cruz.
The survey area is
shown in Figure 3.
The total study area encompasses the Phoenix and
Tucson urban areas and contains approximately 1,470,000 persons --
about 85% of the estimated 1969 population of Arizona.
The Public Health Service (PHS) rapt.d",survey'technique and
PHS emission factors were used for the estimation of pollutant
emissions.
The emissions were calculated from data representative of
the year 1967.
Table I provides a breakdown, by county, of sulfur
dioxide*, total particulate and carbon monoxide emissions in the study
*Emission estimates are based on all oxides of sulfur.
are composed chiefly of sulfur dioxide.
These emissions
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FIGURE 3. EMISSIONS INVENTORY SURVEY AREA.
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...
...
TABLE I
SUMMARY OF AIR POLLUTANT EMISSIONS IN THE PllOENIX-TUCSON STUDY AlIEA. 1967 (TOIlS/YEAR)
Transportation
Motor Vehicles
Fuel Combustion in Stationary Sources
Stesm-
Solid Waste Disposal Industrial
Inciner- Open Process
County
Countv Gasoline Diesel Aircraft Railroad Industrial Residential Other Electric ation Burnil1R Emiuions Aaricu1ture Total
~ Cochise 102 55 N'" 210 90 6 20 N N N 554,000 290 554,800
Gila 54 29 160 35 2 7 1 1 j 629,000 30 629,300
Graham 26 14 160 15 N 4 N 120 300
... Greenlee 12 7 70 10 N 3 422,000 40 422,100
'"
! Maricopa 1,330 370 115 90 37 10 7 37 290 140 2,400
Pima 480 1SO 150 440 15 80 3 4 154,000 230 155,500
Pinal 94 51 180 80 5 20 N N 303,000 600 304,000
rt.I Santa Cruz 22 11 40 10 N 4 N N If 30 100
Total 2,120 690 N 1,090 770 65 1SO 10 41 N 2,062,000 1,480 2,068,000
rt.I Cochise 140 1SO N 570 190 10 40 15 If 410 90 360 1,680
IS Gila 72 81 ! 440 100 4 10 N 1 205 If 30 940
~S GrahBIII 35 39 420 40 2 7 If 105 140 1SO 940
Greenlee 17 19 180 20 1 4 N 80 10 50 380
i Maricopa 1,770 1,020 1,560 310 240 140 30 1SO 120 1,000 5,090 2,220 13,700
Pima 640 400 710 400 1,170 60 170 120 80 200 6,780 290 11,000
Pinal 130 140 N 490 190 9 30 8 N 430 920 780 3,130
Santa Cruz 30 33 N 110 20 2 8 N If 90 N 30 320
Total 2,830 1,880 2,270 2,920 1,970 230 300 290 200 2,SOO 13,000 3,900 32,200
11<1 Cochise 21,800 80 N 320 110 5 15 N If 2,160 N 170 24,700
S
I Gila 11,900 40 1 240 SO N 6 1 1,080 1 20 13,300
GrahBIII 6,170 20 230 20 N 3 560 70 7,070
Greenlee 3,070 10 100 10 N 2 420 20 3,630
!!j Maricopa 321,000 560 8,850 170 130 15 15 390 5,370 310 200 337,000
~ Pima l11,SOO 220 3,090 220 630 4 70 1,070 1,060 50 130 118,000
Pinal 20,300 80 N 270 100 1 10 N 2,270 N 350 23,400
Santa Cruz 4 680 20 N 60 10 N 3 N 490 N 20 5 280
Total SOO, 000 1,030 12 ,000 1,610 1,060 25 120 N 1,460 13,400 360 980 532,000
'" N. Negligible
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13
area according to source type in five general categories.
These cate-
gories are transportation, fuel combustion in stationary sources,
solid-waste disposal, industrial processes, and agriculture.
The
~nformation provided by Table I indicates that industrial processes
account for nearly all of the sulfur dioxide emissions and over 40% of the
particulate emissions in the survey area.
Other source types, including
agricultural sources, railroads, gasoline-powered motor vehicles, open
burning and aircraft all contribute significantly to the particulate
emissions in the survey area.
Over 94% of the carbon monoxide emissions
in the survey area are attributable to gasoline-powered motor vehicles.
Open burning sources and aircraft are, also significant contributors
of carbon monoxide.
Table I indicates that major sources of sulfur dioxide are
located primarily in Gila, Cochise, Greenlee, Pinal, and Pima Counties.
The majority of particulates and carbon monoxide emitted in the survey
area are from sources located within Maricopa and Pima Counties.
Geographic s~ur~e locations over the survey area were d~fined by
the use of grid coordinates based on the Universal Transverse Mercator
(uno System.
Figure 4 shows the numbered .grid system super~posed over
an outline of the 'survey area.
Grid squares 10 kilometers on a side
were used in areas of most dense population and industrialization, while
grid zones 20, 40 and 80 kilometers on a side were used in areas of less
dense urbanization.
A total of 67 grid zones were used.
Figure 5 shows the location of most major "point" sources in the
study area.
These point sources are distinguished from "area"
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14
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FIGURE 4. GRID COORDINATE SYSTEM FOR THE PHOENIX-TUCSON
STUDY AREA.
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N
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(' ! i
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SOURCE TYPE:
8 INDUSTRY
. POWER PLANT
~ AIRPORT
FIGURE 5. MAJOR POINT SOURCE LOCATIONS.
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16
YUMA
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FIGURE 6. SULFUR DIOXIDE EMISSION DENSITIES.
< .0001
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17
COCONINO
APACHE
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FIGURE 7. TOTAL PARTICULATE EMISSION DENsrrIE:
< .0002
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18
N
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FIGURE 8. CARBOH MONOXIDE EMISSION DENSITIES.
