&EPA
United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 2771 1
EPA 600 4 78 02?
May 1978
Research and Development
Meteorological
Conditions During
a Sulfate Episode
in Southern
California PROPERTY OE
DIVISION
OF
METEOROLOGY
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2 Environmental Protection Technology
3. Ecological Research
4 Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7 Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/4-78-022
May 1978
METEOROLOGICAL CONDITIONS DURING A SULFATE
EPISODE IN SOUTHERN CALIFORNIA
by
Gerard A. DeMarrais
Meteorology and Assessment Division
Environmental Sciences Research Laboratory
Research Triangle Park, N.C. 27711
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, N.C. 27711
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DISCLAIMER
This report has been reviewed by the Office of Research and Development,
U.S. Environmental Protection Agency, and approved for publication. Mention
of trade names or commercial products does not constitute endorsement or
recommendation for use.
Mr. DeMarrais is a meteorologist in the Meteorology and Assessment
Division, Environmental Sciences Research Laboratory, Environmental Research
Center, Research Triangle Park, N.C. 27711. He is on assignment from the
National Oceanic and Atmospheric Administration, U.S. Department of Commerce.
n
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ABSTRACT
Meteorological conditions are characterized for a prolonged period in
which an air mass contained high concentrations of sulfate pollutants. The
period occurred in the Los Angeles area from February 26 to March 5, 1975.
In addition, the episode occurred during the off-season and virtually coincided
with an oxidant episode. The meteorological conditions associated with both
episodes were (a) slow moving air; (b) abundant sunshine; (c) elevated
temperatures; (d) limited vertical mixing at the coast and inland vertical
mixing varying from negligible at night to relatively deep in the daytime;
(e) relatively very poor visibilities due to smoke, haze, and fog; and (f) high
relative humidities at all times at the coast and at night at inland locations,
but very low relative humidities in the daytime over inland locations. The
ozone episode ended with the onset of strong winds and rain, while the sulfate
episode persisted into the windy and wet period. Differences in the spatial
patterns in sulfate and oxidant concentrations were observed and these are
attributed to differences in the relative humidities at coastal and inland
locations.
Identification of these meteorological conditions provides information
for air pollution investigators to use in attempting to forecast future sulfate
episodes.
iii
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CONTENTS
Abstract iii
Figures vi
Table , vi1
1. Introduction ..;... 1
2. Conclusions 3
3. Background and Methods 5
Sulfates, reactions producing sulfates, and measuring
sulfate concentrations 5
Ozone data and measuring techniques 6
Meteorological conditions associated with high concentra-
tions of ozone and sulfates 7
Meteorological resources 8
4. Results 10
Oxidant concentrations 10
Sulfate data 10
Surface weather observations and local rawinsonde data. . 12
Synoptic weather situation 14
5. Summary 16
References 18-20
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FIGURES
Number Page
1. Sulfate monitoring stations 21
2. Oxidant monitoring stations 22
3. Maximum hourly oxidant concentrations (pphm), February 25, 1975. 23
4. Maximum hourly oxidant concentrations (pphm), February 28, 1975. 24
5. Maximum hourly oxidant concentrations (pphm) March 3, 1975 ... 25
q
6a. Sulfate concentrations (yg/m } February 25, 1975 26
6b. Sulfate concentrations (yg/m } Febeuary 26, 1975 26
3
7a. Sulfate concentrations (yg/m ) February 27, 1975 27
o
7b. Sulfate concentrations (yg/m ) February 28, 1975 27
8a. Sulfate concentrations (yg/m ) March 1, 1975 28
8b. Sulfate concentrations (yg/m ) March 2, 1975 28
9a. Sulfate concentrations (yg/m3) March 3, 1975 29
9b. Sulfate concentrations (yg/mu) March 4, 1975 29
10. Sulfate concentrations (yg/m ) March 5, 1975
30
11. Comparison of sulfate average concentrations during February 26
through March 5, 1977 with average concentration on all other
days in the same month , 31
12. 500 millibar height contours at 0700 E.S.T., March 1, 1975 32
(Height in feet above mean sea level)
13. Surface map showing isobars, high, low, and fronts, March 1,
1975, 0700 E.S.T 33
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TABLE
Number Page
1 Meteorology during Sulfate Episode 34-35
vii
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SECTION 1
INTRODUCTION
For several decades, sulfates have been recognized as air pollutants
1 2
hazardous to human health ' . In the Meuse Valley (Belgium) fog of
December 1-5, 1930 sulfuric acid in the air was associated with the resulting
'1 2
health catastrophe . In 1955 Hemeon reported that the disasterous smogs of
Donora, Pennsylvania of October 27-31, 1948 and London, Great Britian of
December 5-9, 1952 were rich in sulfates and suggested that sulfate salts may
have been the primary substances responsible for respiratory problems during
the episodes. In the absence of similar calamities since those occurrences,
only slight attention was given to the sulfate problem until the recent CHESS
(Community Health and Environmental Surveillance System) program released its
3
preliminary report . Subsequent to that report, the U.S. Environmental
Protection Agency (EPA) published two documents ' stating all known informa-
tion about sul fates and presenting a strategy for investigating the sulfate
problem. Both documents noted the need for a greater knowledge and understanding
of the meteorology associated with high concentrations of sulfates. The need
for this knowledge is particularly acute because of the sampling technique for
sulfat.es. Whereas sampling techniques for most pollutants show the existence
of a problem (high concentrations) in real time, that for sulfat.es does not
show the existence of a problem until hours and more frequently days after it
occurred. With the benefit of the knowledge being sought, one could expect a
sulfate problem when the right meteorological conditions occurred (or were
predicted) and act accordingly (for example, a control agency could sample for
shorter periods, use more sophisticated analyses and advise those susceptible
to bad reactions to high sulfate concentrations to stay indoors).
