AIR QUALITY ASSESSMENT AND PROJECTION
FOR SUMMIT COUNTY, COLORADO
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fkIR QUALITY ASSESSMENT AND PROJECTION
FOR SUMMIT COUNTY, COLORADO
Air Quality Impacts on
County-wide Land Use Planning
<.S. EPA Region 8 Uora
Denver Colors*1*
March 1976
Final Report
Submitted to Summit County, Colorado, Planning Department
by
AMBIENT ANALYSIS, INC.
1675 Range
Boulder, Colorado 80302
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AIR QUALITY ASSESSMENT AND PROJECTION
FOR SUMMIT COUNTY, COLORADO
Air Quality Impacts on
County-wide Land Use Planning
March 1976
EPA Project Officer: Mr. William J. Basbagill
EPA Contract: No. 68-01-3200
Submitted to Summit County, Colorado, Planning Department
by
AMBIENT ANALYSIS, INC.
1675 Range
Boulder, Colorado 80302
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TABLE OF CONTENTS
PAGE
TABLES AND FIGURES iii
SECTION I 1
A. Introduction 1
B. Summary of Results 2
1. Air Flow 4
2. Carbon Monoxide 5
3. Particles 5
C. Recommendations 6
D. Discussion 6
1. Minimize sources 6
2. Maximize distribution of pollutants 7
3. Monitor air quality 12
4. Develop and use controls 13
SECTION II 14
A. Air Quality Data Base 14
B. Wind Flow and Dispersion Models 14
C. Emission Inventory 14
D. Air Quality Estimates 14
E. Land Use Regulations 15
SECTION III 17
A. Topography and Climate 17
1. Topography 17
2. Climate 18
B. Mountain Valley Flow and Dispersion 20
1. Potential temperature 20
2. Steady state nighttime flow 25
3. Transition from night to day flow 26
4. Daytime flow 27
5. Transition from day to night 28
6. Complicating factors 29
7. Applying circulation model to air
pollution problems 30
C. Sampling Days—Criteria, Weather and Traffic 32
1. Sampling criteria 32
a. Summer 32
h. Winter 32
c. Meteorology 32
2. Weather 33
a. Summer 33
b. Winter 33
3. Traffic volume at Site 2 37
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PAGE
D. Carbon Monoxide and Particle Measurements 41
1. Carbon Monoxide 41
a. Summer vs. winter—197 5 data 41
b. Continuous CO Measurements 43
2. Total suspended particles 43
a. Comparisons of summer and winter
particle mass concentrations 45
b. Particle size distribution 47
c. Significance of particle data 52
E. Effects of Carbon Monoxide and Particles
on Hon 1th 54
1 . (!.i rhon Monox itk' 54
2 . I\i r l i i: I us ,54
3. A i r Po1 IuL ion 55
4. Federal, and State Air Pollution
Standards 56
SECTION IV 57
A. Conclusions 57
REFERENCES 58
ii
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PAGE
2
35
38
39
40
42
44
45
46
56
3
9
10
21
22
23
24
36
36
36
48
49
50
51
52
TA157.ES AND FIGURES
Particle and Carbon Monoxide Summary
Summary of Meteorological. Data
Traffic Count—August 18, 1974
Traffic Count—July 23, 1975
Traffic Count—December 30, 1975
Carbon Monoxide Concentrations
Continuous CO Concentrations
Total Suspended Particles Data
Particle Size Data for 1975
Federal and Colorado Standards
Sampling Sites
Most Critical Air Quality Areas
Land Ownership and Watersheds in Summit
County
Nighttime Valley Flow
Night-to-day Transition Flow
Daytime Valley Flow
Day-to-night Transition Flow
Temperature vs. Height
Wind Velocity vs. Height
Time vs. Height
EM Micrographs, July 23
EM Micrographs, July 23
EM Micrographs, December 30
EM Micrographs, December 30
EM Micrographs, December 30
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SECTION r
A. InL" rod in: t i on
Summit County is a small county in the heart of the Colorado Rockies,
which lias gained ail importance far beyond what its size and population
might imply. It lies just beyond the Continental Divide from Denver,
Colorado's capitol and most populous city. It occupies the vaLley of the
Blue River and its tributaries, and although the Blue River is a tributary
of the Colorado River which flows to the Pacific, Summit County supplies
a large fraction of Denver's water supply. Summit County is a land of vir-
tually unparalleled scenic beauty. It provides a mecca for small-boat
sailors, fishermen, hikers, and road-bound tourists in the summer. it
contains several of the most convenient and best ski resorts in the country.
Clearly, most people who visit Summit County consider it to be an unusually
attractive, essentially unspoiled, mountain resort area.
The resources which make Summit County so attractive are in danger of
being damaged. Further, the damage is being done by the very people who
are seeking to enjoy those resources. Automobile traffic, single and mul-
tiple dwe.l I lugs, roadside restaur, mis, inns, service stations, ski resorts—
these arc: all ostensibly to serve Lhe people who visit the area, but tlicy
can readily destroy the very resources which draw those people. Lf that
happens, it will be a tragic loss for Summit County and for all those who
will not be able to enjoy the recreational opportunities Summit County now
affords.
The Summit County Planning Staff is seeking to make the County's
resources available to the maximum number of people without loss of qual-
ity. The Planning Staff is anticipating the growth of demand on the County's
resources. It is trying to understand what facilities and services will be
needed to meet that demand. It is trying to determine how those facilities
and services can be provided in an orderly way. It is also asking what ef-
fect providing those facilities and services and accepting the people who
use and provide them will have on the basic resources of the area.
A primary concern is the direct effect which people and people-
oriented activities have on the quality of the air. Sparkingly clean air
is one of the area's great attractions. There is also concern for the ef-
fects that polluted air may have on water and vegetation. In a study re-
ported by Holben and Marlatt (1974) an effort was made to use air quality
models and projected pollutant emission rates to predict future concen-
trations of pollutants in Summit County. Those predicted concentrations
were compared to statutory standards. The report by Holben and Marlatt
was generally optimistic about the feasibility of maintaining satisfactory
air quality in Summit County. It did, nonetheless, contain recommendations
that several positive actions be taken to assure that air quality is main-
tained. The recommendations were all directed toward limiting the release
of pollutants in the County.
As a continuing part of the efforts of Summit County to evaluate the
air pollution potential of the County and to understand better the limita-
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Lions that; maintaining good air quality p Laces on human activity and
development, two of the most critical pollutants have been measured by
Ambient Analysis, Inc. at several key points in the County. These measure-
ments were made under disparate meteorological conditions, but at times
when human activity in the County was high. One objective was to learn as
much as possible in a short, low-budget study about current air quality in
the County. A second purpose was to check current air quality against model
predictions. The ultimate goal of the study was to advise the County Plan-
ning Staff on future development in the County.
The meteorological conditions under which measurements were to be made
were those calculated to produce very good and very poor dispersion of pol-
lutant. The places chosen to make the measurements were, with one excep-
tion, in areas where sources were numerous and concentrations were expected
to be high. The exception was a rural site in the north end of the County.
This site was expected to serve .is an Indicator of what air qualiLy in
the County can be in the absence of virtually all polluting sources.
13. Summary of ResuLts
The sites at which measurements were made are shown in Figure 1.1.
The sites and the reasons for selecting them are discussed in Appendix B.
Site 1 is a rural site; all others are in the vicinity of an important high-
way intersection or near a center of human activity. Site 3 at Brecken-
ridge is the only urban site, except that in December Site 2 was in Silver-
thorne. Concentrations of particles and carbon monoxide at all the sites
are summarized in Table 1.1. The measurements were not made with the in-
tent of checking current pollutant levels against statutory standards.
Nonetheless, some comparisons can be made. Air flow was observed carefully
during each observational period. Actual air flow was used in interpreting
other measurements, and it was combined with climatological data and theory
to arrive at an air flow model for Summit County. This model is described
in detail in Section III. A brief description is given here.
TABLE 1.1
Particle and Carbon Monoxide Summary. Particle data are given in micrograms
of the Total Suspended Particulate (TSP) matter per cubic meter of air
(Mg/m3). Carbon monoxide (CO) data are given in parts of CO per million
(ppm) parts of air by volume.
August 18, 1974 July 23, 1975 December 30, 1975
SITE TSP (yg/m3) CO (ppm) TSP (yg/m3) CO (ppm) TSP (yfi/m3) CO (ppm)
1
41
0.2
14
0.5
<4
1.4
2
61
0.5
49
1.5
16
4.5
3
86
0.9
16
0.5
11
7.4
4
37
1.0
10
16.3
5
13
<0.5
12
8.0
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rig. I.l - Sampling Sites. The
site numbers shown here are used
throughout this report. The
letters S and W indicate summer
and winter positions respectively.
Puss
C,o"'ln<./v ¦. \,
'•''V. . V I'
-p
l-'.or-r- u. r /I . , ,r
i'UM' ^'vidn
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1. Air Flow
The flow of air in Summit County is critically important to air
quality. With little air movement, any pollutants which escape into the
atmosphere remain near the source and accumulate. Strong flow through
the county, on the other hand, carries any pollutants away. It is
important also that air from near the surface be mixed upward so that
pollutants are dispersed through a deep layer.
A valley frequently has little air flow because it is protected from
the strong winds which normally flow across the valley above the mountain
tops. There are internal circulations in a valley, however; and in
Summit County these valley winds are highly significant. They blow up
the valley at day and down the valley at night.
At night when the valley is cool and the air is stable, little
vertical mixing occurs. Fortunately, the air which starts down from a
high level in the valley flows out over the air in the lower reaches of
the valley. Thus pollutants from high altitude emission sources do not
mix with pollutants from low altitude sources, and emissions do not
remain near the valley floor for a great distance away from their release
point. The valley floor is high enough at its southern end so that down
valley flow originating there is at mountain top level when it reaches
the northern end of the valley. It can then be carried out of the valley
by the winds above the valley. 1
During the warm part of the day, air flows up the valley. It is
usually unstable near the surface so that any pollutant released there
is mixed through an appreciable depth above the valley floor. Air which
flows up the valley walls and reaches mountain top level is carried away
by the winds above the mountains, carrying its burden of pollutant with
it.
The up valley winds in daytime and down valley winds at night are
both flow systems which help to lift surface level pollutant emissions
away from the ground surface. In Summit County which slopes steeply
downward from south to north, valley winds are normally quite effective
in dispersing emissions; however if they do not develop fully, pollutants
may accumulate. General cloudiness can prevent valley winds from develop-
ing. Winds above the mountains flowing along instead of across a valley
can also prevent valley flow from developing. Thus some side valleys
such as the Snake River Valley may be stagnant when valley flow is fuL.Ly
developed in the Blue River Valley.
The transitLon periods each day when flow changes direction arc essentially
stagnant periods. Transition normaLly occurs earlier in the upper reaches
of the valley than in the lower portions. The down valley to up valley
change occurs shortly after sunrise high in the valley and as late as
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1100 MST in the lower valley. The evening change may start as early as
1600 MST high in the valley and as late as midnight at the lower end.
The transition period varies in length, but winds may be expected to be
light and variable in direction £or about two hours at each transition.
The morning transition is more critical insofar as air pollution is
concerned. During that transition the air on the valley floor is still
stable and little vertical mixing can occur. After the wind shifts and
starts to blow up the valley, the air is likely to remain stable for
one to two hours. Consequently pollutant which is well above the sur-
face in the lower readies of the valley approaches the surface as it
moves up the valley. It is added to the surface emission source pol-
lution, and concentrations increase very near the ground.
2. Carbon Monoxide
The highest one-hour average of carbon monoxide concentration
measured was downwind of the parking lot at Copper Mountain. It was
slightly in excess of 16 parts per million (ppm) by volume. The one-
hour federal standard is 35 ppm. This measurement was made in December
during a period when both 1-70 traffic and traffic into the parking lot
were heavy and continuous for several hours. Dispersion was poor during
that period. Hence, it is quite likely that the average concentration
over an eight-hour period did exceed the federal standard of 9 ppm for
eight hours. This conclusion is not established conclusively but there
can be no doubt that the Copper Mountain parking lot is a source which
is now on the verge of exceeding federal, standards. Those standards
can readily be exceeded in the future when parking lot traffic and traffic-
on adjacent highways are high and dispersion is low.
3. Particles
The highest particle concentration found in the measurements was
86 yg/m^. This was an average for a period of about three hours. It
was observed during a period of the day.when particle concentrations
were expected to be high; consequently it is highly unlikely that the
24 hour average there exceeded either the Colorado Standard of 260 yg/m^
or the Federal Standard of 150 yg/nr* for non-designated areas. Particle
concentrations, in terms of mass per unit volume of air, do not appear
to present a serious limitation to development in most places in Summit
County. Although no measurements were made there, it is known that
blowing dust has at times been a serious problem at the sediment reser-
voirs in the southwest part of the county. Blowing dust can be a problem
in summer anywhere in the county where the soil is disturbed. Dry
conditions and gusty winds then raise dust. The duration of such
blowing dust is normally short.
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cytyna.tij5.Li, One.
Another and potentially more serious problem exists. The filter which
was exposed near the intersection of 1-70 and State 9 in July showed as-
bestos-like fibers in surprisingly large numbers. A second filter exposed
for short periods along T-70 between Silvertliorne and the west portal of
the Eisenhower Tunnel also contained many such fibers. These were Identified
by qualitative x-ray probe as inorganic. Jf subsequent tests show these to
persist in Str.iighL Creek Canyon or elsewhere in Summit County, they are
cause for concern.
C. Recommendations
1. Minimize the number and strength of air pollution sources in every
practical way in Summit County. This is a simple, obvious recommendation,
but acting on it involves making compromises between air quality and econ-
omy, air quality and water quality, etc. This is amplified in Section I.D.
2. Maximize distribution of unavoidable pollutants in every practical
way. Many things can be done. Sources can be distributed judiciously
throughout the valley, placing them at many levels and preventing large
clusters. (A parking lot constitutes a cluster of sources.) Chimneys
and houses can be built so that downwash is minimized. Sources, including
roads, placed in confined valleys will cause more severe pollution problems
than comparable sources placed on hills or hillsides.
3. Monitor air quality in those places where concentrations are
likely to be greatest under adverse conditions.
4. Develop and use controls. These may range Prom restricting fire-
place burning to closing the County to all nonessential traffic.
D. Discussion
The recommendations in Section III.C are brief. Some amplification and
discussion of each is given in this Section.
1. Minimize the number and strength of air pollution sources
Residences, commercial facilities, recreational facilities, lodging,
and dining facilities are all stationary emissions sources. Portable emis-
sions sources are sources which can be moved. According to the State Air
Pollution Control Division, there were no large stationary sources in Sum-
mit County in February 1976. There was one portable emission source with
a potential of 100 tons per year. Indirect sources are usually vehicular-
related and anything such as a recreational parking lot costitutes an in-
direct source. One area source is identified by the State Air Pollution
Control Division; it is the sedimentation reservoir complex in the south-
western part of the County.
The Colorado Air Quality Control Regulations and Ambient Air Quality
Standards which became effective on February 1, 1972, provide the statu-
tory authority for controlling air quality in Colorado. There are a num-
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ber of regulations, each having limited applicabiJity. Since these regula-
tions constitute a legal document, no effort- as made to interpret them,
although attention wii 1 be called to them occasions i J.y .