< .005
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19
sources because of the large quantities of pollutants emitted from
them.
The majority of these large sources are concentrated in the
Phoenix and Tucson urban areas.
Several large sources are located in
Greenlee, Cochise, southern Gila, eastern Pinal and Western Pima
Counties.
Figure 6, 7, and 8 present emission densities for 802' total
particulates, and CO, respectively, based on the grid system.
~e
densities are computed on the basis of emission from both point and
area sources within each grid zone.
The pattern of S02 emissions
shown in Figure 6 corresponds to the development pattern of
the
Phoenix and Tucson urban areas and to the location of major point sources.
A variety of sources contribute significant amounts of total particulate
emissions.
The total particulate emission density map (Figure 7)
reflects the pattern of urbanization in the study area since the
sources themselves are representative of the urban pattern.
Carbon monoxide emissions are attributable primarily to motor
vehicles, as indicated previously; thus, Figure 8 provides an in-
dication of the vehicular traffic density distribution over the
survey area.
As expected, CO emissions are greatest in and around
Phoenix and Tucson and in areas connecting these two cities.
AIR QUALITY ANALYSIS
Introduction
The regional approach to air resource management requires that
those jurisdictions containing the majority of the sources of pollu-
tion in an urban area be included within a single air quality control
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20
region.
The air quality control region should also include juris-
dictions containing the majority of the people and property
adversely affected by air pollutant emissions from those same
sources.
The core area of a region can be roughly defined on the
basis of pollutant point source locations and relative emission
densities.
However, an analysis of ambient air quality is neces-
sary in order that peripheral pollutant receptor areas may be
identified and included in the air quality control region.
This
procedure will result in an essentially self-contained region
which includes within its bounds virtually the entire source-
receptor system for a particular area.
By using this approach,
the possibility of pollutant cross-boundary transport problems
will be minimized.
Two alternate approaches have been used to provide an
indication of air quality in the southern Arizona study area.
The
first approach consists of a review of measured air quality data
in the study area.
The second approach involves the estimation
of air quality over the study area through the use of a meteoro-
logical diffusion model.
This technique was desirable since
existing air sampling data was not complete enough to aid in the
determination of the outer limits of the Region.
TO'Doara'Dhv.. Meteorolo&y. and M~asurpc1 Ai T' QJuI1; toy
The State of Arizona is divided into three distinct regions.
The northeast portion of the State lis part of the Great Colorado
Plateau, whose average elevation varies from 5,000 to 9,000 feet
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21
above sea level.
The Colorado Plateau includes major portions
of Coconino, Navajo and Apache Counties.
The second region is
known as the Mexican Highland mountain region, which stretches
diagonally from the northwest corner of the State to the south-
east corner.
The mountain region is separated from the northern
Plateau region by an abrupt transition slope which also runs
diagonally across the entire State.
The Highland mountain region
varies in width from 150 miles in the State's southeast corner
to 70 miles elsewhere.
The southwest portion of the State com-
prises the third region, known as the Sonoran Desert.
This
region and the Highland mountain region are characterized by
numerous mountain ranges which rise abruptly from plainlike
floors.
The mountain ranges in the Desert region are lower, and
the valleys are wider, than are those in the Highland region.
The highly populated Phoenix and Tucson urban areas lie in
the Sonoran Desert region.
Phoenix is located in the center of
the Salt River Valley, whose elevation is approximately 1,100
feet above sea level.
Here the climate is of a desert type, with
low rainfall and relative humidity.
Mountains bordering Phoenix
have maximum elevations ranging from 2,300 to 4,000 feet above
sea level.
These mountains are located at distances of from 6
to 40 miles from Phoenix.
The valley floor is generally free of
wind, with speeds averaging between 4 and 8 miles per hour.
The
Phoenix wind roses are shown in Figure I-A.
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22
Winds are predominantly from the east in the winter and
from the east and west during the summer.
Wind direction is
dependent not only on the time of year, but also on the time of
day.
Wind flow in Phoenix is greatly influenced by terrain,
which causes winds to shift from west to east, depending on the
time of day.
Mixing depths, which reflect the volume of air into which
pollutants may disperse, are shown in Appendix A.
This data indi-
cates that pollutant dispersion is most restricted during the
morning hours (especially during the winter) and least restricted
during summer afternoons.
Tucson lies in a broad valley through which the Santa Cruz
River passes.
The elevation of the valley floor is approximately
2,400 feet above sea level.
Mountains lie to the east, west, and
north of the city.
The climate in Tucson is also of a desert type.
Like Phoenix, wind flow is greatly influenced by the terrain
surrounding Tucson.
Also, mixing depths in the Tucson area are
subject to the same large seasonal and diurnal variations as is
Phoenix.
Generally, topography is a major determinant of localized
meteorology in many areas of the State.
More specifically,
pollutant dispersion in Phoenix and Tucson is influenced by the
local topography.
The ability of pollutants to carry from the
urban cores is affected by mountains surrounding Phoenix and
Tucson, particularly during periods of restricted vertical
~
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23
movement of pollutants.
Also, pollutants may be channeled in
certain directions and over long distances by the mountain-
valley systems.
The precise impact of topography on meteorology
and on the geographic extent of the air pollution problem
requires more study than has been undertaken, however.
In general, existing air quality data in Arizona is not
sufficiently extensive enough to aid in the determination of the
Region boundaries.
Most of the S02, suspended particulate, and
carbon monoxide sampling has occurred in or very close to Phoenix
and Tucson.
These areas have already been recognized as the core
of the air quality control region in Arizona.
