EPA-650/4-74-037
FEBRUARY 1972
Environmental Monitoring Series
>•*•:•:•:•:•:•:•:•:•:•:•:•:•:•:
LU
O
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EPA-650/4-74-037
ATMOSPHERIC MEASUREMENT
OF PHOTOCHEMICAL SMOG REACTIONS
A PRELIMINARY ANALYSIS
by
R. C. Robbins, and L. A. Cavanagh
Stanford Research Institute
Menlo Park, California 94025
Contract No. 68-02-0010
EPA Project Officer: A. P. Altshuller
Chemistry and Physics Laboratory
National Environmental
Research Triangle Park ,
Prepared
Research Center
\Iorth Carolina 27711
for
COUNCIL
COORDINATING RESE
30 ROCKEFELLER PLAZA
NEW YORK, NEW yORK 10020
and :
OFFICE OF RESEARCH A^D DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
February
1972
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This report has been reviewed by the Environmental Protection Agency
and approved for publication. Approval does not signify that the
contents necessarily reflect the views and pol icier, of the Agency,
nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
11
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ABSTRACT
This research study was a brief feasibility study and field
measurement program to determine whether the San Francisco Bay Area
might provide meteorological and photochemical smog patterns that
were especially conducive to field research on smog reaction
processes. It was concluded from both climatological and field
oxidant sampling that this was the situation if atmospheric data
could be gathered over the waters of the Bay, particularly east and
south of San Francisco. A detailed program to carry out such research
was designed.
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CONTENTS
LIST OF ILLUSTRATIONS Vi
LIST OF TABLES , Vli
I INTRODUCTION 1
II OBJECTIVES AND CONCLUSIONS ..... 3
III RESULTS AND DISCUSSION o
A. Discussion of Sandberg and Thuillier Data 6
B. Discussion of 1971 Smog Season 12
1. Mobile Surface Oxidant Monitoring ii
2. Airborne Oxidant Monitoring 20
IV ANALYSIS AND SUMMARY 33
V RECOMMENDATIONS 37
Appendix A-THE CLIMATOLOGY OF THE SAN FRANCISCO BAY AREA
REFERENCES
V
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ILLUSTRATIONS
Pollution Monitoring Sites,
Figure 2
Figure 3
Figure 4
Figure A-3
ib-.re A-4
Oxidant Peak Houi—Occurrences During
High Oxidant Days in 1967
Displacement of 500 Foot Oxidant Profile
with Time (PST)
]1
31
Oxidant Peak Hours for October 5, 1971 36
Figure A-l A Contour Map of the San Francisco Bay Area A-2
Figure A-2 Prevalent Wind Flow Pattern for October A-6
Normal Annual Total Precipitation A-9
Visibility at the Oakland Airport Compared
with Light Wind Patterns in the San Francisco
Bay Area A-15
VI
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TABLES
Table 1 South San Francisco Smog Oxidant Correlations
for 1967 9
Table 2 Oxidant and Meteorological Factor for Days
that Exceeded 10 pphm Oxidant at South Bay
BAAPCI) Stations During 1967 13
Table 3 Oxidant Concentrations on Peak Hour for the 13
Days in 1971 When Oxidant Exceeded 10 pphm at
Four South Bay BAAPCD Sites 16
Table 4 Meteorological Factors for the 13 Days in 1971
When Oxidant Exceeded 10 pphm at Four South Bay
BAAPCD Sites 17
Table 5 Ground-Based Oxidant Measurements 21
Table 6 Airborne Oxidant Measurements 27
Table A-l Percentage Frequency of Light-Variable Winds in
the San Francisco Bay Area A-4
Table A-2 Frequency and Average Inversion Base Heights by
Month for Oakland A-8
Table A-3
Average Number of Clear Days A-10
Vll
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I INTRODUCTION
Photochemical smog results from photochemical reactions in the
atmosphere that occur when nitrogen oxides and hydrocarbons are present.
The reaction products include ozone, peroxyacyl nitrates (PAN), aldehydes,
and a variety of secondary reaction products. To date, knowledge of the
photochemical smog reaction process is largely based on controlled
experiments in laboratory test chambers and on statistical correlation
analyses using atmospheric data on photochemical smog. In the latter
case, most of the data have come from observations in the Los Angeles
Basin.
As yet not satisfactorily resolved in the smog-forming process is
the question of the importance of specific types of hydrocarbons, i.e.,
the olefins and other highly reactive types as compared to the less
reactive aromatics. Another question is the significance of the ratio
of nitrogen oxides to hydrocarbons in the photochemical mixture. Chamber
experiments are now being used to judge the significance of hydrocarbon
and NO reactivity to HC ratios in order to postulate smog formation
X
mechanisms. Ultimately, such studies could serve as a basis for air
pollution control regulations and air quality standards on photochemical
smog constituents such as NO , hydrocarbons, and oxidant or ozone.
^
Chamber studies cannot simulate all the variabilities of the real atmos-
phere, and thus increased efforts have been made to carry out detailed
aerometric analyses in Los Angeles. A goal is a simulation model of
photochemical smog.
The interpretation of aerometric measurements from Los Angeles,
however, presents major problems. One of the more important is the very
great complexity of the area sources and their emissions. For example,
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any sampling station in Los Angeles will be surrounded by sources of
both hydrocarbons and NO at distances varying from the street just
X.
outside the door to the freeway 20 miles away. As a result, each
sample will contain a wide mixture of emissions that have had various
histories, times for reaction, and exposures to atmospheric influences.
Although partial evaluations of the Los Angeles aerometric data have
been published, because of these and other difficulties, the analyses
leave unanswered many questions about the real photochemical smog
system.
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II OBJECTIVES AND CONCLUSIONS
In the research study reported here, the objectives were:
(1) To review air pollution and meteorological data
pertaining to photochemical smog in the San
Francisco Bay area
(2) To carry out preliminary air sampling analyses
to verify the existence of relative maximum
concentrations of photochemical smog over the
water areas of San Francisco Bay
(3) To determine whether the patterns of photochemical
smog are such that a detailed sampling program would
provide a unique opportunity to investigate the
progress of smog reactions, and, if so, to design a
detailed program to study smog reaction processes
in this area.
In general, the conclusions that we have drawn from this initial
feasibility study are as follows:
(1) Weather patterns in the San Francisco Bay area are
such that air pollutants are carried over the waters
of the Bay during almost all typical weather conditions
and there are indications in local pollutant measurements
that photochemical smog continues to persist after the
contaminated air mass moves over the water. (Appendix A
describes the general weather and climate of the Bay area.)
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(2) Air sampling — especially that done using an airplane
on a heavy smog day — showed that, high oxidant concen-
trations indicative of photochemical smog reactions
persisted over the Bay waters; however, we were unable
to show in our limited sampling that the Bay was an
area of relative maximum concentrations.
(3) The expected weather patterns and our obsei'ved oxidant
data all indicate that detailed analyses of photochemical
processes occurring over the Bay should provide valuable
data on the atmospheric conditions that take place in
time sequence in the development of photochemical smog.
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Ill RESULTS AND DISCUSSION
The general approach to determining the feasibility of using San
Francisco Bay as a site to study photochemical smog reactions was as
follows:
a. Collect the oxidant measurement data upon which Sandberg
and Thuillier1 based their presentation and additional
unpublished data from the Bay Area Air Pollution Control
District. In addition, collect significant meteorological
data from other sources for the smog season of 1967.
These data would then be analyzed to determine if
additional conclusions or different conclusions than
those presented by Sandberg could be developed as a
result of a broader data base.
b. The general climatology of San Francisco was analyzed
based on topographical and meteorological factors with
special emphasis on the historical patterns and trends
of oxidant concentrations.
c. An oxidant measurement program was undertaken, both
ground based and airborne, to add spatial and temporal
resolution to the oxidant measurement data available
from the Control District during the 1971 smog season.
d. The feasibility of undertaking a more comprehensive
study to define photochemical processes over San
Francisco Bay was investigated based on all the
information required during this research program.
Sandberg, J. S., and R. H. Thuillier, Oxidant Levels over San
Francisco Bay and Adjacent Land Stations," Bay Area Air
Pollution Control District, San Francisco, Calif. Presented
to 10th Methods Conference of the State Department of Public
Health, San Francisco, Calif., February 1969.