Controlling the number of sources may not be easy. Doing so limits
growth and development. The current population for Summit County has been
estimated as follows by Mr. David Vince of the Summit County Planning Staff:
Total Unincorporated Areas
Permanent A,336 1,477
Second Home 16,533 11,572
Peak 20,869 13,049
Mr. Vince has also estimated the total potential population, based on
approved zoning, as 99,900, and the potential population in unincorporated
areas to be 53,400.
These figures suggest that the population may grow to four or five
times its present peak level. The distribution between incorporated and
unincorporated areas is not expected to change drastically. Hence popula-
tion density is expected to increase everywhere with an inevitable increase
in emissions sources of most of the types now existing in Summit County.
An increase in source numbers must be accompanied by a decrease in source
strength and better dispersion if air quality is not to deteriorate.
As a first step in exercising control, the County should require that
each prospective developer submit a statement with his plan which shows
that he has considered air quality maintenance in the vicinity of the develop-
ment and how he plans to minimize emissions.
The strength of each emission source can be decreased. Fireplace burn-
ing can be avoided. Clean fuels can be used for space heating. Perhaps
furnaces can be improved so that they produce less pollutant, although
they are probably not serious offenders. Much work is being undertaken to
make the automobile exhaust cleaner. Until recently the effects of alti-
tude on automotive pollution has not been considered in setting performance
standards. In the future automobiles may have to meet prescribed standards
in the area in which they are sold. Because of the high volume of tourist
and cross-country truck traffic in Summit County, altitude effects may con-
tinue to be a problem, however.
Any large inLunsu source should be permitted only after a very careful
study shows that it will not degrade the environment. It appears unLikely
that a source such as a power plant will be acceptable anywhere in the
County.
2. Maximize distribution of unavoidable pollutants
Pollutants are always present. It is only when their concentrations
reach levels which have recognizably undesirable effects that they become a
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problem. Concentrations can be kept low by mixing those pollutants which
cannot be avoided with adequate quantities of air. There are many things
which can be done; there are also limitations.
In a valley dispersion from a single source is related to the broadness
of the valley (particularly at the source l.evel), to the winds blowing in
the valley, and to the st.ibiLity of the air in the valley. These are things
over which man has little control. He is capable of understanding them,
however, and he can place sources where dispersion is good and refrain from
placing them where dispersion is poor. The air flow model discussed in
detail in Section III.B provides general information from which some con-
clusions can be drawn.
Sources should be well distributed both horizontally and vertically
about the valley. Intense sources should be avoided everywhere, but they
should be avoided particularly in small basins. A large parking lot in a
basin can become an intense source. The high concentrations can be avoided
by using a series of small parking lots distributed through an appreciable
valley depth. This would require that public transportation of a non-pollut-
ing type provide transportation from these small lots to the center of at-
traction which the large lot now serves.
A shopping center in an urban area may serve as an intense emissions
source. The cluster of buildings associated with the center causes a num-
ber of sources to be located near each other and at essentially the same
level. These and the autos using the parking lot can readily constitute a
concentration of sources that will cause unacceptable local concentrations.
Again good horizontal and vertical distribution of small shopping facilities
is preferred for air quality preservation.
liven residences should be wel I distributed about the valley if a way
can be found to permit travel to and from them without creating poLLution
problems and provided that they and their access roads do not create undue
visual environmental problems or water problems.
Most of the land in Summit County is under jurisdiction of the Federal
Government. It is assumed in the discussion of the watershed areas below,
that development can occur on either public or private land.
With air flow, valley dimensions, and terrain all considered qualita-
tively, the following statements are offered. Development in the following
areas has reached a level and is of such a nature that carbon monoxide con-
centrations should occasionally be expected to exceed the primary Federal
Standard for undesignated areas: Straight Creek Canyon, Dillon, Silver-
thorne, Frisco, Breckenridge, and the ski areas of Copper Mountain and Key-
stone. These areas in which additional development should be most carefully
controlled are indicated in Figure 1.2.
Figure 1.3 shows the distribution of private and public lands in Summit
County. It also shows the various watersheds. Some statements are made
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Fig. 1.2 - The most oriLical a Lr qua 1.icy
areas in L975 in Summic CounCy are Che
haCched areas shown on this map. Tlie heavy
dashed line encloses these and additional
areas in which the potential for degeneration
of air quality is great enough to warrant,
careful attention as further development
occurs.
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cz/j~na[iji.L±, One.
below about air quality and the opportunity for development in each of
these watershed areas.
Straight Creek. Any further development should be of a non-polluting
kind. The air becomes stagnant frequently at night and 1-70 constitutes a
strong source of both carbon monoxide and particles.
Snake. Limited development is feasible, but it should be clean (i.e.,
pollutant contributions from both direct and indirect sources should be
low) and it should be distributed horizontally and vertically. The north
and east sides of Swan Mountain offer some possibilities. Stagnant, stable
air is more likely in the Snake River Valley than in most other parts of
Summit County. Pollution may be expected to be worse in winter than in sum-
mer .
Swan. The western part of the Swan is most subject to development,
and since the region includes a large area west of the Blue River, consid-
erable development should lie practical here. The west side of Swan Mountain
i.s suitable for development I" ruin Llic air qua.liLy viewpoint. Swan Ki.ver it-
self may be expected to suffer from stagnant, stable air in winter as
Straight Creek and the Snake will. Hence development should be less inten-
sive there than on the west side of the Blue River. Winter is the worst
season for pollution.
Upper Blue. Although the valley here is not broad, it is short and
it is perpendicular to the prevailing winds above the mountains. Conse-
quently, additional development appears feasible, if source strengths are
kept low and the sources are well distributed horizontally and vertically.
Additional, development in the immediate vicinity of Breckinridge is least
desirable. Winter is the season when air quality can be poorest.
Copper Mountain. Further development in the immediate vicinity of
Wheeler Junction must be accompanied by actions to reduce source strengths
if Federal Standards for carbon monoxide are not to be violated. Develop-
ment can occur elsewhere if due regard is paid to source strength and dis-
tribution, although the narrow gorges of Tenmile Creek will tolerate very
little development. Since 1-70 is in the gorge below Wheeler Junction, ad-
ditional pollutant sources should be avoided Lliere. Also any development"
in WesL Tennii I e Creek which includes pollutant emissions should occur well
away from the highway. Particulate matter is like.ly to be a problem in the
upper reaches of Tenmile Creek because of the sediment reservoirs there.
This is a summer problem. In the valleys, particularly at Wheeler Junction,
air pollution will be most serious in winter.
Tenmile. This area offers little terrain which appears suitable for
development, but some development could occur without creating an air qual-
ity problem if the sources are judiciously distributed.
Lower Blue. The Lower Blue is the largest valley in Summit County.
Its terrain is varied enough to permit considerable development without
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concentrating emission sources too greatly at any single level. It can
be expected to have a well-developed valley breeze, and the air which flows
from the valley at night will not often reenter the valley the following
day. On those days when the winds above the mountains are from northwest,
the down-valley wind at night will be disrupted and air from the Blue River
as far away as Kremmling and, indeed, air from all parts of the Colorado
River Valley around Kremmling may enter the Lower Blue. Thus air quality
in the Lower Blue Valley will be better because of the broader Colorado
River Valley to the north if emissions sources there are not excessive.
Strong sources there could create a real problem for the Lower Blue, how-
ever. Again, winter is the most critical period.
Reservoir Area. This includes Dillon, Silverthorne, Frisco, and the
Dillon Reservoir. The highway intersection at Silverthorne is quite im-
portant because it is a focal point for much of the automotive traffic with-
in and through the County. This basin is relatively large and air moves
through it well under most meteorological conditions; these are factors
which favor good air quality. The several clusters of pollutant sources and
the flatness of the terrain have an adverse effect. During stable periods
pollutants released near the ground in this basin tend to remain near the
ground. Thus Dillon can be exposed to its own emissions plus those of
Frisco during ilown-val Icy flow, anil to cm i ss Lous from Dillon, L-70, State 9,
and Silverthorne during up-vn 1.1 ey flow. The area west of 1.-70 between
Silverthorne and Frisco offers the best opportunity for further development
without creating an air quality problem. The area around the junction of
1-70 and State 9 at Silverthorne is one of the most critical areas in the
County; further development there should be undertaken only if it has been
carefully considered and fully justified. Winter is the most critical per-
iod for carbon monoxide. Particulate matter may become a problem in summer.
(See Sections III and LII.E.)
3. Monitor air quality
This study suggests that there are already some areas in Summit County
in which statutory standards are being exceeded. The areas are small. The
excesses are more likely in winter than in summer. (The area around the
sediment reservoirs near Climax may be an exception.) With continued
development pollutant concentrations are likely to get worse in all parts
of the County in each succeeding year unless positive actions are taken to
limit emissions and increase dispersion. Air quality monitoring will dis-
close how well these actions are working.
Although a general knowledge of air flow in the County exists, more
must be known if development is to be done wisely. Hence a number of
meteorological variables should be measured regularly at severaL places in
the County. Measurements which yield hourly average wind speed, direction,
and temperature, or a continuous record like that produced by the MRI mechan-
ical weather station would be very helpful. A single station at a represen-
tative site near Dillon is most essential. Additional stations are desir-
able and representative sites near Keystone and Copper Mountain would be
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most: useful. A few pur J oils ol Intensive observations using teLliered bal-
loon systems and a rawinsonde should also be conducted. A concurrent
study of the synoptic meteorology of the Rocky Mountain Region should be a
part of such studies.
Equally important, good air quality measurements should be made regu-
larly at several locations. A site should be set up near the intersection
of 1-70 and State 9. Another should be placed in an urban area like
Breckenridge. As a control one should be placed in a rural area away
from roads. These should all be equipped to measure carbon monoxide and
particles, either continuously or at times recommended by an air pollution
meteorologist who maintains an awareness of existing and expected weather
in Summit County. The measurements must be done carefully and well. Meas-
uring instruments must be kept in good operating condition and calibrated
often using good calibration standards. These obvious statements cannot be
given too much emphasis, because they are too often not followed.
Periodically particles should be collected along 1-70 on membrane fil-
ters and tested for mineral fibers.
4. Develop and use controls
Control of development has been discussed. The Colorado Air Quality
Control Regulations and Ambient Air Quality Standards provide the statutory
basis for exercising control over air quality. They may not be adequate.
In particular, there is no regulation applicable to indirect sources. Sum-
mit County will have to develop its own method of dealing with indirect
sources. This might include urging adoption of an applicable regulation by
the state.
Even if development is controlled according to a well-conceived plan
which assures good air quality virtually all the time, there will be occa-
sions when nature fails to follow her usual course. Unusual periods of in-
tense stagnation can occur. It is reasonable to take unusual measures to
control pollution in these situations, measures which would not be acceptable
routinely. It is unreasonable to maintain development at such a low level
that there could be no problem under the most adverse meteorological con-
ditions. Therefore, controls which can be imposed in a short time and which
wii .1. cause as little disruption of activity as possible must be considered.
These can range from banning fireplace burning during a few morning hours
to banning all automotive traffic in the County except that which is absol-
utely essential to health and welfare.
It is clear that 1-70 with its high volume of traffic constitutes a
major source of air pollution in Summit County. Perhaps 1-70 traffic can
be changed from an automotive arterial to some other form of mass transpor-
tation. If one could be found which makes use of more efficient and less
polluting vehicles than private automobiles, Summit County's pollution prob-
blem would be considerably simplified. This was recommended in the public
hearings of the Land Use Commission in November 1974.
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<^/fm(jLe.nt c^fna[ijh.i±, One.
SECTION II
A. Air Quality Data Base for Summit County
For the purpose of this study air quality data consist of the chemical
and meteorological measurements of the type needed to state the current air
quality in Summit County and to make a reasonable projection of future air
quality. Data currently available have been summarized by Kahn (1974) and
Holben and Marlatt (1974). Some additional data have become available
since these studies were completed, however. In particular, additional
Hi-Vol particle data have become available at Breckenridge and additional
meteorological data covering a few months duration is available for Silver-
thorne, Breckenridge, and the Breckenridge waste-water disposal plant at
Swan Mountain. These data and environmental impact statements FWHA-COLO-
EIS-74-01-D and FHWA-COLO-EIS-74-02-F were provided by the State Highway
Department.
B. Wind Flow and Dispersion Models
Wind flow in mountainous terrain is poorly understood. Wind flow in
valleys is better understood, however, and a qualitative wind flow model
for a valley can be quite useful. Such a model is discussed in detail in
Section III.B. Success in projecting air quality depends on having an
adequate wind flow model, a good dispersion model and adequate meteorolgical
and pollutant emission data. Most modeling for mountain valleys is done
using a single constant wind velocity and either a box or a Gaussian dis-
persion model. Holben and Marlatt used both of these models with a con-
stant wind in making projections of air quality in Summit County. They also
made limited use of a WINDS model designed by Fosberg, Rango and Marlatt
(1974). This model employs terrain elevation, slope, aspect and surface
roughness and an initial temperature field to calculate local wind flow.
C. Emission Inventory
An inventory of cniLssLons from s La t j ona ry and mobil.e sources was pre-
pared by Holben and Marlatt (1974).
D. Air Quality Estimates
\
Air quality projections made through the use of the models and emis-
sion data discussed above are contained in the report to Summit County by
Holben and Marlatt (1974). Using a box model, they estimated that the air
pollution potential of five regions is high, three regions is medium, and
ten regions is low. The box model is not realistic for a valley with a
steep Iy-sJoping fJoor, and they assumed wind and box depth data. There-
fore their estimates are misleading.
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c^f-m^Le-nt c^fnaiyiii, One.
E. Land Use Regulations
State and county land use regulations pertaining to air quality
are at present limited to the county permit-to-construct process and the
State of Colorado 100 ton stationary emission requirements. The State
has laws which can be interpreted to cover developments of specific
concern to the public. Statutory air quality regulations are found in
the Air Pollution Control Act (66-31). The regulations from that act
which are applicable in Summit County are:
Reg. 1
Fugitive dusts, fuel burning equipment
Reg. 2
Odor control.
Reg. 3
Basic permits.
Reg. 6
Stationary sources.
Reg. 7
Hydrocarbon emissions.
Reg. 8
Hazardous substances
Reg. 9
Automotive pollution restraints.
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PAGE 16 BLANK
cz/f-mtjiznt 1Jnc.
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SECTION III
A. Topography and Climate
Topography and climate are closely related in Summit County. Holben
and Marlatt (1974) provided a short summary of climate and its relation
to topography. In this section those aspects of topography and climate
which bear most directly on the air pollution potential of the County are
reviewed.
1. Topography
Summit County occupies the valleys of the Blue River and its
tributaries. The most important tributaries are Straight Creek, Snake
River, Swan River, and Tenmile Creek. The Straight Creek and the West
Tenmile Creek valleys are small but quite important because 1-70 occupies
each through its full length, and automotive traffic is heavy.
The Blue River Valley is oriented in a generally north-south direction.
The valley is high; its floor ranges in height from 7,500 ft. (2,280 m) at
the north end, where it opens out into the broader Colorado River Valley,
to 10,000 ft (3,050 m) south of Breckenridge. The 10,000 ft contour also
delineates rather well the upper reaches of the valley floor in all of
the principal tributary valleys of the Blue River. The steepness of
the valley floor (it drops 2,500 ft in a distance of approximately 40
miles) is important to its air quality potential.
The walls of the valley are steep nearly everywhere. Peaks in
excess of 13,000 ft (3,960 m) are found in most of the ranges which
form the county boundaries. The steep valley walls and height of the
mountains are also important to the air pollution potential of the
county. The high mountains serve to isolate the valley from the strong
westerly winds which flow across it aloft. The steep walls and floor
assure nearly continuous air motion in the valley. Air motion is
discussed in detail in Section III-B.