Recognizing this need, the investigation reported in this paper was
initiated with the purpose of finding a prolonged period when high sulfate
concentrations were recorded and describing in detail the meteorology associated
with the episode. Since it had been reported that high sulfate concentrations
1
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were likely to develop in the presence of high ozone concentrations, a second
objective of this investigation was to analyze the data for a period when the
sulfate and ozone concentrations were high.
Coal- and oil-burning power plants emit large quantities of sulfur dioxide
(S0?) to the atmosphere; in the United States these plants are responsible for
^ c
more than 75 percent of the man-made release of sulfur . In the process of being
transported downwind by the flow aloft, the SO, has time to be oxidized. Long-
range transport, that is, of the order of several hundred kilometers (km) or
more, combining with the abundant emissions and oxidation cause high sulfate
concentrations to be a widespread phenomenon. In addition, the lonq-ranae
transport frequently causes the high concentrations to be displaced many km
from the sources of the S02 and makes it difficult to associate sulfate
concentrations with suspected source areas. In order to minimize- the effects
associated with long-range transport and more readily detect other meteorological
conditions associated with high sulfate concentrations, data from the western
part of the Los Angeles Basin were sought. The major axis of this area of
concern is less than 100 km in length and the area has no sources to the west
(prevailing winds are from that direction). In an earlier investigation the
author analyzed meteorological and photochemical oxidant (smog) data from this
general area during a period when there was abundant sunshine and high concen-
tractions of ozone (February 25-March 4, 1975) so sulfate data were obtained
for that period. Preliminary examination of these sulfate data indicated the
concentrations to be relatively high, so the period was selected for detailed
analyses.
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SECTION 2
CONCLUSIONS
On the basis of the analyses of the February 25 to March 5, 1975 sulfate,
ozone, and meteorological data for southern California, the following con-
clusions are drawn:
1. There was an off-season episode of 8 days with high sulfate concen-
centrations that practically coincided with an ozone episode; there was a
1-day lag in the beginning and ending of the sulfate episode.
2. The meteorological conditions associated with this sulfate episode
were: a) slow-moving air at the surface and aloft; b) abundant sunshine;
c) elevated temperatures for the time of year; d) limited vertical mixing
at the coast and inland vertical mixing varying from negligible at night
to relatively deep in the daytime; e) relatively very poor visibilities
due to smoke, haze, and fog; and f) high relative humidities (a condition
conducive to the formation of sulfate when S0? is present) at all times
at the coast, and at night at inland locations, but very low relative
humidities in the daytime over inland areas.
3. The ozone episode ended with the onset of strong winds and rain,
whereas the sulfate episode continued into the windy and wet period.
4. The sulfate concentrations did not show the same spatial pattern as
the ozone concentrations. Whereas there was a marked increase in ozone
concentrations from the coast to inland locations, primarily due to
downwind advection and the vertical mixing downward of ozone from aloft
during the daytime, the high sulfate concentrations appeared at the
coast as well as inland. The higher relative humidities at the coast,
particularly in the daytime, allowed for greater sulfate formation in
that area and on occasions this formation process was sufficient to
produce local concentrations greater than those observed in downwind
(due to advection and downward vertical mixing of sulfates) areas.
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5. Although some stations had sulfate concentrations consistently lower
than other stations and some stations had consistently high concentrations,
all stations showed the same relative increases in concentrations (about
fourfold to sevenfold above the February-March average). This indicated
that the same unfavorable conditions prevailed throughout the area and that
location with regard to sources had little effect.
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SECTION 3
BACKGROUND AND METHODS
SULFATES, REACTIONS PRODUCING SULFATES, AND MEASURING SULFATE CONCENTRATIONS
Most sulfur in the atmosphere, land surface, and water exists as the
hexavalent oxidized sulfate ion (SO. ) in such diverse forms as si'lfuric
acid, ammonium bisulfate, calcium sulfate (the major component of gypsum),
magnesium sulfate (epsom salts), sodium and potassium sulfates (in seawater),
and other metal salts, such as copper, nickel, iron, lead, and zinc sulfates .