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A . Discussion of Sandberg and Thuillier Data
The stationary oxidant maximum occurring in the center of the Bay
us inferred from the concentration isopleth maps included within Sandberg
aad Thuillier's presentation. However, insufficient data were available
CD conclude that the oxidant maximum remained stationary in the vicinity
of the San Mateo Bridge. Neither in the text of Sandburg's report nor in
his conclusions does he state that a stable, stationary oxidant maximum
is maintained while wind pattern moves air through this region of high
oxidant content. Five conclusions are drawn by Sandberg and Thuillier
concerning the data obtained as background to this publication.
(1) Although there is no significant Bay effect, positive
or negative, in the mean data, analysis on a case basis
shows that conditions favoring adverse oxidant develop-
ment over the District favor even higher levels over the
Bay itself.
(2) Time-sequence studies demonstrate that the Bay is an
important avenue of transport to oxidant clouds, not a
significant sink or diffusive mechanism.
(3) Models implying lower concentrations over the Bay are
refuted, and those implying higher values are, for an
important class of circumstances, confirmed.
(4) Patterns of oxidant concentration or dosage reinforced
by the midbay data support a broadly distributed
community air pollution level, whose general features
are well established by the existing station network.
(5) These patterns further support the mixing of oxidant
precursors from area-wide sources so that the Bay and
the surrounding land are equally involved as sites
for the photochemical process of oxidant formation.
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Further evaluation of the data on which Sandberg based his con-
clusions tends to substantiate his findings. However, the interpretation
of his data in constructing the isopleth maps may not show the true pic-
ture of the oxidant-forming processes over the Bay,
When the Sandberg measurements were made, May through October 1967,
BAAPCD monitoring stations had not been established at Fremont or at
Burlingame. Therefore, the data available for evaluation in 1967 are
less complete than are available for this study. The data on which
Sandberg's paper is based were available, with the exception of the S:,v.
Leandro monitoring station, and were acquired by SRI for analysis ami
evaluation. The San Leandro data have not been transcribed from recorder
charts and would be expensive and time consuming to recover. In addition,
some unpublished data from 1967 were acquired from the BAAPCD to supple-
ment the available data. Meetings were held between SKI personnel anil
Sandberg and Thuillier to discuss and evaluate the 1967 study.
In 1967 from May through October, peak oxidant concentrations
exceeded 10 pphm at all three stations, San Mateo Bridge, Redwood City,
and San Jose during 37 days. During the same period in 1971, using
Fremont instead of San Mateo Bridge data, peak oxidant exceeded 10 pphi:i
for the three stations during 13 days. Figure 1 shows the pollution-
monitoring sites of BAAPCD, the SRI mobile laboratory, and a typical
aircraft monitoring track.
The Sandberg data were first reviewed with respect to meteorological
conditions as reported at San Francisco Airport. The correlation of
oTcidant to meteorological factors is ahown in Table ] for both those days
of high oxidant (11 pphm up) and those of low oxidant (0 -» 5 pphm) for
the period May through October 1967.
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FRANCISCO
BURLINGAME
WEST
SAN MATEO
BRIDGE
I I
\ I
11
11
li
II
\
I '
SAN
LEANDRO
EAST
SAN MATED
BRIDGE
COYOTE
HILLS
DUMBARTON,
BRIDGE
REDWOOD
CITY
IRVNVGTON
MENLO
PARK
\>,
ALVISO
Bay Area Pollution Control
District Monitoring Sites
Monitoring Sites for the
SR1 Mobile Instrument Van
Typical Aircraft Sampling Flight
SAN JOSE
SA-1035- 1
FIGURE 1 POLLUTION MONITORING SITES
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Table 1
SOUTH SAN FRANCISCO BA\'
SMOG OXIDANT CORRELATIONS FOR 1967
Days When Oxidant
Exceeded 11 pphm
t — ... —
Factors
Skycover
0
<2
Wind speed
<5 knots
--10 knots
: <15 knots
Wind direction
300 to 310°
Days of week
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
Weekends
Av Max Temp
Av AT ( max-min )
Percent
of Occurrences
45
65
30
75
100
80
7.5
17.5
20
15
17.5
10
15
22.5
79.2°F
24.4°F
Days When Oxidant
Was Less Than 6 pphm
Factors
Skycover
0
<2
Wind speed
<5 knots
< 10 knots
Percent
of Occurrences
24
29.7
0
12
<15 knots 74.5
Days of week
Sunday
Monday
Tuesday
Wednesday
Thursday
Friday-
Saturday
Weekends
Av Max Temp
Av AT ( max-min)
19
17.5
11
11
14.3
11
15.9
34.9
67.7°F
14.5CF
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The data clearly indicate relationships with specific meteorological
conditions. The relationships between oxidant concentration and wind
speed, wind direction, maximum temperature inversion height, sky cover,
and temperature difference between daily maximum and Minimum temperature?
.'.ere examined. The daily temperature differential and the wind speed
relate particularly well with oxidant concentration. Inversion height:
should also be related well, but complete data were not available. Also
included in Table 1 are data on frequency of occurrence for both high and
lo* oxidant days with respect to days of the week and weekends. The only
dei'inite trend shows Sunday to be least frequently associated with high
>Mdant and most frequently associated with low oxidant.
Insufficient data are available from 1967 oxidant measurements to
>irnv, any conclusions concerning the formations of oxidant over the Bay
>ther than the general ones drawn by Sandberg. However, analysis of the
'^iJ^nt data from the three available stations does indicate certain
• rends that are not described by Sandberg.
Figure 2 shows the peak-hour of oxidant versus the number of
•ocurrences during the 37 days of high oxidant at San Mateo Bridge,
c.-clwood City, and San Jose. This figure indicates that the peak oxidant
.lours occur sequentially from north to south on the Bay. During the 37
days, nearly 70 percent of the peak hour concentrations occurred later
in San Jose than at the San Mateo Bridge. The peak hour concentration
: iiedwood City occurred later than those of the San Mateo Bridge on
oout 60 percent of the days. Wind speed data obtained at San Francisco
Mrport cannot exactly represent wind speeds over the Bay. Sandberg
-is L-eves topographical factors on the San Francisco Peninsula produce
iijtier winds at San Francisco Airport than will occur a few miles south
and west over the Bay. An examination of wind speeds observed at Woffett
<.••-:• M. I ( located at the southern perimeter of the Bay) indicates that during
10
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15
(/; 10
OJ
CJ
z
(J
O
O
cc
Uj
CD
Z 5 —
San Mateo Bridge
Redwood City
San Jose
10
11
12 13 14
PEAK OXIDANT HOUR
15
16
17
SA
18
1035 7
FIGURE 2 OXIDANT PEAK HOUR—OCCURRENCES DURING HIGH
OXIDANT DAYS IN 1967
11
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:.(.>• 37 days of 1967, average observed wind speeds at Molfett Field were
'Mily 60 percent of the wind speeds observed at San Francisco Airport.
flie data from 1971 also show lower wind speeds over the South Bay;
during the interval from May through October 1971, the average observed
\iiid speeds at San Jose are only 39 percent of the \vind speed averaged
-.!)i San Francisco Airport and Oakland Airport.
The peak oxidant concentrations and the clock hours when peak
Concentration was observed for the three BAAPCD stations during the 37
i i>"s in 1967 when the concentration exceeded 10 pphrn oxidant at all
1 lu'oe stations are summarized in Table 2. In addition, Table 2 gives
••!eorological factors including inversion base height for this interval.
The \\ind speeds are obtained from observations at San Prancisco Airport,
•Ahile the inversion base heights are obtained from Oakland Airport
observations.
In spite of the obviously inadequate wind speed information, an
.-•' tempt was made to correlate the peak-hour times differential between
v i, Han Mateo Bridge and San Jose during the days of interest in 1967
i''i wind speeds. The airline distance from San Mateo Bridge to San
: >-;c is approximately 24 miles. Although there was a wide daily
• 'raation for individual days, the San Francisco wind data and the
-''.«rage difference between the times at which peak concentrations were
''(-'served at the San Mateo Bridge and at San Jose indicates an average
1 '''vel distance of 25 miles. These averaged data thus indicate that
."-.• oxidant maxima moved down the Bay at velocities generally consistent
. j.':h the velocities of the air parcels.