Monitoring in Ajo (Pima County), Douglas (Cochise County),
and Claypool and Hayden (Gila County) has indicated that local
sulfur dioxide concentrations are higher than are corresponding
values recorded in Phoenix or Tucson.
The sampling sites in Ajo,
Douglas, Claypool and Hayden are close to sources which emit
large volumes of gaseous oxides of sulfur.
The precise geo-
graphic extent of the effects of emissions from these sources is
not known, however.
The largest sources of sulfur dioxide in the
State (copper smelters) are located in Ajo, Douglas, Morenci
(Greenlee County), San Manuel and Superior (Pinal County), and
Miami and Hayden (Gila County).
Sulfation data indicates that the Phoenix and Tucson areas
have lower sulfation values than do extensive areas in Pima
County, southern Gila County, western Pima County, and Graham,
Greenlee and Cochise Counties.
State Health Department data
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24
indicates that areas surrounding the copper smelters referred to
above have the highest su1fation values.
The smelters in Pinal
and Gila County are closest to the Phoenix and Tucson urban areas.
Because of the limited data that now exists, the exact extent of
the influence of these sources is not known.
During the period
of the copper strike (July 1967 to March 1968), however, visi-
bi1ity in Phoenix was markedly improved*, while S02 concentrations
and su1fation rates in Tucson were notably lower.**
Sampling for suspended particulates has been conducted over
extended lengths of time at stations located in Maricopa and
Pima Counties.
An average of 1960 to 1968 yearly-average concen-
trations of suspended particulates measured at a site in Tucson
was 108 )lg/m3 .
Similar measurements for Phoenix over these same
years resulted in an average concentration of 168)Ug/m3.
Another
sampling site in Tucson recorded annual average suspended partic-
ulate concentrations ranging from 100 to 115)Ug/m3 over the years
1966 to 1968.
A seaond site in Phoenix recorded an average of
1957 to 1960 yearly average values of 209)Ug/m3.
taken at the Maricopa County Health Department from 1961 to 1967
3
revealed an average of yearly average values of 213 ~g/m. Other
Measurements
sampling stations in Maricopa County recorded yearly average
suspended particulate concentrations ranging from 143)pg/m3 in
Mesa (1966) to 300 fg/m3 at Boys Ranch (1967). Sampling for
* According to U.S. Weather Bureau visibility data taken at Sky
Harbor Airport, Phoenix, and from data at Mummy Mountain
Observatory, Scottsdale, Arizona.
** Based on data collected by the Pima County Health Department.
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25
suspended particulates in Ajo (Pima County), Florence and
Superior (Pinal County), Hayden and Claypool (Gila County),
Douglas (Cochise County), and East Plantsite (Greenlee County)
indicated concentrations which equal or exceed those in Phoenix
and Tucson.
Carbon monoxide sampling in the study area has been limited
to the city of Phoenix and thus provides no indication of the
necessary extent of the Region.
Diffusion MOdel Results*
The meteorological diffusion model has been used to compute
sulfur dioxide, suspended particulate, and carbon monoxide con-
centrations in the ambient air at specified receptor points in
southern Arizona.
The model predicts these concentrations from
a mathematical treatment of pollutant emission and meteorological
data.
A more detailed discussion of the model is presented in
Appendix A.
While the model contains inherent limitations, it
still has merit in providing reasonable spatial distribution of
long term (seasonal and annual)** average pollutant concentra-
tions.
The validity of the model as applied to southern Arizona
is somewhat questionable, however, due to the probable influences
of topography on pollutant dispersion patterns.
The diffusion
model, as applied here, did not consider variations in ground
* Graphic presentation of the model results does not appear here
due to time limitations placed on the production of this
report.
** Averaging times are as follows:
Winter: December, January, and February
Summer: June, July, and August
Annual: All 12 months of the year
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26
elevations.
This fact was considered in the interpretation of
the model results.
The model output indicates that S02 cQncentrations are the
greatest in Phoenix and Tucson and over localized areas of Gila,
Pinal, Graham, Greenlee, Cochise, and Pima Counties.
The con-
centration centers in these outlying areas are caused by large
individual sources of sulfur gas emissions.
The diffusion model indicates that the areas of highest CO
concentrations are the Phoenix and Tucson urban cores.
This was
the expected result since motor vehicle traffic, the prime pro-
ducer of CO pollution, is most dense in these two core cities.
The diffusion model equal concentration contours also indicate
that larger areas of Maricopa and Pima Counties, a major portion
of Pinal County, and lesser portions of the surrounding counties
are likely to experience the greatest concentrations of CO.
The pattern of relative-concentration contours for suspended
particulates was similar to that for CO.
The centers of the
greatest concentrations were predicted to occur in Phoenix and
Tucson.
The diffusion pattern correlates with the distribution
of pollutant emissions indicated in Figure 7.
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27
EVALUATIm OF URBAN FACTORS
INTRODUCTION
The Clean Air Act, as amended, calls for the designation of
air quality control regions based on "jurisdictional boundaries, .
urban industrial concentrations, and obher factors" to provide an
inter-governmental system for the prevention and control of air
pollution.
The designation of air quality control regions must
also be based on a consideration of existing cooperative regional
arrangements, State and local air pollution control programs and
enabling legislation, and patterns and rates of urban growth.
The
following discussion of urban factors will present these consider-
ations as they apply to the State of Arizona.
POPULATION DISTRIBUTION
Human activity in its many forms is the basic cause of air
pollution.
Thus, existing and potential air pollution problems
may be related to geographic areas by studying present and
projected population statistics for those areas.
Table II presents estimated 1969 population statistics for
the State of Arizona.
These statistics indicate that Maricopa
County contains 930,000 persons, or about 53% of Arizona's total
1969 population of 1,741,000.