On a global scale, natural sources contribute about two thirds of the
sulfur compounds in the atmosphere by weight and human activities contribute
the remainder. In the continental United States, probably 90 percent of the
atmospheric sulfur is the result of anthropogenic emissions in the form of
SO,, . Most of the hydrogen sulfide and SO,, is oxidized to the sulfate form
within a few days. This oxidation combined with long-range transport allows
Q
the sulfate receptors to be located hundreds of km from the sources .
g
According to the California Air Resources Board , there are several
important mechanisms contributing to the conversion of S0? to sulfuric acid and
sulfate salts. These mechanisms are:
1. a nonchemical process that occurs when SO,, dissolves in aqueous drop-
lets in the atmosphere, forming sulfite ion, which is subsequently oxidized
to sulfate;
2. a direct photochemical process in which S02 absorbs ultraviolet (UV)
radiation and subsequently reacts with molecular oxygen;
3. an indirect photochemical process in which gaseous SO,, is oxidized by
an unstable compound of photochemically produced ozone and olefinic hydro-
carbons, or other reactive oxidizing species; and
-------
4. A process that may occur when SCL is absorbed on the surface of sus-
pended solid particles, such as soot and metal oxides emitted by com-
bustion sources.
Most of the man-made sulfate problem is believed to be associated with
S02 emitted by large power plants. In the Los Angeles area there are 15 plants
with capacities greater than 25 megawatts, and these plants are concentrated
Q
in the western portion of the Basin . The total capacity of these plants was
10,824 megawatts and individual capacities ranged from 50 to 1982 megawatts.
In the Basin S09 is readily converted to sulfate and the residence time cf
9 10
SOp is generally longer than in the airsheds of other cities . Cox and Penkett
have shown that S09 is oxidized at appreciable rates (3 percent per hour) in
11
the dark in ozone-olefin-air mixtures. Penkett has demonstrated in experiments
that oxidation of S0? at 7 ppb in the presence of water droplets and ozone at
5 pphm can be as large as 12.6 percent per hour. Thus foggy or cloudy air with
photochemical oxidant could be a major contributor to a SO. -forming mechanism
in the Basin, particularly near the coast.
The sulfate data evaluated in this report were supplied by the CHESS
program. CHESS operates seven sulfate monitoring stations in the western part
of southern California. The names and locations of the stations are shown in
Figure 1. The sulfate measurement is.made from a small strip of filter on
which suspended particulate is collected in a high volume air sampler. Each
sampling period is approximately 24 hours and the filters are changed around
11 a.m. each day (all times are Pacific Standard Time). The filter strip is
extracted with water and a portion of the aqueous extract is analyzed for
sulfate by the methyl thymol blue method modified for use in the Auto-Analyzer.
At the present time there is no National Ambient Air Quality Standard
(NAAQS) for sulfates. However, best judgment sulfate levels tentatively
associated with adverse health effects in the preliminary epidemiological
studies were as low as 6 to 10 yg/m (24-hour average) . In this report
concentrations greater than 10 yg/m are labeled high.
OZONE DATA AND MEASURING TECHNIQUES
The ozone monitoring network in southern California is extensive. Ozone
-------
data were obtained for the seven-county area for the stations whose names and
locations are shown in Figure 2. The concentrations at these stations are
determined by instruments utilizing either non-dispersive ultraviolet absorp-
tion or chemiluminescence, both physicochemical processes. Observations are
recorded every hour and a concentration is labeled high in this report whenever
3 12
an hourly concentration exceeds the NAAQS of 160 yg/m or 8 pphm .
METEOROLOGICAL CONDITIONS ASSOCIATED WITH HIGH CONCENTRATIONS OF OZONE AND
SULFATES
There is considerable documentation on the meteorology that correlates
with high oxidant.concentrations, particularly for the southern California
area. In 1950 Middleton et al. reported that high ozone concentrations
occurred with weak winds and stagnant air. Other early comprehensive investi-
14-17
gaticns related variations in concentrations to variations in intensity
and duration of solar radiation, surface temperature, the depth of the polluted
layer (the top coincided with the base of the subsidence inversion), and wind
speed and direction. Following the report that winds aloft in the Los Angeles
area are important in transporting "second-hand" ozone to unsuspecting downwind
18
areas , investigators examined the three-dimensional air movements and trans-
19_?2
port in the 200-km long Basin. Evidence confirms that high ozone concentra-
tions are frequently in the air aloft, even within the subsidence layer, and
that these ozone-laden layers move with the winds aloft. Eventually some of the
ozone is brought down to the surface in daytime mixing. High concentrations
23 24
of ozone are generally restricted to the period of May through October ' .
25
A recent work explained in detail the two combinations of phenomena
that may cause high ozone concentrations. The first combination involves the
downwind advection, by surface winds, of air laden with ozone precursors. This
air is photochemically converted to ozone through solar radiation. The second
combination involves vertical mixing upward of ozone and ozone precursors during
one day, movement with winds aloft during that evening and periods thereafter
and the eventual downward movement of ozone, through vertical mixing, to the
ground. The diurnal variation in ground level ozone concentrations due to
the two different combinations of phenomena are very similar, so it is diffi-
cult to separate the effects of each. Through each combination the typical
concentrations are low at night, increase rapidly a few hours after sunrise,
-------
peak In the early afternoon, and thereafter decrease. Since the polluted layers
are moved with the winds, the concentrations in downwind areas can be partic-
ularly high when the directions of the winds at the surface and aloft coincide.