The only level portions of the valley are those occupied by the
Dillon Reservoir near the center of the county, the Green Mountain
Reservoir in the north and the' sediment reservoirs in the extreme
southwest section of the county. None of these are large, but the
basin-like character of the Dillon area and the relatively high popu-
lation and traffic density there do make it one of the county areas
which is most prone to air pollution problems. The sediment reservoirs
are important because they are a source of particles, and when strong
westerly winds blow, the particles get carried to great height and
dispersed downwind.
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cz/f-mljLznt c^/fnaCyi-ii., fJnc.
The east-west orientation of most of the tributaries of the Blue
River causes them to be less isolated from the prevailing west winds
at mountain-top level than the Blue River. In the Snake River Valley
this may frequently be quite important, but the valleys associated with
the other tributaries are small and steep enough that the westerly winds
aloft will have a lesser effect on the flow in them.
It is important to note that the entire valley is short and that
it opens out on a much larger valley, which is subject to frequent and
thorough scouring by the prevailing west winds. Because of the short-
ness of the Blue River, the Light, diurnal, valley winds are also
capable, most of the time, of carrying away pollutants originating
in the valley. If the valley were longer, these same winds, blowing
down the valley at night and up the valley by day, could cause pollutant
to be trapped and to oscillate up and down the valley, gaining strength
day by day.
2. Climate
Summit County embraces a continuing change of climate from its
lowest to its greatest heights, which is much like the change one mij>ht
encounter in going at sea level from the Northern U.S. to the Canadian
tundra. The valley is cut off from a continuing moisture supply by
high mountains and ils great distance from the oceans. Theret <> re,
cloudiness and precipitation are low, and most of precipitation is in
the form of snow which falls in winter as major storms cross the area.
The snow serves as a water storage mechanism, and water is also stored
in reservoirs. Consequently, although the total precipitation isn't
large, Summit County serves as a source of water for Denver and has
water for a limited resident population and for some agriculture.
Frequent clear skies and high altitude help to assure maximum
radiative heat effects. The sun warms the surface rapidly in the
morning and the days are warm. Likewise, at night clear skies permit
the warm surface to radiate away its heat, and nights are cold. The
diurnal variation of temperature contributes to a well-organized per-
sistent diurnal wind system in the valley. This valley flow is ex-
plained in detail in Section III.B.
In addition to having well-defined diurnal weather changes, Summit
County weather also undergoes a marked annual change. Summer is warm
and dry. The precipitation which falls is usually in the form of brief,
light showers. These occur most frequently over the mountains in the
afternoon and infrequently in the valley. Rarely does a major storm
cross Summit County and cause widespread precipitation there in the
summer.
In winter when a major storm crosses the area, snow falls throughout
the county. The winds aloft (at mountain-top level and above) are from a
southerly direction ahead of a major storm and from north to northwest
behind the storm. Valley winds are disrupted by these storms, and blowing
snow can occur in the valley. Following the passage of a major storm, air
in the valley frequently becomes quite cold.
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cztfmljie.nl c^fnatiji.Li, fJnc.
Minor storms pass through the Central Rockies frequently in winter.
These are accompanied by small changes in wind direction aloft and little
wind in the valley. These minor storms do cause snow to fall on the high
mountains, however, and so contribute to the total snow pack at high
altitudes.
The vertical stability of air near the surface is an important factor
when air pollution is a potential problem. Stable air is generally asso-
ciated with poor vertical air mixing and high pollution potential. Unstable
air is associated with good mixing and good air quality. These concepts
must be applied with reservations in a valley such as the Blue River Valley;
the reason is explained in Section II1.B. Nonetheless, stability is a use-
ful concept. In Summit County the air near the surface becomes stable
nearly every evening. It is most stable early in the morning. At sunrise
the air starts to become less stable, and by noon unstable conditions
generally exist near the ground throughout the County. This diurnal var-
iation occurs in all seasons. As a rule the air is less stable at any hour
of the day in summer than in winter at the corresponding hour.
During storms normal diurnal changes fail to occur. Also each storm
affects the valley in its own way and air flow, temperature, precipitation,
and stability are difficult to describe in a general way for stormy periods.
When precipitation is falling, however, air pollution is not likely to be a
concern; after a winter storm has passed and new snow covers the valley,
air pollution must be considered a threat.
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One.
B. Mountain Valley Flow and Dispersion
Winds in a mountain valley are influenced by so many factors that
they often defy description. On the other hand, when a valley is iso-
lated from the flow of the atmosphere above, winds often follow a pre-
dictable diurnal pattern, flowing down the valley at night and up the
valley during the day. This diurnal change is the dominant weather
feature in some valleys. It is also a feature which causes much con-
cern when air in the valley is being polluted. Since the populated
portion of Summit County is in a valley which experiences a marked
diurnal. wind flow, the characteristics of: that flow are discussed at
some length here. Some attention is also devoted to the influence of
the atmosphere outside the valley as it effects the valley.
The Blue River Valley is the major valley in Summit CounLy. Being
oriented nearly north-south, the prevailing westerly winds in the free
atmosphere above the mountains flow over the valley, often influencing
winds in the valley through only a short distance below the mountain
tops. Figures III.l through III.4 are schematic views of air flow and potential
temperature in a steep-walled, narrow valley with a north-south orientation.
The valley is open on the north. The top drawing in each figure depicts
an east-west cross-section of the valley at a location approximately
midway between the head of the valley and the point at which it opens
out onto a plain or much larger valley and loses its separate identity.
The lower drawing shows a longitudinal section of a part of the valley.
It is a north-south section, the location where the cross-section cuts
it is identified by the number 1. The valley floor slopes steeply
toward the north. The vertical scale is exaggerated in nil of these
figures.
Figure III.L represents a simplified view of the wind flow and the
potential temperature pattern in the valley during the early morning
just before dawn. The arrows represent the wind components in the
plane of the paper, the length of the arrow is proportional to the
wind speed. The symbol© represents wind flowing toward the viewer—
that is a south wind flowing down the valley.
1. Potential temperature as an aid to understanding
stability and air motion
Potential temperature is an artifice which the meteorologist finds
quite useful. As air in the atmosphere moves upward, its sensible (measureable)
temperature drops unless the air is gaining heat. Similarly, as air moves
downward its sensible temperature increases. Its potential temperature,
however, does not change as it changes altitude unless it gains or loses
heat. Normally, air at high altitudes has a higher potential temperature
than air at low altitudes. A layer of air which has higher potential
temperature at the top than at the bottom is said to be stable; it will
not mix unless it is physically stirred. A layer which has lower potential
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EAST <-
WEST
a.
SOUTH
NORTH
-2
0 „-4
>-
Fig. III.l - Nighttime valley flow.
An East-west cross-section is shown in
a., a longitudinal section in b. Arrows
depict wind velocity. Symbol© indicates
,i wind component toward the reader.
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EAST.*.
WEST
V
\
©
,-2
^ 'C V
v © —
\ V.
,'N
So-A
v^:
N c®- 0 "
®
_y
SOUTH
NORTH
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a.
SOUTH - NORTH
¦4-
So"1
Fig. III.3 - Daytime valley flow.
Symbol <8 indicates a wind component
away from the reader. See also
Fig. III.l.
>-3
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)
®
0O-1 i
'< © « a
/
/ ®.
(V
-0 o_2^ ^
_ - - - *
"9 "
1
a.
SOUTH NORTH
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One.
exists. On the contrary, an air parcel originating on a valley wall
(and any pollutant it contains which follows the air flow) will remain
on its own potential surface and flow down the valley above the valley
floor. The very stability which prevents mixing in this situation
assures continued separation of pollutants which originate at different
levels. Thus, during the night when down-valley flow is occurring,
pollutants from sources which are well distributed in altitude in
the valley will not concentrate on the valley floor. This is important
to remember when using the box model for air quality calculations. The
box model is discussed in greater detail in B.7 of this section.
It has been assumed that the flow depicted in Figure III.l is not
influenced by flow outside the valley. This is often nearly true in
nature, but rarely completely true. In Figure III.l, the wind arrows
near the top of the valley suggest motion in the same general westerly
direction as the wind above the mountains. They also suggest up and
down motion. Such motion often occurs and it disturbs the cold air
in the valley. The disturbance is usually limited to a thin layer at
the top of the cold valley air. Sometimes, however, it sets the entire
body of air in the valley in motion like water in a pail which has been
tilted and then suddenly released. Wind aloft which is blowing parallel
to the valley can either aid or hinder nighttime down-valley flow. If
the wind aloft is blowing in a down-valley direction, it will increase
the flow. Air quality in a valley will suffer most if the nighttime
down-valley flow is just barely reversed. The air will remain stable,
and all pollutant will remain and accumulate near the ground as it is
moved slowly up the valley.
3. Transition from night to day flow
As the rising sun starts to warm the east-facing wall of a north-
south valley, the air in contact with that wall also warms. When it
becomes warmer than the air over the valley at its own height, it
starts to rise, thereby decreasing the supply of cold air which has
been maintaining the steady state down-valley flow. The cold air al-
ready in the valley continues to flow out, however, thereby decreasing
its depth in the valley. Figure III.2 shows the flow and potential
temperature patterns in a valley when flow reversal on the west (east-
facing) wall has progressed well down toward the valley floor. Note
that the 0 lines on the west wall now bend down as they approach the
valley wall. Also note that the wind arrows appear to cross the 0 lines.
Actually, an air parcel must still remain on its own potential temperature
surface as long as it neither gains nor loses heat, but as the cold air
drains out of the valley, the potential temperature surfaces sink and so
the air must have a downward component if it is not to change its 0 value.
As the sun continues to rise and warms more of the valley, there
comes a time when all cold air sources are eliminated—indeed, on the
valley walls the flow is reversed. The core of cold air in the valley
will continue to flow outward for a time, deriving kinetic energy from
its potential energy as it moves to a lower position outside the valley
and spreads out. Concurrently, the organized kinetic energy is being
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cjtymHrUnt fJnc.
converted into turbulent energy by friction at the ground. Soon organized
down valley flow ceases and is replaced by up-valley flow, which develops
until it reaches an essentially steady state conditon like that shown in
Figure III.3.
The transition period is a very important one insofar as air
pollution is concerned. As the cold air in the valley shrinks in
depth, the potential temperature surfaces move closer together and
migrate toward the ground. Pollutants which were distributed through
a large vertical depth are now spread through a much smaller vertical
depth near the ground. The area covered is larger; hence concentrations
in terms of mass per unit volume are not changed. More important, immed-
iately after flow has changed to an up-valley wind, the air stratum on
the valley floor is likely to be stable. Now flow up the valley from
surface sources does follow along the ground, warming as it goes. Even
flows from elevated sources approach the ground as they move up the
valley. During this period, pollutant injected at many levels during
the period leading up to the wind reversal can move back up the valley
near the surface. It is added to that pollutant which is being injected
concurrently.
No figure has been prepared to show the late phases of the night-
to-day transition. Figure III.3 illustrates the situation which exists
then except that in Figure III.3, the 0 lines are hooked where they touch
the ground. Without this hook, the air adjacent to the earth's surface
is stable and mixing is quite restricted.
Although this transition starts at sunrise on the highest portion
of the valley wall, the wind on the valley floor may not reverse until
mid-morning or perhaps later. The reversal occurs first in the high
end of the valley and last in the low end. Wind data for the period
May 24 through July 8, 1974, were available simultaneously at the
Breckenridge wastewater treatment plant near the upper end of Dillon
Lake and at the Silverthorne maintenance yard. At the Breckenridge
plant the mean time for onset of the up-valley winds was 0905 MST.
At Silverthorne the mean time was 1106 MST. On four days during that
period the wind failed to reverse at the Breckenridge plant; failure
occurred on six days at Silverthorne. Some wind data exist also for
an earlier period at the city of Breckenridge. During the winter of
1974-75, the transition at Breckenridge occurred at an average time of
0800 MST. These few data help to illustrate the point that Summit County
is a valley in which valley winds are important, and they show that the
night-to-day reversal occurs early in the morning high in the valley and
much later at lower altitudes.
4. Daytime flow
Figure III.3 illustrates flow during a day when only the air immediately
adjacent to the surface is unstable. Above that, the air is slightly on
the stable side of neutral. In this conditon, thermals probably form
frequently along the higher reaches of the valley walls. A thermal is
a stream of air moving nearly vertically upward over a relatively small
area. It is usually warmer than the air around it and it is this
characteristic which gives it its name. Occasionally a thermal may
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form over the valley. Also, winds from mountain-top level frequently
dip well into the valley. This is indicated by the lack of organization
of the wind arrows between the 0O and 0O-1 potential temperature lines
in Figure III.3.a. On a more stable day, pollutants would tend to collect
in the valley; on a less stable day they would be lifted rapidly into the
westerly flow above the mountains and be carried away. On a day like that
shown, cleansing would be sporadic and not complete.
5. Transition from day to night Clow
Figure III.4 illustrates the beginning of the day-to-night transition.
Again the transition starts on the west (east-facing) wall of the valley
because the effect of the loss of the sun's radiation is felt there first.
The surface cools, cooling the adjacent air. This cooling lifts the
potential temperature surfaces adjacent to the shaded valley face, and the
cool air starts to flow downward and out over the valley. At first,
flow from the western valley wall gets caught up in the main flow up
the valley, and so any pollutant injected into the air along the west
wall during this period may start to move downward toward the valley
and then turn and move up the valley. During this early phase of the
transition, pollutant from a higher point on the west wall may reach
a receptor at a lower level but up the valley from the source.
As the east wall of the valley becomes shaded, cool air flows
downward from all sides and starts to accumulate. The cold air accumu-
lating in the valley raises the air above. This lifting is portrayed
in Figure III.4 by showing the wind arrows crossing the 0 lines from
lower to higher values. Again, as in the morning transitions, this
indicates upward migration of the potential temperature surfaces. Con-
tinued cooling of the air in the valley also has the effect of adding
additional potential temperature surfaces as the surfaces present during
the day are lifted. At some time after solar heating has ceased and
radiational cooling of the ground has become predominant, down-valley
flow becomes organized throughout the valley.
The onset of down-valley flow appears earliest in the high reaches
of the valley and latest at the lower end of the valley. It is not
usually as well defined an event as the onset of up-valley winds in
the morning. The data for Breckenridge, the Breckenridge wastewater
treatment plant, and the Silverthorne maintenance yard showed mean
times of 1836, 1933 and 2116 MST respectively for the onset of down-
valley winds. There were 6 days out of the 46 days when no well-defined
change could be identified at the Breckenridge plant, and 8 days when no
change was clearly identifiable at Silverthorne. At the Breckenridge
plant, 90% of the changes in the morning occurred over a three-hour period,
while at night it required an eight-hour period to encompass 90% of the
changes. At Silverthorne, changes in the morning were also well grouped
about the mean, but evening changes were even more scattered than at the
Breckenridge plant.
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(Jnc.
This transition period does not appear to present as great a pollution
problem as the morning period, given equal source strengths. Unfortunately,
there is a long period during which the wind may be light and variable, and
it occurs at the time during which many people are using fireplaces, driving
to dinner, or leaving a day of skiing to drive home.