Pima County, with a present
population of 343,200, contains about 20% of the State's popu1a-
tion.
Together, Maricopa and Pima Counties contain close to
three-fourths of the State's present population.
The city of Phoenix which lies within Maricopa County
contains an estimated 515,000 persons.
The Salt River Valley, in
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N
CD
TABLE II
PRESENT AND PROJECTED POPULATION DATA AND
MANUFACTURING EMPLOYMENT BY JURISDICTION
1969 1980 Additional Estimated
Land 1969 Population 1980 Population Additional Residents! 1967 Ave.
Area Estimated Density Projected Density Residents Mi1e2 % Growth Manufactur!ns
County {Mi. 2) Popu1ation1 (Persons!Mi2) Population 2 (Persons!Mi 2) 1969-1980 1969-1980 1969-1980 Employment
Apache 11,171 46,500 4.2 64,800 5.8 18,300 1.6 39.4 800
Cochise 6,256 66,500 10.6 95,200 15.2 28, 700 4.6 43.2 1,400
Coconino 18,562 56,200 3.0 77 , 400 4.2 21,200 1.2 37.7 1,500
Gila 4,747 26,900 5.7 38,700 8.2 11,800 2.5 43.8 600
Graham 4,618 15,400 3.3 22,300 4.8 6,900 1.5 44.7 200
Greenlee 1,879 9,700 5.2 14,300 7.6 4,600 2.4 47.4 50
Maricopa 9,238 930,000 101 1,284,600 139 354,600 38 38.1 69,800
Mohave 13,227 21,000 1.6 26,500 2.0 5.500 0.4 26.2 600
Navajo 9,910 49.900 5.0 69,500 7.0 19,600 2.0 39.3 1,000
Pima 9,240 343,200 37 473.900 51 130 . 700 14 38.1 8.700
Pinal 5.386 63.600 11.8 91.100 16.9 27.500 5.1 43.3 1.300
Santa Cruz 1.246 14.400 11.5 20.100 16.1 5.700 4.6 39.5 100
Yavapai 8.091 34.700 4.3 49.000 6.1 14.300 1.8 41.2 700
Yuma 9.991 63,000 6.3 87.800 8.8 24.800 2.5 39.4 750
Arizona
TOTAL 113.562 1.741.000 15.4 2.415.000 21.3 674.000 5.9 38.7 78.500
1. 2.
Data obtained from projections of data analysis section, Arizona State Department of Health. based on
U. S. Bureau of Census Data.
3.
From Arizona Basic Economic Data. Research and Information Series No. ECO-2-68. Arizona State Employment
Service. April 1968.
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29
which Phoenix is located, contains four of the remaining five
largest cities in the State:
Scottsdale, Mesa, Tempe, and
Glendale.
Phoenix, together with these four cities and adjacent
urban areas, accounts for the bulk of Maricopa County's total
population -- nearly 750,000 persons.
Phoenix is the central
city for a Standard Metropolitan Statistical Area (SMSA) which
consists of Maricopa County.
The city of Tucson, located within Pima County, contains an
estimated 240,000 persons, or 70% of tbe County's total popula-
tion.
The greater Tucson urban area contains about 300,000
persons, which accounts for an even greater percentage of the
County's total population.
Tucson is the central city for an
SMSA which is Pima County.
The city of Ajo, with a population of
about 10,000, lies approximately 120 miles west of Tucson.
The
remainder of the county is sparsely populated and contains only a
few small, scattered communities.
Figure 9 presents 1969 estimated populations and population
densities for Arizona by county.
This Figure indicates that
Maricopa,and Pima Counties are by far the most densely populated
counties in the State.
Maricopa County has a population density
of 101 persons per sq~are mile while Pima County has a population
density of about 37 p~rsons per square mile.
Pinal, Santa Cruz,
and Cochise Counties follow, with present population densities of
11.8, 11.5, and 10.6 persons per square mile, respectively.
In
terms of total population, however, Cochise, Pinal, and Yuma
Counties, in that order, follow Maricopa and Pima Counties.
All
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30
MOHAVE
21,000/1.6
COCONINO
46,500/4.2
N
1
miles
20
--- -
.- - -
o
20
.to
60
80
POPULATION DENSITY IN
PERSONS / SQUARE MILE
Figure 9.
1969 ESTIMATED POPULATIONS
AND POPULATION DENSITIES
tB
IlZZ1
UJ
D
> 15
10-15
5-10
0- 5
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31
other Arizona counties contain significantly less population or
population densities than do the counties mentioned above.
Figure 10 presents 1980 projected population statistics by
county.
Maricopa and Pima Counties are expected to remain the
most densely populated counties in the State since population
will continue to concentrate itself in the Phoenix and Tucson
urban areas.
Pinal, Santa Cruz, and Cochise Counties, respec-
tive1y, are projected to remain the next most densely populated
counties in Arizona.
As Table II indicates, Maricopa County will add 354,600
additional residents by 1980, followed by Pima County with
130,700 new residents.
Cochise and Pinal Counties each will
experience a population increase of over 25,000 persons.
Figure
11 provides an indication of the growth which the various counties
are expected to undergo in terms of total additional residents
to 1980.
In terms of per square mile growth to 1980, Maricopa and
Pima Counties will increase at the greatest rate, with 38 and 14
additional residents per square mile, respectively.
These are
followed by Pinal, Santa Cruz, and Cochise Counties, with 5.1,
4.6 and 4.6 additional residents per square mile, respectively.
In terms of added residents per square mile, all remaining
Arizona counties will increase at a lesser rate than either Pinal
or Cochise Counties since these remaining Counties possess far
greater land areas.
These statistics are presented in Table II.
