EPA-450/3-74-061
NOVEMBER 1974
DETERMINATION
OF THE FEASIBILITY
OF THE LONG-RANGE
TRANSPORT OF OZONE
OR OZONE PRECURSORS
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
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EPA-450/3-74-061
DETERMINATION
OF THE FEASIBILITY
OF THE LONG-RANGE
TRANSPORT OF OZONE
OR OZONE PRECURSORS
by
D.L. Blumenthal, W.H. White,
R.L. Peace, andT.B. Smith
Meteorology Research, Inc.
Box 637, 464 West Woodbury Road
Altadena, California 91001
(A Subsidiary of Cohu , Inc . )
Contract No. 68-02-1462
EPA Project Officer: E.L.Martinez
Monitoring and Data Analysis Division
Prepared for
ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, N.C. 27711
November 1974
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This report is issued by the Environmental Protection Agency to report
technical data of interest to a limited number of readers. Copies are
available free of charge to Federal employees, current contractors and
grantees, and nonprofit organizations - as supplies permit - from the Air
Pollution Technical Information Center, Environmental Protection Agency,
Research Triangle Park, North Carolina 27711; or, for a fee, from the
National Technical Information Service, 5285 Port Royal Road, Springfield,
Virginia 22161.
This report was furriit.hed to the Environmental Protection Agency by
Meteorology Research, Inc. , Altadena, California, in fulfillment of
Contract No. 68 02 14b2. The contents of this report are reproduced herein
as received from Meteorology Research, Inc. The opinions, findings, and
conclusions exprebsed are those of the author and not necessarily those of
the Environmental Protection Agency. Mention of company or product names
is not to be considered as an endorsement by the Environmental Protection
Agency.
This report was prepared with the cooperation of the California Air Resources
Board, Sacramento, California.
Publication No. EPA-450/3-74-061
n
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TABLE OF CONTENTS
Page
I. INTRODUCTION 1
H. EXPORT OF OZONE AND OZONE PRECURSORS
FROM URBAN AREAS 3
A. Los Angeles Basin 3
1. Background 3
2. July 25, 1973 11
a. Summary of Day 11
b. Trajectory Analysis 15
c. Analysis of Pollutant Data 21
3. September 21, 1972 28
a. Summary of Day 28
b. Trajectory Analysis 28
c. Analysis of Pollutant Data 31
B. Denver on November 21, 1973 38
in. OZONE IN RURAL AREAS 47
A. August 16, 1973, Arrowhead and Hesperia 47
B. Lake Arrowhead on August 24, 1973 57
IV. OZONE ALOFT - MECHANISMS AND PERSISTENCE 72
A. Mechanisms for Trapping Pollutants in
Layers Aloft 72
B. Overnight Persistence of Ozone 75
C. Ozone Persistence in Rain 83
V. ESTIMATES OF POTENTIAL DOWNWIND EFFECTS 86
VI. CONCLUSIONS 89
VII. REFERENCES 90
VIII. ACKNOWLEDGMENTS 92
ill
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TABLE OF CONTENTS (Cont'd)
APPENDIX A - DATA FROM JULY 25, 1973 AND
SEPTEMBER 21, 1972
APPENDIX B - CHARACTERIZATION OF DENVER'S URBAN
PLUME USING AN INSTRUMENTED AIRCRAFT
IV
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LIST OF FIGURES
Figure
Chapter I
Chapter II
II-1
II-2
II-3
II-4
II-5
II-6
II-7
II-8
II-9
II-10
11-11
II-12
Page
No figures
Map of the Los Angeles Air Basin Showing
East and West Basins 4
Los Angeles Basin Mean Wind Flow for Days
with Low Level Inversions During August
1970 at 1600 PDT 6
Results of Metronics, Inc. Tracer Release
October 24, 1972 (Metronics, Inc., 1973) 7
Vertical Profile Over Brackett (BRA)
July 25, 1973, 1707 PDT 9
Surface Ozone Concentrations (pphm),
1600-1700 PDT, July 25, 1973 12
Vertical Cross-Section of bscat for Midday,
July 25, 1973 13
Vertical Cross-Section of bscaf. for Afternoon
of July 25, 1973 14
Vertical Profile Over El Monte (EMT) July 25,
1973, 1655 PDT, After Passage of Sea Breeze
Front 16
Vertical Profile Over Cable (CAB) July 25,
1973, 1636 PDT 17
Trajectory Envelope for Air Arriving at Cable
Airport (Upland) 1600 PDT, July 25, 1973 19
Trajectory Envelope for Air Arriving Over
Redlands at 1800 PDT, July 25, 1973 19
Surface Wind Streamlines - 1600 PDT,
July 25, 1973 20
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LIST OF FIGURES (Continued)
Figure Page
11-13 Approximate Time (PDT) of Arrival of Sea
Breeze, July 25, 1973 20
II- 14 Pollutant Loadings in Surface Mixed Layer
Along Trajectory Arriving at Redlands in
Afternoon of July 25, 1973 22
II- 15 Estimated Ozone Flux from Western to
Eastern Basin, July 25, 1973, 1700 PDT 23
11-16 Vertical Sounding at Brackett (BRA)
July 25, 1973, 1707 PDT 25
11-17 Vertical Profile Over Corona (COR)
July 25, 1973, 1724 PDT 26
11-18 Peak Ozone Concentrations (pphm) Aloft at
Midday, September 21, 1972, 1230-1430 PDT 29
11-19 Peak Ozone Concentrations (pphm) Aloft in
Late Afternoon, September 21, 1972 29
11-20 The Mean Trajectory and Trajectory Envelope
of the Air Arriving Over Redlands at 1730 PDT,
September 21, 1972 30
11-21 Streamline Analysis - 1600 PDT, September
21, 1972 30
11-22 Vertical Profile Over Redlands (RED)
September 21, 1972, 1320 PDT 32
11-23 Vertical Profile Over Redlands (RED)
September 21, 1972, 1736 PDT 33
11-24 Vertical Sounding Over Long Beach (LGB)
September 21, 1972, 1352 PDT 34
11-25 Vertical Sounding Over Brackett (BRA)
September 21, 1972, 1625 PDT 35
VI
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LIST OF FIGURES (Continued)
Figure Page
11-26 Pollutant Loadings in Surface Mixed Layer
Along Trajectory Arriving at Redlands at
1730 PDT, September 21, 1972 36
II-27a Trajectory for Air Arriving at Standley Lake
1130 MST, 11/21/73 39
II-27b Morning Mixing Layer Pollutant Data 39
II-27c Midday Mixing Layer Pollutant Data 39
II-28a Vertical Profiles Over EPA Trailer (Site 1)
on November 21, 1973, 0925 MST 40
II-28b Vertical Profiles Over EPA Trailer (Site I)
on November 21, 1973, 1242 MST 41
II-29a Vertical Profiles Over Henderson (Site 2)
on November 21, 1973, 0915 MST 42
II-29b Vertical Profiles Over Henderson (Site 2)
on November 21, 1973, 1234 MST 43
II-30a Vertical Profiles Over Standley Lake (Site 3)
on November 21, 1973, 0822 MST 44
II-30b Vertical Profiles Over Standley Lake (Site 3)
on November 21, 1973, 1135 MST 45
Chapter III
III-1 Los Angeles Basin and Surrounding Areas 48
III-2 Hourly Average Oxidant Concentrations and
Surface Winds Measured at Skyforest Ranger
Station, August 16, 1973 49
in-3 Vertical Profile Over Arrowhead (ARR)
August 16, 1973, 0939 PDT 50
vii
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LIST OF FIGURES (Continued)
Figure Page
III-4 Vertical Profile Over Arrowhead (ARR)
August 16, 1973, 1645 PDT 52
III-5 Vertical Profile Over Hesperia (HES)
August 16, 1973, 0904 PDT 53
III-6 Vertical Profile Over Hesperia (HES)
August 16, 1973, 1656 PDT 54
III-7 Streamlines for 1600 PDT on 8/16/73 55
III-8 Vertical Profile Over Rialto (RIA)
August 16, 1973, 1337 PDT 58
III-9 Vertical Profile Over Redlands (RED)
August 16, 1973, 1317 PDT 59
III-10 Hourly Average Oxidant Concentrations
Measured at Skyforest Ranger Station,
August 24, 1973 60
III-11 Vertical Profile Over Arrowhead (ARR)
August 24, 1973, 0842 PDT 61
III-12 Vertical Profile Over Arrowhead (ARR)
August 24, 1973, 1530 PDT 62
III-13 Vertical Profile Over Hesperia (HES)
August 24, 1973, 0831 PDT 66
III-14 Vertical Profile Over Hesperia (HES)
August 24, 1973, 1546 PDT 67
111-15 Streamlines for 1600 PDT, 8/24/73 68
III-16 Vertical Profile Over Cable (CAB)
August 24, 1973, 1200 PDT 69
III-17 Vertical Profile Over Rialto (RIA)
August 24, 1973, I32IPDT 70
vna
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LIST OF FIGURES (Continued)
Figure
Chapter IV
IV-1 Vertical Profile at El Monte (EMT) July 25,
1973, 1656 PDT, Showing Undercutting by
the Sea Breeze
IV-2 Vertical Profile Over Brackett (BRA) July 26,
1973, 0825 PDT, Showing Buoyant Plume and
Undercutting by Radiation Inversion
IV-3 Vertical Profile at Rialto (RIA) July 19, 1973,
1738 PDT, Showing Layer Caused by Upslope
Flow
IV-4 Vertical Profile Over Riverside (RAL)
July 26, 1973, 1638 PDT
IV-5 Vertical Profile Over Riverside (RAL)
July 26, 1973, 2239 PDT
IV-6 Vertical Profile Over Riverside (RAL)
July 27, 1973, 0122 PDT
IV-7 Vertical Profile Over Riverside (RAL)
July 27, 1973, 0500 PDT
IV-8 Vertical Profile Over Shepherd (SHE) in the
Rain, October 18, 1972, 1020 PDT
IV-9 Vertical Profile Over Shepherd (SHE) in the
Rain, October 18, 1972, 1357 PDT
Chapter V
V-l Vertical Profile at Redlands (RED)
August 16, 1973, 1700 PDT
Page
73
74
76
79
80
81
82
84
85
87
IX
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LIST OF TABLES
Table Page
Chapter I No tables
Chapter II
II-1 Estimated Average Daily Emissions in 1970
in Metric Tons Per Day 5
Chapter III
III-l August 16, 1973 Pibal Data 56
III-2 August 24, 1973 Pibal Data 63
Chapter IV
IV-1 Overnight Ozone Concentrations 77
x
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I. INTRODUCTION
Recent studies (Kelly, 1970; Ripperton, 1974) have indicated the
presence of ozone in rural areas at levels which exceed the Federal
Ambient Air Standard of 0. 08 ppm. The source of this ozone remains
in doubt, and speculation as to its origin ranges from injection into the
troposphere from the stratosphere to long-range transport of ozone from
urban areas. The Environmental Protection Agency (EPA) is interested
in resolving the question of the source of the high levels of ozone because
of the implications for control strategy and standards setting. This
study attempts to show that at least in some instances, high levels of
ozone in rural areas can be due to transport from urban sources as far
away as 100 km or more.
In the last few years, Meteorology Research, Inc. (MRI), has
conducted numerous and extensive three-dimensional air pollutant
studies using an airborne sampling system. Vertical, as well as
horizontal, data have been obtained for O3 , CO, NOX, SO2, condensation
nuclei, scattering coefficient (bsca^), temperature, turbulence, and
relative humidity. Detailed meteorological data were also obtained during
most of the programs. These studies have been performed in places
such as Los Angeles, St. Louis, Denver, the San Joaquin Valley,
Alaska, New Mexico, and Oregon with the most extensive data package
having been obtained for the Los Angeles (L. A. ) Basin and its sur-
roundings.
The MRI data generally show a background ozone level of 0. 04
ppm or slightly lower in clean air. In all the MRI studies, even in
rural areas, when the Oa level exceeded about 0.05 ppm, a distinct
surface-based mixing layer or layer aloft was definable. Within this
layer other indications of pollutants such as elevated levels of conden-
sation nuclei or light scattering coefficient (bsca{.) were also present.
Outside of the layer, the ozone concentration, as well as those of other
pollutants dropped to clean air values. In general, the polluted layers
aloft were easily explainable in terms of transport aloft from the
surface by normal meteorological means. This indicates that, at least
for the cases studied by MRI, the ozone exceeding the background level
was of surface origin.