6. Complicating factors
Some of the factors which complicate wind flow in a simple, steep,
north-south valley have been mentioned. The wind above the valley is
one factor, and some of its effects have been discussed. Cloudiness
can also change the circulation. Low cloudiness setting in late in the
afternoon after a warm day can greatly delay or perhaps prevent the onset
of the down-valley wind. Similarly, low cloudiness forming near sunrise
after a cold night can delay or prevent an up-valley wind on that day.
The nature of the ground cover also is important. New-fallen snow which
covers trees as well as the ground is an excellent radiator at its tem-
perature and a poor absorber of sunlight. Such a new snow cover can be-
come extremely cold at night and contribute to the nighttime down-
valley wind. By reflecting most of the sunlight the following day, it
can delay or prevent the up-valley wind.
Topography is also important. Canyons entering the valley from
the side participate in the valley flow and complicate it. Broad,
relatively leveL sections Ln an otherwise uniform, steep valley change
the flow. A deep narrow gorge in an otherwise uniform vaI Ley obstructs
flow in both directions. In particular, the walls of the gorge may act
as a dam and back up a deep pool of cold air at night. Summit County has
all of these topographic features in some measure. For example, the
Straight Creek Valley opens into the Blue River Valley at Silverthorne.
The air flowing down Straight Creek will usually arrive at Silverthorne
with a different potential temperature than the air arriving from the south-
east after having crossed Dillon Reservoir. Consequently, the Straight
Creek air will flow under the air from the southeast, if its potential
temperature is lower, or over if its potential temperature is higher. If
the two flows have the same potential temperature, the flow from Straight
Creek will cause large eddies in the larger flow from across Dillon Reservoir,
but the two flows will move along down the canyon mixing as they go. Just
above Silverthorne the Dillon Reservoir is a large flat area in what is
otherwise a sloping valley floor. The water in the reservoir serves as
a heat source in late fall and early winter—at least until it freezes
and is covered by a deep coat of insulating snow. From spring when the
ice thaws until fall, the water is a heat sink which cools air in contact
with it. In its role as a heat source and sink, its influence is quite
different from the land around il. Clearly, the simp.le valley flow model
which has been discussed is not realistic for the Silverthorne area. The
model may provide some useful answers for Silverthorne, nonetheless, if
its limitations are kept in mind. Meteorological sounding data for Silver-
thorne are discussed in Section III.C.
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One.
1. Applying the valley circulation model to air pollution problems
A number of air pollution models arc i.11 use, and most are misused
at times by applying them under circumstances in which they have little
chance of yielding reliable results. The box model is an acceptable
model in valleys in which the sources of the pollutant are uniformly
distributed over a nearly level floor and the air is well mixed from
the surface up to the base of some well-defined inversion. It was used
by Holben and Marlatt (1974) to make estimates of the mean concentrations
in some rather large boxes, using an assumed set of wind data and an
assumed set of mixing heights. They recognized the limitations of the
model, and they state that available meteorological data are woefully
inadequate. There is some confusion in their use of "mixing height" and
"top of the inversion." In the box model, as they used it, the vertical
dimension of the box should be the distance from the earth's surface to
the top of the mixed stratum adjacent to the surface. The top of the
mixed stratum is the base of a stable stratum, either an actual tem-
perature inversion or a well-defined inversion of potential temperature.
The base (not the top) of the inversion is the lid of the box. In a
down-valley (katabatic) wind such as they assumed in their use of the
box model, the base of the temperature inversion is at the earth's
surface, in most instances; the box then has a volume of zero and the
box model is not tenable as they used it. See Section III-C, Figure
III.5 for examples of an inversion at the surface and a shallow mixed layer.
A different kind of box model is more realistic under down-valley
wind conditions. It differs from the model used by Holben and Marlatt
only in that it is assumed that pollutant from each source remains on
the potential surface on which it was released. The potential temperature
surface which passes through the highest source is then the top of the
box. Concentration varies with potential temperature and is a function
of the strength of the sources on each potential temperature surface.
If source strength is fairly evenly distributed with height, this model
can be simplified by letting the height of the highest sources be the
depth of the box and using the model in the usual way.
The Gaussian model is often used for point sources. In its various
modifications it is also used for multiple point sources, for line sources
and for area sources. In a steep valley such as the Blue River Valley,
it can be applied in its basic form and most of its modified forms, if
proper precautions are taken. For example, when a down-valley wind is
blowing, a plume from a single source can be expected to diffuse up and
down from the potential temperature surface on which it comes to equil-
ibrium. Since the floor of the valley falls away from that potential
temperature surface down the valley, the ground cannot act as a reflector
in the way it is usually assumed to act. When an up-valley flow is still
stable above a shallow mixed stratum at the ground, an elevated plume will
approach the ground bodily as it moves away from the source, and as it
approaches the ground it: will, mix nearly uniformly through the shallow
mixed stratum at the ground. Horizontal dispersion in a valley may be
treated as it is normally in the Caussian model until the plume width
approaches the width of the valley. Beyond that point, reflection by the
valley walls can be used, but the results may not be particularly satis-
factory.
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cz/fmljiznt c^f-na[yiL±, LJnc.
The stability categories normally used (e.g. Turner 1969) are
often not satisfactory in a valley. On a bright sunny day in the
period immediately following the onset of an up-valley wind, an
unstable category would be chosen if one followed instructions found
in Turner (1969). A stable category should be chosen in most cases
for one to two hours following onset of the up-valley wind. In some
cases, the stable category will be applicable throughout the day.
Some specialized models have been mentioned in the discussion of
Gaussian models. Specifically, models such as HIWAY, PTMAX, etc. must
be used with great care to avoid misleading results. These ar.e EPA
computer models which are widely used by engineers, they are well
documented, and they are quite useful when properly applied. One
basic assumption in most of these is that the ground is nearly level
and relatively smooth. Clearly, this is not a valid assumption when the
model is used in a steep valley. For example, PTMAX is designed to deter-
mine the maximum ground level concentration and the point at which this
maximum occurs, when one or more individual stacks are the polluting
sources. If applied for a single stack without modifications in a night-
time situation in a steep valley, PTMAS would predict a single maximum
on the ground downwind of the stack. The actual maximum would more
likely be on one of the valley walls and both walls might receive
higher concentrations than the valley floor. These models can some-
times be used in a valley under very restrictive conditions and provide
useful information.
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(Jnc.
C. Sampling Days—Criteria, Weather and Traffic
1. Sampling criteria
The places and times at which air samples should be collected were
determined only after careful study. The goal was to sample on a day
when human activity was high and dispersion was good and on a day when
activity was high and dispersion was poor. Air flow patterns and stability
in the valley vary with season, time of day, and past and present meteoro-
logical conditions over the entire Rocky Mountain region. These had to
be taken into account. The distribution of roads, parking lots, urban
areas, dwelling complexes and rural areas, and the topographical setting
in which these were found were all important. Seasonal tourist activity
was also considered. Each sampling site is discussed in Appendix B. The
criteria for selecting both summer and winter sites anil sampling times
arc summ.irized briefly hi're.
a. Summer
Because the plan was to sample in summer when the air in the valley
was well mixed sampling was done in the afternoon. To be downwind of a
source in the afternoon, each site must normally be up the valley from
its source. Each site had to be far enough from all intense, small
sources, that samples were not unduly influenced by any one such source.
For example, sites in the vicinity of parking lots were located far
enough downwind from the lots so that the sample was indicative of the
general environment of the lot and not of the exhaust at the rear of one
automobile. Likewise, sites located near highways were located far enough
from the roadway to avoid peak concentrations from individual vehicles and
to approximate the concentrations to which roadside residences and businesses
would be exposed.
b. Winter
Samp 1 i ng in winter was to be done when dispersion was poor and
source strengths were high. Preliminary analyses suggested that dis-
persion was poor throughout the nighttime hours when the air stratum
near the ground was stable, and that it would be worst early in the
morning. It was also anticipated that source strengths would be
strongest early in the morning when space heating and traffic to ski
resort areas both were high. Consequently, a cold early morning period
when winter sports activity was expected to be great was selected for
the winter sampling. At that time the air would be flowing down the
valleys, if meteorological conditions were favorable for valley flow.
Consequently, sites were expected to be down the valley from the source
areas to be sampled.
c. Meteorology
It was important in both summer and winter that meteor logical conditions
in the Rocky Mountain area be taken into account. The ideal condition would
be a situation in which skies were nearly cloudless in the morning, wind
at mountain-top levels and above was from a westerly direction and wind
speed was low. This would permit valley flow to prevail. In summer, cloud-
-:32-
-------
cs/fnaLijiL±, (Jno..
less skies permit strong solar heating in the valley and assure good vert-
ical mixing and dispersion in the afternoon. In winter, clear skies
permit the ground to radiate to space and cool, thereby assuring the
cold surface temperatures and stable conditions needed for low dis-
persion. In winter, a fresh snow fall within the last few days was
desirable. This would encourage skiers to come to Summit County and
it would enhance the radiational cooling at the surface. The actual
day of sampling was selected by reviewing the weather map each day
on the several days leading up to the sampling day. Thus the meteoro-
logical history of the county over the week preceding the day selected,
as well as the forecast for the day, were both important in selecting
the day for sampling.
2. Weather
a. Summer
The weather on July 23, 1975, when sampling was conducted at all
five sites is described in Appendix A. Weather on August 18, 1974, when
samples were taken at three sites was very similar to that of July 23,
1975. Dispersion was excellent and the flow was up the valley during
both sampling periods. The primary difference in the weather was that
gusts were stronger on August 18 than on July 23, and more dust was
raised by the wind.
b. Winter
A storm had passed over the Rockies during the weekend following
Christmas and left some new snow in Summit County. Following the passage
of the storm, cold air settled over the Colorado Rockies. This was the
ideal situation for the winter sampling which had been planned, except
that the winds above the mountain tops were from the north. These strong
northerly winds aloft were causing north winds throughout the Blue River
Valley; at times they were strong enough to cause b.l owing snow on the
floor of the valley.
On Sunday, December 28, 197 5, it appeared that by Tuesday morning
the winds above the mountain tops would have shifted to a northwesterly
direction. On Monday, the situation appeared doubtful. Winds aloft were
still northerly, and snow was falling in some mountain areas about Summit
County. The winds were diminishing and starting to back, however, and
the weather did appear promising enough to.warrant starting preparations
to sample the following morning.
At 0400 MST on December 30, skies were clear over the mountains
east of Summit County, but low thin clouds covered parts of the valley.
Under these clouds, very light snow fell occasionally. The air flow
at Silverthorne varied from the south to east, however, indicating
that the down-valley wind was blowing.
-33-
-------
<^fml7L£.nt c^fna[yi.i±, Uric.
Surface meteorological data at the sampling sites are shown in
Table III.l for the morning of December 30. Soundings were taken in
Silverthorne (Site 2) by means of a tethered balloon sounding system
(The TethersondeTM). ihe soundings are shown in Figures III.5 through
III.7.
In general, the anticipated down-valley wind existed at all sites.
At Site 1 whicli was the lowest site, winds were variable from south or
southeast. At Site 2, the infLuence of Straight Creek Canyon can be
seen vividly in the lower levels of the Tethersonde soundings. The
winds near the surface coming down the Straight Creek Canyon were from
east or eastnortheast. At higher levels the soundings show wind from
southeast to south. At Breckenridge (Site 3) winds were generally
southerly until after 0900 MST. They shifted to northerly sometime
before 1000 MST. At Site 4, flow was generally from a westerly direction.
The flow aloft aided the down-valley flow so that the strongest surface
winds observed at any site were observed here. Site 5, located in the
east-west oriented Snake River Canyon shows light, down-canyon winds
early. The northwest winds aloft were impeding the down-valley flow
here; hence direction was variable throughout most of the sampling
period.
Turbulence was quite evident at the Wheeler Junction during much of
the morning as the flows from West Tenmile Creek and Tenmile Creek joined.
A small cloud with its base at about 50 to 100 m and its top at 200 m
formed in Tenmile Creek across the mouth of West Tenmile Creek. Individual
cloud elements formed at the southern end of this c]oud, moved downstream
(northward), and dissipated a short distance downstream of the junction.
Clearly, the air was nearly saturated and lifting of one or both canyon
flows as they joined caused saturation.
The Tethersonde soundings made at Silverthorne are shown in Figures
III.5 through ITT.7. They show a number of Interesting aspects of valley
flow. First, they disclose a temperature inversion at the surface which
lasted throughout the morning until the descent of the final sounding.
Even then a strong inversion overlaid the shallow unstable layer caused by
solar heating at the surface. They show increasing temperature and drying
of the air as time passed at all levels. All temperature increases, except
for those immediately above the surface, were caused by the subsiding of
the cold air as it flowed out of the valley after its source had been cut
off (Figures III.5 and III.6). Note that the temperature increased at the
top of the sounding slowly early in the morning and then more rapidly as
the cold air source dwindled. *
Turbulence in the upper portions of the soundings was absent in the
early morning. It showed up above 375 m (1,200 ft) in the 0808 soundings
which reached 475 m (1,500 ft) above the valley floor (Figure III.7).
Turbulence probably in the form of waves on the upper surface of the
cold air caused the repeated changes of altitude of the balloon. In
this set of soundings neither short period wind speed nor direction
changes were great (Figure III.6).
-34-
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Table III.l
Summary of Surface Meteorological Data in Summit County
Morning of December 30, 1975
TIME (MST)
0510
0610
0710
0730
0740
0815
0900
0915
0930
1015
1030
1045
Site 1
Wind Dir.
112
180
180
158
160
130
140
-
175
_
140
_
Wind Speed
(m/ s)
<1
1
-
1.8
1.8
1.3
<1
-
1
-
<1
_
Temp. (°C)
-9.3
-10.6
-
-12.5
-13. 9
-13.9
-12.2
-
-10.0
-
—
_
Wet Bulb (°
C)
-9.4
-10.6
-
-12.8
-14.6
-13.9
-12. 2
-
-10.0
-
—
_
R.H. (%)
89
100
-
80
78
100
100
-
100
-
-
-
Site 2
Wind Dir.
270
120
-
120
-
120
-
120
-
120
-
_
Wind Speed
(m/s)
<1
<1
-
1.3
-
1.1
-
1.8
-
1.8
—
_
Temp. CO
-
-9.3
-9.4
-
-
-10.8
-
-9.8
-
-7.6
-
-4.8
Wet Bulb (°
C)
-
-9.5
-9.8
-
-
-11.1
-
-10.8
-
-8.8
_
-6.6
R.H. (%)
-
95
82
-
-
82
-
67
-
67
-
58
Site 3
Wind Dir.
180
-
135
135
-
180
-
180
-
045
-
Var.
Wind Speed
(m/s)
1
-
1.3
1.8
-
1.8
-
1
-
1
-
1
Temp. CO
-7.8
-8.3
-8.3
-8.3
-
-12.2
-
-8.3
-
-8.3
-
-5. 6
Site 4
Wind Dir.
040
030
Var.
270
-
240
-
240
-
270
-
240
Wind Speed
(m/s)
<1
1.8
<1
2.2
-
2.7
-
1
-
<1
-
1
Site 5
Wind Dir.
135
135
-
Var.
-
Var.
-
Var.
-
022
—
—
Wind Speed
(m/s)
1.6
1
-
1
-
1
-
1
-
1.3
-
-
-35-
-------
o
o
E
o
o
Fig. III.5 - Temperature vs.
height at Silverthorne, Dec.
30, 1975. Times are MST.
Fig. III.6 - Wind velocity vs.
height at Silverthorne,Dec. 30,
1975. Speeds are m/s.
Time ("lir. ^
Fig. III.7 - Time in^minutes
into flight vs. height at
Silverthorne, Dec. 30, 1975
-36-
-------
c^f-mOriE-nt c^/fnaCyiii, One.