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32
COCONINO
MOHAVE
26.500/2.0
N
1
miles
-.-.----
20
o
20
.4()
60
80
POPULATION DENSITY IN
PERSONS / SQUARE MILE
FIGURE 10. 1980 PROJECTED POPULATIONS
AND POPULA~ION DENSITIES.
,. )20.
IZZ1 10-20
C 5-10
D 0- 5
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33
MOHAVE
5,500
N
1
miles
20
--- -
-- -'.-
o
20
«)
60
80
ADDITIONAL RESIDENTS
FIGURE 11. TOTAL ADDITIONAL RESIDENTS, 1969-1980
J!
(Z)
o
> 25,000
20.000-25,000
10,000-20,000
0-10,000
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34
Table II also indicates that Greenlee, Graham, Gila, Pinal,
and Cochise Counties will experience a percentage growth increase
substantially greater than will the State as a whole.
The per-
centage increase to 1980 for these counties is 47.4%, 44.7%,
43.8%, 43.3%, and 43.2%, respectively.
The increase for the State
as a whole is projected to be 38.7%.
By 1980 Pima and Maricopa
Counties will experience a population increase of about 38% above
present levels.
The population statistics and population density maps
presented above do not provide a good indication of the geographic
distribution of population within the various counties.
It has
been mentioned that the greater Phoenix and Tucson urban areas
account for the bulk of the population within Maricopa and Pima
Counties.
These urban areas account for only a small portion of
the land areas of their respective counties.
Thus, population
densities in these core areas are far greater than are indicated
in Figures 9 and 10, which are based on the land areas of the
entire counties.
The remaining counties in the southern Arizona study area
do not contain single, large urban cores similar to Phoenix and
Tucson, but instead are composed of small, scattered communities.
The majority of Gila County's population is located in the
southern portion of that County, in the cities of Globe, Miami,
Hayden, and Winkelman.
Pinal County's population centers are
scattered throughout its area.
The major cities are Casa Grande,
Eloy and Coolidge in the west-central portion of the County,
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35
Superior and Apache Junction in the northern portion of the
County, and Mammoth, San Manuel and Oracle in the southeast
corner.
Most of Cochise County's population lies in the southern
half of that County.
The majority of Yuma County's development
is at the southwestern corner of the County.
Population centers -
are scattered in a random fashion throughout Graham and Santa
Cruz Counties.
POLLUTANT PRODUCING ACTIVITY
The location of manufacturing activity is helpful in
determining the size of an air quality control region since indus-
trial sources are major contributors of air pollutant emissions.
Manufacturing employment statistics serve as an indicator of the
geographic distribution of industrial activity.
Estimated 1967
yearly average manufacturing employment data is presented in
Table II and Figure 12.
These statistics indicate that Maricopa County employs by
far the greatest number of workers engaged in manufacturing
activities, with 60,800.
Pima County follows with 8,700 manu-
facturing employees.
Most of the workers in Maricopa and Pima
are employed in the Phoenix and Tucson urban areas.
The
majority of manufacturing workers in Maricopa County are employed
in the manufacture of machinery, aircraft parts, apparel and
primary metal production.
Primary and fabricated metals,
machinery, printing and publishing and the production of other
nondurable goods are the major industries in Pima County.
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36
II.t
...
..J
N
1
mIl.,
20
---. -
-- - -
o
20
«>
60
80
MANUFACTURING EMPLOYEES
FIGURE 12. 1967 ESTIMATED YEARLY AVERAGE
MANUFACTURING EMPLOYMENT BY COUNTY
~ > 1500
1000-1500
500-1000
0- 500
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37
Coconino, Cochise, Pinal and Navajo Counties each have 1000
or more manufacturing employees.
Graham, Santa Cruz, and Greenlee
Counties have relatively insignificant numbers of manufacturing
employees.
The bulk of the manufacturing activity in Coconino
County involves the production of wood and paper products.
Manu-
facturing employment in Cochise Coun~y is predominantly located
in the extreme southern portion of that County.
The maj or indus-
tries are involved in the manufacture of garments and vegetable
processing.
In addition, the copper smelting industry in Douglas
accounts for a large portion of Cochise County's manufacturing
employment.
Manufacturing in the west-central portion of Pinal County is
hign1y diversified.
Included are the manufacture of garments,
furniture and fertilizer, and fabricated metal products.
Primary
metal production is the major manufacturing activity in the
eastern portion of the County.
Copper smelters in San Manuel and
Superior account for about one-third of all manufacturing emp1oy-
ment in Pinal County.
The principal manufactured products in Navajo County are
lumber and paper.
Manufacturing employment in Gila County is
primarily associated with mining, copper smelting, food process-
ing and lumber products.
Generally, Arizona's manufacturing industry will increase
its share of the State's total employment.
The percentage of
jobs in Arizona in the manufacturing sector is expected to
increase from 12.9% in 1965 to about 16.7% by 1975.
The
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38
manufacturing industry will show the greatest growth among the
various sectors of Arizona's economy.
By 1975, approximately
125,000 jobs in manufacturing are expected -- nearly double the
number in 1965 (64,900).
Trends indicate a continuing centralization of population,
labor force and employment in the major metropolitan areas of the
State.
Maricopa County's growth in its share of the State's
total employment has been greater than its share of Arizona's
total population growth.
It is projected that by 1975, about 60%
of all jobs in Arizona will be in Maricopa County.
At present,
about 20% of the workers in Maricopa County are employed in
manufacturing.
It can be expected that the bulk of the State's
manufacturing workers will continue to be employed in Maricopa
County in the foreseeable future.
Manufacturing employment in Pima County is expected to remain
second in numbers to that in Maricopa County.
Approximately 48.6%
of Pima County's employed workers are engaged in manufacturing
activity.