The object of the present study is to determine the feasibility of
transport of ozone or its precursors from urban source areas to rural
receptor areas far downwind. This is done by the careful study of selected
pollutant episodes in which various phases of the transport process can
be well documented. While the case histories selected are considered
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typical of pollutant episodes, no attempt is made to relate them to annual
statistics. The data used in this study were obtained under various
contracts with the California Air Resources Board and the Environmental
Protection Agency.
To begin with, the export of ozone or its precursors from Los Angeles
and Denver is documented. Relatively rural areas such as Redlands,
downwind of Los Angeles, and Standley Lake, downwind of Denver, are
considered as receptor areas, and several days when high ozone concen-
trations were observed during the afternoon at these locations are taken
as examples. Using the extensive winds aloft and surface wind data, the
ozone-laden air masses arriving at these locations are traced back for
several hours to sources over industrialized and heavily populated urban
areas. Some of the receptor areas themselves have sources of ozone pre-
cursors which may affect ozone concentrations even further downwind. For
the episodes studied, however, analysis of the pollutant burdens of the air
masses involved indicates that most of the ozone precursors present at
the receptor sites were picked up over the urban areas upwind, and that
most of the ozone measured was either exported directly from the urban
areas or formed en route as the air mass aged in the absence of extensive
new emissions.
The case studies described above present a strong argument to
document the export of ozone or its precursors from urban areas for three
different days. In order to show the potential for multiday transport,
evidence of the overnight stability of ozone at elevated concentrations (more
than 0.10 ppm) in aged polluted air is presented, and the existence of
ozone in the rain is documented.
Examples are also presented of high ozone concentrations confined
to the surface mixing layer in the relatively remote mountain and desert
areas east and northeast of Los Angeles. The ozone-laden air arriving at
these locations is traced back to the probable source of the ozone pre-
cursors in the Los Angeles Air Basin.
The bulk of the evidence indicates that urban areas can be a source
of high concentrations of ozone or ozone precursors found in at least a few
specific rural areas. Based on a specific episode, an estimate of the
potential effect of a city the size of Los Angeles on downwind ozone
concentrations is made. Using standard diffusion estimates, it is shown
that an urban source of this size could cause the ambient air ozone standard
of 0. 08 ppm to be exceeded as far as 260 km downwind of the source.
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II. EXPORT OF OZONE AND OZONE PRECURSORS FROM URBAN AREAS
A. Los Angeles Basin
1. Background
The Los Angeles air basin can be divided into two sub-
basins separated roughly by the Chino Hills, as shown in Fig. II-1.
The western basin encompasses the heavily urbanized portions of Los
Angeles and Orange Counties, while the eastern basin lies in more
rural San Bernardino and Riverside Counties. As indicated in Table II-1,
the estimated daily emissions of primary pollutants in the eastern
basin are much lower than they are in the western basin.
As shown in Fig. II-2 (from Smith et al., 1972),
afternoon surface winds during the summer months are predominantly
westerly, under the influence of the sea breeze. It is clear from the
pattern of the surface winds that air is transported from the western
basin into the eastern basin during a typical summer afternoon. This
has been verified by recent tracer studies conducted for the California
Air Resources Board. On seven summer and early fall days in 1972
and 1973, Metronics Associates, Inc., released color coded fluorescent
particles in the vicinity of Los Angeles (CAP), Torrance (TOA), and
Santa Ana (SNA) (Vaughan and Stankunas, 1973,' 1974). On most of these
days, particles from Los Angeles and Torrance were picked up in
Redlands (RED) by 1600 PDT. An example is shown in Fig. II-3.
Although transport fromthe we stern basin to the eastern
basin is now well documented, the magnitude of its effects on pollutant con-
centrations downwind is difficult to establish without knowledge of their
three-dimensional distribution. As cooler marine air from the coast
is carried inland it is warmed by the ground, and the mixing layer
deepens. The resulting dilution of pollutants by clean air as they mix
through a deepening layer and other meteorological effects tend to
obscure the effects of transport on surface concentrations. This study
uses data obtained during a three-dimensional pollutant mapping program
to gain a better understanding of the transport phenomena at work in the
L.A. Basin and to obtain an estimate of the effects of pollutants exported
from the western basin on the concentrations observed in the eastern
basin.
-------
4
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Table II-1
ESTIMATED AVERAGE DAILY EMISSIONS IN
1970 IN METRIC TONS PER DAY
Los Angeles County* Riverside County*
and Orange County and San Bernardino County*
RHC 1395 135
NO 1210 120
.X
CO 8820 935
SO 2 240 40
Figures are from the State of California Implementation Plan for
Achieving and Maintaining the National Ambient Air Quality Standards,
California Air Resources Board, 1972.
*Only that portion of the county lying within the South Coast Air
Basin is included.
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On numerous summer and early fall days in 1972 and
1973, instrumented MRI aircraft mapped the three-dimensional distri-
bution of pollutant concentrations in the Los Angeles air basin
(Blumenthal et al. , 1973, 1974). The sampling consisted of a series
of vertical spirals over about 15 different locations in the basin on any
given day. Two aircraft were used, and each location was sampled
three times per day. Spirals were generally made from the top of the
mixing layer or haze layer to the surface. The sampling days were
chosen for their high pollution potential, and the aircraft sampling was
coordinated with other on-going experiments (such as the Metronics
tracer studies) as often as possible. A data package was developed for
each sampling day which consisted of the aircraft data as well as surface
meteorological data, upper air wind data, and ground level pollution
data obtained from all available sources.
Figure II-4 is an example of the vertical profiles
produced from the spirals. Pollutant concentrations are plotted versus
altitude over Brackett Airport (BRA on Fig. II- I) at about 1707 PDT on
July 25, 1973. The scale at the bottom of the figure indicates all the
parameters measured, but some of these parameters are often omitted
from the graphs for simplicity or because of instrument malfunction.
In Fig. II-4, an obvious temperature inversion is present. Pollutants
are trapped in the well-mixed layer below the inversion, while con-
centrations above the inversion are much lower. In general, high,
well correlated bscaj. and ozone levels along with low condensation
nuclei and NOX levels indicate a photo chemically aged air mass. High
levels of condensation nuclei and primary pollutants (such as CO and
NOX) along with low ozone levels and a poor correlation between bscat
and ozone indicate fresh emissions below the inversion level. Below
the inversion level, in Fig. II-4, some fresh emissions are mixed into
an aged air mass. The air above the mixing layer, although cleaner,
includes some well-aged pollutants with no fresh emissions.
A useful technique for studying the total pollutant
budget within an air mass is to integrate the pollutant concentration
through the depth of the mixing layer, thus obtaining the total pollutant
burden over a point on the ground. This technique lets one follow the
growth of the pollutant burden in the air mass as the air moves along
a trajectory and yet takes into account changes in depth of the mixing
layer along the way. The integrals of various pollutants throughout the
mixing layer are used in some of the analyses which follow. When
aircraft data are available for a given point, an actual integration is
performed. In some locations, however, ground data are used to
supplement the aircraft data. In these cases, the ground concentration
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is assumed constant throughout the mixing height and is merely
multiplied by the prevailing mixing height in the area. The integral
used Is given below.
MH
GL
In Eq. (1)
X = Any pollutant
[X] = Concentration of X at height Z
jLt
L -IfiG = Background concentration of X
GL = Ground level
MH = Mixing heights
The integral LX will be referred to as the loading of X, distinguished
from the concentration of X. One effect of correcting for background
concentrations in the integral is to render unnecessary the exact
determination of mixing height if there is a relatively clean layer above
the mixed layer. Background concentrations of 1 ppm for CO and 0. 04
ppm for ozone were used in the analyses.
Mixing layer heights were determined from the air-
craft soundings. The soundings were examined for points where values
of the various meteorological and pollutant parameters decreased (or in-
creased) significantly. In general, turbulence was the primary parameter
used, with the bgca^. profile providing the next best source of information.
Temperature and humidity profiles and the vertical profiles of other
pollutants were also used. In identifying a top to the mixed layer, as
much emphasis as possible was placed on the physical consistency
among the various parameters. Discrepancies between the various
parametric definitions were reconciled as they appeared. In many
situations, the definition of the mixing layer height was simple and
unequivocal. In others, the most consistent definition was used.
In the following analyses, surface ozone data obtained
from local air pollution districts are used. Since the calibration method
used by the L. A. APCD is different from that used by all other agencies
in the L.A. Basin, all L.A. APCD ozone data used in this report are
adjusted to be consistent with the other agency calibration procedures.
In the remainder of Section A we study the transport
of ozone and its precursors from the western basin across the eastern
10
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basin to Redlands, identified by the code RED in Fig. II-1. Our
discussion is based on two specimen days for which pollutant loadings
in the mixed layer, together with winds aloft and at the surface, were
measured.
2. July 25, 1973
a. Summary of Day
July 25, 1973 was the second day of a major
smog episode. The California Air Resources Board station at Upland
(CAB on Fig. II-5) reported an average ozone concentration of 60 pphm
for the hour beginning 1600 PDT, the highest such concentration recorded
in the Los Angeles Basin that year. Figure II-5 shows that surface
concentrations were generally high in the northern part of the eastern
basin at this time.
Meteorological conditions on July 25, 1973 were
typical of those associated with heavy smog in the Los Angeles Basin.
Throughout the day a strong subsidence inversion covered the whole
basin at about 1000 m msl while a marine inversion sloped upward from
about 300 m msl near the coast until it merged with the subsidence
inversion roughly 40 km inland. The structure of this double inversion
is revealed in Figs. II-6 and II-7, which show approximately west to east
vertical cross-sections of the light-scattering coefficient, b scat, at
the beginning and end of the afternoon. These figures were prepared
using the aircraft sounding data at the locations indicated.
During the night and morning hours the surface
flow in the basin was either stagnant or had a slight offshore component,
allowing the buildup of pollutants within the surface layer. In Fig. II-6,
the highest concentrations are seen within the source region in the
western basin. Although some of the bscat in this figure is due to
humidity effects, much of it results from emissions accumulated in
a relatively stagnant air mass. At the time represented in Fig. II-6,
the sea breeze had just recently started, and clean air had not yet
come onshore to flush out the basin.
Later in the afternoon, as shown in Fig. II-7,
the sea breeze had ventilated much of the surface layer in the western
basin, replacing air which had had a long residence time over land with
cleaner air with a short time onshore. The sea breeze "front" in
Fig. II-7 is between El Monte (EMT) and Brackett (BRA). The air
just ahead of the "front" had accumulated emissions over the western
basin earlier in the day and possibly during the night before, and had
the longest residence time over strong source areas of any air in the
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basin. Note that the highest concentrations in Fig. II-7 are over Upland
(CAB) at the time which corresponds to the peak ozone reading at
Upland (and in the basin) for the day.
In both Figs. II-6 and II-7 upper layers are seen
between the two inversions in the western basin. Pollutant concentra-
tions remain high in the layers all day, but the aircraft sounding and
pibal data indicate that these layers are decoupled from the air below.
The air in the upper layers is well aged and relatively stagnant
compared to surface air. These layers may be caused by upslope
flow along some of the nearby hills, by lifting or undercutting of polluted
air by the sea breeze, or by other means; but in any case they should
not have a significant effect on the results of the analyses presented in
this section.
The difference between the air in front of and
behind the sea breeze front is seen in Figs. II-8 and H-9. Figure II-8
is a vertical profile over El Monte after the passage of the front. A
surface mixing layer is well defined by the temperature, turbulence,
and pollutant profiles extending up to about 400 m msl. Within this
layer, the bsca^. and ozone values have dropped down from their peaks
for the day. The condensation nuclei values are still high, however,
indicating continuing fresh emissions. The air between about 400 and
600 m msl is moderately well aged but still has a moderate condensation
nuclei population, possibly indicating that this air was previously part
of the surface mixing layer but recently undercut by the advancing sea
breeze. The remainder of the layer aloft could be a remnant of the
layer existing earlier in the midday soundings.
Figure II-9 is a vertical profile at Upland (CAB)
before the passage of the front. The mixing layer is well defined and
pollutant concentrations are high within the layer. The ozone concen-
tration exceeds 0. 5 ppm. The air, within the mixing layer at Upland is
similar to that just above the sea breeze in Fig. II-8. This profile
represents the period of peak ozone concentration at Upland and in the
basin for the day.
b. Trajectory Analysis
Winds aloft on July 25, 1973 were measured at
four stationary sites. Pilot balloons (pibals) were released hourly at
Chino (CNO), in the eastern basin, and at Elysian Park, midway
between Hollywood (HOL) and the Los Angeles Railroad Yard (LARR)
in the western basin. In addition, pilot balloons were released at
1233 PDT from Los Angeles International Airport (LAX), and at 1335
and 1654 PDT from El Monte Airport (EMT).