Discussion of 1971 Smog Season
The measurement objectives of this study were to obtain data during
'•itervals of varied oxidant concentrations at locations both over and
..< i'.;-j;it to Sari Francisco Bay. Due to the limited time frame of this study,
„! ;\ns highly desirable to obtain the measurement data as soon as possible.
12
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Table 2
OXIDANT AND METEOROLOGICAL FACTORS FOR DAYS THAT EXCEEDED 10 pphm
OXIDANT AT SOUTH BAY BAAPCD STATIONS DURING 1967
Da t e
May 7
1-1
15
16
June 24
27
28
29
30
luij 1
'•
11
12
26
27
28
AUK 1
3
8
12
13
17
18
21
riopt 19
20
25
2G
Or t 6
8
13
16
17
18
L9
20
24
San Mateo
Bridge
Peak
Cone
12
14
20
18
10
12
21
16
10
10
10
30
10
17
17
38
16
10
15
25
10
12
21
11
28
35
12
19
11
18
16
34
17
16
26
10
18
Time
(PST)
1510
1450
1635
1350
1320
1310
1150
1015
1145
1225
1155
1320
1245
1245
1425
1230
1340
1155
1210
1350
1310
1250
1320
1215
1535
1520
1250
1325
1310
1450
1220
1515
18201
1220
1425
1510
1125
Redwood City
Peak
Cone
15
13
24
20
13
12
16
19
20
13
12
20
12
16
10
15
11
13
17
15
10
15
11
12
18
29
11
16
12
16
12
17
19
14
19
14
16
Time
(PST)
1350
1550
1635
1430
1455
1340
1155
1120
1250
1220
1150
1255
1410
1315
1320
1320
1335
1230
1240
1410
1440
1235
1235
1215
1450
1545
1250
1255
1345
1500
1315
1420
1325
1130
1410
1130
1320
San Jose
Peak
Cone
19
15
19
29
10
17
25
19
16
15
14
22
13
18
20
Time
(PST)
1705
1720
1820
1620
1335
1435
1255
1310
1530
1340
1430
1340
1340
1145
1435
20 | 1410
16
16
12
16
15
18
14
10
13
21
13
14
10
15
14
13
15
19
15
14
1510
1055'
1140
1335
1530
1400
1345
1445
1410
1140
1415
1330
1530
1455
1430
1315
1200
1415
1615
1325
18 1220
San
f ranciseo
Peak
Cone
7
12
24
14
3
3
3
9
2
2
5
14
2
6
4
6
4
4
5
4
3
2
3
3
21
23
6
8
5
9
6
10
7
8
5
9
Time
(PST)
1110
1400
1610
1200
1340
945
1340
345
1145
1545
930
1030
0345
1030
1430
1030
1310
1045
1040
1040
1230
1630
1030
1045
1450
1120
0210
1115
1200
1450
1040
1403
1130
1140
1420
1130
AT3'4
32
31
32
32
19
19
25
21
21
18
17
31
16
31
31
29
22
20
17
23
21
21
17
13
34
31
14
18
21
24
23
26
29
19
28
19
18
Max " S ky4
1'emp i Cover
82 ' 8
81 j 0
8.) i 0
8b
71
71
77
74
76
71
70
85
70
84
86
87
76
73
72
74
74
75
70
73
92
92
71
74
73
78
77
86
83
72
78
69
69
0
0
1
0
0
0
0
8
0
1
0
9
5
2
1
8
0
0
1
0
0
3
7
2
2
0
3
0
0
0
2
0
1
9
Re s-
ttind
Speed
4.7
4. }
5.7
8.3
10.2
8.9
12.2
11.8
Inv or; iija
l!c-i|,'n
I 'net(,i;
none
i:;90
1000
none
I'lO
260
-bO
l(i()
] 4 . 2 i 90
16.0
14.4
11.7
18.9
12.3
8.8
12.7
7.4
12.5
8.3
14.4
15.7
15.8
18.0
100
i;o
210
140
300
200
220
320
200
200
90
6
13.6 loO
3.5 i 2330
5.0
9.9
10.8
7.6
8.6
10.7
0.2
2.5
15.3
3.1
10.2
7.5
none
190
90
1300
none
2680
2100
1720
2460
13H
131
600
A prior peak occurred at 1400.
A secondary peak occurred at 1500.
AT is daily maximum temp minus daily minimum temp.
Meteorological factors from San Francico Airport,
Inversion heights from Oakland Airport.
13
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on the other hand, oxidant measurements on days when conditions were not
favorable would expend our resources with little benefit. The spring
turough midsummer of 1971 was remarkably free of smog in the San Francisco
r-;ay area. The general trend through the summer indicati.nl that if sampling
,_> ^ initiated only on smoggy days, there was a distiaci possibility that
insufficient data could be obtained during the 1971 sc-.-son to form con-
clusions about the feasibility of an extended measurement program on San
;rancisco Bay.
Even when moderate concentrations of oxidant were present early in
tut? day, strong afternoon winds often caused rapid dilution and short
-------
The Bay Area Air Pollution Control District (BAAPCD) has
several oxiclant measuring stations located on the east and west sides
of San Francisco Bay. The East Bay stations are located in San Leandro
and Fremont. The West Bay sites are located in San Francisco, Bur lingamo,
,iud Redwood City. The South Bay station is located inland at San Jose.
The sites selected for measurement by the SKI vati were located at the
west end of the San Mnteo Bridge, the oast end of the , uti Mateo Bridge,
the west end of the Dumbarton Bridge, Coyote Hills near the east end of
Dumbarton Bridge, and Alviso on the south shore. The above locations
are shown in 1'ig. 1.
The summer and fall of 1971 were remarkably free of days where
observed concentrations exceeded 10 pphiu of oxiclant. The actual occurrence
of oxidant days above the 10 pphm Level decreased 39 percent from 1970
to 1971, with at least 23 percent of the decrease attributed to meteor-
ological factors.2 During the interval from May through October 1971
there were only 13 days where the peak oxidant concentration exceeded 10
pphm at all four South Bay BAAPCD stations; Redwood City, San Leandro,
Fremont, and San Jose. On only 5 of the 13 high oxidant days did the peak
concentrations exceed 15 pphm at all four stations. The presence of high
oxidant concentrations at these four stations was presumed to indicate
high oxidant concentrations throughout the South Bay area and hence, clays
suitable for data analysis.
The peak oxidant concentration and peak hour data are given in
Table 3, and the pertinent meteorological data in Table 4 for the days in
1971 in which the odixant concentration exceeded 10 pphm at all four South
Hay BAAPCD monitoring stations. The peak concentrations and peak hours are
given for the Burlingame and San Francisco BAAPCD stations as well. The
mean wind speed designated central is an average of the winds observed at
2. Bay Area Air Pollution Control District Information Bulletin, San
Francisco, California, January 7, 1972.
15
-------
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San Francisco and Oakland Airports. Likewise, the central maximum
temperature is an average of the maximum temperatures observed at both
San Francisco and Oakland Airports. The stability factor is determined
from soundings at Oakland and San Jose and represents the temperature a1
2300 feet minus the surface temperature. This stabilily iactor should
represent the inversion strength where positive nunber- indicate the
stable conditions of an inversion and negative number^ lapse conditions.
The 13 days tend to be classic examples of conditions con-
ducive to the formation of high concentrations of oxidants. The
unusual aspect is that the oxidant concentrations were not higher, as
*ould be inferred from historical oxidant and meteorological data.
Imring the 13 days, the wind speeds for the central region were 71
percent of the average wind speed for the 6 months' interval from Way
through October. The San Jose wind speeds were only 61 percent of the
ii-month average. The average oxidant day temperatures for the Central
bay and for San Jose were each 16 degrees F higher than the average
temperatures lor all the days of the interval. The factor AT (difference
between daily maximum and minimum temperatures) indicates that insolation
values were high. The stability factor indicates the presence of an
inversion with stable conditions and reduced mixing. All of these
conditions are conducive to the formation and entrapment of oxidant
within the lower level of the atmosphere.