By 1023 MST when the last set of soundings was being made, turbulence
was evident as low as about 200 m. It is shown by balloon height changes,
wind speed changes, and temperature changes. The wind from above mountain-
top level was evidently stirring the air above flight level, mixing parcels
of air with warmer potential temperature down well into the valley. This
mixing from above, warming from below, and flow of the cold air out of
the valley probably continued until the air in the valley was much warmer
and was well mixed throughout or until cooling in the late afternoon
started replenishing the cold air again. It is not known whether an
up-valley wind occurred at Silverthorne on the afternoon of December 30,
but it probably did as soon as subsidence and warming destroyed the near-
surface inversion.
During the period 0610 to 0730 MST the temperature of Breckenridge
(Site 3) remained constant at -8.3°C or 264.8°K. The potential tem-
perature at the surface was determined to be 292°K. In a similar way,
the potential temperature was calculated at various heights above
Silverthorne, using the 0620-0703 MST soundings. During ascent, the
potential temperature at the surface was 288°K, and a potential tem-
perature of 292°K was found at 241 m. The difference in altitude of
the two sites is 246 m. Hence, the potential temperature surface
passing through the Breckenridge site was virtually level at that
time. Later (from the 1023 sounding) after the cold air source was
cut off and the cold air was emptying into the Colorado River Valley
to the north, the 292°K surface had lowered to about 50 m at Silver-
thorne .
3. Traffic volume at Site 2, Silverthorne
Traffic volumes for three different periods on the days when
sampling was done are shown in Tables III.2, III.3, III.4.
-37-
-------
c^fmljient c^fna[ij±i.i, One.
TABLE III.2
Traffic Count Tabulation*
Final Composite
Week 34 beginning August 18, 1974—SH 9
North of
Silverthorne
Day
Sunday
Thursday
Friday
Saturday
Date
18
22
23
24
Hour
09-10
160
164
178
226
10-11
283
213
201
266
11-12
274
169
187
228
12-13
359
185
210
261
13-14
372
176
202
240
14-15
356
209
231
237
15-16
369
185
232
257
16-17
388
218
244
267
Peak Hours - 388, 16-17
Sunday, August 18, 1974
Week 34 beginning August 18, 1975—I-
70 East of
Dillon
Day
Sunday
Thursday
Friday
Sa turday
Date
L8
22
23
24
Hour
09-10
760
745
734
996
10-11
1161
868
890
1181
11-12
1316
882
975
1312
12-13
1620
1002
930
1212
13-14
1649
805
966
1230
14-15
1727
961
1141
.1200
15-16
1823
970
1145
1225
16-17
1832
866
1196
1222
Peak Hours - 1832, 16-17 Sunday, August 18, 1974
^Source - Department of Highways, State of Colorado, Planning and
Research Division. This is a count of vehicle passages
past a given point in both directions.
-38-
-------
cy*fna[yi.L±, {Jnc.
TABLE III.3
Traffic Count Tabulation*
Week 30 beginning July 20, 1975—SH 9 North of Silverthorne
Day
Sunday
Mo nd ay
Tuesday
Wed nesday
Date
20
21
22
23
Hour
09-10
182
174
193
186
10-11
252
193
159
193
11-12
282
192
148
198
12-13
288
163
177
197
13-14
309
185
156
199
14-15
389
202
192
230
15-16
328
181
196
181
Peak Hour
- 389, 14-15, Sunday,
July 20, 1975
Week 30 beginning July 20, 1975—I-
¦70 East of Dillon
Day
Sunday
Monday
Tuesday
Wednesday
Date
20
21
22
23
Hour
09-10
819
720
819
702
10-11
1074
941
642
800
11-12
1297
942
811
908
12-13
1659
828
752
848
13-14
1607
817
744
741
14-15
1711
935
846
900
15-16
1745
878
837
904
Peak Hour
- 1745, 15-16, Sunday,
July 20, 1975
*Source -
Department of Highways
Research Division.
i, State of Colorado, Planning
and
-39-
-------
{Jnc.
TABLE III.4
Traffic Count Tabulation*
Week 53 beginning December 28, 1975—SH 9 North of Silverthorne
Day Sunday Monday Tuesday Wednesday
Date
28
29
30
31
Hour
05-06
2
95
68
63
06-07
27
168
161
156
07-08
21
63
54
4.1
08-09
69
72
81
44
09-10
67
69
78
50
10-11
111
96
97
60
11-12
119
102
118
95
Peak Hour
- 168, 06-07, Monday,
December
29, 1975
Week 53 beginning December 28,
1975-1-70 East
of Dillon
Day
Sunday
Monday
Tuesday
Wednesday
Date
28
29
30
31
Hour
05-06
50
164
97
, 62
06-07
132
211
181
136
07-08
447
442
525
291
08-09
1174
1239
1255
572
09-10
1080
1397
1284
557
10-11
1028
96.1
1076
708
11-12
1073
916
963
599
Peak Hour - 1397, 09-10, Monday, December 29, 1975
^Source - Department of Highways, State of Colorado, Planning and
Research Division.
-AO-
-------
c^fm&ient cz^fna[ij±i±f due..
D. Carbon Monoxide and Particle Measurements
Carbon monixide and particles were measured at three sites on
August 18, 1974, at five sites on July 23, 1975, and again at the same
five sites on December 30, 1975. See Figure 1.1 for site locations.
The general approach was to sample under preplanned conditions and to
preserve and analyze the samples in such a way that the integrity of
each sample was assured. The criteria for selecting sampling sites
and times are given in Section III.C.
1. Carbon monoxide (CO)
Carbon monoxide sampling was done by collecting an air sample in
mylar bags conditioned to the atmosphere of each site. Each sample was
collected at a uniform rate over a one-hour period. A description of
calibration and sampling methods appear in Appendix A.
Analysis of the one-hour samples were performed within two hours of
collection. Results are summarized in Table III.5. The standard refer-
ence material used for calibration of the CO analyses in the 1975 summer
test was a secondary standard. A primary NBS reference was used for the
winter analyses and hence greater precision was possible.
Table III.5 also includes results taken in August 1974 by a grab
sample technique and analyzed by high-sensitivity gas chromatograph.
These are highly accurate measurements of spot concentrations of carbon
monoxide. Although the 1974 data are virtually instantaneous values,
they are considered to be representative because the samples were collected
with great care under specified conditions. Note that the 0.23 ppm value
shown for Site 1 (a rural site) is consistent with background concentrations
measured in other places in the Rocky Mountain area (about 0.2 ppm).
a. Summer vs.winter-1975 data
Comparison of the samples taken in the winter period with those taken
in summer show much higher concentrations of carbon monoxide in the winter
period. Site-by-site comparison reveals the combined effect of sources
and atmospheric dispersion. Site 1 on the Knorr Ranch in the northern
part of the county shows carbon monoxide concentrations characteristic
of air parcels not overly influenced by emissions from combustion. The
concentration of the winter sample is three times that of summer, however,
primarily because of lower winter dispersion. The Silverthorne winter
sample (Site 2) is also three times the average summer sample level. At
Breckenridge (Site 3), Copper Mountain (Site 4), and Keystone (Site 5),
concentrations are all approximately 15 times as great in the winter
samples as in the summer. These are all sites near busy ski areas, and
increased traffic,increased space heating, and lower dispersion are all
instrumental in causing the higher values in winter.
-41-
-------
-------
c^fm&unt c^fna[tj±Li, {Jnc.
Among the goals of Summit County in undertaking this study was
the measurement of concentrations under conditions when air quality
should approach both good and bad extremes. The comparisons between
samples of summer and winter carbon monoxide concentrations show that
the temporal range of concentrations can be large. On the summer day
when vertical mixing was great, the concentrations were well below
Federal and State statutory standards everywhere. On the winter
morning when little vertical mixing was occurring, concentrations
were high enough at all sites, except Site 1, to suggest that current
statutory standards might be exceeded under certain winter conditions.
b. Continuous CO measurements
Continuous CO concentrations were observed at Silverthorne (Site 2)
near the junction of SH 9 and 1-70. Hourly averages from these data are
shown in Table III.6.
Summer data were collected approximately 300 meters south of the
junction (See Figure 1.1) so that they represent the cumulative emissions
from Silverthorne and the two highways during upslope air flow conditions.
Winter data were collected at the Silverthorne Town Hall and are
representative of downslope air flow near the junction of 1-70 and SH 9
and a part of the community of Silverthorne. Data are presented for the
winter condition to document worst dispersion conditions more completely
at Site 2.
There was a combined total of 6,299 vehicle passages for SH 9 and 1-70
at Silverthorne during the period 1000 to 1600 MST on July 23, 1975. (Table
III.3). Air flow was upslope, dispersion was good, and the average carbon
monoxide level for the six-hour period was 1.3 ppm.
The combined traffic total for the period 0500 to 1100 MST on December
30, 1975 at Silverthorne was 5,873 vehicles. (See Table III.4). During
this period air flow was downslope and the average six-hour CO concentration
was 4.4 ppm. Thus the CO concentration was approximately three times as
great in the winter period as in the summer period and the automotive
traffic was less. Some winter pollution was caused by space heating, but
part of the difference in the concentrations noted above was undoubtedly
caused by poorer dispersion in the winter period.
2. Total suspended particles (TSP)
Particle samples were collected by drawing air through membrane
filters at a measured rate. The average exposure time was 170 minutes.
Particle data are shown in Table III.7 and III.8. Great care was taken
to assure that the exposed membranes and the field blanks were care-
fully preserved until the particulate material on them could be analyzed.
Following analysis, the filters were stored for safekeeping at Ambient
Analysis, Inc. and are available for further reference.
-43-
-------
iJnc.
TABLE III.6
One Hour Continuous CO Concentrations Measured at Silverthorne (Site 2)
North of Junction 1-70 & SH 9
South of Junction 1-70 & SH 9
Date
Time ppm CO
Date
Time ppm CO
Dec. 29, 1975
16-17 ~ 2.5
20-21 2.3
21-22 4.0
*D
22-23 2.7
*u
0
23-24 2.0
P
W
Dec. 30, 1975
00-01 2.1
S
N
01-02 2.6
L
S
02-03 2.7
0
L
03-04 2.7
P
0
04-05 3.2
E
P
05-06 2.1
July 23, 1975
+10-11 2.2
15
06-07 2.8
11-12 0.9
107-08 5.2
12-13 0.8
08-09 8.5
13-14 1.9
09-10 4.2
14-15 1.4
10-11 3.6
15-16 0.8
4.4 ppm CO mean for downslope
1.3 ppm CO mean
for upslope
organized flow
organized flow
1'Max. five minute mean: 21.8 ppm
tMax. five minute mean: 11.7 ppm
*The data chosen for comparison are enclosed in boxes. Air flow was
persistently downslope in winter and upslope in summer during the
times for which the data are compared.
-44-
-------
a,
Lhic.
Analysis was done in three ways. The 47-mra filters were weighed
on a Cahn microbalance before and after exposure to determine the total
mass of particulate material collected on them. Dividing this mass by
the volume of air drawn through the filter yields the concentration of
particulate mass per unit volume of air. The units are expressed in
micrograms per cubic meter, which is abbreviated ygm/m3. The filters
were also analyzed by electron microscope to determine particle appearance
(morphology) and size distribution. Finally, particle type was determined
by qualitative x-ray examination. Morphological and x-ray analyses were
both used to determine the general origin and composition of the particles.
Qualitative x-ray identification of single particles was done for the
asbestos-like particles collected at Site 2 in the summer.
a. Comparisons of summer and winter particle mass concentrations
A comparison of winter and summer gravimetric (weight) data for
particles shows a generally lower concentration of TSP for the winter
samples. Data from four of the five sampling stations are indicative
of particle mass concentrations in those county areas where human activity
is concentrated. Gravimetric data for August 18, 1974, and for the two
sampling periods in 1975 are shown in Table III.7.
Gravimetric data at Site 1 show particle concentrations which are
typical of background or baseline values in rural areas. These usually
range from 0 to 40 micrograms per cubic meter, Hoffman, et.al. (1975).
Background, baseline and benchmark are generally used interchangeably;
they are relative terms and background varies from season to season,
region to region, etc. For example, the data in Table LIT.7 for Site 1
show that TSP can vary considerably in summer at a single rural location.
Concentrations at this site are considered to be close to the background
values for the valley during the sampling periods. Particle samples at
Sites 1, 2, and 3 collected in August of 1974 show typical concentrations
when dry and windy conditions contribute to entrainment of particles.
TABLF, III .7
^1 'ota I Si is pi-1 id cd I'.irLiclcs I); it J
Concentrations in ygm/m^ are given in the first column. The
difference between other
background in the second
which is excess is given
sites
column
in the
and Site 1 is shown as ''
The percent of TSP at
third column.
Excess" over
each site
August 18, 1974
July 23, 1975
December 30,
1975
Site
Cone. Excess
(%)
Cone. Excess
(%)
Cone.
Excess
(%)
1
41
14
< 4
2
61 . 20
33
49 35
71
16
>12
>75
3
86 45
52
16 2
13
11
> 7
>64
4
37 23
62
1.0
> 6
>60
5
.13
1.2
> 8
>67
-45-
-------
TABLE III.8
Particle Size Data for 1975
The number of particles collected on each filter and the number per unit volume in the size
range indicated are given in Columns 2 through 5. The mass per unit volume (concentration)
of all particles collected is given in Column 6.
Range of Particle Diameters
TSP
Site
Particles/filter
<1. 0|jm
l-10pm
>10ym
All
yg/m3
1
3.3xl06
3.OxlO5
3.8xl05
1.8xl04
0.7xl06
14
2
8.7xl06
1.3xl06
5.lxlO5
3.6xl0A
1.9xl06
49
3
5.0xl06
7.5xl05
5.3xl05
5.1xl04
1.3xl06
16
4
4.4x10^
8.lxlO5
4.1xl04
6.9xl04
0.9xl06
37
5
2.5xl06
3.lxlO5
2.6xl05
1.6xl04
0.6xl06
13
1 * * * * * <4
2
1.OxlO6
5.5xl04
2.7xl05
1.5xl04
0.3xl06
16
Dec. 30 3
1.8xl06
1.9xl04
2.3xl05
1.3xl04
0.3xl06
11
4
2.9xl06
5.lxlO4
6.2xl05
3.lxlO4
0.7xl06
10
5
1.2xl06
4.3xl04
2.5xl05
1.2x10^
0.3xl06
12
* Too few particles to'yield a statistically reliable count.
< A symbol indicating that the actual value is "less than" the number following the symbol.
> A symbol indicating "greater than."
-46-
-------
c^j-m(jLe.nt c^fna[yiL±, fJnc.
The effects of human activity on total suspended particulate (TSP)
concentrations in Summit County can be inferred from the data. The
difference between the TSP at each site and Site .1 is assumed to be
the excess of TSP caused by human activity. Since some of the TSP at
Site 1 is human-related, the excesses shown arc probably .low or conser-
vativc.
TraLl ic volume Lor the period I 100 lo .1700 MST on August 18, L974, was
higher than during any other sampling period (See 1II-C) with 8,891 vehicles
counted on Highways 9 and 1-70 near Site 2. Thus, heavy traffic contibuted
to the TSP on that day. Gusty winds also contributed by raising dust. It
is noted that dispersion was excellent and that CO values were not particularly
high at Site 2 despite the heavy traffic. Air quality was more affected by
high particle concentrations on that day than it was on all the other sampling
days.