15
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Figures 11-10 and 11-11 show trajectories,
computed from these wind observations, for the air arriving over
Upland (CAB) at 1600 PDT and Redlands (RED) at 1800 PDT. The
extreme northerly and southerly winds within the mixed layer (from
pibal observations) were used to construct an envelope of possible
trajectories, and the mean wind within the mixed layer was used to
construct a characteristic trajectory. Surface wind streamlines for
1600 PDT are shown in Fig. 11-12 for reference purposes. The
trajectories in Figs. 11-10 and 11-11 indicate that much of the air over
Upland at the time of peak ozone at that location was onshore before
the sea breeze started, probably having accumulated pollutants since
the night before, while much of the air over Redlands at the end of
the afternoon had come onshore with the start of the sea breeze. The
air arriving over Upland at 1600 PDT had the longest residence time
in the western basin of any air arriving over Upland that day, which
may account for the timing of the ozone maximum there.
The streamlines and trajectories indicate
that polluted western basin air was advected into the eastern basin
during the afternoon of July 25. This conclusion is corroborated by
the afternoon gradients in surface ozone concentration, which clearly
show the advance of cleaner air from the coast with the onset of the
sea breeze. The hourly average surface ozone concentrations from
1600 to 1700 PDT (shown previously in Fig. II-5) provide a snapshot
of this effect, showing a strong gradient between La Habra (LAH) and
downtown Los Angeles (CAP), which had already been flushed with
marine air, and Azusa (AZU) and Upland (CAB), which had not. By
1600 PDT the marine layer had reached El Monte (EMT), and was
sharply delineated in a vertical sounding made at 1655 PDT (Fig. II-8).
Figure 11-13 shows the approximate times at
which the sea breeze began to flush various locations in the basin
during the afternoon. These times were determined from California
Air Resources Board and local Air Pollution Control Districts
(APCD) ozone data according to an objective criterion: the approximate
time of arrival of the sea breeze is calculated as M:00 PDT, where M
is the first integer i such that X^_|_j ^1/2 X^_ j, Xj being the average
ozone concentration during the hour beginning at i:00 PDT. Comparison
of Fig. 11-13 with the trajectories to Upland and Redlands in Figs. II-10
and 11-11 shows that these trajectories depict air moving just ahead of
the advancing cleaner sea air. From 1600 to 1900 PDT the marine
front moved about 70 km inland for an average speed of about 23 km
per hour, in good agreement with observed wind speeds.
-------
Fig. H-IO. TRAJECTORY ENVELOPE FOR AIR ARRIVING AT CABLE AIRPORT (UPLAND)
1600 PDT, JULY 25, 1973
..Ufa'
Fig. n-Il. TRAJECTORY ENVELOPE FOR AIR ARRIVING OVER REDLANDS AT 1800 PDT, JULY 25, 1973
19
-------
Fig. II-1Z. SURFACE WIND STREAMLINES - 1600 PDT, JULY 25, 1973
Fig. H-13. APPROXIMATE TIME (PDT) OF ARFJVAL OF SEA BREEZE, JULY 25, 1973
(Objective criterion based on ground level ozone concentrations.)
20
-------
c. Analysis of Pollutant Data
Figure 11-14 shows how integrated contaminant loadings
within the surface mixed layer changed along the trajectory to Redlands
(RED). Points on the figure were calculated as described earlier in
Section II. A. 1, and both surface and aircraft data were used. The
aircraft data show that pollutants were well mixed within the mixing
layer and that the top of the surface mixing layer was always well
defined. The western basin points do not include any contribution from
the elevated layers. Data points were calculated for locations in or
near the trajectory envelope shown in Fig. 11-11.
Although there is considerable scatter in the data, the trends
are quite clear. There are large increases in the loadings of CO, Os,
and visibility-reducing particulates between the coast and the boundary
between the western and eastern basin (near Brackett (BRA)) across
an area which includes most of the emission sources in the Los Angeles
Basin. East of Brackett (BRA) loadings of CO actually declined, as
local emissions in the eastern basin were apparently not sufficient to
offset the effects of dilution or reaction. The emissions in the western
basin were sufficient to account for the CO seen along the trajectory in
the eastern basin. Ozone loadings east of Brackett remained relatively
constant, possibly due to continued formation of ozone by previously
emitted precursors and to the lack of fresh emissions to scavenge it.
Nearly all of the CO in the Los Angeles atmosphere comes
from the exhaust of motor vehicles (California Air Resources Board
1972). Motor vehicles are also the source of about 75 percent of the
NOx and 87 percent of the reactive hydrocarbons (Calif. ARB, 1972).
Using CO as a tracer for ozone precursors which were not measured
directly, we can deduce that a large fraction of the ozone precursors
introduced Into the air mass sampled at Redlands was emitted in the
western basin.
Additional information on the amount of ozone transported
into the eastern basin can be obtained by doing a simple flux calculation.
Figure 11-15 shows an estimate of the flux of ozone under the subsidence
inversion from the western basin into the eastern basin at 1700 PDT
on July 25. The western face of the box drawn in the eastern basin
represents the boundary across which transport was calculated, and
the east-west dimension of the box represents the distance covered in
one hour by the moving air. In a steady-state situation in the absence
of diffusion or diffluent winds, the box would thus contain about 185
metric tons of ozone, corresponding to a uniform concentration of
about 25 pphm. For comparison, the average late afternoon concentrations
21
-------
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Fig. II-14. POLLUTANT LOADINGS IN SURFACE MIXED LAYER
ALONG TRAJECTORY ARRIVING AT REDLANDS IN
AFTERNOON OF JULY 25, 1973
(Aircraft measurements plus estimates made
from ground data and mixing height. )
22
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of ozone within the surface mixed layer at Riverside (RAL), Redlands
(RED), Rialto (RIA), and Ontario (ONT) were, respectively, 36, 24,
25, and 13 pphm. (Data were taken from aircraft soundings.) The
flux was calculated for about 1700 PDT since soundings were available
for roughly that time, but 1700 PDT was also roughly the time of
arrival of the sea breeze front. Crude flux calculations for about 2
hours earlier indicated slightly greater flux and a correspondingly
higher average concentration in the box.
In the absence of photochemistry, one ton (as NOs ) of
freshly emitted NOX (mostly NO) could scavenge about one ton of ozone
under conditions of good mixing. The daily emissions of NOX in the
entire eastern basin are estimated to be only about 120 metric tons.
Roth et al. , (1974) found that in the western basin, about 16 percent of
a weekday's total car mileage was driven between 1600 and 1800 PDT.
If this 8 percent per hour figure is used to scale all NOX emissions to
hourly rates (for around 1700 PDT) one obtains an estimate of 10 metric
ton per hour for the NOX emission rate in the eastern basin. This is
inadequate to scavenge more than a small fraction of the ozone advected in.
The estimate of the ozone flux and the corresponding average
concentration in the eastern basin "box" were based on the following
considerations :
1. A quasi- steady state prevailed for at least one hour at
the boundary between the basins. This assumption
was quite good at the boundary even though this was
not the case over the whole western basin as the
progress of the sea breeze in Fig. 11-13 shows.
Pollutants which had accumulated in the western
basin for many hours were flushed out into the eastern
basin by the sea breeze starting about midday. For
this reason, pollutant fluxes out of the western basin
are not directly comparable to pollutant emissions
within the western basin. The western basin was
"emptied" more rapidly than it was "filled", giving
rise to fluxes which were large in comparison with
emission rates.
2. Afternoon soundings at Brackett (BRA.) (Fig. II- 16)
and Corona (COR) (Fig. 11-17) showed a capping subsi-
dence inversion at about 860 m msl. Ground elevations
east of the Chino Hills slope from roughly 310 m msl at
Brackett to 1 65 m msl at Corona; the Chino Hills them-
selves range 400-500 m msl, and the width of the pass
between the western and eastern basins is 25-35 km.
The area across -which the flux was calculated was taken
as 25 km x (860 m ~ 3 10 m) ~ 1.4 x 10 7 m2.
24
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The 1700 PDT winds aloft at Chino (CNO) were above
32 km per hour throughout the mixed layer, and the
1700 PDT surface winds at Chino, La Verne College
(POC), and Ontario (ONT) were all 27 km per hour.
All wind directions in this area were near due west.
The rate at which air was transported into the eastern
basin was taken to be:
1.4 x 107 m2 x 27 km/hr ~ 3. 8 x 1011 m3/hr.
The average ozone concentrations measured between
310 and 860 m msl on the 1700 PDT Brackett and
Corona soundings were, respectively, 33. 5 pphm =
660 flg/m3 and 16.8 pphm = 330 /ig/m3. These were
slightly lower than the corresponding values for the
1500 PDT soundings. The distribution of ozone con-
centrations at the surface indicates that concentrations
between Brackett and Corona were generally inter-
mediate in value. The rate at which ozone was
advected into the eastern basin was estimated to lie
between 3.8 x 1011 m3/hr x 660 jUg/hr ~ 250 metric
tons/hr. and
3.8 x 1011 m3/hr x 330 M/hr ~ 125 metric tons/hr.
Using this crude technique, it is clear that much of the
ozone loading in the eastern basin on the afternoon of July 25 can be
accounted for by advection from the western basin. In light of the
preceding analyses, it is probable that a significant portion of the
24 pphm of ozone within the mixed layer arriving at Redlands at about
1800 PDT had its origin in the western basin. Redlands is approximately
100 km from the area south of Los Angeles where the trajectory origi-
nated, thus it is reasonably certain that large source areas such as
Los Angeles and Orange counties can and do export a significant amount
of ozone and ozone precursors to distant surrounding areas.
July 25, 1973, was used in this analysis since a considerable
amount of data was available for that day, but similar evidence can be
provided for numerous days in the Los Angeles Basin. In Section
II. A. 3, following, another day is analyzed in less detail to support the
conclusions reached here.
Soundings and other data used in this analysis and not
presented here are included in Appendix A.
27
-------
3. September 21, 1972
a. Summary of Day
September 21, 1972 was a day of relatively
light smog. Pollutants were mixed through a deep layer inland, due to
intense surface heating. Surface O3 concentrations were generally below
20 pphm, and the highest concentration encountered aloft was 33 pphm.
Figure 11-18 shows the peak ozone concentrations
measured within the mixing layer in the midday (1230 - 1430 PDT)
aircraft soundings. The morning winds aloft were generally northerly,
and the highest ozone concentrations and loadings measured were found
in the southern part of the western basin. Figure 11-19 shows the
changed situation observed in the afternoon (1600 - 1800 PDT) soundings.
The eastern basin, which was quite clean at midday due to Santa Ana
(northeasterly) winds continuing from September 20, developed elevated
ozone concentrations throughout the mixed layer in the afternoon. The
portion of the western basin sampled had, meanwhile, cleared out
considerably with the advent of the sea breeze which developed after the
Santa Ana condition subsided.
b. Trajectory Analysis
Extensive observations of winds aloft were made
on September 21, 1972 as part of the Metronics tracer study mentioned
earlier, although no tracer was released on this date. From 0700 to
1800 PDT, one pilot balloon was released each hour from each of four
locations which moved along routes shown in Fig. 11-20 as-a series of
squares. The release locations were intended to approximately
follow air parcel trajectories, beginning in the western part of the basin
in the morning and ending in the eastern sections by late afternoon.
Figure 11-20 shows trajectories, computed from
these wind observations, for the air arriving at Redlands at 1730 PDT.
As for July 25, 1973, the extreme northerly and southerly winds
within the mixed layer were used to construct an envelope of possible
trajectories, and the vector mean wind within the mixed layer was used
to construct a characteristic trajectory. As shown in Fig. 11-20, a
probable track of the air arriving at Redlands is from the industrial
section south of Los Angeles through Pomona and Ontario to Redlands.
Surface wind streamlines during the afternoon (Fig. 11-21) support this
conclusion.