In the Los Angeles Basin this is most likely to occur when there are west winds
and in this situation the eastern sections of the Basin do have the highest
concentrations.'
As previously noted, direct and indirect photochemical processes are
important in the production of sulfates, so intense solar radiation and abundant
sunshine are conducive to high concentrations. When there is good vertical
motion in the daytime, which carries ozone aloft in updrafts, S09 aloft is
10
oxidized at appreciable rates at night in the presence of this ozone . The
rate of oxidation of S09 to sulfate is dependent on relative humidity . In
26
a laboratory study no oxidation was detected when the relative humidity was
less than 70 percent, whereas at higher humidities the oxidation rates were
considerable (possibly because catalyst particles changed from solid form to
solution drop form). Sulfate concentrations also vary with rainfall. Early
27
investigators found that the sulfate concentration of rainwater decreased
with an increased rate of rainfall; they suggested that there was a limited
quantity of sulfate in the lower atmosphere which is removed in each period of
28
precipitation. A more recent study reported that the sulfate concentration
usually declined sharply as a result of rainfall and increased rapidly after
the rainfall ended. Sulfate concentrations in urban areas tend to peak in the
third quarter of the year (July, August, September), but occasionally the
29
peak occurs in the second quarter of the year .
METEOROLOGICAL RESOURCES
30 31
The surface meteorological data ' discussed in this report are for the
following stations: Los Angeles International Airport, Los Angeles Civic
Center, and Ontario Airport. The meteorological parameters summarized are
temperatures, wind, relative humidities, percent of possible sunshine, sky
conditions, and weather. The meteorological data aloft are the winds and the
heights and temperatures of the bases and tops of inversions. These above-the-
32
surface data are summarized from special records of the National Weather
Service (NWS) in Los Angeles.
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33
Discussions of the synoptic conditions are based on the Daily Weather Maps
32
and special summaries of the NWS. The Daily Weather Maps are used to locate
high and low pressure centers and fronts. The Daily Weather Maps include two
pertinent maps for each day based on 4 a.m. observations; one map is for the
surface and the other for 500 mb (about 5500 m above the surface).
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SECTION 4
RESULTS
OXIDANT CONCENTRATIONS
The oxidant investigation is dicussed in detail in an earlier report ,
so only the highlights and representative data are presented here. The maxi-
mum hourly concentrations recorded at the stations for February 25, Febru-
ary 28, and March 3 (the beginning, middle, and near the end of the episode)
are shown in Figures 3 through 5. The obvious features of these 3 days are
a) violations of the hourly NAAQS for ozone occurred throughout the area;
and b) a marked increase in concentrations from the coast to inland locations
occurred with maximum concentrations between 30 and 70 km from the coast.
These 3 days are representative in that many stations had concentrations
that were initially just a little greater than the standard, then were
considerably greater than the standard on the second to the sixth day, and
finally, slowly decreased on the seventh and eighth day. There were no NAAQS
violations on March 5, as the concentrations averaged 3 pphm.
It should be noted that the sites having consistently higher concentra-
tions were Temple City, Upland, and Fontana. The sulfate stations of Glen-
dora and West Covina are in the same general area (see Figure 1).
SULFATE DATA
The 24-hour concentrations of sulfate for the period February 25 through
March 5 are shown in Figures 6 to 10. The March 5 data are included because
concentrations remained high through that day; the concentrations on March 6
were only one-eighth of those on March 5, indicating that March 5 was the last
day of the episode.
The data for February 25 (Figure 6a) are interesting because the con-
centrations were low. Since most of these sulfate data were gathered the
first day (from 11 a.m. to midnight) that the area had high oxidant
10
-------
concentrations (see Figure 3), there was a difference in the timing of episodes
for each pollutant.
On February 26 (Figure 6b) only Thousand Oaks in the north and Vista in
3
the south recorded concentrations less than 10 yg/m . Although the inland
station at West Covina had a considerably higher concentration than the
Santa Monica station at the coast, the Glendora site, which is close to West
Covina, did not. Garden Grove, near the coast, had a higher concentration
than the further inland sites of Anaheim and Glendora.
*\
On February 27 (Figure 7a) all concentrations exceeded 10 yg/m and the
sites to the north and south again had concentrations lower than those in
mere densely populated sections. Again the two highest concentrations were
recorded at West Covina and Garden Grove.
On February 28 (Figure 7b) all stations had sulfate concentrations con-
3
siderably in excess of 10 yg/m with the lowest concentrations occuring at Vista
and Glendora. The highest concentration occurred at Santa Monica. Inland,
Garden Grove, Anaheim, and West Covina had practically identical concentrations.
3
On March 1 (Figure 8a) only Vista had a concentration less than 35 yg/m .
West Covina had the highest and Santa Monica the next highest concentration.
On March 2 (Figure 8b) the concentrations were considerably lower than
they had been on the preceding day at all stations except Vista. All stations
still had concentrations well above 10 yg/m with West Covina and Anaheim
having the highest and Thousand Oaks the lowest concentrations.
Or March 3 (Figure 9a) the concentrations at each station were considerably
lower than on March 2. Thousand Oaks and Vista had concentrations less than
10 yg/m while West Covina and Santa Monica had the highest concentrations.