A number of other observations can be made about the particle data.
The variability from site to site is much greater in summer than in winter.
In summer, Site 5 was virtually a rural (background) site, whereas in
winter when ski i.ng drew large crowds, i.t was affected almost as much by
human activity as Sites 2 through 4. Then at non-rural, sites (2 through
4 in summer), the average fraction of TSP which can be ascribed to human
activity is 46%. In winter the average is 66%. Thus, although the summer
values are larger at all sites than the winter values, a much higher fraction
of the winter particulate matter is contributed by human activity. Excluding
Site 1, the winter concentrations are quite comparable at all sites, suggesting
similar sources and similar levels of activity. In summer the concentrations
and the fraction contributed by human activity vary greatly from site to site,
indicating dissimilar sources or levels of activity, and different land use
as affecting air quality.
b. Particle size distribution
The particle size data in Table III.8 show that the number of particles
per unit volume was lower in most size categories at most sites in December
than in July. The most marked difference is in small particles, however.
Microphotographs are shown in Figures III.8 through III.12.
The morphological appearance of the particles shows the winter
samples (Figures III.10, III.11 and III.12) to have the characteris-
tics of combustion particles. Fly ash and combustion nuclei predominate
at Sites 2 through 5. The micrograph for Site 1 shows the exposed filter
to be so clean that its appearance was essentially the same as the field
blanks—see Appendix A.
Snow cover changes the character of the airborne particles. In
the summer with no snow cover, particles were mixtures of inorganic and
organic substances. Wintertime particles were less dense and were almost
wholly organic. They probably have characteristics like liquid aerosols
due to temperature conditions during emission. Qualitative x-ray analyses
of the particles collected at Sites 2 and 4 indicate that the material
was predominately organic.
-47-
-------
_>jmbi&nt c^rfnuLtjxi.x, Due.
*Vy
• .l"*
Fig. 1II.0-EM Micrographs, 210X, July 23, 1975
SITE 1 - Biological & n Inera1 back-
ground particulate - relatively clean
SITE 2 ~ Combustion & mineral particu-
late containing significant percentage
of asbestos-like particles
SITE 2 - Combustion & mineral particu-
late, contains a large fiber of asbes-
tos-like material
SITE 3 - Predominant: mineral, some
carbon aggregates
-------
I niton .7ualtjiii, Line.
I i r- • Ill.y-KM Micro,•.r.iphs, 'MIX, .It Iv !M, I1.)/!)
SITE 4 - Predominant, mineral with car-
bon (fly ash) & biological particles
SITl 5 - Clean light mass loading, rep-
resentative of natural particulate, min-
eral and biological particles.
I-70 - Straight Creek, combustion pan-
iculate, asbestos-like liber and bjo-
^article.
li:i,U l.'il.ANK - note absence of mLiteral
and carbon part icles. Shows light con-
:aminatinn from handling.
-4-9-
-------
I mi. ii.nL -nnc
I'ig- I I I . K)--i;f| Mi.c ro;' raplis , Dec. ')(), 19/3
SITE 2 - Si) vert home - left 250x - right 25GO x
Predominately organic; note Large number of particles around holes and
aggregate. Large fly ash particle on right.
SITE 3
- Breckenridge - left 250 x - right 250Qx
Predominately organic, note large particle on left tha~ appears to be
aggregate of mnnv small particles. -5Q~
-------
Sill1, 'i - (' 11 > | »t1 r Mm i: 11 . i i n S : TK '» - (A)j> j a- r Mdu n t a i n
2'rOx I11 • d->in inaLe Iy iir^'iiiir wi th some 2500 x Clustered aggregate around
I Ly ash holes
SITE 5 - Keystone SJTE 1 ~ Keystone
25Ox Predominately io more Civ 2M)0x Predominately organic more fly
il i-
than Site small combustion than Site 4 small combustion
-------
i n. l a tit
i "I /.'• it ii:. ( ), i.1 /Jl
j
SITE 1 - Knorr Ranch
Note absence of particles, some very
small particles appear between holes
or pores of filter. Compare to field
blanks in Figure 111.9 at lower mag-
nification.
Micrographs from the winter samples disclose a general tendency for
the smaller particles lo clump together so that many of the larger parti-
cles seen in Figures 111.If) through III.12 can be seen to be aggregates
of smaller particles. Irregular angular shapes are the rule for summer
particles, while rounded (almost spherical) shapes are characteristic
of the winter particles. Excluding Site .1, there were on the average
3.4 times as many particles per unit volume in the summer samples as in
winter and 2.4 times as much particulate mass per unit volume.
c. Significance of particle data
The data of July 23, 1975, suggest that vehicular traffic is a major
contributor of particles along highways in Summit County in summer, since
the greatest mass concentrations occurred at sites along 1-70, where •
traffic was heavy. Sites i, 3 and 5 (all sites away from the major
transportation routes have air which is freer of particles than Site 2
at the .Junction of Sll 9 and T-70 and Site 4 at the junction of 1-70 and
Sll 91 .
-r52"
-------
cy^m^LE-nt cjtyna.Ciji.ii, {Jnc.
Particle mass data, microscopic analyses, and x-ray analyses all sug-
gest that the'sources of particles in winter at Sites 2, 3, 4, and 5 are of
similar strengths and that they are principally combustion processes.
Particles in the July 23, 1975, samples have been identified as being as-
bestos-like fibers. (See Figure III.8.)
Airborne particles are characterisically organic in winter when snow
covers the ground. Winter TSP levels, when compared to State and Federal,
standards in areas of great human activity have reached about 25% of the
standard. The organic particle and its relation to health are discussed
in Section III.E.
-53-
-------
£!nc.
E. Effects of Carbon Monoxide and Particles on Health
1. Carbon Monoxide
Carbon monoxide.: (CO) Ls a toxic gas which Ls produced by incomplete
combustion of carbonaceous materials. The best understood biological
effect is its combination with hemoglobin (Hb) to form carboxyhemoglobin
(COHb), thereby rendering the blood less capable of carrying an adequate
supply of oxygen to the body cells, National Research Council (1970).
This action results in acute poisoning of more people each year than any
other single toxic agent except alcohol, Rose (1969). Further damage to
nerve cells caused by oxygen starvation, including brain cells, is per-
manent, since those cells cannot repair themselves.
When a person is exposed to an increased concentration of CO in the
air, the carboxyhemoglobin level in the blood increases. If the ratio of
carboxyhemoglobin to hemoglobin reaches a level of 2 to 5 percent, the
person becomes detectably affected, although he or she may not be aware
of either the CO or its effects, Cobb (1974) and Shulte (1973). Medical
authorities are not in agreement on what constitutes a dangerous level,
but when a level of 5 percent is reached, it is generally agreed that a
persons judgement is impaired and that visual acuity is reduced, Cobb
(1974).
For a person suffering from oxygen deficiency because of physical
exertion or high altitude,' the effects of exposure to CO may occur at
lower levels of COHb in the blood or be more severe at a given level.
Thus people exercising in Summit County are especially vulnerable to CO
exposure. Hence, adhering to statutory standards provides less assurance
of protection in Summit County than at sea level. This was verified by
the Eisenhower Tunnel Carbon Monoxide Standards Advisory Committee (1974).
2. Particles
Airborne particles vary greatly in size and composition. Particles
larger than 5 micrometers (pm) in diameter are less significant physiol-
ogically than smaller particles because the lungs are capable of ridding
themselves of large particles. Smaller particles are not so readily dis-
charged, however, and it has been shown that tissues extract toxic materials
more readily from these, Natusch (1974). These include particles less
than 1.0 ()jm) , all of which are present in some degree in most atmospheric
aerosols. Carcinogens', someti.me.s found among airborne particles, include
organic as well as asbestos and glass like substances.
-54-
-------
fJric.
Unless they are inhaled in high concentrations or over a protracted
period of time, the probability of ill effects from breathing aLrborne
particles is low. When inhaled in high concentrations, however, particles
can cause immediate reactions such as coughing.
3. Air Pollution
In general, health effects of air pollution are not dramatic and
usually do not occur after short exposure. Some indicators are: sputum
increase associated with respiratory discomfort, pulmonary edema and
emphysema, headache and eye irritation. Any of these taken singly may
not be perceived by most people, and many are so desensitized from exposure
in smoke-filled rooms and dirty, urban environments that they can not
detect these physiological warning signs if they encounter them in
unexpected places, such as a ski area parking lot.
Air is highly mobile. Consequently, a pollutant entering the atmos-
phere at one point can spread rapidly and soon envelop a large area. For-
tunately it usually becomes diluted as it does so. The dilution process
for a valley is discussed in detail in Section III B. Any area which con-
tains pollutant sources and does not have adequate ventilation may experience
high pollutant concentrations at times. The most likely such areas in
Summit County are those areas along busy highways, particularly those
which are in basins. People working in service stations and other road-
side businesses and attendants at ski area parking lots are subject to the
highest pollution concentrations normally occurring in Summit County.
These people should be aware that there are some health hazards associated
with the locations where they work.
Concentrations of particles and carbon monoxide in Summit County Qn
two days when human activity was high are given in Table 1.1 and in Sectiqn
III-D. The highest particle concentrations measured were 86 and 49 ygm/m3.
These occurred in Breckenridge and near the intersection of highways 1-70
and State 9 respectively. This three-hour average value is clearly below
both the 24 hour Federal and State standards which are listed in Table
III 9. Unless particles themselves are particularly hazardous, particle
concentration is not now a limiting factor.to growth and activity in
Summit County. The presence of asbestos-like particles in the summer
sample taken at this site and along 1-70 are cause for concern, however.
If future tests prove that these are commonly found in the air anywhere
in the County, the potential for growth and activity Ln that area should
be reassessed.
-55-
-------
!Jnc.
The highest carbon monoxide concentrations were measured downwind
from parking lots at ski resorts on December 30th. An hourly average
value of 16.3 ppm was measured at one site. Because traffic in and out
of these lots was high for a period of several hours, and because dis-
persion was poor during that period, it is highly likely that the average
for an eight-hour period reached or perhaps exceeded the 8 hour Federal
Standard of 9 ppm. Carbon monoxide concentrations were high enough to
suggest strongly that CO emissions are already a limiting factor in
winter in parts of Summit County. It is probable that parking lot atten-
dants at the ski areas are affected adversely by the CO they inhale on a
busy day.
4. Federal and State Air Pollution Standards
Federal and State standards are given in Table III 9. Primary
standards are intended to protect public health. Secondary standards
are intended to protect the public welfare from any known or anticipated
adverse effects of a pollutant. The 1, 8, and 24 hour average values
are not to be exceeded more than once per year.
TABLE III. 9
Federal and Colorado Standards for
Carbon Monoxide and Particles
FEDERAL
COLORADO
Averaging
Time
Primary
Standard
Secondary
Standard
Carbon Monoxide
8 hour
1 hour
9 ppm
35 ppm
Same as
primary
Same as
Federal
Suspended Particles
Annual
24 hour
75 pg/m
260 yg/m"
60 pg/mJ
150 pg/irT
45 pg/m"
150 pg/nT
-56-
-------
fine.
SECTION IV
A. Conclusions
Summit County as a whole has good air quality almost all the time.
There are a few small areas, however, in which pollutants do accumulate
and reach concentrations approaching the statutory limits for undesignated
areas. The areas in which this is most likely are associated with ski. re-
sorts, urban concentrations, and 1-70.
Air pollution is not now a serious problem even in the areas noted
above except during periods when atmospheric conditions do not disperse
pollutants adequately. These conditions are most likely in winter. They
are usually of short duration, occurring during the late night and early
morning hours. . Occasionally after a major storm has passed through the
Rocky Mountain area and winds above the mountain tops are from the north, a
long-term, serious pollution episode could develop. Such an episode could
involve much larger areas of the County than those few suggested in the
last paragraph.
Long-term pollution can be controlled at whatever level is desired by
controlling growth and development in the County. Development can reach a
higher level if pollutant emissions from all sources are kept as low as
possible and if sources are carefully distributed both vertically and hori-
zonta11y.
During poor dispersion episodes pollution may occasionally have to be
controlled for short periods by controlling emissions. Banning fireplace
burning for a few hours may be enough in some instances; under extreme
conditions it may be necessary to ban all automotive traffic in the County
except that essential to health and welfare. The periods during which
controls need .be used can be anticipated a few hours or perhaps a day in
advance by an air pollution meteorologist. They can he Identified when
they occur by monitoring air quaLity as suggested in Section l.D.3.
-57-
-------
cz/f-m&iznt <^/fna[y±Li, 17na.
REFERENCES
Cobb, John C., M.D. M.P.H. "Health Effects of Carbon Monoxide and
Photochemical Oxidant Air Pollution in Denver," Carbon Monoxide
and the People of Denver, Institute of Behavioral Science, U.
of Colorado, 1974.
Fosberg, M.A., A. Rango, and W. E. Marlatt, 197A: "Wind Computations
from the Temperature Field in an Urban Area". Conf. on Urban and
Climate and Second Conference on Biometeorology, Oct. 31-Nov. 2,
1974. Philadelphia, PA.
Hoffman, A. J., T. C. Curran, T. B. McMullen, W. M. Cox, and W. F.
Hunt, Jr., 1975: "EPA's Role in Ambient Air Quality Monitoring."
Science, Oct. 17, 1975, pp. 243-248.
Holben, Brent N. and W. E. Marlatt, 1974: "Air Pollution Analysis
of Summit County". On file in Summit County Planners Office,
Breckenridge, CO.
Kahm, M. A., 1974: Div. of Highways, State of Co.lorado Research
and Special Studies Section, Intradepartment Memo. Denver, CO
File #909.40.
National Research Counci], 1970; "Effects of Chronic Exposure to
Low Levels of Carbon Monoxide", Ind. Hyg. News Report, 12:5,
Jan. 1970.
Natusch, David F. S. and John R. Wallace, 1974: "Urban Aerosol
Toxicity: The Influence of Particle Size". Science, Nov. 22, 1974,
pp. 186.
Rose, E. F., 1969: "Carbon Monoxide Intoxication and Poisoning,"
J. Iowa Med. Soc. , Vol. 49, 1969.
Shulte, J. H., 1973: "Effects of Mild CO Intoxication." AMA,
Archives of Environ. Health, Vol. 7, Nov. 1973.
Turner, D. Bruce, 1969: "Workbook of Atmospheric Dispersion Estimates,"
U.S. Dept. of Health, Education and Welfare.
-58-
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APPENDIX A
SAMPLING CO AND PARTICLES
IN SUMMIT COUNTY, COLORADO
Calibration Methods, and Interim
Results oC Sampling—Summer 1975
October 1975
Interim Report
Submitted to Summit County, Colorado Planning Department
by
AMBIENT ANALYSIS, INC.