28
-------
Fig. II-18. PEAK OZONE CONCENTRATIONS (pphm) ALOFT AT MIDDAY, SEPTEMBER 21, 1972,
12:30 - 14:30 PDT
Fig 11-19. PEAK OZONE CONCENTRATIONS (pphm) ALOFT IN LATE AFTERNOON
SEPTEMBER 21. 1972
29
-------
Fig. 11-20. THE MEAN TRAJECTORY AND TRAJECTORY ENVELOPE OF THE AIR ARRIVING OVER
REDLANDS AT 17:30 PDT, SEPTEMBER 21. 1972
(Times along the trajectory are the times the air passed that line. )
4 «»tD srtCD U
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i UPPCM LEVEL WINDS
Fig. 11-21. STREAMLINE ANALYSIS - 1600 PDT, SEPTEMBER 21, 1972
30
-------
c. Analysis of Pollutant Data
Figures 11-22 and 11-23 compare soundings made
over Redlands at 1320 and 1736 PDT on September 21, 1972. The
light-scattering coefficient observed on the midday flight was below 10 m"
at all levels, and indicated a local v'sual range of 55 km (35 miles) or
more. By afternoon, the light-scattering coefficient was about
4x10 m at all levels, corresponding to a local visual range of about
10 km (6 miles).
The appearance late in the day of elevated O3 and
b concentrations in the eastern basin is difficult to understand in terms
of local sources. No inversion was present during the afternoon in the
eastern basin to hold reactants near the ground at high concentrations.
There was less solar energy to drive reactions in the afternoon than
there had been at midday. There is no reason to assume that diurnal
patterns of emissions in the eastern basin are dramatically different
from those in the western basin, where O3 concentrations nearly always
decrease during the afternoon.
The afternoon increase of O3 concentrations in the
eastern basin is most easily explained in terms of advection, since most
of the eastern basin air sampled in the afternoon sounds was passing
through the western basin during the midday soundings. Figure 11-20 shows
that the air in the 1736 sounding at Redlands (RED) was apparently just
entering the eastern basin through the pass at La Verne (POC) when the
1625 sounding was taken at nearby Brackett Airport (BRA). During the
midday soundings, some of this same air may have been as far west as
Long Beach (LGB) and downtown Los Angeles (CAP).
Figures 11-23, 11-24 and 11-25 show aircraft
soundings taken at Long Beach (1352 PDT), (Brackett 1625 PDT), and
Redlands (1736 PDT), corresponding roughly to the itinerary outlined
above. Figure 11-26 shows how integrated contaminant loadings (L )
changed along this route. The aircraft soundings did not reach the top of
the polluted layer (shown to be about 2000 m msl in other soundings) at
Redlands, and an arbitrary mixing height which encompassed the bulk of
the CO was chosen for the computations at this location. Since only three
aircraft data points were available, ground level data were also used in
preparing Figure 11-26. Ground concentrations were assumed constant
throughout the prevailing mixing height in the area.
A considerable amount of scatter is evident in the
ground data. Much of this results from the complicated flow on this day
in the vicinity of passes. In addition, the effects of local sources on the
loadings calculated from ground ddta are accentuated in the eastern
basin, due to the great depth of the surface mixed layer there. The
general trend of the data, however, is in agreement with the results
of the better-defined situation on July 25, 7973.
31
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SURFACE DATA
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LA APCO 0, DATA ADJUSTED
TO AGREE WITHARB CALIB-
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LNX
1100 1200 1300 1400 1500 1600
Time (PDT) Along Trajectory
1700
1800
Fig. II-26. POLLUTANT LOADINGS IN SURFACE MIXED LAYER
ALONG TRAJECTORY ARRIVING AT REDLANDS AT
1730 PDT, SEPTEMBER 21, 1972 (from aircraft
measurements plus estimates made from ground data
and mixing heights)
36
-------
Figure 11-26 shows that the CO loading of the air
mass sampled in the afternoon sounding at Redlands increased as it passed
over the western basin, from Long Beach to Brackett. Quantitative
estimates of emissions based on the magnitude of this increase are probably
unwarranted, as the data from the Long Beach sounding are somewhat noisy
and the mixing layer structure in general was complicated and difficult to
define precisely. Between Brackett and Redlands there was little apparent
increase in the CO loading, although the vertical distribution of CO con-
centrations changed. At Brackett CO concentrations decreased markedly
with height in the first few hundred meters, indicating recent emissions
at ground level. This conclusion is backed up by the high ground level
CO point at nearby Pomona (POMA). By the time the air mass had reached
Redlands, CO concentrations in the first few hundred meters were virtually
constant, indicating a much lower level of fresh emissions. These observa-
tions indicate that, as would be expected from a comparison of the emissions
in Table II-1 with the trajectories in Fig. 11-20, most of the CO in the air
sampled at Redlands was emitted in the western basin.
Using CO as a tracer for ozone precursors which
were not measured directly, as was done for July 25, 1973 we can deduce
that a large fraction of the ozone precursors introduced into the air mass
sampled at Redlands were emitted in the western basin.
The ozone loading increased between Long Beach
and Brackett, and again between Brackett and Redlands. The ozone concen-
tration over Redlands was nearly uniform with respect to height, indicating
that the half-life of ozone due to scavenging by fresh emissions was relatively
long. It appears likely, on the basis of the foregoing analysis, that most
of the ozone measured at Redlands in the afternoon was produced in the
western basin, or produced in the eastern basin from precursors emitted
in the western basin, again evidence of the transport of ozone or ozone
precursors from urban centers to surrounding areas.
37
-------
B. Denver on November 21, 1973
An example of the transport of ozone and/or its precursors
under conditions quite different from those in Los Angeles is provided by
the data from a study conducted in the Denver, Colorado area on
November 21, 1973 (Blumenthal et al., 1974). The distance over which
the ozone and its precursors and tracers were observed to travel in this
instance was small in comparison to the two Los Angeles cases just
discussed (due to the size of the observing network) but the path and
source of the pollutants is quite clear.
On the morning of November 21, 1973 an urban plume moved
north from metropolitan Denver confined to a surface layer about 90 m
(300 ft) deep. Between 0830 and 0930 MST, aircraft soundings at three
locations north and northwest of Denver measured the vertical distribution
of pollutants in the plume. After another hour of slow northward plume
movement over a suburban area, all surface winds and low-level winds
aloft shifted to easterly, driving the plume westward toward a rural lake,
one of the sites of the morning soundings. A second aircraft sounding
at the lake at 1130 MST confirms that the polluted air had, indeed, arrived
over the lake site with little change in its primary pollutant burden, but
a 100 percent increase in O3 concentrations despite a three-fold increase
in the depth of the mixing layer. At the same time, aircraft soundings at
the other two sites show roughly clean air values for all measured
pollutants.
The data available for November 21, 1973 in the Denver area
were basically the same type of data acquired in the Los Angeles studies - -
vertical soundings of air quality by aircraft, hourly winds aloft observations
and hourly surface winds. Fig. 11-27 shows the three locations where
aircraft soundings -were made at mid-morning and midday. These sities
are numbered one through three. Sites 1,4, and 5 in Fig. II-27a were
ballon-launching sites for hourly -winds aloft observations from 0900 MST
on. The observed -winds at these sites at 90 m (300 ft) were used to
construct the trajectory shown except for the portion from 1030 to 1130
MST. That portion was constructed from the constant wind direction and
the average speed from the surface to 270m (900 ft). Prior to 0830 MST,
only surface winds were observed, and they proved to be light and variable
with a slight tendency toward weak southerly.
In support of the calculated air trajectories, the Denver urban
plume can be traced with NO , which is formed almost exclusively by
combustion sources such as motor vehicles, power plants, and heating
units. The six aircraft soundings are shown in Figs. 11-28, 29, and 30.
Figures II-27b and c show NO and O3 concentrations integrated through
the mixed layer for these soundings. On the morning set of soundings,
38
-------
CONTOURS
seooitiirrt
1mm
, *--J I
iJl DENVER '-I
5^s~
SYAPLgTON '
"1INT. AIRPOR
^J F^
0827 MST
O| 0 mg/m
NOX ZO. 0 mg/m"
3
LAKE
0915 MST
Os 0 mg/m
0925 MS
0 mg/m2
NOZ8.3 mg/ma
1194 MST
O, 16 mg/m2
NO, 31.9 mg/m»
3
LAKE
1234 MST
Oj 5. 1 mg/m*
Slt«
Sit* I
1242 MST
03 5. lmg/m2
NOX 5.9 mg/m8
170
M V?"1
/ROCKY 1!
feTj'
• SiU 4 -
I /'DEmER _ t!STA°NRpORV
r-J
Fig. 11-27. a. TRAJECTORY FOR AIR ARRIVING AT STANDLEY LAKE
1130 MST, 11/21/73
b. MORNING MIXING LAYER POLLUTANT DATA
c. MIDDAY MIXING LAYER POLLUTANT DATA
39
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all three sites showed modest NO totals (see Fig. II-27b). O3 values
in the lowest 90 meters (300 feet) or so are all below the background
count of 4 pphm found at higher levels. (Integrations for ozone (L ) have
been corrected for a background level of 4 pphm. Negative values of
the integral are listed in Fig. 11-27 as zero).
At midday, when the trajectory shows that the surface layer
of air which had been just west of site 1 at 0930 MST should be over
Standley Lake, the only spiral showing a heavy load of NO is that over
site 3 at Standley Lake. The O3 and NO concentrations at: both of the other
sites are nearly at background levels despite the continued presence of a
slightly stable lapse rate.
Comparisons of the data for Site 1 at 0930 MST and that for
Site 3 at 1130 show that the total NO within the surface layer has
remained essentially constant over the two hour track of about 16 km
(10 mi). This indicates that there have been few new emissions en route.
In the absence of scavenging by fresh emissions, O3 concentrations have
built up well above background levels, due to continuing photochemical
reaction.
There is little doubt from the evidence presented that the air
over rural Standley Lake at 1130 acquired its ozone precursors earlier
over Denver, even though the ozone itself did not form until after the air
passed site number 1 at 0930 MST. This is a very similar situation
to that observed over and downwind from Los Angeles.
A. more detailed discussion of the aging of the polluted air mass
en route to Standley Lake is given in the paper by Blumenthal et al. included
as Appendix B.
46
-------
IIL OZONE IN RURAL AREAS
Ozone has frequently been observed in rural areas remote from the
nearest urban complex. Several authors, such as Miller, McCutchan
and Milligan(1972), Edinger at al., (1972) and Miller and Ahrens (1970)
have tried, with varying degrees of success, to relate the ozone to some
urban source. Such a relationship is supported by the foregoing demonstration
that ozone and/or its precursors can be transported relatively long
distances. Several cases of rural ozone of apparent urban origin have
also been noted in recent MRI studies. The following sections are devoted
to two of these cases.
The studies discussed here consisted of special aircraft pollution
observations made over remote mountain and desert locations, together
with observations in the Riverside-San Bernardino air basin on two August
days in 1973. Of particular significance were the measurements made
over Lake Arrowhead and Hesperia (Fig. III-l). Lake Arrowhead is a
mountain resort 21 km northeast of San Bernardino at 1560 m (5110 ft)
msl. It is surrounded by national forest for 16 km (10 mi) or more in all
directions and is about 1 km above the valley to the west. There is little
or no industry and little traffic in the area. A single secondary road encircles
the lake and a second road passes the lake about 2 km to the south. Hesperia
is located in the desert about 30 km north of San Bernardino at an elevation
of 1035 m msl on the north slope of the mountain ridge which includes Lake
Arrowhead.
The aircraft sampling spirals on the two days of interest were conducted
over a small airport north of the lake (ARR), at Hesperia (HES), and in the
eastern portion of the LA basin. Winds were observed every two hours at
Strawberry Mountain Lookout southwest of the lake, and the Air Pollution
Research Center of the University of California at Riverside made hourly
observations of wind, temperature, and oxidant at the Skyforest Ranger
Station along the highway south of Lake Arrowhead.
A. August 16, 1973, Arrowhead and Hesperia
August 16, 1973 was a day of moderate smog in the Riverside-
San Bernardino air basin, with ozone values in excess of 30 pphm observed
by aircraft. The day began with surface oxidant concentrations at Skyforest
near background levels (Fig. III-2), indicating an absence of local pollution
sources. Surface winds at both Skyforest and Strawberrry Mountain were
northerly all night, bringing in air from the forest, mountains, and desert
to the north of Lake Arrowhead. Fig. HI-3 shows the morning sounding made
at 0939 PDT over Lake Arrowhead. This sounding shows clean air with nitro-
gen oxides, ozone, and t>scat at or near background.