On March 4 (Figure 9b) the concentration at each station was higher than
it had been on March 3. Santa Monica had the highest and West Covina the next
highest concentration, while Vista and Thousand Oaks had the lowest concentra-
tions.
On March 5 (Figure 10) the concentrations were generally a little less
than on March 4 and all exceeded 10 pg/m . The highest concentrations were at
Santa Monica and Glendora and the lowest was at Garden Grove.
11
-------
In order to indicate the excess concentrations occurring during this sul-
fate episode, the average daily concentrations for each station for February 26
through March 5 were compared to the averages for February and March exclusive
of the episode days. The result is shown in Figure 11; the concentrations were
four to seven times higher during the episode than they were during the non-
episode.
SURFACE WEATHER OBSERVATIONS AND LOCAL RAWINSONDE DATA
The pertinent meteorology observed at the three local weather stations is
shown in Table 1. The maximum temperatures compared to normals reveal whether
relatively warm temperatures prevailed and station comparisons show where the
hotter locations existed. Warmer locations tend to have greater daytime
vertical mixing. The diurnal range of temperature (this day's maximum minus
the next day's minimum) shows where radiation inversions likely formed at night;
when the range is 14°C or greater at a location in southern California, a
34
nocturnal surface-based inversion usually formed . The winds indicate whether
stagnation, as shown by winds of variable directions or low speeds, persisted.
The sky condition (clouds reduce the amount of solar radiation reaching the
surface) and the percent of possible sunshine give an indication of the intensity
of solar radiation. Visibility measurements may be indicative of the relative
sulfate concentration since sulfates have been found to be major contributors to
or OC op
reductions in visual range ' ; sul fates are generally subrr.icron aerosols
37
in the size range associated with reductions in visibility . Obscurring
phenomena, such as haze and fog, are optical evidence of pollution; when the
haze and fog persist, stagnation is indicated. Fog and high relative humidity
values are conducive to sulfate formation '
The maximum temperatures at the three stations (Table 1) reveal that the
period averaged slightly warmer than normal at the coast, while inland it was
3°C to 6°C warmer than average. However, these temperatures were about 6°C to
8°C colder than those of July (about the middle of the season when high ozone
and sulfate concentrations are usually observed). The maximum temperatures
show the usual condition of marked increases from the coast inland. Los
Angeles Airport maxima were nearly constant and averaged 16°C while at Ontario
Airport the maxima ranged from 21°C to 28°C. These higher temperatures inland
12
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indicate that vertical mixing to greater heights occurred inland. The comoari-
32
son of the Los Angeles Airport and El Monte midday sounding data (limited to
Monday through Friday) also show that vertical mixing to greater heights
occurred inland.
The maximum-minimum temperature ranges indicate that inland locations had
nocturnal inversions almost every night while these surface-based inversions
were absent at the coast; this finding was supported by a comparison of the
32
Los Angeles Airport and El Monte morning sounding data . The inland locations
did have periods of warming and cooling with relatively warm days occurring on
February 28 and March 3.
The winds were generally light and variable in direction except during
the third quarter of the day when tnere was a Seabreeze with a general
v/est-to-east flow.
The sunshine record for the Civic Center reveals that there was about
80 percent of the possible sunshine on the first 6 days and then markedly
less on March 4 and 5.
The sky conditions and the temperatures at Ontario indicate that the
inland locations had greater amounts of sunshine than the coastal locations.
The visibilities were markedly low. During this 8-day period
visibilities seldom exceeded 16 km (16 km or 10 miles is the California
visibility standard for periods when the relative humidity is less than 70
percent) until the last day at Los Angeles Airport, yet there were only 2
other days in the months of February and March when this visibility was not
exceeded. Usually during this episode the visibilities were lower at Ontario
than at Los Angeles Airport.
Smoke, haze, or fog were consistently present at the Ontario site and at
Los Angeles Airport there were only a few occasions when they were not observed.
It should be noted that when low visibilities are recorded due to fog, the
presence of smoke and haze are frequently ignored. The smoke, haze, and
fog at Ontario Airport were so dense throughout this period that the sky was
partially obscured each day. '
The relative humidities show an interesting contrast. Not only did Los
13
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Angeles Airport have consistently higher relative humidities, it also never
had an observation when the California standard for visibility could be
evaluated; all humidities were 70 percent or greater. The contrast in the third
quarter of the day is particularly noteworthy; at the coast the afternoon
humidities were 75 percent or greater while at Ontario, prior to March 4, they
were 30 percent or less.