The peak oxidant concentrations and the clock hour when these
concentrations were reached at the BAAPCD monitoring stations (shown in
Table 3) definitely indicate the trend of an oxidant maximum moving down
the Bay. In general, the peak hour occurred somewhat earlier at the
sites on the western side of the Bay than at complementary locations on
the Fast Bay side. San Francisco peak hours were often anomalous and
cannot be related to the peak hours of the more southern station. The
peak hour of oxidant at Burlingame usually preceded the peak hour
18
-------
observed at Redwood City. The peak hour observed at Kedwood City usually
preceded that observed at San Jose. Similarly, on the Last Bay sites,
the oxidant peak hour occurred iirst at San Leandro, followed by Frerion' ,
then finally at San Jose. In three instances, noted in 'iablt 3, a
secondary peak was observed at a time that tended to s ipport the concept
u" a moving oxidant maximum. The peak hour time diiit 'otitial with
r-.'^pect to observed wind speeds tends to indicate thai the r.'te ol travel
oi the oxidant maximum is somewhat less than could b•• alii Bay, ^"d quite possibly the observed wind '-peeds are not
representative of the area of interest.
'[^D types of sampling patterns were used to obtain t no oxniui)1
data with the SHI van. First, measurements were obtained sequentially j :.
i fircular pattern at sites as follows: Menlo Park, V.est and East San
Ma too Bridge, Hayward, Coyote Hills, Alviso, Dumbarton Bridge, Coyote
Hills, Alviso, and Menlo Park. This sampling pattern was designed to
oDUun data during the anticipated peak oxidant hours at the San Mateu
1'r.idge, and then to proceed southward for measurements at the southern
sites prior to peak oxidant hour. '["he SI! I van was located at eacii
Cample site about one-half hour,
\ variation of this circular pattern, but only encompassing
the southernmost end of the Bay, was also used for oxidant sampling.
In another pattern, the van was located at a sampling site for longer
intervals to observe the passage of the oxidant peak. The van was then
moved and relocated at a more southerly site to observe the peak
oxidant passage. Obviously the second technique limit,- the number of
.-ample sites at which measurements can be made during a single sampling
day. However, a more accurate determination of peak oxidant hour can be
obtained through the use of the second sampling pattern with Longer
sampling intervals at a few selected sites.
19
-------
Table 5 shows the oxidant concentration data long the pertinent
meteorological factors on the days during May through October when
oxidant measurements, both surface and airborne, '.vere i .ade by SHI. In
addition, the measurements from the BAAPCD monitoring stations are
included. SRI made measurements on 16 days, 6 of which coincided with
the 13 days when oxidant levels exceeded 10 pphm ot 1 rd.vood City, San
Leandro, Fremont, and San Jose. The oxidant coiicent.L-.it ion values
obtained by the SRI mobile van are seldom inconsistent with the rtoving
uxidant peak hypothesis. The sampling rationale of 1 lie mobile van, as
described previously, does not lend itself to locating the peak oxidan1
hours at a number of sites during any one day. However, the K.easureme-, t
of oxidant concentrations at times other than the peak hours can provirv
useful information concerning- trends of oxidant concentrations and
oxidant transport within the South Bay. On only one sampling day,
May 19, 1971, were the observed concentrations inconsistent with the
moving oxidant maximum hypothesis. On two days, June 18 and September 14,
1971, the data are not definitive because they were not in the right
location at an appropriate time for observation of the peak concentration.
The remainder of the days definitely indicate a southward transport of
the oxidant maximum.
The data show a general trend of higher oxidant concentrations
and a later peak hour sequentially from northwest to southeast during
days conducive to oxidant formation. Since this sequence correlates well
with wind direction and velocity, it substantiates the hypothesis that
area of oxidant maximum moves down the Bay as a function of the wind.
2. Airborne Qxidant Monitoring
On October 4 and 5, 1971, aerial oxidant surveys were made
over San Francisco Bay. These were days of high oxidant level with high
temperatures, light winds, and well-developed inversion layers at about
2000 feet.
20
-------
Table 5
GROUND-BASED OXIDANT MEASUREMENTS
Da1 !•
M;iv 1 1
I
to', 17
M n 14
Location
SF
Burl
RC
MP
U
S 1
djlv
SI,
c;i
I- re
M
T.url
V. San Mat Br
HC
MP
A!
S I
Oak
SL
CH
1 i-o
SI
Bar)
V, San Mat Br
F San Mai Br
RC
Mr
Al
SJ
Oak
fa I,
CH
Fro
Peak
Oxid
Cone
;j
3
5
5
j
7
•1
5
3
3
5
5
5
6
6
6
1
--
4
4
7
5
5
5
G
8
Time
(PST)
0930
1010
1040
1100
1330
1320
1300
1300
1300
0510
1010
1330
1355
1300
1500
1450
1115
--
0210
2350
1910
1230
1410
1220
1235
1240
Observed
Oxid
Cone
4
4
1
4
5
5
6
5
5
5
4
5
Time
(PST)
1030
1200
1500
i no
0835
1000
0915
1420
1252
1320
1540
1410
Wind
Speed
22
15
9
5
4
IS
15
10
9
10
Avei a}ir
W j ml
Speed
13.2
1.13
9.8
13.2
5. 2
11.7
15.7
4.0
10.9
A\
In i1
27O
270
290
270
270
28O
,Ll -.
l.'K.f
e;
79
67
68
77
71
67
75
66
1
18
10
22
21
17
15
S kyeovor
0
0
3
'>
5
4
St abi 1 i t v
Facto
i
'
I
1
-8
1
~'2
2
SF
Burl -
RC-
MP
Al
SJ
Oak -
SL
CH
Fre -
vSan Francisco ^
Burling
Redwood
Menlo P
A 1 vi so
San Jos
Oakland
ame E
Ciu
ark
e
San Leandro
Coyot e
Fremont
Hills
San Mat Br - \vest San Ma too Bridge
San Mai Br - Kast San Matoo Bridge
21
-------
Table 5 (Continued)
Dale
M.i, 16
L
'LIUC 17
June iH
Location
SF
Burl
W San Mat Br
E San Mat Br
RC
IIP
Al
SJ
Oak
SL.
CH
Fru
SF
Burl
W San Ma-t Br
E San Mai Br
RC
MP
A]
EJ
Oak
SL
CH
Fre
Si
Burl
RC
MP
SJ
Oak
SL
Fro
Peak
Oxid
Cone
2
6
11
11
6
3
6
3
5
8
9
6
10
15
3
2
3
3
4
4
5
Time
(PST)
0850
1015
1200
1200
1110
1320
1250
0510
1010
1215
1230
1110
1220
1220
0215
0040
1030
1045
1120
1100
1100
Observed
Oxid
Cone
4
3
3
4
5
8
9
1
3
6
7
1
2
3
4
3
8
3
2
2
2
Time
(PST)
1250
1332
0«00
1015
1100
1130
1230
1300
1410
1030
1100
0900
1000
1100
1400
1442
1130
1345
0900
1110
1310
Wind
Speed
10
10
25
3
20
Average
Wind
Speed
11.2
3.7
3.2
12.1
3.9
7.3
12.8
5 . 3
9.8
Av
Dir
290
290
270
260
290
270
Max
'1 emp
83
L't
'17
i
95
bl
83
93
77
70
81
70
24
29
21
16
13
Sky cover
')
3
1
1
5
5
S labili I v
Kau i or
11
15
6
11
0
5
22
-------
lable 5 ,'C'oul inuedl
1 M t r-
,'iiH 9
, _ ........ .
u'l- 10
\\' 12 I' '
'.u.- 19
t.nca I ion
Si-
Burl
W San Mai Br
1' San Mai i,r
IX
Mr
SJ
Oak
SI
1 re
Si-
Burl
HC
MP
Al
S f
Oak
ril,
CH
(• re
M-
Hur i
'V San Mat Br
i', Sjn Mat Br
W
MP
A I
S I
Oak
S!,
CH
Tre
KK
Lurl
W San Mat 13 r
E San Mai Br
RC
MP
Al
SJ
Oak
SL
CH
>'re
Peak
Oxicl
Cone
1
L
.1
2
;j
2
3
i
•>
-7
17
7
6 . 5
15
2
1
5
7
1
4
5
3
--
6.0
5
7
7
6
18
Time
(PST'i
1200
2120
1733
1030
1210
1450
1055
0150
0420
1320
1 153
13JO
1413
1415
0235
0105
12 10
1235
Oh-er^ec!