47
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By the time the afternoon Lake Arrowhead sounding was made
at 1645 PDT, conditions had changed considerably with ozone and bscat show-
ing moderately high values in the lower 300 m (900 ft) for such a remote,
rural area. This sounding is given in Fig. III-4, where two features are
of special interest. First, the increase in ozone and bgcat are confined to
the layer below 1900 m (6300 ft) msl, and second, the ozone and bgcat are
well correlated in this layer while the condensation nuclei count is quite
low. The low ozone level at the top of the sounding (above 6300 ft) suggests
that the ozone did not descend from higher altitudes. Furthermore, the
high correlation between bscat and ozone and the absence of condensation
nuclei within the pollution layer indicate a well-aged polluted air mass,
devoid of fresh emissions. While the aircraft at Lake Arrowhead was measuring
ozone concentrations of 0. 10 - 0. 13 ppm, the Skyforest Ranger Station was
recording a one-hour average oxidant concentration of 0. 40 ppm. The difference
in these concentrations is attributed primarily to the fact that the Ranger Station
was situated just below the crest of the mountains bordering the Riverside-
San Bernardino Air Basin, several miles upwind of Lake Arrowhead airport.
The above observations strongly suggest that the ozone is ground-
based and that the ozone precursors were not of local origin. The surface
winds at Skyforest ranged from 8 to 13 km/hr (5 to 7 mph) and those at
Strawberry Mountain about 11 to 22 km/hr (6 to 12 mph) for the 7-hour period
between the two soundings. Under these conditions, the aged pollution would
have entered the atmosphere somewhere upwind of the forest, which the air
traverses in less than two hours.
A similar sequence of events is shown in Figs. IEI-5 and III-6
which represent soundings made at 0904 PDT and 1656 PDT at Hesperia.
Figure III-5 shows relatively clean air at all levels on the morning sounding
while Fig. III-6 indicates that ozone and b values have increased substantially
in the lowest 460 m (1500 ft) by the late afternoon. Again, the ozone and b
profiles are well correlated while the lack of condensation nuclei indicates
aged pollution.
The streamline pattern for 1600 PDT is shown in Fig. III-7. The
San Bernardino winds aloft in Fig. III-7 show that air over Lake Arrowhead
and Hesperia has a previous trajectory over San Bernardino or Rialto. Fig.
III-7 shows one streamline passing through Cajon Pass (from RIA to HES)
which represents a typical exit route for air leaving the Los Angeles Basin.
The figure also shows clearly the wind flow pattern up the heated slopes east
of Cajon Pass (near SBD and RED) which is characteristic of the mountain slopes
along the north and east portions of the basin during the afternoon. With the
observed wind velocities of 10 to 20 km/hr (see pibal summary, Table III-l), air
51
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GROUND LEVEL
(Elevation 1035 m)
50
NO,
Oi ***
co n»
TKU'CftATVftf *C
NCIATIVK HUMMTT %
I....I IO-V-' «
CN e«r».l04 X
1VMULUCI tlPnttf1 t
Fig. Ill-5. VERTICAL PROFILE OVER HESPERIA
(HES) AUGUST 16, 1973, 0904 PDT
53
-------
2600
I«OO
5
w
§ 1600
5
MOO
1200
•00
too
AGED POLLUTION
GROUND LEVEL
(Elevation 1035 m)
NO,
O,"
A *-
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JJQ MELATIVf HUMOITT %
4 h
CM
ItMULMCI
em-» . 10' X
UI>/>MCJ E
Fig. Ill-6. VERTICAL PROFILE OVER HESPERIA
(HES) AUGUST 16, 1973, 1656 PDT
54
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TABLE III-l
AUGUST 16, 1973 PIBAL DATA
Height WD WS(km/hr)
LAX -
Sfc
1000
2000
3000
4000
6000
7000
8000
1230 PDT
250
220
250
225
290
320
320
0
18
13
7
4
11
15
7
0
SBD - 1320 PDT
2000 230
3000 255
4000 225
5000 200
6000 190
7000 225
8000 220
9000 230
SBD -
Sfc
2000
3000
4000
5000
6000
7000
8000
9000
10,000
1615 PDT
240
210
255
210
180
200
215
220
225
260
13
9
7
9
11
17
22
11
9
18
9
7
17
22
30
24
28
15
Height WD WS(km/hr)
EMT - 1332 PDT
Sfc
1000
2000
3000
4000
5000
6000
7000
8000
9000
10,000
11,000
230
225
290
240
280
315
295
265
245
245
200
215
17
18
9
7
17
15
7
7
9
13
7
15
EMT - 1520 PDT
Sfc
1000
2000
3000
4000
5000
6000
7000
8000
9000
10,000
11,000
12,000
240
240
260
265
285
295
280
240
250
240
205
235
230
17
17
11
9
19
15
9
6
13
11
7
15
22
56
-------
arriving at Arrowhead or Hesperia around 1600 PDT should have
passed over the San Bernardino, Rialto area one to two hours previously.
Figures III-8 and III-9 show vertical soundings made at Rialto
and Redlands at 1337 PDT and 1317 PDT, respectively. The soundings
show a polluted layer of about 760 m depth (2500 ft) at both locations.
High values of both ozone and bscat are observed in the layer which
indicate the generally aged nature of the pollution. Some evidence of
fresh emissions is shown by the moderate level of condensation
nuclei, but there was insufficient NO production locally to reduce the
ozone values substantially.
The foregoing data indicate that the polluted layer observed
near Rialto and Redlands moved upslope to the Lake Arrowhead area
and through Cajon Pass to Hesperia by late afternoon, bscaf and ozone
values are reduced in nearly a proportionate manner during this travel
period due mainly to dilution with cleaner air. At the same time, the
condensation nuclei, in both cases, decreased markedly as the aging
process of coagulation with larger aerosols occurred.
This sequence of events is further supported by surface
oxidant measurements which show a peak value at San Bernardino at
1500 PDT and a peak at Skyforest at 1700 PDT. This difference in peak
times is most readily accounted for by a simple transport of an air
mass containing ozone or precursors from San Bernardino to Skyforest.
The streamline pattern shown in Fig. HI-7 was established
about 1000 PDT and continued through 1900 with little change in
directional characteristics. As indicated in an earlier chapter, the
most probable source of the air contributing to the 1500 PDT peak at
San Bernardino is the central Los Angeles area from which the air
parcels, stagnating in the early morning hours, begin to move at about
1000 PDT along the indicated streamlines into the Rialto-San Bernardino
area.
B. Lake Arrowhead on August 24, 1973
Conditions on August 24 were similar to those on the 16th.
Figure III-10 shows the hourly oxidant concentrations recorded at the
Skyforest Ranger Station. Figures III-11 and III-12 show the morning
sounding in clean air over Lake Arrowhead and an afternoon sounding
with high ozone and bscaj. levels in the lowest 500 m. The surface
winds at Strawberry Mountain, San Bernardino, and Riverside were
southwesterly at 11 to 40 km/hr all day and winds aloft at San
Bernardino and Banning were south to west at almost all levels and
all four observational times (see Table III-2). Surface winds at
Skyforest were not measured.
57
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TABLE, in-2
AUGUST 24, 1973 PIBAL DATA
Height WD WS(km/hr
Height WD WS(km/hr
BAN - 1000 PDT
EMT - 1332 PDT
Sfc
3000
4000
5000
6000
7000
8000
9000
1000
BAN -
Sfc
3000
4000
5000
6000
7000
8000
9000
10,000
LAX -
Sfc
1000
2000
3000
4000
6000
7000
8000
9000
10,000
280
270
250
220
170
180
210
240
250
1200 PDT
280
250
250
210
160
190
200
210
220
1230 PDT
260
250
85
110
75
105
120
235
280
265
22
41
17
15
13
15
26
24
22
24
30
31
28
17
13
20
26
24
17
9
7
7
7
9
7
9
18
13
Sfc
1000
2000
3000
4000
5000
6000
7000
8000
9000
10,000
11,000
SBD -
2000
3000
4000
5000
6000
7000
8000
BAN -
Sfc
3000
4000
5000
6000
7000
8000
9000
10,000
250
235
230
195
115
105
90
110
235
245
245
245
1345 PDT
245
235
230
160
145
155
190
1400 PDT
270
260
270
250
200
240
230
230
220
11
15
7
6
9
17
17
11
9
9
18
9
15
20
7
11
17
24
26
22
39
30
30
33
15
26
32
33
63
-------
TABLE III-2
AUGUST 24, 1973 PIBAL DATA (Continued)
Height WD WD(km/hr
BAN - 1600 PDT
Sfc
3000 250 31
4000 260 46
5000 260 31
6000 260 22
7000 220 9
8000 240 22
9000 230 26
10,000 220 31
64
-------
A similar sounding pattern is shown in Figs. Ill-1 3 and
III-14 •which give morning and afternoon soundings at Hesperia. The
primary difference between the data for August 16 and 24 is the
occurrence of moderate values of condensation nuclei at both Lake
Arrowhead and Hesperia during the late afternoon.
The streamline pattern for 1600 PDT on August 24 is shown
in Fig. Ill-15. The pattern is essentially the same as shown in Fig.
Ill-7 for August 16. Flow through Cajon Pass toward Hesperia and up
the heated slopes toward Lake Arrowhead is clearly indicated. This
pattern was also established by 1000 PDT and continued with little
change until 1900 PDT.
The flow pattern shown in Fig. Ill-15, together with the
observed winds, indicate that the air passing over Arrowhead and
Hesperia had a previous trajectory over the San Bernardino, Rialto,
and Upland (CAB) area about 1-2 hours earlier. Figures III-1 6 and
III-17 show the aircraft soundings made at CAB and Rialto at 1208 and
1321 PDT, respectively. CAB shows a well-mixed layer to 670 m
(2200 ft) above ground level while Rialto shows mixing to 1070 m
(3500 ft) above ground. Subsequent soundings in these areas showed
even larger mixing depths by late afternoon. Both soundings show high
ozone, high bscat, and moderate condensation nuclei characteristics
indicative of aged pollution, but with some fresh emissions.
Comparisons of the ozone and bscat values at Hesperia and
Arrowhead (Figs. Ill-12 to III-14) with the earlier soundings at Upland
and Rialto (Figs. III-16, III-17) indicate slightly reduced values at
Hesperia and Arrowhead. Again, the ozone and bscat values tend to be
proportionately similar, although some reduction in ozone values at
Arrowhead appears to have occurred (Fig. Ill-1 2) relative to the bscaj.
values. It is suggested that the primary changes in ozone and bscat
values occurred as a result of dilution with cleaner air.
The trajectory of the polluted air from near Rialto to
Arrowhead is further supported by peak times of surface oxidant values.
On August 24, peak concentrations occurred at 1600 PDT at San
Bernardino and at 1800 PDT at Skyforest. The relatively late time of
the peak occurrence at Skyforest argues rather strongly against any
local generation of the oxidant.
As discussed earlier, the trajectories of the air at Upland
and Rialto can be traced back to the central Los Angeles area along the
streamlines shown in Fig. Ill- 15. Air parcels arriving at the peak
oxidant period in the San Bernardino area are likely to have originated
65
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AUGUST 24, 1973, 0831 PDT
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(HES) AUGUST 24, 1973, 1546 PDT
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in the western Los Angeles basin during the stagnant period prior to
onset of the flow pattern shown in Fig. II- 15.
Data from both August 16 and 24 suggest strongly that ozone
or precursors originating in the metropolitan area moved eastward
through the Los Angeles Basin, through Cajon Pass, and up the mountain
slopes. Evidence is shown of the arrival of these air parcels at Arrow-
head and Hesperia (about 90-100 km downwind of the central Los Angeles
area).
71
-------
IV. OZONE ALOFT - MECHANISMS AND PERSISTENCE
Previous chapters have shown the feasibility of the export of large
quantities of ozone from urban areas and the transport, in a single day,
of ozone to rural areas. This chapter shows that, in the absence of
scavenging substances, ozone is stable for long periods of time and
that multiday transport is possible. One method of isolating ozone
from fresh emissions or other scavengers is to confine it to a layer
aloft. There has recently been much discussion of the source of ozone
in layers aloft, and this chapter also presents several examples of
normal meteorological mechanisms for transporting ozone and other
pollutants from the surface to elevated layers.
A. Mechanisms for Trapping Pollutants in Layers Aloft
Numerous mechanisms exist for creating well-defined layers
aloft that contain air which was previously in contact with the surface.
The examples presented here are divided into two categories: (1)
creation of layers by undercutting of air that was previously within the
surface mixing layer and (2) creation of layers by buoyant lifting or
transport of air from the surface.
Examples of undercutting include the isolation of air aloft by
the formation of a radiation inversion below and the undercutting or
lifting of one air mass by another. Figure IV-1 is a repeat of a vertical
profile over El Monte, California on July 25, 1973 (previously Fig. II-8).
In this figure, the sea breeze extends from the surface to about 450 m
and has undercut the air mass above. The air between 450 m and about
700 m msl was previously part of the surface mixing layer, but was isolated
from the surface by the onset of the cooler marine air below. On a much
larger scale, frontal systems act much like the sea breeze in Fig. IV-1
with one air mass lifting or undercutting another. The sea breeze in
effect is a miniature cold front.