1675 Range
Boulder, Colorado 80302
-------
TABLE OF CONTENTS
PAGE
List of Tables & Figures ii
1.0 INTRODUCTION 1
2.0 DISCUSSION OF SUMMER SAMPLING 1
2.1 Summit County - Weather 1-4
3.0 SAMPLING & ANALYSIS 5
3.1 CO Sampling Techniques 5
3.1.1 Mylar Bags 5
3.1.2 "Ecolyzer" 5
3.2 Particulate Sampling Techniques 7
3.3 Calibration Procedures 7
3.3.1 Needle Flowrates (CO) 7
3.3.2 Filter Flowrates 7
3.3.3 "Ecolyzor 7
3.3.4 Meteorological Equipment 9
4.0 RESULTS 9
4.1 Discussion of Table 4.1 & Sampling - July 11 9
4.2 Discussion of Table 4.2 9
4.2.1 Gravimetric Analysis 14
4.2.2 Site Specific Interpretations 14
4.3 Interpretation of Boundary Layer Data
from the Tethersonde Sounding 14
4.4 Discussion of Tables 4.1, 4.2 and 4.3 18
5.0 FUTURE WORK 18
References 19
Appendix A 20-22
Appendix B
23-24
-------
LIST OF TABLES & FIGURES
PAGE
TABLE 2.2 - Meteorological Data by Site - July 23, 1975 3
TABLE 3.1 - Parameters According to Sampling Sites 6
TABLE 4.1 - Spot Carbon Monoxide (CO) Concentrations Found
at Various Points Summit County, Colorado-
July 11, 1975 10
TABLE 4.2 - Carbon Monoxide (CO) and Total Suspended Particles
(TSP) Concentrations found at Five Sampling Sites
in Summit County, July 23, 1975 11
TABLE 4.3 - CO Concentrations found at various points in
Summit County, Colorado 12
TABLE 4.4 - Size Disbribution of TSP by Site (Particles/
Filter) 13
FIGURE 2.1 - Site Locations 2
FIGURE 3.2 - Particle Filter Holder 8
FIGURE 4.1 - Vertical Profiles of Dewpoint, Temperature,
Wind Direction and Velocity 15
FIGURE 4.2(a) - SEM Micrographs 210X 16
FIGURE 4.2(b) - SEM Micrographs 210X 17
ii
-------
INTERIM REPORT - SUMMER SAMPLING
IN SUMMIT COUNTY
1.0 INTRODUCTION
This report ls an update on activities by AMIJLIiNT ANALYSLS, INC.
(AAI) for EPA contract number 68-01-3200, Air Quality Impact Statement
for Summit County, Colorado. In this document, the results of the
summer sampling episode are covered along with a short discussion of
plans for remaining work.
2.0 DISCUSSION OF SUMMER SAMPLING
Two major criteria were set up to designate the day on which con-
centrated sampling would be performed. The first called for a general
upslope wind condition near the surface with vertical mixing in the
air adjacent to the surface due to convective and mechanical turbulence.
This condition was expected on days with temperatures in excess of about
50°F. See section for atmospheric sounding data.
The second criteria called for recreational, weekday traffic density.
This was expected to occur on any day that the weather encouraged tourist
travel.
The day chosen was Wednesday, July 23, 1975. On this day, a five
member team from AAI proceeded to five sampling sites in Summit County.
These site locations are shown in Fig. 2.1. Appendix A contains a dis-
cription of these sites. Appendix B is an outline of the operational plan
utilized on July 23.
Prior to July 23, two members of AAI visited Summit County and made
spot checks of CO at various sites. On September 30, another two member
team visited Summit County to correlate suspended particulate samples
taken by AAI with those of the State of Colorado Hi-volume Air Sampler.
Spot CO measurement were also made during this visit.
2.1 Summit County - Weather
July 23 had been chosen for sampling because it was anticipated that
the air in the valley would be well mixed and hence that any pollutant re-
leased near the surface would soon mix through a deep layer. Weather maps
for July 23 show that there was little large scale motion over Colorado and
suggest that local circulations dominated.
The day started out nearly cl.oudless, and visibility was good. The
wind in the vicinity of Dillon Reservoir was blowing down the valley during
the early morning. By 1100 MDT it was blowing consistently up the valley
at Dillon Reservoir. This was the local circulation anticipated. See Table
2.2.
-1-
-------
cytynatijiLi, One.
FOR I'IC. 2.1, SI'K PACI', I 01' TIIK RKl'OKT
-2-
-------
1040
NNW
4
18.9
13.1
51
1010
W
6
18.9
11.1
36
1110
NW
4
17.7
9.4
30
1050
W
9
TABLE 2.2
Meteorological Data by Site - July 23, 1975
1055 1125 1220 1300 1315 1340 1415
1445
1500
1515
NNW
NW
NWW
NW
NW
NW
NWW
NW
NW
A NW
4
5+
7.5
4
4
4
2
2
4
8-10
19.2
21.1
21.7
20.8
-
19.4
-
21.1
-
17.8
13.6
13.9
14.3
12.8
-
12.2
-
12.8
-
13.6
53
44
44
38
-
41
-
36
-
63
1030 1100 1140 1210 1225 1320 1340 1415
1540
W
NW
WNW
NW
WNW
WNW
NW
-
WNW
7
9
9
8
8
4
7
-
5
19.4
20.0
-
20.6
19.4
21.7
22.2
20.6
21.7
11.7
11.1
-
10.6
11.1
12.2
11.7
12.2
11.7
37
31
—
24
33
30
24
35
27
1120
1200
1210
1220
1225
1230
1315
1330
1410
1450
1500
1510
NW
N
NNE
N
_
NNW
NW
NNW
N
NNW
NNW
NNW
4.5
7
3.5
7
-
7
4
5
6
10
3
-
-
19.3
-
18.2
-
18.9
-
18.4
-
-
16.1
-
-
10.3
-
9.8
-
9.4
-
9.3
-
-
7.8
-
-
30
-
31
-
25
-
25
-
-
27
1100
1150
1220
1225
1315
1330
1345
1355
1415
1455
1500
1520
w
W
W
WNW
W
w
W
-
-
W
w
W
9
4
7
8
10
11
15
0
0
10
7
10
-3-
-------
SITE 5
1030 1040 1050 1150 1200 1210 1220 1230 1245
WD SSW SW SW W W NW N W WSW
WS 7.5 4.5 6.5 8 2.5 5.5 9 9 8.5
1440 1500 1510 1550
WD SW NW - SW
WS 6 10 0 6
*See Figure 2.1 and Appendix A for site location and description
-3a-
1250
W
4
1300
SW
2.5
1330
W
5.5
1350
0
1410
W
6
-------
One.
As the valley floor grew warmer, small cumulus clouds with bases
higher than the mountain tops, started appearing over the mountain slopes
around the valley. Occasionally one would appear over the valley itself.
These cumuli grew in size and number. By mid-afternoon rain was falling
from some of them. Occasionally light showers reached the ground here
and there, but in many places none fell. Surface winds became gusty in
the vicinity of the showers; the wind shifted direction frequently; and
dust was carried into the air in places momentarily.
The air in the valley was being mixed about as thoroughly as it ever
is. VLsLbLLily was excel lent throughout the day except Ln the occasional
brief showers. A qucsL ion .irises nonetheless about the m i x Lnj; mechanism
when one attempts to understand the ili.sLributi.on of pollutants in <1
valley. The following appears to explain the observed circulation in
the BJue River VaLiey on that day.
As the air warmed near the ground, it started moving up the slopes
including the valley floor. That motion became well organized by noon.
Lapse rates in places became superadiabatic. Vertical air motions were
then accelerated and the upward flow formed cumulus clouds. This was most
general above the steep slopes near the mountain tops. Although the flow
up the valley fed these cumuli continously, they did not appear to interfere
with the nearly steady flow along the valley floor. A return flow may have
developed over the valley at high levels, but such a flow was not obvious.
It seems more likely that the air flowing out of the valley via the cumuli
was replaced by inflow at the lower end of the valley. In other words, the
valley did not contain a closed circulation on that day, although such closed
circulations may occur under some circumstances.
In those places where cumuli formed over the valley itself, the air
flowing upward into the cloud had to be replaced by air flowing inward
toward the updraft at low levels. That inflow was fed either by generally
increased flow up the valley below the cumulus and decreased flow up the
valley above it or by general subsidence of the air around the updraft.
In either event, the updrafts over the valley (away from the steep mountain
slopes) were of fairly limited extent surrounded by nearly horizontal flow
of much greater extent.
Although the presence of cumuli and gusty winds indicates vertical
air motion and mixing, surface air containing pollutants may move nearly
horizontally for long distances before being lifted off the surface.
Occasionally, however, the air at a pollutant source may be swept up in
a cumulus updraft virtually immediately. Thus, even on a day when mixing
is obviously occurring, air in the valley is not homogeneous. Pollutants
released near the surface may remain near the surface for many minutes;
they are not likely to accumulate in the valley, however.
-4-
-------
mtrienk c^fnatij±Li., LJnc.
3.0 SAMPLING AND ANALYSIS
Two chemical parameters were sampled and from two to five meteoro-
logical parameters were sampled at each site. (See Table 3.1)
3.1 CO Sampling Techniques
Carbon monoxide (CO) was sampled by two different methods. Mylar
bags were used at all five sites to collect grab samples. At sLtes 2
and 4 real time instruments were also used.
3.1.1 Mylar Bags
Each Mylar bag had an approximate filled volume of 80 liters and
was housed in a rigid, air tight container. Evacuation of the bags was
accomplished by connecting them directly to a vacuum pump. Filling the
bag was accomplished by connecting a vacuum pump to the box and evacuating
it which caused the bag to fill with outside air.
Prior to collecting the sample for analysis, the bags were filled and
evacuated twice at their respective sites to insure removal of any con-
tamination the bags might have retained from their last use. This pro-
cedure also conditioned the interior surface of the bags to the ambient
relative humidity, aerosol loading and approximate gas concentrations.
The analytical sample was collected by connecting the box to the
vacuum pump with a hypodermic needle.1 This regulated the flow so that
the bag was filled uniformly over a time period of 25 minutes to an hour,
providing a time-integrated sample.
The procedures used in the bag sampling were developed at the National
Center for Atmospheric Research in Boulder, Colorado.
After all sampling had been completed, each team member proceeded to
Site 2 where each bag was analyzed by attaching it to an "Ecolyzer". The
bags were again analyzed with the same "Ecolyzer" the next day in AAI's
Boulder laboratory where calibration could be carried out under carefully
controlled conditions.
3.1.2 "Ecolyzer"
A Model 2800 "Ecolyzer" was used for spot checks on July 11 and
September 30 and at Sites 2 and 4 (two instruments) on July 23, it was
also used to analyze the bag samples. This instrument operates on the
electrochemical oxidation principle for CO detection. For detailed in-
formation of its operation and sensitivity refer to references - 2,3,4 and 5.
CO data were recorded on July 23 at Site 2 on a strip chart recorder.
Readings at Site 4 were made intermittently by the site operator.
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CJnc.
TABLE 3. 1.
Parameters According to Sampling Sites
Site
Parameter
Method
Duration
Carbon monoxide
Particulates
Condensation Nuclei
Barometric Pressure
Temperature
Relative Humidity
Wind Speed
W ind I) iruct ion
Carbon monoxide
Carbon monoxide
Particulates
Temperature
Relative Humidity
Wind Speed
Wind Direction
Vertical Wind-temp. Profile
Carbon monoxide
Particulates
Temperature
Relative Humidity
Wind Speed
Wind Direction
Carbon monoxide
Carbon monoxide
Particulates
Wind Speed
Wind Direction
C;irbon monoxide
Pa r t Leu I a tes
Wind Speed
Wind Direction
Mylar bag
Nuclepore filters
Sling psychrometer
Sling psychrometer
"Dwyer wind meter"
Magnetic compass
Mylar bag
"Ecolyzer"
Nuclepore filter
Sling psychrometer
Sling psychrometer
"Dwyer wind meter"
Magnetic compass
"Tethersonde"
Mylar bag
Nuclepore filter
Sling psychrometer
Sling psychrometer
"Dwyer wind meter"
Magnetic compass
Mylar bag
"Ecolyzer"
Nuclepore filter
"Dwyer wind meters"
Magnetic compass
Myl.ir bags
NucIepore filter
"Dwyer wind meter"
Magnetic compass
59 min.
190 min.
Intermittant
Intermittant
Intermittent
Intermittent
Intermittent
Intcrm i ttenl
57 min.
Continuous
184 min.
Intermittent
Intermittent
Intermittent
Intermittent
30 min.
53 min.
180 min.
Intermittent
Intermittent
Intermittent
Intermittent
40 min.
Intermittent
180 min.
Intermittent
Intermittent
25 min.
I 80 in i n .
I.nterm L t ten t
Intermittent
-6-
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I
00
I
PARTICLE FILTER HOLDER
<3
SUPPORT
(Screen side forward)
FILTER
(Shiny side forwcrd)
RETAINING RING
—
-n
n
—
o
"Sj
c,
r"
TO
—
L-J
rr
U>
_
N3
c~
a.
o
PROTECTIVE PLASTIC CAP
(Remove during use)
-------
(^/fm&iant {Jnc.
3.3.4 Meteorological Equipment
The thermometers, Dwyer Wind Meters, and compasses were not
calibrated.
The "TETHERSONDE'1 sensors were calibrated in a chamber by the
manufacturer. They were also checked against ground based sensors to
insure proper operation immediately prior to launch.6
4.0 RESULTS
The results acquired from the sampling are presented in the following
tables and figures:
Table 4.1 - gives the location, time and concentration of CO
found at various points in Summit County on July 11, 1975.
Table 4.2 - presents the results of the concentrated sampling
effort performed on July 23, 1975.
Figure 4.1 - Tethersonde data of July 23.
Table 4.3 - gives the CO results obtained from a moving car on
December 12, 1974 and on September 30, 1975.
Table 4.4 - gives the size distribution of the total suspended
particles (TSP) for July 23 and spot measurements of condensation
nuclei particles (CN).
Figure 4.2 - scanning electron microscope pictures of Summit County
part ic1es.
4.1 Discussion of Table 4.1 and Sampling July 11
These data were gathered with the "Ecolyzer" in the car. The intake
tube was extended out of the window.
During the stay at the Copper Mountain parking lot, two Mylar bags
were filled with ambient air samples and later analyzed by NDIR at Coors
laboratories. The resuLts from Coors for each of the bags stated that
CO concentrations were less than 10 ppm.
4.2 Discussion of Table 4.2
Carbon monoxide and total suspended particulate results arc shown
in Table 4.2. The d.il.i .ire cons i sI en L will) oilier baseline data already
collected in Summit County. (See Si.le Location Report 1975)
Baseline mass loading for non-urban continental U.S. has been
estimated at 37 micrograms per cubic meter (pg/m3)- The measurements
from which this average mass loading was dveloped were made with High
Volume filter devices most of which are located near urban centers. It
Is possible that results are skewed toward higher mass loading because
of the sampling locations. There is also a possibility of bias due to
location (on top of building) and the method of determining mass loading.
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fJnc.
TABLE 4.1
Spot Carbon Monoxide (CO) Concentrations Found at Various Points
Summit County, Colorado - July .11, 1975
Site Time ppm CO*
Driving west on 1-70, East side of
tunnel at 10,000 ft. 0900 9-10
Just entering east end of tunnel 30
Center of tunnel 50
About to leave west end of tunnel 45
3/4 mile west of tunnel 10
Holiday Center (Frisco) 0915 4
Frisco Town Hall 0922 3
Summit County health offices (outside) 0930 2 -3
Highway west of Frisco 1300 4 -8
Parked by road west of Frisco -
traffic heavy and fast 1313 2-10
Following a string of slow moving
cars in Ten Mile Canyon 1320 40-55
Following a string of cars - road
wider, traffic faster (alt. 9711) 1322 6
Copper Mountain 1326 <2
Copper Mountain parking lot 1415 <2
Silverthorne Interchange and
Dillon Straight-Creek . , 1530 20-75
Entering tunnel heading east 1540 55-70
"ppm CO - parts per million by volume of CO
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Chic.