O\l<
Cone
i
1
1
1
1
4
fa
6
6
3
;;
3
2
1
3
1115
12 15
1246
012O
_-
1240
1150
1320
1330
1420
1435
3
3
2
1
2
e
Tune
' I '.VI ^
1020
1 0 10
1.125
1..25
1452
\V i ml
Speed
15
15
211
20
.V,-vi'>c
Uu-uT
S
"'"'"'
, i.,.:-
i
1223
1540
1350
1320
1123
1200
1025
1520
1555
1125
14
5. 2
h.9
l.'i . 7
3.3
f
s
7.5
1255
1410
1215
1140
1550
1425
=
12 . ')
1 '
13. '2
«.6
5. 1
10.9
A\
Dir
270
270
5O()
Ma\
'j I Tip
1,7
77
<>r
75
280
270
270
^90
280
95
7 1
71
H2
dfc
75
1
81
fob
I ;
10
19
14
14
9
23
15
Skv enver
3
!
1
1
1
5
3
4
M ahi 1 i i
1 aetoi
j
1
_9
-2
l
i
2 -
2(, i
1
1
1
0
13
12
-------
Table 5 (Continued)
Dale
S ep 1 3
.Hi pt 9
,'M'JJl 1 1
,
Location
SF
Burl
RC
MP
Al
SJ
Oak
SL
Fro
SL
Burl
W San Mai Br
E San Mat Br
RC
MP
Al
SJ
Oak
SL
at
Fre
SF
Burl
W San Mat Br
E San Mat Br
RC
MP
Al
SJ
Oak
SL
CH
Fre
Peak
Oxid
Cone
,j
4
11
19
12
!•]
15
3
5
10
6
11
8
10
28
15
19
15
t8
29
Time
( PST N
1420
1235
1410
1420
1625
1415
1440
0050
1120
1255
1500
1345
1200
1245
1250
1425
1330
1335
1655
1540
Observed
Oxid
Cone
15
2
3
7
10
4
4
2
10
5
10
10
10
9
10
10
5
10
Time
(PST^
1530
1055
1130
1425
1330
1050
1430
1155
1500
1035
1605
1215
1248
1305
1526
1540
1010
1345
Wind
Speed
Average
Wind
Speed
8.2
3 . 2
6.2
11. 1
.1.1
6.6
7.5
2. 5
5.9
At
Dir
290
310
290
300
280
310
Max
Temp
,s4
L'\
>»t
KH
79
79
89
76
103
108
96
22
27
19
38
29
Sky cover
o
!
0
2
0
0
S t aba 1 1 " v
Factor
2
2
10
11
17
19
24
-------
Table 5 ('Concluded)
Dale
sepl 15
0; I 1
'• I ^
Localion
SF
Burl
U' San Mat Br
I- San Mat Br
KC
V.P
u
SJ
Oak
SL
< U
t re
SI
Burl
Ba> Cti Alem
San Mai Bi
Dumbarton Br
Al
KC
SJ
Oak
SL
tre
SK
i'.ur]
( a i re r a 1 1 "I
2 rni N SM Br
0.0 PI S SM Br
2.9m S SM Br
RC
3,1
Oak
SL
Fre
Peak
Oxi d
Cone
5
14
19
19
19
22
29
7
8
14
14
12
20
21
8
14
14
17
19.5
22
19
27
32
Time
(PST )
1015
1115
1335
1550
1550
1315
1450
1400
1450
1420
1545
1710
1430
1550
1120
1245
1220
1320
1420
1515
1710
1430
1550
Observed
Oxid
Co ne
5
11
10
12
3
8
11
1 1
13
19
8
9
7
Time
(PST^
948
1410
1029
1425
0833
1616
11 15
1100
1230
IjlO
1436
1440
1446
Wind
Speed
Average
Wind
Speed
8
2.3
8.2
6.6
1.8
6.6
9.1
1.9
12
Av
Dir
300
320
290
290
290
310
Max
1 en>p
4,".
i 'I
•• ,
UK;
91
85
89
85
82
92
80
0 5
35
28
26
Sk/covei
0
0
0
0
0
0
Stability
I aeior
\
l.'j
17
l
!
1
14
16
14
15
25
-------
The October 4 flight was of relatively short duration, from
1345 to 1445 PST, and there were some difficulties. One double profile
was flown at 500 feet. The measured concentration of oxidant showed a
peak just south of San Francisco, with the concentrati •:: nearly cons tar.;
at 8 pplim over most of the South Bay. During the Octc.jer 5 flight, foi::
hours of oxidant data were accumulated over San Franc; iro 15;>y at 500-,
700-, and 1000-foot altitudes. Four double profiler \.erv executed —
iirst north, then south along the center line of the Uay. The first
started from Palo Alto Airport, north to 10 miles north of the- Haywnrd-
San Mateo Bridge, then south to Alviso. The other three double profile
started at Alviso at the southern end, to one mile sourh of the Bay
bridge at the northern end and return to Alviso. The iir.st rioublt-
rrofj.lt> v/as flown at an altitude of 500 feet, the second at 1000 i'ei-1 ,
the third at 750 feet, and the fourth ui 500 feet. \tter the fourth
double profile, a rectangular flight path was made from Aiviso at 500
feet, north up the east side of the Bay to the Hayward-San Mateo Bridge,
then west over the Bridge to the we&t side of the Bay, then t-.outh to
Palo Alto.
The data for October 4 and 5 are given in Table 6.
An analysis of the data shows the movement of the oxidant
profiles indicate the movement of the air down the Bay. The principal
region of high oxidant concentrations that was observed at 500 feet
was first located about 2-1/2 miles north of the Hayward-San Mateo
Bridge at 1220 with a peak oxidant concentration of 14 pplim, as shown
in Figure 3. At 1000 feet on the next traverse bet'vee'i about 1240 and
1315, the average profile was similar to that at 500 feet with concen-
trations averaging about 13 pplim north of the Bridge, and 11 pplim to
the south. At 750 feet between about 1320 and 1400, the peak concen-
tration shown by an average profile was 19 pphm and was located about
26
-------
Time
(PST)
Table 6
AIPJ3ORNE OX I DA NT MEASURE.VEXTS
(October 4, 1971)
Oxidunt
(pphm)
500 feet
1355
1357
1 105
1408
1410
1415
1420
1425
1427
1430
1434
1436
1438
1440
1442
1444
1446
1448
Leave Palo \lto
Airport
1 mile bouth
Dumbarton Bridge
A1 vi s o -Tu r n a r on ru 1
Dumbarton Bridge
Hayward-San XL; Ceo
Bridge
Off NAS Alameda
1 mile south
Bay Bridge-
Turnaround
Hayward-San Mateo
Bridge
Dumbarton Bridge
AIviso-Turnaround
8
8
8
8
14 (Peak)
8
8
9
8
8
9
8
5
7
7
See Fig. 1 for track
27
-------
Table 6 (Continued)
AIRBORNE OXIDANT MEASUREMENTS
(October 5, 1971)
Time
( PST)
1200
1210
1213
1215
1216
1217
1219
1220
1221
1222
1224
1225
1226
1227
1228
1229
1230
1231
1232
1234
1235
1237
1238
1239
1240
1241
Oxidant
(pphrn)
Leave Palo Alto
Airport
X-
500 j-eet
Dumbarton Bridge 12
11
Hayward-San Mateo 9
Bridge
13
12
14
12
11
Turnaround
14
16
15
Hayward-San Mateo 11
Bridge
11
11
11
Dumbarton Bridge 12
13
14
14
Alviso 12
1000 Feet
13
High voltage 12
transmission towers
11
11
Time
(PST)
1242
1243
1244
1245
1246
1247
1248
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
Dumbarton Bridge
Hayward-San Mateo
Bridge
Hunters Point
Turnaround
Hayward-San Mateo
Bridge
Dumbarton Bridge
Alviso
Oxidant
(pphrn)
10
10
10
13
11
10
11
1-1
14
12
12
12
12
14
13
14
15
14
14
13
13
14
14
13
10
11
12
13
15
10
10
11
12
14
500-foot data shown by Fig. 3
28
-------
Table 6 (Continued)
Tin e
v ^ T)
750 Feet
1318
1320
;32i
i •- 2 2
',(23 Dumbarton Bridge
L3J4
' _ Li 5
J32t'
1327 Hayward-San Mateo
Bridge
'328
:32y
1330
1331
1332
1333
1334
1335 Hunters Point
1330
1337
1338 Turnaround
1339
1340
1341
1342
1343
1345
1347 Hayward-San Mateo
Bridge
1348
1350
1352 Dumbarton Bridge
1354
1357 Alviso Turn
Ox id ant
(pplun)
13
11
10
9
9
11
12
11
16
18
17
16
18
17
16
18
18
12
18
10
20
18
17
10
17
20
17
12
12
14
12
rir.ie
(PST)