The overall indication is that the sulfate episode was not associated
with particularly high temperatures. The concentrations did increase with the
first warming inland (February 28), then decreased with the cooling (March 2),
but did not increase with the second warming (March 3). The air did move slowly
over the area. Inland there was limited nocturnal vertical mixing and relatively
deep daytime mixing, while near the coast this marked diurnal change in mixing
did not occur. This contrast in vertical mixing appeared to contribute to the
gradient in ozone concentrations from inland to the coast , but did not appear
to have the same effect on sulfate concentrations. The drastically reduced
visibilities combined with the presence of smoke and haze throughout the period
indicated that an aerosol in the size range of sulfates was constantly present
in fairly high concentrations. The relative humidities were always conducive to
sulfate formation at the coast and inland they favored formation throughout most
of the nighttime hours. This contrast in daytime relative humidites may in part
account for the differences in the spatial patterns of oxidant and sulfate
concentrations. Whereas there was a marked increase in concentrations of ozone
moving inland, due to downwind transport and mixing with ozone from aloft ,
there was no consistent pattern of marked inland increases in sulfate concen-
trations, probably because the moist air near the coast was more conducive
to sulfate formation; the greater production of sulfate in the coastal areas
at times compensated for the effects due to downwind transport and vertical
mixing of sulfates. The presence of fog, particularly at night, was a further
indication that the conditions for sulfate formation were excellent.
SYNOPTIC WEATHER SITUATION
The 500-mb map for the western United States for March 1, 1975, the day with
the highest sulfate concentrations (see Figure 8a), is shown in Figure 12. The
height gradient on this day was a little tighter than it was on other days
between February 26 and March 3, but the weak ridge that dominated the maps for
14
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those days is obvious. This condition ended on March 4 when cool, moist air
moved into the area with an upper level low pressure area. The low was still
the dominant feature on March 5. Figure 13, the surface map for March 1, is
typical of the maps for the period of February 26 to March 3. The weak pressure
gradient over southern California allowed for a weak onshore flow. Cn March 4
there was a moderate onshore gradient; rain fell on some areas of southern
California. On March 5 the winds were relatively strong and from the southeast,
and the rainfall was extensive and relatively heavy over southern California.
Both the surface and the 500-mb data indicate that the episode started
and intensified with slow-moving air. The high sulfate concentrations did not
end with the light rainfall of the 4th nor the heavy rainfall of the 5th;
27
there was no support for the finding of an earlier study that there was a
limited amount of sulfate that would be readily washed out of the lower
atmosphere. It could not be determined whether the concentrations decreased
28
with the rainfall and then increased, as was found in another earlier study ,
because the sulfate measurements reported here are 24-hour averages.
15
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SECTION 5
SUMMARY
In the investigation of the correlations of high ozone concentrations
and high sulfate concentrations and meteorology, the following were determined:
1. An 8-day period with high sulfate concentrations (episode) in southern
California practically coincided with an 8-day period with high ozone
concentrations.
2. The near-simultaneous occurrence of the episodes for the two pollutants
occurred in a season when the concentrations of each pollutant are usually
low.
3. The start and termination of the sulfate episode lagged at the begin-
ning and ending of the ozone episode by one day.
4. The meteorological conditions associated with the beginnings and inten-
sifications of the two episodes were: 1) slow-moving air at the surface and
aloft; 2) abundant sunshine; 3) elevated temperatures for the time of year;
4) limited vertical mixing at the coast and vertical mixing varying from
negligible at night to relatively deep in the daytime at inland sites;
5) relatively very poor visibilities due to smoke, haze, and fog; and
6) high relative humidities (a condition conducive to sulfate formation
when SCL is present) at all times in coastal areas and at night in inland
areas, but very low relative humidities in the daytime at inland sites.
5. The ozone episode terminated with the onset of strong winds and rain,
but the sulfate episode persisted into the relatively windy and wet period.
6. The ozone concentrations showed a spatial pattern with inland (downwind)
locations having higher concentrations than the coastal areas, while the
sulfate concentrations did not show a similar pattern; the three stations
having the highest sulfate concentrations were one inland (West Covina),
16
-------
one near the coast (Garden Grove), and one at the coast (Santa Monica).
The ozone concentrations also showed a diurnal pattern with hourly peaks
occurring in the afternoon and low values occurring at night. Because the
coastal areas have few upwind sources, the daytime winds advect in rela-
tively clean air. Conversely, air advected into inland areas is laden with
ozone precursors. Due to the differences in the contents of the advected
air, inland areas have higher peak concentrations. Differences in the vert-
ical mixing and ozone concentrations aloft, between coastal and inland
areas, are also partially responsible for the spatial difference in the
peak ozone concentrations. Sulfates, on the other hand, are monitored
every 24 hours, can be formed from the oxidation of SCL throughout the day,
and are more likely to form where relative humidities are high. During the
sulfate episode the humidities were always high at the coast and very low
inland during the daytime. On some days the sulfate formation processes at
and near the coast must be sufficient to compensate for the effects of the
downwind transport of high sulfate concentrations to inland locations.
7. The sulfate monitoring stations which were located the greatest dis-
tances from heavily populated and industrialized areas, Thousand Oaks and
Vista, generally had the lowest concentrations while the sites with the
highest concentrations were close to or downwind of the source area.
8. The relative increases in concentration during this episode, ranging
from four to seven times greater than the February-March average, were
about as great at the less polluted sites as they were at the sites with
the highest concentrations; the locations of receptors with regard to
sources had little effect on the relative intensity of the episode.
9. The markedly low visibilities together with the observations of
smoke and haze during the period indicate that an aerosol in the size
range of sulfates was present much of the time; there was nc other period
in February or March when similar conditions prevailed.