Employment in all other counties is expected to remain
relatively low with respect to the number of workers employed,
and the percentage of total employees engaged in manufacturing
activities.
Mining and quarrying operations and the production of primary
and fabricated metals, especially copper, constitute a major por-
tion of Arizona's economy.
The economy of several counties in the
State is dominated by copper mining and smelting operations.
The
location of these operations is an important consideration since
copper smelting is a major source of pollution in Arizona.
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39
Copper mining and smelting are the primary sources of employ-
ment in the northern and eastern portions of Pinal County.
The
principal towns in these areas are Superior, Kearny, and Winkelman
in the County's northern projection and Mammoth, San Manuel and
Oracle in the County's southeast corner.
Copper smelters are
located in Superior and San Manuel.
The mining and smelting of copper provides employment for
over one-third of the work force in Gila County.
Mining opera-
tions are concentrated in the Globe-Miami area.
Copper smelters
are located in Miami and Hayden at the southern tip of the County.
Copper mining and smelting operations are concentrated in
the extreme southern part of Cochise County.
Mines are located
chiefly in Bisbee, while a smelter is located in Douglas.
Copper
mining and smelting form the core of Greenlee County's economy.
Clifton, the Greenlee County seat, is a large copper mining dis-
trict.
A smelter is located in the town of Morenci.
Nearly half
of all workers in Greenlee County are engaged in copper mining and
smelting activities.
Copper mining activities in Maricopa County are not very
extensive.
In Pima County, however, mining and smelting activities
account for a large portion of that County's economy.
More per-
sons are employed by mining and quarrying activities in Pima
County than in any other Arizona County.
A copper smelter is
located in Ajo in the western sector of the County.
All remaining
counties within the State contain relatively limited mining opera-
tions and no smelters.
.
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40
EXISTING REGIONAL ARRANGEMENTS
The geographic extent of regional councils, planning agencies,
State-defined planning and economic development districts, and
region-wide statistical data-gathering bases are an important con-
sideration affecting air quality control region boundaries.
The
designation of a region compatible with existing regional arrange-
ments is desirable since the implementation of a regional air
pollution program is dependent upon cooperation at the various
levels of government and since region planning programs may be
capable of providing assistance in the development of air quality
standards and a plan to implement those standards.
In Arizona, multi-county planning regions are non-existent.
Furthermore, State planning and development districts have not
been determined.
The two Standard Metropolitan Statistical Areas
in Arizona -- Phoenix and Tucson -- consist only of the county in
which each of these cities are located CMaricopa County and Pima
County, respectively).
The Counties surrounding Maricopa and Pima Counties are, to
varying degrees, tied economically and socially to the Phoenix
and Tucson urban areas.
Pinal County, because of its geographic
location, is tied to both these major urban areas.
It is expected
that Pinal County will be affected by Phoenix and Tucson growth
forces.
A system of new and improved highways passing through
Pinal County, including Interstate 10 and U.S. Highways 80-89, will
connect portions of that County to Phoenix and Tucson.
As a
result af this improved accessibility, these highways should
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41
stimulate development and caus~ Phoenix and Tu~son to grow toward
one another.
Portions of eastern Pinal County'have developed
social and economic ties ~ith Globe and other major towns in Gila
County due' to their remoteness'from other communities in western
Pinal County.
The populated portions of southern Gila County are connected
to the Phoenix urban area. by U.S. Routes 60 and 70.
Gila County
provides recreational facilities and scenic attractions for the
res~dents of Central Arizona, which contains the Salt River
Canyon
and the White Mountain recreation areas.
Generally, the basic-trading area for Gila, Graham, Greenlee,
Pinal, Yavapai and the remainder of Maricopa County is Phoenix.
The basic trading'area for Pima County is Tucson.
EXISTING AIR POLLUTION CONTROL PROGRAMS
In Arizona, statewide responsibility for air pollution control
rests with the Air Pollution Control Division of the Arizona State
Department of Health. - The.current law authorizes the Division to
identify air sheds and establish air pollution control districts,
to determine the quality and nature of air pollutant emissions, and
to determine meteorological conditions and other matters related
to the ,problem of air pollution.
Further" ,the Division is author-
ized to conduct air monitoring, determine standards, conduct
inspections, hold hearings, prepare and develop a comprehensive
State p1aL. for the abatement and control of air pollution, and
encourage political subdivisions of the State to handle air po11u-
tion problems within their respective jurisdictions.
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42
The present law states that the abatement of air pollution
shall be primarily by the county except when a county or region
specifically requests that the Division assume jurisdiction over
a part or all of the county, or when a source in one county causes
air pollution beyond the territorial limits of that county, or
when a county has failed to establish an adequate contre1 program.
The Division of Air Pollution has established rules and
regulations for reducing visible emission, air-borne or wind-
borne particulate matter and vapor emissions from storage tanks.
In addition, emission standards for particulate matter have been
established for a~l sources except incineration and fuel burning
equipment.
State law authorizes the board of supervisors of a county to
investigate the degree to which the atmosphere of the county is
contaminated by air pollution.
The board of supervisors is further
authorized to adopt rules and regulations, or to establish a mu1ti-
county air quality control region with one or more counties by
agreement with the board of supervisors of the other county or
counties.
A region formed in this manner is to be governed by all
of the provisions in the State law applicable to a county.
County air pollution control agencies are authorized to study
air pollution within a county and study possible effects on adjoin-
iog counties, hold hearings, adopt rules and regulations, issue
permits, and conduct inspections.
At the present time, Maricopa
County and Pima County have the largest county control programs in
the State.