: 0 Feet
1400
1401
1402
14U3
1 105
1407
1408 Haywf.rd-t.an Mateo
Bridge
1410
1412
1413
1415
1416 Hunters 1'uint
1418 Turnaround
1420
1421 Momentary Max.
1422
1423
1426
1427 Hayward-San Mateo
Bridge
1430
1432 Dumbarton Bridge
1435
1437 Alviso Turnaround
1440
1442
1443 East «nd Dumbarton
Bridge
1445
1447 \ Turn to West at
Hayward-San Mateo
Bi'j dge
1448
Oxj da ill
(pplun)
16
14
12
14
18
IS
18
15
21
20
34
18
20
16
24
13
15
17
20
20
13
9
20
14
13
12
20
20
18
-------
Table 6 (Concluded)
Time
(PST)
Oxidani
(pphin)
1449
1450
1451
1453
1455
1456
1459
Minimum just east
of high part of
bridge
South on western
shore
\\est end of
Dumbarton Bridge
Arrive Palo Alto
Airport
15
13
19
20
14
14
30
-------
I I
I I I I
.'0
I
1220
MAXIMUM
14 pphm
I I I
1320
MAXIMUM
17 pphm
1420
MAXIMUM
19 1/2 pphm
BASED ON
750' AND
1000' DATA
1220
V .
MOVEMENT OF
MINIMUM OXIDANT
I I I
I I I
BAY
BRIDGE
SAN MATED
BRIDGE
DUMBARTON
BRIDGE
ALVISO
SA-1035-2
FIGURE 3 DISPLACEMENT OF 500 FOOT OXIDANT PROFILE WITH TIME (PST)
31
-------
at the Bridge, The southward advection of the oxidant peak was clearly
shown by the second 500-foot average profile taken between 1400 and 1500.
The peak concentration was 19 pphm and was three miLes south of the
Bridge. Figure 3 shows three north-south profiles at r.OO feet — the
averages for the first or 1220 track, the fourth or 1430 track, and an
estimated 1320 profile based on an analysis of the fo^;1 available profiles,
The combined data are consistent with wind advection of the oxidant peak
at a speed of ab_out 3 mph, which is comparable to the observed winds at
Oakland .Airport of 3.5 to 5 mph during the interval of interest. During
this time the data indicate that an oxidant minimum was moving about t/,o
miles ahead of the maximum at 500 feet, with an oxidant level of 10 pplun
at 1220, which increased to 11 pplim by 1420. • The flight over land areas
along the east and west sides of the Bay between about 1440 and 1500 did
not detect significant differences in oxidant concentrations between the
Bay and land areas.
A secondary oxidant maximum was observed developing 14 miles
north of the principal maximum and about one hour later.
32
-------
IV ANALYSIS AND SUMMARY
The original Sandberg data implied that oxid.i.it '.^reduction
reactions pred-jir.inate over diffus.ion.al dilution, i...1. .u , j.nd other
j.idant loss mechanisms within the i-i r parcels ti'txi-].' ted dov, nvind
i roiM Sun rraiicisco. Oxidant continues TO increa^i.- nn:ai. it recedes
'•owe arbitrary point in the J-iay. ! ',:•'! thi". point n. ia,u , n.i space.
ul.'.in,;
iJi a more or less stationary "\jdaul Maximum &or.ie.wliere ju the ISay.
One mechanism that could account L'or this inrerprut at ic n\ \stmid
ne that the most reactive hydrocarbons present in the plume of s ,u
I rancisco were consumed very rapidly (within about one Hour) duriiu;
transit to the Bay Center. After depletion of t lit be very reactive
hydrocarbons, the rate of reaction vith the lesser reactive species
decreased so abruptly that dilution uecarue the dominant mechanism. The
•)x:dant loss rate thus greatly exceeded the production rate and resulted
.11 an apparent stationary area of oxidant maxima.
The van and airborne oxidant measureme- svts marie in the SRI survey
added spatial resolution to the Sand berg ^t'.uiy, and proved that the
• \xidant maximum is not stationary but moves at or near the speed of the
air parcel for the time required to traverse the Hay.
The most important information developed is that oxidant maxima
continue to increase in value during the entire Bay trnverse. Analysis
of the data shows that the rate of increase of oxid-int ,, ith time reaches
• i maximum at about 2 hours after the peak hour occurs in S;ui Francisco
and that it remains positive for at least 3 hours. This 3-hour period
.'•ith the usual 8- to 12-mph northwest winds is sufiicient time for the
ir parcel to travel from San Francisco to the south end of the Bay.
33
-------
This general trend of a continuing oxidant increase during advection
to the southeast indicates that two mechanisms nay be responsible for and
quite likely do contribute to the ooserved phenomena. As stated pre-
viously, the highly reactive hydrocarbons react phococ 'rmieally and result
initially in a rapid increase in oxidant concent ra I '.0'\ during' the early
portion of the traverse down the Bay. The role uL o\.'lant formation
resultant from reactions of the let-ser reactive hyd'-m .a-bons bt_-c:oues more
pronounced as the highly reactive species become depleted. The general
Kay area meteorological factors of increasing wine; .;\ ed in 1 he lute
afternoon would tend to increase the contribution of dilution with an
Apparent decrease in the rate of oxidant formation.
Over the entire Bay, the oxidant formation reactions are domin; nt
processes on days of photochemical smog. This trend of continuing
oxiilant increase during advection is shown in Figure 4.
Hased on the above data interpretations, it appears that San
Francisco Bay can provide simplified yet ''real" conditions necessary to
define photochemical processes. The net oxidant formations and, by
inferred similarity, net changes in the other smog components may be
utilized along with diffusion theory to model the San Francisco Bay
smog system. A single area source and a continuously reacting system
involving nitrogen oxides and a succession of hydrocarbon and organic
reactants can be assumed.
No special or unusual transport mechanisms appear to be required
to satisfy the observations as we interpreted them.
The proposed expanded Bay Area study should provide a basis for
relating actual atmospheric observations with reaction chamber data.
The concentration of primary reactants and secondary reactants will be
measured, many in real time, within a single air parcel during transport
34
-------
and aging. The measurements will include NO, NO , hydrocarbons, oxidant
aldehydes, organo-nitrates, and solar radiation intensity.
The proposed study should alho provide unequivocal data to
identify the important oxidant formation reaction and elucidate the
mechanism of transport.
35
-------
35
30
25
20
rj
.<
Q.
Q.
15
10
(2.9 mil
south)
(2 miles
north)
(0 5 miles
south)
-San Francisco
-San Mateo Bridge
-Burlmgame
-Redwood City
-San Leandro
-Fremont
-San Jose
11 00 12.00 13 00 14 00 15:00 16:00 17'00 IS'OO
CLOCK HOUR
SA-1035-6
FIGURE 4 OXIDANT PEAK HOURS FOR OCTOBER 5, 1971
36
-------
V RECOMMENDATIONS
The surface and airborne data obtained during th.s program
indicate that a more comprehensive program—in which nitrogen oxides,
hydrocarbons, formaldehyde, and carbon monoxide, as \vtll as oxidants ,
are measured—would provide a means of analysis of real photochemical
sinog systems. Such a program would be possible because of the undib-
turbcd course of photochemical reactions in air masses traveling
ncross the water of San Francisco Bay where fresh reactants are not.
beinj introduced.