Figure IV-2 is an early morning vertical profile over
Brackett Airport on July 26, 1973, one day after the profile in Fig. IV-1.
Several distinct layers are seen in this figure. The layers between 450
m msl and the top of the graph exist in a very stable atmosphere. These
layers have been isolated from the surface (and from surface emissions)
by the nocturnal radiation inversion, and the ozone aloft has probably
remained from the previous day. The ozone below 450 m msl, however,
has been depleted by fresh emissions into the surface layer.
The layer roughly between 520 and 730 m msl is an example
of a pollutant layer aloft created by buoyant lifting from the surface.
The situation in this case is quite complicated. This layer was just
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described as being isolated from the surface. Actually, the high b
s cat
and other pollutant readings are due to a point source plume with enough
buoyancy to penetrate the radiation inversion. Since the atmosphere
is stable, the plume has reached an equilibrium height where it is no
longer buoyant and has stabilized to form a layer. The buoyant plume
was able to penetrate the inversion, but other emissions at ground level
were prevented by the inversion from mixing higher than about 450 m
msl. Note that the ozone was also somewhat depleted by NO emissions
in the plume. In the presence of strong sunlight however, it is probably
possible under some circumstances to produce ozone photochemically
in an elevated point source plume.
Other examples of buoyancy mechanisms which can generate
layers aloft are: urban heat islands which cause urban air to be warmer
(more buoyant) than surrounding air and can generate elevated urban
plumes under certain conditions, convective cells which occur over
heated terrain and lift air from the surface, and heated mountain slopes
which can cause localized heating and upslope flow. Figure IV-3 is a
profile at Rialto, California, near the San Gabriel Mountains. Two layers
are evident in the figure separated by a layer of relatively clear air.
The surface mixing layer is capped by a slight inversion topping at
about 1050 m msl; however, air near the mountains is heated by contact
with the slopes and flows upslope to an altitude at which it is at equil-
ibrium, forming a second layer.
B. Overnight Persistence of Ozone
The ability of ozone to survive in the absence of sunlight can
be demonstrated by observation of the vertical distribution of O, at
various times through the night in a layer separated from surface
sources by a stable layer. The data for such a demonstration has been
provided by a 24-hour study of pollutants over the San Bernardino-
Riverside air basin east of Los Angeles on July 26 and 27, 1973. As
part of an observational program, aircraft soundings were made over
six locations at about 1700 and 2300 PDT on July 26 and about 0200 and
0500 PDT on July 27.
The names and three letter identifiers of the six sampling
locations are listed in Table IV-1. Their locations can be found in any
of the several foregoing figures showing maps of Los Angeles and
vicinity. The results of the overnight observation of O_ are also
summarized in Table IV-1. Ozone data were studied for an elevated
layer free of surface influences. The layer between 1000 and 1500 m
(3000 to 4500 ft) msl was selected so that all soundings would be
continuous to the top of the layer, and the bottom of the layer would be
above the surface inversion on all 24 soundings. Averages of observed
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Table IV-1
Overnight Ozone Concentrations
Times PDT
Location
Ontario
(ONT)
Rialto
(RIA)
Redlands
(RED)
Riverside
(RAL)
Corona
(COR)
Bracket
(BRA)
July 26
17 PDT
20.4
16.8
10.4
12.3 '
9.7
20.7
/ A\
{"4)
July 26
23 PDT
July 27
2 PDT
July 27
5 PDT
13-4
4.8
n si
(1'5)
11.0
o.i
10'6
0.2
{4 5)
( ' '
0.1
Average
The upper left hand number in each set is the average Oj concentration (pphxn)
between 1000 m and 1500 m. The lower left hand number is the average Oj
concentration (pphm) in the first 200 m above ground. The number in parentheses
is the temperature °C at 1000 m minus the average temperature in the first 200 m
above ground.
77
-------
ozone were calculated for both this layer and for first the 200 m above
the surface for all soundings. The upper number in each group of
three in Table IV-1 is the mean O,, concentration for the elevated layer
while the lower number is for the surface 200 m thick layer. The
number in paretheses in each group is an indicator of stability of the
layer below about 1000 m (3000 ft) msl. The number is the difference
in temperature in degrees centigrade between the 1000 m msl temperature
and the average temperature in the first 200 m above the ground.
There are many reactions known which can consume 03 in
the lower atmosphere. By far the fastest of these is the following:
NO + O3 —> NO2 + O2.
The rate constant for this reaction is about 0. 3 pphm"^ min~*
(Johnston and Crosby, 1954), which means that, at a constant NO
concentration of 1 pphm, the half-life of 03 for this reaction is less
than 3 minutes. In the absence of the solar radiation necessary to
produce 03, NO from the fresh exhaust of combustion sources therefore
quickly scavenges 03 . This is seen in Table IV-1 where 03 concen-
trations near the ground fall below the 4 pphm background value during
the night due to the continuous introduction of fresh emissions into the
surface layer.
As the temperature differentials in Table IV-1 indicate, air
above about 1000 m is isolated from the surface layer throughout the
night by a strong ground based temperature inversion that is established
at all locations between 1700 and 2300 PST. Cut off from sources of NO,
03 at the upper levels appears to be quite stable, as shown by concen-
trations of 12-13 pphm - well above background - that persist through
the night. In all 24 soundings studied, 03 and bscat were well correlated
between 1000 and 1500 m, and condensation nuclei (CN) counts at these
levels were low. These conditions are typical of well-aged polluted air.
Examples of the soundings from one location, Riverside, are
given in Fig. IV-4 to IV-7. The high ozone levels existing throughout
the night above the surface mixing layer are evident in these figures.
From these figures and Table IV-1 one can see that the ozone aloft is
quite stable and that the concentrations do not decrease significantly
throughout the night, indicating a half-life for ozone in the atmosphere
of something greater than 12 hours.
Thus, the data show that ozone, once formed and in the
absence of other pollutants to scavenge it, is stable in the atmosphere
at high concentrations for many hours, even in the absence of sunlight.
78
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C. Ozone Persistence in Rain
Figures IV-8 and IV-9 show profiles made over Shepherd
Airport (SHE) in the Los Angeles area. These traverses were made
on a fairly clear, rainy day during which photochemical processes
should have been minimal. In the absence of photochemistry, the ozone
is destroyed by the primary pollutants and the depth to which the polluted
air has mixed during the day is indicated by the depth of the ozone deficit.
The morning sounding indicates a mixing depth of about 300 m msl while,
by afternoon, the fresh pollutants had mixed up to 1000 m. Note that in
Fig. IV-8 in the quite clean air at 1600 m, the ozone level is between 0.03
and 0. 04 ppm (approximately background level) even in the rain.
Even though ozone is quite reactive, the above data show
that, in the absence of other reactants, it is stable and will remain in
the atmosphere a long time. This would be in agreement with Junge
(1963) who has mentioned that the residence time of ozone in the tropo-
sphere should be on the order of one to two months.
83
-------
two
t«OO
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1200
1000
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Ground Elevation
66 m
MIXED LAYER WITH OZONE
DEFICIT DUE TO FRESH
EMISSIONS
MI1Q f
4 h
10
j RfL4Tivi HUWMTT %
b...t PO-Sr'
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C
T
N
B
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I
Fig. IV-8. VERTICAL PROFILE OVER SHEPHERD
(SHE) IN THE RAIN, OCTOBER 18, 1972,
1020 PDT
84
-------
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Fig. IV-9. VERTICAL PROFILE OVER SHEPHERD
(SHE) IN THE RAIN, OCTOBER 18, 1972,
1357 PDT
85
-------
V. ESTIMATES OF POTENTIAL DOWNWIND EFFECTS
The Los Angeles Air Basin is a natural area in which to study the
formation and meso-scale transport of ozone, because of the frequency of
occurrence of high ozone concentrations and their extensive documentation.
The complicated topography surrounding the basin makes it less than ideal,
however, for the study of long-range transport. For this purpose it is
instructive to employ standard diffusion estimates to calculate the effects
that an ozone source the size of the Los Angeles urban region could have
downwind in flat terrain. This chapter presents the results of such an
exercise.
The calculations were based on a number of simplifying but con-
servative assumptions. These are listed below.
1. Ozone concentrations can be maintained for extended periods
in the absence of scavengers such as NO. On the basis of
elevated layer observations in the Los Angeles area, a life-
time of at least 12 hours is indicated.
2. The polluted layer increases in depth by a factor of two during
the 12-hour period. This factor was put in to be conservative.
Typical mixing layers tend to be less than 1200 m deep.
3. The urban plume continues to diffuse according to standard
diffusion laws with no effects of terrain.
4. No new emissions are injected into the urban plume, and no
new ozone is produced by photochemical reaction.
The urban plume was assumed gaussian, and August 16, 1973 was
selected as a representative day for the purpose of establishing the plume
parameters. Figure V-l shows the afternoon aircraft sounding for
Redlands on this day, taken at 1700 PDT. An average ozone level of about
0. 35 ppm is indicated for the layer from the surface to a height of 640 m
(2100 ft) above ground. Surfa.ce oxidant values indicate that the crosswind
width of the Los Angeles Metropolitan Area urban plume extended at least
from San Bernardino past Riverside (approximately 24 km or 15 miles).
Accordingly, a peak ozone concentration of 0. 35 ppm (0. 31 ppm above
background levels) and a width of 24 km ( a = 5.6 km) were taken as the
initial conditions of the plume.
For the purposes of estimating downwind concentrations, it is
appropriate to assume a C stability category (Turner, 1969). The wind
speed was assumed constant at 5 m/s. Under these conditions, a o-
86
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(crosswind) value of 5. 6 km would occur at a distance of 95 km downwind
of an effective point source. At a distance of 200 km from. Redlands (295
km from the hypothetical source), the
-------
VI. CONCLUSIONS
1. Analyses of observational data on two days in the Los Angeles
Basin indicate that ozone and/or its precursors were transported
from the metropolitan area approximately 100 km downwind to the
eastern portion of the Basin. The data indicate that most of the
ozone and other pollutant burdens (above background level) at the
downwind locations in the afternoon were due to precursors
emitted earlier in the day or even during the previous night in
the western basin upwind. The meteorology of the basin is
such that pollutants which accumulate during the night and morning
hours over the western basin are transported eastward in a
daily pulsing fashion. The contribution to the ozone burden in
the eastern basin due to the western basin appears to be sufficient
to cause the ambient air standard (0.08 ppm) to be exceeded even
in the absence of any local contributions.
2. Observations of ozone in layers aloft both at night and in the rain
indicate that ozone is stable in the absence of other substances to
scavenge it. Ozone has been observed to remain undiminished at
high concentrations in layers aloft out of contact with the ground
for periods in excess of 12 hours, indicating a lifetime in the
atmosphere of considerably greater than 12 hours.
3. Ozone has been observed in rural areas at concentrations as high
as 0.3 ppm with no possible local source. Wind trajectories,
vertical profiles of pollutants, and surface pollutant data all
indicate the source of the ozone precursors to be urban areas, in
some cases as far away as 100 km.
4. Using data from a single (but typical) day in the Los Angeles air
basin, extrapolating to flat terrain and using standard diffusion
techniques, it has been shown that a source area like the central
Los Angeles area could cause ozone concentrations to exceed the
Federal standard of 0.08 ppm at locations as far away as 260 km.
This estimate is believed to be conservative.
5. From the data presented, it is believed that urban sources can
have a substantial effect on ozone concentrations in downwind
areas and that this effect can carry over more than one day.
89
-------
VII. REFERENCES
Blumenthal, D. L. , et aL , 1974; Three-dimensional pollutant gradient
study - 1972-1973 program. Final Report MRI 74 FR-1262 submitted
to California Air Resources Board,,
Blumenthal, D. L. , J. A. Anderson, and G. J. Sem, 1974: Characteri-
zation of Denver's Urban Plume Using an Instrumented Aircraft,,
Paper MRI 74 Pa-1173 presented to the 67th Annual Meeting of the
Air Pollution Control Association, Denver, June 9-13.
Blumenthal, D. L. , et aL , 1973: Three-dimensional pollutant gradient
study - 1972 program. Interim Report MRI 73 FR-1083 submitted
to California Air Resources Board.
California Air Resources Board, 1972: State of California Implementation
Plan for Achieving the Maintaining the National Ambient Air Quality
Standards.
Edinger, J. G. , M. H. McCutchan, et al. , J. V. Behar (1972):
Penetration and Duration of Oxidant Air Pollution in the South
Coast Air Basin of California, Journal of the Air Pollution
Control Association, Vol. 22, No. 11.