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43
THE PROPOSED REGION
Subject to the scheduled consultation, the Secretary,
Department of Health, Education, and Welfare proposes to desig-
nate an air quality control region for the Phoenix and Tucson,
Arizona intrastate urban area.
The proposed Region consists of
the following jurisdictions in the State of Arizona:
Gila County
Maricopa County
Pima County
Pinal County.
As so proposed, the Phoenix-Tucson Intrastate Air Quality
Control Region would consist of the territorial area encompassed
by the outermost boundaries of the above jurisdictions and the
territorial area of all municipalities located therein and as
defined in Section 302(f) of the Clean Air Act, as amended
(42 U.S.C. l857h(f».
Figure 13 shows the geographic relationship of the proposed
Region to surrounding counties and to the State of Arizona as a
whole.
The proposed Region covers an area of 28,611 square miles
and contains 1,363,700 persons.
.....
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44
"
I I '
I I
.
. I
~ I
I
,Jr I I
I
1"- I
(r' I I
I I
f COCONINO I ~
I
I I
. L1
MOHAVE I
="' "
I .'\ I i
. .,,~. I
I "\...., . I
I
. L.ot . NAVAJO I APACHE"
/ I I I
I ~._.-"I I I
I I !
I
. --1 ' I
I YAVAPAI I I I
I . i
I .
I
I
t
I
.
} ,J-
r
.~./!
YUMA '" I ~
, ....
I Z
. w
I :
\ u
GRAHAM \"
\
)
i
. - - - - .......- - '---
N
1 COCHISE
mtles
--- -
-- - -
20
o
20
~
60
80
FIGURE 13. PROPOSED PHOENIX-TUCSON INTRASTATE AIR
QUALITY CONTROL REGION.
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45
DISCUSSION OF PROPOSAL
To implement a successful air resource management program, an
air quality control region should be ~ufficient1y large so as to
encompass most pollution sources as well as most people and property-
affected by'those sources.
The boundaries should a1so encompass those
locations where present development creates, or where projected
urbanization and industrialization will create, significant air
pollution problems.
Finally, the proposed region should be com-
patib1e with or hopefully even foster unified and cooperative
governmental administration of the air resource.
The proposed
Phoenix-Tucson Intrastate Air Quality Control Region was designed
to satisfy these requirements to the greatest degree possible.
The nature and location of pollutant sources were revealed
by the inventory of air pollutant emissions.
The inventory survey
area encompassed 8 of Arizona's 14 counties and about 85% of the
State's population.
The concentration of pollutant point sources
and the density of total particulate and CO emissions generally
are greatest in the Phoenix and Tucson urban cores.
Total par-
ticu1ate and CO emissions are also relatively high in portions of
Gila, Pinal and Cochise Counties.
Major individual stationary
sources of sulfur dioxide pollution are-located in western Pima~
southern Cochise, southern Gila, eastern Pinal and Greenlee
Counties.
The results of the emission inventory indicate that Phoenix
and Tucson are the logical core areas for the Region.
T~s
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Maricopa and Pima Counties are recommended for inclusion in the
Region.
Pinal County is also recommended due to its significant
contribution of air pollutants and its geographic proximity to
both the Phoenix and Tucson urban areas.
Source areas in southern
Gila County are adjacent to receptor areas in Pinal County and
V1ce versa.
Gila County has been suggested for inclusion in the
region because of its potential source-receptor interaction with
Pinal County, and under more extreme circumstances, with greater
Phoenix.
Topography in southern Arizona has a great effect upon both
localized and large-scale air flow patterns.
Air pollution prob-
lems in Phoenix and Tucson are likely to be accentuated under
certain conditions where limited pollutant mixing depths and
negligible wind speeds exist.
Both these Phoenix and Tucson urban
areas lie in valleys surrounded by mountain ranges at various
distances from those cities.
The mountains are likely to
affect the horizontal dispersion of air pollutants.
Similarly,
pollutants are likely to be channeled into these populated urban
cores over long distances as a result of the mountain-valley
systems.
Inclusion in the region of major source areas in Gila
and Pinal Counties, along with Maricopa and Pima Counties, should
create, under all but the most extreme conditions, an essentially
self-contained air quality control region.
Air monitoring data indicates that Phoenix and Tucson are
areas of significant pollutant concentrations.
This data also
indicates that pollutant concentrations equal to or exceeding
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47
those in Phoenix and Tucson exist in smaller communities in the
study area, including Florence and Superior (Pinal County), Hayden
and Claypool (Gila County), Douglas (Cochise County), Ajo (Pima
County), and East P1antside (Greenlee County). The large concen-
trations of particulates and S02' and the high su1fation rates in
the smaller communities, generally reflect the impact of nearby
large stationary sources.
The air pollution problem in these
areas is not reflective of a large-scale problem caused by com-
bined emissions from a vast number of individual sources.
Diffusion model results reflect the geographic pattern and
relative intensity of air pollutant emissions over the survey
area.
Centers of high concentrations, from a relative viewpoint,
occur in Phoenix and Tucson and at the scattered locations of
large individual pollutant sources.
The proposed 4-county Region
will include within its bounds the areas where widespread urban-
area air pollution problems exist, as well as most of the large
isolated sources of air pollution.
Population statistics indicate that Maricopa and Pima
Counties are presently the most highly populated counties in
Arizona.
The statistics also indicate that Maricopa and Pima
Counties are the mest densely populated in the State.
The bulk of
Maricopa County's population lies within the Phoenix urban area,
while the Tucson urban area accounts for the majority of Pima
County's population.
Projected population data indicates that
these two counties will undergo by far the greatest absolute
growth to 1980.
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Employment statistics reveal that Maricopa County has the
greatest number of manufacturing workers, followed by Pima County.