17
-------
REFERENCES
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Sur les causes des accidents dans la vallee de la Meuse, lors des
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Arch. Ind. Health, 11:397-402, 1955.
3. Human Studies Laboratory. Health Consequences of Sulfur Oxides: A Report
from CHESS, 1970-1971. EPA-650/1-74-004, U.S. Environmental Protection
Agency, Research Triangle Park, North Carolina, 1974. 368 pp.
4. Strategies and Air Standards Division. Position Paper on Regulation of
Atmospheric Sulfates. EPA-450/2-75-007, U.S Environmental Protection
Agency, Research Triangle Park, North Carolina, 1975. 87 pp.
5. Office of Research and Development. Statement of Sulfates Research Approach.
EPA-600/8-77-004. U.S. Environmental Protection Agency, Washington, D.C.,
1977. 43 pp.
6. Greeley, R. S., R. P. Quellette, J. T. Stone, and S. Mil cox. Sulfates and
the Environment-A Review. The MITRE Corporation, McLean, Virginia, 1975.
131 pp.
7. DeMarrais, G. A. A Prolonged, Large Scale, Off-Season Photochemical Oxi-
dant Episode. EPA-600/4-78-014, U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina, 1978. 32 p.
8. Altshuller, A. P. Atmospheric Sulfur Dioxide and Sulfate. Environmental
Science and Technology, 7(8):709-712, 1973.
9. Air Resources Board. An Assessment of the Aerosol-Visibility Problem in
the South Coast Air Basin. State of California (Staff Report 75-20-3),
Sacramento, California, October 28, 1975. 72 pp.
10. Cox, R. A., and S. A. Penkett. Photo-Oxidation of S0? in the Atmosphere.
J. Chem. Soc., Faraday Soc., 68:1735, 1972. *
11. Penkett, S. A. Oxidation of SO, and Other Atmospheric Bases by Ozone in
Aqueous Solution. Nature (Physical Science), 240:105-106, December 4,
1972.
12. National Air Pollution Control Administration. Air Quality Criteria for
Photochemical Oxidants. AP-63. U.S. Department of Health, Education,
and Welfare, Washington, D.C., 1975. 178 pp.
18
-------
13. Middleton, J. T., J. B. Kendrick, and H. C. Schwalm. Injury to Herbaceous
Plants by Smog or Air Pollution. Plant Disease Reporter, 34(9): 245-252,
1950.
14. Neiburger, M., and J. Edinger. Meteorology of the Los Angeles Basin.
Report No. 1, Southern California Air Pollution Foundation, Los Angeles,
California, 1954. 97 pp.
15. Renzetti, N. A., Editor. An Aerometric Survey of the Los Angeles Basin,
August-November 1954. Report No. 9, Air Pollution Foundation, Los Angeles,
California, 1955. 334 pp.
16; Hitchcock, L. B., W. L. Faith, M. Neiburger, N. A. Renzetti, and L. H.
Rogers. Air Pollution Situation in Los Angeles-An Aerometric Survey. In:
Proceedings of the Third National Air Pollution Symposium, Pasadena,
California, 1955. pp 12-23.
17. Rogers, L. H. Report on Photochemical Smog. J. of Chem. Education,
35(6):30-313, 1958.
18. Lea, D. A. Vertical Ozone Distribution in the Lower Troposphere Near
an Urban Complex. J. Appl. Meteorol., 7:252-267, 1968.
19. Edinger, J. 6. Vertical Distribution of Photochemical Smog in Los Angeles
Basin. Environ. Sci. Techno!., 3:247-252, 1973.
20. Gloria, H. R., G. Bradburn, R. F. Reinisch, J. N. Pitts, Jr., J. V. Behar,
and L. Zafonte. Airborne Surveys of Major Air Basins in California. J. Air
Poll. Control Assoc., 24(7): 645-652, 1974.
21. Blumenthal, D. L., L. A. Farrow, and T. A. Weber. The Effects of Variations
in Bulk Meteorological Parameters on Ozone Concentrations. In: Symposium
on Atmospheric Diffusion and Air Pollution (Preprint Volume), Amer.
Meteorol. Soc., Santa Barbara, California, 1974. pp 115-120.
22. Kauper, E. K. and B. L. Niemann. Los Angeles to Ventura Over Water Ozone
Study. Report prepared for California Air Resources Board by Metro Monitor-
ing Services, Covina, California, 1975. 54 pp.
23. Schuck, E. A., A. P. Altshuller, D. S. Barth, and G. B. Morgan. Relation-
ships of Hydrocarbons to Oxidants in Ambient Atmospheres. J. Air Poll.
Control Assoc., 20:279-302, 1970.
24. Dimitriades, B. Photochemical Oxidants in the Ambient Air of the United
States. EPA-600/3-76-017, U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina, 1976. 182 pp.
25. Karl, T. R., and G. A. DeMarrais. Meteorological Conditions Conducive to
High Levels of Ozone. In: International Conference on Photochemical
Oxidant Pollution and Its Control . Proceedings, Volume 1. EPA-600/3-77-001a,
U..S. Environmental Protection Agency, Research Triangle Park, North Carolina,
1977. 576 pp.