TABLE 4.2
Carbon Monoxide (CO and Total Suspended Particles (TSP) Concentrations
found at Five Sampling Sites in Summit County, July 23, 1975
TSP
Site*
ppm CO
(Mg/m3)
l-(Knorr Ranch)
0.5
14
2-(Intersection 1-70 and
Highways 9 and 6)
] .5
49
3-(Breckenridge)
0.5
] 6
4-(Copper Mountain)
1.0
37
5-(K.eystone)
<0.5
13
Continuous CO Concentrations taken at Site 2
(Hourly Averages)
Site 2 (Intersection 1-70
and Highways 9 and 6)
Time ppm CO
1000 2.2
1100 0.9
1200 0.8
1300 1.9
1400 1.4
1500 0.8
Mo.i n 1.34
Standard Deviation 1.98
"See Figure 2.1 and Appendix A - sampling period approximately 1
hour each site.
^The maximum observed five minute mean value was 11.7 ppm CO.
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fJnc.
TABLE 4.3
CO Concentrations found at various points
in Summit County, Colorado
December 12, 1974*
ppm
CO
Place
Time
Avg.
Max,
Silver Plume
_
<2
Tunnel
1040
25
50
Straight Creek
-
<2
7
Ten Mile & Copper Mountain
-
3
5
Vail Pass
-
3
5
West Vail
1150
3
18
Vail Covered Parking
1200
6
-
West Vail
-
7.5
-
Vail Pass (Trailing Traffic)
-
15
40
Copper Mountain
1230
3
-
Frisco
1242
5
15
Enroute Breckenridge
-
<2
-
Breckenridge
-
3
10
*Cloudy, cold and snow showers
September 30, 1975*
Silver Plume
0930
2
40
Tunnel
0940
40
55
Straight Creek
-
<2
30
Dillon Interchange
-
<2
-
Frisco
-
2
-
Ten Mile (Heavy Traffic)
1410
25
50
Vail Pass (Heavy slow traffic)
1434
10
35
West Vail Pass (In construction
traffic stop and start)
-
5
150
Straight Creek
-
5
-
Tunnel
1915 .
40
75
*Well ventilated sunny day
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mljiznt cy^natijiii, (Jnc.
TABLE 4.4
S i x.e I") i sL r i Im t i on of 'I'SI' by Site; ( I'.i r L i t: I cs / F i I Lcr)
Sample Total
Site
Volume (m3)
<1.0 pm
1-10 ym
>10
ym
Particles
1
4.62
1.4 x 106
1.8 x 106
8.3
x 104
3.3 x 106
2
4.67
6.1 x 106
2.4 x 106
1.7
x 105
8.7 x 106
3
3.74
2.8 x 106
2.0 x 106
1.9
x 105
5.0 x 106
4
3.47
2.8 x 106
1.4 x 105
2.4
x 105
4.4 x 106
5
4.23
1.3 x I.06
1.1 x 106
6.9
x 104
2.5 x 1.06
Spot Measurements of Condensation Nuclei (CN)/cm3
Place
Eisenhower Tunnel
Dillon/Silver t home
Vail Pass
Knorr Ranch (Site 1)
7/11/75
>106cn/Cm3
l.lO^cn/ o
cm-3
1.104cn/cm3
7/23/75
>10 cn/cm3
S-ioScn/J
*4. l(Pcn/cm3
9/30/75
>106cn/cm3
6.10^cn/cm3
>1C)6cn/cm3
'•average from 1100 to 1500 hours
-13-
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c^fm&Unt c^/fna[ij±Li., One.
On any given day in Colorado, the wind will usually blow strongly enough
for some period to cause larger particles with more mass to become
entrained in the nir flow. lli-Vol data ore the result of extended
sampling times and will therefore include high mass loading periods.
Authors of aerosol studies in northern Colorado have remarked at the
absence of large numbers of particles in the size range >0.15y in
comparison to aerosol studies near urban centers.^ The data from
Table 4.3 can be contrasted with those collected in August, 1975.
Differing conditions may account for the lower mass seen on the samples
in July 1975 compared with August 1974. Harvest and h.lying had taken
place in August 1974 and not in Jul.y 1975. Wind was generally stronger
in 1974 than in 1975 and visible dust was observed then, in contrast
to sampling on July 23.
4.2.1 Gravimetric Analysis
Analytical precision for the filter weights on this study (1975) was
about + 20 |ig in contrast to + 10 ug in (1974). This can be explained by
the different instrument being used for gravimetric analysis. Flow was
calibrated carefully and volume measurement should be considered accurate.
These data are characteristic of a very clean day in Summit County and
should serve to contrast with worst dispersion characteristics to be
sampled this winter.
4.2.2 Site Specific Interpretations
Size distribution was fairly uniform for ail sites except number
two. Site 2 was representative of average downwind characteristics to
be expected from a large highway intersection. This site also had the
only asbestos-like particles observed for this sampling period.® Site
4 also shows the effect of mixed downwind flow from a major highway and
the size distribution show a greater distribution in particles greater
than 10 microns that the other site. Site 5 was relatively clean, in-
dicative of the low vehicle traffic near the site. See Fig. 4.2 for
photomicrographs of particles collected at some sites.
4.3 Interpretation of Boundary Layer Data from the Tethersonde Sounding
The Tethersonde sounding data in Fig. 4.1 illustrates clearly that
the air was well mixed—
The lapse rates during both ascent and descent were nearly adiabatic.
The dewpoint lapse rate was nearly zero during both ascent and descent.
The winds showed no systematic increase in speed with height, suggest-
ing that the normally stronger winds from aloft were mixing downdward.
The air was in general dry—the difference between temperature and
dewpoint temperature being about 20°C near the surface. This suggests
that with thorough mixing the clouds bases should have been found at
about 2000 m above the surface. That would place the cloud bases at
about 6,500 ft. above the site or about 2,000 ft. above the surrounding
mountain tops. They were indeed observed to have been well above mountain
top level.
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c^f-m(jLg.nt fJnc.
FIGURE 4.1
Vertical Profiles of Dewpoint, Temperature, Wind Direction and Velocity
•ASCENT: 1508
a DESCENT [569
300
LU
To. I
WIND VEL(Ts)
DESC.: ; ASC.
\ S2 4.3 W£
a si ^ ^-r.^ &\ ^ADIABAT
^ 8J \ 3.3
CO O ¦
tr \ 8.3 4.8
200 uj • « ^ 2.3
\ „ Ni 5.2 \ as
\
• 5.6 —> 5.2
aa^ 5.6
(9
100 . &\ 92
\ 1.5
\i0.7
m
H
<3> !
\ 3.5 ® T S
• S| ^3
\ 3.0 *,: (»
a 70 a °
v V 28 ®® : z
52 * cj
0^ ^ „ j m
o
\ 4.4 "i
\ 2.9
0 ® ^0.7
jr.-
i ©
-4 -2 0 2 4 6 8 10 12 14 16 18'20 22
TEMP °C
m
o
>
—I
>
-15-
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Pages 16 and 17 are Included in the
body of the report as pages 48 and 49.
One.
-16-
-17-
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cztf-mfjiznt c^/fnaCtj±is., LInc.
4.4 Discussion of Tables 4.1, 4.2 and 4.3
These Carbon monoxide values were determined in the same in.inner
as was used on July 11 (Table 4.1). That is, the "Ecolyzer" was in
the car with the intake tube outside the window.
Data from July 11 were characteristic of highway concentrations
encountered in December 1974 except for the measurements from Silver-
thorne up Straight Creek to the Eisenhower Tunnel. The atmospheric
dispersion was relatively good on this day and though traffic was
heavy around 1500 an average 40 ppm was unexpectedly high in route
to the tunnel. Presumably, the organized flow up the creek was
serving to concentrate emissions from the highway as well as any
pollutant entrained throughout the county.
Table 4.2 shows a correlation between total particle mass loading
and carbon monoxide concentrations. These values are comparable to
data collected in August 1974. They will serve as ample reference to
compare to winter data.
Table 4.3 documents concentrations taken in two different seasons
and adds to the data baseline for later reference. Comparison of these
data may be difficult because of inadequate VMT data. Liaison with the
State Highway Department is ongoing in order to develope traffic docu-
mentation to correlate to the meteorological and chemical data.
5.0 FUTURE WORK
AAI lias one major task yet to accomplish to compLete the work
called for in this contract for Summit County.
This is the winter sampling operation scheduled to take place
sometime in November or December 1975. During this operation, sampling
comparable to that performed during the summer at the same sites ( i.P
appropriate) will be done.
Any site location change recommendation will be communicated to
Summit County and the EPA Project officer.
-18-
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c^fmljient c^f-naCiji.L±., (Jric.
REFERENCES
1 James P. Lodge, John B. Pate, Blair E. Ammons and Glenda A. Swanson,
The Use of Hypodermic Needles as Critical Orifices in Air Sampling,
APCA Journal, Vol. 16, No. 4, April 1966.
2 H. W. Bay, K. F. Blutron, J. M. Sedlak, and A. M. Valentine,
Electrochemical Tehcnique for the Measurement of Carbon Monoxide,
Analytical Chemistry, Vol. 46, No. 12, October 1974.
3 Energetics Science, Inc., F.co I yzcr Instruction Ma nun 1, December L 9 7 3 .
^ Steven Arnold, Testing and Review of the "Ecolyzer" Portable Carbon
Monoxide Monitor, August 1973.
^ C. Frederick Smith, Performance of a Commercial Electro Chemical Carbon
Monoxide Analyzer, May 1974.
6 A. L. Morris, David B. Call, and Robert B. McBeth, A Small Tethered
Balloon Sounding System, AMS Bulletin, Vol. 56, No. 9, Sept. 1975.
7 G. M. Hidy, R. Bleck, J. H. Blifford, Jr., P. M. Brown, G. Langer,
J. P. Lodge, Jr., J. R. Osinski, and J. P. Shedlovski, Observations
of Aerosols over North-eastern Colorado NCAR-TN-49, June 1970.
8 K. R. Spurny, W. Stoeber, E. R. Ackerman and J. P. Lodge, Jr.,
A Note on the Sampling and Electron Microscopy of Asbestos Aerosol
in Ambient Air by Means of Nuclepore, APCA, 1974.
-19-
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c^fmHriznt c^-fna[ys.Lif Una.
APPENDIX B
Air Quality Study, Site Location Report
Summit County - June 1975
SITE 1
A site 350 meters south of Highway 9 on the Knorr Ranch in the
northern part of Summit County has been selected. It is situated in a
hayfield between Squaw Creek on the east and Brush Creek on the west.
The terrain slopes gently toward the north at the site, which is
located in a nearly horizontal basin approximately three miles in
diameter. In upslope flow, air from the north will flow over Green
Mountain Reservoir and through an appreciable depth. Well-organized
downslope flow will carry air from most of the county over the site
if the flow endures long enough. This flow will occur when the air
is hydrostatically stable, and although air motion near the surface will
be slightly turbulent, motion at higher levels is likely to be very nearly
laminar. In general emissions from a high source will pass over the site
at a higher level than emissions from a lower source.
The net effect at this site could be an elevated stratum containing a
relatively high concentration of carbon monoxide. Localized motion down
the sides of mountain ranges, i.e., the Continental Divide to the northwest
and Gore Range to the southwest, is not expected to ''wash" the site with
cleaner air from higher elevations.
SITE 2
This site was selected to show general emissions from the major
transportation arteries. It is located near the intersection of 1-70
and Highways 9 and 6. The site will be placed south of 1-70 for upslope
or good dispersion measurements and north to be downwind for the poor
dispersion analysis. The site will be about 300 meters from the highway
to avoid short-term concentrations associated with traffic bursts and local
turbulence which might obviate a representative test. The ground slopes
downward to the northwest to the Blue River below Dillon Dam, and then the
terrain climbs steeply to the Gore Range. This is one of the broadest valley
areas in Summit County. To the south the dominant topographic feature is
Dillon Dam and Reservoir. To the east 1-70 alters the Straight Creek drain-
age with a sharp grade to the Eisenhower Tunnel. The terrain slopes upward
from the Blue River to the west and southwest toward Frisco and Ten Mile
Canyon. During downslope, air will include pollutants that are emitted in
every part of the county from Wheeler Junction to the southwest, Breckenridge
to the south, Keystone and Swan Mountain developments along the Snake in-
cluding Dillon, and Straight Creek to the east. Elevation at the upslope
site is 8790 feet ASL.
The major pollutant source will be automobile and truck traffic and
associated dust-producing activities in the summer. Winter air pollutants
are expected to contain the by-products of space heating, in addition to the
sources mentioned above. Upslope air motion over this area should be fairly
clean, containing some emissions from a relatively small number of dwellings
-20-
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(3nc.
and rural ranching activity to the north. A power plant near Green Mountain
Reservoir and Heeney did not unduly influence sulfur dioxide concentrations
during an upslope condition analyzed in August 1974. Cumulative effects
from energy-related activities to the northwest of Summit County are not
expected to influence carbon monoxide and particle concentrations materially
at this location.
SITE 3
Site 3 is located near the south end of the county at an elevation
of 9,578 in Breckenridge. The site is located at the north end of the
tennis courts, across a street south from a parking lot which serves a
small supermarket and some other shops. The Blue River flows northward
about 50 meters to the east of the site. The valley is not wide here and
the terrain slopes steeply upward both east and west of the river. Since
the valley is deep and relatively narrow here and is oriented in a north-
south direction, it will frequently be isolated from the westerly flow
which prevails above the mountain tops.
This site was selected to obtain data representative of a typical
urban community. Sites L, 2 and 3 were all used for measurements under
good dispersion in August of 1974, when samples were collected simultaneously
under upslope, turbulent flow. Carbon monoxide concentrations at Breckenridge
were about four times the concentrations at Site 1. An interpretation of this
is that the approximate 1 ppm in Breckenridge constitutes a cumulative addition
from combustion emissions four times that of background or baseline, as re-
presented at Site 1. Analysis of other pollutants support the observation
that Site 1 was indeed at or near background levels, especially when compared
to other data of near geochemical background concentrations. Data collected
support the concept of selecting a site near the south end of Summit County
to provide a measurement of carbon monoxide accumulated in organized air
movement up the valley during upslope flow. Downslope conditions will re-
quire a site north of town to be representative of the community. If the
objective should be one of obtaining clean air to serve as reference, however,
the site should be located south of town so that clean air from higher reaches
is sampled before emissions are accumulated. Coose Pasture Tarn at a height
of 10,000 feet might be an acceptable site. Summit County planning and- pro-
ject management personnel will be consulted on these potential Site 3
locations before fall and winter sampling. No decision is needed for the
summer sampling operation.
SITE 4
A survey has been conducted for Site 4 in the vicinity of the Copper
Mountain ski area. While a representative downslope flow in Ten Mile Canyon
must include contributions from both Ten Mile Creek and West Ten Mile Creek,
the recommended site will be west of Wheeler Junction, far enough to avoid
the confluence of the two flows. A site in a major parking lot about one-
half to one mile west of Wheeler Junction seems most appropriate for both
upslope and downslope conditions. The terrain slopes steeply upward to the
ski slopes to the south; the rise to the west is more gradual. The valley
floor li.is n modest slope downward to the north and east toward the creeks.
Beyond the creek to the north it rises slowly to the level of U.S. 6, beyond
which the canyon wall rises precipitously.
-21-
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c^/f-mdrUnt cz/f-naitjiLi.,
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