37
-------
Appendix A
THE CLIMATOLOGY OF THE SAN FRANCISCO BAY \RE\
1 . Introduction
The pollution climate of an area is a sunuviary cJ the !U't«-'
-------
FIGURE A-1 A CONTOUR MAP OF THE SAN FRANCISCO BAY AREA
A2
-------
contour map of the San Francisco Bay area. The "Bay" (San Pablo and
San Francisco Bays) is the world's largest natural harbor, covering
approximately 400 square miles. High densities of population and
industrial activity have settled on the low lands surrounding the Bay.
Modification of the natural surface is very extensive ,tiui is likely to
continue or accelerate.
3. Meteorologica 1 Fact ors
a. Winds
The semipermanent Pacific high that dominates the Bay area
^uiunier climate reaches its maximum intensity in August. Characteristic
features of the high are the persistent west-northwest flow and the
i-'trong subsidence inversions, both of which control the generation of a
ruld marine layer and its attendant stratus cloud system. Large scale
temperature gradients are at their maximum because a thermal Low pressure
aron develops over the great Central Valley north and south of Sacramento.
During the fall, the Pacific high moves southeastward, merging occasion-
ally with continental high cells to form large, stagnant blocking systems.
', i:id speeds decrease, become northerly or northeasterly, arid in turn
drastically reduce the on-shore movement of the cold marine layer. Shorter
>i;-ys, clear nights, and light winds contribute to the lessening of tne
large-scale thermal gradient between the ocenri and Central California and
bring about a strong seasonal influence on the wind patterns.
Within the Bay area, a certain amount of wind flow distortion
i.s apparent when air is channeled by terrain features and forced to rise
"ibove or move around hills. Wind observations in the Bay area often show
i pattern of opposing or converging and diverging directions that can be
related back to physical features in the terrain. Differential heating
plays a large role in determining wind patterns in the Bay area, where
the total water surface is not much less than the total land surface.
A-3
-------
The familiar pattern of land-sea breezes is strongest in the summer, but
with. decreasing solar radiation over the land area in the fall, the on-
shore sea breeze flow weakens accordingly. Light and variable wind
conditions are prevalent favoring air pollution accumulation. Highest
frequency of light and variable winds occurs during .November, as evi-
denced by Smalley's findings1 shown in Table A-l.
Table A-l
PERCENTAGE FREQUENCY OF LIGHT-VARIABLE WINDS IN
THE SAN FRANCISCO BAY AREA
(1952 to 1955)
Month
Jan
Feb
Mai-
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Time of Day (PST)
0400
(Cc)
39
41
31
33
31
17
12
9
38
52
58
35
1000
(rc)
32
29
30
19
14
7
5
15
38
39
44
27
1600
(Cc)
30
20
4
1
2
0
0
0
2
5
23
22
2200
(rc)
35
43
26
13
14
6
4
4
22
34
51
31
33
24
24
All Hours
34
33
23
16
15
7
5
7
22
32
44
29
22
A-4
-------
Smalley's study includes a summary of prevalent »vind flow patterns
that occurred over a four-year period. Figure A-2L is an October pattern
showing a wind flow typical of the transition from summertime westerly
flow Lo a wintertime north-northeasterly flow. Incidentu of nmriiie air
intrusions over mountain tops and passes is restricted i Iso by the lowering
• li the inversion. The implication of such a wind patter-, for air pollution
problems is obvious with pollutants generated in San Francisco and western
partt> of the area being carried to the east and especially southeast across
San Francisco Bay.
b. Thermal Stability
Temperature inversions occur in the Bay area as two general types:
the summer subsidence inversion and the winter radiation inversion. Fall
oppears to be a period of transition between the seasonal extremes of a high
subsidence inversion and a low radiation inversion. Subsidence inversions
.;re usually higher over the Bay area when accompanied by stratus clouds,
Aiiereas radiation inversions are surface based and best developed under
-l.mdless skies. Often in the fall, both types of inversions can be found
together or merged when conditions favor the simultaneous development
<-'t both types. During clear northwesterly and westerly wind conditions
the inversion base averages 650 feet. When north to northeast winds pre-
vail, the inversion base is less than 200 feet.2 An SKI study found the
'uiyt frequently occurring inversion base height during October to be less
man 350 feet. The height of the inversion base is slightly lower over the
: -mth Bay than over the North Bay.3 More recent observations by the
"etoorology Department at San Jose State College show that, for any one
:. ustance, the height and the intensity of the subsidence inversion vary
'•'>-r the Bay area. Typically, the inversion is lowest over the Bay itself,
increasing in height toward the hills and the sea.4
A-5
-------
SA-1035-4
FIGURE A-2 PREVALENT WIND FLOW PATTERN FOR OCTOBER. Mean Wind Speed
at San Francisco - 9 mph; Oakland - 6 mph.
A6
-------
Diurnal variations are reflected in radiation inversions that
are more closely linked to surface or local changes. Average inversion
base heights for Oakland in the fall months are listed in Table A-2.5
A lowering of the inversion base from September to Novei her shows the
transition from a summer subsidence to a winter radiation type. Two early
morning and two early evening observations serve to point out that local
effects have much more influence on radiation inversion^ than on sub-
sidence inversions. Most radiation inversions have dissipated by 1600
PST, whereas subsidence inversions persist with only Alight diurnal
changes.
Surface temperatures of the Bay area in September are comparable
Io summer temperatures. Sites located near the Bay exhibit a much smaller
diurnal range than inland sites. Some heating of the air is evident as it
moves off the Pacific into the Bay.
c. Precipitation and Cloud Cover
Rainfall is greatly affected by local terrain. Heavier amounts
are found at high elevations or on slopes that, induce mechanical lifting.
In the Bay area, precipitation amounts along the western ridges exceed
amounts found to the east. The spatial pattern in Figure A-36 is probably
reliable, although the rainfall totals may show variation from year to
year. Precipitation producing mechanisms are synoptic in scale, with a
trend in the fall toward a gradual increase in precipitation from a summer
nanimum to a winter maximum. A similar trend of increasing cloud cover is
also evident from September to November. Table A-3G indicates that the
number of clear days decreases from August through November.
A-7
-------
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3
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a
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ft
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33
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0)
b" 3
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0)
5° 3
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fi
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SH £-1
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w
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Tj* t^ 00
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t* o m
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t£ "* CO
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CJD CN CC
05 N O
•H CD CM
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[>• f^ ^]
35 t^ CT1
O CK X
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O> X X
0) SH
X! ri CD
g o ja
0 X! g
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0! O ^
199?
TOOC MOT; 39
A-8
-------
FIGURE A-3 NORMAL ANNUAL TOTAL PRECIPITATION (Inches)
A9
-------
Table A-3
AVERAGE NUMBER OF CLEAR DAYS
Site August September October November December
Oakland 14 16 14 11 9
San Francisco 19 18 16 12 9
international
Airport
Cloud cover and precipitation show clearly that the late summer
and fall months typically have negligible rain and maximum sunshine.
Thus this is the period most conducive to the occurrence ol photo-
chemical smog.
d. Oxidant
1. Trends in the Bay Area
The occurrence of high oxidant levels in the Bay Area
varies considerably from year to year. The BAAPCD uses certain
Monitoring stations throughout the district where long-term historical
oxidant concentration data are available to serve as benchmark stations
for the district. These stations are San Francisco, San Leandro, San
Jose, Redwood City,Walnut Creek, and San Rafael. The number of days
where the high hourly average of 15 pphm or greater was reached at these
benchmark stations was 57 in 1965, 28 in 1966, 44 in 1967, 36 in 1968,
44 in 1969, 31 in 1970, and 19 in 1971. The randomness or grouping of
such days can be better correlated with meteorological factors than
with the variation in anthropogenic emissions.
Several trend studies have been made by the BAAPCD7'8 to
determine the oxidant concentration trends throughout the district from
1954 through 1972. Both emissions, reactive organics and NO , and
x
A-10
-------
meteorological factors must be considered in data analysis to provide
information on oxidant concentration trend within the control district.
Three factors are associated with photochemical smog
development:
(1) A supply of reactive organic compounds and nitrogen
oxides
(2) Extensive solar radiation to initiate the ph'>to-
chenieal reactions
(3) Poor ventilation to entrap the pollutants and prevent
their dilution.