Johnston, H, S. , and H. J. Crosby (1954): J. Chem. Phys. , 22_t
689.
Junge, C. E. , 1963: Air Chemistry and Radioactivity. Intern.
Geophys. Ser. , Vol. 4, New York, Academic Press, 49-58.
Kelly, J. J. , 1970: Atmospheric ozone investigation at Barrow,
Alaska, during 1966-1967. Rept. No. 2, Dept. of Atmos. Sci. ,
University of Washington, Sci. Rept. to Office of Naval Research,
NR 307-252.
Miller, P. R. , M. H. McCutchan, and H. P. Milligan (1972): Oxidant
air pollution in the central valley, Sierra Nevada Foothills, and
Mineral King Valley of California. Atmospheric Environment
Pergamon Press, _6, 623-633.
Miller, A., and D. Ahrens (1970): Ozone within and below the west
coast temperature inversion. Tellus XXII, 3.
Ripperton, L. A., and J. B. Tommerdahl, and J. B. B. Worth,
1974: Airborne ozone measurement study. Presented to the
67th APCA annual meeting, Denver, June 9-13, 1974.
90
-------
REFERENCES (Continued)
Roth, P. M. , et al. , 1974: Mathematical modeling of photochemical
air pollution--II. A model and inventory of pollutant emissions.
Atmos. Environ., jj, 97-130.
Smith, T. B., D. L. Blumenthal, J. R. Stinson, and V. A. Mirabella,
1972: Climatological wind survey for aerosol characterization
program. Final Report No. MRI 72 FR-1000 prepared for North
American Rockwell Science Center, Thousand Oaks, California.
P. O. 262-1366.
Turner, D. B. , 1969: Workbook of Atmospheric Dispersion Estimates,
U. S. Department of Health, Education, and Welfare, Public
Health Service, Consumer Protection and Environmental Health
Service. PHS Publ. No. 999-AP-26, 84pp.
Vaughan, Leland M. , and Alexander R. Stankunas, 1974: Field study
of air pollution transport in the south coast air basin. Technical
Report No. 197. Final Report prepared for State of California
Air Resources Board by Metronics Associates, Inc. Contract
No. ARE-658.
Vaughan, Leland M. , and Alexander R. Stankunas, 1973: Field study of
air pollution transport in the south coast air basin0 Technical
Report No, 1860 Prepared for the State of California Air Resources
Board by Metronics Associates, Inc. Contract Nos. ARB-658 and
ARB-2-349.
91
-------
VIII. ACKNOWLEDGMENTS
The primary data used in this study were obtained in experimental
programs performed by MRI and funded by the California Air Resources
Board (ARE) and by the Environmental Protection Agency (EPA). The
authors would like to thank the ARB for their interest in and
cooperation with this EPA-funded study and to compliment both
agencies on the degree of interagency cooperation shown throughout
the project.
We would also like to thank Metronics Inc. for their cooperation
in providing much of the upper air wind data used in the analysis.
Other sources of data were: Loren Crow, consultant; the National
Weather Service; the U.S. Forest Service; McDonnell Douglas Aircraft
Co.; and the Los Angeles, Orange, San Bernardino, and Riverside
County Air Pollution Control Districts.
This report would not have been possible without the many hours
of effort put forth by the staff of MRI in collecting and analyzing data
and in helping prepare the report. The authors greatly appreciate this
effort.
-------
APPENDIX A
DATA FROM JULY 25, 1973
AND SEPTEMBER 21, 1972
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APPENDIX B
CHARACTERIZATION OF DENVER'S URBAN PLUME
USING AN INSTRUMENTED AIRCRAFT
-------
Characterization of Denver's Urban
Plume Using an Instrumented
Aircraft
by
D. L. Bluraenthal and J. A. Anderson
Meteorology Research, Inc.
Altadena, California
and
G. J. Sem
Thermo-Systems, Inc.
St. Paul, Minnesota
Paper No. 74-266
For presentation to the 67th Annual Meeting of the Air Pollution Control
Association, Denver Convention Center, Denver, Colorado, June
9-13, 1974.
MRI 74 Pa-1173
-------
Abstract
Paper No. 74-266
As part of an EPA coordinated air pollution study, an extensive
three-dimensional air pollution mapping program was carried out in
the Denver area during a 10-day period in mid-November, 1973.
An aircraft instrumented to continuously measure scattering coefficient,
condensation nuclei, O3 , NO x , CO, SO3, and flight parameters was
used in the study. The aircraft was also equipped •with instrumentation
to measure the size distribution of grab samples.
The sampling pattern was designed to study the characteristics
of the fresh pollutants in the morning drainage wind and those of aged
pollutants in the plume later in the day. The urban plume was sampled
during inversion conditions when it was trapped in a shallow mixing
layer and also during periods of good mixing and ventilation.
The plume was found to be well defined and well mixed. High
pollutant concentrations were observed aloft in power plant plumes
which were subsequently ventilated to the ground as the mixing layer
deepened. Photochemical processes were found to be important,
and the ozone level in the plume was found to vary from 0. 00 to 0. 08 ppm.
The background level outside the plume was always measured at between
0. 03 and 0. 05 ppm. The aerosol size distribution was also found to
change character as the plume aged.
-------
Introduction
Airborne measurements of gaseous and particulate pollutants as
well as meteorological parameters affecting the pollutants -were made with
MRI's Cessna 205. The aircraft was flown during a ten-day portion of
a major field experiment sponsored by the Environmental Protection
Agency and undertaken in the Denver area during November 1973.
Although a number of different agencies participated in the experiments,
the purpose of this paper is to present selected airborne measurements
and discuss these data in terms of their contribution to the understanding
of urban plume produced by Denver, Colorado.
A major emphasis of the experiment was to study the physical and
chemical characteristics of Denver's urban plume and the transport
processes that affect the plume. In particular, the choice of both the
airborne sampling paths and ground site locations were made to best
study the aging processes that take place in the plume.
Previously, Riehl and Herkhof1'2, Crow3, and Riehl and Crow4
have reported meteorological factors that affect air quality in the Denver
area. We are unaware of any previous airborne measurements made on
the Denver plume. Similar work, however, has been done in other areas
such as St. Louis5'6'7.
Description of the Program
The MRI aircraft as described by Blumenthal and Ensor8 has been
used extensively to measure the three-dimensional distribution of air
pollutants. The sampling instrumentation used in the aircraft for the
Denver study included fast time response monitors for O3, NOX, SO2,
CO, condensation nuclei, scattering coefficient, temperature, relative
humidity, turbulence, altitude, and position. In addition, measurements
of the size distribution of grab samples were made by installing a TSI
Model 3030 electrical aerosol size analyzer in the plane. Liu et al.
-------
have described the use of such an instrument for the measurement of
submicron aerosol size distributions. The size distributions were
obtained in the aircraft by rapidly filling a large plastic bag (about
60 liters) to obtain the grab sample and then immediately analyzing
the aerosol in the bag with the size analyzer.
Blumenthal ° has described considerations for plume sampling as
being dependent on the specific objectives of the particular study. One
of the dominant meteorological factors in the Denver area is the drainage
flow that normally exists during the morning hours. This flow carries
the urban pollutant discharge northeast along the Platte river valley.
Thus to optimize sampling, horizontal traverses and spirals were made
at the points shown on Figure 1. Traverses at various altitudes were
made along the routes marked I, II, or III and spirals were made at
Standley Lake, Henderson, and near the EPA trailer location. Both the
Henderson and EPA spiral locations were chosen because of ground
measurements being made at these points and their close proximity to the
expected plume centerline. The Standley Lake spiral was normally made
to obtain useful background data, Unfortunately, sampling path II had
to be terminated at Interstate SOS since flights over the Rocky Mountain
Arsenal were prohibited.
Upper level -wind data were obtained at both Arvada and the EPA
trailer using pilot balloons (pibals). These data, as well as summaries
of surface wind data, have been used in this paper and are based on
information collected during the study and reported by Crow11. Other data
used in this paper, including portions of the gas and bscat data that were
obtained at the EPA trailer and reported by Durham, et al1 3, were
also used to support the conclusions arrived at in this paper.
-------
Experimental Results
Aircraft sampling was performed a total of six days in November
1973. Data from two of these days are presented here to illustrate
various urban plume phenomena.
November 20 - Urban Plume Structure
November 20 represents an excellent reference point to begin an
air pollution episode. A snowstorm invaded the Denver area in the after-
noon of the 19th and lasted until the early morning hours of the 20th.
Surface winds for the 20th were generally from the south throughout the
day, and thus the plume consisted of fresh pollutants which aged as they
traveled northward. The freshly cleaned air mass outside the plume and
the relatively constant net flow produced an almost ideal sampling
situation and a plume with a fairly simple structure. Figure 2 indicates
the streamlines at 11:00 a.m. as well as an outline of the urban plume
as determined by horizontal traverses and photographs.
Figure 3 shows a cross section of the plume obtained at 6200 ft msl
along sampling route II (see Figure 1 ) from Highway 287 to Highway 805
at about 10:00 a.m. A distinct increase inNOx, CO, and scattering
coefficient at approximately the 1. 5 mile point indicates the western edge
of the urban plume. A further increase in NO x , SO2, and scattering
coefficient and a slight decrease in ozone at the 4. 5 mile point probably
indicate penetration of the bottom edge of the Cherokee power plant plume.
The decrease on O3 is due to scavenging of ozone by freshly emitted NO.
Figure 4 is a vertical profile taken near the EPA trailer at 10:55,
an hour after the cross section in Figure 3. The temperature profile
indicates a slightly stable lapse rate with a weak inversion starting at
6400 ft msl (about 1200 ft above ground). Up to about 5800 ft msl, the
-------
various pollutants are well mixed and occur in about the same concentra-
tions as were seen throughout the urban plume cross section shown in
Figure 2. Between 5900 ft and 6600 ft msl, however, the power plant
plume is superimposed on the urban plume in a distinct, well defined
layer, the power plant plume being confined by the weak inversion layer.
Characteristics of the power plant plume include high levels of
primary pollutants such as NOX, SOS, and participates and a very low
level of ozone due to scavenging by NO. This type of layer aloft contain-
ing high concentrations of pollutants (in this case NO x > 0. 5 ppm) can
persist for long periods of time and can be transported many miles
before being ventilated to the ground when finally entrained by a deepen-
ing mixing layer.
Above the inversion at about 6700 ft msl, the pollutant levels drop
off to virtually clean air values. Note however that the ozone level is
approximately 0. 04 ppm. This level has been observed in many areas
of North America in very clean air and often represents the ozone
1 3
background level . In the urban plume below the power plant plume, the
ozone level is considerably higher than the background level indicating
photochemical production of ozone.
Figure 5 is a vertical profile taken in the urban plume at Henderson
shortly before the one in Figure 4. Since the power plant plume seen in
Figure 4 was not directly over Henderson at this time, no indication of
it is seen in the profile. The temperature profile at Henderson indicates
a slightly stable lapse rate with a weak inversion beginning at 6200 ft msl,
about 200 ft lower than the one at the EPA trailer. The higher inversion
level at the EPA trailer may be an indication of the urban heat island effect.
The pollutant levels measured in the urban plume at Henderson are
similar to those presented earlier and indicate a plume which is well
mixed both horizontally and vertically. The plume at Henderson is fairly
-------
uniform in concentration up to a level of about 5900 ft where mixing is
impeded and concentrations start to drop off, reaching clean air values
near 6400 ft.
Figure 6 is a vertical profile of the urban plume over the EPA
trailer at about 2:00 p.m. The wind is still from the south. Due to
surface heating, the mixing layer has deepened, yet pollutants are still
confined to a layer about 2000 ft thick. The power plant plume is no
longer well defined on this or other afternoon traverses and has evidently
been entrained in the surface mixing layer. Integration throughout the
mixing layer shows that the total pollutant budget is clearly higher than
during the morning flight reflecting the entrainment of the power plant
plume and the overall accumulation of pollutants during the day. It is
interesting to note that photochemical processes are active, even at
temperatures of 0°C and that the ozone level in the mixing layer is
approximately equal to the ambient air standard of 0.08 ppm.