19
-------
26. Cheng, R. T., J. 0. Frohliger, and M. Corn. Aerosol Stabilization for
Laboratory Studies of Aerosol-Gas Interaction. J. Air Poll. Control Assoc.,
21:138-142, 1971.
27. Larson, T. E., and I. Hettick. Mineral Composition of Rainwater. Tell us 8:
191-197, 1956.
28. Wagman, J., R. E. Lee, Jr., and C. J. Axt. Influence of Some Atmospheric
Variables on the Concentration and Particle Size Distribution of Sulfate
in Urban Air. Atmospheric Environment 1:479-489, 1967.
29. Frank, N. H., and N. C. Possiel, Jr. Seasonality and Regional Trends in
Atmospheric Sulfates. Paper presented to American Chemical Society,
San Francisco, California, August 30-September 3, 1976.
30. U.S. Department of Commerce, National Oceanic and Atmospheric Administration.
Local Climatological Data. Published monthly for Los Angeles, 1975. 2 pp.
31. National Climatic Center. Surface Weather Observations, Ontario Airport,
February 25-March 5, 1975 (Xerox copies of original records.).
32. Lust, E. (Air Pollution Forecaster, National Weather Service, Los Angeles).
Daily worksheets for air pollution forecasts and radiosonde data for Los
Angeles and El Monte, February 24-March 5, 1975.
33. U.S. Department of Commerce, National Oceanic and Atmospheric Administra-
tion. Daily Weather Maps. Published weekly 1975. 8 pp.
34. DeMarrais, G. A., G. C. Holzworth, and C. R. Hosier. Meteorological Sum-
maries Pertinent to Atmospheric Transport and Dispersion Over Southern
California. Technical Paper No. 54. U.S. Department of Commerce, Weather
Bureau, Washington, D.C., 1965. 86 pp.
35. Waggoner, A. P., A. H. Vanderpol, R. J. Charlson, S. Larsen, L. Granat, and
C. Tragardh. Sulphate-Light Scattering Ratio as an Index of the Role of
Sulphur in Tropospheric Optics. Nature, 261:120-122, May 13, 1976.
36. Charlson, R. J., A. H. Vanderpol, D. S. Covert, A. P. Waggoner, and
N. C. Alquist. H2SO./(NH.)2 SO. Background Aerosol: Optical Detection
in the St. Louis Region. Atmospheric Environment 8:1257-1267, 1974.
37. Whitby, K. T.s R. B. Husar, and B. Y. H. Liu. The Aerosol Size Distribution
of Los Angeles Smog. In: Aerosols and Atmospheric Chemistry, G. M. Hidy,
ed. Academic Press, New York, 1972. pp. 237-264.
20
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I 1~L«NTURA_\_SOUTH
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Figure 7B. Sulfate concentrations (jug/m3) February 28, 1975.
27
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Figure 9B. Sulfate concentrations
29
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-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
- 78-022
2.
3. RECIPIENT'S ACCESSIOI*NO.
4. TITLE AND SUBTITLE
METEOROLOGICAL CONDITIONS DURING A SULFATE EPISODE
IN SOUTHERN CALIFORNIA
5. REPORT DATE
May 1978
6.
ORGANIZATION CODE
7. AUTHOR(S)
Gerard A.
8. PERFORMING ORGANIZATION REPORT NO.
DeMarrais*
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Sciences Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
10. PROGRAM ELEMENT NO.
1AA603 AD-07 (FY-78)
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory - RTP, NC
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Inhouse 4/77-1/78
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES
*0n assignment from the National Oceanic and Atmospheric Administration,
U.S. Department of Commerce
16. ABSTRACT
Meteorological conditions are characterized for a prolonged period in which
an air mass contained high concentrations of sulfate pollutants. The period
occurred in the Los Angeles area from February 26 to March 5, 1975. In addition,
the episode occurred during the off-season and virtually coincided with an oxidant
episode. The meteorological conditions associated with both episodes were (a)
slow moving air; (b) abundant sunshine; (c) elevated temperatures; (d) limited
vertical mixing at the coast and inland vertical mixing varying from negligible
at night to relatively deep in the daytime; (e) relatively very poor visibilities
due to smoke, haze, and fog; and (f) high relative humidities at all times at the
coast and at night at inland locations, but very low relative humidities in the
daytime over inland locations. The ozone episode ended with the onset of strong
winds and rain, while the sulfate episode persisted into the windy and wet period.
Differences in the spatial patterns in sulfate and oxidant concentrations were
observed and these are attributed to differences in the relative humidities at
coastal and inland locations.
Identification of these meteorological conditions provides information
for air pollution investigators to use in attempting to forecast future sulfate
episodes.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COS AT I Field/Group
* Air pollution
* Sulfates
* Meteorological data
* Evaluation
Ozone
Los Angeles, CA
13B
07B
04B
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
iiNr.i
21. NO. OF PAGES
44
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
36
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reports, CHECK HERE TJ , tear off label, and return it to the
above address
EPA-600/4-78-022
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