The continued centralization of population, labor force, and
employment in the major metropolitan areas of the State -- Phoenix
and Tucson -- indicates that Maricopa and Pima Counties will con-
tain the bulk of Arizona's induotrial activity in the foreseeable
future.
On the basis of population and employment statistics,
Maricopa and Pima Counties form a logical core for an air quality
control region.
Pinal County, which has been recommended for inclusion in the
Region, is expected to undergo a significant population growth
during the next decade.
Much of Pinal County's growth is expected
to result from Phoenix and Tucson growth forces.
Pinal County is,
because of its geographic location, tied both economically and
socially to both Phoenix and Tucson.
A system of new and improved
highways connecting Phoenix and Tucson will strengthen these ties
as a result of increased accessibility.
In addition, portions of
eastern Pinal County have developed ties to major towns in Gila
County.
The inclusion of both Gila and Pinal Counties in the
Region will reflect the economic and social ties which have devel-
oped between those two counties and Maricopa and Pima Counties.
Because of the nature of the problem of air pollution, there
is always the possibility that pollutant transport into or out of
the region may exist.
An air quality control region can never be
completely self-contained with respect to sources and receptors of
air pollution.
The 4-county Region proposed by the Federal
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Government is considered to be the most cohesive and yet inclusive
area within which an effective regional effort can be mounted to
prevent and control air pollution.
Official designation of the Region will follow the formal
Consultation with appropriate State and local officials, and after -
due consideration of comments presented for the record at the
Consultation or of those written comments received by the
Commissioner of the National Air Pollution Control Administration.
~
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APPENDIX A.
DESCRIPTION OF DIFFUSION MODEL
The diffusion model is based on the Gaussian diffusion
equation, described by pasqui111,2 and modified for long-term
averages3,4 for application to the multiple-source situation typical
of an urban complex.
The basic equation assumes that the concentra-
tion of a pollutant within a plume has a Gaussian distribution about
the plume centerline in the vertical and horizontal directions.
The
dispersion of the plume is a function of the emission rate, effec-
tive sources and receptor~eights, atmospheric stability and the
distance from the source.
The plume is assumed to move downwind
according to the mean wind.
The model was used to predict concentrations of S02 and CO, and
total suspended particulates.
The averaging times were the summer
and winter seasons and the year.
In order that the theoretical
pollutant levels could be determined, it was necessary to evaluate
certain meteorological input parameters.
These parameters are wind
direction and frequency of occurrence in each direction, effective
wind speeds for each direction, and mixing depths for various
averaging times.
Figure I-A shows the wind roses for the SUDDl1er, winter, and
year for the Phoenix area taken from u.S. Weather Bureau data.*
They represent graphically the frequency of occurrence of the wind
from the various compass directions.
This data, along with
* Wind data recorded at Sky Harbor Airport, ~oenix, Arizona, 1951
through 1960.
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WINTER
ANNUAL
51
SUMMER
FIGURE 1-A. WIND DIRECTION PER CENT FREQUENCY OF OCCURRENCE
FOR VARIOUS AVERAGING TIMES.
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effective wind speeds for the respective compass directions, was
used as input data to the computerized model.
The characteristic
prevailing wind dire~tions for each of the averaging times, as
,
depicted by the length of the wind rose radials~ produce a direct
influence over the dispersion of pollutants.
Table I-A shows average mdxing depths for the seasons and for
the annual averaging period.* A significant "diurnal variation in
the mixing depth is indicated.
These mixing depths define the vol-
ume of air above the surface through which pollutants are allowed
to mix, and are assumed to have no spatial variation (1.e., mixing
depth is constant) over the receptor grid system.
Table I-A
I
Average Mixing Depths for Phoenix
by Season and Time of Day (meters)
'. ,
,.A.1 ..
Afternoon' "
Morning ~verage, ~orn:l,ng
Season Average Average ' and Af,ternoon .'.
,
Winter 205 1250 728
Spring 295 2700 1498
Summer 280 3300 1790
Fall 220 2000 1110
Annual
(four seasons) 250 2312 1281
The diffusion model was used to compute the ground level con-
centrations of pollutants at 225 receptor points.
Their locations
were defined by an orthogonal grid system with mesh points 15
* Computed mixing depths documented by Holzworth5,6 and by recent
tabulations furnished to the Meteorological Program, NAPCA, by
the National Weather Record Center, ESSA.
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53
kilometers apart.
An effective source height of 75 meters was
assumed for all pollutant point sources, while topographical
features were neglected for area-source emissions and for the 225
receptor points.
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APPENDIX A.
REFERENCES
1.
pasqui11, F. "The Estimation of the Dispersion of Windborne
Material," Meteorology Magazine, 90, 33-49, 1961.
2.
Pasqui11, F. Atmospheric Diffusion, Van Nostrand Co., New
York, New York, 190 pp., 1962.
3.
Public Health Service. Workbook of Atmospheric Dispersion
Estimates. Publication No. 999-AP-26, Environmental Health
Series, U.S. DREW, National Center for Air Pollution Control,
Cincinnati, Ohio, 1967.
4.
Martin, D.O., Tikvart, J. A. "A General Atmospheric Diffusion
Model for Estimating the Effects on Air Quality of One or More
Sources," Paper No. 68-148, 61st Annual Meeting, APCA, St.
Paul, Minnesota, June 1968.
5.
Holzworth, G. C. '~ixing Depths, Wind Speeds and Air
Pollution Potential for Selected Locations in the United States,"
J. App1. Meteor., No.6, pp. 1039-1044, December 1967.
6.
Holzworth, G. C. "Estimates of Mean Maximum Mixing Depths in
the Contiguous United States," Mon. Weather Rev. 92, No.5,
pp. 235-242, May 1964.
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