The data from November 20 verify several statements made by
Riehl and Herkhof 2. In a discussion of turbulent transport, they surmise
that "during daytime, the polluted layer must extend well above 100 m
with characteristics almost those of a mixed layer. " Figures 4,5, and
6 indicate that,at least on November 20, the polluted layer was well mixed
during the day and extended up to about 900 ft (or 300 m) in the morning and
to 2000 ft (or 650 m) by midafternoon. Similar characteristics were also
observed on other days. In addition, they conclude that "non-persistence
of a temperature inversion through the noon hours is not a good guide for
current and subsequent air pollution levels. " Figures 5 and 6 indicate
the problem associated with using the inversion level to predict the depth
of the mixed layer and thus to some extent the surface concentrations.
Using the inversion level in Figure 5 as a guide to mixing depth would
lead to an assumed mixing layer height of 6200 to 6400 ft msl or 1000 to
-------
1200 ft above ground level. Using the actual pollutant concentrations as
an indicator of mixing layer height leads to an actual mixing depth of only
600 to 800 ft. In Figure 6, no significant inversion is indicated, yet the
pollutants are reasonably well confined to a layer about 2000 ft deep.
November 21 - Pollutant Characteristics in the
Urban Plume
November 21 represents the second day of an episode which
began during the morning hours of November 20. During the late
afternoon and evening of November 20, winds were light and variable
and a strong radiation inversion developed. Thus, pollutant levels
increased over the city. The morning of November 21 was clear
with light surface winds from the south producing streamlines
similar to those shown in Figure 2. By late morning, the wind
field had started to shift to an easterly flow, and shortly after noon
the wind speed increased abruptly to a strong flow from the east,
moving the pollutants up against the foothills to the west of Denver.
Figure 7 is a vertical profile taken at 0925 MST near the
EPA trailer site, and Figure 8 is another profile taken at the same
location at 1242 MST. Figure 7 shows a dense polluted urban plume
trapped beneath a strong radiation inversion with clean air above
the mixing layer. At this time, photochemical production of ozone
within the mixing layer had not yet exceeded the scavenging of ozone
by freshly emitted NO or by NO which had accumulated overnight.
The ozone level in the mixing layer was thus depressed from the
clean air level above.
Figures 9 and 10 illustrate in more detail the character of
the urban plume during the morning. The figures show aerosol size
distributions obtained at the low point of the spirals shown in Figures
7 and 8, respectively. Both surface and volume distributions are
plotted.
-------
Whitby and his associates14*1 have shown that combustion sources
generate fresh aerosol in the size range under 0. 1 |jm diameter. However,
as the aerosol ages and photochemical generation of new aerosol material
occurs, the size distribution will shift, and the aerosol will coagulate
and accumulate in the 0. 1-1 (am diameter size range. This process is
accelerated if the fresh combustion aerosol is emitted into a background
of aged polluted air already containing large amounts of particulates in
the 0.1-lM-m size range.
The surface distribution shown in Figure 9 includes both a
large peak at 0.4|j.m diameter (called the "accumulation mode" by Whitby)
and a smaller inflection in the distribution at 0. 04^m diameter. This
indicates that the morning urban plume at this location consists of a
mixture of well-aged pollutants accumulated over night plus freshly
emitted effluents.
By the time the 1242 MST sounding (Figure 8) near the EPA
trailer was made, the wind shift mentioned earlier had occurred.
Cleaner, rural air had replaced the urban plume existing at this loca-
tion earlier in the day (0925 MST, see Figure 7). In Figure 8, the ozone
level is at a clean air value, other pollutant levels are quite low, and
the temperature inversion has disappeared. The surface area distri-
bution shown in Figure 10 indicates a small amount of fresh combustion
aerosol from an unidentified source nearby, but no large "accumulation"
mode is present.
Figure 11 is a profile taken over Standley Lake at 1134. This
profile shows the change in character of the urban plume as it ages.
The air in the mixing layer had probably traveled north from Denver
and then moved westward with the wind shift. It had thus had a chance
to age for a few hours since passing over a concentrated source
area. The profile was taken before the abrupt increase in wind speed
and an inversion layer is still present. The mixing layer has deepened
since the morning sounding due to surface heating, but the plume is
still confined within a layer about 1000 feet deep.
7
-------
Primary pollutants such as CO, SO2, and NO x have remained at
relatively high values; but ozone, a secondary pollutant, has now increased
above the clean air value, equaling the Federal ambient air standard of
0.08 ppm in places. Figure 12 is a size distribution obtained at the
bottom of the spiral shown in Figure 11. A well-developed "accumu-
lation" mode is seen with little evidence of fresh combution aerosol.
Thus, as the urban plume ages in the absence of fresh emissions
and in the presence of sunlight, the aerosol size distribution shifts to
the "accumulation" mode, the rate of production of ozone surpasses the
rate of scavenging, and the ozone level increases. Although it was not
measured independently by the aircraft, the EPA van data show that, as
the plume ages, the NO x shifts from being mostly NO to mostly NO2.
This is consistent with the increase in the ozone level.
Riehl and Herkhof~ in their studies had assumed that aerosol
mass was a good indicator of the source strength of the city and that
it was a. conservative quantity. It is evident from our results that
photochemical processes occur in the Denver area, and that the size
distribution in the plume changes with time. One must use caution
when assuming that aerosol mass or other aerosol parameters are
conservative quantities since photochemical production of aerosol is
a definite possibility.
Conclusions
1. Under the conditions measured, Denver was shown to have a
well-developed and well-mixed urban plume which varied in
thickness from 500 to 2000 feet depending on the stability and
the amount of surface heating. The temperature lapse rate,
however, was not always a good indicator of mixing depth.
2. Large buoyant stationary source plumes generate layers aloft
which are ventilated to the surface when the mixing layer deepens.
-------
These plumes are characterized by high levels of primary
pollutants and a deficit of ozone relative to the surrounding
air.
3. The chemical and physical characteristics of the urban plume
constituents change as the plume ages. In the presence of NO
sources and in the absence of photochemistry, ozone is scavenged;
but when sunlight is present^ photochemistry is important, and
ozone levels in the urban plume can reach or exceed the Federal
ambient air standards. Photochemical production of aerosol
may also occur in the plume.
4. The aerosol size distribution changes shape as the plume ages,
and the submicron aerosol accumulates in the 0. 1 to 1 |j.m diameter
size range.
5. The ozone level in clean air outside the urban plume was measured
at 0. 03 to 0. 05 ppm on all flights, while the level in the plume
varied from 0. 00 to 0. 08 ppm depending on the level of photochemical
activity and the amount of scavenging by other pollutants.
Acknowledgments
This research was funded by the Environmental Protection Agency,
and was performed in cooperation with Dr. Jack Durham and Dr. William
Wilson of EPA. Some of the instrumentation used on board the air-
craft was kindly made available to the project by the California Air
Resources Board.
-------
References
1. H. Riehl and D. Herkhof, "Weather Factors in Denver Air Pollution,"
An abridged version of the final report to the U. S. Dept. of Health
Education and Welfare, Dept. of Atmospheric Science, Colorado State
Univ., ASPflSS, 1970.
2. H. Riehl and D. Herkhof, "Some aspects of Denver air pollution
meteorology," J. Appl. Meteor., 11, 1040(1972).
3. L. W. Crow, "Air Pollution in the Denver Area, " Public Service
Company of Colorado, 1967. (Pamphlet)
4. H. Riehl and L. W. Crow, "A Study of Denver Air Pollution, "
Atmospheric Science Technical Report No. 33, Colorado State
Univ., 1962.
5. R. B. Husar, D. L. Blumenthal, J. A. Anderson, and W. E. Wilson,
"The Urban Plume of St. Louis, " presented at the 166th National
Meeting of the American Chemical Society, Los Angeles, California
(April, 1974).
6. J. F. Stampfer and J. A. Anderson, "Locating and some of the charac-
teristics of the St. Louis urban plume at 80 and 120 km, " submitted
to J. Atmos. Environ.
7. Fate of Atmospheric Pollutants Study, NCAR, personal comments.
8. D. L. Blumenthal and D. S. Ensor, "The Use of Light Aircraft
to Measure the Three-Dimensional Distribution of Air Pollutant, "
presented at 1972 Annual Meeting of the Air Pollution Control
Association, Pacific Northwest International Section, Eugene,
Oregon (November 1972).
9. B. Y. H. Liu, K. T. Wbitby, and D. Y. H. Pui, " Portable
Electrical Aerosol Analyzer for Size Distribution Measurement
of Subrnicron Aerosols, " Paper No. 73-283 presented at the
66th Annual Meeting of the Air Pollution Control Association,
Chicago, Illinois (June 1973).
10. D. L. Blumenthal, "Measurement of Physical and Chemical Plume
Parameters Using an Airborne Monitoring System," Paper No.
73 AP16 presented at the 1973 Annual Meeting of the Air Pollution
Control Association, Pacific Northwest International Section,
Seattle, Washington (November 1973).
10
-------
11. L. W. Crow, "Airflow Study Related to EPA Field Monitoring
Program Denver Metropolitan Area November, 1973," Report
LWC #128 prepared for Chemistry and Physics Laboratory,
Environmental Protection Agency, February 1, 1974.
12. J. Durham, T. Ellestad, and R. Patterson, Denver 1973 EPA
Mobile Lab Data, final distribution of the AARS mobile lab's
meteorological, gas, and bgca^. data, February 1, 1974,
13. This topic is discussed in a report being prepared by Blumenthal,
et al., Meteorology Research, Inc., for the California Air
Resources Board, to be released in the summer of 1974. A
report on ozone background levels is also presently in prepara-
tion by R. Rassmussen of Washington State University for the
National Academy of Sciences.
14. K. T. Whitby, R. B. Husar, and B. Y. H. Liu, "The aerosol
size distribution of Los Angeles smog," J. of Colloid and Interface
Science, 39, 211 (1972).
15. K. T. Whitby and R. B. Husar, "Growth mechanisms and size
spectra of photochemical aerosols, " Environ. Sci. and Technol.,
7, 3, 241 (1973).
11
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18
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-450/3-74-06
3. RECIPIENT'S ACCESSION-NO.
4 TITLE AND SUBTITLE
Determination of the Feasibility of the Long-Range
Transport of Ozone or Ozone Precursors
5. REPORT DATE
November 1974
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
D. L. Blumenthal, W. H. White, R. L. Peace,
and T. B. Smith
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Meteorology Research, Inc.
Box 637, 464 W. Woodbury Road
Altadena, Calif. 91001
(A subsidiary of Cohu, Inc. )
1O. PROGRAM ELEMENT NO.
11. CONTRACT/GRAN r NO.
68-02-1462
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Protection Agency
Office of Air and Waste Management
Office of Air Quality Planning and Standards
Research Triangle Park, N. C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES Thig report was prepared with the cooperation of the
California Air Resources Board, Sacramento, California.
16. ABSTRACT
In the last few years, Meteorology Research, Inc. (MRI) has conducted numerous
studies of the three-dimensional distribution and transport of air pollutants. From the
extensive data base collected, the export of ozone or its precursors from the Los Angeles-
and Denver metropolitan areas was documented. Analysis of the July 25, 1973 smog
episode in the Los Angeles Air Basin indicated that ozone was being exported from the
western, heavily urbanized, portion of the basin at rates exceeding 100 metric tons per
hour during much of the afternoon. High ozone concentrations confined to the surface
mixing layer in the relatively remote mountain and desert areas east and northeast of
Los Angeles were documented and traced back to their probable source in the -Los Angeles
Air Basin. The stability of ozone at elevated concentrations was documented by observations
in the Los Angeles Air Basin during July 26-27, 1973 which revealed a layer of aged
polluted air above the surface mixing layer, with ozone concentrations which remained
undiminished at 0. 12 - 0. 13 ppm throughout the night. Standard diffusion estimates based
on one episode indicated that, over flat terrain in the absence of scavenging mechanisms, an
ozone source the size of the Los Angeles metropolitan area could cause ozone concentrations
to exceed the Federal standard of 0. 08 ppm at locations as far away as 260 km. From the
data studied, it was concluded that urban sources can have a substantial effect on ozone
concentrations in downwind areas, and that this effect can carry over more than one day.
17.
a
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Ozone
Transport
Meteorology
Photochemical
Measurements
Airborne
b.IDENTIFIERS/OPEN ENDED TERMS
t. COSATI Field/Group
13 DISTRIBUTION STATEMENT
Release unlimited
19 SECURITY CLASS (This Report)
N/A
NO. OF PAGES
20 SECURITY CLASS (This page)
N/A
22 PRICE
EPA Form 2220-1 (9-73)
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INSTRUCTIONS
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17. KEY WORDS AND DOCUMENT ANALYSIS
(a) DESCRIPTORS - Select from the Thesaurus of Engineering and Scientific Terms the proper authorized terms that identify the major
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EPA Form 2220-1 (9-73) (Reverse)
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