In the first two trend studies, 1954 through 1962 and 19«v
through 1966, days with comparable meteorological conditions were compared
with similar days through the interval of interest. The maximum daily
temperature observed in the proximity of the measurement station was made
the criterion for comparable days in these early trend studies. The
results indicated that the general trend of annual oxidant concentration
was increasing from 1954 through 1965, In 1966 there was a marked
decrease in average oxidant concentration at all stations with an average
decrease of 25 percent. Prior to 1971, 1966 was the cleanest year of the
decade in terms of days when the oxidant exceeded 15 and 20 pphm levels.
In the later trend9 studies, vertical dilution data based on
"Aversion data from the NOAA radiosonde ascents at Oakland Airport were
included with temperature data to identify meteorologically similar days.
For the next four years, 1967 through 1970, the oxidant
levels stabilized at a lower level than had been observed jn 1954 through
1965 for meteorologically similar days.
A-ll
-------
In 1971 another significant decrease, exceeding 16 percent,
was observed. The actual decrease from 1970 to 1971 was 39 percent with
23 percent attributable to meteorological factors.
The broad climatological patterns of the ii.iv Area indicate
that the most severe oxiclant episodes will be encountered in the .sheltered
inland valleys, downwind of the urbanized central district. The oxidant
.season is usually regarded as April through October. However, in 1962
through 1967, over 16 percent of the days where oxidant concent rations
exceeded 10 pphm occurred in October. IJata analysi:- indicates that on
days of high oxidant concentrations, the oxidant concentration peak hour
iV'.morally occurs sequentially from northwest to southeast on both the
vest and east sides of the Bay. In general, oxidant concentration level;-:.
also oqcur in a similar pattern with the more southerly stations reporting
higher concentrations on a given day. The monitoring stations on the Ea:-t"
(jay perimeter generally report higher concentrations than those on the
Uest Bay perimeter. Sandberg's data indicate that the oxidant concen-
trations at the Day center often exceed those observed at the perimeter.
2. Discussion of San Jose State Ozone Soundings
Most studies of oxidants associated with air pollution have
concentrated on the meteorological and photochemical processes that affect
the production of ozone. Miller arid Ahrens ' ° report that the destruction
rate of oxidant in polluted air may be a much more significant factor in
determining the observed surface concentrations of oxidant. Miller made
ozone soundings at half-hour intervals on August 29, 1968 at two points
in the lower Santa Clara Valley with the following results:
(1) The ozone concentration increases sharply when the
temperature inversion breaks down between 0900 and
1000 PST and decreases rapidly after about 1800 PST,
as the inversion forms again.
A-12
-------
(2) Between 1000 PST and 1500-1600 PST, the ozone
concentration increases at all levels up to 2700 m.
These observations seem to indicate that ozone concentration is closely
linked to the degree of vertical mixing but this is 'n ,. sense contrary
to the idea of pollutant trapping. The mean destructi' ri rate \vitinn tin.
surface layer depends directly on the intensity of the. • Jdy i.rjxir,'.:; and
inversely on the depth of the mixing Layer; thus, the existence oi1 a
temperature inversion does not necessarily lead to high concentration
<'C oxidants. Miller also found that a btrutified layer ot higlur court u-
iration of ozone was formed just above the inversion, in air that has
he
-------
Miller hypothesis may, however, help explain the frequently observed
occurrence of the oxidant peak hour in San Francisco very early, often
before sunrise.
•!, Summary
Climatic characteristics that strongly favor the occurrence of
air pollution situations are typical of the San Francesco Bay area
during: the fall months. Weather patterns are conducive to restricted
transport and dispersion of pollutants. Winds are Light and variable,
often terrain channeled. Dispersion is limited by persistent and
frequent inversions. Precipitation washout poses no real threat. For
llie investigation of oxidants, the typical long over-water trajectory
nimmizes changes of contamination from other route sources. The
prevalence of clear, warm days indicates the availability of a radiation
climate necessary for the production of oxidants and photochemical smog.
A ii.aximum in air stagnation is paralled by a maximum of air pollutants,
as shown in Figure A-4 where Oakland visibility and wind circulation
are shown.
A-14
-------
50
40
D D
Percentage of time visibility 6 miles or
less at the Oakland Airport 1950-1955.
Percentage of time Bay Area circulation
typed as "light variable", 1952-1955.
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEPT
OCT
NOV
DEC
FIGURE A-4 VISIBILITY AT THE OAKLAND AIRPORT COMPARED WITH
LIGHT WIND PATTERNS IN THE SAN FRANCISCO BAY AREA
A-15
-------
REFERENCES
1. Smalley, C. L., "A Survey of Air Flow Patterns in the San
Francisco Bay Area," Preliminary Report, U.S. V.cathcr Bureau,
San Francisco International Airport, 1 March 1957,
unpublished, 110 pp.
. Patton, C. P., "Climatology of Summer Fogs in the San Francisco
Bay Area," University of California Publications ju Geography,
University of California Press, Berkeley, _10 (3): 113-200, 1956.
. Stanford Research Institute, "The Use of Meteorological Data in
Large Scale Air Pollution Surveys," Bureau of Air Sanitation,
State of California, Berkeley, 1958, 110 pp.
. Ahrens, D. and A. Miller, "Variations of the Temperature
Inversion over the San Francisco Bay Area," Department of
Meteorology, San Jose State College, February 1969, 51 pp.
Holzworth, G.C., G. B. Bell, and G. A. DeMarrais, "Temperature
Inversion Summaries of U.S. Weather Bureau Radiosonde Observations
in California," U.S. Weather Bureau and State of California,
Berkeley, California, 1963, 75 pp.
i. Environmental Science Service Administration, "climate of the
States, Climate of California, Clinia tography of the United
States, No. 60-4," U.S. Department of Commerce, Washington, D.C.,
June 1970, 57 pp.
. Trend of Oxidant Concentrations in the San Francisco Bay Region,
1959-1962.
. Supplemental Study of Oxidant Concentration Trends in Bay Area Air
Pollution Control District Information District.
>. \ Study of Oxidant Concentration Trends Information Bulletin 1-7-72.
'. Miller, A., and C. D. Ahrens, "Ozone Within and Below the West Coast
Temperature Inversion," Department of Meteorology, San Jose State
College, March, 1969, 74 pp.
A-16
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing,!
i 1 REPORT NO.
I EPA-650/4-74-037
4. TITLE AND SUBTITLE"
| Atmospheric Measurement of Photochemical Smog
Reactions - A Preliminary Analysis
3 RECIPIENT'S ACCESSIOtfNO.
PB 210-1*22
5 REPORT DATE
February 1972
6. PERFORMING ORGANIZATION CODE
P
i
7 AlifHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
B.C. Robbins, L.A. Cavanagh
9 PERFORMING ORGANIZATION NAME AND ADDRESS
Stanford Research Institute
Menlo Park, Caligornia 9^025
12 SPONSORING AGENCY NAME AND ADDRESS
Coordinating Research Council, Inc., 30 Rockefeller
Plaza, New York, NY and Environmental Protection
Agency, Research Triangle Park, WC 27711
SRI Project 1035
10. PROGRAM ELEMENT NO.
11 CONTRACT/KSKBGOtKK
68-02-0010
Ci;C!-APKAC-CAPA-7-7Q-12
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
Releasable to the public June 1972
16. ABSTRACT
This research study was a brief feasibility study and field measurement program to
determine whether the San Francisco Bay Area might provide meteorological and
photochemical smog patterns that were especially conducive to field research on smog
reaction processes. It was concluded from both climatological and field oxiiant
sampling that this was the situation if atmospheric data could be gathered o^er
the waters of the Bay, particularly east and south of San Francisco.
!
1 7.
KEY WORDS AND DOCUMENT ANALYSIS
a DESCRIPTORS
1 Hydrocarbons
Ox ia an Is
Ozone
> i-ro '.yacyl Nitrates.
i Aldenydes
Photochemical
C"T'OP
Meteorological
Climatological
Air Pollution
( PAN )
13 DISTRIBUTION STATEMENT
Unlimited
b. IDENTIFIERS/OPEN ENDED TERMS
San Francisco Bay,
California
19 SECURITY CLASS (This Report)
Unclassified
20. SECURITY CLASS (This page)
Unclassified
c. COSATI Held/Group
7C
UA
21. NO. OF PAGES .
60
22. PRICE
fc'PA Form 2220-1 (9-73)
A-17
------- |